Draft - TSpace Repository: Home...Draft Facile approach for synthesis of stable, efficient and...

Draft

Facile approach for synthesis of stable, efficient and

recyclable ZnO through pulsed sonication and its application for degradation of recalcitrant azo dyes in wastewater

Journal: Canadian Journal of Chemistry

Manuscript ID cjc-2017-0696.R1

Manuscript Type: Article

Date Submitted by the Author: 26-Mar-2018

Complete List of Authors: Gunasekaran, Kumaravel; Indian Institute of Science Education and

Research Bhopal, Chemical Engineering Ramesh, Saranya; University of Dublin Trinity College, Department of Physics

Keyword: pulsed ultrasound, advanced oxidation process, water treatment, decolourization, azo dye

Is the invited manuscript for consideration in a Special

Issue?: N/A

https://mc06.manuscriptcentral.com/cjc-pubs

Canadian Journal of Chemistry

Draft

Facile approach for synthesis of stable, efficient and recyclable ZnO through pulsed

sonication and its application for degradation of recalcitrant azo dyes in wastewater

G Kumaravel Dinesh*

Department of Chemical Engineering

Indian Institute of Science Education and Research Bhopal

Bhopal (M.P.)

India

Rameshkumar Saranya

Polymeric Materials & NanoComposites (PMNC)

Department of Physics

Trinity College Dublin

University of Dublin

Dublin, Ireland

*Corresponding author

Email: [email protected], [email protected] (G Kumaravel Dinesh)

Tel: +91 755 669 2571

Fax: +91 755 669 2392

Page 1 of 29



Draft

Highlights

•Synthesis of ZnO using ultrasound-assisted sol–gel and hydrothermal method.

•ZnO synthesized via ultrasound has large specific surface area and high pore volume.

•ZnO is better for adsorption and sonocatalysis.

•Simultaneous application of sonolysis and photolysis gives highest decolorization.

•97% decolorization in 20 minutes and 87% COD removal in 17 minutes were achieved.

Abstract

In the present study, the ultrasound in pulsed mode used as a part of advanced oxidation

method. The influence of pulsed ultrasound mode for the preparation of zinc oxide wurtzite

nanoparticle were synthesized. The catalysts synthesized were analysed using SEM, TEM,

EDAX, BET surface area, XRD and DRS to study about their morphological and structural

characterizations. The ZnO nanoparticles exhibited highly hexagonal structure from pulsed

sonication synthesis route. The efficiency of the decolourization of RR4 were studied under

different operation parameters like dye concentration, initial solution pH, antioxidants like

H2O2 concentration and catalyst loading. The hybrid combined process of pulsed sonolysis,

pH (4.0), H2O2 (17.64 mmol) and Catalyst (0.35 g/L)) achieved 97% degradation and 87.5%

COD removal in about 20 minutes of reaction time. The cyclic degradation studies of RR4

removal with 0.35 g/L of ZnO showed the reusability of catalyst upto 5th removal cycle with

negligible loss in the catalytic performance. GC–MS study, used for the detection of the RR4

intermediates revealed the oxidation/reduction reaction by the reactive radicals proceeded via

the reductive cleavage of the azo bonds. The studied process based on the pulsed ultrasound

is found to be effective for the degradation of RR4 dye.

Keywords: pulsed ultrasound, azo dye, advanced oxidation process, reactive red 4, water

treatment, decolourization.

Page 2 of 29



Draft

1. Introduction

In the recent decades the disposal of wastewater from the different types of industries

like pesticides, cosmetics, paper, textiles and leather has been increasing day by day. Among

all textile and dying industry are the major contributor of wastewater. The accumulation of

toxic compounds in the water resources have been entailed as unsolved puzzle for the

environment and more hazardous to human health. In fact, approximately 200 litres of water

required to produce l kg of textiles [1]. About 20% of the dyes and dye products enter into the

water resources through the discharge of textile industries. The azo dyes constitute the major

dye used in textile and dying industries exceeding over 60% of the dye used [2]. The

intermediates of the dye compounds have adverse effects as deplete the dissolved oxygen in

aquatic system and endanger to flora and fauna. Hence it is more essential to treat with an

efficient method to transform all these dyes and intermediates into toxic free compounds [3].

Moreover, the anaerobic and incomplete degradation of dyes generates aromatic amines and

other recalcitrant secondary pollutants which are more toxic and carcinogenic [4]. Hence,

there is a need for an efficient oxidation method to treat the dyes and its by-products before

being disposed into water resources. For decades advanced oxidation processes have proved

to be an efficient and powerful tool to eliminate these dyes from wastewater [5].

Environmental sonochemistry is an example for advanced oxidation process which is

widely followed treatment methods for the complete destruction of recalcitrant pollutants in

the wastewater [6]. The physical and chemical effects of the ultrasound produced cavitation

bubbles in the aqueous solution generates high temperature and pressure within the liquid

during the collapse of the bubbles deals with the destruction of complex compounds [7]. The

effective treatment is caused by the increased rate of generation of ●OH radicals and other

reactive moieties. The degradation kinetics followed by the sonochemical treatment can be of

zero order, first order depend upon the in situ production of ●OH radicals and their degree of

contact with the contaminants present in the wastewater [8]. The limitations of the individual

process can be eliminated by the process integration of ultrasound with the addition of

catalyst. Further the turbulence in the aqueous solution created by the ultrasound helps in

catalyst fragmentation and de-agglomeration thus increasing the activity of the catalyst [9].

Recently the pulsated ultrasound treatment has been studied for improving the efficiency of

the degradation kinetics.

Ultrasound has a uniqueness as the chemical free treatment method utilizing the

generated ●OH radicals i.e., short lived oxidants [10]. Major hinderance is the high

Page 3 of 29



Draft

operational energy being wasted in the continuous mode. The shielding effect of the bubbles

created when these bubble accumulate near the irradiating source [11]. This energy wastage

can be reduced by the several ways like modification of the reactor, integrating the ultrasound

with other techniques and the pulsed mode ultrasound. The pulsed mode ultrasound is usually

operating ultrasonic equipment in cyclic repetition such as ON and OFF mode repeatedly.

This process has been developed to deliver more rapid effects both in time and life cycle of

the generated cavitation bubbles [12]. In recent years the highlights of the ultrasound

performance in degradation of pollutants has been reported as the effective method among

advanced oxidation process.

The technologies employed in degradation studies still produces incomplete

intermediates after the oxidation process [13]. The usage of catalyst helps in transforming

these complex intermediates into harmless compounds [14]. Recently the piezoelectric and

electronic properties of wurtzite ZnO crystals showed the generation of electric dipole where

the wonderful cation-anion displacement occurs promoting the formation of oxidative

radicals very rapidly [15]. When these semiconductor catalysts coupled with the pulsed

ultrasound in the degradation of azo dyes showed a beneficial synergetic effects. This

strategy helped inducing a high efficiency technology to remove the organic pollutant from

wastewater. The aim of this work was to assess the performance of pulsed ultrasound with

ZnO semiconductor catalyst as a part of advanced oxidation process for degradation of azo

dyes, studying the effects of various other parameters like pH, anti-oxidants, dye

concentration and volume on the rate of decolourization. Moreover, the synergetic efficiency

of the combined parameters with pulsed ultrasound process was evaluated.

2. Experimental procedure

2.1. Chemicals

Reactive Red 4 was obtained from Sigma Aldrich (Colour Index No. 18105, EC No. 241-

663-8, molecular weight: 995.21) and was used as supplied. High purity reagents, sulphuric

acid (Merck), sodium hydroxide (Merck), zinc acetate (Merck), ethanol and hydrogen

peroxide solution (30% w/w, Merck) were used for the solution. All the solutions were

prepared using Millipore water. All chemicals and reagents used were of analytical grade and

used without any further purification. Ultrasonic processor (Sonics & Materials, VCX 500)

was used for the experimental study.

Page 4 of 29



Draft

2.2 Synthesis of catalyst

The ZnO particles are prepared in an ultrasonic processor using zinc acetate and sodium

hydroxide as precursors. 0.005 M zinc acetate and 0.02 M sodium hydroxide in the

stoichiometric ratio of 1:2 were dissolved in water [16]. Following the hydrothermal process,

the solution was sonicated for 30 min with an ultrasonic probe. The milky white precipitate

was filtered and washed with ethanol 5 times to remove the impurities. The obtained ZnO

nanoparticle was dried in a vacuum oven at 105°C for 24 hours to remove the moisture.

2.3 Catalyst characterization

The morphology of synthesized catalysts ZnO was investigated using scanning electron

microscopy (SEM) images (JEOL, Hitachi Corporation, Japan). The elemental composition

of the prepared catalyst by the energy-dispersive analysis of X-rays (EDAX) conjugating

with SEM confirms the formation of ZnO. The surface area and pore volume of the

synthesized catalyst were measured using BET (Brunauer–Emmett–Teller) surface area and

particle analyser (ASAP 2020, Micromeritics, USA). The phase purity and composition of

the synthesized catalyst were studied using X-ray diffraction (XRD) (Cu Kα radiation, D8

advance Bruker, Germany). XRD patterns were recorded in the 2θ range between 20° and

80°. By using the Scherrer formula the average crystallite size (D) of the catalyst was

calculated (Eqn. 1).

0.9 λD =

β cos θ, Eqn. 1

where k is the X-ray wavelength and b is the full width at half maximum (FWHM) obtained

at a corresponding 2θ angle. UV–visible diffuse reflectance spectra (DRS) were recorded to

determine the absorption capacity of the catalysts prepared. Specord (Analytikjena) S-600

UV–visible spectrophotometer was used in the wavelength range of 200–800 nm to obtain

the DRS spectra [17].

2.4 Experimental procedure

0.01004 mmol (1000 ppm) concentration of Reactive Red 4 stock solution was prepared with

Millipore water and used for the experimental study. The degradation studies were carried out

using 1000 mL dye solution placed in water cooled jacketed beaker at room temperature 25º

C. Fig 1a. represents the scheme of the experimental setup. The pH of the Reactive Red 4

solution was adjusted either by adding drops of 0.05N sulphuric acid solution or 0.05N

Page 5 of 29



Draft

sodium hydroxide solution. A small dosage in steps of H2O2 concentrations (8.82, 17.64,

26.46, 35.28, 44.1, 52.62, 61.74, 70.56, 79.38, 88.2, 97.02 and 105.84 mmol) was added to

study its effect of anti-oxidants on RR4 dye colour removal. For all the experiments, the

ultrasound was irradiated for an hour and the decolourization of RR4 was monitored using

UV–vis spectrophotometer for every 15 min with intermittent sampling.

2.5 Analytical Procedure

The optical absorption spectra of the Reactive Red 4 dye solutions were determined by

JASCO UV–Visible spectrophotometer equipped with equipped with a photoelectric detector

at the maximum absorption wavelength of 517 nm. The UV–vis spectrum and the chemical

structure of RR4 are shown in Fig. 1b. The aromatic intermediates after degradation studies

were analysed using GC-MS (Perkin Elmer). The GC was equipped with Elite-5 (5%

Diphenyl) Dimethylpolysiloxane series capillary columns of length 30m, inner diameter

0.53mm, film thickness 1.50mm and interfaced directly to the MS. The GC column was

operated at a temperature of 80 oC for 2 minutes then increased to 250

oC at the rate of 15

oC

min-1

. The other experimental conditions were: Electron ionization voltage 70 eV, helium as

carrier gas, injection temperature 280 oC and source temperature 80

oC.

Fig 1a and Fig 1b

3. Results and Discussions

3.1 Effect of pulsed sonication treatment

The experiments were conducted in continuous sonication and pulsed sonication system,

respectively to illustrate the degradation potential of the individual processes. As shown in

Fig.2, the colour hardly decreased when both the processes were applied to 0.01004 mmol

concentration of reactive red 4 solution. It is due to the fact that only a small amount of •OH

radicals were formed in the presence of only sonolysis [18]. It was also confirmed that little

colour removal was achieved when pulsed sonication was applied such that during the ON

and OFF time interval (5 seconds) the dye molecules have been decomposed at the bubble

water surface. Therefore, the decolorization efficiency was also increased from 29% to 36%.

Similarly, the produced •OH radicals were not enough for complete degradation RR4 as mere

ultrasound was inefficient for the complete removal of the recalcitrant pollutant molecules

[19].

Fig 2

Page 6 of 29



Draft

3.2 Effect of pH

The effect of pH on decolourization of RR4 was also performed. Fig. 3 shows that the low

pH favors high decolourization with small differences in the range 2.0-4.0, and lower rate at

alkaline pH [20, 21]. The natural pH of the solution is 6.71, during acidification the dye

would become hydrophobic and easily available for ultrasound treatment. Similar studies

reveal that the degradation kinetics increased for RR4 dye molecules in the acidic medium.

Also at acidic condition the H+ ions will be readily activated, generates more

•OH radicals

during ultrasound treatment. Under alkaline condition there is a gradual decrease in the

degradation rate. This is due to the formation of conjugate base of the dye molecule which

makes the dye molecule more hydrophilic and deactivates the formation of •OH radicals

resulting in lesser degradation. The colour removal rate of the dye is maximum of 42.19%

when the pH is 4 [22]. The colour removal rate was increased little from natural pH to pH 7.0

due to the availability of more •OH radicals than normal solution pH. When compared with

ultrasound (US) treatment alone, the solution pH shows high colour removal rate.

Fig 3

3.3 Effect of H2O2 concentration

The effect of ultrasound with oxidants were evaluated using hydrogen peroxide

addition at different concentration to the RR4 aqueous dye sample at solution pH. In the

presence of ultrasonication the generation of •OH radicals increases according to the

concentration of H2O2 added [23]. Fig. 4 illustrate the decolourization efficiency at different

H2O2 concentration. The increase in •OH radicals generation was because the dispersed H2O2

tended to act as additional nuclei available at the cavitational hot spot for the pyrolysis of

water molecules and formation of •OH radicals and can thus be used to quantify the

effectiveness in generating the desired reactive radicals [24]. Therefore 66% colour removal

due to higher oxidation activities when 8.82 mmol of H2O2 was added. The higher colour

removal of 68% was achieved with the increase of concentration to 17.64 mmol of H2O2 than

with the ultrasound alone. This ensures the formation of the powerful oxidizers like HO2/O2- ,

•OH whose oxidation–reduction potentials are +1.5 and +2.8 eV respectively. Moreover, the

scavenging reaction takes place when the concentration of H2O2 increased further [25] where

the large of number of •OH radicals interact and form H2O and H2O2 where the extinction of

•OH happen resulting in low colour removal rate.

Page 7 of 29



Draft

Fig 4

3.4 Effect of dye concentration

The influence of initial dye RR4 concentration of the sample solution was

investigated with different concentration ranging from 10ppm to 1000ppm on colour removal

rate. As illustrated in Fig. 5, the dye colour removal changed inversely to the initial dye

concentration of RR4 [26]. Higher colour removal rate was obtained for the process study

where the initial dye concentration of 10ppm solution relative lower initial concentration

while the dye concentration was increased 10 times further. For an instance, in 60 min, the

simple pulsed sonication achieved 26% decolorization, while 24% decolorization could be

achieved in the process when the dye solution concentration increased by 10 folds. The

possible explanation might be that the ratio of •OH radicals to dye molecules in the solution

decreased when the concentration of the dye molecules increased 10 folds [27], resulting in

an excess of dye molecules regarding to •OH radicals generated during the sonication

process. As a result, the decolorization rate lowered for the high initial dye concentration than

the lower dye concentration.

Fig 5

3.5 Catalyst Characterization

SEM images were recorded on catalysts synthesized by both continuous, pulsed mode

sonication and shown in Fig.6a and Fig. 6b. We can see the smooth, uniform texture and

agglomerated pseudo spherical structure of ZnO [28, 29]. The agglomeration observed was

due to the van der Waals forces among the gap energy between the particles. The

transformation of surface morphology is from agglomeration to wurtzite relatively due to the

shock wave applied during the sonication [30]. During the pulsed sonication ZnO was

subjected to some changes in its crystallinity [31]. These changes are significant in pulsed

sonication when compared to continuous mode. After the drying in the hot air oven for 24

hours the different structure evolves from both the continuous and pulsed mode of sonication.

TEM and EDAX characterization also confirms the formation of ZnO nanoparticles using

sonication Fig. 6c and Fig. 6d.

Fig 6a, 6b, 6c and 6d

Fig. 7 shows the XRD pattern of the synthesized ZnO catalyst having average diameters. The

structure was subjected to sonication with continuous or pulsed mode yielding agglomerated

Page 8 of 29



Draft

or wurtzite crystal structure.XRD patterns are shown for ZnO samples in Fig. 6. Diffraction

peaks appeared in the pattern are enumerated and listed. The peaks are in accordance with the

standard diffraction pattern of ZnO (JCPDS: 036-1451). To understand the crystallinity, the

peaks at 2θ angles of 31.6, 34.2 and 36.2 were selected. The angular location of these peaks

suggests that the planes of (100), (002) and (101) correspond to the hexagonal crystal lattice

existing along with a slight residual tensile stress [32]. Also the lattice parameters showing

sharp reflections where the presence of Zn(OH)2 has been identified along with the ZnO

amorphous nanoflakes [29, 30]. When the ZnO particles subjected to pulsed sonication the

lattice during the nucleation and growth gains thermal energy for entropic configuration thus

increasing its crystallinity.

Diffuse reflectance spectra (DRS) shows the absorption properties of the catalyst depends

upon the angle of incidence, the refractive index and surface roughness. DRS obtained were

analysed using the (Kubelka–Munk theory) Kubelka–Munk equation at any wavelength Eqn

2

2(1-R)F(R) =

2R Eqn 2

where R represents the absolute reflectance and F(R) as Kubelka–Munk function. Fig. 8

shows the diffused reflectance for ZnO nanopowders [33]. It is clearly seen that the diffused

reflectance increased with increasing wavelengths. The optical transitions in semiconductor

catalyst occurs due to direct and indirect transitions. The optical band gap Eg was calculated

by using the fundamental absorption, such that the electron excitation from the valance band

to the conduction band. The optical band gap was calculated by using the following equation

Eqn 3

n

g

F(R)hυ(αhυ) = = A(hυ-E )

tEqn 3

where A represents an energy-independent constant and Eg as the optical band gap, n -

constant determines the type of optical transitions and for indirect allowed transition, n=2;

and indirect forbidden transition, n=3, for direct allowed transition, n=1/2; for direct

forbidden transition, n=3/2. The optical band gap of the samples was calculated from the

plots of (F(R)hυ/t)2 as a function of photo energy hυ. The optical band gap of ZnO

nanoparticles were found to be 3.19eV further in good agreement with the band gap from

diffused reflectance previously calculated by other researchers equals to 3.22eV [34].

Page 9 of 29



Draft

The variation in the thickness and density of the synthesized catalyst were shown by the BET

adsorption-desorption curve. The obtained curve corresponds to type IV hysteresis loop the

characteristics of mesoporous particles. The surface area of the synthesized ZnO particles

were found to be 3.93 m2/g (Fig. 8), approximately equals to the surface area of ZnO

nanoparticles reported earlier [35]. The ZnO agglomerated assemblies with sufficient surface

area and more mesoporous structures also acts as adsorbents while used for the treatment of

dye pollutants.

Fig 7 and Fig 8

3.6 Effect of catalyst loading

ZnO catalyst upon sonication produce electrons from the conduction band or generate

holes in the valence band (Eqns. 4 and 5) thereby splitting the water molecule as H+ and

●OH

radicals (Eqn. 6). Amount of ZnO concentration plays an essential role in influencing the

generation of ●OH radicals for the degradation processes [36]. In this treatment process,

various concentrations of ZnO were studied to obtain its optimal concentration for the higher

colour removal rate. The results for effect of catalyst concentration on degradation of RR4

are shown in Fig. 9. From the experimental results it reveals that decolorization rate of RR4

increases upto the catalyst concentration 0.3 g/L. Addition of ZnO above 0.35 g/L did not

affect the decolorization kinetics. The decolorization percentage of RR4 started to decrease

slowly when the concentration of ZnO was increased above 0.40 g/L. The reduction in the

colour removal rate was due to the catalytic decomposition effect of ZnO. It is known that the

scavenging of ●OH radical happens when its concentration is increased, they recombine to

form less oxidative OH- ions. The catalytic effect also accordingly decreases as its

concentration was higher. ZnO also undergoes a reaction with hydroxyl ions to form Zn(OH)2

[37] which has lower catalytic activity (lesser redox potential of conduction and valence

band) (Eqn. 7).

US 2+ •-

2ZnO Zn + O→ Eqn 4

US - +

CB VBZnO ZnO(e + h )→ Eqn 5

US2+ + 2+ -

2Zn + H O H +Zn -OH� � �� Eqn 6

2+ -

2Zn + 2OH Zn(OH)→ Eqn 7

Page 10 of 29



Draft

Fig 9

3.7 Combined effect of pulsed sonolysis, pH, H2O2 and Catalyst

The complete degradation of dyes into CO2 and H2O were studied in this treatment process

and analysed by the COD. The COD values can be related to the concentration of organics

present in the dye. The colour removal from the wastewater cannot be considered as complete

oxidation [38]. Many researchers have reported that there were reaction intermediates present

in the solution after the decolourization studies [39]. In our studies, the intermediates from

RR4 which will form aromatic ring structure intermediates were long lived and more

carcinogenic to the aquatic life. Thus, the optimum operating conditions of pH, initial

concentration of the dye, ZnO catalyst concentration, H2O2 concentration and pulsed

sonication, applied for the degradation of aromatic contents and mineralisation of dye were

analysed. Fig 10 shows that the decolourization percentage of RR4 in the hybrid process

(Combined effect of pulsed sonolysis, pH (4.0), H2O2 (17.64 mmol) and Catalyst (0.35 g/L))

achieved 97% degradation in about 20 minutes of reaction time. Furthermore, it also shows

that 87.5% reduction of COD occurring at a faster reaction rate than colour removal

achieving with in the time interval of 17 minutes. Thus the combined effect prevails to be

more beneficial in COD removal rather than simple decolourization.

Fig 10

3.8 Degradation Pathway of RR4

The formation of intermediates as the chromophores of RR4 evolved as the

degradation of dye proceeds reflect in the UV-vis spectra. The spectral changes are attributed

to the change in the π → π* transition related to the –N=N– group, C–C group, C–N group,

benzene and naphthalene rings of the RR4 molecule [40]. The absorption peak of RR4

decreases rapidly when the degradation reaction proceeds. After the reaction time when there

was no peak in the absorption peak indicating that the azo bonds and the conjugated

molecules of the dye molecule were completed destroyed and converted into simpler

molecules. The intermediates formed during the degradation after the reaction time 60

minutes were analysed by GC/MS. During the degradation process the byproducts like

sulfonic acid, heneicosane, 3-Hexadecene, 1-Octadecene etc were detected. Moreover, there

were several pathways through the degradation process followed [41]. The cleavege of –

Page 11 of 29



Draft

N=N– group, C–C group, C–N group, benzene and naphthalene rings of the RR4 molecule

follow several concurrent pathways by the oxidation of mainly ●OH radicals have been

indicated and the corresponding plausible pathway have been proposed in Fig.11. Eventually

the destruction of RR4 aromatic rings were formed and all the complex molecules were

degraded into smaller molecules.

Fig 11

3.9 Reusability of catalyst for RR4 removal

The reusability and stability of the catalyst material for the degradation reveals the

cost effectiveness. The catalyst effect on degradation of RR4 was carried out with ZnO (0.30

g/L) for 10 ppm concentration at the solution pH 6.71. After the pulsed sonication for the

removal of RR4, the COD was reduced 37%. The catalyst was filtered and treated with 1 M

NaOH and 1 M ethanol then washed repeated 3 times with Millipore water and dried at

120°C successively to regenerate for the next cycle of degradation studies. The degradation

studies were experimented with 4 cycles. Fig. 12 shows the COD values of the repeated

degradation studies using the regenerated catalyst. It revealed that after 3 cycles the catalyst

showed 30% COD reduction as there was a slight decrease in the catalytic activity due to the

lesser number of active sites in the catalyst [42]. The decrease in sites may be due to the

subsequent attack by the dye molecules and reducing the catalytic efficiency. Moreover, the

catalyst stands effective after regeneration and further indicating that the catalyst potential for

wastewater treatment applications.

Fig 12

Conclusion

The ultrasound in pulsed mode alone have negligible effect on the decolourization of RR4.

However, when ultrasound combined with other parameters like pH variation, catalyst

loading, dye concentration and H2O2 addition gave faster decolourization rate. The synergetic

effect of AOP can be explained by the formation of hydroxyl radicals helps in the faster

decolourization kinetics. When the concentration of H2O2 increased there was an increase of

decolourization reaching a maximum (asymptotic value). Moreover, the increase in

antioxidant intuitively describes that the excessive addition can favour the radical scavenging

resulting in decrease in the removal kinetics. Under the hybrid combined experimental

conditions, the dye solution could be completely decolorized within 20 minutes a very short

Page 12 of 29



Draft

reaction time. The rate for colour removal is much faster and similar that of COD removal.

All the aromatic ring, azo bond were cleavaged within 20 min, and ended in simpler

compounds. Finally, the plausible degradation path of RR4 was predicted.

References

(1) Verma, A.K.; Dash, R.R.; Bhunia, P. J. Environ. Manage. 2012, 93, 154.

(2) Liang, C.Z.; Sun, S.P.; Li, F.Y.; Ong, Y.K.; Chung, T.S. J. Membr. Sci. 2014, 469,

306.

(3) Wang, S.; Li, D.; Sun, C.; Yang, S.; Guan, Y.; He, H. Appl. Catal. B: Environ. 2014,

144, 885.

(4) Cai, M.; Jin, M.; Weavers, L.K. Ultrason. Sonochem. 2011, 18, 1068.

(5) Tisa, F.; Raman, A.A.A.; Daud, W.M.A.W. J. Environ. Manag. 2014, 146, 260.

(6) Bagal, M.V.; Gogate, P.R. Ultrason. Sonochem. 2014, 21, 1.

(7) Harichandran, G.; Prasad, S. Ultrason. Sonochem. 2016, 29, 178.

(8) Jawale, R.H.; Tandale, A.; Gogate, P.R. Ultrason. Sonochem. 2017, 38, 402.

(9) Jordens, J.; Appermont, T.; Gielen, B.; Van Gerven, T.; Braeken, L. Crys. Growth

Des. 2016, 16, 6167.

(10) Teh, C.Y.; Wu, T.Y.; Juan, J.C. Chem. Eng. J. 2017, 317, 586.

(11) Jin, Q.; Kang, S.T.; Chang, Y.C.; Zheng, H.; Yeh, C.K. Ultrason. Sonochem.

2016, 32, 1.

(12) Soltani, R.D.C.; Safari, M. Ultrason. Sonochem. 2016, 32, 181.

(13) Weng, C.H.; Lin, Y.T.; Yuan, H.M. Sep. Purif. Technol. 2013, 117, 75.

(14) Weng, C.H.; Lin, Y.T.; Liu, N.; Yang, H.Y. Coloration Technol. 2014, 130, 133.

(15) Al-Zahrani, H.Y.; Pal, J.; Migliorato, M.A. Nano Energy. 2013, 2, 1214.

(16) Shen, X.; Liang, Y.; Zhai, Y.; Ning, Z. J. Mater. Sci. Technol. 2013, 29, 44. (17) Daneshvar, N.; Aber, S.; Dorraji, M.S.; Khataee, A.R.; Rasoulifard, M.H. Sep. Purif.

Technol. 2007, 58, 91. (18) Ziylan-Yavas, A.; Ince, N.H. Chemosphere. 2016, 162, 324. (19) Adewuyi, Y.G. Environ. Sci. Technol. 2005, 39, 3409.

(20) Gore, M.M.; Saharan, V.K.; Pinjari, D.V.; Chavan, P.V.; Pandit, A.B. Ultrason.

Sonochem. 2014, 21, 1075.

(21) Ghodbane, H.; Hamdaoui, O. Ultrason. Sonochem. 2009, 16, 593.

(22) Saharan, V.K.; Badve, M.P.; Pandit, A.B. Chem. Eng. J. 2011, 178, 100.

Page 13 of 29



Draft

(23) ElShafei, G.M.; Yehia, F.Z.; Dimitry, O.I.H.; Badawi, A.M.; Eshaq, G. Ultrason.

Sonochem. 2014, 21, 1358.

(24) Acisli, O.; Khataee, A.; Karaca, S.; Karimi, A.; Dogan, E. Ultrason. Sonochem. 2017,

34, 754.

(25) Yang, Y.; Pignatello, J.J.; Ma, J.; Mitch, W.A. Environ. Sci. Technol. 2014, 48, 2344. (26) Liu, N.; Xie, X.; Yang, B.; Zhang, Q.; Yu, C.; Zheng, X.; Xu, L.; Li, R.; Liu, J.

Environ. Sci. Pollut. Res. 2017, 24, 252.

(27) Tehrani-Bagha, A.R.; Mahmoodi, N.M.; Menger, F.M. Desal. 2010, 260, 34.

(28) Mishra, P.; Yadav, R.S.; Pandey, A.C. Ultrason. Sonochem. 2010, 17, 560.

(29) Zak, A.K.; Wang, H.Z.; Yousefi, R.; Golsheikh, A.M.; Ren, Z.F. Ultrason. Sonochem.

2013, 20, 395. (30) Carp, O.; Tirsoaga, A.; Ene, R.; Ianculescu, A.; Negrea, R.F.; Chesler, P.; Ionita, G.;

Birjega, R. Ultrason. Sonochem. 2017, 36, 326. (31) Liu, X.; Pan, L.; Lv, T.; Lu, T.; Zhu, G.; Sun, Z.; Sun, C. Catal. Sci. Technol. 2011, 1,

1189.

(32) Azizi, S.; Mohamad, R.; Bahadoran, A.; Bayat, S.; Rahim, R.A.; Ariff, A.; Saad, W.Z.

J. Photochem. Photobio. B. 2016, 161, 441. (33) Chakma, S.; Moholkar, V.S. Ultrason. Sonochem. 2015, 22, 287. (34) Guo, M.Y.; Ng, A.M.C.; Liu, F.; Djurisic, A.B.; Chan, W.K.; Su, H.; Wong, K.S. J.

Phys. Chem. C. 2011, 115, 11095. (35) Wang, J.; Xia, Y.; Dong, Y.; Chen, R.; Xiang, L.; Komarneni, S. Appl. Catal. B:

Environ. 2016, 192, 8. (36) Ahmad, M.; Ahmed, E.; Hong, Z.L.; Ahmed, W.; Elhissi, A.; Khalid, N.R. Ultrason.

Sonochem. 2014, 21, 761. (37) Kozlova, E.A.; Cherepanova, S.V.; Markovskaya, D.V.; Saraev, A.A.; Gerasimov,

E.Y.; Parmon, V.N. Appl. Catal. B: Environ. 2016, 183, 197. (38) Liang, C.Z.; Sun, S.P.; Li, F.Y.; Ong, Y.K.; Chung, T.S. J. Membr. Sci. 2014, 469,

306. (39) Bhaumik, M.; Maity, A.; Gupta, V.K. J. Colloid Interface Sci. 2017, 506, 403. (40) Niu, C.G.; Wang, Y.; Zhang, X.G.; Zeng, G.M.; Huang, D.W.; Ruan, M.; Li, X.W.

Biores. Technol. 2012, 126, 101. (41) Cai, M.; Jin, M.; Weavers, L.K. Ultrason. Sonochem. 2011, 18, 1068. (42) Miao, J.; Jia, Z.; Lu, H.B.; Habibi, D.; Zhang, L.C. J. Taiwan Inst. Chem. Eng. 2014,

45, 1636.

Page 14 of 29



Draft

Page 15 of 29



Draft

List of Figures

1a. Schematic representation of experimental setup

1b. Absorbance spectra and structure of RR4 dye

2. Decolourization of RR4 dye solution with the variation mode of ultrasound

3. Decolourization of RR4 dye solution with the variation of initial solution pH

4. Decolourization of RR4 dye solution with the variation of H2O2 Concentration

5. Decolourization of RR4 dye solution with the variation of dye Concentration

6. SEM images of ZnO by A) Continuous mode and B) Pulsed Mode C) EDAX

D)TEM

7. XRD and DRS of ZnO

8. BET Surface area of ZnO

9. Decolourization of RR4 dye solution with the variation of dye Concentration

10. COD and Colour removal by the combined effect

11. Plausible degradation pathway

12. Reusability of the synthesized catalyst

Page 16 of 29



Draft

OH•

radicals

Ultrasound

Probe

)))

Water out

Cooling water in

Fig 1a Model experiment setup

Figure 1b Absorbance Spectra and Structure of RR4

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

200 300 400 500 600 700 800

Absorbance

Wavelength (nm)

y = 0.0138x + 0.0872R² = 0.9921

0

0.5

1

1.5

2

0 20 40 60 80 100

Absorbance

Concentration (ppm)

Page 17 of 29



Draft

Figure 2 Decolourization of RR4 dye solution with the

variation mode of ultrasound [US Irradiation time—1 h, RR4 conc.

10 ppm].

0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40 50 60 70

Ct / C0

Time (minutes)

Sonolysis

Pulsed

Page 18 of 29



Draft


variation of initial solution pH [US Irradiation time—1 h, RR4 conc.

10 ppm].

0

5

10

15

20

25

30

35

40

45

2 3 4 5 6 7 8 9 10 11

% Decolourization

pH

sonolysis

Pulsed

Page 19 of 29



Draft


variation of H2O2 Concentration [US Irradiation time—1 h, RR4 conc.

10 ppm].

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40 50 60

Ct / C0

Time (minutes)

8.82 mmol

17.64 mmol

26.46 mmol

35.28 mmol

44.1 mmol

Page 20 of 29



Draft


variation of dye Concentration [US Irradiation time—1 h, pH-6.71].

0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40 50 60 70

Ct / C0

Time (minutes)

10ppm 50ppm

100ppm 500ppm

1000ppm

Page 21 of 29



Draft

Figure 6 SEM images of ZnO by A) Continuous mode and B) Pulsed Mode C) EDAX

D)TEM

A B

C D

Page 22 of 29



Draft10 20 30 40 50 60 70 80

(202)

(004)

Intensity (a.u.)

(100)

2θ Position

(002)

(101)

(102)

(110)

(103)

(200)

(112)

(201)

Figure 7 XRD and DRS of ZnO

Page 23 of 29



Draft

Figure 8 BET Surface area of ZnO

0

5

10

15

20

25

30

0 0.2 0.4 0.6 0.8 1

Quantity Adsorbed (cm

3/g STP)

Relative Pressure (P/P0)

Desorption

Adsorption

0

0.01

0.02

0.03

0.04

0.05

1 10 100Pore volume (cm

3/g)

Pore width (nm)

Page 24 of 29



Draft


variation of dye Concentration [US Irradiation time—1 h, pH-6.71]

0.5

0.6

0.7

0.8

0.9

1

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6

% Decolourization

ZnO Catalyst (g/L)

sonolysis

pulsed

Page 25 of 29



Draft

Figure 10 COD and Colour removal by the combined effect [ Ultrasonic Irradiation –

1h, pH - 4.0, H2O2 - 17.64 mmol and Catalyst - 0.35 g/L]

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 2 4 6 8 10 12 14 16 18 20 22 24

Ct / C0

Time (minutes)

COD

Colour

Page 26 of 29



Draft

O

NH OH

S

N

-OO

O

S

N

O-

O

O

S

NH

-O

O

O

N N

N NH

Na+ Na+

Na+

Cl

S

O-O

O

Na+

NH2 OH

SO3Na

NH2

SO3Na

NH2

N N

N NH

Cl

SO3Na

SO3Na

ONa

ONa

H2N

NO

SO3Na

O

SO3Na

OH NHCOCH3

H2N

OH NHCOOH

H2N H2N

OH NH2

HO

OH OH

CH3

NH2

COOH

NH2

NH2 OH

OH

OO

HO

HO

OOH OH

OH

O O

HO

H2N

SO3

SO3NH2

N N

N NH2Cl

Figure 11 Plausible degradation pathway

Page 27 of 29



Draft

Figure 12 Reusability of the synthesized catalyst [US Irradiation time—1 h, pH-6.71,

Catalyst - 0.35 g/L]

0

10

20

30

40

1 2 3 4

% COD removal

Cycle

Page 28 of 29



Draft

Graphical abstract

Facile approach for synthesis of stable, efficient and recyclable ZnO through pulsed

sonication and its application for degradation of recalcitrant azo dyes in wastewater

GK Dinesh* and R Saranya**

*Department of Chemical Engineering, Indian Institute of Science Education and Research

Bhopal, Bhopal (M.P.), India

**Polymeric Materials & NanoComposites (PMNC), Department of Physics, Trinity College

Dublin, University of Dublin, Dublin, Ireland.

�

H2O

●OH

H2O

●OH

H2O

●OH

H2O

●OH

H2O

●OH

Cavitation Bubble Interior

Hot Spot Zone

Gas Phase

5000 – 10000 K, 1000 atm

Radical generation

Pyrolysis mechanism

Molecular dissolution

Bubble-liquid Interface:

2000 K, 1 atm

Free radicals formation and

react with parent molecules

Thermal decomposition

�

H2O

●OH

e-

h+H2O

●OH

�

e-

h+

H2O

●OH

�

e-

h+

H2O

●OH

�

e-

h+

H2O

●OH

�

e-

h+

e-

h+

H2O

●OH

�

ZnO

agglomerated

H2O

●OH

On the hybrid process of pulsed sonolysis combined with ZnO catalyst produced more ●OH

radicals for attacking the pollutants thus decolorization of 97% achieved in short time.

Page 29 of 29



Draft - TSpace Repository: Home...Draft Facile approach for synthesis of stable, efficient and...

Documents

Transcript of Draft - TSpace Repository: Home...Draft Facile approach for synthesis of stable, efficient and...