photocatalytic degradation of congo red dye on thermally activated zinc oxide

International Journal of Scientific Research in Environmental Sciences, 2(12), pp. 457-469, 2014

Available online at http://www.ijsrpub.com/ijsres

ISSN: 2322-4983; ©2014; Author(s) retain the copyright of this article

http://dx.doi.org/10.12983/ijsres-2014-p0457-0469

457

Full Length Research Paper

Photocatalytic Degradation of Congo Red Dye on Thermally Activated Zinc Oxide

Tapas Kumar Roy, Naba Kumar Mondal*

Environmental Chemistry Laboratory, Department of Environmental Science, The University of Burdwan, Burdwan, 713104,

India

*Corresponding Author: [email protected]

Received 12 October 2014; Accepted 28 November 2014

Abstract. Congo Red in aquatic system has been recognized as a serious problem in living organism because of its toxic nature

and therefore, its degradation is highly essential. In the present work, the efficacy of thermally activated ZnO was studied for

photo-catalytic degradation of Congo red (CR) dye. The batch operation was carried out by irradiating the aqueous solution of

dye in the presence of semiconductor. The effect of various parameters such as catalyst loading, pH, oxidant dose, intensity

variations and initial concentration of the dye on degradation was investigated. The maximum degradation capacity of ZnO for

CR was found to be 11.8 mg g-1

at optimized condition [303 K, 60 min, pH (8), dose (0.05g)]. The pseudo-second-order kinetic

model described the CR degradation process with a good fitting. Thermodynamic parameters such as ΔH, ΔS, and ΔG were

calculated, which indicated that the process was spontaneous and exothermic in nature, that was evident by increasing the

randomness of the dye at the solid and liquid interface. The high CR degradation ability and regeneration efficiency of this

photocatalyst suggest its applicability in industrial systems and data generated would help in further upscaling of the

degradation process.

Keywords: Congo Red; Kinetic model; Photo-catalytic degradation; Thermodynamic study; Zinc Oxide

1. INTRODUCTION

Environmental problems associated with organic

pollutants promote the development of fundamental

and applied research in the area of environment

(Ahmad et al., 2011). Several of these chemicals such

as azo dyes, herbicides and pesticides are actually

present in rivers and lakes, and are in part suspected of

being endocrine-disrupting chemicals (Ohko et al.,

2001; Coleman et al., 2000; Wang and Hong, 2000;

Hong et al., 1998). Synthetic dyes are the major

industrial pollutants and water contaminants

(Modirshahla et al., 2007). These dyes are used

extensively in the textile industry for dying nylon,

cotton, wool, and silk, as well as for colouring oils,

fats, waxes, varnishes, and plastics. The paper, food,

cosmetic, and leather industries are also major

consumers of these dyes (Chen, 2007).

The discharge of dye-coloured wastewaters into

the aquatic ecosystem represents both environmental

and public health risks because of the negative

ecotoxicological effects and bioaccumulation in

wildlife. Most importantly, many dyes contained in

wastewaters can decompose into carcinogenic

aromatic amines under aerobic conditions which can

cause serious health problems to humans and animals

(Akar et al., 2009; Kiran et al., 2009). Also, dyes can

cause allergy, dermatitis, skin irritation and cancer in

humans (Fiorentina et al., 2010). Additionally, colour

in surface water may affect photosynthesis by

preventing light penetration, thereby compromising

aquatic life (Senturk et al., 2010).

Excess use of various dyes in the textile industry

has led to the severe water contamination by releasing

the toxic and coloured effluents, which are usually

disposed by various physical and chemical methods,

such as coagulation or flocculation (Golob et al.,

2005; Allegre et al., 2004), electrocoagulation

(Alinsafi et al., 2005), coagulation/carbon degradation

process (Papic et al., 2004), adsorption, advanced

oxidation process (AOP). However, most of the

methods barely transfer the pollutants from one phase

to another without destruction or have the other

limitations (Wang et al., 2007). But advanced

oxidation process (AOP), a photo-catalytic reaction is

a promising and emerging process for the purification

of water and air (Suzuki et al., 2008). In recent years,

as a promising tool to surrogate the traditional

wastewater treatment, semiconductor-assisted photo-

catalysis has fascinated the public concern for its

ability to convert the pollutants into the harmless

substances directly in the waste water (Kulkarni et al.,

Roy and Mondal


458

2014; Habib et al., 2013; Khattab et al., 2012). Till

now, many kinds of semiconductors have been studied

as photo-catalysts including TiO2, ZnO, CdS, WO3,

and so on (Baruah et al., 2012; Ram et al., 2012;

Yogendra et al., 2011) among them ZnO is the most

extensively used effective photo-catalyst for its high

efficiency, photochemical stability, nontoxic nature,

and low cost. The wide spread use of ZnO as an

effective photo-catalyst in practical application which

is sensitive to UV light (Rao and Chu, 2009).

Therefore, continued study of ZnO is quite

necessary when illuminated with an appropriate light

source, the photocatalyst generates electron/hole pairs

with free electrons produced in the empty conduction

band leaving positive holes in the valence band. The

photogenerated electron/hole pairs are capable of

initiating a series of chemical reactions at the catalyst

surfaces, which involve adsorbed organic pollutants

and surficial water species that result in the

decomposition of the organic compounds. The

formations of relatively harmless end products

represent another attractive feature of this process

(Rego et al., 2009). It is well known that the highly

reactive OH˙ radicals and holes are generated on the

surface of photocatalyst under the radiation of UV

light. Due to the fact, the photocatalytic property is a

surface reaction (Farbod and Jafarpoor, 2012),

thermally activation process which can improve the

high effective surface area. These nanoparticles have

been reported as efficient photocatalysts against

Congo Red dye at different conditions such as

optimum catalyst dosage and effective pH level. A

ZnO-assisted photocatalytic degradation study of

these Congo Red dyes under UV light (254-nm)

irradiation has been sparse.

In the last few decade, most of the removal

techniques of Congo Red by normal zinc oxide with

uv illumination were studied the optimized condition

of different parameters, adsorption kinetics and

isotherm models. But there have been no report

regarding the thermal activation of ZnO with

optimization of process parameters, adsorption

kinetics and thermodynamic feasibility and

spontaneity of photodegradation of Congo Red.

Kinetic and thermodynamic data can be used to

predict the rate and spontaneity of degradation

respectively. Therefore the aim of the present study

was formulated for degradation efficiency of CR onto

thermally activated ZnO by the illumination of uv

with optimized conditions.

2. MATERIALS AND METHODS

2.1. Thermally activation of ZnO

Thermally activated ZnO powder was obtained by

heating the pure ZnO powder at 500º

C in a muffle

chamber by using nickel crucible. The sample was

heated at 500º C for 30 minutes and cooled slowly at

room temperature. After cooling the sample is ready

for dye degradation study.

2.2. Adsorbate and other chemicals

All chemicals were used of analytical grade. Congo

Red (CR), the typical anionic dye was selected as the

adsorbate in the present study. A stock solution of

1000 ppm was prepared by dissolving 1000 mg of CR

in 1L deionized water. The intermediate solution was

prepared by appropriate dilution of the working

solution. The pH of the solution was adjusted by

addition of either 0.1M HCl or 0.1M NaOH solutions

respectively.

2.3. Experimental procedure

In all experiments, the required amount of thermally

heated ZnO was suspended in 100 ml of Congo Red

dye using a magnetic stirrer. pH was measured by

using pH meter (Eutech 700). At predetermined times;

5 ml of reaction mixture was collected and centrifuged

(4,000 rpm, 15 minutes) in a centrifuge. The

absorbance at 497 nm wavelengths of the supernatants

was determined using ultraviolet-visible

spectrophotometer (Systronics- 1203). Photocatalytic

reaction was carried out in a homemade photoreactor

equipped with a Philips120W, high pressure mercury

lamp as a source for near-UV radiation. The reactor

was consisted of graduated 400 cm3 Pyrex glass

beaker and a magnetic stirring setup. The lamp was

positioned perpendicularly above the beaker. The

distance between the lamp and the graduated Pyrex

glass was 10 cm. The whole photocatalytic reactor

was insulated in a wooden box to prevent the escape

of harmful radiation and minimized temperature

fluctuations caused by draughts.

2.4. Degradation experiment

Degradation measurement was determined by batch

experiment of known amount of the adsorbent with

100 ml of aqueous Congo Red solution of known

concentration (4-10 ppm) in a series of 250 ml conical

flasks. Dye concentration in the reaction mixture was

calculated from the calibration curve. Degradation

experiments curve were conducted by varying initial

concentration of the dye, pH, contact time, catalyst


459

dose under the aspect of degradation kinetics. The

amount of dye adsorbed onto zinc oxide powder at

time t, qt (mg/g) was calculated by the following mass

balance relationship.

(1)

The dye removal efficiency i.e., % of degradation

was calculated as

(2)

where Co is the initial dye concentration (mg/L), Ct

is the concentration of the dye at any time t, V is the

volume of solution (L) and m is the mass (g) of zinc

oxide powder (ZnO).

Table 1: The dye removal capacity at different wave lengths

Sl No. Parameter Removal (%) Degradation capacity (mg/g)

1 Only UV(Without ZnO) 0.00 0.00

2 Only ZnO(without UV) 47.95 5.70

3 Both ZnO & UV 96.45 11.57

Table 2: Summery of parameters for various kinetic models

Kinetic model Equation Constants qexp (mgg-1

) qcal(mgg-1

)

Pseudo first

order

Pseudo second

order

)

R2 = 0.995

KL = 0.0819 min-1

R2 = 0.9999

K2 = 0.0586 g.mg-

1min

-1

11.8 mg.g-1

11.50

12.03

qt and qe are the amount of dye adsorbed (mg g-1) at time t and at equilibrium and KL (min-1) is the Lagergren rate constant of first-order degradation and K2 (g mg-1 min-1) is the second-order degradation rate constant.

Table 3: Thermodynamic parameters for adsorption of Congo Red onto ZnO particles Temperature(K)

303 -10.0680 -6.335 11.45

323 -9.6690

343 -10.1138

373 -10.8370

2.5. Photocatalysis

Photocatalysis may be termed as a photoinduced

reaction which is accelerated by the presence of a

catalyst (Mills et al., 1997). These types of reaction

are activated by absorption of a photon with sufficient

energy (equal or higher than the band gap energy of

the catalyst (Carp et al., 2004). The absorption leads

to a charge separation due to promotion of an electron

(e-) from valence band of the semiconductor catalyst

to the conduction band, thus generating a hole (h+) in

the valence band (Gaya et al., 2008). The

recombination of the electron and the hole must be

prevented as much as possible if a photocatalyst

reaction must be favoured. The ultimate goal of the

process is to have a reaction between the activated

electrons with an oxidant to produce a reduced

product and also a reaction between the generated

holes with a reductant to produce an oxidant product.

The photogenerated electrons could reduce the dye or

react with electron acceptors such as O2 adsorbed ZnO

surface or dissolved in water, reducing it to

superoxide radical anion O2-

(Konstantinou et al.,

2004). The photongenerated holes can oxidize the

organic molecule to form R*, or react with OH- or

H2O oxidizing them into OH radicals. The resulting

OH radicals, being a strong oxidizing agent (standard

Roy and Mondal


460

reduction potential +2.8V) can oxidise most azo dyes

to the mineral product.

3. RESULTS AND DISCUSSIONS

3.1. Degradation and photocatalytic degradation

CR degradation experiments were carried out by

photocatalytic agent thermally activated zinc oxide

into 100 ml of solution in the dark at 300C with

degradation accelerated by magnetic stirring at 400

rpm. Photocatalytic degradation was assessed in the

presence or absence of UV irradiation provided by a

120 w middle lamp producing an intensity of 2.1 mw

/cm2 with the main emission wave length of 254 nm

positioned 10 cm from the surface of the solution. To

saturate the surface degradation capacity of the

nanomaterials, each solution was determined by uv-

visible spectro-photometrically.

0.02 0.03 0.04 0.05 0.06

40

50

60

70

80

90

100

B

C

Catalyst Dose(g)

Rem

oval

(%)

8

10

12

14

16

18

Deg

rada

tion

Cap

asity

(mg/

g)

Fig. 1: Effect of catalyst dose on photodegradation of CR dye (6 ppm), pH (8.0), Temp. (303K), (254 nm), Time (60 min)

4 6 8 10

94

96

B

C

pH

Rem

oval

(%)

11.15

11.20

11.25

11.30

11.35

11.40

11.45

11.50

11.55

11.60

Deg

rada

tion

Cap

asity

(mg/

g)

Fig. 2: Effect of pH on photodegradation of CR dye (6ppm), ZnO (0.5mg/L), Temp. (303K), (254 nm), Time (60 min)

3.2. Effect of pH

The effect of initial solution pH on the degradation

capacity at equilibrium conditions is shown in Figure

2. The results indicate that the dye degradation

capacity increased from 11.2 mg/g to 11.8 mg/g with

an increase in the value of pH from 5 to 8. However

the dye degradation capacity was decreased from 11.8

to 11.3 when pH increased further from 8.5 to 10. This

behaviour can be explained by the zero point charge

of the photocatalyst. Since the pHzpc of ZnO is

9.3 0.2 (Bahnemann et al.,1987), the surface of the


461

catalyst is positive below pH 9.3. Again the given pKa

for Congo Red is 4.1, therefore Congo Red is

negatively charged above pH 4.1 that might result in

electrostatic attraction between the nanocatalyst and

Congo Red and will increase the degree of

photodegradation. It was further observed that the

degradation efficiency increases with increasing pH

value from 5 to 9 and above decreases. Hence the

maximum degradation range was shown at the pH of 8

- 9. The final pH of photocatalytic treatment were 8.5

that means the photocatalytic removal of colour and

degradation were observed to be faster in slightly

alkaline pH than in acidic or neutral pH range

(Neppolian et al., 2002; Tang et al., 1995; Bahnemann

et al., 1994; Hustert et al., 1992).This is due to two

reason: (a) at very low pH, ZnO particle

agglomeration reduces the dye degradation as well as

photon absorption and (b) in Congo Red, the azo

linkage (-N=N-) is particularly susceptible to

electrophilic attack by hydroxyl radical. However, in

very low pH, the concentration of H+ ions is in excess

and H+ ion interact with azo linkage decreasing the

electron densities at azo group. Consequently the

reactivity of hydroxyl radical by electrophilic

mechanism is also decreased (Gladius et al., 2009).

Hence at acidic pH range, degradation efficiency is

minimum.

Finally the isoelectric point of ZnO (8.7 – 10.3) is

the pH at which a particular molecule or surface

carries no net electrical charge. In isoelectric point

(IEP), ZnO surface in aqueous suspension are

generally assumed to be covered with hydroxyl

species, Zn-OH. At pH value above the IEP, the

predominate surface species is which is less

interacted with anionic dye(CR) while at pH values

below the IEP, species predominate

which is more interacted (Haruta, 2004; Brunelle,

1978).

3.3. Effect of Initial Dye Concentration on

photocatalytic degradation of CR dye

The effect of initial dye concentration on the rate of

photocatalytic degradation was studies by keeping all

other experimental conditions constant at light

intensity equal to 254nm , ZnO catalyst dosage was

0.05 g/100ml, pH dye solution was (8) temperature at

303K and changing the initial dye concentration in

range (4-10). The results are plotted in Figure 3. These

results indicate that the rate of photocatalytic

degradation increased with the decreasing of initial

dye concentration. As the initial concentration of a

dye increases, the colour of dye solution becomes

deeper which results in the reduction of penetration of

light to the surface of the catalyst, decreasing the

number of excited dye molecules. Due to increase of

initial concentration of dye more and more organic

substances are adsorbed on the surface of ZnO.

Therefore, the generation of hydroxyl radicals is

reduced, since there are only fewer active sites in the

system causing little adsorption of hydroxyl ions,

which in turn leads to the decrease in the generation of

hydroxyl radicals (Daneshvar et al., 2004). Thus, the

rate of hydroxyl radical generation on the catalyst

surface, accordingly, will decrease. Similar results

have been reported by other researcher for the

photocatalytic oxidation of pollutants (Nikazar et al.,

2007; Mrowetz and Selli, 2006; Mahmoodi and

Arami, 2006; Muruganandham and Swaminathan,

2006; Mahmoodi et al., 2006; Kartal et al., 2001;

Goncalves et al., 1999).

4 6 8 10

50

60

70

80

90

100

B

C

Concentration(ppm)

Rem

oval

(%)

8

10

12

Deg

rada

tion

Cap

asity

(mg/

g)

Fig. 3: Effect of concentration on photodegradation of CR dye pH (8.0), ZnO (0.5mg/L), Temp. (303K), (254 nm), Time (60

min)

Roy and Mondal


462

240 260 280 300 320 340 360

70

72

74

76

78

80

82

84

86

88

90

92

94

96

98

B

C

Wave Length(nm)

Rem

oval

(%)

8

10

12

Deg

rada

tion

Cap

asity

(mg/

g)

Fig. 4: Effect of wave length on photodegradation of CR dye, (6 ppm), pH (8.0), ZnO (0.5mg/L), Temp. (303K), Time (60

min)

3.4. Effect of catalyst loading

The amount of catalyst loading is one of the main

parameters for the degradation studies. The results for

the dye degradation using various amounts of ZnO

(0.02-0.06 g/100ml) are shown in Figure 1. In order to

avoid the use of excess catalyst it is necessary to find

out the optimum loading for efficient removal of dye.

The results showed that when catalyst dosage was

increased from 20-50 mg, the decolourization

increases from 41% to 98.5%. However, on further

increase in dosage of the catalyst beyond 60 mg, there

is a slight decrease in the dye removal rate. Table 1

also demonstrated that the colour removal was

unchanged in the absence of ZnO indicating that CR

dye is difficult to be oxidized by only UV light. The

increase in degradation rate with increase in the

catalyst loading is due to increase in total active

surface area i.e. availability of more active sites on

catalyst surface (Goncalves et al., 1999). However, it

increases significantly upon addition of ZnO due to

the production of higher amount of hydroxyl radical

through the interaction of UV with ZnO. But above 50

mg of ZnO, the colour removal efficiency

significantly decreased due to decrease of formation

of hydroxyl radicals. It should be pointed out that, the

catalyst loading affects both the number of active sites

on photocatalysts and the penetration of UV light

through the suspension (Daneshvar et al., 2003). With

increasing catalyst loading the number of active sites

increases, but the penetration of UV light decreases

due to shielding effect (Gouvea et al., 2000). It should

also be noted that the optimum value of catalyst

loading is strongly depended on the type and initial

concentration of the pollutant and the operating

conditions of the photoreactor (Gogate et al., 2004).

The optimum concentration of the catalyst for

efficient UV photodecolorization and degradation is

found to be 0.05 mg/100ml in Figure 1.


463

20 30 40 50 60 70 80 90 100 110

94

96

B

C

Temperature(C)

Re

mo

val(

%)

11.30

11.35

11.40

11.45

11.50

11.55

11.60

De

gra

da

tion

Ca

pa

sity

Fig. 5: Effect of temperature on photodegradation of CR dye (6ppm), pH (8.0), ZnO (0.5mg/L), (254 nm) , Time (60 min)

0 20 40 60 80 100

84

86

88

90

92

94

96

98

100

B

C

Contact Time(min)

Rem

oval

(%)

10

12

Deg

rada

tion

capa

sity

Fig. 6: Effect of contact time on photodegradation of CR dye (6 ppm), pH (8.0), ZnO (0.05mg), Temp. (303K), (254 nm)

3.5. Effect of wave length of uv light

The influence of UV light intensity on the degradation

efficiency has been examined on dye solution (6 ppm)

at a pH 8.5 and ZnO loading of 0.05 g/100ml. It is

evident from the results that the experiment was

conducted by three different wave length (254, 312,

365 nm) and percentage degradation increases with

decrease in wave length of uv light in Figure 4. The

UV irradiation generates the photons required for the

electron transfer from the valence band to the

conduction band of a semiconductor photo catalyst

and the energy of a photon is related to its wavelength

and the overall energy input to a photocatalytic

process is dependent on light intensity. The rate of

degradation increases when more radiation falls on the

catalyst surface and hence more hydroxyl radicals are

produced. The degradation efficiency is found to be

maximum (i.e. 25 W/m2) in the middle area of the

photoreactor. Also similar results were reported by

Habib et al. (2012); Karimi et al. (2011); Karimi et al.

(2010); Akpon et al. (2009).

Roy and Mondal


464

Fig. 7: Pseudo-first-order kinetics for degradation of Congo Red by photocatalytic agent ZnO

Fig. 8: Pseudo-second-order kinetics for degradation of Congo Red by photocatalytic agent ZnO

3.6. Effect of uv irradiation

The effect of UV irradiation on the decolorization of

CR was also investigated. There was no observable

loss of color when the dye is irradiated with only UV

which suggests that the dye is resistant to direct UV-

photolysis. The combined action of UV and ZnO

however produced an increase from 47.95% to 98.5%

in decolorization compared to that of ZnO alone due

to the reaction of hydroxyl radicals generated upon

photolysis. A higher percentage of removal by

ZnO/UV showed that Zn- catalyzed decolorization

with UV was more efficient than that of UV-catalyzed

in producing the hydroxyl radical responsible for the

oxidation of the dye. For ZnO/UV system, a complete

color removal was observed after 60 min of

irradiation. The high efficiency of this process is due

to the formation of more hydroxyl radical which is

attributed to zinc/UV-catalyzed (homogeneous and

heterogeneous). Table 1 summarized the results for

the color removal of CR by all system investigated in

this work (Habib et al., 2012; Karimi et al., 2011;

Karimi et al., 2010).

3.7. Effect of Irradiation Time

The contact time necessary to reach equilibrium

depends on the initial dye concentration. The effects

of contact time on the decolouration of Congo Red at

60 min are illustrated in Figure 6. Figure 6 clearly

indicates that dye decolouration increase with contact

time. Hence it appears that a rapid initial degradation

occurs with equilibrium reached in 60 minutes. The

first degradation of dye molecule is due to effective

interaction of semiconducting materials and dye

molecule is faster than the solute – solute interaction

(Dogan et al., 2006). However, Movahedi et al.,

(2009) pointed out that (CR) is strongly adsorbed on

thermally heated ZnO particles surfaces through the

two oxygen atoms, of the sulphonate group of the dye

molecules.


465

Fig. 9: plot of lnK versus 1/T for the degradation of CR on ZnO

3.8. Kinetics of Photocatalytic Degradation of

Congo Red

3.8.1. Pseudo first order kinetic model

In this study degradation data are applied to the

pseudo first order kinetic models to find the rate

constants of dye degradation according to Eq. 3

) (3)

The first order rate constant KL can be obtained from

the slope of plot between ) versus time t

is shown in Figure 7.

3.8.2. Pseudo second order kinetic model

A pseudo second order model can be used to explain

the dye degradation kinetics. The pseudo second order

model can be expressed as

(4)

Where t is the contact time (min), qe and qt are the

amount of dye adsorbed (mg/g) at equilibrium and at

any time t. A plot between t/qt versus t gives the value

of the constant K2 is shown in Figure 8 and also qe can

be calculated.

As it can be seen from Table 2, the degradation did

not comply well with the pseudo first order model

because of the absence of linearity between

) Vs t. In this study pseudo second order model

fitted better when compare with the first order kinetic

model in Table 2. From this study we can described

that the experimental value of qe of first order model

are not well matched with the calculated value

whereas in case of second order model, the

experimental value of qe are very close to the

calculated value. So the photocatalytic degradation of

(CR) by zinc oxide in aqueous phase is well fitted

with the second order kinetic model.

3.9. Thermodynamic study

Thermodynamic parameters can be determined from

the thermodynamic equilibrium constant K0, where K0

is the ratio of degradation capacity (mg.g-1

) and

concentration at equilibrium state. The

thermodynamic parameters (∆G, ∆H and ∆S) of the

degradation of CR on ZnO were calculated using

equations and ∆G = –RT ln K0, where R is the ideal

gas constant, T is the temperature (K) and K0 is the

distribution coefficient calculated from the

experiment. The values of ∆H and ∆S were calculated

from the slope and intercept of the Van’t hoff plots in

Figure 9 and listed in Table 3. The thermodynamics of

Congo Red degradation has been investigated

extensively. The negative value of free energy

(Table 3) indicates the feasibility of the process and its

spontaneous nature in Table 3. The experimental

values of at different temperatures are negative.

The negative values of for all the systems confirm

the exothermic nature of process. The positive values

of ∆S observed for the removal of CR molecule

suggested increased the randomness during the

process. The thermodynamic values of parameters for

the CR reported in the present study and in good

agreement with literature (Vijayakumar et al., 2012).

4. CONCLUSION

The active species generated in the degradation of CR

under uv light irradiation were studied using thermally

heated ZnO as model systems. The present

investigation shows that zinc oxide can be utilized for

the removal of hazardous dye from aqueous solution.

The removal process is a function of shaking time,

Roy and Mondal


466

pH, temperature and catalyst dose. It was observed

that the removal process followed the pseudo second

order kinetic model. The values of qe calculated from

pseudo second order plot are in good agreement with

the experimental value. The thermodynamic study

showed that the process is spontaneous and

exothermic in nature. Therefore, it can be concluded

that the hazardous dye such as CR can be comfortable

degraded by using thermally heated ZnO under uv

light irradiation.

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Mr T. K. Roy received his M.Sc. degree in Chemistry (Organic Chemistry) from the faculty

of Science, Visva-Bharati Unviersity, Santiniketan.

Dr Naba Kumar Mondal presently holding the position as Assistant professor in the

department of Environmental Science, The University of Burdwan, India. Dr Mondal has

experience more than 16 years of teaching and research in both Education and

Environmental Science (masters degree). His research interest includes: Pure

Science:Adsorption Chemistry, Nutrient dynamics, indoor pollution, soil Chemistry, Plant

Physiology, Social Science: corporal punishment, development of teaching methodology,

noise and its impact on school children etc. Dr Mondal also published more than 130

research papers in reputed International and National Journals and four (04) Ph.D. scholars

(upto May’ 2014) and has been serving as an guest Editor and reviewer in many prestigious

International Journals.

photocatalytic degradation of congo red dye on thermally activated zinc oxide

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