SYNTHESIS AND CHARACTERIZATION OF NEW HYDROGELS …
Transcript of SYNTHESIS AND CHARACTERIZATION OF NEW HYDROGELS …
SYNTHESIS AND CHARACTERIZATION OF NEW
HYDROGELS AND THEIR APPLICATIONS ON WATER
TREATMENT
Submitted to GC University Lahore
In partial fulfillment of the requirements
For the award of degree of
DOCTOR OF PHILOSOPHY
In
CHEMISTRY
By
AISHA HAMEED
SESSION 2014-2017
Registration No. 2014.PHD.CHEM.04
DEPARTMENT OF CHEMISTRY
GOVT COLLEGE UNIVERSITY
LAHORE (PAKISTAN)
In the Name of Allah, the most beneficent, the most Merciful
Praise is to Allah, Lord of the Worlds, The beneficent, the Merciful,
Master of the Day of judgment, Thee (alone) we worship thee
(alone) we ask for help. Show us the straight path, the path of those
whom Thou hast favored; Not the path of those who earn Thine
anger nor of those go astray.
DEDICATED TO:
My Great Father
Dr. Rana Abdul Hameed (Late)
Ex Principal Medical Officer,
Nishtar Medical University, Multan.
Who taught me
To believe upon ALLAH,
(Whatever the Circumstances),
Ask ALLAH
(Whatever I do need)
And
Always seek Guidance from ALLAH.
ABSTRACT
The present work in this thesis consists of Synthesis, Characterization and the
Applications of newly synthesized Carboxymethyl cellulose based Hydrogels. The
prepared hydrogels were characterized by studying their physical properties,
swelling behavior, Swelling kinetics, Fourier Transform Infrared spectroscopy
(FT-IR), scanning electron Microscopy (SEM), powdered x-ray diffractometery
(PXRD), thermogravimeteric analysis (TGA) and atomic absorption spectroscopy
to know their ability in removing heavy metal ions from water. In this work, the
synthesis of two novel hydrogels, Carboxymethyl cellulose/Potato Starch/Amylum
Strach (CMC/PS/AS) based Hydrgel (SAP). Modified Starch (MS) and Modified
Starch based Hydrogel (MSAP) were synthesized using Aluminium sulfate
octahydrate as a crosslinking agent. By taking into consideration, FT-IR analysis
done primarily to evaluate the structure of hydrogels, the structures in results were
according to the expected structures of hydrogels. The hydrogels then subjected to
the thermal gravimetric analysis to evaluate out the thermal stability of hydrogel
i.e. more than its ingredients. Hydrogels were then examined morphologically by
SEM. The swelling ability of both hydrogels were more in basic medium rather
than acidic, moreover it shows swelling and de-swelling behavior in water,
ethanol, acidic and basic buffers and in salt solutions when inferred by the swelling
experiment. A high swelling behavior was shown by SAP and MSAP in deionized
water, at pH 6.8 and 7.4 while no reasonable swelling at pH 1.2 was observed.
Furthermore, its potential as an intelligent drug delivery system was confirmed by
a remarkable swelling and de-swelling behavior of SAP in water and ethanol, in
acidic (pH 1.2) and basic (pH 7.4) media and in water and normal saline solution.
The thermal analysis of SAP and MSAP’s major degradation steps those takes
place above 200ºC represent their extra-ordinary stability. The PXRD anlysis
shows that there may be a distortion in the CMC’s crystallization and an increase in
SAP hydrogel’s amorphous region. The possible cause of it can be the chemical
crosslinking between the starches, CMC and SAP. These results indicate that due
to a reduction in the crystalline behavior during the gel formation. . The success of
the reaction in the FT-IR spectrum of SAP was revealed by an ester carbonyl
distinct signal’s appearance at 2341 cm−1 in spectra of CMC which was the major
constituent of hydrogel, jumps to a relatively higher wavenumber at 2345 cm−1
soon after the formation of its SAP. It also indicates the absorption of Carbon
dioxide at the time of reaction completion.
From the aqueous solution of Cd2+, Pb2+ and Fe2+ ions, these metal ions were then
separated by the hydrogel. The order of selectivity towards different metal ions of
the hydrogel as tested was Cd2+> Pb2+ >Fe2+. The observation revealed the fact
that the capacity of the hydrogel to bind with heavy metal ions was dependent on
the interaction of metal ions with the hydrogel monomers.
LIST OF ABBREVIATIONS
Description Abbreviation
Carboxymethyl Cellulose CMC
Carboxymethyl Cellulose Sodium CMC-Na
Modified Starch MS
Super Absorbent Polymer SAP
Modified Starch based Super Absorbent Polymer MSAP
Potato Starch PS
Amylum Starch AS
Fourier Transform Infrared Spectroscopy FT-IR
Scanning Electron Microscopy SEM
Powdered X- ray Diffractrometery PXRD
Thermogravimeteric Analysis TGA
Potassium Bromide KBr
Sodium Chloride NaCl
Micrometer μm
Nannometer nm
Centrifuge Retention Capacity CRC
Equilibrium degree of Swelling Qe
normalized degree of swelling Qt
Carr’s Index C
TABLE OF CONTENTS
Chapter 1
Introduction:
1.1: General…………………………………………………………………………
1
1.2: Classification of Carbohydrates……………………………………………….
1
1.2.1: Monosaccharides……………………………………………………………...
3
1.2.2: Disaccharides………………………………………………………………….
4
1.2.3: Oligo and Polysaccharides…………………………………………………...
5
1.3: Starches………………………………………………………………………...
7
1.4: The Properties of Hydrogels…………………………………………………..
8
i) Hydrogen Bonding……………………………………………………….
8
1.5: The Hydrogels………………………………………………………………...
9
1.6: Classification of Hydrogel……………………………………………………..
9
i) Classification on the Basis of Ionic Charge…………………………
10
1.7: Swelling Behavior of Hydrogels……………………………………………...
10
i) The Swelling De-swelling Behavior in response to External Stimuli. 10
1.8: Preparation of Hydrogel………………………………………………………. 11
1.9: Absorption of Metal ions……………………………………………………...
13
1.10: FTIR Spectroscopy……………………………………………………………
13
1.11: Powder X-ray Diffraction (PXRD)……………………………………………
15
1.12: Scanning Electron Microscopy (SEM)………………………………………...
16
1.13: Thermogravimetric Analysis…………………………………………………. 18
1.14: Atomic Absorption Spectroscopy……………………………………………... 20
1.15: Application of Hydrogel on Water Treatment……………………………….
21
Chapter 2
Review of Literature:
Chapter 3
22
Materials and Methods:
26
3.1:
Methodology…………………………………………………………………….
26
3.1.1: Preparation of Superabsorbent Polymer (SAP)………………………………….
26
3.1.2: Preparation of Modified Stach (MS)……………………………………………
26
3.1.3: Preparation of Modified Strach based superabsorbent polymer (MSAP)……. 26
3.2: Characterization…………………………………………………………………. 27
3.2.1: Flow-ability Parameters of SAP………………………………………………...
27
3.2.1.1: Angle of Repose. ………………………………………………………………..
27
3.2.1.2: Bulk and Tap Density. …………………………………………………………..
27
3.2.1.3: Hausner Ratio and Carr’s Index………………………………………………….
28
3.2.1.4: Moisture Content……………………………………………………………….. 28
3.2.1.5: Centrifuge Retention Capacity…………………………………………………
28
3.2.1.6: Swelling Capacity. ……………………………………………………………...
28
3.2.1.7: Dynamic and Equilibrium Swelling……………………………………………..
28
3.2.1.8: Swelling Kinetics………………………………………………………………..
29
3.2.1.9: The Swelling and de-swelling behavior in response to external stimuli………...
29
3.2.2: Scanning electron microscopy (SEM)…………………………………………..
30
3.2.3: FTIR Analysis…………………………………………………………………..
30
3.2.4: PXRD Analysis………………………………………………………………….
30
3.2.5: Thermogravimetric Analysis (TGA)…………………………………………….
31
3.3: Applications of Hydrogel on Water Treatment………………………………..
31
3.3.1: Atomic Absorption Spectroscopy………………………………………………
31
3.3.2: The Aims and Objectives of Study……………………………………………...
Chapter 4
32
Results and Discussion
34
4.1: Physical properties of SAP………………………………………………………
34
4.2: Swelling Behavior of Hydrogels and its Ingredients……………………………
36
4.2.1: Swelling Behavior of Potato Starch ……………………………………………
36
4.2.2: Swelling Behavior of Amylum Starch ………………………………………….
37
4.2.3: Swelling Behavior of Carboxymethyl cellulose………………………………..
38
4.2.4: Swelling Behavior of Modified Starch………………………………………….
39
4.2.5: Swelling Behavior of SAP………………………………………………………
40
4.2.6: Swelling Behavior of MSAP……………………………………………………
41
4.3: pH responsive swelling of Hydrogels…………………………………………..
42
4.3.1: pH responsive swelling of SAP…………………………………………………. 42
4.3.2: pH responsive swelling of MSAP………………………………………………
44
4.4: Swelling and de-swelling kinetics in response to external stimuli……………..
46
4.4.1:
Swelling and de-swelling behavior of SAP in water and ethanol……………….
47
4.4.2: Swelling and De-swelling behaviour of SAP in Acidic and Basic Buffers……..
48
4.5: Scanning Electron Microscopy (SEM)………………………………………..
49
4.5.1: SEM Micrographs of Potato Starch………………..…………………………...
50
4.5.2: SEM Micrographs of Amylum Starch…………………………………………
50
4.5.3: SEM Micrographs of Carboxymethyl Cellulose……………………………...... 51
4.5.4: SEM Micrographs of SAP……..……………………………………………….
52
4.5.5: SEM Micrographs of Modified Starch…………………………………………..
53
4.5.6: SEM Micrographs of Modified Starch based SAP…..…………………………
54
4.6: Fourier Transform Infrared Spectroscopy (FTIR)………………………………. 55
4.7: PXRD Analysis………………………………………………………………….
59
4.8: Thermogravimeteric Analysis…………………………………………………...
62
4.9: Applications of water treatment ………………………………………………..
68
4.9.1 Atomic Absorption spectroscopy 68
4.9.2 Adsorption Isotherms 69
4.10:
4.11:
Conclusion………………………………………………………………………..
Research work Published from this work………………………………………..
Chapter 5
References
73
75
76
LIST OF FIGURES
Fig 1.1: Illustration of a disaccharide maltose molecule’s glycosidic bond between
two molecules of glucose linked by an α-1,4-glycosidic
bond………………………………………………………………………..
2
Fig 1.2: Smallest monosaccharides “trioses”……………………………………… 3
Fig 1.3: Two structural formulae of glucose i.e. open chain and ring form ………. 4
Fig 1.4: Different forms of monosaccharrides in aqueous solution……………….. 4
Fig 1.5: Structure of common diasaccharides……………………………………... 5
Fig 1.6: Structure of some of the oligosaccharides………………………………... 6
Fig 1.7: Different types of polysaccharides 1st row: Non-mammalian 2nd row:
Mammalian polysaccharides………………………………………………
7
Fig 1.8: Structure of amylose and amylopectin in starch………………………….. 7
Fig 1.9: Illustration of hydrogen bonds (dotted line) in DNA by Watson and Crick’s
Model …………………………………………………………….
8
Fig 1.10: Schematic illustration of hydrogel structure having hydrophilic polymer
chains connected through cross-linking polymers………………………...
11
Fig 1.11: Hydrogen bonding in PVA………………………………………………. 11
Fig 1.12: Illustration of a hydrogel preparation……………………………………. 12
Fig 1.13: Schematic illustration of hydrogel network with different types of water.. 13
Fig 1.14: A block diagram of IR-imaging………………………………………….. 15
Fig 1.15: Major units in x-ray diffraction…………………………………………… 16
Fig 1.16: Construction of a scanning Electron microscopy………………………... 17
Fig 1.17: SEM image of a TiO2 nano-tubes……………………………………….. 18
Fig 1.18: A typical thermogravimetry apparatus with differential thermogravimetry
(DTG) facility…………………………………………
19
Fig 1.19: A typical thermogravimetric analysis plot of different compounds……… 19
Fig1.20(a&b): Single beam spectrometer (b) double beam spectrometer………………. 21
Fig 4.1(a): Swelling data of SAP obtained in water and buffers of pH 1.2, 6.8 and
7.4…………………………………………………………………………..
42
Fig. 4.1(b): Swelling data and kinetics of SAP obtained in buffers of pH 6.8 and 7.4..
43
Fig 4.1(c): Swelling data of SAP between time (min) and Qt(mg/g) obtained in water
and buffers of pH 1.2, 6.8 and 7.4…………………………………………
43
Fig4.1(d):
Fig 4.2(a):
Swelling data of SAP between time(min) and t/Qt(min(mg/g)) obtained in
water and buffers of pH 1.2, 6.8 and 7.4………………………………….
Swelling data of MSAP obtained in water and buffers(1.2,6.8 and 7.4)
44
44
Fig. 4.2(b): Swelling data and kinetics of MSAP obtained in buffers(6.8 and 7.4)……
45
Fig 4.2(c): Kinetic Studies of MSAP between time(min) and Qt (mg/g) at different
pH……………………………………………………………………………
45
Fig 4.2(d): Kinetic Studies of MSAP between time(min) and t/Qt (mg/g) at different
pH……………………………………………………………………………
46
Fig 4.3(a): The Swelling and de swelling of SAP in aqueous and ethanol media……..
46
Fig 4.3(b): The Swelling and de swelling of MSAP in aqueous and ethanol media…...
47
Fig 4.4(a): Swelling and de-swelling behavior of SAP in basic and acidic buffers…….
47
Fig 4.4(b): Swelling-deswelling behavior of MSAP in basic and acidic buffers……….
48
Fig 4.5(a): Swelling-deswelling behaviour of SAP in deionized water and 0.9% NaCl
solution………………………………………………………………………
49
Fig 4.5(b): Swelling-deswelling behaviour of MSAP in deionized water and
0.9%NaCl…………………………………………………………………….
49
Fig. 4.6: FTIR Spectra of Potato Starch………………………………………………. 56
Fig. 4.7: FTIR Spectra of Amylum Starch……………………………………………. 56
Fig. 4.8 : FTIR Spectra of Carboxymethyl cellulose………………………………….
56
Fig. 4.9: FTIR Spectra of SAP………………………………………………………...
57
Fig. 4.10: Combined FTIR Spectra of Potato, Amylum starches, CMC and SAP…….. 57
Fig 4.11: FTIR Analysis of MSAP…………………………………………………….
58
Fig.4.12: PXRD Analysis of Potato Starch……………………………………………
59
Fig.4.13: PXRD Analysis of Amylum Starch…………………………………………. 59
Fig.4.14: PXRD Analysis of Carboxymethyl cellulose-Sodium……………………… 60
Fig.4.15: PXRD Analysis of SAP……………………………………………………... 60
Fig 4.16: PXRD Analysis of Modified Starch…………………………………………
61
Fig 4.17:
PXRD Analysis of MSAP…………………………………………………...
61
Fig.4.18: Overlying graph of thermo-gravimetric (TG) straight line of SAP indicating
thermal stability of sorbent…………………………………………………..
62
Fig 4.19: Thermogravimeteric Analysis of Potato Starch……………………………..
62
Fig 4.20: Thermogravimeteric Analysis of Amylum Starch………………………….
63
Fig 4.21 Thermogravimeteric Analysis of Carboxymethyl Cellulose………………...
64
Fig 4.22 Overlying graph of thermo-gravimetric (TG) straight line of SAP,
indicating thermal stability imparted in sodic form of sorbent throughout
the degradation profile……………………………………………………….
64
Fig 4.23 Thermogravimeteric Analysis of Potato, Amylum Starchces,
Carboxymethyl Cellulose Sodium and SAP…………………………………
65
Fig 4.24 Thermogravimeteric Analysis of SAP (Graph between Temperature and
Weight Loss of both Derivatives)……………………………………………
65
Fig 4.25 Thermogravimeteric Analysis of Modified starch…………………………..
66
Fig 4.26 Thermogravimeteric Analysis of Modified Starch (Graph between
Temperature and Weight Loss of both Derivatives)…………………………
66
Fig 4.27 Thermogravimeteric Analysis of MSAP…………………………………….
66
Fig 4.28 Thermogravimeteric Analysis of MSAP (Graph between Temperature and
Weight Loss of both Derivatives)……………………………………………
67
Fig 4.29 Thermogravimeteric Analysis of Modified Starch, Carboxymethyl
Cellulose Sodium and Modified starch based SAP………………………….
67
Fig 4.30 Metal ion adsorption ratio profiles of SAP at room temperature…………… 68
Fig4.31 Metal ion adsorption ratio profiles of MSAP at room temperature……….
68
Fig 4.32 Graphical representation of Cadmium ion absorption in SAP between
Ce(mol/L) and Qe (mol/L)…………………………………………………...
69
Fig 4.33 Graphical representation of Cadmium ion absorption in MSAP between
Ce(mol/L) and Qe (mol/L)…………………………………………………...
69
Fig 4.34 Graphical representation of Fe2+ ion absorption in SAP between Ce(mol/L)
and Qe (mol/L)………………………………………………………………
70
Fig 4.35 Graphical representation of Fe2+ ion absorption in MSAP between
Ce(mol/L) and Qe (mol/L)…………………………………………………...
71
Fig 4.36 Graphical representation of Pb2+ ion absorption in SAP between Ce(mol/L)
&Qe (mol/L)…………………………………………………………………
71
Fig 4.37 Graphical representation of Pb2+ ion absorption in MSAP between
Ce(mol/L) and Qe (mol/L)…………………………………………………...
72
LIST OF TABLES
Table 1.1: Classification of Carbohydrates………………………………………… 2
Table 3.1: Conditions for PXRD Analysis for all six Samples……………………..
30
Table 4.1: Phyical Properties of SAP……………………………………………….
34
Table 4.2: Physical Properties of MSAP…………………………………………... 34
Table 4.3: Observed FT-IR bands and their Assignments………………………….
58
Table 4.4: Freundlich and Langmiur Equation fitted Parameters………………….. 72
LIST OF IMAGES
Image 4.1(a,b,c,d): SEM micrographs of Potato Starch………………………..
50
Image 4.2(a,b,c,d): SEM micrographs of Amylum Starch…………………… 50
Image 4.3(a,b,c,d): SEM micrographs of Carboxymethyl cellulose…………...
51
Image 4.4(a,b,c,d): SEM micrographs of SAP………………………………… 52
Image 4.5(a,b,c,d): SEM micrographs of Modified Starch based SAP ……….
53
Image 4.6(a,b,c,d): SEM micrographs of Modified starch ……….
54
Chapter 1
INTRODUCTION
Chapter 1: INTRODUCTION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 1
1.1 General
Carbohydrates are most abundant, natural organic compounds utilized by animals, plants as
well as micro-organisms. These are one of the macro-nutrients essential for human activity
providing metabolic energy by glucose oxidation. Not only as a source of energy, but a chief
source of fuel, clothes and building material. At molecular level, carbohydrates are the
essential components of neucleotides carrying the genetic information in all living animals.
Moreover, when they are conjugated with other biomolecules e.g. steroids, covert them water
dispersible and make them transportable from one part of body to other in the form of
glycosides [1]. Carbohydrates are divided into different classes depending on their molecular
weight and complexity. Types of carbohydrates include low-molecular-weight
monosaccharides (glucose, fructose, rabinose, xylose and mannose) and disaccharides
(maltose, sucrose and lactose), in addition to the high-molecular-weight oligosaccharides
(dextrins) and polysaccharides (chitin, cellulose, chitosan, agarose, inulin, xylan, amylose and
amylopectin) [2]. More simply, there exist two types of Carbohydrates; simple (glucose,
fructose, maltose and sucrose) and complex (cellubiose, amylose, dextrins, starch, cellulose
and fibres). Carbohydrates level in the body plays a part in physiological and metabolic
functions i.e. an increased intake of simple carbohydrates may lead to obesity and non-insulin
dependent diabetes which in turn, can lead to further disorders [3].
In many important biological processes, carbohydrates play an important role e.g. cell-cell
interactions, bacterial and viral infections and immune response. These are, not only and
important source of DNA and RNAs but also an important source of energy for many
organisms [4].
1.2 Classification of Carbohydrates
Carbohydrates can be classified as below
Simple carbohydrates as one to two sugar molecules combine by a simple chemical
reaction e.g. fructose, maltose, ribose, sucrose present in different types of foods like
carbonated beverages, fruit juice, table sugar and honey
Complex carbohydrates formed by a complex reaction of oligo or polysaccharides
e.g. cellobiose, amylose, dextrin and cellulose present in foods like broccoli, lentils,
apple and in brown rice having a gradual effect on level of blood sugar
Starches having glucose molecules in large number, produced by plants e.g.
chickpeas, pasta, wheat and potato.
Fiber: may be soluble or insoluble fibers help to decrease cholesterol and LDL level
and in regularity of bowel movements respectively. A non-digestible carbohydrate
having the main components pectin, cellulose and hemicellulose e.g. oats, fleshy
fruits, potato skins and brown rice [5].
The biological role of carbohydrates is prominent in assembly of organisms and complex
multicellular organs requiring an interaction between cells and their surrounding matrix.
Numerous macromolecules and cells in nature carry out a building block i.e. simple
sugar molecule attached covalently to other ones (monosaccharide) or a chain of sugar
Chapter 1: INTRODUCTION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 2
molecules (oligosaccharides) generally referred as “glycans”. They are present on outer
surface of a cell or secreted macromolecules and many of them are capable to mediate
numerous cell-matrix, cell-molecules and cell-cell interactions for the function and
development of a complex multicellular organism or even in between different organism
i.e. between parasite, symbiont or pathogen to their hosts. Within the nucleus, protein-
bound glycans are most abundantly present in nucleus and cytoplasm serving as a
regulatory switch [6].
In nature, carbohydrates are present mostly in complex form by the joining of simpler
molecules through glycosidic linkages as well as in different structural forms i.e. ring or
open chain structure in which different atoms are substituted by other ones like
hydroxymethyl and N-acetyle etc. The different orientation and confromations of these
molecules make them complex ones for theory and experimental point of view [7]..
Fig 1.1: Illustration of a disaccharide maltose molecule’s glycosidic bond between two
molecules of glucose linked by an α-1,4-glycosidic bond [8].
According to recent research, excessive intake of carbohydrates specially sugars e.g. fructose
may lead to some detrimental metabolic effects. However, in mixed carbohydrate sources,
fructose doesn’t exert some specific metabolic effects and doesn’t take part primarily in an
increase of body weight. In a recent Asian cohort study, the excessive carbohydrate was not
associated with mortality of ischemic heart disease. In contrast to this, a diet shifts to a lower
carbohydrate intake, like vegetables, whole grain and fruits account for a lower risk of
ischemic heart disease [9].
Table 1.1: Classification of Carbohydrates [10]
Group Sub-group Principal components
Sugars (mono- and di-
saccharides)
Monosaccharides Fructose , Galactose,
Glucose
Disaccharides Trehalose, Sucrose, maltose,
lactose
Sugar-alcohols (polyols) Sorbitol, xylitol, lactitol,
maltitol, mannitol,
isomaltitol, erythritol
Chapter 1: INTRODUCTION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 3
Oligosaccharides Maltooligosaccharides
(alpha-glucans)
Maltodextrins
Non-alpha-glucan
oligosaccharides
Raffinose, fructo- and
galacto-oligosaccharides,
polydextrose, inulin,
stachyose
Polysaccharides Starch (alpha-glucans) Modified starches, Amylose,
Amylopectin
Non-starch polysaccharides Pectins, Cellulose,
hemicellulose, hydrocolloids
(e.g., beta-glucans, gums,
mucilages)
1.2.1 Monosaccharides
Carbohydrates can be described in terms of polyhydroxyketones or polyhydroxyaldeheydes,
larger compounds and their simple derivatives, where the large compounds can be
hydrolyzed into simpler units. Monosacharides are defined as building blocks of
carbohydrates that can’t be hydrolyzed further having a carbonyl group on an inner carbon
atom (ketone) or at the carbon chain’s end (aldehyde). Thus can be ketoses or aldoses
respectively [6].
The empirical formula for monosaccharides is (CH2O)n. These are important building blocks
of many biological molecules carrying out cellular functions i.e. nucleic acids. D- and L-
glyceraldehyde and Dihydroxyacetone are simplest monosaccharides for which n=3 also
called as “trioses” while others with carbon atom ranging from four to seven are named as
tetroses, pentoses, hexoses and heptoses.
Fig 1.2: Smallest monosaccharides “trioses” [11].
In simple words, monosaccharides are the simplest, fundamental and most basic
carbohydrates having formula C6H12O6 e.g. glucose, fructose and galactose. They exist in the
form of five membered furanose form and six membered pyranose form adopting the shape to
minimize the eclipsing interactions [12].
Chapter 1: INTRODUCTION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 4
Fig 1.3: Two structural formulae of glucose i.e. open chain and ring form [6]
In an aqueous solution, monosaccharides exist in different forms as describe below in figure:
Fig 1.4: Different forms of monosaccharrides in aqueous solution [13]
1.2.2 Disaccharides
Two monosaccharides are joined together via glycosidic linkage to form a disaccharide
molecule mostly by an O-glycosidic linkage. Examples of abundant disaccharides are
sucrose, maltose and lactose. These glycosidic linkages are cleaved by their respective
enzymes e.g. sucrose enzyme for the breakdown of sucrose into parent molecules.
Chapter 1: INTRODUCTION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 5
Fig 1.5: Structure of common disaccharides [8]
1.2.3 Oligo and Polysaccharides
In living organisms, monosaccharides alone rarely occur in nature rather, they join with other
molecules of same specie or other to form large molecules. The most common of which is the
covalent linking of a sugar with an aglycone may be lipid, protein or other carried out by the
formation of a glycosidic linkage i.e. bond between the hydroxyl group of the aglycone and
anomeric carbon of sugar. The resulting specie thus called as oligosaccharide with less than
dozen monosaccharides or polysaccharides containing more than a dozen monosaccharides
and there may be repeating units in the structure of polysaccharides. This assemblage creates
a vast variety and diversity of macromolecules which makes carbohydrates to play functional
and vital role in living organisms [14].
Many types of oligosaccharides are occurring in nature and most important of them are
fructooligosaccharides (FOS), Lactulose derived galactooligosaccharides (LDGOS),
Galactooligosaccharides (GOS), Arabinooligosaccharides (AOS), Xylooligosaccharides
(XOS) and algae derived marine oligosaccharides (ADMO).
In recent research, pre-biotics of oligosaccharides are gaining attention as their effect is now
extended as an anti-obesity, antidiarrheal substance in addition to its promising role in
suppressing diabetes type 2. In future, there may be a development of pre-biotic and pro-
biotic combination for a synergistic effect which can used to combat many ailments in human
beings [15].
Chapter 1: INTRODUCTION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 6
Fig 1.6: Structure of some of the oligosaccharides [15]
In polysaccharides, there present a diverse range of functional groups like ester, hydroxyl,
carboxylate and amino groups. Therefore, they can be modified to attain a diverse group of
derivatives [16]. Basically, polysaccharides are classified into two main classes on the basis
of their structure i.e. homopolysaccharides or homoglycans and heteropolysaccharides or
heteroglycans. The first defines the formation of polysaccharide chain by same
monosaccharides e.g. glycogen, starch, chitin and cellulose while the later one is formed by
two or more types of monosaccharides e.g. glycosaminoglycans. Another classification of
polysaccharides is based on morphology i.e. long chains or branched molecules or on their
function i.e. structural polysaccharides (agar, chitin and pectin) or storage polysaccharides
(starch, glycogen). Some living organisms also secrete polysaccharides in order to prevent
themselves from drying out as an evolutionary adaptation or to get adhered to the surface like
bacteria, fungi and algae. In addition, polysaccharides can also be divided on the basis of
their electrical charge i.e. cationic, neutral and anionic as well as by their sources i.e. plants,
micro-organisms and animals [17].
Chapter 1: INTRODUCTION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 7
Fig 1.7: Different types of polysaccharides 1st row: Non-mammalian 2nd row:
Mammalian polysaccharides [18]
1.3 Starches
A type of polysaccharides and a mixture of two glucose polymers i.e. amylopectin a highly
branched molecules (with (1→6) α-linkages as well as (1→4) α-linkages) and may comprise
over 100,000 glucose residues and amylose, which has (1→4) α-linked chains comprises up
to several thousand glucose units. Amylose occurs mostly in tuber starch than cereal ones
having a few long branches but highly branched. Most of the starches contains 70-80%
amylopectin while, 20-30% amylose and their ratio can be altered by transgenic engineering
or some mutations in biosynthetic pathway [19].
Fig 1.8: Structure of amylose and amylopectin in starch [20]
Chapter 1: INTRODUCTION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 8
In a starch granule, about 30% of its mass is considered as crystalline mainly composed of
amylopectin while, 70% is considered as amorphous having amylose as major component
with a considerable amount of amylopectin. The gelatinization of starch is a three step
mechanism involving thermal hydration-plasticization of the polymeric network in which
first step includes the swelling of hydrophilic starch granule by the absorption of water while,
the second step is destruction of the granular structure by dissolving it thermally and resulting
in leaching of amylose. The major third step is the retrogradation step in which by cooling,
the starch-hydrogel network is created, recrystallization occurs partially and polysaccharide
structure is regenerated. Temperature of gelatinization and the amount of starch are the two
main factors affecting the gel formation [20].
1.4 The Properties of Hydrogels
1.4.1 Hydrogen Bonding
It is a type of interaction between an electronegative acceptor atom “Y” (usually N, O or F)
and an electropositive donor covalent bond group X-H. The bond thus created X-H----Y
imposes different properties chemically and physically in a compound in correlation with the
electronegative atom. This hydrogen bonding is crucial to carry out major metabolic events in
living organisms as well as in the formation of essential biomolecules e.g. nucleic acids,
proteins and many others. Various factors like pressure, temperature, electronegativity of
donors and acceptors, bond angle, bond length and the local dielectric constant [21].
Fig 1.9: Illustration of hydrogen bonds (dotted line) in DNA by Watson and Crick’s
Model [22]
Chapter 1: INTRODUCTION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 9
We can say, conventional bonds of hydrogen in a biomolecular structure respresent a major
stabilizing force. This bond is usually shared between a donor and an acceptor atom by a
slightly varying degree. The most common way to discover hydrogen bond is by measuring
the bond length between the groups of donors and acceptors. Moreover, spectroscopic
signature is also a common way to detect hydrogen bond with some accuracy [23].
1.5 The Hydrogels
Also called the hydrophilic gels, these are actually the polymeric networks swollen
extensively with water, sometimes found as colloidal gels in dispersion medium as water. In
other words, hydrogel is a water swollen, cross-linked polymeric network produced by
monomers, having the ability to retain a large volume of water within its structure without
dissolving in it [24].
The first reference to hydrogels appeared in 1894 claiming it a colloidal gel made up of
inorganic salt. The term “hydrogels” was then used to describe a 3D network of polymers
formed chemically of physically. The idea of biological use of hydrogels was devised in
1960 by Wichterle and Lim and since then, a large number of ideas were applied on
hydrogels providing useful evidences in biomedical research. The term “smart hydrogels”
refers to a type of hydrogels which respond to a minute change in its environment differing
with ordinary hydrogels which undergo only a swelling and de-swelling behavior in water
medium. Smart hydrogels undergo volume and structural phase transition in response to
external stimuli providing a potential for scientific observation and different technological
applications [25].
1.6 Classification of Hydrogel
Two main classes of hydrogels include the natural and synthetic hydrogels. Among these,
natural hydrogels include fibrin, collagen, matrigel, hyaluronic acid and derivatives of natural
products e.g. chitosan and alginate. These are the physiological hydrogels as they are the
components of extracellular metrix in vivo. Drawbacks of natural hydrogels include their
final properties and microstructures which are difficult to control reproducibly in addition to
their difference in properties due to natural origin. Synthetic hydrogels include poly (acryl
amide), poly (ethylene glycol) diacrylate, poly (vinyl alcohol) which are more reproducible
but their final structure also depends on polymerization condition. They can be tuned or
selected to be biodegradable and hydrolysable over selected period of time [26]. The
resistance to dissolution and their ability to absorb water are due to functional-groups
attached to their backbone and their cross-linked network respectively. Due to high gel
strength, long service life and high capacity of water absorption, synthetic hydrogels are now
widely used today. Fortunately, the synthetic hydrogels possess well-defined structures that
can be tailored for the required functionality and degradability [24].
Due to their unique properties, hydrogels are used commonly for a wide range of
experimental and clinical practices as diagnostics, cellular immobilization, tissue engineering
and regenerative medicine, separation of cells or biomolecules and as barrier molecules for
the regulation of biological adhesions [27].
Chapter 1: INTRODUCTION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 10
1.6.1 Classification on the Basis of Ionic Charge
Based on ionic charge, method of preparation or physical character, hydrogels are divided
into different categories. Hydrogels having ionic charge on backbone polymer are called
ionic hydrogels and are classified as neutral hydrogels (uncharged), anionic hydrogels
(negative charge only), cationic hydrogels (positively charged hydrogels) and ampholytic
hydrogels (having both positive and negative charges). On the basis of method of preparation,
hydrogels are classified as homopolymer hydrogels (made by cross-linking of only one type
of hydrophilic monomer unit), copolymer hydrogels (made by cross-linking of chains having
at least one hydrophilic unit to make them water swellable) and multi-polymer hydrogels
(produced by reaction of three or more comonomers). By considering the physico-chemical
properties, hydrogels are divided as amorphous (possessing covalent cross-links) and semi-
crystalline (may or may not possess covalent bond) hydrogels [28].
1.7 Swelling Behavior of Hydrogels
In other words, hydrogels are macromolecular networks having ability to absorb water and
then releasing it in specific environmental stimuli. This specific behavior to a specific stimuli,
make it a suitable substance to design a smart device in various fields of technology and
biomedical sciences [29]. The swelling behavior of hydrogels occurs in relation to the
presence of hydrophilic groups in their polymeric chain, elasticity of network in hydrogel, the
porosity and extent of the cross-linker. A super-porous hydrogel SPH is composed of a 3D
network of polymer having the ability to absorb a large amount of water in a relatively less
time due to the interconnected microscopic pores network [30]. New ideas regarding
hydrogels include enhanced mechanical hydrogels structures, super-porous hydrogels, comb-
type grafted structure having a fast response time and self-assembled hydrogels made from
specific co-polymers [31].
1.7.1 The Swelling De-swelling Behavior in Response to External Stimuli
Today, hydrogels can be formed with responses that can be controlled accordingly as to
expand or shrink desirably with some changes in the environment. Dramatic transitions in
volume of hydrogels can be observed with chemical or physical stimuli as physical stimuli
include pressure, sound, electric or magnetic fields and temperature, while, chemical stimuli
include solvent type and composition, pH, molecular species and ionic strength [24].
Swelling and de-swelling in response to a particular stimulus is a unique property carried out
by hydrogels. The extent of swelling tells about the network and structure of hydrogels and it
depends on the following four important parameters;
The ratio of swelling i.e. involvement of mass swelling ratio (Qm) and the volume
swelling ratio (Qv)
The polymer volume fraction in the swollen state (υ2,s)
The number average molecular weight between cross-links (Mc)
The network mesh size (ξ)
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Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 11
Fig 1.10: Schematic illustration of hydrogel structure having hydrophilic
polymer chains connected through cross-linking polymers [32]
As previously described, hydrogels have a three dimensional structure in which molecules are
held together by some specific type of forces i.e. Van der Waals forces, hydrogen bonding
and covalent bonds. The most important factors in the preparation of a hydrogel are type of
cross-linker and its concentration, types of initiator, monomers and their concentration,
inorganic particle types (if used), rate of stirring, surfactant type, reactor type, polymerization
method and the temperature of reaction [20].
1.8 Preparation of Hydrogel
Preparation of hydrogel basically involves the polymerization of molecules under optimum
temperature and pressure for the reactants to react. Cross-linking the molecules is the basic
technique in the preparation of a hydrogel. Two methods of cross-linking are applied in the
preparation a hydrogel i.e. physical crosslinking and chemical cross-linking. Physically cross-
linked gels got an attention due to the absence of special cross-linkers used in the preparation.
Following are the physical methods to introduce cross-linking in molecules;
By hydrogen bonds (e.g. polymethacrylic acid and polyacrylic acid complex with
PEG, PVA)
Fig 1.11: Hydrogen bonding in PVA [33]
Chapter 1: INTRODUCTION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 12
By ampiphilic grafting and block polymers (e.g. polymers of PLGA and PEG)
Cross-linking by crystallization in homopolymer system (Polyvinyl alcohol) and by
stereocomplex formation (mixture of PLLA and PDLA at 230ºC)
By ionic interactions (Alginate gels)
By protein interaction from genetically engineered proteins (biocompatible
ProLastins) and by antigen-antibody interactions (grafting of IgG to chemically cross-
linked polyacrylamide)
Some of the chemical methods for cross-linking are given below;
By chemical reaction of complementary groups i.e. with aldehydes (PVA cross-
linking with glutaraldehyde), by addition reactions (Polysaccharides cross-linking by
1,6-hexamethylenediisocyanate) and by condensation reactions (e.g. gelatin
hydrogels)
By high energy radiation i.e. gamma rays to polymerize unsaturated compounds
By free radical polymerization i.e. from enzyme as catalysts or by UV polymerization
Using enzymes e.g. reaction between the ε-amine group of lysine and γ-carboxamide
group of the PEG-Qa catalyzed by transglutaminase [34].
Fig 1.12: Illustration of a hydrogel preparation [35]
Presence of water is hydrogel is a most important tool to carry out all the transport of active
ingredients through the gel. A hydrogel is associated with different types of water i.e. bound,
semi-bound, interstitial and free or bulk water as given below in figure;
Chapter 1: INTRODUCTION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 13
Fig 1.13: Schematic illustration of hydrogel network with different types of water [33]
1.9 Absorption of Metal ions
Hydrogels possess a unique property to absorb metal ions from aqueous solutions. This
property leads to some of the most important applications. The absorption of metal ions by
hydrogels can be calculated by concentration of metal ions in initial and equilibrium phase in
aqueous solution, the volume of hydrogel used and by the weight of hydrogel. Moreover, the
metal absorption is affected by the salt concentration of solution and pH [36].
In recent times, various methods are employed to treat the polluted water by means of
physical and chemical methods e.g. removal of heavy metal ions. Various studies analyzed
the methods of using hydrogels for the removal of heavy metal ions and reported
considerable results [37]. In this study, we will examine the treatment of contaminated water
with heavy metal ions by the use of hydrogels.
1.10 FTIR Spectroscopy
Fourier transform IR (FTIR) spectroscopy is a technique to assess the biochemical
information and images and widely used for research purposes. The spectral domain obtained
after the FTIR spectroscopy, helps in chemical identification, and when used with
microscope, the examination of heterogeneous samples and complex tissues becomes
possible. An IR active substance comprises of molecules having an electric dipole moment
that can be changed by atomic displacements having some natural vibrations. An IR
spectroscopy measures these vibrational modes quantitatively and provides a label-free
method to study the composition and dynamics of molecules without changing or affecting
the sample [38].
It is a widely used technique for the investigation of samples in gaseous, solid or liquid phase
based on the interaction of natural vibrations of chemical bonds present in atoms and
electromagnetic radiation. There are two conditions for an element to absorb the infrared
radiations,
i) The frequencies between the molecular vibrations and the infrared radiations must
resonate
Chapter 1: INTRODUCTION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 14
ii) There must be a change in dipole moment during vibration by natural vibrations
Two types of vibrations are present in a molecule; one of them changes the bond angle and
the other, bond length. Moreover, wavelength (λ) is used to represent the position of the
absorption band spectra. However, the commonly used term used in IR spectra is
wavenumber (v¯) having the unit cm-1, and is directly prop. to frequency (v) and energy (E)
of the radiation as given below;
E= h v = h c / λ
C= Speed of light in vacuum
H= Plank’s constant
Absorbance and transmittance are two terms used to describe the band intensity.
Transmittance (T) is defined as the ratio between intensities of the transmitted (I) and
incident (Io) beams. On the other hand, absorbance (A) is the logarithm (base 10) of the
reciprocal of the transmittance;
A =log10 (1/T) = log10 (Io /I)
The transmitted radiant energy depends on the thickness (x) and absorption coefficient (α) of
the sample
I = I0eαx
In Infrared, there are three spectral regions, i.e., the near (NIR – from 4,000 to approx. 14,000
cm-1), mid (MIR – from 400 to 4,000 cm-1) and far-infrared (FIR – from approx. 25 to 400
cm-1) regions [39].
The intensities of absorbance and frequencies of the infrared bands don’t contain isolated
peaks rather complex contours and unique bands are displayed for the quantification,
characterization and isolation of the sample under consideration [40].
Modern IR spectrometer are mostly Fourier transformed in which the main part is
Michealson’s Interferometer, the main technique of which is the interference of two beams of
light produced by a broadband light source [41]. A discrete fourier transform is a
mathematical function which is able to transform a function from time to frequency domain.
A fast fourier transform algorithm is present which makes the discrete fourier transfer to
compute so there is a recognizable absorbance spectrum by these raw signals inversely
besides this interferometer. Moreover, the analysis of samples in different conditions (liquid,
suspended, powered or dehydrated) is responsible for the expansion in scientific and
technical applications by the use of chemo-metric tools by which quantitative and qualitative
analysis can be done by the spectra. A standardized experimental protocol which is available
for media preparation, temperature and incubation time, sample preparation, cell harvesting
conditions and FT-IR measurement should be followed in order to obtain a reproducible data
[40].
Chapter 1: INTRODUCTION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 15
In many research areas, the combination of FTIR and chemometric techniques is being used
as a reliable tool for quantitative and qualitative analysis. There exists a varierty of
chemometric methods used to carry out analysis which includes Canonical Variate Analysis
(CVA), Hierarchical Cluster Analysis (HCA), Principal Component Analysis (PCA), Partial
Least Squares Regression (PLS), Soft Independent Modelling by Class Analogy (SIMCA),
Artificial Neural Network (ANN) and Discriminant Analysis (DA). The use of FTIR
spectroscopic technique has a wide range of applications from the analysis of microscopic
organisms to the geographical discrimination and classification of seeds, pods and fruits [42].
Fig 1.14: A block diagram of IR-imaging [43]
1.11 Powder X-ray Diffraction (PXRD)
Powder X-ray diffraction is a source to obtain an accurate structural data of polycrystalline
substance since early 90s. A crystalline structure can be successfully determined by the use of
PXRD data. Moreover, the further use of solid-state NMR spectroscope can validate and
significantly enhance the data obtained by the PXRD analysis [44]. A type of X-ray
diffraction in which the sample is used in the form of powder and is considered as a non-
destructive, non-invasive and a quick tool for the identification of solid phases. The pattern of
PXRD analysis is unique for a particular crystalline form, so identification of the compound
can be done by it. This technique is mostly used for the pharmaceutical ingredients for the
identification of drugs also known as “bulk characterization method” because it uses a bulk
mass of powder to analyze it [45].
Powdered X-ray diffraction is a modified form of X-ray diffraction whose history lies in 1912
when Max Van Loue and co-workers discovered that crystalline substances can work as a 3D
diffraction grating for x-ray wavelengths. Later, it became a successful tool for the
identification of crystal lattice and atomic structure. An x-ray diffratcometer work is based on
the constructive interference of a crystalline sample and monochromatic x-rays in which a
cathode ray tube produces x-rays and then collimated to make them concentrated and
Chapter 1: INTRODUCTION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 16
directional towards the sample under study. This interaction produces a constructive
interference when Bragg’s law is conditioned:
nλ= 2dsinθ
n = an integer
λ = wavelength of the X-rays
d = the inter-planar spacing generating the diffraction
θ= diffraction angle.
This law relates the spacing of a lattice in a crystalline sample and wavelength of
electromagnetic radiation to the diffraction angle. These diffracted X-rays are then detected,
processed, and counted and all possible diffraction directions of the lattice can be attained by
scanning the sample through a range of 2θ angles due to the random orientation of the
powdered material. Due to unique d-spacings for each compound, we can convert the
diffraction peaks to d-spacings that allow identification of the sample. More elaborately, we
can achieve this by comparing d-spacings with some standard reference pattern [46].
Fig 1.15: Major units in x-ray diffraction [45]
Many types of XRD are present today, PXRD is one of them which allow the non-invasive
and accurate imaging of the powdered sample under study and we can say, PXRD patterns
are actually the fingerprints of crystalline substances. The data collection time is 20-30min
for identification purposes. Identification of the peaks is done in phases of a straight-forward
automatic technique by matching the ones obtained by sample against all the possible peaks
of a crystalline compound in the powder diffraction file and a computer software is available
for this purpose [47].
1.12 Scanning Electron Microscopy (SEM)
It is a modified form of “Transmission electron microscopy (TEM)” which is introduced in
late 1930s. SEM was made by attaching scan coils to a TEM and first introduced
commercially by Cambridge Instrument Company in 1965 as the “Stereoscan” and first scan
of nylon fibres was done in US where it was shipped firstly. Since that time, SEM has been
used as a most useful tool to gather information even at sub-nanometer scale and widely used
Chapter 1: INTRODUCTION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 17
as a research and analytical tool. Due to the use of electron instead of light as a source for
illumination, it can resolve or evaluate structure as tiny as 0.4nm [48].
A SEM has the ability to magnify a sample 20–130,000× and provides an intense detail and
high-quality resolution image. A vacuum is necessary in SEM for the electron source to shoot
off electrons, in this way; the electrons are directed with electromagnets and can be focused
to hit the sample to produce a topographical image in a scanning manner. Moreover, this
vacuum environment helps the electrons in preventing to come in contact with air particulates
and gas molecules which in turn, prevent them from interacting with the sample, which can
result in a poor-quality image [49].
Fig 1.16: Construction of a scanning Electron microscopy [50]
The detectors in SEM are of various types having the ability to ensure the most detailing
image of the sample and to detect the composition of a substance. SEM gives a 3D
topographical image that reveals even minor or nano details of a substance. It has a wide
range of applications including the examination of food particles, ingredients, biological
substances, micro-organisms etc. The SEM and associated software are easy to use yet
expensive to operate. The main advantage of SEM is its limitation to inorganic and solid
sample that can be adjusted inside the vacuum chamber [50, 51].
Modification in SEM is useful in carrying out the desired visualization of the sample by using
affordable methods. In this way; we get different types of SEM i.e. atmospheric scanning
electron microscopy, Field Emission Scanning Electron Microscope (FESEM), and ultra-high
resolution SEM etc [52,53] By using elastically scattered electrons, mass measurements can
now be done regularly on a wide range of molecular and supra-molecular structures. The
scanning transmission electron microscope it is an efficient tool for mapping the chemical
composition of biological samples according to the recent progress in the acquisition and
analysis of electron energy-loss spectroscopy data [54].
Chapter 1: INTRODUCTION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 18
Fig 1.17: SEM image of a TiO2 nano-tubes [55]
1.13 Thermogravimetric Analysis
It is a thermoanalytical technique in which a thermobalance measures changes in sample
mass, where, thermobalance is consists of an appropriate temperature controller and an
electronic microbalance with a furnace. A thermogravimetric analysis is done to findout the
weight loss in different procedures like oxidation, loss of volatiles (moisture in a temperature
range) and decomposition giving the data in the form of a plot most of the times as a
temperature (or time)/mass (or mass percentage) plot. Though there arises some difficulty in
interpreting the polt data of composite compounds, but can be overcome by comparing the
plot with reference plots or adequate samples to carry out the compositional analysis.
Moreover, it is a useful tool to determine the life expectancy of a compound, the oxidative
and thermal stability, moisture and volatile contents and decomposition profile [56].
More precisely, it is a rapid technique of thermal analysis which, under a set of conditions
and at a fixed rate heats a substance and change is mass is measured as a function of
temperature. This loss of mass tells much about a compound’s properties in addition to its
kinetic parameters and energy of activation may require to design and operate the
thermochemical conversion equipment [57].
Chapter 1: INTRODUCTION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 19
Fig 1.18: A typical thermogravimetry apparatus with differential thermogravimetry
(DTG) facility [58]
Fig 1.19: A typical thermogravimetric analysis plot of different compounds [59]
Likewise other equipment, TG apparatus also couples with other instruments to get desired
results e.g. coupling it with mass spectrometer which can help in the identification of gaseous
compounds in the process of combustion [60].
Chapter 1: INTRODUCTION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 20
TG has a wide range of applications from the energy analysis of electronic waste products to
the estimation of carbon release from silicone products to estimate the effects on pollution
[61,62]. Not only for research purposes, TG can be useful in identifying the polymer in
forensic sciences [63]. TG analysis can predict the thermal stability and vapor pressure
behavior of a volatile substance [64]. Moreover, in pharmaceutical development, it is a useful
tool in accurate measurement of even a tiny heat change to develop a more suitable drug
product in addition to its wide range of application in quality control of pharmaceuticals [65].
It is helpful in determining the components of biomass e.g. lignocellulosic and fuels in
addition to their energy estimation [66, 67].
1.14 Atomic Absorption Spectroscopy
It is an analytical technique used to get information about any compound quantitatively. The
technique based on the absorbance of the electromagnetic radiation by gaseous atoms at some
specific wavelength to produces signals which can be detected and identified further. In the
optical path, the concentration of those free absorbing atoms influences the absorption signal.
This whole operation requires the conversion of the sample into gaseous state and for this
purpose, an atomizer is used. Atomic absorption spectrometry (AAS) is of categorized into
two types on the basis of atomizer i.e. flame atomic absorption spectrometry (FAAS) and
electrothermal atomic absorption spectrometry (ETAAS). The former type provides the
continuous signals while the later provides the signals in discontinuous mode i.e. 2-
4min/sample. In both types of AAS, the liquid samples are introduced to the analyzer easily
and more elaborately, an aerosol while using FAAS and microliter sample in case of ETAAS.
The methods of cold vaporization and hydride generation introduces gas molecules in
atomizer [68].
It is relatively an inexpensive technique used for the quantitative analysis and widely used for
low-budget research projects. There exist many types of AAS on the basis of its construction
having respective pros and cons and can be selected easily on the basis of type of analyte
[69].
A spectrometer consists of a light source, an atomizer, a wavelength detector and a signal
detector. Based on the configuration, two types of AAS are developed i.e. single beam
spectrometer in which light source, atomizer and detector are aligned and the selected
wavelength is directed to the detector, double-beam spectrometer which has a beam-splitter
by which beam splits to an atomizer and other acts as a reference for a continuous
comparison of the two lights [70].
Chapter 1: INTRODUCTION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 21
Fig. 1.20(a): Single beam spectrometer (b) double beam spectrometer [70]
1.15 Application of Hydrogels on Water Treatment
Hydrogels possess a unique property to absorb metal ions from aqueous solutions. This
property leads to some of the most important applications. The absorption of metal ions by
hydrogels can be calculated by concentration of metal ions in initial and equilibrium phase in
aqueous solution, the volume of hydrogel used and by the weight of hydrogel. Moreover, the
metal absorption is affected by the salt concentration of solution and pH [36].
In recent times, various methods are employed to treat the polluted water by means of
physical and chemical methods e.g. removal of heavy metal ions. Various studies analyzed
the methods of using hydrogels for the removal of heavy metal ions and reported
considerable results [37]. In this study, we will examine the treatment of contaminated water
with heavy metal ions by the use of hydrogels.
Chapter 1: INTRODUCTION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 22
Chapter 2
LITERATURE REVIEW
Chapter 2: REVIEW OF LITERATURE
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 22
2. REVIEW OF LITERATURE:
Since after the first preparation of hydrogels, it is widely studied and researched and many of
its properties are evaluated.
(Slaughter et al., 2009) studied their properties, methods of preparation, biocompatibility
and their physical characters, they can be used in regenerative medicine [71].
(Gong et al.,2010) revealed another progress for hydrogels is the formation of a double
network gel having a relatively high toughness and strength mainly consisting of two types of
networks with opposite in nature. This double network gel showed some common features
with ductile and brittle nano composite materials e.g. dentins and bones [72].
( Bhattarai et al.,2010) made use of chitosan as a polymeric material in the gel led the
formation of a drug delivery vehicle that releases the payloads in varying stimuli
Furthermore, chitosan possesses the superiority over other polymers being biodegradable,
low toxic and biocompatible substance [73].
(Nguyen et al., 2010) prepared injectable biodegradable copolymer hydrogels which undergo
a sol-gel transition under stimuli of pH and temperature have found uses in biomedical and
pharmaceutical sciences e.g. drug delivery and cell-growth [74].
(Burdick et al., 2010) worked in the field of tissue regeneration, hyaluronic acid derived
hydrogels present a promising effect in tissue repair and regeneration by delivering the cells
and therapeutic agents [75].
(Sun et al.,2012) find out that the hydrogels have uses in various fields from tissue
engineering to drug delivery as a vehicle, from optics and fluidics as actuator to biological
studies as model extracellular metrices However, sometimes their role gets limited due to
their mechanical properties as most of the hydrogels do not show high stretchability like
alginate hydrogels, some are brittle. The gel’s toughness may be attributed to two main
factors i.e. hysteresis by unzipping the network of ionic crosslinks and crack bridging by the
network of covalent crosslinks. In contrast, the crosslinking property of the hydrogel can
preserve its initial state upon unloading and the un-zipped network though can cause damage
but can be re-zipped [76].
(Hennink et al.,2012) used hydrogels as a vehicle for drug delivery, the hydrogel’s strength
can be increased by the use of chemical cross-linkers which can be toxic and may give
unwanted reactions. However, physical cross-linkers may substitute these chemical
compounds) [77].
(Appel et al.,2012) prepared another type supramolecular crosslinkers lead the formation of
novel supramolecular polymeric hydrogels having directional, specific and dynamic non-
covalent interactions which can be the basis for many new discoveries [78].
Chapter 2: REVIEW OF LITERATURE
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 23
(Phadke et al.,2012) find out permanently cross-linked hydrogels can be edited or engineered
to make them a self-healing substance in an aqueous environment and this kind of hydrogel
can withstand multiple cycles of self-healing without compromising its mechanical status and
kinetics [79].
(Malda et al.,2013) find out the Biofabrication is the formation of a bio-engineered tissue
made by cells and biomaterials. Cell-laden hydrogels are an important part of this
biofabrication process and also called as “bio-inks” as they have the features of natural extra
cellular matrix and they permit the encapsulation of cells in a hydrated 3D environment [80].
(Sun et al.,2013) studied another type of molecules called the polyampholytes polymers
having some randomly dispersed cationic and anionic repeat groups, have the ability to make
a viscoelastic and tough hydrogels having comparable multiple mechanical properties. This
approach may prove helpful in the formation of a tough hydrogels for further applications
[81]. Incorporation of the nano-particles within the polymeric structure yield out a
nanocomposite having superiority in physical, chemical and biological properties opening out
a field for further research and study [82].
(Gaharwar, et al.,2014) studied Dynamic modulations in the hydrogel structure physically
and chemically lead to changes in its properties which in turn, may open doors of further
research and study [83].
(Lee et al.,2018) recently discovered that hydrogels can take part in deciding the cell fate.
The stress/strain time dependent changes in interaction with cells, the degradation process by
the cell mediation and synthesis of matrix can influence cell status and tissue repairing. This
can be categorized as a biophysical property of hydrogels [84].
(Caliari et al.,2016) determined that the standard cell culture does not play a significant role
in recapitulating native cellular milieus, hydrogels most importantly the commercially
available hydrogel may take part as a cell culture medium due to their unique properties [85].
(Bodenberger et al.,2016) found that by biofabrication of hydrogels, their structure can be
manipulated i.e. creation of a pore in structure of the hydrogel may alter the physicochemical
properties of hydrogel a bit and cancer cell lines were seen adhered to the wall of the pore
[86].
(Li et al.,2016) working in the field of pharmaceutical manufacturing found that the
hydrogels play a significant role as drug delivery, release time, degradation and dissolution
when employed with drug dosage form. In this way, hydrogels have the ability to carry out
the spatial and temporal control over the drug whether macromolecular of having small
molecules in its formation [87]. Apart from the hydrogel structure manipulating, 3D printing,
double network cross-linking and drug release development, hydrogels can be used as a
cartilage repair.
(Vega et al.,2017) studied the hydrogels structure with respective mechanical properties can
be supplemented within the cartilage structure that may improve its quality and strength [88].
Chapter 2: REVIEW OF LITERATURE
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 24
(Perale et al.,2011) developed a technique in which the biomaterial is injected to the site of
injury which carries the cells or drugs and delivers it at the site of injury. Among these
biomaterials, synthetic, natural or composite hydrogels are considered as a reasonable
substance which swells when comes in contact with water. These hydrogels may improve the
healing process of the spinal cord injury [89].
(Kornev et al.,2018) studied in biomedical sciences, hydrogels may possess the ability to
repair or replace the damaged brain cell inside the brain. These 3D structures can act as a
promising tool for regeneration of brain tissues due to their biological, physical and chemical
properties. Hydrogels prepared from different polymers i.e. hyaluronic acid, chitosan,
alginate, collagen type I, methylcellulose, fibrin, gellan gum, Matrigel, proteins and self-
assembling peptides, poly(ethylene glycol), methacrylamides and methacrylates are
implemented in recent brain injury studies. And among them, self-assembling peptide and
collagen I based hydrogels showed an attractive properties for neuroregeration [90].
(Kirshner et al.,2012) employed hydrogels in a bio-sensitive system by embedding a thin,
pH-responsive hydrogel within the sensor in which it can sensed a tiny change in pH by
triggering the pressure sensor due to its swelling properties. So as with volume changes, the
hydrogel was tuned to sense volume changes in response to pathological pH values [91].
(Gao et al.,2016) In another study, nanoparticle-hydrogel system was employed for drug
delivery and called it “NP-gel”. This NP-gel showed a promising response in drug delivery
(passively-controlled, stimuli-responsive, site specific) and detoxification. Integration of
therapeutic nano-particles with hydrogels makes a hybrid biomaterial system that extensively
affected the localized delivery of drug [92].
(Gao et al.,2016) did modification of naturally occurring extracellular matrix
glycosaminoglycan hyaluronic acid (HA) was studied in a recent study so that it may release
photo-crosslinkable hydrogels having an increased long-term stability and mechanical
stiffness with little or no decrease in cytocompatibility. These tailor-made methacrylated
hyaluronic acid (MeHA) gels proved useful for bone tissue engineering and 3D bioprinting
within a narrow window of concentration [93].
(Gao et al.,2015) Employed hydrogels to recycle rare earth metals. The immobilized gel
particles were formed by doping poly-γ-glutamate (PGA) and sodium alginate (SA). This
composition showed an excellent capacity in the absorption of rare earth metals. By applying
different techniques like Scanning electron microscopy (SEM) and Fourier transform infrared
(FT-IR) spectroscopy, it was revealed that carboxyl group in the composite played a major
role in absorbing and recycling the rare earth metals from waste water [94].
(Lau et al.,2015) Formation of a multicompartment hydrogels having unique properties
imparted its role in biomaterials with desired properties. This multicompartment system with
engineered enhanced mechanical properties presented multiple biological properties and
implemented its role in tissue engineering, cancer and gene therapy [95].
Chapter 2: REVIEW OF LITERATURE
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 25
(Lauren et al.,2017) In another study in biomedical sciences, the surgical sutures were
employed with nanofibrillar cellulose-alginate (NFCA) in rats and mice tissues. Adding 8%
sodium alginate in NCFA hydrogel system increased its viscosity and coating strength. The
study showed that these NFCA coated sutures presented as a useful tool in cell-based therapy
and in treatment after the surgery [96].
(Pérez-Luna et al.,2018) studied the cross-linked nature of hydrogels is not only suitable for
the delivery of proteins at the site of action, but they can be used to encapsulate the cells with
therapeutic drugs. They can form a system for the controlled release of drugs from the
encapsulated cells thus making them a really helpful and easy way in combating the disease
[97].
Chapter 2: REVIEW OF LITERATURE
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 26
Chapter 3
MATERIALS AND METHODS
Chapter 3: MATERIALS AND METHODS
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 26
3. Materials and Methods
The Commercially available powders of Potato starch (laboratory grade), Amylum starch
(laboratory grade with no further purification) and sodium salt of Carboxymethyl cellulose
were purchased from scientific store located in Lahore, Pakistan (average molecular
weight=90000) (DS = 0.7). The Carboxymethylcellulose along with these starches was used
for the synthesis of superabsorbent polymers (SAP) [118]. To crosslink the polymer complex,
Aluminum sulfate octadecahydrate (reagent grade) was also used [119].
3.1 Method
3.1.1 Preparation of Superabsorbent Polymer (SAP)
By using a magnetic stirrer in a large beaker, about 20g of sodium salt of Carboxymethyl
cellulose was mixed with distilled water (2.0L). Soon after the mixing, these two starch types
(1.2g) were subjected to gelatinization at 80°C in distilled water (50ml) for 45 min. In CMC
solution, previously gelatinized starch was added and they were allowed to mix for 1hour.
Aluminum sulfate in some variable amounts was then introduced in to the beaker for another
30 minutes and the whole mixture was allowed to mix thoroughly. The whole solution was
placed on Teflon baking pans and dried at 70°C till the formation of a film. With the help of a
blender and pestle mortar, the film was shredded and grinded into a powder respectively
[120-121]. Soon after the addition of more than 2.3% of Aluminium sulfate, the polymer
exhibited an over-crosslinked complex. The resulting complex develops into a structure
carrying a lot of connections rendering too small voids for optimal water absorbency [122].
3.1.2 Preparation of Modified Starch (MS)
Native potato starch, hydrochloric acid 37 %, ethanol and sodium hydroxide were purchased
from Merck. All other chemicals were of analytical grade and used without further
purification. Distilled water was used throughout the work. The granular cold water-soluble
starch was prepared following the method of Chen and Jane (1994a) with slight
modifications. 10g starch was suspended in 40 g ethanol (40 %) at two different temperatures
(25 and 35 °C) and stirred mechanically for 10 min. This was followed by adding 12 g NaOH
(3 M on the solvent basis) at rate of 4 g/min. The suspension was gently stirred for 15 min;
afterwards an additional 40 g ethanol (40 %) was added slowly and stirred for another 10
min. The slurry was left at room temperature (25 °C) for 30 min in order to give sufficient
time for the treated starch to settle down. The settled granules were washed with fresh ethanol
solution (40 %), neutralized with 3MHCl in absolute ethanol, and then washed with 60 % and
95 % ethanol solutions. The obtained starch was dehydrated with absolute ethanol, and
finally oven-dried at 80 °C for 3 h.
Chapter 3: MATERIALS AND METHODS
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 27
3.1.3 Preparation of Modified Strach based Superabsorbent Polymer (MSAP)
Carboxymethyl cellulose sodium salt (20 g) was mixed with 2.0 L of distilled water in a
large beaker using a magnetic stirrer. Modified starch (2.4g) was gelatinized in 50 mL of
distilled water at 80°C for 45 min. The gelatinized starch was added to the CMC solution and
allowed to mix for 1 h. Then varying amounts of aluminum sulfate were added to the beaker
and the solution was allowed to mix for another 30 min. The solution was then spread on
Teflon baking pans and dried at 70°C until a film is formed. The film was shredded with a
blender and then ground into a powder with a mortar and pestle [120-121]. The addition of
more than 2.3% of Aluminium sulfate, it was observed that polymer was over-crosslinked
and the complex had too many connections making the void spaces too small for optimal
water absorbency [122].
3.2 Characterizations
3.2.1 Flow-ability Parameters of SAP
3.2.1.1 Angle of Repose.
Fixed funnel method was used to find out angle of repose for the purpose of studying
the flow property of hydrogel [123]. Through a fixed funnel placed previously on a graph
paper, hydrogel (powdered) was then allowed to fall. Angle of repose (θ) was calculated by
the following equation;
h
Tanr
(1)
h=height of heap
r=radius of heap
3.2.1.2 Bulk and Tap Density.
By the placement of the hydrogel (1.0 g) in graduated cylinder, we can measure the volume
of hydrogel Vb. The tapped volume (Vt) was noted after tapping 100 times the graduated
cylinder. Tap density (Dt) and Bulk density (Db) were calculated by using equations (2) and
(3) respectively;
( )
t
t
WeightofHydrogelD
VolumeofHydrogel V (2)
( )
b
b
WeightofHydrogelD
VolumeofHydrogel V (3)
Chapter 3: MATERIALS AND METHODS
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 28
3.2.1.3 Hausner Ratio and Carr’s Index.
The specific hydrogel’s flow properties can be determined by means of Hausner ratio and
Carr’s index [123]. “Hausner ratio is the ratio of tap density to bulk density” as mentioned in
equation (4);
( ) t
b
DHausnerratio h
D (4)
“Carr’s index is the percentage ratio which represents arrangement of particles” and it can be
measured by using the equation (5);
'sin ( ) 100 (1 )t
b
DCarr dex C
D (5)
Where Db and Dt are bulk and tap densities, respectively.
3.2.1.4 Moisture Content.
Before and after drying, the weight of hydrogel was calculated at 105 °C (1 hour).
3.2.1.5 Centrifuge Retention Capacity.
“Water retention capacity is the ratio of wet sediment mass to dried mass”. Centrifuge
retention capacity or water retention capacity was measured by centrifuging the freshly
prepared solution of hydrogel (1% w/w) at 4500 rpm (30 min) in deionized water at 25ºC.
Weight of wet paste was measured after decanting the supernatant. Weight of the dried mass
was checked after completely drying the paste at 70°C [124-125].
3.2.1.6 Swelling Capacity.
The tapped volume was measured by tapping the graduated cylinder 100 times in which the
powdered hydrogel (1.0g) was placed. Then, in de-ionized water, hydrogel was mixed
thoroughly and the volume was adjusted to 100 cm3. After keeping for 24 hours of these
swollen hydrogel’s sediment, its volume was observed and Swelling Capacity(v/v) was
calculated by using equation (6);
SwellingCapacity(v/ v)SwollenVolume
TappedVolume (6)
3.2.1.7 Dynamic and Equilibrium Swelling.
In order to find out the pH dependent swelling, SAP (0.1 g each) were placed in the
bags of cellophane which were soaked into phosphate buffers (pH 6.8 and 7.4), HCl buffer
(pH 1.2) and deionized water for 24 hours. The weights of these swollen hydrogels were
Chapter 3: MATERIALS AND METHODS
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 29
checked after regular intervals for 24 hours. The swelling capacity (g/g) in each case was
calculated as;
( / ) t O c
O
W W WSwellingCapacity g g
W
(7)
Wt = weight of swollen hydrogel (with wet cellophane bag)
W0= weight of dry hydrogel
Wc= weight of wet cellophane bag
The normalized degree of swelling (Qt) is a ratio between media (buffers of pH 1.2, 6.8, 7.4
and de-ionized water) penetrated into gel and initial weight of hydrogel at time t as given in
equation (8).
s d tt
d d
W W WQ
W W
(8)
Ws =weight of swollen hydrogel at time t
Wd =weight of dried hydrogel at time t=0
Wt =weight of water penetrated into hydrogel at time t.
Qe =(Normalized equilibrium degree of swelling) is the ratio of media penetrated into
hydrogel
at t∞ to weight of dried hydrogel at t=0. It can be calculated by equation (9);
d ee
d d
W W WQ
W W
(9)
W∞=weight of swollen hydrogel at time t∞ (swelling remains constant)
Wd =weight of dried hydrogel (t=0)
We =amount of water absorbed by hydrogel (t∞)
3.2.1.8 Swelling Kinetics.
To find out the kinetic order of swelling, normalized degree of swelling (Qt) and normalized
equilibrium degree of swelling (Qe) values can be used [126]. The second order kinetics
equation (10) can be calculated by using the following equation [127].
2
1
t ee
t t
Q KQ Q (10)
3.2.1.9 The Swelling and De-swelling Behavior in Response to External Stimuli.
SAP has ability to show swelling and de swelling in different aqueous and non-aqueous
media. The Gravimetric method was employed for its analysis.
Chapter 3: MATERIALS AND METHODS
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 30
1. The swelling of hydrogel was observed while keeping its cellophane bag (0.1g) in
deionized water, allowed to stand for 1hour and its weight was measured . Then by
placing it in pure ethanol for 1 hour, its weight was again measured as a function of its
de-swelling time.
2. By using buffer solutions (pH 7.4 and 1.2), the swelling & de-swelling behaviors were
studied in another experiment. The swelling was observed by keeping its cellophane
bag (0.1g) in a buffer (pH 7.4) for 1 hour and after that its de-swelling was observed
by keeping in another buffer solution (pH 1.2) for one more hour.
3. As above mentioned, the swelling and de-swelling behavior was also observed in
water and aqueous NaCl solution (0.9%).
As decrease in the osmotic pressure occurs due to addition of salt between hydrogel and
water, similar phenomenon happens in the present case and the swelling decreases and vice
versa. In other words de-swelling occurs due to the fact that water molecules moves out of
hydrogel rendering it flaccid [128-129].
3.2.2 Scanning Electron Microscopy (SEM)
The internal structure and superficial morphology of SAP was analyzed by a 10 kV operating
scanning electron microscope (NanoSEM 450, FEI Nova). In deionized water (2ml), dried
hydrogel (0.1 g) was allowed to mix by mixer mill. This mixture was subjected to sonication
for 30 min in order to remove air bubbles from it. Then, resulting swollen SAP was placed at
-20°C, allowing it to get frozen and was subjected to freeze-drying. Moreover, sharp blade
was used to get the cross-sections of hydrogel transversely and vertically to reveal its porous
nature.
3.2.3 FTIR Analysis
Fourier transform infrared spectroscopy (FT-IR, KBr, 4000–400 cm−1) was performed on
Carboxymethyl cellulose Sodium (CMC.Na), Potato, Amylum starches, and SAP by using an
IR-Prestige-21instrument (Shimadzu, Japan). The obtained spectra by FT-IR were measured.
3.2.4 PXRD Analysis
Powdered X-ray Diffractrometry of all four samples was performed under the given
conditions.
Table 3.1: Conditions for PXRD Analysis for all six Samples
Anode material Cu
Generator voltage 40
Tube current 40
Monochromator used NO
Chapter 3: MATERIALS AND METHODS
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 31
K-Alpha1 wavelength 1.540598
K-Alpha2 wavelength 1.544426
Ratio K-Alpha2/K-Alpha 0.5
File date and time 13-08-18 12:42
h k l 0 0 0
Scan type CONTINUOUS
Scan axis Gonio
Scan range 20-80
Scan step size 0.02
No. of points 3000
Phi 0
Time per step 0.2
3.2.5 Thermogravimetric Analysis (TGA)
Thermogravimetric Analysis (TGA) was performed on all four samples i.e Carboxymethyl
cellulose Sodium (CMC.Na), Potato, Amylum starches, and SAP. On the basis of results
obtained from the above said method, the maximum and final thermal decomposition
temperatures were investigated. The obtained data was analyzed by using Universal Analysis
2000 and Microsoft Excel 2010 software.
3.3 Applications of Hydrogels on Water Treatment
The novel gel was then used in dried form for removal of metal ions from their standard
solutions, for this purpose Atomic Absorption Spectrophotometer was used.
3.3.1 Atomic Absorption Spectroscopy
To get the optimized amount, the 10, 20, 40, 60,80 and 100 mg of SAP was used to add in
100 mg/L solutions of Cd+2 , Pb+2,Fe+2 and then stirred at the temperature of 298K, at the rate
of 130r/min for 30 minutes. The samples were analyzed on “Flame Atomic Absorption
Spectrophotometer; Shimadzu AA-7000F”. All values of metal analysis were recorded in
parts per million (ppm: mg/L). For calibration curve, four standards i.e. 0.5, 1.0, 2.0 and
4.0ppm were also used. To study the adsorption behavior, two empirical adsorption models
named Freundlich and Langmuir models were used. The obtained experimental data at pH 7
Chapter 3: MATERIALS AND METHODS
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 32
was analyzed by applying Freundlich and Langmuir equations. The Freundlich and Langmuir
isotherms are given by eq. (10) and (11), respectively:
KF= Freundlich constants related to adsorption capacity
N = Freundlich constants related to intensity
Ce =equilibrium concentration of metal ion in the solution.
Ce/Qe = Ce/Qmax + 1/bQmax (11)
Qmax and b = Langmuir constants related to maximum monolayer adsorption capacity and
adsorption energy
3.3.2 The Aims and Objectives of Study
A hydrogel can be defined specifically as a substance consists of hydrophilic polymers
arranged in a three-dimensional pattern to form a network. The wide range of applications of
a hydrogel is attributed to its ability to absorb a large amount of water by swelling up and
keeping its structure retained. It is all due to its cross-linked structure with solutions or water
molecules and this fact was reported firstly by Lím and Wichterle in 1960 [98]. A hydrogel
normally contains 10% water of its weight. The hydrogels possess relatively high grade
flexibility because of their high water contents like natural tissues. Moreover, hydrogels may
show a hydrophilic property because of the presence of some hydrophilic groups (-COOH, -
NH2, -OH, -CONH2 and SO3H [98]. On the basis of their flow behavior, they can be
categorized into weak and strong hydrogels [99]. Because of the wide range of their
applications , they’re also used in the food industry i.e. some edible gels are used as gelling
polysaccharides at a large scale [100]. In short, the term hydrogel may be described as a
structure of three-dimensional network with cross-linked molecules. Irrespective of their
source, either obtained from synthetic or natural class of polymers, they contain similar a
property of swelling up by absorbing a significant amount of water [101].
Heavy metal pollution is considered as one of the serious environmental hazards not
only for human beings but also for all living organisms due to its toxic and carcinogenic
effects. In recent years, the methods like ion exchange, chemical precipitation, membranous
separation and adsorption have been employed to reduce such a type of environmental
pollution. Due to its economic and technical applications among all the above discussed
methods, the most reliable choice to reduce this type of pollution is the method of adsorption.
[102-103].
Human activities like mining, smelting, alloy manufacturing, textile operations, use of
pesticides, fertilizers, electronics and paint industry, resultantly cause Cadmium(Cd2+)
Iron(Fe2+) and lead(Pb2+) to accumulate these highly toxic environmental pollutants in the
ground water reservoirs[104-105]. Almost all these above mentioned activities can also result
in accumulation of heavy metals in environment and ultimately these metals penetrate in the
living tissues and become a part of food chain [106]. High levels of these metal ions in
Chapter 3: MATERIALS AND METHODS
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 33
human body can lead to some serious and major problems i.e. cancer [107-108], kidney
dysfunction, prostate carcinogenesis[109], multiple bone fractures, hypertension [110] and
weight loss [111]. Some cellulosic materials such as agriculture waste [112-113] and
carboxylated cellulose nano-crystals [114], fruit peels and plant barks[115] (low-cost
sorbents) are reported to depict a relatively high capability for metal binding and removal of
heavy metal ions and they can be considered useful as they are abundant and renewable
sources in nature. In view of above described hazards, there arises an increased need of an
efficient method with a high and defined sorption capacity with a specific type of functional
group preferably. Among all the renewable biopolymers occurring naturally, cellulose
possesses some modifiable hydroxyl groups [116]. By modifying these hydroxyl groups and
grafting the polysaccharides on the resulting carboxylate group, the exchange of cations in
aqueous solutions can be made possible [117].
Therefore, by chemically modifying the substances containing cellulose/
polysaccharide structures, we can enhance its ability to uptake of metal ions from the
solution. Synthesis of a super-absorbent hydrogel by commercially available low cost
polysaccharide, i.e. Carboxymethylcellulose, combined with other starch, i.e. Potato and
Amylum starch was studied extensively in the following described experiments. Moreover,
the cross-linked polymer complexes (CMC) associated with aluminum ions by non-
permanent chemical bonds were also studied, when further observed in the presence of water,
which showed their swelling behavior. These cross-linked starch and CMC can create an
environment friendly biopolymer based SAP which may help to reduce the hazardous metal
ions from human consumption substances [117].
Chapter 3: MATERIALS AND METHODS
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 34
Chapter 4
RESULTS AND DISCUSSION
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 34
4. Results and Discussion
The Novel gel was investigated and characterized by
1. Analysis of its Physical Properties
2. Swelling Behavior on the basis of changes in pH temperature and medium with time laps
3. FTIR (Fourier Transform Infared Spectroscopy)
4. SEM (Scanning Electron Microscopy)
5. TGA (Thermogravimeteric Analysis)
6. PXRD (Powdered X-ray Difractrometery)
4.1Physical Properties of SAP
The physical properties of hydrogel are as follow;
Table 4.1: Phyical Properties of SAP
Moisture content (%) 20 ± 0.20
Average particle size (μm) ≈228
Angle of repose 3± 0.25
Bulk density (g/cm3) 0.8 ± 0.01
Tapped density (g/cm3) 0.66 ± 0.01
Carr’s index (%) 17.5 ±1.50
Hausner ratio .825 ± 0.06
Swelling capacity on 24 h (g/g) 37.33±2.00
Centrifuge retention capacity
(%) 70 ± 1.11
Table 4.1and 4.2 reflects different parameters obtained from physical study of prepared hydrogel
(SAP) and (MSAP). These results were obtained by grinding the completely dried gel with pistal
and mortar and by passing through sieve of 0.5 mesh.
Table 4.2: Physical Properties of MSAP
Moisture content (%) 19 ± 0.20
Average particle size (μm) ≈172
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 35
Angle of response 2.6± 0.25
Bulk density (g/cm3)
Tapped density (g/cm3) 0.66 ± 0.01
Carr’s index (%) 17.5 ±1.50
Hausner ratio .825 ± 0.06
Swelling capacity on 24 h (g/g) 35.2±2.00
Centrifuge retention capacity (%) 66 ± 1.11
Hausner ratio, Carr’s index and angle of repose are indicative of poor flow property of powdered
SAP and MSAP.
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 36
4.2 Swelling behavior of Hydrogels and its Ingredients
4.2.1 Swelling Behavior of Potato Starch
a:Swelling Behavior at 30oC b:Swelling Behavior at 37OC
c:Swelling Behavior at pH 2.1 d:Swelling Behavior at pH 6.8
e: Swelling Behavior at pH 7.4
y = 0.0029x + 0.2141R² = 0.4655
0
0.05
0.1
0.15
0.2
0.25
0.3
0 5 10 15
Wei
ght
of
Sam
ple
aft
er
swal
low
ing
(g)
Time (min)
y = 0.0029x + 0.2141R² = 0.4655
0
0.05
0.1
0.15
0.2
0.25
0.3
0 5 10 15
Wei
ght
of
Sam
ple
aft
er
swel
low
ing
(g)
Time (min)
y = 0.0403x + 1.1637R² = 0.7354
0
0.5
1
1.5
2
0 5 10 15
Wei
ght
of
Sam
ple
aft
er
swel
low
ing
(g)
Time (min)
y = 0.0296x + 0.7367R² = 0.6925
0
0.2
0.4
0.6
0.8
1
1.2
0 5 10 15
Wei
ght
of
Sam
ple
aft
er
swel
low
ing
(g)
Time (min)
y = 0.09x + 0.532R² = 0.8056
0
0.5
1
1.5
2
0 5 10 15Wei
ght
of
Sam
ple
aft
er
swel
low
ing
(g)
Time (min)
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 37
4.2.2 Swelling Behavior of Amylum Starch
a:Swelling Behavior at pH 30OC b:Swelling Behavior at pH 37oC
c:Swelling Behavior at pH 2.1 d:Swelling Behavior at pH 6.8
e: Swelling Behavior at pH 7.4
y = 0.0144x + 0.2323R² = 0.6428
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0 5 10 15
Wei
ght
of
Sam
ple
aft
er
swel
low
ing
(g)
Time (min)
y = 0.0573x + 1.247R² = 0.6709
0
0.5
1
1.5
2
0 5 10 15
Wei
ght
of
Sam
ple
aft
er
swel
low
ing
(g)
Time (min)
y = 0.0244x + 0.2323R² = 0.5807
0
0.1
0.2
0.3
0.4
0.5
0.6
0 5 10 15
Wei
ght
of
Sam
ple
aft
er
swel
low
ing
(g)
Time (min)
y = 0.0571x + 0.7037R² = 0.8863
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 5 10 15
Wei
ght
of
Sam
ple
aft
er
swel
low
ing
(g)
Time (min)
y = 0.0988x + 0.524R² = 0.6476
0
0.5
1
1.5
2
0 5 10 15Wei
ght
of
Sam
ple
aft
er
swel
low
ing
(g)
Time (min)
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 38
4.2.3 Swelling Behavior of Carboxymethyl cellulose
a:Swelling Behavior at 30oC b:Swelling Behavior at 37oC
c:Swelling Behavior at pH 2.1 d:Swelling Behavior at pH 6.8
e:Swelling Behavior at pH 7.4
y = 0.0822x + 0.544R² = 0.8791
0
0.5
1
1.5
0 5 10 15Wei
ght
of
Sam
ple
aft
er
swel
low
ing
(g)
Time (min)
y = 0.1082x + 0.2883R² = 0.8605
0
0.5
1
1.5
0 5 10 15Wei
ght
of
Sam
ple
aft
er
swel
low
ing
(g)
Time (min)
y = 0.0373x + 0.354R² = 0.6586
0
0.2
0.4
0.6
0.8
1
0 5 10 15
Wei
ght
of
Sam
ple
aft
er
swel
low
ing
(g)
Time (min)
y = 0.0434x + 0.4273R² = 0.7239
0
0.2
0.4
0.6
0.8
1
0 5 10 15
Wei
ght
of
Sam
ple
aft
er
swel
low
ing
(g)
Time (min)
y = 0.0741x + 0.6597R² = 0.8181
0
0.5
1
1.5
0 5 10 15
Wei
ght
of
Sam
ple
aft
er
swel
low
ing
(g)
Time (min)
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 39
4.2.4 Swelling Behavior of Modified Starch
a:Swelling Behavior at 30oC b:Swelling Behavior at 37oC
c:Swelling Behavior at pH 2.1 d:Swelling Behavior at pH 6.8
e: Swelling Behavior at pH 7.4
y = 0.0324x + 0.3953R² = 0.5864
0
0.2
0.4
0.6
0.8
0 5 10 15Wei
ght
of
Sam
ple
aft
er
swel
low
ing
(g)
Time (min)
y = 0.0343x + 0.672R² = 0.5716
0
0.2
0.4
0.6
0.8
1
1.2
0 5 10 15Wei
ght
of
Sam
ple
aft
er
swel
low
ing
(g)
Time (min)
y = 0.0773x + 0.74R² = 0.8316
0
0.5
1
1.5
2
0 5 10 15Wei
ght
of
Sam
ple
aft
er
swel
low
ing
(g)
Time (min)
y = 0.0243x + 0.5567R² = 0.8034
0
0.2
0.4
0.6
0.8
1
0 5 10 15Wei
ght
of
Sam
ple
aft
er
swel
low
ing
(g)
Time (min)
y = 0.0252x + 0.1683R² = 0.9236
0
0.1
0.2
0.3
0.4
0.5
0 5 10 15
Wei
ght
of
Sam
ple
aft
er
swel
low
ing
(g)
Time (min)
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 40
4.2.5 Swelling Behavior of SAP
a:Swelling Behavior at 30oC b:Swelling Behavior at 37oC
c: Swelling Behavior at pH 2.1 d:Swelling Behavior at pH 6.8
e: Swelling Behavior at pH 7.4
y = 0.0296x + 0.4817R² = 0.6983
0
0.2
0.4
0.6
0.8
1
0 5 10 15
Wei
ght
of
Sam
ple
aft
er
swel
low
ing
(g)
Time (min)
y = 0.0645x + 0.833R² = 0.7508
0
0.5
1
1.5
2
0 5 10 15
Wei
ght
of
Sam
ple
aft
er
swel
low
ing
(g)
Time (min)
y = 0.0506x + 0.7757R² = 0.779
0
0.5
1
1.5
0 5 10 15
Wei
ght
of
Sam
ple
aft
er
swel
low
ing
(g)
Time (min)
y = 0.0449x + 0.4423R² = 0.8361
0
0.2
0.4
0.6
0.8
1
1.2
0 5 10 15
Wei
ght
of
Sam
ple
aft
er
swel
low
ing
(g)
Time (min)
y = 0.0277x + 0.3413R² = 0.8146
0
0.2
0.4
0.6
0.8
0 5 10 15Wei
ght
of
Sam
ple
aft
er
swel
low
ing
(g)
Time (min)
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 41
4.2.6 Swelling Behavior of MSAP
a:Swelling Behavior at 30oC b:Swelling Behavior at 37oC
c:Swelling Behavior at pH 2.1 d:Swelling Behavior at pH 6.8
e:Swelling Behavior at pH 7.4
y = 0.0327x + 0.2483R² = 0.9607
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 5 10 15Wei
ght
of
Sam
ple
aft
er
swel
low
ing
(g)
Time (min)
y = 0.0428x + 0.5647R² = 0.5297
0
0.2
0.4
0.6
0.8
1
1.2
0 5 10 15Wei
ght
of
Sam
ple
aft
er
swel
low
ing
(g)
Time (min)
y = 0.0182x + 0.2133R² = 0.8754
0
0.1
0.2
0.3
0.4
0.5
0 5 10 15Wei
ght
of
Sam
ple
aft
er
swel
low
ing
(g)
Time (min)
y = 0.0378x + 0.26R² = 0.8412
0
0.2
0.4
0.6
0.8
0 5 10 15Wei
ght
of
Sam
ple
aft
er
swel
low
ing
(g)
Time (min)
y = 0.0193x + 0.1467R² = 0.8179
0
0.1
0.2
0.3
0.4
0.5
0 5 10 15
Wei
ght
of
Sam
ple
aft
er
swel
low
ing
(g)
Time (min)
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 42
4.3. pH Responsive Swelling of Hydrogels
4.3.1 pH Responsive Swelling of SAP
Buffers of pH 1.2, 6.8 and 7.4 were made according to the pH values of stomach, and the
different parts of intestine, to check the swelling behavior of SAP upon them. The swelling
behavior of hydrogel in deionized water was found to be more as compared to acidic and basic
buffers(pH 1.2, 6.8, 7.4). We can infer that it may be due to the protonation of carboxylic groups,
located at the terminal ends of polymer chains. The capability of anion formation of carboxylic
acid increases as the pH rises in contrast with the alkaline media. Moreover in basic buffers,
there appeared a relatively low swelling capacity in comparison to its behavior in deionized
water. In alkaline media, the screening effect of excess cations may be responsible for this
relatively low swelling capacity which stops the anion-anion repulsions due to carboxylate
anion’s shielding effect. According to the literature, many other hydrogels’s water absorbent
property depend upon their pH values. [128-129].As explained by 2nd order kinetic mode, the
pH dependent swelling of hydrogel is controlled by the relaxation of polymer chain and diffusion
of solvent [36].
Figure 4.1(a): Swelling data of SAP obtained in water and buffers of pH 1.2, 6.8 and 7.4
On the basis of data obtained from swelling study it depicts the property of prepared hydrogel to
show more swelling behavior more in basic rather than acidic medium, i.e at pH 7.4 and 6.8.
The kinetic study that was performed on data obtained by the swelling behavior of SAP shown in
buffers of pH 6.8 and 7.4 and in deionized water is given below;
0
1
2
3
4
5
6
7
0 200 400 600 800 1000 1200
We
igh
t (g
)
Time (min)
water
pH 2.1
pH 6.8
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 43
The swelling behavior of hydrogel in deionized water was found to be more as compared to
acidic and basic buffers(pH 1.2, 6.8, 7.4).
Fig. 4.1(b): Swelling data and kinetics of SAP obtained in buffers of pH 6.8 and 7.4
From the swelling data, the values of Qt (mg/g) and t/Qt (min/(mg/g)) were finded out, and were
plotted against the time(min).
Figure 4.1(c): Swelling data of SAP between time (min) and Qt(mg/g) obtained in water and
buffers of pH 1.2, 6.8 and 7.4
The swelling behavior of hydrogel in deionized water was found to be less as compared to
basic buffers(pH 6.8, 7.4) and more than acidic one (pH 2.1).
0
1
2
3
4
5
6
7
0 200 400 600 800 1000 1200
We
igh
t (g
)
Time (min)
pH 6.8
pH 7.4
0
10
20
30
40
50
60
0 200 400 600 800 1000 1200
Qt(
mg/
g)
Time (min)
Qt (Water)
Qt (Ph 2.1)
Qt (Ph 6.8)
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 44
Figure 4.1(d): Swelling data of SAP between time(min) and t/Qt(min(mg/g)) obtained in
water and buffers of pH 1.2, 6.8 and 7.4
In practical applications, a higher swelling rate is required as well as a higher swelling capacity.
The swelling kinetics for the absorbents is significantly influenced by factors such as swelling
capacity, size distribution of powder particles, specific size area, and composition of polymer.
4.3.2 pH Responsive Swelling of MSAP
The kinetic studies were performed on swelling data of Modified starch based SAP obtained in
water and at pH 6.8 and 7.4. Fig.1(a) and (b)
0
5
10
15
20
25
30
35
40
0 200 400 600 800 1000 1200
t/Q
t(m
in/(
mg/
g))
Time (min)
t/Qt (Water)
t/Qt (Ph 2.1)
t/Q (Ph 6.8)
t/Qt (Ph 7.4)
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0 200 400 600 800 1000 1200
We
igh
t (g
)
Time (min)
water
pH 2.1
pH 6.8
pH 7.4
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 45
Figure 4.2(a): Swelling data of MSAP obtained in water and buffers(1.2,6.8 and 7.4)
It has been observed that the swelling behavior of MSAP hydrogel was more in basic buffers
(pH6.8, 7.4) than in acidic buffer (pH 2.1).
Fig. 4.2(b): Swelling data and kinetics of MSAP obtained in buffers(6.8 and 7.4)
. The swelling behavior of MSAP hydrogel in deionized water was found to be less as compared
to acidic and basic buffers(pH 1.2, 6.8, 7.4).
Fig 4.2(c): Kinetic Studies of MSAP between time(min) and Qt (mg/g) at different pH
0
1
2
3
4
5
0 200 400 600 800 1000 1200
We
igh
t (g
)
Time (min)
pH 6.8
pH 7.4
0
5
10
15
20
25
30
35
40
45
50
0 200 400 600 800 1000 1200
Qt
(mg/
g)
Time (min)
Qt (Water)
Qt (pH 2.1)
Qt (pH 6.8)
Qt (pH 7.4)
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 46
Fig 4.2(d): Kinetic Studies of MSAP between time(min) and t/Qt (mg/g) at different pH
When the graph was plotted against time and t/Qt (min/mg/g) it was found to be opposite as
compared to time versus weight.i e distilled water has heighest values than those of all buffers.
4.4 Swelling and De-swelling Kinetics in Response to External Stimuli
4.4.1 Swelling and De-swelling Behavior of SAP in Water and Ethanol
Due to the less affinity of ethanol with hydrogel than water, the hydrogels usually de-swells
rapidly in ethanol (Fig. 2). In contrast, the dielectric constant (24.55) and a low polarity of
ethanol than that of water (80.40) are responsible for formation of hydrogen bonding to a lesser
extent with ethanol. Moreover, a less dielectric constant causes a drop in swelling capacity i.e.
de-swelling of the polymer and ionization of ionizable groups.
Fig 4.3(a): The Swelling and de swelling of SAP in aqueous and ethanol media
0
5
10
15
20
25
30
35
0 200 400 600 800 1000 1200
t/Q
t (m
in/m
g/g)
Time (min)
t/Qt (water)
t/Qt (pH 2.1)
t/Qt (pH 6.8)
t/Qt (pH 7.4)
0
1
2
3
4
5
6
0 50 100 150 200 250 300 350 400
We
igh
t (g
)
Time (min)
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 47
Once the SAP swells by keeping in distilled water, by immersing the gel bag in ethanol
suddenly washes out all the water molecules when observed by weighing it after regular
intervals. The swelling of hydrogel after placing it again in water is probably due to the result of
extensive hydrogen bonding with water and a swift wash out of ethanol molecules.
Fig 4.3(b): The Swelling and de swelling of MSAP in aqueous and ethanol media
The same phenomena of swift wash out of water molecules happens on immersing MSAP
hydrogel in absolute ethanol as discussed earlier.
4.4.2 Swelling and De-swelling Behaviour of SAP in Acidic and Basic Buffers
By using different types of buffers, swelling and de-swelling behavior of hydrogel in acidic and
basic media was evaluated. According to the observations, SAP swells in basic buffer (pH 7.4)
whereas a de-swelling behavior was shown by the hydrogel in acidic buffer (pH 1.2). This
swelling and de-swelling behavior of SAP was observed four times and the measurements of
these experiments (off and on) were recorded in form of a graph as shown in Fig.
Fig. 4.4(a): Swelling and de-swelling behavior of SAP in basic and acidic buffers.
0
0.5
1
1.5
2
2.5
3
3.5
4
0 50 100 150 200 250 300 350 400
We
igh
t (g
)
Time(min)
0
1
2
3
4
5
6
0 100 200 300 400
We
igh
t (g
)
Time (min)
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 48
Fig. 4.4(b): Swelling-deswelling behavior of MSAP in basic and acidic buffers.
Maximum swelling (99 g/g) was obtained at pH 8. In the pH region from 1 to 3, most
carboxylate groups were in the form of OCOOH, and the low swelling values of the hydrogels
could be attributed to the presence of nonionic hydrophilic COOH and OOH groups in the
hydrogel network. The swelling ratio increased rapidly as the pH of the solutions was increased
from 4 to 8. At higher pHs (4–8), some carboxylate groups were ionized, and the electrostatic
repulsion between COOH groups caused an enhancement of the swelling
capacity. The reason for the swelling loss of the highly basic solutions (pH 8) was the charge-
screening effect of excess Na in the swelling media, which shielded the carboxylate anions and
prevented effective anion–anion repulsion. Similar swelling pH dependence has been reported
for other hydrogel systems.
4.4.3 Swelling and De-swelling Behavior of SAP in NaCl Solution and Deionized Water
By immersing SAP in water and Sodium Chloride (0.9%) solution, the swelling and de-swelling
of SAP was observed respectively. Generally, the swelling ability of anionic hydrogels in various
salt solutions is appreciably decreased in comparison with the swelling values in distilled water.
This well-known undesired swelling loss is often attributed to a charge-screening effect of the
additional cations causing a nonperfect anion–anion electrostatic repulsion. Therefore, according
to the Donnan membrane equilibrium theory, the osmotic pressure resulting from the mobile ion
concentration difference between the gel and aqueous phases decreased, and consequently, the
absorbency decreased. In addition, in the case of salt solutions with multivalent cations,
ionic crosslinking at the surfaces of the particles caused an appreciable reduction in the swelling
capacity.
0
1
2
3
4
5
0 50 100 150 200 250 300 350 400
We
igh
t(g)
Time(min)
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 49
Fig. 4.5(a): Swelling-deswelling behaviour of SAP in deionized water and 0.9% NaCl
solution
Fig. 4.5(b): Swelling-deswelling behaviour of MSAP in deionized water and 0.9% NaCl
When studied at regular intervals, SAP shows a swelling behavior in de-ionized water while
shrinkage observed in the solution of NaCl (Fig. 4). Among hydrogel and water, the addition of
salt causes a decrease in osmotic pressure making the water molecules moved out of hydrogel
render it to shrink was measured in various salt solutions (Figs. 4.5(a) 4.5(b))
4.5 Scanning Electron Microscopy (SEM).
In order to study the surface morphology and porosity of a dried SAP, Scanning electron
microscopy (SEM) was used. The presence of interconnected macropores were confirmed by the
SEM photographs of transversely cut cross sections of a hydrogel (Fig. 5) ranging the size of 228
μm. When analyzed by SEM, the longitudinal cross sections of hydrogel, an inter-connected
network of macropores were also observed in the form of macroporous tubes, through which the
transfer of solvents and water takes place. By this investigation, we can expect, that SAP may be
used for water treatment, diapers, cosmetics, pharmaceuticals and controlled drug release.
0
1
2
3
4
5
6
7
0 100 200 300 400
We
igh
t (g
)
Time (min)
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0 100 200 300 400
We
igh
t (g
)
Time(min)
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 50
4.5.1 SEM Micrographs of Potato Starch
Image 4.1(a,b,c,d): SEM images of Potato Starch
Fig shows the micrographs of little granules of potato starch, partially soluble in water having
capability of gel formation along with CMC in presence of a crosslinking agent .some r small
enough with 225nm while some particles r large with 600nm.
4.5.2 SEM Micrographs of Amylum Starch
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 51
Image 4.2(a,b,c,d): SEM images of Amylum Starch
Fig shows the micrographs of hexagonal granules of Amylum starch, partially soluble in water
with multiple surfaces for water interaction having capability of gel formation along with CMC
in presence of a crosslinking agent .some r small enough with 190nm while some particles r
large with 400nm.
4.5.3 SEM Micrographs of Carboxymethyl Cellulose
Image 4.3(a,b,c,d): SEM images of Carboxymethyl cellulose
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 52
The micrographs of CMC.Na shows a rough irregular surface and amorphous nature with
10micrometer to 1 micrometer resolution of electron microscope.
4.5.4 SEM Micrographs of SAP
Image 4.4(a,b,c,d): SEM images of SAP
Scanning electron micrographs of transverse (a) and (b) with average pore size 228 μm at
different magnifications.The fig shows the magnified images of prepared hydrogel, in which
empty spaces between gel folds can be seen clearly. The hydrophilic groups present in the empty
spaces may have an ability to trap the smaller ions e.g. Fe2+, Cd2+, Pb2+.
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 53
4.5.5 SEM Micrographs of MSAP
Image 4.5(a,b,c,d): SEM images of MSAP
To reveal the relationship between structure and water-holding capacity of the hydrogels with
different ions , SEM images of the cross-sections of the lyophilized hydrogels (Fig4.5 a,b,c,d)
were observed . The porous structure could be observed in the cross-section surface of both SAP
and MSAP, and the pore size of entry SAP was larger than that of entry MSAP. This indicates
that SAP N=23.5 × 10−3could swell a large amount of water, but its loose structure could also
hold water molecules inside of the gel as compared to the highly developed structure of MSAP
where n= 36.3 × 10−3. In the case of entry 1 whose n=6.4 × 10−3, a porous structure in the cross-
section surface could not be observed, and thus the structure could not retain water inside of the
gel, thereby resulting in the low water absorbency and low water-holding capacities.
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 54
4.5.6 SEM Micrographs of Modified Starch
Image 4.6(a,b,c,d): SEM images of Modified starch
Amorphous small granules like structure of modified starch with very small particle size was
observed in micrographs.
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 55
4.6 Fourier Transform Infrared Spectroscopy (FTIR)
FTIR was performed on all of the four samples i.e. CMC.Na, Potato and Amylum starches and
SAP respectively.
Fig. 4.6: FTIR Spectra of Potato Starch
The figure shows Infrared Spectrum of cationic potato starch, microwave assisted.3200, 2800,
1572, 1315, 1134, 980, 652 cm-1. For the cationic potato starch, (Figure 3), the broad peak at
3300cm-1 is due to the H2O stretching vibration. The two bands at, 2880cm-1 are due to
antisymmetric and symmetric stretch respectively, and 1134 cm-1 are due to the C–O stretching
vibration. The peak at 1572cm-1 is due to the first overtone of O–H bending or H2O
deformation. The band at 1315 cm-1 is due to CH2, CH deformation. The bands at 980 cm-1 are
due C-OH stretch vibration, and the band at 652cm-1 CH2–O–CH2 correspond at ring mode
stretching vibration.
Fig. 4.7: FTIR Spectra of Amylum Starch
The figure shows Infrared Spectrum of Amylum starch, microwave assisted. 3227, 2890, 1593,
1101, 980, 650 cm-1. For the Amylum starch, the broad peak at 3300cm-1 is due to the H2O
stretching vibration. The two bands at, 2890cm-1 are due to antisymmetric and symmetric
65
2.2
84
98
0.2
9 11
34
.97
13
15
.75
15
72
.94
28
98
.01
32
57
.69
0
20
40
60
80
100
120
0 500 1000 1500 2000 2500 3000 3500 4000 4500
Inte
nsi
ty (
T%)
Wave number (cm-1)
65
0.4
2
98
0.2
9 11
01
.43
11
72
.25
15
93
.44
28
92
.41
32
27
.87
0
20
40
60
80
100
0 500 1000 1500 2000 2500 3000 3500 4000 4500
Inte
nsi
ty (
T%)
Wave number (cm-1)
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 56
stretch respectively, and 1101 cm-1 are due to the C–O stretching vibration. The peak at 1593cm-
1 is due to the first overtone of O–H bending or H2O deformation. The bands at 980 cm-1 are due
C-OH stretch vibration, and the band at 650cm-1 CH2–O–CH2 correspond at ring mode
stretching vibration.
Fig. 4.8 : FTIR Spectra of Carboxymethyl cellulose
The figure shows Infrared Spectrum of carboxymethyl cellulose sodium, microwave assisted.
1521, 1177, 489, 386, 273,176 cm-1 .In fingerprint region, bands that show the ether bond in
CMC are 1050 cm-1. The presence of a new and strong absorption band around 1520 cm-1 is
confirms the stretching vibration of the carboxyl group (COO¯) and 1177 cm-1 is assigned to
carboxyl groups as it salts.
Fig. 4.9: FTIR Spectra of SAP
17
6 27
3
38
6
48
9 11
77
15
21
0
20
40
60
80
100
120
0 500 1000 1500 2000
Inte
nsi
ty (
T%)
Wave number (cm-1)
CMC
65
0.4
2
97
0.9
72
15
30
.07
28
12
.28
0
20
40
60
80
100
120
0 500 1000 1500 2000 2500 3000 3500 4000 4500
Inte
nsi
ty (
T%)
Wave number (cm-1)
SAP
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 57
Fig. 4.10: Combined FTIR Spectra of Potato, Amylum starches, CMC and SAP
The absorption was observed at 3270 cm-1 (hydroxyl stretch influenced by hydrogen bond), 1569
cm-1 and 1388 cm-1 (carbonyl stretch), 980 cm-1 (b-1,4-glycosidic bond) and 2942 cm-1 and 2838
cm-1 (methylene), which were characteristic absorptions in cellulose and methylcellulose
structures. The obtained FT-IR (KBr), by the analysis of potato, Amylum starches, CMC and
SAP are clearly shown in figures above in order to elaborate the desired modifications.
Fig 4.11: FTIR Analysis of MSAP
The success of the reaction in the FT-IR spectrum of SAP was revealed by an ester carbonyl
distinct signal’s appearance at 2000 cm−1 in spectra of CMC which was the major constituent of
hydrogel, jumps to a relatively higher wavenumber at 2812 cm−1 soon after the formation of its
SAP. It also indicates the absorption of Carbon dioxide at the time of completion of reaction. In
98
0.2
9
28
38
.37
32
76
.33
98
0.2
9
13
88
.43
15
69
.21
32
07
.37
0
20
40
60
80
100
120
0 500 1000 1500 2000 2500 3000 3500 4000 4500
Inte
nsi
ty (
T%)
Wave Number (cm-1)
Potato Strach
Amylum Starch
CMC
SAP
0
20
40
60
80
100
120
0 500 1000 1500 2000 2500 3000 3500 4000 4500
Inte
nsi
ty
Wave number cm-1
CMC
Modified Starch
Hydrogel
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 58
addition. The salt formation can be indicated by the absorption of carboxylate ion in the
spectrum from 460 cm−1 of CMC to 464cm-1 of SAP.
Table 4.3: Observed FT-IR bands and their Assignments
Material
v(O
-H)
v(C
-H) A
liphatic
HO
H D
eform
ation
𝛅(O
-H) In
plan
e
𝛅(C
H2 )
𝛅(C
H)
𝛅A
SY
M b
ridged
oxygen
v(C
-O-C
)
V(C
-C) A
rabin
osy
l side
Chain
𝛅A
SY
M (O
ut o
f plan
e 𝛃-
Gly
cosid
ic bond
Poly
mer B
ackbone
Unassig
ned
Potato
Starch
3134,
3560
296
0
164
9
-
142
1
1350
124
0
107
0
-
995,92
3,852
653,
605
1139,
2140
Amylum
Starch
3466,
3487
290
4
164
1
-
142
7
1350,
1338
- -
101
0
952,85
0
651,
553
1132,
2904
Carboxy
methyl
cellulose
3552
288
5
159
7
146
2
- - -
106
6
- 916
648,
590
704
Modified
Starch
3209
287
7
168
1
-
140
9
- - -
100
1
999,93
1,860
661,
559
2175,
1132
SAP
3444,
3361
287
9
160
2
-
142
7
1336 -
106
6
-
985,92
7.879
665,
586
833,6
65
MSAP 3585
288
1
164
5
-
141
7
1327 - -
100
1
912
663,
570
1525
Table 4.3 represents the remarkable peaks of both hydrogels and their ingredients
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 59
4.7 PXRD Analysis
Some very clear and sharp diffraction signals can be seen at 28,33,38,45,68,70,74, and 80 in the
CMC’s diffractogram by X-ray diffraction (XRD) method (Figure 4.12-4.17),
Fig.4.12: PXRD Analysis of Potato Starch
Potato starch has its strongest diffraction peak at around 17° 2 θ , relatively medium peaks at
around 5°, 15°, 22°, and 24° 2 θ and a couple of weak peaks scattered around 10° and 19° 2 θ .
The pattern of peaks seen in the diffractogram of potato starch is characteristic of a B-type
crystalline structure.
Fig.4.13: PXRD Analysis of Amylum Starch
Amylum starch has its strongest diffraction peak at around 21° 22 θ , relatively medium peaks at
around 24°, 26°, 27°, and 36° 2 θ and a couple of weak peaks scattered around 17° and 19° 2 θ .
The pattern of peaks seen in the diffractogram of potato starch is characteristic of a B-type
crystalline structure.
0
20
40
60
80
100
120
140
0 10 20 30 40 50 60 70 80 90
Inte
nsi
ty (
T%)
Diffraction angle ()
0
50
100
150
200
0 10 20 30 40 50 60 70 80 90
Inte
nsi
ty (
T%)
Difraction Angle ()
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 60
Fig.4.14: PXRD Analysis of Carboxymethyl cellulose-Sodium
CMC represented two prominent peaks at 2 θ = 30.60° and 36.12°, whereas the crystalline state
of CMC was also evident in its PXRD diffractogram; displaying intense and characteristics
peaks at 2 θ = 20.75, 22.23°, 23.03°, 24.85°, 28° and 34.43.
Fig.4.15: PXRD Analysis of SAP
SAP represented two prominent peaks at 2 θ = 25.33° and 35.07°, whereas the crystalline state of
SAP was also evident in its PXRD diffractogram, displaying intense and characteristics peaks at
2 θ = 21.75, 25.33°, 30.87°, 35.84°, 46.93° and 51.85. which are actually a characteristic of
cellulose. In contrast, these diffraction signals at 28,33,38,45,68,70,74, and 80 were not observed
in the XRD diffractogram of SAP, only some peaks at 38, 67 and 68 were observed i.e. there
may be a distortion in the CMC’s crystallization and an increase in SAP hydrogel’s amorphous
region. Its possible cause may be the chemical crosslinking between the starches, CMC and SAP.
These results indicate a reduction in the crystalline behavior during the gel formation and
resultantly metal ions can easily penetrate into the hydrogel folds. In view of above description,
we can say that the SAP hydrogel beads may have a relatively high tendency for metal ions
absorption.
0
10
20
30
40
50
60
70
80
0 10 20 30 40 50 60 70 80 90
Inte
nsi
ty (
T%)
Difffraction Angle ()
0
20
40
60
80
100
120
140
0 10 20 30 40 50 60 70 80 90
Inte
nsi
ty (
T%)
Diffraction angle ()
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 61
Fig 4.16: PXRD Analysis of Modified Starch
Modified starch represented two prominent peaks at 2 θ = 31.59° and 42.25°, whereas the
crystalline state of MS was also evident in its PXRD diffractogram; displaying intense and
characteristics peaks at 2 θ= 56.49,66.01, 75.23.
Fig 4.17: PXRD Analysis of MSAP
The maximum intensity of peaks of Potato starch, Amylum, CMC were at 127, 156, 56
respectively while that of SAP was at 128 represents the crosslinking between both starches and
CMC, however, the diffraction peaks have completely vanished in case of SAP. Thus, we can
reasonably assume the reason lying behind i.e. the formation of co-ordination bonds of hydrogel
with the carboxyl groups of CMC and starches.
Carboxymethyl cellulose sodium shows some crystallinity due to hydrogen bonding among its
hydroxyl groups. However, during IPN formation with copolymer, these hydroxyl functional
0
20
40
60
80
100
120
140
0 20 40 60 80 100
Inte
nsi
ty T
%
Diffraction Angle ()
0
10
20
30
40
50
60
0 20 40 60 80 100
Inte
nsi
ty T
%
Diffraction Angle ()
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 62
groups forms chemical bond with copolymers (as it was also evident from free carboxyl % and
FTIR analysis) and thus crystalline peaks of diffractogram of carboxymethyl cellulose sodium is
not likely to be present in its IPN with copolymer. XRD of CMC sodium, SAP and MSAP gel is
shown in Fig. From this figure it is observed that CMC sodium shows three crystalline peaks at
14.3◦, 21.3◦ and 37.1.The hydrogel SAP, being amorphous shows no crystalline peak.
However, the crystalline peaks of CMC sodium are absent in its graph i.e. as observed in the
same figure.
4.8 Thermogravimeteric Analysis
The thermal analysis of Potato starch, Amylum Strach, CMC-Na and SAP were recorded for
comparison
Fig.4.18: Overlying graph of thermo-gravimetric (TG) straight line of SAP, indicating
thermal stability of sorbent.
By analyzing the thermal analysis of SAP’s major degradation steps above 200ºC, we can
conclude that the SAP possesses a relatively higher thermal stability as indicated in graph given
below. This increase in thermal stability can be helpful for the purpose of increasing the
sorbent’s shelf-life, suggesting its future use in some commercial applications.
y = 6.5889x + 55.119R² = 0.9812
0
100
200
300
400
500
600
700
-20 0 20 40 60 80 100
Tem
pe
ratu
re (
ºC)
Weight Loss (%)
y = 4.9937x + 77.486R² = 0.9543
0
200
400
600
800
-20 0 20 40 60 80 100 120
Tem
pe
ratu
re D
eg
C
Weight Loss
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 63
Fig 4.19: Thermogravimeteric Analysis of Potato Starch
Fig 4.19 shows the thermogravimetric curves of potato starch at different heating rates. These
curves present three primary mass loss parts. The initial temperature of each part was identified
as the critical point in the TG curves. The initial stage is the desiccation, which starts instantly
when the temperature just rises and ends at about 120 °C. The percentage of mass loss in this
part depends on the moisture content of the starch samples. The second stage is the main
degradation stage, which finishes at around 400 °C. Pyrolysis of starches in this step has been
reported to release water, carbon dioxide, carbon monoxide, acetaldehyde, furan, and 2-methyl
furan. Thermal decomposition has usually been regarded as the important process associated
with the degradation mechanisms of starches. The degradation of amylose and amylopectin
happened in this step. The last step ends with the formation of carbon black between 300 and 600
°C. The foremost degradation temperatures were 60, 65, 76, and 80 °C at heating rates of 5, 10,
15, and 20 °C·min−1, respectively.
Fig 4.20: Thermogravimeteric Analysis of Amylum Starch
Fig 4.20 shows the thermogravimetric curves of Amylum starch at different heating rates. These
curves present three primary mass loss parts. The initial temperature of each part was identified
as the critical point in the TG curves. The initial stage is the desiccation, which starts instantly
when the temperature just rises and ends at about 120 °C. The percentage of mass loss in this
part depends on the moisture content of the starch samples.
y = 4.7599x + 85.435R² = 0.9442
0
100
200
300
400
500
600
700
-20 0 20 40 60 80 100 120
Tem
pe
ratu
re D
egC
Weight Loss
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 64
Fig 4.21: Thermogravimeteric Analysis of Carboxymethyl Cellulose
The TGA of CMC showed residual weight of 19.6 and 34.2%, respectively, at 600 °C, which
indicates the presence of a fraction of non-volatile components.
Fig 4.22: Overlying graph of thermo-gravimetric (TG) straight line of SAP, indicating
thermal stability imparted in sodic form of sorbent throughout the degradation profile.
As shown by the thermal analysis of SAP’s major degradation steps that takes place above
200ºC, above to potato Amylum and CMC-Na, therefore we can conclude that the SAP
possesses a thermal stability that is extraordinary in some ways, which can also be observed
throughout the TG straight line. This increase in thermal stability can be helpful for the purpose
of increasing the sorbent’s shelf-life, revealing its future use in some commercial applications.
y = 6.7192x + 31.689R² = 0.883
0
100
200
300
400
500
600
700
-20 0 20 40 60 80 100
Tem
pe
ratu
re D
eg
C
Weight Loss
y = 6.5889x + 55.119R² = 0.9812
0
100
200
300
400
500
600
700
-20 0 20 40 60 80 100
Tem
pe
ratu
re
Weight Loss
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 65
Fig 4.23: Thermogravimeteric Analysis of Potato, Amylum Starchces, Carboxymethyl
Cellulose Sodium and SAP
From the figure it is clear that the major degradation of all the ingredients from 280-320oC.and
complete weigh loss of all potato amylum and SAP takes place except that of CMC having some
of the residual products like water, carbon dioxide, carbon monoxide, acetaldehyde, furan, and 2-
methyl furan.
Fig 4.24: Thermogravimeteric Analysis of SAP (Graph between Temperature and Weight
Loss of both Derivatives)
SAP is reported to produce two derivatives at250 and 280OC respectively and decomposes at
300-3200C.and complete decomposition takes place at 6000C.
0
20
40
60
80
100
120
-20
0
20
40
60
80
100
120
0 100 200 300 400 500 600 700
We
igh
t lo
ss %
Temperature (DegC)
PotatoStrach
AmylumStarch
CMC
-3
-2
-1
0
1
2
-1
0
1
2
3
4
5
0 200 400 600 800
We
igh
t Lo
ss
Temerature DegC
1st Derivative
2nd Derivative
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 66
Fig 4.25: Thermogravimeteric Analysis of Modified starch
Fig 4.26: Thermogravimeteric Analysis of Modified Starch (Graph between Temperature
and Weight Loss of both Derivatives)
MS is reported to produce two derivatives at250OC respectively and decomposes at 295-
3200C.and complete decomposition takes place at 6000C.
Fig 4.27: Thermogravimeteric Analysis of MSAP
y = 0.0222x - 23.787R² = 0.9172
-20
0
20
40
60
80
100
0 1000 2000 3000 4000 5000 6000
Tem
pe
ratu
re D
egC
Weight Loss
-4
-3
-2
-1
0
1
2
3
4
5
-1
0
1
2
3
4
5
6
7
8
0 100 200 300 400 500 600 700
We
igh
t Lo
ss (
1st
De
riva
tive
)
Temperature DegC
1st Derivative
2nd Derivative
y = 6.0907x + 45.078R² = 0.9922
0
200
400
600
800
-20 0 20 40 60 80 100
Tem
pe
ratu
re D
egC
Weight Loss
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 67
Fig 4.28: Thermogravimeteric Analysis of MSAP (Graph between Temperature and
Weight Loss of both Derivatives)
MSAP is reported to produce two derivatives at 228-205OC respectively and decomposes at 251-
2740C.and complete decomposition takes place at 6000C.
Fig 4.29: Thermogravimeteric Analysis of Modified Starch, Carboxymethyl Cellulose
Sodium and Modified starch based SAP
The thermal analysis of Potato starch, Amylum Strach, CMC-Na and SAP were recorded for
comparison. Fig. 4.23 and 4.29 show an overlying pattern of the TG Curves of all the ingredients
and SAP, and a straight line for the decomposition of SAP. The minimum degradation (Tdm) in
SAP’s first degradation step appeared at 231.46°C, which is slightly higher than the Tdm of both
starches whereas less than that of CMC-Na. Likewise, Tdi of SAP’s second degradation step was
596ºC and almost 35ºC higher than starches whereas equal to that of CMC-Na. In the last
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5
-0.5
0
0.5
1
1.5
2
2.5
3
3.5
4
0 100 200 300 400 500 600 700
We
igh
t Lo
ss
Temperature DegC
1stDerivative(data)2ndDerivative(data)
-10
0
10
20
30
40
50
60
70
80
90
0
100
200
300
400
500
600
700
-20 0 20 40 60 80 100
SAP
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 68
degradation step, with the remaining wt. of 21.97%, a complete decomposition of the starches
were observed. From major degradation steps, the obtained thermal data reveals significantly
higher values of Tdi, Tdm and Tdf of SAP as compared to its ingredients. As observed throughout
the TG curves, we may infer an extraordinary thermal stability of the sorbent. In order to
increase the sorbent’s shelf life; this increase in thermal stability can be used as a beneficial tool
especially for commercial applications.
4.9 Applications on Water Treatment
4.9.1. Atomic Absorption Spectroscopy
Fig 4.30: Metal ion adsorption ratio profiles of SAP at room temperature
Fig 4.31: Metal ion adsorption ratio profiles of MSAP at room temperature
The above figure shows the metal ion absorption rates in the SAP solution. An increase in
concentration of SAP results an increase in the adsorbed quantity of metal ions. The 14, 12, and
0
2
4
6
8
10
12
14
16
0 20 40 60 80 100 120
Me
tal D
ete
cte
d (
pp
m)
Weight of Hydrogel (mg)
Detection forCadmium (ppm)
Detection for Iron(ppm)
Detection for Lead(ppm)
0
2
4
6
8
10
12
14
0 20 40 60 80 100 120
Me
tal D
ete
cte
d (
pp
m)
Weight of Hydrogel (mg)
Detection forCadmium (ppm)
Detection for Iron(ppm)
Detection for Lead(ppm)
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 69
10ppm concentration for Cd2+, Pb2+, and Fe2+ indicates maximum absorption respectively. In
fact, a relatively stronger attraction of oxygen atom of carboxyl group is the reason for an
increased absorption rate of Cd+2 ion than other metal ions, which is helpful in reaction with
Cd(II), Fe(II) or Pb(II) forming a relatively stable complexes with Cd(II) [131]. When the
concentration of metal ions get lower than 0.2 mmol/L, the absorption ratio for Fe(II) exceeds to
95% and the absorption percentage for Cd(II) and Pb(II) becomes higher than 99%. An increase
in the concentration causes the adsorption ratio to decrease and a better adsorption capacity was
seen by hydrogel for the metals under consideration, hence we can infer a relatively higher
adsorption capacity of the SAP hydrogel beads ,so the hydrogel can be taken into consideration
for the recovery of metal ions from solutions.
Qe = (Co-Ce) V/W (12)
Km = (1-Ce/Co) 100 (13)
Where Co and Ce are the initial and equilibrium metal ions concentrations (mol/L), respectively.
V is the volume of the solution (L) and W is the weight of the dried hydrogel beads (g).
4.9.2 Adsorption Isotherms
To study the adsorption behavior, two empirical adsorption models named Freundlich and
Langmuir models were used. In this work, the analysis was done by applying Freundlich and
Langmuir equations on the experimental data obtained at pH 7. [132-133] The Freundlich and
Langmuir isotherms are given by eq. (11) and (12), respectively:
Log Qe = log KF + 1/n log Ce (14)
KF= Freundlich constants related to adsorption capacity
N = Freundlich constants related to intensity
Ce =equilibrium concentration of metal ion in the solution
Fig 4.32: Graphical representation of Cadmium ion absorption in SAP between Ce(mol/L)
and Qe (mol/L)
y = 28.503x + 0.0001R² = 0.6679
0
0.001
0.002
0.003
0.004
0.005
0 0.000020.000040.000060.00008 0.0001 0.00012
Qe
(m
ol/
L)
Ce (mol/L
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 70
Fig 4.33: Graphical representation of Cadmium ion absorption in MSAP between
Ce(mol/L) and Qe (mol/L)
According to the results shown in (Fig 4.32 -4.33) and taking into account the values of the
correlation coefficients (R2 ), which are between 0.66 and 0.59, in case of SAP and MSAP.
These values show less adsorption of Cd2+ than that of Pb2+ but more than Fe2+. We conclude that
the results conform to the Langmuir model. It was generally observed that the adsorption values
are high and increase with increasing pore size of the matrix, pore volume and water content.
Fig 4.34: Graphical representation of Fe2+ ion absorption in SAP between Ce(mol/L) and
Qe (mol/L)
y = 19.014x + 0.0003R² = 0.5925
0
0.0005
0.001
0.0015
0.002
0.0025
0.003
0.0035
0 0.000020.000040.000060.00008 0.0001 0.00012Q
e (
mo
l/L)
Ce (mol/L)
y = 18.75x + 0.0004R² = 0.3371
0
0.001
0.002
0.003
0.004
0.005
0 0.000020.000040.000060.00008 0.0001 0.00012
Qe
(m
ol/
L)
Ce (mol/L)
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 71
Fig 4.35: Graphical representation of Fe2+ ion absorption in MSAP between Ce(mol/L) and
Qe (mol/L)
Variation of the mass of the hydrogel correlated with the less adsorption of Fe2+ ions R2=.33 for
SAP swollen in water. From the above isotherm for Fe2+ that increasing the concentration of the
ion in the solution increases the electrostatic repulsion between the charged groups on the
network and a concentration gradient inside and outside the hydrogel governed by the Donnan
potential. On the other hand, it is also possible that is occurred the displacement of water
molecules by the Fe2+ ions that are directed into the polymer matrix.
Fig 4.36: Graphical representation of Pb2+ ion absorption in SAP between Ce(mol/L) &Qe
(mol/L)
According to the results shown in Fig 4.36 -4.37 and taking into account the values of the
correlation coefficients (R2 ), which are between 0.95 and 0.87, We conclude that the results
conform to the Langmuir model. It was generally observed that the adsorption values are high
and increase with increasing pore size of the matrix, pore volume and water content. The
deviation in case of Cd2+ and Fe2+ isotherm is behavior is attributed to the fact that having a
lower density of crosslinking in the matrix, there is a greater possibility of diffusion, higher
y = 15.969x + 0.0004R² = 0.8154
0
0.001
0.002
0.003
0.004
0.005
0 0.00005 0.0001 0.00015 0.0002 0.00025
Qe
(m
iol/
L)
Ce (mol/)
y = 13.07x + 0.0003R² = 0.9501
0
0.0002
0.0004
0.0006
0.0008
0.001
0.0012
0 0.00001 0.00002 0.00003 0.00004 0.00005 0.00006 0.00007
Qe
(m
ol/
L)
Ce (mol/L)
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 72
density of adsorption sites and adsorption volumetric capacity and that the functional groups
capable of complexing the metal, can be rearranged more easily.
Fig 4.37: Graphical representation of Pb2+ ion absorption in MSAP between Ce(mol/L) and
Qe (mol/L)
The sorption capacity depends on the extent of crosslinking and decreases with the increase in
the extent of crosslinking. This is because of the restricted diffusion of the ions through the
polymer networks and reduced chain flexibility. Metal ion uptake of the modified SAP was
more than SAP. Partitioning of ions between polymeric matrices and liquid phase is reflected
with high values of partition coefficients (Kd). Structure of polymeric networks has significant
effect on ion-uptake, which is reflected in low retention capacities (Qr).
Table 4.4: Freundlich and Langmiur Equation fitted Parameters
Freundlich
Equation
Metal Ions KF n R2
SAP Cd2+ 1.63 1.85 .898
Fe2+ 1.008 .88 .798
Pb2+ 1.57 2.22 .955
MSAP Cd2+ 1.46 2.38 .726
Fe2+ 1.56 2.42 .923
Pb2+ 1.47 1.69 .881
Langmiur
Equation
Metal Ions Qmax b R2
SAP Cd2+ 222 .095 .923
Fe2+ 476 .026 .882
Pb2+ 84 .16 .716
MSAP Cd2+ 111 .136 .955
Fe2+ 100 .128 .898
Pb2+ 222 .09 .798
From Freundlich Eqaution, the observed KF values for Cd2+, Fe2+ and Pb2+are 1.63, 1.008,
1.57for SAP and1.46, 1.56, 1.47 for MSAP respectively. The adsorption studies demonstrate that
the both hydrogels have a potential application in removal and recovery of heavy metal ions
from waste water.
y = 19.602x + 0.0002R² = 0.8726
0
0.0005
0.001
0.0015
0 0.00001 0.00002 0.00003 0.00004 0.00005
Qe
(m
ol/
L)
Ce (mol/L)
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 73
4.10 Conclusion
The prepared hydrogels were characterized by studying their physical properties, Swelling
behavior, Swelling kinetics, Fourier Transform Infrared spectroscopy (FT-IR), Scanning electron
Microscopy (SEM), Powdered X-ray diffractometery (PXRD), Thermogravimeteric analysis
(TGA) and Atomic Absorption spectroscopy to know their ability in removing heavy metal ions
from water. In this work, the synthesis of two novel Hydrogels, Carboxymethyl cellulose/Potato
Starch/Amylum Strach (CMC/PS/AS) based Hydrgel (SAP), A Modified Starch (MS) and a
Modified Starch based Hydrogel (MSAP) were synthesized by using Aluminium Sulfate
Octahydrate as a crosslinking agent. By taking into consideration, FT-IR analysis done primarily
to evaluate the structure of hydrogels, the structures in results were according to the expected
structures of hydrogels. The hydrogels then subjected to the thermal gravimetric analysis to
evaluate out the thermal stability of hydrogel i.e. more than its ingredients. Hydrogels were then
examined morphologically by SEM. The swelling ability of both hydrogels were more in basic
medium rather than acidic, moreover it shows swelling and de-swelling behavior in water,
ethanol, acidic and basic buffers and in salt solutions when inferred by the swelling experiment.
A high swelling behavior was shown by SAP and MSAP in deionized water, at pH 6.8 and 7.4
while no reasonable swelling at pH 1.2 was observed. Furthermore, its potential as an intelligent
drug delivery system was confirmed by a remarkable swelling and de-swelling behavior of SAP
in water and ethanol, in acidic(pH 1.2) and basic (pH 7.4) media and in water and normal saline
solution. The thermal analysis of SAP and MSAP’s major degradation steps that takes place
above 200ºC,which represents their extra-ordinary stability. The PXRD anlysis shows that there
may be a distortion in the CMC’s crystallization and an increase in SAP hydrogel’s amorphous
region. The possible cause of it can be the chemical crosslinking between the starches, CMC and
SAP. These results indicate that due to a reduction in the crystalline behavior during the gel
formation. . The success of the reaction in the FT-IR spectrum of SAP was revealed by an ester
carbonyl distinct signal’s appearance at 2341 cm−1 in spectra of CMC which was the major
constituent of hydrogel, jumps to a relatively higher wavenumber at 2345 cm−1 soon after the
formation of its SAP. It also indicates the absorption of Carbon dioxide at the time of reaction
completion.
From the aqueous solution of Cd+2, Pb+2 and Fe+2 ions, these metal ions were then separated
by the hydrogel. The order of selectivity towards different metal ions of the hydrogel as tested
was Cd+2> Pb+2 >Fe+2. The observation revealed the fact that the capacity of the hydrogel to
bind with heavy metal ions was dependent on the interaction of metal ions with the hydrogel
monomers.
A high swelling behavior was shown by SAP and MSAP in deionized water, at pH 6.8 and 7.4
while no reasonable swelling at pH 1.2 was observed. Furthermore, its potential as an intelligent
drug delivery system was confirmed by a remarkable swelling and de-swelling behavior of SAP
in water and ethanol, in acidic(pH 1.2) and basic (pH 7.4) media and in water and normal saline
solution. The FT-IR spectrum of SAP, by the appearance of a distinct ester carbonyl signal at
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 74
2341 cm−1 in spectra of CMC (the major constituent of hydrogel), moved to higher wavenumber
at 2345 cm−1 after its SAP formation and it all revealed the success of the reaction. The
macroporous nature of dried hydrogel by SEM analysis was confirmed predicting it a
superabsorbent material. SAP proves itself not only a potential candidate for water treatment, but
an effective substance in targeted and sustained delivery of drugs in colon and small intestine on
the basis of higher adsorption in basic media. XRD Spectra revealed a lower the crystalline
property of hydrogel beads in comparison to that of the pure CMC. It is proved that Tdi, Tdm
and Tdf of SAP are significantly higher than those of ingredients as the thermal data of major
degradation steps was analyzed. It is therefore inferred that the sorbent has thermal stability at
some extraordinary level which can be observed throughout the TG curve. In view of the whole
study, it is concluded that these hydrogels have a higher selectivity towards Cd(II) and Pb(II) and
over 90% recovery was attained after repeating its use for almost five times. From Freundlich
Eqaution, the observed KF values for Cd2+, Fe2+ and Pb2+are 1.63, 1.008, 1.57for SAP and1.46,
1.56, 1.47 for MSAP respectively. The adsorption studies demonstrate that the both hydrogels
have a potential application in removal and recovery of heavy metal ions from waste water.
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 75
Publications
Synthesis and Characterization of Carboxymethyl cellulose based Hydrogel and its Applications
on water Treatment.
(Desalination and Water Treatment Journal) (Published)
Synthesis, Characterization and Metal Ion removing Capability of Novel Carboxymethyl
Cellulose based Hydrogel.
(Journal Of Envoironmental Chemistry) (Submitted)
CHAPTER 4: RESULT AND DISCUSSION
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 76
Chapter 5
REFERENCES
REFERENCES
Synthesis and Characterization of New Hydrogels and their Applications on Water Treatment 76
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