photocatalytic degradation of malachite green dye...

73

CHAPTER III

PHOTOCATALYTIC DEGRADATION OF MALACHITE

GREEN DYE USING ZINC SULPHIDE NANOPARTICLES

PREPARED BY A NEW METHOD

Dyes are major pollutants causing environmental and health problems to human

beings and aquatic animals. Textile industries are the major generators of liquid effluent,

due to the high quantity of water used in dyeing processes. Fifteen percent of the total

world production of dyes is lost during the dyeing process and is released in textile

effluent. Malachite green (MG) a cationic dye, is widely used for coloring purposes amongst

all other dyes of its category [1]. This triarylmethane dye is used in the aquaculture industry

worldwide as a biocide as well as in the silk, wool, cotton, leather, paper and acrylic

industries as a dye. It is also employed as therapeutic agent to treat parasites, fungal and

bacterial infections in fish and fish eggs and also as an antiseptic for external applications

only on the wounds and ulcers. Despite its extensive use, MG is a highly controversial

compound due to its toxic properties which are known to cause carcinogenesis,

mutagenesis, teratogenesis, respiratory toxicity and also, it will bring irretrievable

damage to the environment if discharged into water body. Therefore, the removal of MG

from wastewater before discharging is necessary and very important. Over the last decade,

different catalytic techniques have been investigated as a possible solution for the ever

increasing serious environmental pollution problems. Nowadays, many efforts have been

devoted to utilize photocatalysis to eliminate organic dyes in contaminated water to

decrease their impact on the environment [2–9]. Heterogeneous photocatalysis is a well

accepted technique with great potential to control aqueous contaminants or air pollutants.

The photoinduced degradation of several toxic inorganic and organic compounds

by photochemically active semiconductors is one of the most challenging and interesting

topics of global energy and environmental management [3]. Semiconductor nanoparticles

with suitable band gap and flat band potential energy levels are generally used as

photocatalysts. Much of the processes in photocatalysis is mainly focused on TiO2 based

materials and they are most widely used due to their superior properties such as suitable

band gap energy, chemical stability, non-toxicity and high photocatalytic activity [10, 11].

Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.

74

However, the activity of TiO2 based materials is limited mainly in the UV region because

of their wide band gap. Consequently, there is considerable demand for materials which

are active in the visible region, since visible light is the main component in solar light and

indoor illuminations [12].

In order to utilize the visible light and also to improve the efficiency of photocatalysts,

considerable attention has been focused on designing the visible light sensitive

photocatalysts. To this end, several metal oxides (e.g., CuO, ZnO, MnO2, Fe2O3, Fe3O4,

Co3O4, Al2O3) and metal sulphides (e.g. CdS, CuS, ZnS, MnS, Sb2S3, In2S3) have been

used as catalysts for photodegradation purpose [13, 14]. In recent times, transition-metal

sulphides, particularly ZnS and CdS have been intensively studied because of their

unique optical properties. Zinc sulphide (ZnS) is a promising material for use in various

applications such as nanosized sensors, photodiode and photocatalyst for the degradation

of organic dyes. It is an important semiconductor with a higher band gap (3.72 eV for

cubic zinc blende and 3.77 eV for hexagonal wurtzite), large exciton binding energy

(40 meV) and a small Bohr radius (2.4 nm). Besides, ZnS is available in abundance and

non-toxic similar to titanium dioxide (TiO2). ZnS nanomaterials have been used for the

photocatalytic degradation of organic pollutants such as dyes, p-nitrophenol and

halogenated benzene derivatives in waste water treatment [15].

Yu et al., studied the mechanism of formation of surface photocatalytic behavior

of ZnS based semiconductor nanomaterials [16–18]. ZnS is also used as a key material

for light-emitting diodes (LED), cathode ray tubes, thin film electroluminescence,

reflector, dielectric filter, chemical/biological sensors and window layers in photovoltaic

cells [19–24]. The synthetic methods that have been generally employed to prepare ZnS

nanocrystals are sol–gel process, sonochemical preparation, microwave irradiation,

hydrothermal or solvothermal route, template method, reverse micelle, chemical vapor

deposition (CVD), chemical bath deposition and thermolysis of single source precursor

(SSP) [25–38].

In this chapter, we present a simple method for the preparation of zinc sulphide

nanoparticles (ZnS NPs) using eggshell membrane (ESM), characterization with several


75

state of the art analytical techniques and its efficiency towards the photodegration of an

organic dye malachite green (MG) upon irradiation with UV light.

EXPERIMENTAL DETAILS

Materials used

Analar grade zinc acetate dihydrate, thiourea, ammonia, malachite green and

hydrogen peroxide (30 %) were used as such without any further purification. Commercial

chicken eggs purchased from local market were used to obtain the required membrane.

Preparation of zinc sulphide nanoparticles using eggshell membrane

Eggshell membrane was separated from chicken eggs as reported [39], washed

several times with copious amount of distilled water and used as a membrane to control

the diffusion of ions. 1mM aqueous solution of zinc acetate was taken in a two neck

round bottom flask and the pH of the reaction medium was adjusted to 7, 8, 9, 10 & 11

respectively by adding dilute ammonia solution with constant stirring. Then, 1mM

aqueous solution of thiourea was taken in a test tube, covered with ESM and inverted into

the RB flask containing Zn2+

ions at different pH as mentioned in the previous sentence

in such a way that the portion of the test tube covered with ESM was completely

immersed into the metal salt solution in order to facilitate diffusion of thiourea solution

into the RB flask followed by the release of S2-

ions. A reflux condenser was fitted to the

another neck of the flask and heated in an oil bath maintained at 100 °C for 2 h with

stirring until the appearance of dirty white color due to the formation of ZnS NPs. The

resulting solution was centrifuged, the residue was washed several times with distilled

water and vacuum dried at room temperature for 2 days to get the nanocrystalline

powders of ZnS NPs.

Characterization

The prepared ZnS NPs at different pH values were re-dispersed in distilled water

using ultrasonicator and used to record UV-visible absorption spectrum at room

temperature with JASCO UV-visible spectrophotometer applying quartz cell of 1 cm

optical length. The powder X- ray diffraction patterns were recorded using P analytical

X – ray diffractometer (Cu- Kα radiation, λ= 1.54A) employing a scanning rate of 0.02º/ sec


76

in 2θ range from 10- 80°. Scanning electron microscopic (SEM) images of the samples

were recorded on JEOL JSM- 6490L A instrument. Transmission electron microscopic

(TEM) images of the samples were taken using a JEOL JEN 2010 operated at 200 KV

accelerating voltage using a copper grid dipped in ethanol containing dispersed ZnS NPs.

Raman scattering was measured at room temperature using Renishaw Raman instrument

with Ar+ laser operating at 514.5 nm. The specific surface area of the samples was

obtained from N2 adsorption analysis using quantachrome instruments.

Binding studies

To a solution of MG dye (2 ml, 1x10-4

M), calculated volume of colloidal ZnS

NPs was successively added in several portions (0.1 ml per addition) at room temperature

and the UV- visible absorption spectra of the mixture was recorded for each portion in

the range of 200- 800 nm.

Photocatalytic experiment

Photodegradation experiment was carried out using 1x10-4

M MG as substrate

with different concentrations of ZnS NPs as catalyst. A known quantity of the catalyst

was added to the substrate solution, stirred in the dark to establish adsorption/desorption

equilibrium between MG dye and ZnS NPs followed by illumination under 2mW UV

source (λ=365 nm) to induce a photochemical reaction. Aliquots of fixed volume (3 ml)

were taken at 20 min. interval and the remaining concentration of non-degraded MG was

determined from UV-visible absorption spectral measurements. A series of photodegradation

experiments were carried out by changing the ratio between the substrate and the catalyst

employed as 1:0.1, 1:0.2, 1:1, 1:2 and 1:3. The experiment was also carried out by

changing the pH of the degradation medium with a view to choose the most suitable

condition to degrade MG dye.

RESULTS AND DISCUSSION

The UV-visible absorption spectrum of the ZnS nanoparticles prepared at

different pH values was measured by dispersion in distilled water and given in Figure.3.1.


77

Figure 3.1: UV-visible absorption spectra of ZnS NPs prepared as a function of pH.

(a) pH 7, (b) pH 8, (c) pH 9, (d) pH 10 and (e) pH 11

The absorption spectra revealed the formation of nanosized ZnS, having an

absorption in the range of 370-385 nm, which is similar to that of the reported value [40] and

there is no absorption occurred >400 nm. Further, a red shift was observed in the absorption

spectra of ZnS nanoparticles synthesized at various pH values ranging from 7 to 11.

This phenomenon of red shift in absorption edge has been ascribed due to an increase in

particle size. It is well known that in the case of semiconductors, the gap between the valence

and conduction band decreases as the size of the particles increases. This results in a shift of

the absorption edge towards higher wavelength. The magnitude of the shift depends on the

particle size of the ZnS. Since ZnS is a typical direct band gap semiconductor, when the size

becomes smaller than the exciton radius, a remarkable quantum size effect leads to a

size–dependent increase in the band gap and a blue shift in the absorption onset [41].

It can be best correlated as the increase in particle size would have an increase in

red shift due to decrease in band gap energy of ZnS between HOMO and LUMO. Band

gap energy values for ZnS nanoparticles synthesized at different pH is calculated from

the following equation and given in Table 3. 1.

E = hc/λ

Where, E – Band gap energy, h - Planck‟s constant, λ – Absorption maxima, c – Velocity

of light.


78

Table 3.1: Calculated band gap values of ZnS nanoparticles.

S. No pH Band gap (eV)

1 7 3.41

2 8 3.36

3 9 3.24

4 10 3.21

5 11 3.21

Though, there is a slight red shift in the absorption edge of the ZnS nanoparticles

with pH, there is no appreciable change in the band gap values. This indicates that with

increase in pH there is no change in lattice parameters and hence no phase transformation

in the system as observed in the case of ZnS nanoparticles [42], i.e., the crystalline phase

formed is stable in all pH conditions and the red shift can be correlated to a slight

aggregation of the nanostructures leading to some specific morphologies.

Powder X-ray diffraction pattern

Powder X-ray diffraction patterns for ZnS nanoparticles prepared at pH 7, 8, 9, 10

and 11 is given in Figure 3.2. All the diffractions can be attributed to hexagonal phase of

ZnS [JCPDS File No.89-2424]. It is observed from the diffraction data that there are no

definite diffractions for ZnS NPs, prepared at pH 7 and this indicates the poor crystal

quality. Upon increasing the pH, well defined peaks with line broadening exists for the

(010), (011) and (002) diffractions up to pH 10 and there is no appreciable difference for

pH 11, indicating the existence of nanocrystallites. Among (010) and (011) diffraction

planes, the ratio between the peaks increases with the pH and this may be due to the

growth along c- axis rather than a-axis. In order to achieve more confirmative

information, the Scherrer formula (D=0.95λ/ βcosθ) has been applied to calculate the

grain size of nanoparticles and the results are given in Table 3.2. Here „D‟ is the coherent

length, „λ‟ is the wavelength of x-ray radiation, „β‟ is the full width at half maximum

(FWHM) of the peak and „θ‟ is the angle of diffraction. Crystallite size data clearly

depicts the agglomeration of the nanograins along c or z- axis upon rise in the pH of the

medium and is in agreement with the difference in peak ratios.


79

Figure 3.2: Powder X-ray diffraction pattern for ZnS NPs prepared at different pH.

(a) pH 7, (b) pH 8, (c) pH 9, (d) pH 10 and (e) pH 11

Scanning electron microscopy

The surface morphology of the ZnS NPs were analyzed using scanning electron

microscopic images and presented in Figure 3.3. Morphology of the material changes

with respect to different pH conditions from spherical particles in pH 8, star like in pH 9,

then almond shell like morphology in pH 10 and finally at pH 11 these nanostructures

aggregate together to give rise to a banana bunch like nanostructures. SEM image of the

ZnS prepared at pH 9 (Figure 3.3 (b)) depicts the formation of defects on the material and

these defects acts as nucleating sites for the further growth of nanoparticles leading to

above mentioned morphologies. These results were in good agreement with the powder

X-ray diffraction analysis.


80

Figure 3.3: SEM images of ZnS nanoparticles (a) pH 8, (b) pH 9, (c) pH 10 and (d) pH 11

Transmission electron microscopy

TEM image of the ZnS NPs prepared at pH 11 provided in Figure 3.4 displayed a

star like morphology with interconnections between the stars those have been originated

from the agglomeration of few almond like structures. Selected area electron diffraction

(SAED) pattern of the ZnS posseses individual diffraction spots rather the rings, depicts

the well crystalline nature of the material.


81

Figure 3.4: TEM image of ZnS NPs prepared at pH 11 (a) Lower magnification,

(b) Higher magnification, (c) Selected area electron diffraction pattern and

(d) HR-TEM image of ZnS NPs

Raman spectrum

Figure 3.5 shows the Raman spectrum of the prepared ZnS at pH 11. In case of

ZnS, there are mainly two types of lattice phonons observed. Al branch in which the

Raman-active phonon is polarized in the z direction and E1 branch in which the phonon

polarized in the xy plane which is Raman active. E2 modes of ZnS is originated at

84.2 cm-1

as the strongest vibration. The TO mode of both Al and E1 symmetry was

observed at 336 cm-1

and the LO mode also of Al and E1 symmetry was located at

444.85 cm-1

. These vibrational modes (TO and LO) did agree well with the literature

reports on Raman investigations of ZnS [43, 44].


82

Figure 3.5: Raman spectrum of ZnS NPs prepared at pH 11

Surface area analysis

Nitrogen adsorption-desorption analysis revealed that the surface area of ZnS NPs

prepared at pH 11 was found to be 26.8 m2/g which is higher than that of the same

prepared at pH 10 (18.9 m2/g).

Binding of ZnS NPs with MG dye

The UV-visible absorption spectrum of MG dye exhibited a strong absorption at

600 nm, in addition to three weak broad bands observed at 426 nm, 360 nm and 230 nm

as presented in Figure 3.6. It is to be noted that addition of ZnS nanoparticles to MG dye

led to an enhancement in the absorption intensity at 230 nm, 360 nm and 426 nm with

significant reduction in the same of 600 nm band without bathochromic or hypsochromic

shifts. The results suggest an interaction between the nanoparticles and MG dye occurred

upon adding them.


83

Figure 3.6: Binding interaction between ZnS NPs and MG dye and Stern–Volmer plot for

MG binding with ZnS NPs

In order to support the interaction of ZnS NPs with the substrate, the Stern-

Volmer constant and the linear regression was analyzed using the Stern-Volmer plot

according to the relation,

I0/I = 1+KS. V [ZnS] --------------------------------------------------(1)

Where, I0 and I are the absorption intensities of MG in the absence and the

presence of ZnS NPs respectively. A plot of I0/I Vs [ZnS] is linear and the regression co-

efficient was found to be 0.994 with y-intercept of 1.095.

The exact binding constant (K ) was calculated using the Lineweaver – Burk equation

1/ (I0-I) = [(1/ I0) + (1/ K I0)] / [ZnS] -----------------------------(2)

and found to be 1.44x104 M

-1. The magnitude of binding constant proved the presence of

a strong binding between the ZnS NPs and MG dye that can be attributed to the

interaction between the „N‟ atom of the MG dye and the surface active sites on ZnS NPs.

Photocatalytic degradation studies of MG dye

The efficiency of chosen catalyst i.e., ZnS NPs to degrade the MG dye was

estimated using a solution containing MG dye, photoinitiator (H2O2) and ZnS NPs and

irradiated with UV light. At periodic intervals of time, aliquots of the sample was

withdrawn and its absorption spectrum was recorded for each case. The extent of

degradation of MG dye (1.0×10−4

M) was identified with respect to different concentrations

of ZnS NPs and H2O2 as a function of time at different pH conditions (pH 2, 5 & 9).


84

Optimization of the reaction variables

Catalyst quantity and role of H2O2

In order to identify the suitable catalyst concentration for effective degradation,

experiments were conducted with 0.1x10-4

M, 0.2x10-4

M, 1x10-4

M, 2x10-4

M and 3x10-4

M concentrations of catalysts with a constant quantity of MG (1x10-4

M) in the presence

or absence of H2O2 at room temperature and the results were given in Figure 3.7. In all

the experiments, high performance in photodegradation was observed only with H2O2 and

hence revealed the significance of photoinitiator. To our surprise, just negligibly small

percentage degradation of the substrate dye was noticed in the absence of H2O2.

The degradation efficiency (% degradation) increases with time of photoirradiation and it

was calculated using the following expression.

Efficiency of degradation = [(A0-A)/A0 X 100]

Where, A0 and A are the concentration of dye before and after irradiation at time

„t‟ respectively. Further, it was understood from the bar chart that, the extent of

degradation increases upon catalyst loading and it was maximum for 1:3 substrate:

catalyst ratio at more acidic condition (pH 2) and this may be due to the availability of

more active catalytic sites for the interaction of dye and hence the facilitates reaction

between the adsorbed substrate and OH.

3.4

24.8 26.9

38.9

56.8 66.8

4.5

56.2 59.99 61

82.15

93.78

0

20

40

60

80

100

0 0.1 0.2 1 2 3

% D

egr

adat

ion

Catalyst concentration (10-4) M


85

Figure 3.7: Effect of catalyst concentration on the extent of degradation of MG

Kinetics of the degradation was determined by plotting At/A0 Vs t and it obeys

pseudo-first order kinetics and hence rate constant for photocatalysis was calculated form

the following expression.

lnA0/At = Kt

Where Kt represents the rate constant of the degradation reaction at time„t‟, A0 and At are

the absorption intensities at t= 0 and t= 100 min.

Figure 3.8: Degradation trend of MG as a function of dye- photocatalyst ratio

pH of the medium

As well known in photocatalysis, pH of the degradation medium do has an impact on

the efficiency of the system. Hence, to achieve maximum degradation efficiency, we carried

out the experiments at three different pH conditions by adjusting the same to 2, 5 and 9 by

adding either hydrochloric acid or ammonia and the result was shown in Figure 3.9.

By keeping the catalyst-substrate ratio as a constant, the efficiency was better at pH 2 than

the other two conditions in the presence of free radical generator (H2O2). Though higher

percentage of degradation of cationic dye (MG) was expected in alkaline pH conditions as

reported by C.C. Chen et al., [45], we obtained the the result in contrary. The observed

behavior can be explained by considering the reason that the cationic dye MG interacts more

strongly with OH- at alkaline pH rather than with ZnS which itself is a Lewis base. Hence the


86

reaction proceeds in an unexpected manner and led to a maximum degradation in acidic

condition (pH 2).

Figure 3.9: Effect of pH on the degradation of MG

The extent of degradation of MG upon irradiation with UV light at pH 2 using

ZnS NPs as a photocatalyst in presence of a free radical generator (H2O2) was further

identified from the decrease in the intensity of the dye color as a function of irradiation

time as shown in Figure 3.10.

Figure 3.10: Decolorization of MG dye upon photocatalysis as a function of time (min.)

66.8

51.9

36.42

93.78

73.2

54.86

0

10

20

30

40

50

60

70

80

90

100

2 5 9

% D

egr

adat

ion

pH of the degradation medium


87

REFERENCES

1. G. Crini, H. N. Peindy, F. Gimbert, C. Robert, Sep. Purif. Technol., 53 (2007) 97.

2. A. Fujishima, T. N. Rao, D. A. Tryk, J. Photochem. Photobiol. C, 1 (2000) 1.

3. M.R. Hoffmann, S.T. Martin, W. Choi, D.W.Bahnemann, Chem. Rev., 95 (1995) 69.

4. M. A. Fox,M. T. Dulay, Chem. Rev., 93 (1993) 341.

5. J. C. Zhao, T. X. Wu, K. Q. Wu, K. Oikawa, H. Hidaka, N. Serpone, Environ.

Sci. Technol., 32 (1998) 2394.

6. W. Choi, S. Kim, Environ. Sci. Technol., 36 (2002) 2019.

7. C. C. Wong, W. Chu, Environ. Sci.Technol., 37 (2003) 2310.

8. Y. M. Xu, C. H. Langford, Langmuir, 17 (2001) 897.

9. W. Ho, J. C. Yu, J. Lin, P. Li, Langmuir, 20 (2004) 5865.

10. A. L. Linsebigler, G. Lu, J. T. Yates, Chem. Rev., 95 (1995) 735.

11. W. Zhao, C. Chen, X. Li, J. Zhao, H. Hidaka, N. Serpone, J. Phys. Chem. B,

106 (2002) 5022.

12. Y. He, D. Li, G. Xiao, W. Chen, Y. Chen, M. Sun, H. Huang, X. Fu, J. Phys.

Chem. C, 113 (2009) 5254.

13. J. S. Hu, L. L. Ren, Y. G. Guo, H. P. Liang, A. M. Cao, L. J. Wan, C. L. Bai,

Angew. Chem., Int. Ed., 44 (2005) 1269.

14. G. Lin, J. Zheng, R. Xu, J. Phys. Chem. C, 112 (2008) 7363.

15. X. Fang, T. Zhai, U. K. Gautam, L. Li, L. Wu, Y. Bando, D. Golberg, Prog.

Mater. Sci., 56 (2011) 175.

16. X. Yu, J. Yu, B. Cheng, B. Huang, Chem. Eur. J., 15 (2009) 6731.

17. J. Yu, J. Zhang, S. Liu, J. Phys. Chem. C, 114 (2010) 13642.

18. J. Yu, J. Zhang, M. Jaroniec, Green Chem., 12 (2010) 1611.

19. T. Yamamoto, S. Kishimoto, S. Iida, Physica B, 308 (2001) 916.


88

20. M. Bredol, J. Merikhi, J. Mater. Sci., 33 (1998) 471.

21. Y. Kavanagh, M. J. Alam, D. C. Cameron, Thin Solid Films, 447 (2004) 85.

22. L. X. Shao, K. H. Chang, H. L. Hwang, Appl. Surf. Sci., 212 (2003) 305.

23. Z. Wang, L. L. Daemen, Y. Zhao, C. S. Zha, R. T. Downs, X. Wang, Z. L. Wang,

R. J. Hemely, Nat. Mater., 4 (2005) 922.

24. I. A. Banerjee, L. Yu, H. Matsui, J. Am. Chem. Soc., 127 (2005) 16002.

25. V. Stanic, T. H. Etsell, A. C. Pierre, R. J. Mikula, Mater. Lett., 31 (1997) 35.

26. J. R. Li, J. F. Huang, L. Y. Cao, J. P. Wu, H. Y. He, Mater. Sci. Technol., 26

(2010) 1269.

27. L. Wang, L. Chen, T. Luo, Y. Qian, Mater. Lett., 60 (2006) 3627.

28. J. Li, Y. Xu, D. Wu, Y. Sun, Solid State Commun., 130 (2004) 619.

29. T. Zhai, Z. Gua, Y. Maa, W. Yang, L. Zhaoa, J. Yao, Mater. Chem. Phys., 100

(2006) 281.

30. J. Zhang, B. Han, J. Liu, X. Zhang, G. Yang, H. Zhao, J. Supercritical Fluids,

30 (2004) 89.

31. E. Y. M. Lee, N. H. Tran, J. J. Russell, R. N. Lamb, J. Phys. Chem. B,

107 (2003) 5208.

32. E. Y. M. Lee, N. H. Tran, J. J. Russell, R. N. Lamb, J. Phys. Chem. B,

108 (2004) 8355.

33. J. Cheng, D. B. Fan, H. Wang, B. W. Liu, Y. C. Zhang, H. Yan, Semicond. Sci.

Technol., 18 (2003) 676.

34. D. A. Johnston, M. H. Carletto, K. T. R. Reddy, I. Forbes, R. W. Miles, Thin

Solid Films, 403 (2002) 102.

35. Y. J. Hsu, S. Y. Lu, Langmuir, 20 (2004) 194.

36. J. Mu, Y. Zhang, Appl. Surf. Sci., 252 (2006) 7826.

37. C. Lan, K. Hong, W. Wang, G. Wang, Solid State Commun., 125 (2003) 455.

38. M. Nyman, M. J. Hampden-Smith, E. N. Duesler, Inorg. Chem., 36 (1997) 2218.


89

39. N. Daneshvar, M. A. Behnajady, Y. Zorriyeh Ashgar, J. Hazard. Mater. B, 139

(2007) 275.

40. M. Kemary, H. Shamy, J. Photochem. Photobiol. A: Chem., 205 (2009) 151.

41. X. U. Gue You, H. Wang, Trans. Nanoferrous. Mat. Soc. B., 16, (2006) 105.

42. Y. Zhao, H. Liu, F. Wang, J. Liu, K. C. Paaark, M. Endo, J. Solid state Chem.,

182 (2009) 875.

43. G. Lucovsky, E. Lind, E.A. Davis, II-VI Semiconducting Compounds,

International Conference, New York, 1967, 1150.

44. X. Zhang, Y. Zhang, Y. Song, Z. Wang, D. Yu, Physica E, 28 (2005) 1.

45. C. C. Chen, C. S. Lu, Y. C. Chung, J. L. Jan, J. Hazard. Mater., 141 (2007) 520.


photocatalytic degradation of malachite green dye...

Documents