WS₂ as an Effective Noble-Metal Free Cocatalyst Modified TiSi₂ for Enhanced Photocatalytic Hydrogen Evolution under Visible Light Irradiation

Abstract

A noble-metal free photocatalyst consisting of WS₂ and TiSi₂ being used for hydrogen evolution under visible light irradiation, has been successfully prepared by in-situ formation of WS₂ on the surface of TiSi₂ in a thermal reaction. The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The results demonstrate that WS₂ moiety has been successfully deposited on the surface of TiSi₂ and some kind of chemical bonds, such as Ti-S-W and Si-S-W, might have formed on the interface of the TiSi₂ and WS₂ components. Optical and photoelectrochemical investigations reveal that WS₂/TiSi₂ composite possesses lower hydrogen evolution potential and enhanced photogenerated charge separation and transfer efficiency. Under 6 h of visible light (λ > 420 nm) irradiation, the total amount of hydrogen evolved from the optimal WS₂/TiSi₂ catalyst is 596.4 μmol·g⁻¹, which is around 1.5 times higher than that of pure TiSi₂ under the same reaction conditions. This study shows a paradigm of developing the effective, scalable and inexpensive system for photocatalytic hydrogen generation.

1. Introduction

Due to growing environmental concerns and increasing energy demands, hydrogen, as the highest energy density carrier per unit weight and an environmentally friendly energy source, has attracted great attention [1,2,3,4,5,6]. Since the discovery of hydrogen evolution through the photoelectrochemical water splitting on the TiO₂ electrode [7], photocatalytic water splitting to produce hydrogen under solar light irradiation has been considered as one of the most important approaches to meet the world energy demands and to solve environmental issues. However, TiO₂ as a photocatalyst for practical use is restricted by the low visible-light absorption and fast photogenerated electron-hole recombination [7,8,9]. To develop a novel, efficient, and cost-effective visible-light-driven photocatalyst is indispensable to realize the aim of applicable solar energy conversion [10,11,12].

Titanium disilicide (TiSi₂) is an excellent semiconductor material due to its high thermodynamic stability and excellent optical properties [13]. The band gap of TiSi₂ is in the range of 1.5 to 3.4 eV, suggesting that the absorption spectrum of TiSi₂ can cover almost the whole visible range and a part of the ultraviolet. The application of TiSi₂ for photocatalytic water splitting was first reported by Demuth et al. [14]. Using co-catalysts, such as RuO₂ and graphene, can further enhance the photocatalytic activity of TiSi₂-based catalyst, since electron-hole recombination is retarded [15].

As it is well known, the photocatalytic hydrogen production systems generally have two serious limitations: a high electron-hole recombination rate and a large hydrogen production overpotential [7,8,9]. In order to overcome these limitations, the most widely used approach is to use noble metal nanoparticles such as Pt as a co-catalyst [16,17,18]. However, high cost and a limited source of noble metals may have an adverse effect on the practical applications. Therefore, it is critical to develop a noble-metal free system for efficient photocatalytic hydrogen generation.

Transition-metal dichalcogenides, such as molybdenum disulphide (MoS₂) and tungsten disulphide (WS₂), have been used as co-catalysts and charge-transfer facilitators to improve the photocatalytic hydrogen production, owing to their graphene-like layered structure, high electron mobility, moderate bandgap, and rich active sites [19,20,21,22,23]. Since Guo’s group first reported that WS₂ could efficiently improve the rate of H₂ evolution from TiO₂ under visible light irradiation [24], considerable progress has been made toward developing the WS₂-containing photocatalyst for H₂ production from water [25,26,27,28,29]. However, their interactions with semiconductors are rarely discussed.

In this paper, WS₂ modified TiSi₂ hybrid composite (WS₂/TiSi₂) has been successfully fabricated via a two-step method: ultrasonic deposition and postcalcination. Postcalcination at a moderate temperature was found to be effective for forming the heterojunction structure between WS₂ and TiSi₂. Compared with TiSi₂, the as-prepared WS₂/TiSi₂ hybrid exhibited a more negative conduction band level and better photoexcited-charge separation efficiency. The optimal WS₂/TiSi₂ composite was proved to be a robust and effective photocatalyst for water-reduction to produce hydrogen under visible light irradiation.

2. Results and Discussion

2.1. Morphology and Structure

For convenience, the prepared catalyst samples were labeled as WS₂-x/TiSi₂-y, where x is the weight percentage of WS₂ in the sample and y stands for the calcination temperature. Figure 1 presents the XRD (X-ray diffraction) patterns of WS₂-1/TiSi₂ prepared at different calcination temperatures for 2 h. For comparison, the XRD pattern of commercial TiSi₂ is also included in the figure. TiSi₂ shows characteristic diffraction peaks at 39.2°, 42.3°, 43.2° and 49.8°, corresponding to the (311), (040), (022) and (331) orientations of the orthorhombic structure of TiSi₂ (JCPDS: 35-0785) [30]. The X-ray diffraction patterns of the WS₂-1/TiSi₂ catalysts prepared at different temperatures demonstrate the same patterns as TiSi₂, indicating that the TiSi₂ moiety of the catalyst is stable and keeps the orthorhombic structure during the thermal treatment. Interestingly, the intensity of the diffraction peaks increases obviously as the calcination temperature increases, which demonstrates that the thermal-treatment increases the crystallinity of the TiSi₂ moiety of the catalyst. However, no diffraction peaks can be assigned to the WS₂ moiety of the catalyst, which may be due to the low content and high dispersity of WS₂ on TiSi₂.

Figure 2 shows the SEM images of the commercial TiSi₂ and WS₂-1/TiSi₂-723. The ball-milled TiSi₂ particles exhibit irregular shape with a size in the range of 0.5–2.5 μm (Figure 2A). The morphology of WS₂-1/TiSi₂-723 shows almost no change compared with that of TiSi₂ and the size of WS₂-1/TiSi₂-723 is in the range of 0.5–3 μm (Figure 2B). The elemental distributions of Ti, Si, W and S at the micro scale were determined by SEM-EDX (energy dispersive X-ray spectrometry) mapping and the corresponding results are displayed in Figure 2C–F. From these figures we can see that Ti and Si are the main components of the sample and the content of the W and S elements are much lower than that of Ti and Si, which is ascribed to the low ratio of WS₂ to TiSi₂. In addition, it can also be clearly observed that WS₂ is very uniformly dispersed on the surface of the TiSi₂ moiety.

In order to further research the morphology of the samples and the interfacial junction structure between WS₂ and TiSi₂, TEM characterization was carried out on TiSi₂ and WS₂-1/TiSi₂-723. As displayed in Figure 3, the surface of pure TiSi₂ is smooth and clear; while for the WS₂-1/TiSi₂-723 sample, a layer of rough material is coated on the TiSi₂ surface, which indicates that the layered WS₂ particles are intimately covered on the surface of TiSi₂.

2.2. TG-DTA (Thermogravimetric-Differential Thermal Analysis) and XPS Analysis

Since WS₂ in the WS₂/TiSi₂ composite was converted from the precursor (NH₄)₂WS₄, the thermal decomposition behaviour of (NH₄)₂WS₄ was investigated by differential thermogravimetry under an N₂ atmosphere. As Figure 4A shows, the thermal decomposition curves of (NH₄)₂WS₄, presented as a TG curve, demonstrated two steps of weight loss. The first step of weight loss occurred at 473 K and ended at 573 K. The weight loss at this stage was 17.2%, demonstrating that (NH₄)₂WS₄ decomposed to WS₃, NH₃ and H₂S shown as Equation (1) (calc. 19.6 wt %). The intermediate product WS₃ appeared to be stable between 573 K and 623 K. When the sample calcined at higher temperature (>623 K), the second weight loss step occurred, the experimental weight loss for the second step is 9.3%, implying that WS₃ decomposed to WS₂, shown as Equation (2) (calc. 9.2 wt %) [31]. Exceeding 673 K, the slight weight loss can still be observed, mainly due to the sluggish decomposition or condensation of WS₂ at a high temperature.

(NH₄)₂WS₄→WS₃ + 2NH₃↑ + H₂S↑

(1)

WS₃→WS₂ + S

(2)

XPS spectra of the WS₂-1/TiSi₂ samples calcined at different temperatures are shown in Figure 4B. For both the samples calcined at 473 and 623 K, the W 4f peaks were observed at 35.7 and 37.9 eV, suggesting that tungsten existed as W⁶⁺ in the samples. When the calcination temperature increased to 673 and 723 K, the W 4f peaks shifted to 32.6 and 34.7 eV, indicating that tungsten transformed from W⁶⁺ to W⁴⁺ in the samples [26,32,33]. At a higher calcination temperature (~773 K), the XPS spectrum basically does not change, showing that W species loaded on TiSi₂ is stable over a relatively wide temperature range. Combining the results of TG-DTA and XPS, we concluded that (NH₄)₂WS₄ loaded on TiSi₂ was first decomposed to WS₃ and then to WS₂ in the calcining process (>673 K). The XPS spectrum of the S 2p regions for WS₂-1/TiSi₂-723 demonstrated the peaks located at 162.4 and 163.6 eV, confirming that the S element existed as S²⁻ in the sample (Figure S1). The Ti 2p high resolution XPS spectra of TiSi₂ and WS₂-1/TiSi₂-723 are shown in Figure 4C. For the TiSi₂ sample, the weak peak centred at 453.1 eV belongs to Ti⁰ 2p_3/2, indicating that trace metallic Ti exists on the surface of TiSi₂. The other two strong peaks, centred at 458.95 and 464.75 eV, could be ascribed to Ti⁴⁺ 2p_3/2 and 2p_1/2, respectively, demonstrating that the surface layer of TiSi₂ in the depth of XPS measurement (ca. 2.5–10 nm) is highly oxidized [14,15]. For the WS₂-1/TiSi₂-723 catalyst, the binding energy of Ti⁴⁺ 2p shifts slightly to the higher energy and the peak of Ti⁰ 2p_3/2 disappeared, indicating that the Ti metal in the surface of Ti-Si has been oxidized in the pyrolysis process. Si 2p high resolution XPS spectra of TiSi₂ and WS₂-1/TiSi₂-723 are shown in Figure 4D. The TiSi₂ sample shows two peaks centred at 98.65 and 102.59 eV, corresponding to Si⁰ 2p_3/2 and Si⁴⁺ 2p_1/2, respectively [14]. The positive shift of the binding energies of Si⁰ 2p_3/2 and Si⁴⁺ 2p_1/2 in WS₂-1/TiSi₂-723 was also observed. Meanwhile, the intensity of the peak corresponding to Si⁰ 2p_3/2 decreased greatly in WS₂-1/TiSi₂-723. The shifts of the binding energies of both Ti and Si indicate that some kind of chemical bonds, such as Ti-S-W and Si-S-W, might have formed at the interface of the TiSi₂ and WS₂ components.

2.3. Optical and Photoelectrochemical Properties

The results of the linear sweep voltammetry (LSV) for TiSi₂ and WS₂-1/TiSi₂-723 electrodes are displayed in Figure 5A. The proton reduction potential of the TiSi₂ electrode is ca. −0.20 V vs. RHE (reversible hydrogen electrode), but it changes to −0.13 V vs. RHE for the WS₂-1/TiSi₂-723 electrode, indicating that the introduction of WS₂ can reduce the hydrogen evolution potential [34,35], which is a property that is usually demonstrated by the noble metal nanoparticles such as Pt [36]. The replacement of Pt by WS₂ apparently can offer an opportunity to create an inexpensive photocatalyst system for H₂ evolution. In order to further investigate the role of WS₂, the flat band potentials of the TiSi₂ and WS₂-1/TiSi₂-723 electrodes were measured respectively. The flat band potential (E_fb) was determined by the onset potential of the Mott-Schottky (M-S) plots [37]. As demonstrated in Figure 5B, both TiSi₂ and WS₂-1/TiSi₂-723 electrodes exhibit a positive slope, indicating an n-type semiconductor feature [38]. The E_fb of the TiSi₂ electrode estimated from the x intercepts of the linear region of the MS plot is ca. −0.39 V vs. RHE, while it is ca. −0.77 V vs. RHE for the WS₂-1/TiSi₂-723 electrode. The results show that combining of TiSi₂ and WS₂ may shift the flat potential of the composite to a more negative position. Since the flat band potential of an n-type semiconductor may be considered approximately as the conduction band edge, the shift of the flat potential of the composite indicates that WS₂-1/TiSi₂-723 has a higher electron donor level, which is beneficial for water reduction.

The optical band gap of semiconductors was determined by the Tauc equation [39]:

$${(\mathsf{\alpha }h\mathrm{v})}^n=A(h\mathrm{v}-E_g)$$

where α is the measured absorption coefficient, hν is the photon energy, A and n are constant, and E_g is the optical band gap energy. The value of n is 0.5 and 2 for the indirect and direct band gap, respectively. Since both TiSi₂ and WS₂ have a direct band gap, the value of n is 2. E_g is estimated by the intercept of the photon energy axis, obtained by extrapolating the linear region of the plot [40]. The Tauc plots (Figure 5C,D) show that the optical band gaps are 2.41 for TiSi₂ and 2.15 eV for WS₂-1/TiSi₂-723. The decrease of the optical band gap of WS₂-1/TiSi₂-723, which may be attributed to the interaction between TiSi₂ and WS₂, is beneficial for the composite photocatalyst to respond to the visible light in a wider range. From the discussion above, we can estimate the band levels of pure TiSi₂ (E_VB = 2.02, E_C = −0.39 V vs. RHE) and the WS₂-1/TiSi₂-723 composite (E_VB = 1.38, E_CB = −0.77 V vs. RHE). The variation of the bandgap and the band edges indicates the strong interaction between TiSi₂ and WS₂ moieties, mostly occurred at the surface.

It is well known that the photoluminescence (PL) spectroscopy could be useful to reveal the photo-generated charge transfer process. The PL spectra of TiSi₂ and WS₂-1/TiSi₂-723 excited at 532 nm are shown in Figure S2. Both TiSi₂ and WS₂-1/TiSi₂-723 display an emission peak centred at 600 nm, however, the PL intensity of WS₂-1/TiSi₂-723 is much lower than that of TiSi₂ and the calculated quenching efficiency for WS₂-1/TiSi₂-723 is 43.6%, indicating an efficient photoexcited electron transfer from TiSi₂ to WS₂.

A photoelectrochemical study was conducted to investigate the photoinduced charge separation and transfer processes at the electrode interface. As shown in Figure 6A, a prompt and reversible photocurrent response can be observed from both the TiSi₂ and WS₂-1/TiSi₂-723 electrode under chopped light irradiation. The WS₂-1/TiSi₂-723 electrode shows higher photocurrent density than pure TiSi₂, indicating that formation of the heterojunction structure in WS₂-1/TiSi₂-723 results in better charge separation, as well as excellent incident light harvesting. Figure 6B shows the electrochemical impedance spectra (EIS) of TiSi₂ and WS₂-1/TiSi₂-723 electrodes presented as Nyquist plots. The radius of the plot of WS₂-1/TiSi₂-723 is much smaller than that of TiSi₂. The fact demonstrates that the charge transfer resistance is significantly decreased on the WS₂-1/TiSi₂-723 interface [41,42], which is in agreement with the results of photocurrent responses measurements. The transfer resistance decreases, so the rate of charge separation is accelerated, and the photocurrent is enhanced.

2.4. Photocatalytic Hydrogen Evolution

Firstly, the influence of calcination temperature on H₂ evolution rate of the WS₂-1/TiSi₂ sample was investigated. Figure 7A shows the influence of the catalysts calcined at different temperatures from 623 to 773 K on the rate of H₂ evolution. With the increase of the calcination temperature, the H₂ evolution rate of the catalyst increases gradually. The maximum H₂ evolution rate was obtained from the WS₂-1/TiSi₂-723 catalyst (99.4 μmol·h⁻¹·g⁻¹). However, further increasing the calcination temperature, the rate of H₂ evolution decreases instead. As discussed above, 623 K is the temperature starting to form WS₂, and 773 K is the temperature at which WS₂ gets stabilized. The influence of calcination temperature may be attributed to the fact that the catalyst calcined at proper temperature may strengthen the junction formation between TiSi₂ and WS₂, which is beneficial for the photocatalytic activity of the catalyst. However, higher calcination temperature may cause the surface areas of the catalyst to decrease or even the formed heterojunction to collapse, resulting in a photocatalytic efficiency decrease. Figure 7B shows the influence of the ratio of TiSi₂ and WS₂ of the composite catalyst on the photocatalytic activity. For comparison, the photocatalytic results of pure TiSi₂ and 1 wt % Pt modified TiSi₂ (Pt-1/TiSi₂) are also included in the figure. The catalyst loading with ca. 1 wt % WS₂ demonstrated the highest photocatalytic activity among all WS₂/TiSi₂-723 catalysts with various WS₂ loading. In 6 h visible light irradiation, WS₂-1/TiSi₂-723 produced about 596.4 μmol·g⁻¹ hydrogen, which was even higher than that of Pt-1/TiSi₂ (532.9 μmol·g⁻¹). However, further loading of WS₂ on TiSi₂ led to a catalytic efficiency decrease, which may be attributed to the fact that the excess WS₂ on TiSi₂ may produce a light shading effect or introduce charge recombination sites [27]. The similar phenomena were also found in several other photocatalyst composites [21,34].

The stability of the WS₂-1/TiSi₂-723 catalyst was estimated by performing recycling photocatalytic experiments and the results are shown in Figure 8. For comparison, the stability of pure TiSi₂ was also estimated under the same reaction conditions. After 6 h of visible light irradiation, TiSi₂ produced ca. 416.0 μmol·g⁻¹ H₂ in the first cycle, while WS₂-1/TiSi₂-723 produced ca. 596.4 μmol·g⁻¹ H₂. Both activities of TiSi₂ and WS₂-1/TiSi₂-723 were slightly reduced (348.5 μmol·g⁻¹ and 525.6 μmol·g⁻¹) in the second cycle. In the next three cycles, the amount of H₂ produced from TiSi₂ was still reduced, which was mainly due to the surface oxidation of TiSi₂ [14,43]. On the other hand, the amount of H₂ produced from WS₂-1/TiSi₂-723 was basically unchanged. The above results demonstrate that the WS₂/TiSi₂ photocatalyst might be a promising candidate for photocatalytic water reduction to produce hydrogen under solar-light irradiation since it possesses higher photocatalytic activity, higher stability and lower fabrication cost.

The proposed mechanism of photocatalytic H₂ evolution on the WS₂/TiSi₂ catalyst is shown in Scheme 1. Under visible-light irradiation, the electrons in the valence band (VB) of TiSi₂ are stimulated to the conduction band (CB). Then, the photo-generated electrons transfer from the conduction band of TiSi₂ to the WS₂, where H⁺ is reduced to hydrogen. The holes that remained on the valence band of TiSi₂ transfer to the surface and react with the oxalic acid in the solution. This process efficiently inhibits the photo-generated charges recombination, and significantly enhances the photocatalytic hydrogen evolution efficiency.

3. Materials and Methods

3.1. Synthesis

TiSi₂ was purchased from the J&K Company (Shanghai, China) and other chemical reagents were purchased from the Sinopharm Chemical Reagent Company (Shanghai, China). The commercial TiSi₂ powder was ball-milled for 4 h at the speed of 210 rpm (rotation per minute) in advance and other chemicals were used without further purification.

Ammonium tetrathiotungstate ((NH₄)₂WS₄) was prepared using the method described in the literature [44]. In a typical experiment, 5 g of ammonium tungstate was dispersed in a 50 mL NH₃ aqueous solution (6 M). H₂S gas was then bubbled into the above dispersed solution at 333 K for 4 h. After being cooled to room temperature, the reaction solution was put into a refrigerator and maintained at 278 K overnight. The precipitate of orange-yellow (NH₄)₂WS₄ crystals was isolated by filtration, rinsed with isopropanol and dried under vacuum.

The WS₂/TiSi₂ photocatalyst was prepared by ultrasonic deposition combined with postpyrolysis method. (NH₄)₂WS₄ aqueous solution was mixed with the ball-milled TiSi₂ powder under magnetic stirring, and then the mixture was ultra-sonicated for 5 h. The resulting (NH₄)₂WS₄/TiSi₂ precursor was dried in a vacuum oven at 323 K. Finally, the solid powder was calcined in Ar atmosphere at different temperatures in the range from 473 to 773 K for 2 h, resulting in WS₂ modified TiSi₂ photocatalyst, in which the content of WS₂ could be adjusted by tuning the weight ratio of the precursors of (NH₄)₂WS₄ and TiSi₂. According to the decomposition process of (NH₄)₂WS₄, the weight percentage of WS₂ in the sample was calculated by supposing that the (NH₄)₂WS₄ was completely converted to WS₂.

3.2. Characterization

X-ray powder diffraction (XRD) measurements were carried out on a Philips diffractometer (X‘Pert-Pro MRD, Amsterdam, Netherland) using Ni-filtered Cu Kα radiation in the range 20°–80° (2θ). Scanning electron microscopy (SEM) and Energy dispersive X-ray spectrometry (EDX) mapping measurements were taken on a Hitachi S-4700 microscope (Hitachi Corporation, Tokyo, Japan). Transmission electron microscopy (TEM) studies were conducted using a transmission electron microscope (JEOL JEM-2100, JEOL Ltd., Tokyo, Japan) operating at an accelerating voltage of 200 kV. TG-TDA curves of the decomposition of (NH₄)₂WS₄ were recorded by using differential thermal analysis/thermogravimetric equipment under a N₂ flow with the heating rate of 10 K/min. X-ray photoelectron spectroscopy (XPS) of the samples was taken on a Thermo Scientific ESCALA 250Xi XPS spectrometer (Kratos Analytical Ltd., Manchester, UK). Room temperature UV-vis diffuse reflectance absorption spectra (DRS) were measured on a UV-1800 SPC spectrophotometer (Shimadzu, Kyoto, Japan). Photoluminescence (PL) spectra of the samples were recorded on an Edinburgh PLS920 fluorospectrophotometer (Edinburgh Instruments Ltd., Edinburgh, UK).

3.3. Photoelectrochemical Measurements

The measurements of photoelectrochemical properties of the samples were performed by dipping a clean indium tin oxide (ITO) glass (1 × 2.5 cm) into the ethanol suspension of the relative catalyst several times and drying under a vacuum at 323 K as a working electrode. The measurements were carried out on a CHI 660D potentiostat/galvanostat electrochemical analyser (CH Instruments Inc, Shanghai, China) in a three-electrode system consisting of the working electrode, a saturated calomel electrode (SCE) as a reference electrode and a platinum wire as a counter electrode. The electrodes were immersed in a 0.5 M Na₂SO₄ aqueous solution (pH ~ 6). During the measurement, the working electrode was irradiated by a GY-10 xenon lamp (150 W, Tian Jin Tuo Pu Instruments Co., Ltd, Tianjin, China). The electrochemical impedance spectra (EIS), displayed as a Nyquist plot, were carried out in the similar system except that the electrodes were immersed in a 5.0 mM solution of K₃[Fe(CN)₆]/K₂[Fe(CN)₆] (1:1). The Mott-Schottky (M-S) plots were measured with a frequency of 1000 Hz.

3.4. Photocatalytic Reaction

The photocatalytic reaction was carried out in a 70 mL quartz flask equipped with a flat optical entry window. In a typical photocatalytic experiment, 50 mg of the as-prepared photocatalyst and 60 mL of oxalic acid aqueous solution (0.005 M) were added into the quartz flask whilst stirring [45]. The system was deaerated by bubbling argon into the solution for 30 min before the reaction. A 150 W xenon lamp with a 420 nm cut-off filter was used as the visible light source. The lamp was positioned ca. 10 cm away from the optical entry window of the reactor. The produced hydrogen gas was analysed with an online gas chromatograph (GC1650) equipped with a thermal conductivity detector (TCD) (Ke Xiao Instruments Co., Ltd, Hangzhou, China) and 5 Å molecular sieve columns using argon as the carrier gas. The standard H₂-Ar gas mixtures of known concentrations were used for GC signal calibration.

4. Conclusions

In summary, a novel WS₂/TiSi₂ hybrid composite has been successfully synthesized and used for photocatalytic hydrogen evolution. The photocatalytic activity of TiSi₂ under visible light (λ > 420 nm) irradiation can be enhanced by loading WS₂ as a cocatalyst, and the activity of optimal WS₂/TiSi₂ composite is even higher than that of platinized TiSi₂ under the same reaction conditions. The junction formed between TiSi₂ and surface WS₂, together with the excellent H₂ evolution property of WS₂, is supposed to be responsible for the enhanced photocatalytic activity of the WS₂/TiSi₂ composite catalyst. This study shows a paradigm of developing the eco-friendly, cost-effective photocatalyst for hydrogen production from water.