Accepted Manuscript Title: Remarkable photo-catalytic degradation of malachite green by nickel doped bismuth selenide under visible light irradiation Author: Chiranjit Kulsi Amrita Ghosh Anup Mondal Kajari Kargupta Saibal Ganguly Dipali Banerjee PII: DOI: Reference:
S0169-4332(16)31932-8 http://dx.doi.org/doi:10.1016/j.apsusc.2016.09.063 APSUSC 33992
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Received date: Revised date: Accepted date:
24-5-2016 14-9-2016 15-9-2016
Please cite this article as: Chiranjit Kulsi, Amrita Ghosh, Anup Mondal, Kajari Kargupta, Saibal Ganguly, Dipali Banerjee, Remarkable photo-catalytic degradation of malachite green by nickel doped bismuth selenide under visible light irradiation, Applied Surface Science http://dx.doi.org/10.1016/j.apsusc.2016.09.063 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Remarkable photo-catalytic degradation of malachite green by nickel doped bismuth selenide under visible light irradiation
Chiranjit Kulsi1, Amrita Ghosh2, Anup Mondal2, Kajari Kargupta3, Saibal Ganguly4, Dipali Banerjee1*
Department of Physics, Indian Institute of Engineering Science and Technology, Shibpur,
Howrah 711103, West Bengal, India 2
Department of Chemistry, Indian Institute of Engineering Science and Technology, Shibpur,
Howrah 711103, West Bengal, India 3
Department of Chemical Engineering, Jadavpur University, Kolkata 700032, West Bengal,
Department of Chemical Engineering, BITS Pilani, K K Birla Goa Campus, NH 17B Bypass
Road, Zuarinagar, Sancoale, Goa 403726, India
*Corresponding author. Tel No: +91-9830299253 Email address: [email protected]
, [email protected]
Bi2Se3 and Ni doped Bi2Se3 were synthesized by solvothermal approach to investigate the photo-catalytic performance.
The presence of nickel was confirmed by X-ray photoelectron spectroscopy (XPS) measurement in doped Bi2Se3.
Complete degradation of malachite green (MG) dye was achieved within five minutes with Ni doped Bi2Se3 in presence of H2O2 with rate constant value 1.21 min-1 under visible-light illumination.
Explanation of the remarkable photo-catalytic degradation has been presented based on the modification of band structure of bismuth selenide by doping with nickel.
Scavenger test show degradation of MG is dominated by .OH oxidation process and oxidation action of generated .O2- radicals.
Abstract: Bismuth selenide (Bi2Se3) and nickel (Ni) doped Bi2Se3 were prepared by a solvothermal approach to explore the photo-catalytic performance of the materials in degradation of malachite green (MG). The presence of nickel was confirmed by X-ray photoelectron spectroscopy (XPS) measurement in doped Bi2Se3. The results showed that the nickel doping played an important role in microstructure and photo-catalytic activity of the samples. Nickel doped Bi2Se3 sample exhibited higher photo-catalytic activity than that of the pure Bi2Se3 sample under visible-light irradiation. The photo-catalytic degradation followed first-order reaction kinetics. Fast degradation kinetics and complete (100% in 5 minutes of visible light irradiation) removal of MG was achieved by nickel doped Bi2Se3 in presence of hydrogen peroxide (H2O2) due to modification of band gap energies leading to suppression of photo-generated electron-hole recombination.
Keywords: Photo-catalysis; Bismuth selenide; Solvothermal; Nickel doping.
1. Introduction: Water pollution has become a major environmental problem in recent days due to worldwide rapid growth of industries. Degradation of highly toxic organic dye pollutants is important in the context of environmental protection, public health and social economy . Semiconductor based photo-catalytic degradation is an efficient way for waste-water treatment . In photo-catalytic degradation, the photo-catalyst is excited by the photons to generate electron-hole pairs, then the photo-induced charges separate and migrate to the active reaction sites and finally on the surface of the photo-catalyst the pollutant is reduced and degraded. This complete phenomenon faces few challenges such as the recombination of photo-generated electron-hole pairs and inability to utilize visible light, which consists about ~43 % of the total light [3, 4]. Among different metal oxide semiconductors, TiO2 is an ideal photo-catalyst because it is nontoxic, cheap and inert in nature [5-7]. However, being a wide-band-gap semiconductor, TiO2 absorbs only ultraviolet irradiation . Thus use of TiO2 as photo-catalyst hinders the effective utilization of the solar spectrum, resulting in poor photo-catalytic performance. Similar to TiO2, ZnO, being another popular photo-catalyst, does not ensure the widespread practical usage due to narrow absorption spectral range associated with it [9, 10]. For broadening the absorption range as well as to improve the catalytic activity other semiconductors such as chalcogenides are explored. Bismuth chalcogenides (Bi2X3, where X is O, Se, and S) are promising visible-light reactive semiconductors with great research interest as potential photo-catalysts [1-2, 11-15]. There are very few reports on the photo-catalytic properties of nano-structured bismuth selenide [1, 12, 13]. This chalcogenide has a wide range of applications in the field of sensors , topological
insulators , electrochemical  and thermoelectric devices . It is reported in the literature that bismuth selenide nano-particles degraded rose bengal (RB) and methylene blue (MB) dyes by 93% and 94% respectively, within 120 minutes under ultraviolet light radiation . Doping with sulphur  and molybdenum  improved the photo-catalytic activity of bismuth selenide, on the degradation of MB and rhodamine B (Rh-B) dyes respectively, under visible-light irradiation. This improvement may be attributed to the doping induced modification in band gap energies. Reported results of degradation of malachite green (MG) dye under visible and ultraviolet light using different photo catalysts show various values of rate constants, which are tabulated in table 1 for a clear comparison [2, 20-30]. Narayana et al have reported Fe doped TiO2 prepared by solgel method for decolorizing basic green dye malachite-green under visible-light  (rate constant 0.8/h). Fe3+ doped ZnS (Zn0.95Fe0.05S) synthesized by chemical precipitation method for decolorizing malachite-green dye under UV radiation has been investigated by Rajabi et al  (rate constant 5.27 x 10-2 min-1).
Kadi el al have studied F doped ZnO produced via
hydrothermal method for MG degradation under visible-light  (rate constant value 11712 x 10-5 min-1). A highest photo-catalytic activity of 0.3 wt% Pt/ZnO composite with 0.8 g/l loading on MG dye degradation under visible-light irradiation was observed by Mohamed et al  (rate constant 13861 x 10-5 min-1). In the present work, bismuth selenide and nickel doped bismuth selenide, have been synthesized, characterized and tested as photo-catalysts for degradation of malachite green under visible-light. Effects of nickel doping on the micro-structure, photo-catalytic activities were analyzed. Furthermore, the effect of presence of hydrogen peroxide on the rate of degradation has been
studied. Fast and complete degradation (100% in five minutes) of dye was observed with nickel doped photo-catalyst and hydrogen peroxide. 2. Experimental: 2.1 Materials Used: Bismuth nitrate pentahydrate (Bi (NO3)3, 5H2O), ethylene glycol, nickel nitrate, ethanol and hydrogen peroxide were purchased from Merck. Selenium dioxide was obtained from Spectrochem and deionized water from Hydrolab, India. Malachite green dye was purchased from Himedia, India. Sodium oxalate (SO), p-benzoquinone (BQ) were obtained from Fisher Scientific, Potassium persulfate (K2S2O8) from Sigma Aldrich and tert-butanol (TBA) from s d fine-chem limited (SDFCL). All the chemicals received, were of analytical reagent grade and were used without further purification. 2.2 Synthesis of bismuth selenide: One gm bismuth nitrate in 20 ml ethylene glycol was taken in a beaker. In order to achieve uniform dispersion, the solution was sonicated for 15 minutes each time after successive addition of 0.125 gm EDTA and 0.34 gm selenium dioxide. 0.02 gm (five mol %) nickel nitrate was added to the solution for nickel doping. After vigorous stirring for 20 minutes, the solution was transferred into a 20 ml container, which was sealed and kept in an autoclave at 1650 C for 24 hours. After reaching room temperature, the resultant solution was centrifuged at 3000 rpm for 15 minutes and washed with absolute ethanol and distilled water several times to remove all impurities. The solid product was then dried in a vacuum oven at 600C for four hours . 2.3 Characterization: Structural characterization: X-ray diffraction patterns (XRD, Bruker, D8 Advance) of the prepared samples were obtained using Cu–Kα radiation (λ=1.5418 Å) with scan range 100–800 at a rate 50/min. Surface
morphologies of the samples were recorded with a field emission scanning electron microscope (FESEM, Hitachi, S-4800), operating at 20 KV. Morphologies of the samples were obtained by transmission electron microscope (TEM, JEOL JEM-2011) along with energy dispersive X-ray pattern (EDAX). Results of EDAX were used to identify the composition of the prepared samples. X-ray photoelectron spectra of the samples were generated from the Omicron Multiprobe (Omicron NanoTechnology, UK) ultrahigh vacuum (UHV) system (base pressure ∼5.0 X 10−10 mbar), fitted with an EA125 hemispherical electron analyzer and two light sources. The optical properties of the samples and photocatalytic measurements were carried out using a ‘JASCO V-530’ UV-VIS spectrophotometer. Absorbance spectra of the samples were taken by dispersing in ethanol. In order to analyze optical property and band gap of the samples, data were recorded within the wavelength range of 400-1100 nm. The Brunauer-Emmett-Teller (BET) surface area of the samples were measured by N2 adsorption at temperature 77 K using ‘Quantachrome Instruments Autosorb 1C, surface area analyzer’. Photo-catalytic characterization: Photo-catalytic activity of the materials was examined using malachite green (MG) dye as the probe molecule under visible-light irradiation. Irradiation of light was carried out using a 200 W tungsten lamp (≥410 nm) and a 1 M NaNO2 solution was used as the UV cut-off filter . The following experimental procedure was employed to assess the photo-catalytic activity: 25 mg of each sample was added in 50 ml aqueous solution of 10-5 M malachite green and stirred for 30 minutes in darkness to accomplish adsorption-desorption equilibrium between catalyst and dye. A tungsten lamp was then placed vertically over the reaction vessel at a distance of 10 cm. The optical irradiance at the surface of pollutant solution was about 70 mW cm–2. 3 ml of dye solution was withdrawn at regular intervals from the reactor to quantify the dye concentration in
the solution by monitoring the absorption intensity of the dye with time. To understand the effect of H2O2, the experiment was repeated by adding one ml H2O2 (30%, W/W) in the aqueous solution of the dye. 3. Result and discussions: 3.1 XRD analysis: XRD patterns of the samples are shown in Fig. 1. All the indexed peaks correspond to the hexagonal structure of Bi2Se3 with lattice parameters a =4.139Å and c = 28.63Å (space group R3̅m) according to reported values (JCPDS 33-0214). No impurity phase related to the nickel doping is found, which may be due to low impurity content and very high dispersion . The diffraction peaks shift to higher angles with the doping of nickel pointing to incorporation of nickel (Ni2+) in Bi2Se3 lattice with the lattice parameter becoming smaller . This is in conformity with the fact that ionic radius of Ni2+ (0.072 nm)  is smaller than Bi3+ (0.103 nm) . From Williamson-Hall plots , as shown in Figs. 2(a and b), the relative contributions of crystallite size and lattice strain in the broadening of XRD peaks have been determined from the intercepts and slopes using the formula,
2Sin (1) D where β is FWHM in radians, θ is the diffracting angle, K is the shape factor(0.94), λ is the
wavelength, D is average crystallite size and Є is the lattice strain. The average crystallite sizes are estimated to be 85 and 63 nm for Bi2Se3 and nickel doped Bi2Se3 respectively. The lattice strains have been calculated to be 8x10-4 and 64x10-4 for undoped and doped samples respectively. 3.2 FESEM images:
FESEM images in Fig. 3(a) show plate like structures stacked one above the other for undoped bismuth selenide, with the average dimensions of 1-2 μm. The doping of nickel changes the dimension of the plates in the range 300-800 nm, with decreasing overlap between successive plates (Fig. 3(b)). It seems that doping results in thinner 2D flake like structures. 3.3 TEM and EDX analysis: A hexagonal morphology is observed from TEM images of Bi2Se3 shown in Fig. 4(a). Single crystalline nature is confirmed by the selected area diffraction (SAED) pattern (Fig. 4(b)) revealing a hexagonal symmetry for Bi2Se3. Morphology of the nickel doped Bi2Se3 indicates flake like structure (Fig. 4(c)) with its SAED pattern indicating hexagonal symmetry is shown in Fig. 4(d). Lattice fringes with estimated inter-planar spacing of 0.47 nm (Fig. 4(e)) corresponding to (006) plane of nickel doped Bi2Se3 confirms single crystal nature. In Fig. 4(f), EDAX spectrum of the sample verifies the presence of nickel (3 at %) in nickel doped Bi2Se3. 3.4 Optical characterization: To understand the band structures of these materials, optical absorption study has been carried out in the wavelength (λ) range 400-1100 nm as shown in Fig. 5(a). A significant absorption peak is found in nickel doped Bi2Se3 at 652 nm compared to undoped Bi2Se3 at 658 nm. This has been investigated for evidence of direct transition in case of Bi2Se3 . The direct transition dependence of ‘α’ on photon energy (hν) is given by, Ah E g 2 1
Where A is a constant, Eg is the band gap. Plots of (αhν) 2 as a function of hν as shown in Figs. 5 (b & c) are used to estimate the band gaps of Bi2Se3 and nickel doped Bi2Se3 which are 1.2 and 1.3 eV respectively. Almost linear nature of the curves further confirms the direct optical transition in these materials.
3.5 XPS analysis: X ray photoelectron spectra have been analyzed for nickel doped Bi2Se3 sample to examine Bi, Se and Ni states as shown in Figs. 6 (a, b & c). The binding energies obtained from the nickel doped Bi2Se3 for Bi4f states are 157.9 and 163.2 eV respectively. A shift towards lower energy for doped sample is observed in comparison to literature value for pure Bi2Se3 (158.6 and 163.9 eV respectively). Similar shift for Bi4f has been reported by Nascimento et al . For Se3d, binding energy for nickel doped Bi2Se3 is at 53.7 eV indicating a shift towards higher energy compared to pure Bi2Se3 (53.3 eV). The chemical shifts observed here are clear signatures of charge transfer indicating the bonds in the crystal have some ionic character. This is in conformity with a band structure calculation predicting the metal atoms to be positively charged and the chalcogen atoms to be negatively charged . The peak for Ni2p3/2 state, binding energy occurs at 853.1 eV (literature value 852.9 eV) . So it can be concluded that Ni2p3/2 could change the chemical states on the surface of the sample which is imparting excellent photocatalytic activity for nickel doped Bi2Se3. 3.6 Surface area and pore size analysis: Fig. 7(a) shows isotherm adsorption/desorption curve with relative pressure for Bi2Se3 and Ni doped Bi2Se3 and it is seen that adsorption/desorption is greater for doped sample than for undoped sample. The specific surface areas of the samples are 26 and 41 m2/g for undoped and doped samples respectively . Fig. 7(b) shows cumulative pore volume distribution curve for both samples indicating lower pore volume with respect to pore width for undoped samples. For doped samples, higher pore volume is observed which is a signature of a more porous morphology. Pore volume for undoped and doped samples becomes 0.0030 and 0.0037 cm3/g. Fig. 7(c) shows differential pore volume with pore width for both the samples.
3.7 Photo-catalytic properties: The photo-catalytic degradation of malachite green (MG) dye has been examined under visiblelight. The decay of the characteristic peak intensity of MG dye at 618 nm has been observed with time for all samples in absence and presence of hydrogen peroxide. The photo-catalytic activities of both undoped and doped samples with H2O2 are shown in Figs. 8 (a & b). It reveals that the time taken for complete degradation of the dye is five minutes (100%) and ten minutes (98%) when nickel doped and undoped samples are used, respectively. The relative concentration (Ct/C0) with irradiation time for all the samples are shown in Fig. 9. It is seen that without catalyst the photo degradation of dyes are very less for the same working time. With catalyst, the photo degradation improves up to 9% for Bi2Se3 and for nickel doped sample it increases up to 26% within ten minutes. Again with H2O2, the photo degradation increases up to 98% for undoped Bi2Se3 within ten minutes while for nickel doped sample the degradation reaches about 100% within five minutes. So, the presence of H2O2 greatly enhances photo-catalytic activity. The first-order rate constants have been calculated from the plots of ln (Co/Ct) vs. irradiation time for all the samples. The first-order rate constants obtained without H2O2 and with H2O2, for Bi2Se3 are 0.00945 min-1 and 0.4281 min-1, respectively. Whereas, for nickel doped Bi2Se3, the first-order rate constants become 0.02989 min-1 and 1.21303 min-1, for without and with H2O2, respectively. A list of rate constants and degradation percentage for both the samples are summarized in table 2. Modification of bismuth-related nano-materials by doping with elements or coupling with other semiconductors has been considered as the most effective way to improve photo-catalytic efficiency [1, 11-15, 40]. These techniques aim at widening photo-absorption region, mediating energy band configuration and suppressing recombination of electron–hole pairs, thus making
band gap modification. In the nickel doped Bi2Se3 system, nickel atom creates impurity level in the forbidden band of Bi2Se3. This strategy aims to create an acceptor level below the original conduction band of the narrow band gap semiconductors. Dopant element has been chosen considering the fact that the Fermi level of the dopant atom must lie below the CB edge of semiconductor to facilitate the down-hill flow of electron to the dopant level from the CB of semiconductor. This structure effectively suppresses the photo-generated electron-hole recombination. As shown in Fig. 10, the band structure of Bi2Se3 matches well with the Fermi level of nickel, in which the conduction band (CB) edge of Bi2Se3 is higher than the Fermi level of nickel, while the valence band (VB) edge of Bi2Se3 is lower than the Fermi level of nickel. Under visible-light irradiation, the electrons on the CB of Bi2Se3 quickly move to the acceptor level of nickel, effectively realizing the charge separation process in the narrow band gap semiconductor. Electrons present in CB of Bi2Se3 can easily react with dissolved O2 to produce reactive superoxide radical anion (.O2-) as CB of Bi2Se3 lies higher than the reduction potential of O2/.O2- (+0.07 V) . Superoxide radical anion is a very reactive species and readily reacts with water to give H2O2. Photo oxidation and photo reduction of H2O2 occur with electrons and holes at the catalyst surfaces. Photo oxidation leads to the formation of .OOH and H+, while photo reduction produces .OH and OH-. .OH radicals degrade the organic dye molecules into small colorless degraded products. MG is also excited under visible light irradiation to MG*. LUMO of MG matches well with VB of Bi2Se3 [42, 43]. Photo-generated electron transfer from MG* to VB of Bi2Se3 takes place quite efficiently. Water also can take a hole from HOMO level of MG to produce .OH directly as HOMO of MG lies lower than the oxidation potential of H2O/.OH (+2.8 V) . The proper matching of all the energy levels makes the doped system to be an excellent visible light active photo-catalyst.
Addition of H2O2 enhances the degradation rate which also supports the proposed degradation mechanism. All these results convincingly demonstrate that the doping of Bi2Se3 with nickel can effectively promote the photo-activity of Bi2Se3. The proposed photo-catalytic degradation mechanism follows the steps: Bi2Se3
(h+VB + e-CB) Bi2Se3
(e-CB) Bi2Se3 + O2
H2O + .O2-
(e-CB) Bi2Se3(e-) H2O2 + (e-) Ni
H2O2 + (h+VB ) Bi2Se3 H2O2 + .OOH Dye
(5) + OH-
OOH + H+
+ H2O + O2
Dye* (e-LUMO + h+HOMO) + (h+VB) Bi2Se3 H2O+ (h+HOMO) Dye .OH
+ .O2- + Dye+
Dye+ + Bi2Se3
Colorless degraded products
(10) (11) (12)
To understand the nature of the primary active species involved in the photo-catalytic degradation of MG over nickel doped Bi2Se3 sample under visible-light irradiation, the photo degradation of MG has been repeated in presence of different scavengers, such as tert-butanol (TBA) as OH. scavenger, Sodium Oxalate (SO) as h+ scavenger, K2S2O8 as e− scavenger and pbenzoquinone (BQ) as .O2- scavenger. As shown in Fig. 11, the addition of different scavengers induce different extent of inhibition in MG photo-degradation. The photo-degradation of MG is greatly suppressed by the addition of e-, h+, OH. and .O2- scavengers, indicating their important
roles in the degradation process. These results show that the degradation of dye over nickel doped Bi2Se3 sample is dominated by the .OH oxidation process and partly by the oxidation action of the generated .O2- radicals on the surface of the photo-catalyst. Before scavenging experiment, the mixture of photo catalyst, dye solution and scavenger was kept in dark under stirring for 30 minutes to reach adsorption-desorption equilibrium. So, the effect due to adsorption will not hamper the degradation process. In addition, to confirm the stability of the excellent photo-catalytic performance of the nickelBi2Se3 samples, recycling experiment for the photo-degradation of MG has been conducted. The nickel doped Bi2Se3 sample has excellent cycling stability with no practical decay in its photocatalytic activity even after five cycles. 4. Conclusions: Bi2Se3 and nickel doped Bi2Se3 have been successfully prepared by solvothermal approach. XPS measurement clearly indicates the presence of nickel within nickel doped Bi2Se3. The introduction of nickel doping facilitates the charge separation in the photo-catalyst and significantly improves the photo-catalytic property of Bi2Se3 as visible-light-driven photocatalyst for dye degradation. This study demonstrates that the construction of doped structure is an interesting strategy to enhance the photo-catalytic activity. The excellent photo-catalytic activity of the doped sample can be attributed to the higher light absorption characteristics in the visible region and separation efficiency of electron–hole pair. Effect of H2O2 on the photocatalytic properties for both un-doped and doped samples has been investigated. A remarkable rate constant value (1.21 min -1) has been achieved for nickel doped Bi2Se3. Acknowledgement
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Fig. 1. Comparison of X-ray diffraction (XRD) patterns of (a) Bi2Se3 and (b) Ni doped Bi2Se3 respectively.
Fig. 2. Williamson-Hall plots of (a) Bi2Se3 and (b) Ni doped Bi2Se3 respectively.
Fig. 3. FESEM images of (a) Bi2Se3 and (b) Ni doped Bi2Se3 respectively.
Fig. 4. (a) TEM image and (b) SAED pattern of Bi2Se3; (c) TEM image, (d) SAED pattern, (e) lattice spacing and (f) EDAX spectrum of Ni doped Bi2Se3 respectively.
Fig. 5. (a) Comparison of optical absorption spectra of Bi2Se3 and Ni doped Bi2Se3, Evaluation of band gap (b) Bi2Se3 and (c) Ni doped Bi2Se3 respectively.
Fig. 6. X- ray photoelectron spectra (XPS) for Ni doped Bi2Se3 (a) Bi4f, (b) Se3d and (c) Ni2p.
Fig.7. (a) Isotherms, (b) cumulative and (c) differential pore volume distribution for Bi 2Se3 and Ni doped Bi2Se3 respectively.
Fig. 8. UV–VIS absorption spectral changes of an aqueous solution of MG dye (10-5 M) in presence of (a) Bi2Se3 (b) Ni doped Bi2Se3 (25 mg in 50 ml dye solution) with 1 ml H2O2 (30%, W/W) under visible-light irradiation.
Fig. 9. Relative concentration of aqueous MG solution (10-5M) against specific time interval under various conditions with catalyst concentration (25 mg in 50 ml dye solution), in presence of H2O2; one ml of H2O2 (30%, W/W) taken in the solution.
Fig. 10. Schematic representation of the proposed mechanism.
Fig. 11. Photo degradation of MG in presence of different scavengers.
Table1 Comparison of Kinetic parameters of malachite green using different photo catalyst under visible and ultraviolet light : Photocatalyst
Rate Constant / Degradation time
Ni doped Bi2Se3 with H2O2
1.21 min-1 (5 minutes)
0.0175 min-1 (250 minutes)
Sayikan et al 
0.0202 min-1 (60 minutes)
Asiltürk et al 
Narayana et al 
Co doped TiO2
Fe doped TiO2(Under
0.8/h (3h in both case)
(under visible-light) Sn4+ doped TiO2(under UV radiation) Fe3+ doped TiO2 (under UV radiation)
Visible-light) ZnO thin films (under UV
0.008 min-1(polymeric one)
0.0138 min-1(complexing agent)(210
Keneva et al 
minutes in both case) Mn doped BiOCl (under
0.0347 min-1(120 minutes)
Pare et al 
5.27x10-2 min-1(120 minutes)
Rajabi et al 
97% (60 minutes)
Zhang et al 
visible-light) Fe3+ doped ZnS (Zn0.95Fe0.05S) (under UV radiaion) La1-xBaxCoO3 (under visible-
light) Ni and Zn doped Bi2O3
Malathy et al 
0.0101 min-1 (120 minutes)
Charanpahari et al
(under visible-light) Bi doped TiO2-ZrO2 (under visible-light) F doped ZnO (Under visible-
 11712x10-5 min-1(20 minutes)
Kadi et al 
13861x10-5 min-1(15 minutes)
Mohamed et al 
Baeissa et al 
light) 0.3 wt% Pt/ZnO (Under visible-light) Au doped NaNbO3(Under visible-light)
Table2 Comparison of kinetic parameters for undoped and doped sample without and with H2O2 under visible-light: Sample
Rate constant (min-1)
Bi2Se3 without H2O2
Ni doped Bi2Se3 without H2O2
Bi2Se3 with H2O2
Ni doped Bi2Se3 with H2O2