Research Article Membrane Made of Cellulose Acetate with...

Research ArticleMembrane Made of Cellulose Acetate withPolyacrylic Acid Reinforced with Carbon Nanotubes andIts Applicability for Chromium Removal

J A Saacutenchez-Maacuterquez1 R Fuentes-Ramiacuterez1 I Cano-Rodriacuteguez1 Z Gamintildeo-Arroyo1

E Rubio-Rosas2 J M Kenny3 and N Rescignano3

1Departamento de Ingenierıa Quımica Division de Ciencias Naturales y Exactas Universidad de GuanajuatoCampus Guanajuato Noria Alta SN 36050 Guanajuato GTO Mexico2Centro Universitario de Vinculacion y Transferencia de Tecnologıa Prolongacion de la 24 Sur y Avenida San ClaudioCiudad Universitaria Colonia San Manuel 72570 Puebla PUE Mexico3Instituto de Ciencia y Tecnologıa de Polımeros de Madrid CSIC CJuan de la Cierva 3 28006 Madrid Spain

Correspondence should be addressed to R Fuentes-Ramırez rosalbaugtomx

Received 22 August 2015 Revised 9 November 2015 Accepted 10 November 2015

Academic Editor Yiqi Yang

Copyright copy 2015 J A Sanchez-Marquez et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

Membranes made of carbon nanotubes and cellulose acetate with polyacrylic acid were designed in order to study their propertiesand their applicability for chromium removal The membranes were prepared by phase inversion method using cellulose acetateand polyacrylic acid Carbon nanotubes were added to the membrane during their process of synthesis in proportions of 1 byweightThe pores in the material are formed in layers giving the effect of depth and forming a network Both the carbon nanotubesand membranes were characterized by IR Raman and SEM spectroscopy In addition the concentration of acidic and basic sitesand the surface charge in the materials were determinedThe concentration of acid sites for oxidized nanotubes was 40meqgTheremoval of Cr(VI) was studied as a function of contact time and of initial concentration of Cr(VI) The removal of Cr(VI) (sim90)mainly occurs in a contact time from 32 to 64 h when the initial concentration of Cr(VI) is 1mgL

1 Introduction

Many investigations have been focused on the developmentof new polymeric membranes for different applications [1]Nowadays these membranes are used for the recycling ofmetals for the removal of toxic products or chemical speciesand for obtaining high purity chemicals and clean wastes [2]In order to reach these important applications a great efforthas been placed on the design of new membranes with highselectivity and chemical resistance Furthermore it is possibleto impose on the membranes an additional requirementrelated to the possibility of controlling their selectivity ortheir properties by changing some external parameters [3]Thus a variety of polymeric membranes can be preparedby altering certain parameters in the initial mixture such as

composition initial concentration of the polymer thermaltreatments fillers solvents and additives [4 5]

The addition of fillers in polymers is an attractive methodin order to obtainmaterials with novel properties Nowadayscarbon nanotubes are used as fillers to produce newmaterialsHowever when new applications for carbon nanotubes areproposed these materials need to be supported on othermaterials to obtain attractive composite structures with abetter performance than the performance shown by pureinitial components The physicochemical characteristics ofthe membranes obtained from the polymer mixture can bechanged if the membrane is prepared using different mixingratios of the polymers [6]

In this work synthetic polymer membranes made frompolyacrylic acid cellulose acetate and graphitic materials

Hindawi Publishing CorporationInternational Journal of Polymer ScienceVolume 2015 Article ID 320631 12 pageshttpdxdoiorg1011552015320631

2 International Journal of Polymer Science

were prepared and characterized in order to evaluate theirproperties stability and possible application in chromiumremoval The use of polymers provides support to carbonnanotubes and permits their use in continuous processes forthe removal of ions This idea is based on previous studiesshowing that these materials have great potential in theadsorption of heavy metals [7ndash9]

Previous studies have demonstrated the technical feasibil-ity of using carbon nanotubes (CNTs) for the removal of diva-lent ions (Ni2+ Cu2+ Pb2+ Cd2+ Zn2+ andCo2+) from aque-ous solutions These studies were based mainly on chemicalinteractions that occur between ions and surface groups of theCNTs CNTs were regenerated and reused for several cyclesof water treatment this feature is ideal if you want to havelow-cost processes [7] Furthermore CNTs have been used instudies of speciation for Cr(III) Cr(VI) and total Cr Thesemethods were successfully applied showing optimal condi-tions comparable to the procedures reported in the literaturesuch as quantitative recovery values low detection limitshigh selectivity high capacity and a larger range of pH valuesfor speciation of chromium [8] In addition studies for theremoval of Cr(VI) have been performed using oxidized CNTsas adsorbents These studies showed that the CNTs can effi-ciently remove Cr(VI) from aqueous solutions under a widerange of experimental conditions without significant releaseof Cr(III) Chromium removal takes place primarily becauseof the functional groups located on the surface of the CNTsThese functional groups provide adsorption sites for Cr(VI)[9]

Chromium is a heavy metal and has been identified asa contaminant of water and soil Chromium pollution isproduced from numerous industrial activities such as thetextile industry the chemical industry andmetallurgy [10 11]Cr(III) is poorly soluble and stable is found primarily infood and is essential to maintain normal glucosemetabolismin humans On the other hand Cr(VI) is less stable andmore soluble and is considered an environmental pollutantand is also toxic and carcinogenic to humans Hexavalentchromium is harmful to health relating to certain diseases ofthe liver kidney and lungs and different kinds of cancer [12]

The polymer made from cellulose acetate (CA) andpolyacrylic acid (PA) can be used as support of the graphiticmaterials Cellulose acetate is one of themost commonly usedmaterials for polymeric membrane fabrication [13] It canproduce membranes of adequate porosity and low binding[14] CA is a hydrophilic material with good resistance tosoiling and moderate chlorine resistance its price is low andit has good biocompatibility However some disadvantages ofthismaterial are poormechanical strength low thermal resis-tance and low chemical resistance [15 16] Some studies haveshown that it is possible to control the porosity of amembraneobtained from cellulose acetate and polyacrylic acid Themembranes made from the reaction of two organic polymersshowed pore diameters that ranged between 3 and 100microns just by varying the time of immersion in hot waterThe pore size shows a nonlinear behavior as a function of thetemperature of the immersionmedium [17]The possibility ofcontrolling the pore through an external factor such as water

temperature immersion introduces these membranes asattractive materials for adsorption processes Finally it isimportant to stress that the performance of nanomaterial inthe polymer matrix must be evaluated from the study of con-ditions such as load degree of oxidation polymer featuressynthesis conditions and carbon nanomaterial productionand precursors All these features play an important role inthe final properties of membranes for chromium removal

2 Materials and Methods

21 Synthesis of Polymer Membranes In order to carry outthis work the followingmaterials were used cellulose acetate(Sigma Aldrich) with a molecular weight of 50000 by gelpermeation chromatography (GPC) and a degree of acety-lation of 397w and polyacrylic acid in aqueous solution(Sigma Aldrich) with a molecular weight of 30000 gmolminus1and a percentage of 35wAll commercial reagentswere usedwithout any further purification step Polymer membraneswere prepared according to a procedure previously reported[9] Initially a solution was prepared dissolving 8 g of cellu-lose acetate in 100mL of glacial acetic acid at room tempera-ture Then when the cellulose acetate had been completelydissolved 10mL of polyacrylic acid was added slowly withconstant medium agitation this solution was heated at 60∘Cunder agitation for 30min allowing the reaction betweenthe cellulose acetate and the polyacrylic acid to take placeThe final solution was cooled down to room temperature andstored for 3 days before use To obtain the membranesseveral samples were poured into flat glass molds of 10 cmin diameter leaving the molds with the solution floating oniced water at 4∘C allowing the solution to reach the sametemperature of iced water Thereafter the mold with thepolymer solution was completely immersed carefully into thecold water until the membranes formed and subsequentlypermitted to rest for 15min to allow the solidification of poly-mer solution Once the membranes were formed they werewithdrawn from the iced water and immediately placed intoa bath of hot water at 60∘C This procedure was applied tomembranes both with and without carbon nanotubes usingconcentrations of 1 by weight

22 Oxidation of Carbon Nanotubes (CNTs) Multilayer nan-otubes (Cheaptubes Co) with purity greater than 95 10to 30 microns in length and diameters between 20 and30 nm were oxidized through a chemical treatment based ona mixture of sulfuric acid (Jalmek purity 95ndash98 MW =9808 gMol) and nitric acid (Fermont purity 69 MW =6301 gmol) in a 3 1 volume ratio The oxidation was con-ducted at 85∘C for 3 hWhen the reaction finished the samplewas washed with distilled water and dried for 12 h at 40∘C

23 Surface Characterization The characterization of poly-mer and carbon nanotubes was made by Fourier TransformInfrared spectroscopy with attenuated total reflectance(FTIR-ATR Vertex Model 70) in pressed KBr pellets(100mgKBr and 1mg of sample) of graphitic materials ForFTIR spectroscopy the samples were dried at 333 K for 24 h

International Journal of Polymer Science 3

The characterization by FTIR was complemented with aRaman analysis (Renishaw Raman Microscope Invia ReflexWotton-under-Edge UK) The thermal properties werestudied using a TGA analyzer (TA-Q500 TA Instruments)The TGA measurements were performed using nitrogenin a temperature range of 25ndash700∘C (10∘Cminminus1) Themorphology of cross-linked polymer was investigated withthe aid of the scanning electron microscope (Jeol JSM-6610LV) operated in the high vacuummode at an accelerationvoltage of 20 kV and a pressure of 20 Pa the materials werepreviously coated with gold The SEM images for the restof the materials were determined with an environmentalscanning electron microscope (MEBA Philips Model XL30)operated in the high vacuum mode too The effective surfacearea and pore size distribution of the graphite materials weredetermined using N

2-BET (ASAP 2010 V503) About 02 g

of sample was degassed in nitrogen at 120∘C for 6-7 h beforeundergoing analysis The pore size distributions with specificsurface areas were measured by N

2adsorptiondesorption

according to the BET method

24 Potentiometric Titrations The surface charge and pointof zero charge of the materials were evaluated using a poten-tiometric titration method proposed by Loskutov and KuzinFor the titration a pHmeter (PinaracleModel 540)was usedThe experiments were conducted in a 50mL flask Initially100mg of adsorbent material and 20mL of 01MNaCl wereadded to the vessel Then a sample between 005 and 5mL ofa titrant solutionwas added to obtain a curve over the range ofpHThe solution with the adsorbent material was kept underconstant stirring for 48 hours until it reached equilibriumThen the final pH value of titrant solution was measuredThus we obtained a curve that showed the variation of pHvalue of the solution as a function of volumeof titrant solutionwith adsorbent Another similar curve for the solutionwithout adsorbent was obtained These plots were used todetermine the volumes of the different titrants solutions atthe same final pH The surface charge and point of zerocharge of the materials were evaluated using the equationsproposed by Loskutov andKuzin Finally a curve that showedthe variation of surface charge as a function of pH wasobtained The point of zero charge (PCC) was placed as thepH value where the surface charge is zero The concentrationof acidic and basic sites in thematerials was determined usinga method of acid-base titration proposed by Boehm For thetitration a pH meter (Pinaracle Model 540) was used Theexperiments were conducted in a 50mL flask The acid siteswere neutralized with basic standard solution (01 NNaOH)and the basic sites with an acid standard solution (01 NHCl)Initially a neutralizing solution and 1 g ofmaterial were addedto the vessel The flask was partially immersed in water at25∘C and it was left in contact with water for 5 days to reachequilibrium The flask was manually stirred two times a dayThen a sample of 10mL was taken and titrated with 01 Nsolution of HCl or NaOH The titration was performed intriplicate for all cases The concentrations of acidic and basicsites were calculated using the equations proposed by Boem

25 Chromium Removal Studies All experiments were con-ducted in plastic tubes under ambient conditions by usingbatch technique A sample of adsorbentmaterial and a certainamount of synthetic solution of Cr(VI) were added to eachtube The tubes were kept in constant agitation After theperiod of shaking time the solid phase was separated fromthe solutionThe contact time (adsorption kinetics) the doseof graphitic material the effect of pH the effect of the initialconcentration of the synthetic solution and finally the effectof temperature on the removal were studied The data ofthe adsorption kinetics were simulated using pseudo-first-order models pseudo-second-order models Elovich modelmodel function of power and kinetic rate law for threevalues of 119899 (0 2 and 3) The data of the amount of Cr(VI)adsorbed on the polymer graphitic materials (q mgg) andthe concentration of Cr(VI) remaining in solution (CemgL)were simulated using models of Langmuir and Freundlichfor the temperatures studied The total Cr concentration insolutionwasmeasured by atomic absorption spectrophotom-etry using spectroscopy (AA Analyst HA-100 SpectrometerPerkin Elmer)

3 Results and Discussion

31 Infrared Spectroscopy (FTIR-ATR)

311 Oxidation of Carbon Nanotubes The IR spectra of rawnanotubes and oxidized nanotubes are compared in Figure 1The spectrum for raw nanotubes shows signals associatedwith stretching vibrations of C-C bond in the 1300ndash1100 cmminus1range and stretching vibrations of C=C bond at 1670 cmminus1These bands are characteristic of graphiticmaterials After thechemical modification the spectrum for oxidized nanotubesshows a peak at 3435 cmminus1 and another at 3778 cmminus1 asso-ciated with stretching vibrations of the hydroxyl group Inaddition the signal at 1720 cmminus1 can be attributed to stretch-ing vibration of the carbonyl group present in the carboxylgroups The peaks at 1533 and 1340 cmminus1 can be assignedto symmetric and asymmetric stretching of carboxyl grouprespectively Finally the peak at 1040 cmminus1 can be associatedwith stretching vibrations of the C-OH bond and the signalat 632 cmminus1 with out-of-plane movements of the -OH bondThe presence of oxygen in the IR spectra of the nanotubes isevidence of its oxidized state

312 Molecular Interactions between Different PolymersMolecular interactions between materials were studied byobtaining their FTIR spectra The IR spectra of celluloseacetate polyacrylic acid and the polymer (AC-PA) are shownin Figure 2The spectrum for polyacrylic acid shows the typi-cal bands for carboxylic acids with the stretching absorptionassociated with the hydroxyl groups (O-H) in 3384 cmminus1while the carbon-oxygen (C=O) absorption peak charac-teristic of carbonyl was observed at 1701 cmminus1 In additionpeaks for C=C and C-C stretching were observed at 1629 and1234 cmminus1 Finally the band in 1452 cmminus1 can be assigned tothe in-plane bending of the hydroxyl group The spectrum


100

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84

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3778

3435

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1040

11001300

1670

1533

1340

Wavenumber (cmminus1)

T(

)

Raw CNTOxidized CNT

Figure 1 Infrared spectra of the raw nanotubes and the oxidizednanotubes

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3384

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1452

903

4000 3500 3000 2500 2000 1500 1000


T(

)

Polyacrylic acidCellulose acetate

Polymer (AC-PA)

Figure 2 Infrared spectra of the different polymers

for cellulose acetate also showed an absorption band asso-ciated with the -OH stretching region in 3487 cmminus1 whilethe carbon-oxygen (C=O) absorption peak characteristic ofcarbonyl was observed at 1756 cmminus1 Peaks observed at 2958could be attributed to symmetric and asymmetric stretchingvibrations while the signals placed at 1436 and 1368 cmminus1can be attributed to symmetric and asymmetric bendingvibrations of the carbon-hydrogen bonds present in themethyl group Peaks observed between 1227 and 1048 cmminus1are characteristic of materials based on cellulose and they canbe associated with the carboxylate group the link betweenrings C-O-C and the pyranose ring respectively Finally theband in 903 cmminus1 can be assigned to the out-of-plane bendingof hydroxyl groupWhen the cellulose acetate and polyacrylicacid reacted the bands associated with the carboxylic groups(C=O and OH) of the polyacrylic acid and the hydroxyl and

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3389

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T(

)

Polymer (CA-PA)Polymer-raw CNT (1)

Polymer-oxidized CNT (1)

Figure 3 Infrared spectra of the polymer (AC-PA)without andwithraw and oxidized CNT

acetyl groups of cellulose acetate decrease significantly Thissuggests that the interaction between polyacrylic acid andcellulose acetate has occurred

Different graphitic materials were added to the polymer(AC-PA) The IR spectra of polymer with carbon nanotubesare shown in Figure 3 In these spectra we can observe thecharacteristic peaks of the polymer (AC-PA) In addition it isnot possible to observe interactions between the polymer andgraphite materials from IR spectra

32 Raman Spectroscopy

321 Oxidation of Carbon Nanotubes The Raman spectrumof raw carbon nanotubes presents four characteristic peaksFigure 4 The first band at 1574 cmminus1 can be associated withtheG band of graphite In the nanotubes this band is split dueto the loss of symmetry by the curvature and the electroniceffects present Another peak at 116 cmminus1 can be associatedwith the radial breathing modes (RBM simultaneous radialdisplacement of all carbon atoms) The third band located at1346 cmminus1 can be attributed to induced modes by disorderThis band is known as D band Finally a peak at 2687 cmminus1known asG1015840 band corresponds to amodewith the same sym-metry as the band D After we oxidize nanotubes the D bandintensity increases due to the increment in the number ofdefects present in the material

322 Molecular Interactions between Different Polymers ARaman spectrum consists of bands which are caused byinelastic scattering from chemically bonded structures asshown in Figures 5 6 and 7 The fundamental bands ofcellulose acetate have been annotated in Figure 5The charac-teristic Raman signals for cellulose were present at 2934 and1121 cmminus1 which are attributed to C-H stretching and asym-metric stretching vibration of the C-O-C glycosidic linkagerespectively In addition we observed the pyranose ringsignal at 1081 cmminus1 and the band associated with the C-OH


Raw CNTOxidized CNT

500 1000 1500 2000 2500 3000

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0

Cou

nts

RBM (116)

D (1346)G (1574)

Raman shift (cmminus1)

G998400 (2687)

Figure 4 Raman spectra of the raw CNTs and oxidized CNTs

30002500200015001000500

659

906

978

834

11211081

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1382

1435

1736

2723

2934

Cellulose acetate

20000

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Cou

nts


O

O

OO

O O

O

O

O

O O

OO

HOHO

n

CH3

CH3

CH3

CH3

lowast

Figure 5 Raman spectrum for cellulose acetate

905

12241496

2935

1678

1654

1306

Polyacrylic acid

20000

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60000

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0

Cou

nts

30002500200015001000500


lowast

n

H

H H

C C

C

O

OH

Figure 6 Raman spectrum for polyacrylic acid

1731

1431

1368

1157

11211081

654

906

834974

2939

Polymer (CA-PA)

10000

8000

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14000

16000

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20000

0

Cou

nts

30002500200015001000500


minus2000

Figure 7 Raman spectrum for the polymer (CA-PA)

bonds present in the rings at 1265 cmminus1 The characteristicRaman signals for the acetyl group can be observed at1736 1435 and 1382 cmminus1 corresponding to vibration of thecarbonyl group (C=O) and asymmetric and symmetric vibra-tions of theC-Hbondpresent in the acetyl groupsThe signalsobserved at 978 906 834 and 659 cmminus1 can be associatedwith C-O C-H O-H and C-OH bonds respectively

The spectrum for the polyacrylic acid is shown inFigure 6 The characteristic Raman signals can be observedat 3444 and 1678 cmminus1 corresponding with the oxygen-hydrogen bond vibration and carbonyl group (C=O) vibra-tion present in the carboxylic groups The stretching vibra-tions of the carbon-carbon double bond (C=C) appear at1654 cmminus1 while in-plane bending of the O-H bond can beplaced at 1496 cmminus1 Finally the bands at 1306 1224 and905 cmminus1 correspond to C-O bond vibrations The peak at1224 cmminus1 had a contribution fromC-C bonds presentWhenthe polymers (AC and PA) are mixed the spectrum obtainedshows primarily the characteristic Raman signals for cellu-lose acetate while polyacrylic acid has remained undetectedbecause their bands partially overlapped those of celluloseacetate as shown in Figure 7 The characteristic Raman sig-nals for polymer (PA-AC) were present at 2939 and 1121 cmminus1which are attributed to C-H stretching and asymmetricstretching vibration of the C-O-C glycosidic linkage respec-tively In addition we observed the pyranose ring signal at1081 cmminus1 and the characteristic Raman signals for the acetylgroup at 1731 1431 and 1368 cmminus1 corresponding to vibrationof the carbonyl group (C=O) and asymmetric and symmetricvibrations of the C-H bond present in the acetyl groupsrespectively Finally the signals observed at 978 906 834and 659 can be associated with C-O C-H O-H and C-OHbonds respectively For the polymer (CA-PA) we cannotobserve the band associated with the C-OH bonds presentin the glycosidic rings at 1265 cmminus1 and we cannot see thecharacteristic Raman signals at 3444 and 1678 cmminus1 cor-responding with the oxygen-hydrogen bond vibration and


O OH

OH

OH

OH

OH

OH

OH

R R R

OHR

O

O

O

O

O

O

O

O

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O

HO

HO

HO

HO

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HO

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R

O

H+ OH+

+

+ +

+

+

CH3

CH3

CH3

CH3CH3

CH3CH3

CH3

CH3

CH3

CH3

CH3

CH3

H3C

H3C

H3C H3C

H3C

H3C

n

n

n n

n

n

H2O

O+

O+

H+

Figure 8 Mechanism based on reaction between carboxylic groups and acetyl groups [18]

carbonyl group (C=O) vibration present in the polyacrylicacid neither

We considered two reaction mechanisms associated withpossible interactions between cellulose acetate and acrylicacidThe firstmechanism is based on the idea that the oxygenpresent in the carbonyl group has weak basic propertiesas shown in Figure 8 In the presence of an acid the fewprotonated molecules are much more reactive to a nucle-ophile as the electronic deficiency of the carbonyl carbonis increased This affirmation is supported by the resonanceforms Reactions of carboxylic acids occur in an acidic envi-ronment Thus interference of OH group acidity is avoidedand carbon nucleophilicity is increased as partial protonationof the carbonyl group occurs In the initial stage the carbon of

the carboxyl group changes from sp2 hybridization (trigonalplanar) to sp3 (tetrahedral) In this stage the nucleophileprotonated in acidic medium is added In the final stagethe carbon present in the carboxylic group recovers its sp2hybridization As the initial proton is recovered the amountof acid required for these reactions is catalytic The incipientwater molecule formed in the previous step is easily removedand the result is a new material produced by the loss of anelectron Hence the map of reactivity of a carboxylic acid ismarked first by the high acidity of OH group and second bythe electrophilicity of carbonyl carbon

The second mechanism considers that hydrogen bondedto highly electronegative atoms can generate partial chargesin the elements which would transform into electrostatic


Table 1 Thermal parameters of polymer (CA-PA) with raw and oxidized CNTs

Samples Graphitic material ()Thermogravimetric parameters

Residue at 700∘C ()Stage I Stage II119879

0(∘C) Interval (∘C) 119879max II (

∘C) Interval (∘C) 119879max III (∘C)

Polymer (CA-PA) 0 200 mdash mdash 271ndash414 360 103Polymer (CA-PA)with raw CNTs 1 200 190ndash262 239 271ndash412 358 135

Polymer (CA-PA)with oxidizedCNTs

1 204 193ndash262 264 272ndash410 359 138

OR

O

O

O

O

O

O

O

O

O

O

O

OO

O

O

O

O

O

O

O

O

O

HO

HOHO

HO

O

O

O

OH

OHOH

OHR

OR

OR

CH3

CH3

CH3

CH3

CH3

CH3

H3CH3C

n


attraction as shown in Figure 9 An OH bond is polarized bythe very high electronegativity of oxygen and by the fact thatthe attraction of bonding electrons by the hydrogen nucleusis weak Electrons present in the OH groups are closer tothe oxygen than the hydrogen therefore partial negativecharges on oxygen and partial positive charges on hydrogenare generated The presence of positive and negative partialcharges causes thematerials to act likemagnets so those partswith partial positive charges attract parts with partial negativecharges

323 Thermal Properties Table 1 summarizes the TGAresults for the different materials studied The polymer (CA-PA) shows one main thermal event observed around 360∘Ccorresponding to its thermal degradation process When thegraphitic materials were added to the polymer (CA-PA) weobserved twomain thermal eventsThefirst onewas observedaround 190ndash274∘C corresponding to the degradation of theimpurities present in the graphitic materialThe second stagewas associated with the degradation of polymer and it wasobserved around 360∘CThe residue at 700∘Cwas between 10and 13 for all cases The weight loss per grade centigradeat 360∘C is greater in the polymer without graphitic mate-rial than the membranes with graphitic materials at 1wFigure 10

324 Scanning Electron Microscopy The images obtainedfrom electron microscopy are shown in Figure 11 The figurescorrespond to the different kinds of membranes synthetizedCellulose acetate has been traditionally used for polymeric

membrane fabrication It can produce membranes of ade-quate porosity [13] In accordance with the results obtainedfrom the microscopic characterization it can be seen thatthe polymeric membranes have pores of variable size This isconsistent with results obtained in previous works where thepore sizes showed an irregular behavior as a function of tem-perature of the immersionmedium [17] In somemembranespolymer (CA-PA) the pores are formed in layers giving theeffect of forming a deep network Figures 11(a)-11(b) In thecase of membranes with raw carbon nanotubes the finalstructure of the polymer is messier than the original struc-ture Figure 11(c)When the nanotubes are oxidized the orig-inal structure is conserved and it looks like a network of neatpores Figure 11(d)

325 Determination of the Surface Area and Pore Size Dis-tribution in the Carbon Nanotubes The BET analysis wasapplied to carbon nanotubes to determine the effective sur-face area and the pore size distribution of the materials Theraw nanotubes presented a surface area of 14972m2g and apore size of 1599 nm The oxidized nanotubes showed a sur-face area of 9199m2g and an average pore size of 2477 nmThe adsorption-desorption isotherms obtained by BET anal-ysis (Figures 12 and 13) showed a characteristic behaviorof the isotherm of type 3 proposed by Brunauer whichshows that the adsorption occurs by a physical mechanismFrom adsorption-desorption isotherms obtained we can seethat the analyzed samples have a hexagonal tubular capillary

Both the raw nanotubes and oxidized nanotubes show apore diameter distribution between 10 and 100 nm and a very


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Wei

ght (

)

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Temperature (∘C)

Polymer (CA-PA)Polymer-raw nanotubes 1Polymer-oxidized nanotubes 1

(a)

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Temperature (∘C)


18

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Der

iv w

eigh

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∘C)

(b)

Figure 10 Thermogravimetric curves of polymer (CA-PA) with raw and oxidized carbon nanotubes (1w)

(a) (b)

(c) (d)

Figure 11 Sequence of scanning electron microscope images for different polymeric materials

small portion of pores in a range of 3 to 4 nm Figure 14 Theanalyzed samples have macropores and mesopores in theirstructure

326 Concentration of Acidic Sites and Basic Sites Bothacidic and basic sites were calculated in carbon nanotubesand polymeric materials using a method proposed by Boehm

based on an acid-base titration For the carbon nanotubesconcentration values for only the acid sites were obtainedThe value obtained for oxidized carbon nanotubes was40meqg Both acidic and basic sites on the membraneswithout graphitic material were calculated using the methodproposed by Boehm The concentration of acidic sites in thepolymeric material (49meqg) is 125 times higher than the


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dsor

bed

(cm3g

) STP

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Adsorption processDesorption process

Raw CNTRelative pressure (PP0)

Figure 12 Adsorption-desorption isotherm of raw nanotubes


Oxidized CNT

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dsor

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(cm3g

) STP

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Relative pressure (PP0)

Figure 13 Adsorption-desorption isotherm of oxidized nanotubes

concentration of base sites (39meqg) The basic sites in thepolymeric material may be associated with unreacted siteson the cellulose while the acid sites can be ascribed to sitesvacated in the polyacrylic acid during the synthesis process ofthe copolymer For the membranes with carbon nanotubesno significant changes in the concentration values of the siteswere observed

327 Surface Charge and Zero Point Load The surface chargeof the carbon nanotubes and reinforced membranes wasplaced using amethod proposed by Loskutov Kuzin based ona potentiometric titrationThe zero point load for the carbonnanotubes was determined in a pH value of 56 Thus thematerial is positively charged at pH values lower than loadpoint zero and negatively charged at pH values higher thanload point zero Figure 15(a) For the polymeric membranes

08

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Pore

vol

ume (

cm3g

)

10 100

Pore diameter (A)

Oxidized nanotubesRaw nanotubes

Figure 14 Pore size distribution in raw nanotubes and oxidizednanotubes

the zero point load was placed in a pH value of 22Figure 15(b) The surface of polymeric membranes is posi-tively charged at pH values higher than the zero point loadand negatively charged at pH values lower than the zero pointload The behavior of the surface charge of the membranesis opposite to the behavior shown by graphite materials Themembranes with graphitic material showed a zero point loadplaced at pH values higher than those shown for the mem-branes without graphitic material Figure 15(c) The surfaceof polymeric membranes with graphitic material is positivelycharged at pH values higher than the zero point load andnegatively charged at pH values lower than the zero pointload

33 Performance of the Different Polymeric Materials inthe Process of Removal of Metal Ions

331 Effect of Contact Time The removal of Cr(VI) fromaqueous solutions using polymeric materials made fromcellulose acetate and polyacrylic acid with carbon nanotubeswas studied as a function of contact time at a pH value of 22From the adsorption kinetics obtained it can be seen that theremoval of Cr(VI) increases when the contact time increasesThe removal of Cr(VI) mainly occurs in a contact time from32 to 64 h when the initial concentration of Cr(VI) is 1mgLand the charge of graphitic material in the membranes is 1by weight Figure 16

332 Kinetic Models The data of the adsorption kineticswere simulated using pseudo-first-order models pseudo-second-order models Elovich model model function ofpower and kinetic rate law for three values of 119899 (0 2 and3) Kinetic data were described in a better way by the pseudo-first-order model and pseudo-second-order model as shownin Table 2


10000

5000

0

minus5000

minus10000

minus15000

minus20000

Oxidized nanotubes

3 4 5 6 7

pH

CS

(Cm

2)

(a)

Polymer (CA-PA)

0 2 4 86 10 12

pH

40000

20000

60000

0

minus20000

minus40000

minus60000

CS

(Cm

2)

(b)

Polymer-oxidized nanotubes

20 25 30 35 40 45 50

pH

40000

50000

30000

20000

10000

60000

70000

80000

0

minus10000

minus20000

minus30000

CS

(Cm

2)

(c)

Figure 15 Distribution of the surface charge in the different materials (a) oxidized carbon nanotubes (b) polymer (CA-PA) and (c) polymer(CA-PA) with carbon nanotubes

Table 2 Constants for the adsorption kinetics of Cr(VI) frompolymer membranes with CNTs

Modelparameters Polymer-oxidized nanotubesa

Pseudo-first-order119870

1015840

1(Lh) 01034119902

119890(mgg) 09135119877

2 09984Pseudo-second-order

119870

1015840

2(Lh) 09288119902

119890(mgg) 09212119877

2 09992aPolymer (CA-PA) with carbon nanotubes (1w)

333 Effect of Initial Concentration of Cr(VI) The effect ofinitial concentration of Cr(VI) on its removal was studied

using polymeric materials with carbon nanotubes The datawere obtained at a pH value of 22 and different temperaturesFor the materials studied the percentage of Cr(VI) removaldecreases when its initial concentration increases When thedose of the graphitic material is constant the availability ofsurface adsorption sites also remains fixed in this way theremoval percentage decrease is due to electrostatic repul-sion between ions When the concentration increases thecompetition between ions also increases thus increasing theelectrostatic repulsion

The kinetic adsorption data were simulated with Lang-muir and Freundlich Model respectively The results arelisted in Table 3 From the values of 1199032 Langmuir Modelfits the experimental data best between the two models Thevalues of adsorption capacity calculated frommodels indicatethat sim84 can be adsorbed to material after contact time of32 h


Table 3 Parameters of Langmuir Model and Freundlich Model

Adsorbent Temperature Langmuir Model Freundlich Model(∘C) 119902max (mgg) 119870

119871(Lmg) 119903

2119873 119870

119865(mgg) 119903

2

Polymer (CA-PA) 25 0340 0570 09606 1613 1707 0912835 0211 0851 09795 1850 1391 09006

Polymer-oxidized nanotubes 25 0843 13118 09982 3909 1560 0836235 0833 4570 09978 2662 1913 08281

0 10 20 30 40 50 60 70

Contact time (h)

100

80

60

40

20

0

Cr(V

I) ad

sorb

ed (

)

Polymer (CA-PA)Polymer-oxidized nanotubes

Figure 16 Chromium adsorption kinetics for polymeric mem-branes with carbon nanotubes (pH 22)

4 Conclusions

The results obtained show that it is possible to designpolymers with carbon nanotubes whose pores are formedin layers giving the effect of depth forming a network Itcan be seen that the graphitic material is deposited on theoutside of the polymericmaterialThe adsorption-desorptionisotherms obtained by BET analysis showed that the adsorp-tion occurs by a physical mechanism and that the analyzedsamples have a hexagonal tubular capillary Besides theisotherms of adsorptiondesorption obtained for graphitegraphite oxide and graphene oxide showed characteristicssimilar to those of the carbon nanotubes For the carbonnanotubes concentration values for only the acid sites wereobtained These acid sites can be associated with the pres-ence of carboxylic groups inserted during oxidation of thegraphitic materials The basic sites in the polymeric materialmay be associated with unreacted sites on the cellulose whilethe acid sites can be ascribed to sites vacated in the polyacrylicacid during the synthesis process of the polymer (CA-PA)For the membranes with carbon nanotubes no significantchanges were observed in the concentration values of thesites The carbon nanotubes are positively charged at pHvalues lower than load point zero and negatively charged atpH values higher than load point zero whereas the surfaceof polymeric membranes is positively charged at pH values

higher than the zero point load and negatively charged atpH values lower than the zero point load Thus the behaviorof the surface charge of the membranes is opposite to thebehavior shown by carbon nanotubes

From these studies of removal of Cr(VI) we can establishthe following conclusions

(a) The removal of Cr(VI) using polymeric membraneswith andwithout carbonnanotubes is strongly depen-dent on the pH values Besides the adsorption ofCr(VI) decreases with the increase of pH value

(b) The adsorption of Cr(VI) using polymeric mem-branes with and without carbon nanotubes is fast inthe beginning of the process and then becomes slowwith increased contact time

(c) The removal of Cr(VI) takes a considerable timewhenusing polymericmembranes with andwithout carbonnanotubes as adsorbents

(d) The kinetics of absorption of Cr(VI) can be rep-resented by pseudo-second-order and pseudo-first-order models

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The authors are grateful to Universidad de Guanajuato andPRODEP for financial supportThey also thankM T Carrillofor her help in revising the paper J A Sanchez-Marquezthanks CONACYT for financial support during his PhDstudies Grant no 267260

References

[1] Z F Wang B Wang X M Ding et al ldquoEffect of temperatureand structure on the free volume and water vapor permeabilityin hydrophilic polyurethanesrdquo Journal ofMembrane Science vol241 no 2 pp 355ndash361 2004

[2] M Sivakumar D RMohan and R Rangarajan ldquoStudies on cel-lulose acetate-polysulfone ultrafiltration membranes II Effectof additive concentrationrdquo Journal of Membrane Science vol268 no 2 pp 208ndash219 2006

[3] R Rodrıguez and VM Castano ldquoSmart membranes a physicalmodel for a circadian behaviorrdquo Applied Physics Letters vol 87no 14 Article ID 144103 pp 1ndash3 2005


[4] C Stropnik L Germic and B Zerjal ldquoMorphology variety andformation mechanisms of polymeric membranes prepared bywet phase inversionrdquo Journal of Applied Polymer Science vol 61no 10 pp 1821ndash1830 1996

[5] T D Nguyen T Matsuura and S Sourirajan ldquoEffect of non-solvent additives on the pore size and the pore size distributionof aromatic polyamide RO membranesrdquo Chemical EngineeringCommunications vol 54 no 1ndash6 pp 17ndash36 1987

[6] M Sivakumar D Mohan and R Rangarajan ldquoPreparation andperformance of cellulose acetatendashpolyurethane blend mem-branes and their applications Part 1rdquo Polymer International vol47 no 3 pp 311ndash316 1998

[7] R Gadupudi L Chungsying and S Fengsheng ldquoSorption ofdivalentmetal ions fromaqueous solution by carbonnanotubesa reviewrdquo Application of Nanotechnologies in Separation andPurification vol 58 pp 224ndash231 2007

[8] M Tuzen and M Soylak ldquoMultiwalled carbon nanotubes forspeciation of chromium in environmental samplesrdquo Journal ofHazardous Materials vol 147 no 1-2 pp 219ndash225 2007

[9] J Hu C Chen X Zhu and X Wang ldquoRemoval of chromiumfrom aqueous solution by using oxidized multiwalled carbonnanotubesrdquo Journal of HazardousMaterials vol 162 no 2-3 pp1542ndash1550 2009

[10] S D Kim K S Park and M B Gu ldquoToxicity of hexavalentchromium to Daphnia magna influence of reduction reactionby ferrous ironrdquo Journal of Hazardous Materials vol 93 no 2pp 155ndash164 2002

[11] G Donmez and Z Aksu ldquoRemoval of chromium (VI) fromsaline wastewaters by Dunaliella speciesrdquo Process Biochemistryvol 38 no 5 pp 751ndash762 2002

[12] N Todorovska I Karadjova S Arpadjan and T Stafilov ldquoOnchromium direct ETAAS determination in serum and urinerdquoCentral European Journal of Chemistry vol 5 no 1 pp 230ndash2382007

[13] O Kutowy and S Sourirajan ldquoCellulose acetate ultrafiltrationmembranesrdquo Journal of Applied Polymer Science vol 19 no 5pp 1449ndash1460 1975

[14] S Park and J Crank Diffusion in Polymers Academic PressNew York NY USA 1968

[15] M Sivakumar RMalaisamy C J Sajitha DMohan VMohanand R Rangarajan ldquoUltrafiltration application of celluloseacetatendashpolyurethane blend membranesrdquo European PolymerJournal vol 35 no 9 pp 1647ndash1651 1999

[16] M Sivakumar RMalaisamy C J Sajitha DMohan VMohanand R Rangarajan ldquoPreparation and performance of cellu-lose acetate-polyurethane blend membranes and their applica-tionsmdashIIrdquo Journal of Membrane Science vol 169 no 2 pp 215ndash228 2000

[17] R F E Guerrero E Rubio Rosas and V Rodriguez LugoldquoNonlinear changes in pore size induced by temperature in thedesign of smartmembranesrdquoPolymer Journal vol 42 no 12 pp947ndash951 2010

[18] S N Ege Organic Chemistry Structure and ReactivityHoughton Mifflin Company New York NY USA 4th edition1999

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of



CeramicsJournal of


CompositesJournal of

NanoparticlesJournal of



International Journal of

Biomaterials


NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


were prepared and characterized in order to evaluate theirproperties stability and possible application in chromiumremoval The use of polymers provides support to carbonnanotubes and permits their use in continuous processes forthe removal of ions This idea is based on previous studiesshowing that these materials have great potential in theadsorption of heavy metals [7ndash9]

Previous studies have demonstrated the technical feasibil-ity of using carbon nanotubes (CNTs) for the removal of diva-lent ions (Ni2+ Cu2+ Pb2+ Cd2+ Zn2+ andCo2+) from aque-ous solutions These studies were based mainly on chemicalinteractions that occur between ions and surface groups of theCNTs CNTs were regenerated and reused for several cyclesof water treatment this feature is ideal if you want to havelow-cost processes [7] Furthermore CNTs have been used instudies of speciation for Cr(III) Cr(VI) and total Cr Thesemethods were successfully applied showing optimal condi-tions comparable to the procedures reported in the literaturesuch as quantitative recovery values low detection limitshigh selectivity high capacity and a larger range of pH valuesfor speciation of chromium [8] In addition studies for theremoval of Cr(VI) have been performed using oxidized CNTsas adsorbents These studies showed that the CNTs can effi-ciently remove Cr(VI) from aqueous solutions under a widerange of experimental conditions without significant releaseof Cr(III) Chromium removal takes place primarily becauseof the functional groups located on the surface of the CNTsThese functional groups provide adsorption sites for Cr(VI)[9]

Chromium is a heavy metal and has been identified asa contaminant of water and soil Chromium pollution isproduced from numerous industrial activities such as thetextile industry the chemical industry andmetallurgy [10 11]Cr(III) is poorly soluble and stable is found primarily infood and is essential to maintain normal glucosemetabolismin humans On the other hand Cr(VI) is less stable andmore soluble and is considered an environmental pollutantand is also toxic and carcinogenic to humans Hexavalentchromium is harmful to health relating to certain diseases ofthe liver kidney and lungs and different kinds of cancer [12]

The polymer made from cellulose acetate (CA) andpolyacrylic acid (PA) can be used as support of the graphiticmaterials Cellulose acetate is one of themost commonly usedmaterials for polymeric membrane fabrication [13] It canproduce membranes of adequate porosity and low binding[14] CA is a hydrophilic material with good resistance tosoiling and moderate chlorine resistance its price is low andit has good biocompatibility However some disadvantages ofthismaterial are poormechanical strength low thermal resis-tance and low chemical resistance [15 16] Some studies haveshown that it is possible to control the porosity of amembraneobtained from cellulose acetate and polyacrylic acid Themembranes made from the reaction of two organic polymersshowed pore diameters that ranged between 3 and 100microns just by varying the time of immersion in hot waterThe pore size shows a nonlinear behavior as a function of thetemperature of the immersionmedium [17]The possibility ofcontrolling the pore through an external factor such as water

temperature immersion introduces these membranes asattractive materials for adsorption processes Finally it isimportant to stress that the performance of nanomaterial inthe polymer matrix must be evaluated from the study of con-ditions such as load degree of oxidation polymer featuressynthesis conditions and carbon nanomaterial productionand precursors All these features play an important role inthe final properties of membranes for chromium removal

2 Materials and Methods

21 Synthesis of Polymer Membranes In order to carry outthis work the followingmaterials were used cellulose acetate(Sigma Aldrich) with a molecular weight of 50000 by gelpermeation chromatography (GPC) and a degree of acety-lation of 397w and polyacrylic acid in aqueous solution(Sigma Aldrich) with a molecular weight of 30000 gmolminus1and a percentage of 35wAll commercial reagentswere usedwithout any further purification step Polymer membraneswere prepared according to a procedure previously reported[9] Initially a solution was prepared dissolving 8 g of cellu-lose acetate in 100mL of glacial acetic acid at room tempera-ture Then when the cellulose acetate had been completelydissolved 10mL of polyacrylic acid was added slowly withconstant medium agitation this solution was heated at 60∘Cunder agitation for 30min allowing the reaction betweenthe cellulose acetate and the polyacrylic acid to take placeThe final solution was cooled down to room temperature andstored for 3 days before use To obtain the membranesseveral samples were poured into flat glass molds of 10 cmin diameter leaving the molds with the solution floating oniced water at 4∘C allowing the solution to reach the sametemperature of iced water Thereafter the mold with thepolymer solution was completely immersed carefully into thecold water until the membranes formed and subsequentlypermitted to rest for 15min to allow the solidification of poly-mer solution Once the membranes were formed they werewithdrawn from the iced water and immediately placed intoa bath of hot water at 60∘C This procedure was applied tomembranes both with and without carbon nanotubes usingconcentrations of 1 by weight

22 Oxidation of Carbon Nanotubes (CNTs) Multilayer nan-otubes (Cheaptubes Co) with purity greater than 95 10to 30 microns in length and diameters between 20 and30 nm were oxidized through a chemical treatment based ona mixture of sulfuric acid (Jalmek purity 95ndash98 MW =9808 gMol) and nitric acid (Fermont purity 69 MW =6301 gmol) in a 3 1 volume ratio The oxidation was con-ducted at 85∘C for 3 hWhen the reaction finished the samplewas washed with distilled water and dried for 12 h at 40∘C

23 Surface Characterization The characterization of poly-mer and carbon nanotubes was made by Fourier TransformInfrared spectroscopy with attenuated total reflectance(FTIR-ATR Vertex Model 70) in pressed KBr pellets(100mgKBr and 1mg of sample) of graphitic materials ForFTIR spectroscopy the samples were dried at 333 K for 24 h














100

98

96

94

92

90

88

86

84

4000 3500 3000 2500 2000 1500 1000 500

3778

3435

1720

1040

11001300

1670

1533

1340


T(

)

Raw CNTOxidized CNT


10

20

30

40

50

60

70

80

90

100

110

0

3487 2958

1753 12271048

1368

1436

1701

3384

1629

1452

903

4000 3500 3000 2500 2000 1500 1000


T(

)


Polymer (AC-PA)



80

85

90

95

100

1238 1045

904

1368

1629

1731

3389

4000 3500 2000 1500 1000


T(

)










Raw CNTOxidized CNT

500 1000 1500 2000 2500 3000

14000

12000

10000

8000

6000

4000

2000

0

Cou

nts

RBM (116)

D (1346)G (1574)


G998400 (2687)


30002500200015001000500

659

906

978

834

11211081

1265

1382

1435

1736

2723

2934

Cellulose acetate

20000

40000

60000

0

Cou

nts


O

O

OO

O O

O

O

O

O O

OO

HOHO

n

CH3

CH3

CH3

CH3

lowast


905

12241496

2935

1678

1654

1306

Polyacrylic acid

20000

10000

40000

30000

60000

70000

50000

0

Cou

nts

30002500200015001000500


lowast

n

H

H H

C C

C

O

OH


1731

1431

1368

1157

11211081

654

906

834974

2939

Polymer (CA-PA)

10000

8000

6000

4000

2000

12000

14000

16000

18000

20000

0

Cou

nts

30002500200015001000500


minus2000





O OH

OH

OH

OH

OH

OH

OH

R R R

OHR

O

O

O

O

O

O

O

O

O

O

HO

HO

HO

HO

HO

HO

HO

HO

HO

HO

HO

HO

HO

HO

O

O

H

H

O

O

O

O

O

O

O

O

O

O

O

O

R

H

H

O

O

O

O

O

O

O

O

O

O

O

O

RO

O

OO

O

O

O

O

O

O

O

O

R

O

O

O

O

O

O

O

O

O

O

O

O

RO

O

O

O

O

O

O

O

O

O

O

O

R

O

H+ OH+

+

+ +

+

+

CH3

CH3

CH3

CH3CH3

CH3CH3

CH3

CH3

CH3

CH3

CH3

CH3

H3C

H3C

H3C H3C

H3C

H3C

n

n

n n

n

n

H2O

O+

O+

H+














1 204 193ndash262 264 272ndash410 359 138

OR

O

O

O

O

O

O

O

O

O

O

O

OO

O

O

O

O

O

O

O

O

O

HO

HOHO

HO

O

O

O

OH

OHOH

OHR

OR

OR

CH3

CH3

CH3

CH3

CH3

CH3

H3CH3C

n









100

80

60

40

20

0

Wei

ght (

)

100 200 300 400 500 600 700

Temperature (∘C)


(a)

100 200 300 400 500 600 700

Temperature (∘C)


18

16

14

12

10

08

06

04

02

00

Der

iv w

eigh

t (

∘C)

(b)


(a) (b)

(c) (d)






400

350

300

250

200

150

100

50

0

Volu

me a

dsor

bed

(cm3g

) STP

00 02 04 06 08 10





Oxidized CNT

400

350

300

250

200

150

100

50

0

Volu

me a

dsor

bed

(cm3g

) STP

00 02 04 06 08 10





08

06

04

02

00

Pore

vol

ume (

cm3g

)

10 100

Pore diameter (A)








10000

5000

0

minus5000

minus10000

minus15000

minus20000

Oxidized nanotubes

3 4 5 6 7

pH

CS

(Cm

2)

(a)

Polymer (CA-PA)

0 2 4 86 10 12

pH

40000

20000

60000

0

minus20000

minus40000

minus60000

CS

(Cm

2)

(b)


20 25 30 35 40 45 50

pH

40000

50000

30000

20000

10000

60000

70000

80000

0

minus10000

minus20000

minus30000

CS

(Cm

2)

(c)





1015840

1(Lh) 01034119902

119890(mgg) 09135119877


119870

1015840

2(Lh) 09288119902

119890(mgg) 09212119877








119871(Lmg) 119903

2119873 119870

119865(mgg) 119903

2

Polymer (CA-PA) 25 0340 0570 09606 1613 1707 0912835 0211 0851 09795 1850 1391 09006


0 10 20 30 40 50 60 70

Contact time (h)

100

80

60

40

20

0

Cr(V

I) ad

sorb

ed (

)



4 Conclusions










Acknowledgments


References



























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials
















100

98

96

94

92

90

88

86

84

4000 3500 3000 2500 2000 1500 1000 500

3778

3435

1720

1040

11001300

1670

1533

1340


T(

)

Raw CNTOxidized CNT


10

20

30

40

50

60

70

80

90

100

110

0

3487 2958

1753 12271048

1368

1436

1701

3384

1629

1452

903

4000 3500 3000 2500 2000 1500 1000


T(

)


Polymer (AC-PA)



80

85

90

95

100

1238 1045

904

1368

1629

1731

3389

4000 3500 2000 1500 1000


T(

)










Raw CNTOxidized CNT

500 1000 1500 2000 2500 3000

14000

12000

10000

8000

6000

4000

2000

0

Cou

nts

RBM (116)

D (1346)G (1574)


G998400 (2687)


30002500200015001000500

659

906

978

834

11211081

1265

1382

1435

1736

2723

2934

Cellulose acetate

20000

40000

60000

0

Cou

nts


O

O

OO

O O

O

O

O

O O

OO

HOHO

n

CH3

CH3

CH3

CH3

lowast


905

12241496

2935

1678

1654

1306

Polyacrylic acid

20000

10000

40000

30000

60000

70000

50000

0

Cou

nts

30002500200015001000500


lowast

n

H

H H

C C

C

O

OH


1731

1431

1368

1157

11211081

654

906

834974

2939

Polymer (CA-PA)

10000

8000

6000

4000

2000

12000

14000

16000

18000

20000

0

Cou

nts

30002500200015001000500


minus2000





O OH

OH

OH

OH

OH

OH

OH

R R R

OHR

O

O

O

O

O

O

O

O

O

O

HO

HO

HO

HO

HO

HO

HO

HO

HO

HO

HO

HO

HO

HO

O

O

H

H

O

O

O

O

O

O

O

O

O

O

O

O

R

H

H

O

O

O

O

O

O

O

O

O

O

O

O

RO

O

OO

O

O

O

O

O

O

O

O

R

O

O

O

O

O

O

O

O

O

O

O

O

RO

O

O

O

O

O

O

O

O

O

O

O

R

O

H+ OH+

+

+ +

+

+

CH3

CH3

CH3

CH3CH3

CH3CH3

CH3

CH3

CH3

CH3

CH3

CH3

H3C

H3C

H3C H3C

H3C

H3C

n

n

n n

n

n

H2O

O+

O+

H+














1 204 193ndash262 264 272ndash410 359 138

OR

O

O

O

O

O

O

O

O

O

O

O

OO

O

O

O

O

O

O

O

O

O

HO

HOHO

HO

O

O

O

OH

OHOH

OHR

OR

OR

CH3

CH3

CH3

CH3

CH3

CH3

H3CH3C

n









100

80

60

40

20

0

Wei

ght (

)

100 200 300 400 500 600 700

Temperature (∘C)


(a)

100 200 300 400 500 600 700

Temperature (∘C)


18

16

14

12

10

08

06

04

02

00

Der

iv w

eigh

t (

∘C)

(b)


(a) (b)

(c) (d)






400

350

300

250

200

150

100

50

0

Volu

me a

dsor

bed

(cm3g

) STP

00 02 04 06 08 10





Oxidized CNT

400

350

300

250

200

150

100

50

0

Volu

me a

dsor

bed

(cm3g

) STP

00 02 04 06 08 10





08

06

04

02

00

Pore

vol

ume (

cm3g

)

10 100

Pore diameter (A)








10000

5000

0

minus5000

minus10000

minus15000

minus20000

Oxidized nanotubes

3 4 5 6 7

pH

CS

(Cm

2)

(a)

Polymer (CA-PA)

0 2 4 86 10 12

pH

40000

20000

60000

0

minus20000

minus40000

minus60000

CS

(Cm

2)

(b)


20 25 30 35 40 45 50

pH

40000

50000

30000

20000

10000

60000

70000

80000

0

minus10000

minus20000

minus30000

CS

(Cm

2)

(c)





1015840

1(Lh) 01034119902

119890(mgg) 09135119877


119870

1015840

2(Lh) 09288119902

119890(mgg) 09212119877








119871(Lmg) 119903

2119873 119870

119865(mgg) 119903

2

Polymer (CA-PA) 25 0340 0570 09606 1613 1707 0912835 0211 0851 09795 1850 1391 09006


0 10 20 30 40 50 60 70

Contact time (h)

100

80

60

40

20

0

Cr(V

I) ad

sorb

ed (

)



4 Conclusions










Acknowledgments


References



























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




Raw CNTOxidized CNT

500 1000 1500 2000 2500 3000

14000

12000

10000

8000

6000

4000

2000

0

Cou

nts

RBM (116)

D (1346)G (1574)


G998400 (2687)


30002500200015001000500

659

906

978

834

11211081

1265

1382

1435

1736

2723

2934

Cellulose acetate

20000

40000

60000

0

Cou

nts


O

O

OO

O O

O

O

O

O O

OO

HOHO

n

CH3

CH3

CH3

CH3

lowast


905

12241496

2935

1678

1654

1306

Polyacrylic acid

20000

10000

40000

30000

60000

70000

50000

0

Cou

nts

30002500200015001000500


lowast

n

H

H H

C C

C

O

OH


1731

1431

1368

1157

11211081

654

906

834974

2939

Polymer (CA-PA)

10000

8000

6000

4000

2000

12000

14000

16000

18000

20000

0

Cou

nts

30002500200015001000500


minus2000





O OH

OH

OH

OH

OH

OH

OH

R R R

OHR

O

O

O

O

O

O

O

O

O

O

HO

HO

HO

HO

HO

HO

HO

HO

HO

HO

HO

HO

HO

HO

O

O

H

H

O

O

O

O

O

O

O

O

O

O

O

O

R

H

H

O

O

O

O

O

O

O

O

O

O

O

O

RO

O

OO

O

O

O

O

O

O

O

O

R

O

O

O

O

O

O

O

O

O

O

O

O

RO

O

O

O

O

O

O

O

O

O

O

O

R

O

H+ OH+

+

+ +

+

+

CH3

CH3

CH3

CH3CH3

CH3CH3

CH3

CH3

CH3

CH3

CH3

CH3

H3C

H3C

H3C H3C

H3C

H3C

n

n

n n

n

n

H2O

O+

O+

H+














1 204 193ndash262 264 272ndash410 359 138

OR

O

O

O

O

O

O

O

O

O

O

O

OO

O

O

O

O

O

O

O

O

O

HO

HOHO

HO

O

O

O

OH

OHOH

OHR

OR

OR

CH3

CH3

CH3

CH3

CH3

CH3

H3CH3C

n









100

80

60

40

20

0

Wei

ght (

)

100 200 300 400 500 600 700

Temperature (∘C)


(a)

100 200 300 400 500 600 700

Temperature (∘C)


18

16

14

12

10

08

06

04

02

00

Der

iv w

eigh

t (

∘C)

(b)


(a) (b)

(c) (d)






400

350

300

250

200

150

100

50

0

Volu

me a

dsor

bed

(cm3g

) STP

00 02 04 06 08 10





Oxidized CNT

400

350

300

250

200

150

100

50

0

Volu

me a

dsor

bed

(cm3g

) STP

00 02 04 06 08 10





08

06

04

02

00

Pore

vol

ume (

cm3g

)

10 100

Pore diameter (A)








10000

5000

0

minus5000

minus10000

minus15000

minus20000

Oxidized nanotubes

3 4 5 6 7

pH

CS

(Cm

2)

(a)

Polymer (CA-PA)

0 2 4 86 10 12

pH

40000

20000

60000

0

minus20000

minus40000

minus60000

CS

(Cm

2)

(b)


20 25 30 35 40 45 50

pH

40000

50000

30000

20000

10000

60000

70000

80000

0

minus10000

minus20000

minus30000

CS

(Cm

2)

(c)





1015840

1(Lh) 01034119902

119890(mgg) 09135119877


119870

1015840

2(Lh) 09288119902

119890(mgg) 09212119877








119871(Lmg) 119903

2119873 119870

119865(mgg) 119903

2

Polymer (CA-PA) 25 0340 0570 09606 1613 1707 0912835 0211 0851 09795 1850 1391 09006


0 10 20 30 40 50 60 70

Contact time (h)

100

80

60

40

20

0

Cr(V

I) ad

sorb

ed (

)



4 Conclusions










Acknowledgments


References



























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




O OH

OH

OH

OH

OH

OH

OH

R R R

OHR

O

O

O

O

O

O

O

O

O

O

HO

HO

HO

HO

HO

HO

HO

HO

HO

HO

HO

HO

HO

HO

O

O

H

H

O

O

O

O

O

O

O

O

O

O

O

O

R

H

H

O

O

O

O

O

O

O

O

O

O

O

O

RO

O

OO

O

O

O

O

O

O

O

O

R

O

O

O

O

O

O

O

O

O

O

O

O

RO

O

O

O

O

O

O

O

O

O

O

O

R

O

H+ OH+

+

+ +

+

+

CH3

CH3

CH3

CH3CH3

CH3CH3

CH3

CH3

CH3

CH3

CH3

CH3

H3C

H3C

H3C H3C

H3C

H3C

n

n

n n

n

n

H2O

O+

O+

H+














1 204 193ndash262 264 272ndash410 359 138

OR

O

O

O

O

O

O

O

O

O

O

O

OO

O

O

O

O

O

O

O

O

O

HO

HOHO

HO

O

O

O

OH

OHOH

OHR

OR

OR

CH3

CH3

CH3

CH3

CH3

CH3

H3CH3C

n









100

80

60

40

20

0

Wei

ght (

)

100 200 300 400 500 600 700

Temperature (∘C)


(a)

100 200 300 400 500 600 700

Temperature (∘C)


18

16

14

12

10

08

06

04

02

00

Der

iv w

eigh

t (

∘C)

(b)


(a) (b)

(c) (d)






400

350

300

250

200

150

100

50

0

Volu

me a

dsor

bed

(cm3g

) STP

00 02 04 06 08 10





Oxidized CNT

400

350

300

250

200

150

100

50

0

Volu

me a

dsor

bed

(cm3g

) STP

00 02 04 06 08 10





08

06

04

02

00

Pore

vol

ume (

cm3g

)

10 100

Pore diameter (A)








10000

5000

0

minus5000

minus10000

minus15000

minus20000

Oxidized nanotubes

3 4 5 6 7

pH

CS

(Cm

2)

(a)

Polymer (CA-PA)

0 2 4 86 10 12

pH

40000

20000

60000

0

minus20000

minus40000

minus60000

CS

(Cm

2)

(b)


20 25 30 35 40 45 50

pH

40000

50000

30000

20000

10000

60000

70000

80000

0

minus10000

minus20000

minus30000

CS

(Cm

2)

(c)





1015840

1(Lh) 01034119902

119890(mgg) 09135119877


119870

1015840

2(Lh) 09288119902

119890(mgg) 09212119877








119871(Lmg) 119903

2119873 119870

119865(mgg) 119903

2

Polymer (CA-PA) 25 0340 0570 09606 1613 1707 0912835 0211 0851 09795 1850 1391 09006


0 10 20 30 40 50 60 70

Contact time (h)

100

80

60

40

20

0

Cr(V

I) ad

sorb

ed (

)



4 Conclusions










Acknowledgments


References



























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials











1 204 193ndash262 264 272ndash410 359 138

OR

O

O

O

O

O

O

O

O

O

O

O

OO

O

O

O

O

O

O

O

O

O

HO

HOHO

HO

O

O

O

OH

OHOH

OHR

OR

OR

CH3

CH3

CH3

CH3

CH3

CH3

H3CH3C

n









100

80

60

40

20

0

Wei

ght (

)

100 200 300 400 500 600 700

Temperature (∘C)


(a)

100 200 300 400 500 600 700

Temperature (∘C)


18

16

14

12

10

08

06

04

02

00

Der

iv w

eigh

t (

∘C)

(b)


(a) (b)

(c) (d)






400

350

300

250

200

150

100

50

0

Volu

me a

dsor

bed

(cm3g

) STP

00 02 04 06 08 10





Oxidized CNT

400

350

300

250

200

150

100

50

0

Volu

me a

dsor

bed

(cm3g

) STP

00 02 04 06 08 10





08

06

04

02

00

Pore

vol

ume (

cm3g

)

10 100

Pore diameter (A)








10000

5000

0

minus5000

minus10000

minus15000

minus20000

Oxidized nanotubes

3 4 5 6 7

pH

CS

(Cm

2)

(a)

Polymer (CA-PA)

0 2 4 86 10 12

pH

40000

20000

60000

0

minus20000

minus40000

minus60000

CS

(Cm

2)

(b)


20 25 30 35 40 45 50

pH

40000

50000

30000

20000

10000

60000

70000

80000

0

minus10000

minus20000

minus30000

CS

(Cm

2)

(c)





1015840

1(Lh) 01034119902

119890(mgg) 09135119877


119870

1015840

2(Lh) 09288119902

119890(mgg) 09212119877








119871(Lmg) 119903

2119873 119870

119865(mgg) 119903

2

Polymer (CA-PA) 25 0340 0570 09606 1613 1707 0912835 0211 0851 09795 1850 1391 09006


0 10 20 30 40 50 60 70

Contact time (h)

100

80

60

40

20

0

Cr(V

I) ad

sorb

ed (

)



4 Conclusions










Acknowledgments


References



























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




100

80

60

40

20

0

Wei

ght (

)

100 200 300 400 500 600 700

Temperature (∘C)


(a)

100 200 300 400 500 600 700

Temperature (∘C)


18

16

14

12

10

08

06

04

02

00

Der

iv w

eigh

t (

∘C)

(b)


(a) (b)

(c) (d)






400

350

300

250

200

150

100

50

0

Volu

me a

dsor

bed

(cm3g

) STP

00 02 04 06 08 10





Oxidized CNT

400

350

300

250

200

150

100

50

0

Volu

me a

dsor

bed

(cm3g

) STP

00 02 04 06 08 10





08

06

04

02

00

Pore

vol

ume (

cm3g

)

10 100

Pore diameter (A)








10000

5000

0

minus5000

minus10000

minus15000

minus20000

Oxidized nanotubes

3 4 5 6 7

pH

CS

(Cm

2)

(a)

Polymer (CA-PA)

0 2 4 86 10 12

pH

40000

20000

60000

0

minus20000

minus40000

minus60000

CS

(Cm

2)

(b)


20 25 30 35 40 45 50

pH

40000

50000

30000

20000

10000

60000

70000

80000

0

minus10000

minus20000

minus30000

CS

(Cm

2)

(c)





1015840

1(Lh) 01034119902

119890(mgg) 09135119877


119870

1015840

2(Lh) 09288119902

119890(mgg) 09212119877








119871(Lmg) 119903

2119873 119870

119865(mgg) 119903

2

Polymer (CA-PA) 25 0340 0570 09606 1613 1707 0912835 0211 0851 09795 1850 1391 09006


0 10 20 30 40 50 60 70

Contact time (h)

100

80

60

40

20

0

Cr(V

I) ad

sorb

ed (

)



4 Conclusions










Acknowledgments


References



























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




400

350

300

250

200

150

100

50

0

Volu

me a

dsor

bed

(cm3g

) STP

00 02 04 06 08 10





Oxidized CNT

400

350

300

250

200

150

100

50

0

Volu

me a

dsor

bed

(cm3g

) STP

00 02 04 06 08 10





08

06

04

02

00

Pore

vol

ume (

cm3g

)

10 100

Pore diameter (A)








10000

5000

0

minus5000

minus10000

minus15000

minus20000

Oxidized nanotubes

3 4 5 6 7

pH

CS

(Cm

2)

(a)

Polymer (CA-PA)

0 2 4 86 10 12

pH

40000

20000

60000

0

minus20000

minus40000

minus60000

CS

(Cm

2)

(b)


20 25 30 35 40 45 50

pH

40000

50000

30000

20000

10000

60000

70000

80000

0

minus10000

minus20000

minus30000

CS

(Cm

2)

(c)





1015840

1(Lh) 01034119902

119890(mgg) 09135119877


119870

1015840

2(Lh) 09288119902

119890(mgg) 09212119877








119871(Lmg) 119903

2119873 119870

119865(mgg) 119903

2

Polymer (CA-PA) 25 0340 0570 09606 1613 1707 0912835 0211 0851 09795 1850 1391 09006


0 10 20 30 40 50 60 70

Contact time (h)

100

80

60

40

20

0

Cr(V

I) ad

sorb

ed (

)



4 Conclusions










Acknowledgments


References



























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




10000

5000

0

minus5000

minus10000

minus15000

minus20000

Oxidized nanotubes

3 4 5 6 7

pH

CS

(Cm

2)

(a)

Polymer (CA-PA)

0 2 4 86 10 12

pH

40000

20000

60000

0

minus20000

minus40000

minus60000

CS

(Cm

2)

(b)


20 25 30 35 40 45 50

pH

40000

50000

30000

20000

10000

60000

70000

80000

0

minus10000

minus20000

minus30000

CS

(Cm

2)

(c)





1015840

1(Lh) 01034119902

119890(mgg) 09135119877


119870

1015840

2(Lh) 09288119902

119890(mgg) 09212119877








119871(Lmg) 119903

2119873 119870

119865(mgg) 119903

2

Polymer (CA-PA) 25 0340 0570 09606 1613 1707 0912835 0211 0851 09795 1850 1391 09006


0 10 20 30 40 50 60 70

Contact time (h)

100

80

60

40

20

0

Cr(V

I) ad

sorb

ed (

)



4 Conclusions










Acknowledgments


References



























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






119871(Lmg) 119903

2119873 119870

119865(mgg) 119903

2

Polymer (CA-PA) 25 0340 0570 09606 1613 1707 0912835 0211 0851 09795 1850 1391 09006


0 10 20 30 40 50 60 70

Contact time (h)

100

80

60

40

20

0

Cr(V

I) ad

sorb

ed (

)



4 Conclusions










Acknowledgments


References



























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials


























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



Research Article Membrane Made of Cellulose Acetate with...

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Transcript of Research Article Membrane Made of Cellulose Acetate with...