Novel development of nanocrystalline kesterite Cu2ZnSnS4 thin film with high photocatalytic activity under visible light illumination

Accepted Manuscript Novel development of nanocrystalline kesterite Cu2ZnSnS4 thin film with high photocatalytic activity under visible light illumination Andigoni Apostolopoulou, Sandip Mahajan, Ramphal Sharma, Elias Stathatos PII:

S0022-3697(17)31311-2

DOI:

10.1016/j.jpcs.2017.09.005

Reference:

PCS 8198

To appear in:

Journal of Physics and Chemistry of Solids

Received Date: 17 July 2017 Revised Date:

5 September 2017

Accepted Date: 6 September 2017

Please cite this article as: A. Apostolopoulou, S. Mahajan, R. Sharma, E. Stathatos, Novel development of nanocrystalline kesterite Cu2ZnSnS4 thin film with high photocatalytic activity under visible light illumination, Journal of Physics and Chemistry of Solids (2017), doi: 10.1016/j.jpcs.2017.09.005. 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.

ACCEPTED MANUSCRIPT

“Novel development of nanocrystalline kesterite Cu2ZnSnS4 thin film with high photocatatalytic activity under visible light illumination” by Andigoni Apostolopoulou et.al

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Graphical Abstract:

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Novel development of nanocrystalline kesterite Cu2ZnSnS4 thin film with high photocatatalytic activity under visible light illumination.

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Andigoni Apostolopoulou1,2, Sandip Mahajan1,3,4, Ramphal Sharma3,4 and Elias Stathatos1,*

Nanotechnology and Advanced Materials Laboratory, Department of Electrical

Patras, Greece.

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Physics Department, University of Patras, 26500 Patras, Greece.

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Engineering, Technological-Educational Institute of Western Greece, GR-26334

Thin Film and Nanotechnology Laboratory, Department of Physics, Dr. Babasaheb Ambedkar Marathwada University, Aurangabad-431004, (M.S.), India.

Department of Nanotechnology, Dr. Babasaheb Ambedkar Marathwada University,

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Aurangabad-431004, (M.S.), India.

*Corresponding author: Department of Electrical Engineering, TechnologicalEducational Institute of Western Greece GR-26334 Patras, Greece. Phone/Fax: +30 2610-369242, e-mail: [email protected] (Dr. E. Stathatos) 1

ACCEPTED MANUSCRIPT Abstract Cu2ZnSnS4 (CZTS) represents a promising p-type direct band gap semiconductor with large absorption coefficient in the visible region of solar light. In the present study, a kesterite CZTS nanocrystalline film, with high purity, was

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successfully synthesized via the combination of successive ionic layer adsorption and reaction (SILAR) and chemical bath deposition (CBD) technique. The morphology and structural properties of the CZTS films were characterized by FE-SEM

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microscopy, porosimetry in terms of Brunauer-Emmett-Teller (BET) technique, X-ray diffraction and Raman spectroscopy. The as-prepared films under mild heat treatment

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at 250 oC in the presence of sulfur atmosphere exhibited fine nanostructure with 35 nm average particle size, high specific surface area of 53 m2/g and 9 nm pore diameter. The photocatalytic activity of the films was examined to the degradation of Basic Blue 41 (BB-41) and Acid Orange 8 (AO-8) organic azo dyes under visible

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light irradiation, demonstrating 97.5 % and 70 % discoloration for BB-41 and AO-8 respectively. Reusability of the CZTS films was also tested proving good stability

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over several repetitions. The reduction of photocatalyst’s efficiency after three successive repetitions didn’t exceed 5.6 % and 8.5 % for BB-41 and AO-8

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respectively.

Keywords Kesterite CZTS, p-type semiconductor, photocatalysis, visible light activation, Basic Blue 41, Acid Orange 8. 2

ACCEPTED MANUSCRIPT 1. Introduction Since the industrial revolution, serious environmental problems have emerged due to the toxicity of many compounds that many processes produce. In fact, the most industrial activities, that require organic dye materials for their applications, release a

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remarkable fraction of effluent water [1]. The degradation of such organic dye laden water constitutes a landmark for the mitigation or even the elimination of the industrial sewage. Many processes have been employed in order to remove the dye

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compounds, including biodegradation, adsorption on activated carbon, ultrafiltration,

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reverse osmosis and advanced oxidation processes (AOPs) [2-6]. Among these, AOPs include photolysis, hydrogen peroxide, ozonation and photocatalysis [7-10]. The heterogeneous photocatalysis, as an advantageous method, facilitates reactions through the excited electrons and holes, leading to the production of oxidized species and thus to the degradation of the organic dye pollutants. Photocatalytically active

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semiconductors have extensively studied under light illumination. Both n-type (TiO2, ZnO, WO3, BiVO4, Fe2O3) [11-16] and p-type (Cu2S, Ag2O, CZTS, CuI) [17-21]

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semiconductors have been reported for their excellent photocatalytic behavior. Sunlight contains only a small fraction of ultraviolet (UV) light, contradicting

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to common semiconductors such as TiO2 that are excited in UV region due to the wide band gap that they present. Many attempts have been made to lower their band gap and broaden the absorption range in the visible region; either loading with metal (noble or not) or non-metal elements [22-26]. Another efficient approach to reduce the recombination rate of the produced excitons, is based on coupling either the same type of semiconductors with matched energy levels [27-29] or a p-type with an n-type semiconductor (p-n heterojunction), providing better charge separation and thus improved photocatalytic performance [30-32]. 3

ACCEPTED MANUSCRIPT Mostly, p-type semiconductors are preferred for purifying the contaminated air. Particularly, air pollutants, like CO2, require low potential of semiconductor’s conduction band edge for its reduction, constituting p-type materials more suitable compared to their n-type counterparts [21]. Aiming to the better elimination of NO

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pollutant, a remarkable attempt has been made in order to switch the n-type to p-type behavior of a semiconductor for better photocatalytic efficiency [33]. Furthermore, ptype semiconductors have been implemented as photocatalysts for the degradation of

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organic azo dye solutions in visible light, exhibiting excellent photocatalytic activity

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[17,19].

Among p-type semiconductors, kesterite CZTS is recognized as a promising candidate for solar applications (photovoltaics, photocatalysis, hydrogen production), owing to the direct band gap (1.1-1.6 eV) and the large absorption coefficient that possesses in the visible range (104 cm-1) [34-37,19]. Its structure is characterized for

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nontoxicity, good photostability and the elements that contains are abundant in the nature and low cost. Their ability to present high values of photocorrosion resistance

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either in air or in aqueous solutions, has given the motivation to further study the construction of kesterite CZTS by various deposition methods [38]. Widespread

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techniques have been reported resulting in the creation of pristine kesterite CZTS phase deposited uniformly in substrates; including sol-gel synthesis, sputtering, electrodeposition, pyrolysis, pulsed laser deposition (PLD), chemical bath deposition (CBD) and successive ionic layer adsorption and reaction (SILAR) [39-45]. In the present work, we have successfully synthesized the quaternary CZTS films via the combination of SILAR and CBD methods. Initially, the morphology and the elemental and structural properties of the prepared films were investigated in order to confirm and identify the purity of the material. Additionally, we made a first 4

ACCEPTED MANUSCRIPT attempt to test the film as a photocatalyst for the discoloration of Basic Blue 41 (BB41) and Acid Orange (AO-8) under visible light illumination. The results proved that CZTS films exhibit excellent photoreactivity and photocatalytic performance in almost total decomposition of BB-41 and most of AO-8 quantity, while exhibited high

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reproducibility. 2. Experimental methods

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2.1 Materials

Copper(II) sulfite pentahydrate (CuSO4•5H2O, 99%), zinc acetate dihydrate

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(Zn(CH3COO)2•2H2O, 99%), tin chloride dihydrate (SnCl2•2H2O, 99%), thiourea (SC(NH2)2, 99%), thioacetamide (C2H5NS, 99%), triethanolamine ((HOCH2CH2)3N, 98%) and anhydrous ammonia (NH3, ≥99.9%) were purchased from Sigma-Aldrich. Both azo dyes: Basic Blue 41 (Empirical Formula C20H26N4O6S2, 40% dye content)

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and Acid Orange 8 (Empirical Formula C17H13N2NaO4S, 65% dye content) were also obtained from Sigma-Aldrich. 2.2 Films preparation

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The CZTS films were fabricated on borosilicate glass with size (60x20x1)

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mm. The glass substrates were washed successively with detergent, acetone and distilled water, while the SILAR method was then implemented for the preparation of the CZTS film. Initially, a mixed aqueous solution was prepared by adding 0.1 M CuSO4 and 0.05 M SnCl2 for the cationic precursor while 0.2 M C2H5NS aqueous solution was made for the anionic precursor. The procedure followed by the immersion of the glass substrate in the cationic precursor for 20 s, in order to let the Cu and Sn ions to be adsorbed on the surface of the substrate. The excessive ions that were not adsorbed were finally removed by vigorous rinsing of the glass with distilled 5

ACCEPTED MANUSCRIPT water. Afterwards, the prepared films were immersed in the anionic precursor for 30 s, to adsorb sulfur ions. Similarly, the excessive amount of un-adsorbed ions was removed by rinsing the films with distilled water. The procedure was repeated for 60 successive times till the desired deep brown colored films was achieved.

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Finally, the CBD method was followed, by immersing the prepared films in an aqueous solution, consisting of 0.1 M Zn(CH2COO)2•2H2O and 0.2 M SC(NH2)2, while a few drops of TEA and NH3 were added as complexing agents, to control the

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precipitation reaction and maintain the desirable pH of the solution (pH=11). The bath temperature was kept at 80 oC for 90 min. Thereafter, the deposited substrates were

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rinsed by distilled water and dried at 250 oC for 60 min under sulfur gas atmosphere in vacuum and then cooled down naturally at room temperature. The total thickness of CZTS films was around 850-900 nm according to cross section FE-SEM images. For reasons of comparison in photocatalytic experiments, TiO2 films were

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prepared on glass slides. Thus, a layer of TiO2 paste was deposited on borosilicate glass slide by doctor blade technique followed by heating to 500 °C. The preparation

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of TiO2 paste is as follows: 3 g of TiO2-Degussa P25 powder was mixed with 0.5 mL of acetic acid in a mortar for almost 3 min. Thereafter, 2.5 mL of extra pure Millipore

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water and 17.5 mL of ethanol were alternately added to break all TiO2 aggregates and form a homogeneous solution. The solution was transferred to a crucible with 50 mL of ethanol and was mixed with 10 g of terpineol and an amount of ethyl cellulose. The solution was ultrasonicated for ∼2 min, and then the crucible was placed in a rotary evaporator at 40−45 °C to remove the excessive solvent and form the TiO2 paste.

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ACCEPTED MANUSCRIPT 2.3 Characterization The surface morphology of the CZTS films was studied by field emission scanning electron microscopy, (FE−SEM, FEI InspectTM F50). The crystallinity and phase confirmation of the sample was investigated by X-ray diffraction (XRD), with a

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Bruker diffractometer (D8 Advance) with CuKα (λ=1.54Å) radiation, and Raman spectroscopy, by a HR 800 micro-Raman system (JY) using 442 nm excitation wavelength emitted from a HeCd laser. The BET surface area and the pore size

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distribution of the prepared CZTS film was measured by Micromeritics Tristar 3000

semiconductor

and

dye

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analyzer equipped with a SmartPrep degasser. Optical absorption spectra of the solutions

were

carried

out

employing

UV-Vis

spectrophotometer (Hitachi model U-2900).

2.4 Photocatalytic activity of CZTS film

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The photocatalytic experiments were performed, using the same experimental setup with a cylindrical reactor that has already been presented in previous publications [46, 24]. Briefly, CZTS films with total surface area of 60 cm2 were

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placed in the reactor while the whole area was covered with 80 mL of 2.5·10-5 M BB41 or AO-8 aqueous solution. The reactor was kept in the dark for 30 min in order to

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let the dye be adsorbed on the CZTS film. After 30 min, equilibrium was reached and the photocatalytic process started when four fluorescent lamps, of 4 W nominal power, were placed around the reactor (for visible light illumination).

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discoloration rate for each dye was examined by monitoring the absorption spectra of BB-41 and AO-8 solutions after various irradiation times. For the repetition study of the CZTS photocatalyst, the films washed and dried at 80 oC before reuse.

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ACCEPTED MANUSCRIPT 3. Results and Discussion The morphology of the CZTS sample was examined by FE-SEM microscopy (Fig. 1), where surface image of annealed CZTS film, at 250 oC, showed the grain growth structure. Mostly, the grain boundaries are relatively regular and less

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aggregated, delineating a homogeneous composition with uniform porous allocation. The average size of CZTS particles ranges from 28.5 nm to 44.9 nm, indicating nanostructured morphology. Besides, the particles are well dispersed with no

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extended aggregation while the film appears to be porous with large gaps in respect to

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the particles’ size.

A Bruker’s X-ray diffractometer (XRD) with CuKa radiation (λ=1.54Å) was used to study in depth, the crystal structure of the CZTS sample (Fig. 2). The diffraction peaks observed at 2θ=28.6o, 32.2o, 47.3o and 56.4o correspond to (112),

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(200), (220) and (312) crystal planes (JCPDS(PDF#26-0575)) confirming the kesterite phase of the CZTS prepared film. The XRD pattern was also used in order to determine the crystal size of nanoparticles (D), by using the Scherrer equation

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(D=0.9λ/βcosθ), where λ is the wavelength, β is the full width at half maximum (FWHM) and θ is the Bragg angle. The average crystal sizes for each peak were

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calculated, getting the values 37.97 nm, 26.81 nm, 29.76 nm and 27.41 nm. Taking into consideration that Scherrer’s formula provides a lower or almost equal bound on the particle size, due to the inhomogeneous strain and crystal lattice imperfections, the values are close enough, compared with the nanoparticles’ size evaluated by the FESEM images. To confirm the formation of kesterite CZTS, the sample was further characterized by Raman spectroscopy (Fig. 3). Three discriminative peaks appear at 256 cm-1, 338 cm-1 and 370 cm-1 corresponding the crystallized CZTS phase. Regarding secondary phases, low peak observed at 472 cm-1 confirming the presence 8

ACCEPTED MANUSCRIPT of Cu2-xS phase [47]. No peaks are observed at positions for SnS, SnS2, ZnS and Cu2SnS3, indicating the absence of other secondary phases. The optical properties of the CZTS films were examined by UV-Vis spectrophotometer. As can be seen in Fig.4, CZTS has a broad absorption in the

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visible-light region. This result could be interesting in terms of semiconductor’s performance in photocatalytic procedures under visible light. For a direct band gap semiconductor such as CZTS the absorbance at the curve bend point is described by

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the formula: hv=(ahv)2, where hv is the photon energy and a is the absorbance. The

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corresponding plot for the CZTS film is shown as an inset in Fig.4. The band gap is estimated to be about 1.49 eV by linear extrapolation.

Multi-layer adsorption of gas molecules was used in order to determine the structural properties of the CZTS powder scratched from thick films on glass.

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Nitrogen and helium sorption-desorption isotherm as well as pore size distribution (inset), are presented in Fig. 5. BET specific surface area (S), pore volume (Vp) and pore diameter (Dpor) were determined by the Brunauer, Emmett Teller technique

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(Table 1). The isotherm loop, which is representative of type H3, does not exhibit any limiting adsorption at high P/Po values [48]. The hysteresis between adsorption –

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desorption loop indicates the existence of mesoporosity (pore width: 2-50 nm). This is also confirmed by the pore size distribution, where a peak at 3.63 nm was observed while the maximum pore volume ranges from 2.6 nm to 7 nm pore diameter. The specific surface area, which is measured at low values of P/Po, estimated to be 52.8 m2/g, while the pore volume was 0.148 cm3g-1. It presents high specific surface area close enough to the commercial TiO2 photocatalyst (TiO2, Evonik-Degussa P-25, 43.04 m2/g [49]). This is an evidence for high surface contact with the photocatalyst, which usually has beneficial effect to the photocatalytic efficiency. 9

ACCEPTED MANUSCRIPT CZTS nanocrystal films were performed and examined for the degradation of the organic compounds BB-41 and AO-8, under visible light. Primarily, when the CZTS films are irradiated, hole˗electron pairs are generated due to the narrow bandgap value. The hole charge carriers are then trapped by the adsorbed dye molecules on

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the catalyst (direct photocatalytic pathway) or react with H2O or OH-, producing hydroxyl radical groups (•OH) (indirect photocatalytic mechanism). Besides, the electron charge carriers react with O2 and H2O producing •OH at a smaller extent than

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holes, due to the lower reducing power that electrons present (Fig. 6) [19, 20]. Hydroxyl radicals are highly reactive species and responsible for the oxidization of

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the organic dyes. Both BB-41 and AO-8 consist of nitrogen double bonds –N=N– (azo bond), which are the most active bonds in azo-dye molecules, responsible for the coloration of the dye and can be oxidized by hydroxyl radical or hole scavengers [50]. In visible light, both colored dyes (BB-41 and AO-8) may present a photosensitized

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photocatalytic procedure, where excited dye molecules operate as photosensitizers, but this could happen in a small scale, especially due to the dark color of the CZTS

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films which absorb light to a greater extend. The prepared films were immersed separately in the dye solutions for 30 min

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in the dark until equilibrium was reached, where afterwards the absorbance of the dyes was decreased, indicating the extent of adsorption of the dye on the CZTS surface. Then, the illumination in visible light was started, where the rate of discoloration was monitored. The photogenerated holes, from the CZTS films, react with the adsorbed dye molecules in the CZTS surface (either by the direct or the indirect pathway) resulting in the degradation of the dye. The absorption peak of the dye diminished with time until total decomposition take place (Fig. 7(a,b)). CZTS, as an efficient photocatalyst in visible light, proved by the narrow band gap that presents 10

ACCEPTED MANUSCRIPT (Eg=1.49 eV), has the ability to discolorate organic compounds in less time compared with other photocatalysts, such as the conventional TiO2 which presents a wide band gap (Eg=3.2 eV) [50]. Initially, for the decomposition of BB-41 dye in aqueous solution, the

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absorbance of the dye (610 nm) after the equilibrium reached (30 min), decreased about 36%, which means an efficient contact between CZTS and dye molecules for the fully degradation of BB-41. The photocatalytic experiments that performed,

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demonstrated a complete decomposition of the dye within 180 min (Fig. 8), where the

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absorbance band diminished and the discoloration rate reached 97.5%. The hydroxyl groups and the BB-41 dye contribute efficiently for total degradation. Nevertheless, in case of the AO-8, the absorbance of the dye solution after 30 min in the dark, decreased almost at 26%. As a consequence, the discoloration rate that achieved was 70% after 300 min illumination (Fig. 9), which means that CZTS could not

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completely decompose AO-8, due to anionic nature of the dye. After 300 min illumination time a plateau was reached with no further dye discoloration, which

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means that the photocatalyst was no further active. The absorbance of AO-8 exhibits a high band at 490 nm and a smaller shoulder around 400-420 nm (Fig. 7(b)). This

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occurs because AO-8 presents two forms, the hydrazone and the azo form. The high band of absorption at 490 nm is attributed to the hydrazone form while the low shoulder around 400-420 nm derives from the azo form. The hydrazone form dominates when the dye is diluted in water [51-52], which means that the oxygen species, that this form presents, do not contribute efficiently with the p-type CZTS, for more effective discoloration. For the reproducibility in the long term, the CZTS photocatalyst was tested three times for both BB-41 and AO-8 degradation (Figs. 8,9). Finally, it has been 11

ACCEPTED MANUSCRIPT proved that the CZTS films don’t present any notable loss to their efficiency for both dyes. Specifically, decrease of the discoloration rate over repetition times doesn’t exceed 5.6 % for BB-41 and 8.5 % for AO-8. For each case, the constant rate (kapp) was calculated by the slope of the lines

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in the graphs of ln(Co/C) versus irradiation time (Table 2). The maximum value is observed for the BB-41 degradation (21.31 min-1), without substantial reduction over repetitions (Inset in Fig. 8). The constant rate for AO-8 degradation found to be quite

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low (4.12 min-1) as it was expected from its incomplete discoloration (Inset in Fig.9).

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4. Conclusions

In this work we proposed a simple and cost effective method for making nanocomposite p-type CZTS films, combining the SILAR and CBD techniques, aiming to the photodegradation of BB-41 and AO-8 under visible light illumination.

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The kesterite phase was confirmed by X-ray diffractogram where the stronger peak of (112) crystal plane was appeared at 2θ=28.6o while the purity of the CZTS material was also confirmed by Raman spectroscopy. The narrow band gap (1.49 eV) and

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structural properties of CZTS film were beneficial to the successful photocatalytic decomposition of two azo dyes under visible light leading to 97.5% discoloration for

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BB-41 and 70% for AO-8, without any important loss to their reuse. The results verify that CZTS corresponds to a promising photocatalyst in the visible range of solar light while it could be also used for other potential pollutants removal in water. Acknowledgement: Sandip Mahajan is thankful to Erasmus Mundus Lot 13 project 2013-2540/001-001EM2 for providing financial support and research facility.

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ACCEPTED MANUSCRIPT References [1] E. Forgacs, T. Cserháti, G. Oros, Removal of synthetic dyes from wastewaters: a review, Environ. Int. 30 (2004) 953-971.

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[2] K. Paździor, J. Wrębiak, A. Klepacz-Smółka, M. Gmurek, L. Bilińska, L. Kos, J. Sójka-Ledakowicz, S. Ledakowicz, Influence of ozonation and biodegradation on toxicity of industrial textile wastewater, J. Environ. Management 195 (2017) 166-173.

SC

[3] K. Kadirvelu, K. Thamaraiselvi, C. Namasivayam, Removal of heavy metals from industrial wastewaters by adsorption onto activated carbon prepared from an

M AN U

agricultural solid waste, Bioresour. Technol. 76 (2001) 63-65.

[4] M. R. Muthumareeswaran, M. Alhoshan, G. P. Agarwal, Ultrafiltration membrane for effective removal of chromium ions from potable water, Sci Rep. 7 (2017) doi:10.1038/srep41423.

TE D

[5] Y. Yoon, R. M. Lueptow, Removal of organic contaminants by RO and NF membranes, J. Membr. Sci. 261 (2005) 76-86.

EP

[6] M. Pera-Titus, V. García-Molina, M. A. Baños, J. Giménez, S. Esplugas, Degradation of chlorophenols by means of advanced oxidation processes: a general

AC C

review, Appl Catal B. 47 (2004) 219-256. [7] G. M. Colonna, T. Caronna, B. Marcandalli, Oxidative degradation of dyes by ultraviolet radiation in the presence of hydrogen peroxide, Dyes Pigm. 41 (1999) 211220. [8] S. Yang, P. Wang, X. Yang, L. Shan, W. Zhang, X. Shao, R. Niu, Degradation effeciencies of azo dye Acid Orange 7 by the interaction of heat, UV and anions with

13

ACCEPTED MANUSCRIPT common oxidants: persulfate, peroxymonosulfate and hydrogen peroxide, J. Hazard. Mater. 179 (2010) 552-558. [9] H. Kusic, N. Koprivanac, A. L. Bozic, Minimization of organic pollutant content in aqueous solution by means of AOPs: UV- and ozone-based technologies, Chem.

RI PT

Eng. J. 123 (2006) 127-137.

[10] J. Saien, Z. Ojaghloo, A. R. Soleymani, M. H. Rasoulifard, Homogeneous and

SC

heterogeneous AOPs for rapid degradation of Triton X-100 in aqueous media via UV light, nano titania hydrogen peroxide and potassium persulfate, Chem. Eng. J. 167

M AN U

(2011) 172-182.

[11] S. H. S. Chan, T. Y. Wu, J. C. Juan, C. Y. The, Recent developments of metal oxide semiconductors as photocatalysts in advanced oxidation processes (AOPs) for treatment of dye waste-water, J. Chem. Technol. Biotechnol. 86 (2011) 1130-1158.

TE D

[12] C. Bogatu, D. Perniu, C. Sau, O. Iorga, M. Cosnita, A. Duta, Ultrasound assisted sol-gel TiO2 powders and thin films for photocatalytic removal of toxic pollutants,

EP

Ceram Int. 43 (2017) 7963-7969.

[13] H. Wang, C. Wang, Q. Chen, B. Ren, R. Guan, X. Cao, X. Yang, R. Duan, photocatalysis

of

mesocrystalline

ZnO

assembly

AC C

Interface-defect-mediated

synthesized in-situ via a template-free hydrothermal approach, Appl. Surf. Sci. 412 (2017) 517-528.

[14] Y. Gu, Q. Zhuo, D. Wu, Large-mesopore hierarchical tungsten trioxide hydrate with exposed high energy facets: facile synthesis and enhanced photocatalysis, Mater. Sci. Semicond. Process. 53 (2016) 18-27.

14

ACCEPTED MANUSCRIPT [15] Y. Gao, X. Yang, F. Ma, K. Li, L. Xu, X. Yuan, Y. Guo, Additive-free controllable fabrication of bismuth vanadates and their photocatalytic activity toward dye degradation, Appl. Surf. Sci. 256 (2010) 2215-2222. [16] Y. M. Hunge, Photoelectrocatalytic degradation of 4-chlorophenol using

RI PT

nanostructured α-Fe2O3 thin films under sunlight illumination, J. Mater. Sci. - Mater. Electron. 28 (2017) 11260-11267.

SC

[17] G. Mondal, S. Jana, A. Santra, M. Acharjya, P. Bera, D. Chattopadhyay, A. Mondal, P. Bera, Single-source mediated facile electrosynthesis of p-Cu2S thin films

M AN U

on TCO (SnO2:F) with enhanced photocatalytic activities, RSC Adv. 5 (2015) 5223552242.

[18] Y. W. Harn, T. H. Yang, T. Y. Tang, M. C. Chen, J. M. Wu, Facet-dependent photocatalytic activity and facet-selective etching of silver(I) oxide crystals with

TE D

controlled morphology, ChemCatChem. 7 (2015) 80-86.

[19] X. Hou, Y. Li, J. J. Yan, C. W. Wang, Highly efficient photocatalysis of p-type

EP

Cu2ZnSnS4 under visible-light illumination, Mater. Res. Bull. 60 (2014) 628-633. [20] Z. Zhou, P. Zhang, Y. Lin, E. Ashalley, H. Ji, J. Wu, H. Li, Z. Wang, Microwave

AC C

fabrication of Cu2ZnSnS4 nanoparticle and its visible light photocatalytic properties, Nanoscale Res. Lett. 9 (2014) doi:10.1186/1556-276X-9-477. [21] T. Baran, S. Wojtyla, A. Dibenedetto, M. Aresta, W. Macyk, Photocatalytic carbon dioxide reduction at p-type copper(I) iodide, ChemSusChem. 9 (2016) 29332938. [22] D. Dvoranová, V. Brezová, M. Mazúr, M. A. Malati, Investigations of metaldoped titanium dioxide photocatalysts, Appl Catal B. 37 (2002) 91-105.

15

ACCEPTED MANUSCRIPT [23] R. Konta, T. Ishii, H. Kato, A. Kudo, Photocatalytic activities of noble metal ion doped SrTiO3 under visible light irradiation, J. Phys. Chem. B 108 (2004) 8992-8995. [24] A. Rapsomanikis, A. Apostolopoulou, E. Stathatos, P. Lianos, Cerium-modified

Photobiol. A Chem. 280 (2014) 46-53.

RI PT

TiO2 nanocrystalline films for visible light photocatalytic activity, J. Photochem.

[25] H. Choi, S. Khan, J. Choi, D. T.T. Dinh, S. Y. Lee, U. Paik, S. H. Cho, S. Kim,

photocatalysts, Appl. Catal., B 210 (2017) 513-521.

SC

Synergetic control of band gap and structural transformation for optimizing TiO2

M AN U

[26] S. A. Bakar, C. Ribeiro, A comparative run for visible-light-driven photocatalytic activity of anionic and cationic S-doped TiO2 photocatalysts: A case study of possible sulfur doping through chemical protocol, J. Mol. Catal. A: Chem. 421 (2016) 1-15. [27] F. X. Xiao, Construction of highly ordered ZnO-TiO2 nanotube arrays

TE D

(ZnO/TNTs) heterostructure for photocatalytic application, ACS Appl. Mater. Interfaces 4 (2012) 7055-7063.

EP

[28] Y. Yamin, N. Keller, V. Keller, WO3-modified TiO2 nanotubes for photocatalytic elimination of methylethylketone under UVA and solar light irradiation, J.

AC C

Photochem. Photobiol. A Chem. 245 (2012) 43-57. [29] H. Wang, S. Baek, J. Lee, S. Lim, High photocatalytic activity of silver-loaded ZnO-SnO2 coupled catalysts, Chem. Eng. J. 146 (2009) 355-361. [30] S. Li, S. Hu, K. Xu, W. Jiang, J. Hu, J. Liu, Excellent visible-light photocatalytic activity of p-type Ag2O coated n-type Fe2O3 microspheres, Mater. Lett. 188 (2017) 368-371.

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ACCEPTED MANUSCRIPT [31] L. V. C. Lima, M. Rodriguez, V. A. A. Freitas, T. E. Souza, A. E. H. Machado, A. O. T. Patrocínio, J. D. Fabris, L. C. A. Oliveira, M. C. Pereira, Synergism between n-type WO3 and p-type δ-FeOOH semiconductors: High interfacial contacts and enhanced photocatalysis, Appl. Catal., B 165 (2015) 579-588.

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[32] Z. Zhang, C. Shao, X. Li, C. Wang, M. Zhang, Y. Liu, Electrospun nanofibers of p-Type NiO/n-Type ZnO heterojunctions with enhanced photocatalytic activity, ACS

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Appl. Mater. Interfaces 2 (2010) 2915-2923.

[33] J. Luo, G. Dong, Y. Zhu, Z. Yang, C. Wang, Switching of semiconducting

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behavior from n-type to p-type induced high photocatalytic NO removal activity in gC3N4, Appl. Catal., B 214 (2017) 46-56.

[34] H. Katagiri, K. Jimbo, W. S. Maw, K. Oishi, M. Yamazaki, H. Araki, A. Takeuchi, Development of CZTS-based thin film solar cells, Thin Solid Films 517

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(2009) 2455-2460.

[35] C. Steinhagen, M. G. Panthani, V. Akhavan, B. Goodfellow, B. A. Korgel, Synthesis of Cu2ZnSnS4 nanocrystals for use in low-cost photovoltaics, J. Am. Chem.

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Soc. 131 (2009) 12554-12555.

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[36] S. S. Mali, P. S. Patil, C. K. Hong, Low-cost electrospun highly crystalline kesterite Cu2ZnSnS4 nanofiber counter electrodes for efficient dye-sensitized solar cells, ACS Appl. Mater. Interfaces 6 (2014) 1688-1696. [37] J. Wang, P. Zhang, X. Song, L. Gao, Surfactant-free hydrothermal synthesis of Cu2ZnSnS4 (CZTS) nanocrystals with photocatalytic properties, RSC Adv. 4 (2014) 27805-27810.

17

ACCEPTED MANUSCRIPT [38] L.Wang, W. Wang, S. Sun, A simple template-free synthesis of ultrathin Cu2ZnSnS4 nanosheets for highly stable photocatalytic H2 evolution, J. Mater. Chem. 22 (2012) 6553-6555. [39] N. K. Youn, G. L. Agawane, D. Nam, J. Gwak, S. W. Shin, J. H. Kim, J. H. Yun,

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S. J. Ahn, A. Cho, Y. J. Eo, S. K. Ahn, H. Cheong, D. H. Kim, K. S. Shin, K. H. Yoon, Cu2ZnSnS4 solar cells with a single spin-coated absorber layer prepared via a

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simple sol-gel route, Int. J. Energy Res. 40 (2016) 662-669.

[40] M. Yang, Z. Jiang, Z. Li, S. Liu, Y. Lu, S. Wang, Effects of different precursors

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on Cu2ZnSnS4 thin film solar cells prepared by sputtering method, Mater. Sci. Semicond. Process. 56 (2016) 238-242.

[41] A. Tang, J. Liu, J. Ji, M. Dou, Z. Li, F. Wang, One-step electrodeposition for targeted off-stoichiometry Cu2ZnSnS4 thin film, Appl. Surf. Sci. 383 (2016) 253-260.

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[42] Y. M. Hunge, M. A. Mahadik, V. L. Patil, A. R. Pawar, S. R. Gadakh, A. V. Moholkar, P. S. Patil, C. H. Bhosale, Visible light assisted photoelectrocatalytic degradation of sugarcane factory wastewater by sprayed CZTS thin films, J. Phys.

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Chem. Solids 111 (2017) 176-181.

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[43] A. V. Moholkar, S. S. Shinde, A. R. Babar, K. U. Sim, Y. B. Kwon, K. Y. Rajpure, P. S. Patil, C. H. Bhosale, J. H. Kim, Development of CZTS thin films solar cells by pulsed laser deposition: Influence of pulse repetition rate, Sol. Energy 85 (2011) 1354-1363.

[44] T. R. Rana, N. M. Shinde, J. H. Kim, Novel chemical route for chemical bath deposition of Cu2ZnSnS4 (CZTS) thin films with stacked precursor thin films, Mater. Lett. 162 (2016) 40-43.

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ACCEPTED MANUSCRIPT [45] K. Patel, D. V. Shah, V. Kheraj, Influence of deposition parameters and annealing on Cu2ZnSnS4 thin films grown by SILAR, J. Alloy Compd. 188 (2017) 368-371. [46] E. Stathatos, D. Papoulis, C.A. Aggelopoulos, D. Panagiotaras, A. Nikolopoulou,

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TiO2/palygorskite composite nanocrystalline films prepared by surfactant templating route: synergistic effect to the photocatalytic degradation of an azo-dye in water, J.

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Hazard. Mater. 211–212 (2012) 68–76.

[47] P. A. Fernandes, P. M. P. Salome, A. F. da Cunha, Study of polycrystalline

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Cu2ZnSnS4 films by Raman scattering, J. Alloys Compd. 509 (2011) 7600-7606. [48] K. S. W. Sing, D. H. Everett, R. A. W. Haul, L. Moscou, R. A. Pierotti, J. Rouquerol, T. Siemieniewska, Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity, Pure & Appl.

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Chem. 57 (1985) 603-619.

[49] T. Georgakopoulos, A. Apostolopoulou, N. Todorova, K. Pomoni, C. Trapalis, E. Stathatos, Evaluation of photoconductive and photoelectrochemical properties of

EP

mesoporous nanocrystalline TiO2 powders and films prepared in acidic and alkaline

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media, Journal of Alloys and Compounds 692 (2017) 313-321. [50] M. A. Rauf, S. Salman Ashraf, Fundamental principles and application of heterogeneous photocatalytic degradation of dyes in solution, Chem. Eng. J. 151 (2009) 10-18.

[51] A. S. Ozen, V. Aviyente, G. Tezcanli-Güyer, N. H. Ince, Experimental and modeling approach to decolorization of azo dyes by ultrasound: degradation of the hydrazone tautomer, J. Phys. Chem. A. 109 (2005) 3506-3516.

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ACCEPTED MANUSCRIPT [52] M. Stylidi, D. I. Kondarides, X. E. Verykios, Pathways of solar light-induced photocatalytic degradation of azo dyes in aqueous TiO2 suspensions, Appl. Catal., B.

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40 (2003) 271-286.

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ACCEPTED MANUSCRIPT Tables Table 1. Structural properties of the CZTS films. Table 2. Constants of BB-41 and AO-8 discoloration rate under visible light for three

Figures Figure 1. FE-SEM image of the CZTS film.

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Figure 2. XRD pattern of the CZTS film.

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successive repetitions.

Figure 3. Raman spectra of CZTS film.

Figure 4. UV-Vis absorption spectrum of CZTS film and band gap estimation graph

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(inset).

Figure 5. Nitrogen and helium sorption-desorption isotherm for CZTS. Inset: Pore size distribution for CZTS.

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Figure 6. Basic mechanism of photocatalytic reactions of CZTS catalyst.

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Figure 7. Absorbance spectra of (a) BB-41 and (b) AO-8 using CZTS as a catalyst. Figure 8. Photodiscoloration of BB-41 under visible light by CZTS and TiO2 catalyst as a function of irradiation time. Reproducibility of the CZTS catalyst for three successive times. Inset: ln(Co/C) as a function of irradiation time. Figure 9. Photodiscoloration of AO-8 under visible light by CZTS and TiO2 catalyst as a function of irradiation time. Reproducibility of the CZTS catalyst for three successive times. Inset: ln(Co/C) as a function of irradiation time.

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ACCEPTED MANUSCRIPT Table 1. Structural properties of the CZTS film.

CZTS film

SBET (m2/g) 52.8

Pore diameter (nm) 9.18

Pore volume (cm3/g) 0.148

Pore width (nm) 11.22

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Table 2. Constants of BB-41 and AO-8 discoloration rate under visible light for three successive repetitions.

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3rd time

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AO-8 kapp (·10-3 min-1) 4.12

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BB-41 kapp (·10-3 min-1) 21.31

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(2 2 0)

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Figure 1. FE-SEM image of the CZTS film.

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Figure 2. XRD pattern of the CZTS film.

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472 cm

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Figure 3. Raman spectra of CZTS film.

Figure 4. UV-Vis absorption spectrum of CZTS film and band gap estimation graph (inset)

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0.014 0.012 0.010 0.008 0.006 0.004

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(cm 3g-1 nm -1 )

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Figure 6. Basic mechanism of photocatalytic reactions of CZTS catalyst.

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(a)

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Absorbance (a.u.)

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Figure 7. Absorbance spectra of (a) BB-41 and (b) AO-8 using CZTS as a catalyst.

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Figure 9. Photodiscoloration of AO-8 under visible light by CZTS and TiO2 catalyst as a function of irradiation time. Reproducibility of the CZTS catalyst for three successive times. Inset: ln(Co/C) as a function of irradiation time.

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Highlights

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1. Nanostructured Cu2ZnSnS4 films prepared with combined SILAR and CBD method. 2. Highly porous kesterite CZTS nanocrystalline film with high purity and small average particle size. 3. Enhanced photocatalytic properties in the visible region of light.