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Article

Interfacial Engineering of S-Scheme WO3/In2S3 Heterojunction for Efficient Solar-Driven CO2 Photoreduction

by
Yameng Wang
1,
Ao Xu
1,
Jihui Lang
1,
Bin Zuo
1,
Zihan Yu
1,
Keyu Cui
2,
Xuefei Li
1,
Kewei Zhang
3,
Xin Li
1,*,
Maobin Wei
1,* and
Jian Cao
1,*
1
Key Laboratory of Functional Materials Physics and Chemistry of Ministry of Education, Jilin Normal University, Changchun 130103, China
2
Key Laboratory of Preparation and Applications of Environmental Friendly Material of the Ministry of Education, College of Chemistry, Jilin Normal University, Changchun 130103, China
3
State Key Laboratory of High Pressure and Superhard Materials, College of Physics, Jilin University, Changchun 130012, China
*
Authors to whom correspondence should be addressed.
Catalysts 2025, 15(5), 460; https://doi.org/10.3390/catal15050460
Submission received: 28 February 2025 / Revised: 30 April 2025 / Accepted: 6 May 2025 / Published: 8 May 2025
(This article belongs to the Special Issue Mineral-Based Composite Catalytic Materials)
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Abstract

:
CO2 photoreduction technology offers significant potential for addressing energy and environmental challenges, though its practical application is hindered by insufficient photo-absorption and rapid carrier recombination. Herein, we constructed the WO3/In2S3 S-scheme heterojunction through hydrothermal assembly of two-dimensional WO3 nanosheets and scale-like In2S3 nanoflakes. Systematic characterization via XRD, XPS, SEM, and TEM verified the successful preparation of hierarchical nanostructures with optimized interfacial contact in the WO3/In2S3 composites. UV-Vis DRS analysis showed that the photo-absorption range of the catalyst was significantly widened. Photoelectrochemical investigations (EIS, TPR, PL, and LSV) revealed enhanced carrier separation efficiency and reduced recombination kinetics in the heterojunction system. The optimized WO3/In2S3 (WI-60) catalyst had a CO evolution efficiency of 55.14 μmol·g−1 under the UV-Vis light, representing a 3.9-fold enhancement over the pure In2S3 (14.08 μmol·g−1). Mechanistic studies through the XPS and band-structure analysis confirmed the establishment of an S-scheme carrier’ transfer pathway, which simultaneously preserved strong redox potentials and promoted the separation process of carriers. This research provides a validated strategy for developing efficient S-scheme photocatalytic systems for solar fuel generation.

Graphical Abstract

1. Introduction

The excessive combustion of fossil fuels has triggered an alarming surge in atmospheric CO2 concentrations, precipitating severe environmental crises, including ocean acidification, glacier retreat, and ecosystem collapse [1,2,3]. Photocatalytic CO2 reduction, harnessing inexhaustible solar energy to convert CO2 into value-added hydrocarbons (CO, CH4, and CH3OH), emerges as a promising carbon-neutral strategy. Nevertheless, this approach faces three fundamental challenges: (1) The thermodynamic stability of linear CO2 molecules (C=O bond energy: 750 kJ/mol) impedes effective adsorption and activation on catalyst surfaces [4]; (2) multi-electron transfer pathways (2e−→8e−) yield unpredictable product selectivity [5]; and (3) conventional wide-bandgap semiconductors (TiO2, ZnO, SnO2) suffer from limited visible-light utilization (<5%) and rapid carrier recombination [6,7,8], resulting in unsatisfactory quantum yields. Thus, it is very important to design and construct new catalytic materials for the CO2 photoreduction process.
In recent years, researchers have carried out a lot of research on the design of new photocatalytic materials. Yu et al. proposed a new concept of S-scheme heterojunction in view of the problems and challenges in thermodynamics and kinetics of the traditional Z-type photocatalytic mechanism, which provided a new vision for the preparation of a new generation of photocatalyst [9,10,11]. Unlike conventional type-II heterojunctions that sacrifice redox potential, S-scheme configurations strategically combine oxidation photocatalyst (OP) and reduction photocatalyst (RP) semiconductors through Fermi-level (Ef) equilibration. This process generates an internal electric field (IEF) and band bending, enabling the selective recombination of low-energy electrons (OP) with low-energy holes (RP) while preserving high-potential carriers [12]. The resultant synergy of enhanced charge separation and retained strong redox capacity makes S-scheme systems particularly suited for CO2 photoreduction.
Indium sulfide (In2S3, Eg ≈ 2.07 eV), a prominent RP candidate, exhibits exceptional CO2 activation ability due to its highly negative conduction band (−0.86 V vs. NHE) and sulfur-rich surface sites that facilitate *COOH intermediate formation [13], attracting extensive attention in the CO2 photoreduction field. For example, we previously used In2S3 as the main catalyst and used Au and rGO modification to construct a multi-channel electron transport mode ternary composite material photocatalyst for efficient CO2 reduction [14]. Its photocatalytic performance remains constrained by severe bulk charge recombination. The construction of the S-scheme heterojunction is an effective means to enhance its catalytic activity, so the selection of OP materials is particularly important. Tungsten trioxide (WO3, Eg ≈ 2.63 V), with its positive valence band (+2.93 V) and exceptional hole mobility, serves as an ideal OP partner to construct S-scheme systems. In the previous research, we used CdS as the RP and WO as the OP to construct the S-scheme, which effectively promoted the separation of carriers and obtained good photocatalytic activity [15]. The complementary band structures of WO3 and In2S3 suggest the potential for creating an IEF-driven heterojunction that simultaneously enhances visible-light harvesting, suppresses carrier recombination, and optimizes surface redox dynamics.
In the present study, we selected the In2S3 semiconductor, known for its excellent visible light response, to construct a WO3/In2S3 S-scheme heterojunction for efficient CO2 photoreduction through a controlled hydrothermal reaction. A series of characterization methods were carried out to probe the structural and photoelectrochemical properties of the materials. By adjusting the loading amount of In2S3, we aimed to identify the optimal ratio for CO2 photoreduction. The photocatalytic performance of the materials was tested without the use of any molecular cocatalysts or sacrificial agents. The remarkable performance was attributed to the S-scheme carrier transfer mechanism. This work provides a new perspective for designing S-scheme heterojunction photocatalysts, promoting effective CO2 activation and enhancing the conversion of CO2 to CO.

2. Results and Discussion

The crystalline structure and phase composition of prepared materials were systematically characterized using X-ray diffraction (XRD). The diffraction patterns were recorded in the 2θ range of 10–80°, with a scanning rate of 5° min−1. Figure 1a presents the XRD pattern of pristine WO3 NSs, where the distinct diffraction peaks at 23.1°, 23.7°, 24.1°, 34.1°, and 49.3° can be unambiguously indexed to the (001), (020), (200), (220), and (400) crystallographic planes of monoclinic WO3 (JCPDS No. 20-1324), respectively [16]. For pure In2S3, three prominent diffraction peaks at 27.3°, 33.1°, and 47.7° were observed, corresponding to the (311), (400), and (440) planes of cubic β-In2S3 (JCPDS No. 65-0459) [17]. The absence of secondary phases confirmed the phase purity of the synthesized indium sulfide. The XRD pattern of the WI-60 composite (Figure 1a) clearly exhibited characteristic diffraction peaks from both the WO3 and In2S3 phases. The slight XRD peak displacement of In2S3 in the composite can be attributed to the interfacial interaction between the W atoms in WO3 and the In or S atoms in In2S3. This interaction modified the local atomic arrangement of In2S3, thereby influencing the lattice spacing. Furthermore, during the formation of the heterojunction, the mutual diffusion of atoms, chemical bonding, and stress effects at the interface collectively induced lattice distortion in In2S3, ultimately causing the observed peak shift. This dual-phase coexistence indicates that the crystalline structures of both components remained intact during the modified hydrothermal synthesis reaction. In Figure 1b, the intensity evolution of In2S3 diffraction peaks (particularly the (311) plane at 27.3°) in all WO3/In2S3 binary composites exhibited a positive correlation with increasing In2S3 content in the composite series, confirming the controllable composition modulation through our synthesis protocol.
The surface morphology and nano-structural feature of the materials were investigated through scanning electronic microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HR-TEM). As shown in Figure 2a, pristine WO3 exhibited uniform square-shaped nanosheets (NSs) with smooth surfaces, with a thickness of about 50 nm and lateral dimensions of about 300 nm. In contrast, pure In2S3 displayed a well-defined micro-flower spherical structure and an obvious flaky structure on its surface (Figure 2b), where the hierarchical structure provided abundant active sites for surface reactions [18,19]. For WO3/In2S3 composites (Figure 2c–f), progressive decoration of WO3 NSs with In2S3 nanoflakes was observed with increasing In2S3 content. At optimal loading (WI-60), the WO3 NSs were uniformly coated with In2S3 nanoflakes, forming an intimate heterointerface (Figure 2e).
Figure 2g exhibits the TEM and HR-TEM images of pure WO3. The WO3 had regular square-shaped nanosheets, just like the results in the SEM. The HR-TEM result revealed distinct lattice fringes with interplanar spacings of 0.365 nm, corresponding to the (200) plane of the monoclinic WO3 [20]. Additionally, the TEM result of WI-60 is displayed in Figure 2h, and we can ascertain that the loading of In2S3 did not change the nanosheets structure of WO3 NSs. Moreover, a large number of flocculent structures appeared on the surface of the WO3 NSs, which corresponded to the flaky structure of In2S3. The HR-TEM image of WI-60 is shown in Figure 2h1, and it reveals that the crystal plane spacing of the lattice was about 0.322 nm, corresponding to the (311) plane of cubic In2S3 [21]. The SAED result from the HR-TEM of WO3/In2S3 is shown in Figure 2h2. It can be seen that the main body of the SAED data was a regular lattice structure, which corresponded to the single-crystal structure of WO3. In addition, we can also observe relatively regular but low-brightness concentric diffraction rings, which corresponded to the (311) and (440) crystal planes of In2S3 with a small amount of loading in WI-60. The simultaneous existence of a uniform single-crystal diffraction lattice and concentric circular diffraction rings further indicated the good crystal symmetry of the WO3/In2S3 composite. The above results showed that the WO3/In2S3 composites were successfully prepared.
To research the surface elemental composition, chemical states, and interfacial electron transfer between WO3 and In2S3, X-ray photoelectron spectroscopy (XPS) was tested, as shown in Figure 3. The survey spectrum of WO3/In2S3 in Figure 3a proves the co-existence of the C, O, W, In, and S elements. The high-resolution C 1s spectra of all samples (Figure 3b) exhibited characteristic peaks at about 284.8, 286.4, and 289.0 eV, corresponding to the typical C-C, C-O, and C=O bonds in the previous research, respectively [22]. In the In 3d spectrum of pure In2S3 (Figure 3c), the binding energies at 444.9 eV and 452.3 eV were caused by the In 3d5/2 and In 3d3/2 splitter peaks, which verified the +3 state of indium. The S 2p spectrum of pure In2S3 in Figure 3d displayed doublet peaks at 161.3 eV (S 2p3/2) and 162.6 eV (S 2p1/2), characteristic of the S2− species [23]. Notably, the W 4f and O 1s spectra of pure WO3 (Figure 3e,f) all revealed two distinct peaks. The peaks at about 35.4 eV (W 4f7/2) and 37.50 eV (W 4f5/2) were caused by the presence of the W6+ species. The components at 530.1 eV and 532.2 eV can be attributed to the lattice O2− and adsorbed oxygen species [24]. In addition, it can be seen that after the combined process, the In 3d XPS peaks moved towards the direction of low-binding energy, while W XPS peaks shifted towards the direction of high-binding energy, which indicates that the In element lost electrons and the W element gained electrons after coupling. These binding energy shifts suggest electron transfer from In2S3 to WO3 during hybridization, generating an IEF from In2S3 to WO3 at the heterojunction interface. The formed IEF effectively promoted the spatial separation of photogenerated carriers, accounting for the enhanced CO2 photoreduction activity [25].
Brunauer–Emmett–Teller (BET) analysis was carried out to research the surface characterization of samples, and the corresponding curves are shown in Figure 4. N2 adsorption/desorption results in Figure 4a showed that the composite had a type-IV isotherm with an H3 hysterescence ring, a feature of the mesoporous material that may be due to the flaky structure of In2S3 [26]. The specific surface area was augmented from 32.1 m2/g (WO3) to 68.7 m2/g (WI-60). CO2 adsorption isotherms in Figure 4b demonstrated WI-60’s superior CO2 uptake compared to WO3, attributed to synergistic effects between hierarchical porosity and surface structure. The great surface characteristics were conducive to the CO2 photoreduction process [27].
To explore the CO2 photoreduction ability of the prepared catalyst, the CO2 photocatalytic reduction experiment over the prepared catalysts was carried out under the irradiation of a 300 W Xe lamp (purchased from Beijing Zhongjiao Jinyuan Technology Co., Ltd., Beijing, China) within the UV-Vis light range. The photocatalytic CO2 reduction performances of materials are presented in Figure 5. The CO2 photoreduction activities of diverse materials were investigated under UV-Vis light irradiation for 4 h, and the main gas product was CO. Figure 5a compares the CO generation rates of In2S3 and WO3/In2S3 composites with varying ratios. The CO yield of In2S3 as the catalyst was approximately 14.08 μmol·g−1. The CO production rates of WO3/In2S3 composite photocatalysts significantly surpassed those of pure-phase In2S3. However, the catalytic activity of composite materials first increased and then decreased with the loading amount of In2S3, with WI-60 demonstrating the highest CO yield (55.14 μmol·g−1). Further increasing the In2S3 content reduced the CO yield, potentially due to excessive In2S3 affecting the photogenerated carrier transfer processes between WO3 and In2S3 in the composite. These results confirmed the critical importance of intimate interfacial contact and strong interactions in the composite for efficient CO2 photoreduction. During the photocatalytic CO2 reduction process, the utilization efficiency of photogenerated electrons (R(electron)) played a decisive role in reaction kinetics. Therefore, the R(electron) value was systematically investigated (Figure 5b). The calculation formula was defined as: R(electron) = 2r(CO) + 8r(CH4) [28]. Based on this equation, the electron utilization efficiencies of different catalysts were calculated. The CO2 photoreduction process clearly showed that WI-60 achieved the highest electron utilization efficiency (27.57 μmol·g−1·h−1). These results further demonstrated that WI-60 possessed superior CO2 photoreduction performance, compared to the pure In2S3 and other composite catalysts. To further investigate whether CO came from the CO2 photoreduction process, the photoreduction performances of WI-60 were examined under different conditions. As shown in Figure 5c, no CO production can be found in the absence of either the catalyst or CO2, confirming that the detected reduction products originated from the photocatalytic CO2 reduction over WI-60 [29]. Meanwhile, catalyst stability represents a crucial parameter for practical photocatalytic CO2 reduction applications. The stability of WI-60 was evaluated through four consecutive photocatalytic CO2 reduction cycles. The results in Figure 5d indicate that the composite maintained excellent catalytic stability throughout the cycling tests [30].
To further compare the catalytic performance of the WI-60 sample, we compared its photocatalytic CO2 reduction performance with that of other sulfide-based photocatalytic materials reported recently. The specific results are shown in Table 1. It can be clearly seen from the data in the table that the catalyst we prepared performed outstandingly in several key indicators. Compared with the other sulfide-based photocatalysts, WI-60 exhibited a significant advantage in terms of CO2 conversion efficiency. Its CO generation rate reached 55.14 μmol·g−1, which was higher than that of most of the comparative samples.
The photo-absorption properties of the synthesized catalysts constituted a critical fac-tor influencing their photocatalytic property. The photo-absorption performance directly determines the photon utilization efficiency of photocatalysts [40]. Thus, we employed UV-Vis diffuse reflectance spectroscopy (UV-vis DRS) to analyze the photo-absorption characteristics and bandgap width of the obtained samples, with detailed results presented in Figure 6. As shown in Figure 6a, pure WO3 NSs and In2S3 exhibited absorption edges at about 462 nm and 594 nm, respectively. The WI-60 composite demonstrated combined absorption features from both constituent materials. Notably, in contrast to pure WO3, the WI-60 composite exhibited a discernible red shift in its absorption edge. This phenomenon served as a clear indication of its augmented visible-light utilization capacity, which empowered a greater number of photons to partake in the CO2 photoreduction process. The calculated bandgap widths of WO3 and In2S3 are shown in Figure 6b, yielding values of approximately 2.89 eV and 2.30 eV, respectively. Similarly, the composite material exhibited hybrid band characteristics associated with both components, providing further evidence for the successful fabrication of the heterostructure. This synergistic combination of optical properties in the composite aligns with the observed enhancement in photocatalytic performance.
The photoelectrochemical (PEC) properties of catalysts are the key factors affecting their catalytic activity. Therefore, the PEC performances of WO3, In2S3, and WI-60 were systematically investigated through electrochemical impedance spectroscopy (EIS), transient photocurrent response (TPR), photoluminescence (PL) spectroscopy, and linear sweep voltammetry (LSV). As shown in Figure 7a, the WI-60 composite demonstrated a smaller Nyquist arc radius, compared to pristine WO3 and In2S3 in EIS curves. This suggested a decrease in the resistance to carrier transfer at the heterojunction interface. (The equivalent circuit is shown as the inset in Figure 2). This structural configuration facilitated the separation and transfer of photogenerated electron–hole pairs [41]. TPR analysis in Figure 7b revealed an enhanced transient photocurrent response for WI-60 under the UV-Vis light illumination, suggesting superior charge carrier generation and separation efficiency, compared to the pure WO3 and In2S3. The rapid current stabilization further confirmed efficient charge transfer kinetics in the composite system [42]. In Figure 7c, the PL spectra of prepared samples exhibited characteristic emission peaks at 468 nm (WO3) and 529 nm (In2S3), with a significantly quenched intensity observed in the composite material. This fluorescence suppression directly evidenced the effective separation of photogenerated carriers through interfacial charge transfer processes [43]. LSV measurement results of pure WO3, In2S3, and WI-60 are shown in Figure 7d. Compared with pure-phase WO3, WI-60 had lower overpotential at the same current density, which contributed to the occurrence of the CO2 reduction reaction. The overpotential of WI-60 was lower under light, which proved that the CO2 reduction reaction was easier to carry out under the same conditions. The enhanced catalytic activity originated from the synergistic effects of improved charge separation and optimized surface reaction kinetics [44].
To elucidate the photogenerated carrier transfer mechanism at the WO3/In2S3 heterojunction interface, the Mott–Schottky test was carried out to determine the flat-band potentials. As shown in Figure 8, the flat-band potentials of WO3 and In2S3 were measured to be +0.58 V and −1.51 V vs. Ag/AgCl in Figure 8a,b, respectively. Thus, the conduction band minima edge positions (ECB) of WO3 and In2S3 can be determined to be +0.78 V and −1.31 V (vs. NHE) by the conversion process (ENHE = EAg/AgCl + 0.197 V) [45]. The valence band maxima edge positions (EVB) of WO3 and In2S3 can be calculated as +3.67 V and +0.99 V (vs. NHE) using the formula: EVB = ECB +Eg [46]. Additionally, the corresponding band structures are depicted in Figure 8c. As the typical N-type semiconductors, the Fermi level (Ef) positions of WO3 and In2S3 were slightly lower than the ECB. Since the ECB of In2S3 was much higher than that of WO3, we can infer that their Ef were in the same trend, that is, the Ef of In2S3 was much higher than that of WO3. Owing to the higher Ef of In2S3 compared to WO3, electrons spontaneously transferred from the semiconductor with a higher Ef to that with a lower Ef [47,48,49]. Consequently, upon dark contact, electron migration occurred from WO3 to In2S3 until Ef equilibration was achieved. This process established an electron accumulation layer at the WO3 interface and an electron depletion layer at the In2S3 interface, generating an IEF and band bending (Figure 8d). Under light irradiation, the IEF-driven band bending facilitated the recombination of electrons photogenerated in the CB of WO3, with holes photogenerated in the VB of In2S3 [50,51,52]. Meanwhile, the retained photogenerated electrons in the CB of In2S3 and holes in the VB of WO3 exhibited enhanced redox capabilities, actively participating in the photocatalytic CO2 reduction to CO, as illustrated in Figure 8e. These experimental and theoretical discoveries collectively demonstrated the S-scheme electron transfer mechanism in the WO3/In2S3 heterojunction. The S-scheme band alignment in the WO3/In2S3 photocatalyst promoted spatial separation and the directional transfer of charge carriers, thereby prolonging charge lifetime and significantly improving the CO2-to-CO conversion efficiency (Figure 8f).

3. Materials and Methods

3.1. Materials

The ammonium paratungstate hydrate ((NH4)10W12O41·5H2O, APT, 99.9%, Aladdin, Nashville, TN, USA), hydrochloric acid (HCl, Sinopharm, Beijing, China), oxalic acid dihydrate (OA, C2H2O4·2H2O, 99.5%, Macklin, Shanghai, China), indium chloride tetrahydrate (InCl3·4H2O, 99.99%, Alfa Aesar, Haverhill, MA, USA), L-cysteine (C3H7NO2S, AR, Sinopharm), ethanol (C2H5OH, AR, Sinopharm, Shanghai, China), and glycerin (C3H8O3, AR, Sinopharm, Shanghai, China) used in this paper were analytical-grade materials without further purification. High-purity CO2 gas (99.999%) was obtained from Changchun Juyang Gas Co., Ltd. (Changchun, China).

3.2. Synthesis of Catalysts

3.2.1. Fabrication of WO3 Nanosheets (WO3 NSs)

Two-dimensional WO3 nanosheets were synthesized through an acid-mediated hydrothermal process. (a) Specifically, 0.3 g of APT was added into 30 mL of deionized water under magnetic stirring for 30 min. The solution pH was adjusted to 3.0 ± 0.1 using a 3 M HCl solution delivered through a calibrated burette. Subsequently, 0.6 g of OA was introduced as a structure-directing agent. The mixture was heated in a water bath to 90 °C under vigorous stirring for 3 h using a PTFE-coated magnetic bar. The resulting yellow precursor (P-WO3) was obtained via the centrifugation processes and then washed with water and alcohol three times, respectively. (b) Final crystallization was achieved by calcining P-WO3 in a muffle furnace under static air at 500 °C for 2 h (5 °C/min).

3.2.2. Construction of WO3/In2S3 Heterojunctions

The WO3/In2S3 composites were synthesized through a modified hydrothermal reaction. (c) A precursor solution was prepared by dissolving stoichiometric In2S3·4H2O and C3H7NO2S in 60 mL of deionized water, adding 15 mL of ethanol and 5.5 mL of glycerol to the deionized water. Four composite samples with varying theoretical mass ratios (In2S3:WO3 = 0.2, 0.4, 0.6, 0.8) were prepared by dispersing 200 mg of pre-synthesized WO3 NSs into respective solutions via 30 min ultrasonication, followed by magnetic stirring. The homogeneous suspensions were transferred to 100 mL of Teflon-lined autoclaves and hydrothermally treated at 160 °C for 12 h. After that, the products (denoted as WI-20, WI-40, WI-60, and WI-80 based on In2S3 content) were washed via centrifugation with ethanol/water and dried at 60 °C under vacuum for 12 h. Pure In2S3 control samples were synthesized identically without WO3 addition. A schematic representation of the synthesis process is provided in Scheme 1.

3.3. Characterization

X-ray diffraction (XRD) patterns of samples were tested using a powder XRD (MAC science, Yokohama, Japan, Ni-filtrated Cu-Kα radiation). The nanostructure property of prepared catalysts was analyzed using scanning electron microscopy (FE-SEM, JEOL (Tokyo, Japan), 7800F) and transmission electron microscopy (TEM, FEI Tecnai (Hillsboro, OR, USA) G2F20 instrument). The elemental composition and chemical states of the catalyst were studied using X-ray photoelectron spectroscopy (XPS) (PerkinElmer PHI 5300, a monochromatic Mg Kα source, Waltham, MA, USA), and the C 1s peak position at 284.6 eV was used as the standard for calibrating the XPS data. The photo-absorption ability of the prepared samples was researched using a UV–Vis spectrophotometer (UV-3600P; Shimazu, Tokyo, Japan). Photocurrent experiments were conducted on an electrochemical system (CHI 660B, Shanghai, China) with a standard three-electrode quartz cell. An AgCl and a Pt wire served as reference and counter electrodes, and samples served as the working electrodes. A 0.5 M Na2SO4 solution was the electrolyte. Electrochemical impedance spectroscopy (EIS) was performed in a 0.5 mM Fe(CN)63−/4− and KCl solution at 10 mV sine amplitude and 0.1 Hz–100 kHz frequency on the same system. The photoluminescence (PL) spectra were analyzed by a FLS1000 photoluminescence spectrometer (Edinburgh Instrument Company, Edinburgh, UK). N2 adsorption and desorption/CO2 adsorption curves were measured by a specific surface area analyzer (Micromeritics, ASAP2460, Norcross, GA, USA). CO2 photoreduction process: a Xe lamp (Education AU-light, Beijing, China) was selected as the light source. The Xe lamp was positioned approximately 15 cm away from the liquid surface, resulting in a total optical power of about 50.1 mW/cm2 incident on the mixed liquid. The reaction was conducted in a 200 mL, fully transparent quartz reactor. The experimental procedure was as follows: 0.02 g of the catalyst was dispersed in 50 mL of deionized water in the reactor. Subsequently, CO2 gas was purged into the reactor for 10 min. The suspension was then continuously stirred at a speed of 500 rpm and irradiated for 4 h before analysis. After the photoreduction process, the gas product was detected and analyzed through an off-line gas chromatography system (GC-8670M, Nanjing Dongcun Scientific Instrument Co., Ltd., Nanjing, China).

4. Conclusions

In this paper, serious WO3/In2S3 S-scheme heterojunction photocatalysts were successfully synthesized via a facile hydrothermal method for CO2 photoreduction. The Fermi level difference between components triggered interfacial electron transfer, establishing an IEF directed from In2S3 to WO3. This IEF facilitated directional charge migration and substantially enhanced the separation efficiency of photoinduced carriers. UV-Vis DRS analysis and photoelectrochemical characterization revealed that the optimized WI-60 composite exhibited an extended photo-absorption range and effective CO2 activation on In2S3 surfaces, synergistically contributing to the superior photocatalytic performance. Without requiring molecular co-catalysts or sacrificial agents, the WI-60 heterostructure achieved a CO evolution rate of 55.2 μmol·g−1 under 4 h of UV-Vis irradiation, representing a 3.9-fold enhancement compared to pristine In2S3 (14.1 μmol·g−1). Cyclic tests demonstrated exceptional stability, with the composite retaining 89.3% of initial activity after four consecutive runs. Mechanistic investigations combining XPS analysis and energy band alignment studies conclusively validated the S-scheme charge transfer pathway, wherein high-energy electrons in WO3 and holes in In2S3 were preserved for redox reactions while low-energy carriers underwent recombination. This work provides fundamental insights into designing IEF-driven S-scheme systems for solar fuel production.

Author Contributions

Conceptualization: A.X. and Y.W.; data curation: A.X., Y.W., Z.Y. and B.Z.; investigation: A.X. and Y.W.; validation/visualization: A.X. and Y.W.; writing—original draft preparation: Y.W.; writing—review and editing, X.L. (Xin Li) and M.W.; supervision: J.C., X.L. (Xuefei Li), and K.Z.; project administration: J.L. and K.C.; funding acquisition: J.L., X.L. (Xin Li), M.W., X.L. (Xuefei Li), B.Z. and K.C. All authors have read and agreed to the published version of the manuscript.

Funding

We gratefully acknowledge the financial support of the program for the National Natural Science Foundation of China (22378158), the Development of Science and Technology of Jilin province (YDZJ202301ZYTS246, 20220402031GH, 20230508040RC, 20240601047RC, YDZJ202401470ZYTS), the program for the Science and Technology of the Education Department of Jilin Province (grant no. JJKH20250941KJ), Training Program of Innovation and Entrepreneurship for College Students (202410203037), Young Teachers Research Ability Cultivation and Promotion Program of Jilin Normal University (0521426), and the Doctoral Research Project of Jilin Normal University (0420355).

Data Availability Statement

The datasets used and/or analyzed during the current study are available from the corresponding author upon reasonable request.

Conflicts of Interest

The authors declare no conflicts of interest.

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Catalysts 15 00460 g001
Figure 1. XRD patterns of prepared WO3, In2S3, WI-60 (a), and the binary composites with different amounts of In2S3 (b).
Figure 1. XRD patterns of prepared WO3, In2S3, WI-60 (a), and the binary composites with different amounts of In2S3 (b).
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Catalysts 15 00460 g002
Figure 2. SEM images prepared of WO3 (a), In2S3 (b), and the binary composites with different amounts of In2S3 (c–f); TEM and HR-TEM images of WO3 (g) and In2S3 (h,h1); SAED of WI-60 (h2).
Figure 2. SEM images prepared of WO3 (a), In2S3 (b), and the binary composites with different amounts of In2S3 (c–f); TEM and HR-TEM images of WO3 (g) and In2S3 (h,h1); SAED of WI-60 (h2).
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Catalysts 15 00460 g003
Figure 3. XPS total spectrum of WI-60 (a); high-resolution XPS spectra of C 1s (b), In 3d (c), S 2d (d), W 4f (e), and (f) O 1s.
Figure 3. XPS total spectrum of WI-60 (a); high-resolution XPS spectra of C 1s (b), In 3d (c), S 2d (d), W 4f (e), and (f) O 1s.
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Catalysts 15 00460 g004
Figure 4. N2 adsorption–desorption isotherm (a) and CO2 adsorption curve (b) of pure In2S3, WO3, and WI-60.
Figure 4. N2 adsorption–desorption isotherm (a) and CO2 adsorption curve (b) of pure In2S3, WO3, and WI-60.
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Catalysts 15 00460 g005
Figure 5. Performance of CO2 conversion to CO after 4 h via all samples (a), electron utilization rate of each sample (b), control experiment under different experimental conditions (c), and performance of the photoreduction of CO2 to CO performed 4 times, with WI-60 as catalyst (d).
Figure 5. Performance of CO2 conversion to CO after 4 h via all samples (a), electron utilization rate of each sample (b), control experiment under different experimental conditions (c), and performance of the photoreduction of CO2 to CO performed 4 times, with WI-60 as catalyst (d).
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Catalysts 15 00460 g006
Figure 6. UV-Vis DRS spectra of WO3 NSs, In2S3, and WO3/In2S3 (a); WO3 and In2S3 bandgap widths were calculated by Tauc curves (b).
Figure 6. UV-Vis DRS spectra of WO3 NSs, In2S3, and WO3/In2S3 (a); WO3 and In2S3 bandgap widths were calculated by Tauc curves (b).
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Catalysts 15 00460 g007
Figure 7. EIS (a), TPR (b), PL (c), and LSV (d) results of the prepared sample.
Figure 7. EIS (a), TPR (b), PL (c), and LSV (d) results of the prepared sample.
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Catalysts 15 00460 g008
Figure 8. Mott–Schottky curves of pure WO3 and In2S3 (a,b); the formation process of IEF (c,d); the transfer process of the photogenerated carriers (e); and the CO2 photoreduction process of the WI-60 S-scheme heterojunction (f).
Figure 8. Mott–Schottky curves of pure WO3 and In2S3 (a,b); the formation process of IEF (c,d); the transfer process of the photogenerated carriers (e); and the CO2 photoreduction process of the WI-60 S-scheme heterojunction (f).
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Catalysts 15 00460 sch001
Scheme 1. The prepared processes of the samples, P-WO3 (a); WO3 NSs (b) and WI composites (c).
Scheme 1. The prepared processes of the samples, P-WO3 (a); WO3 NSs (b) and WI composites (c).
Catalysts 15 00460 sch001
Table 1. A comparative analysis of the performance of our catalyst vs. reported catalysts production from CO2 photoreduction.
Table 1. A comparative analysis of the performance of our catalyst vs. reported catalysts production from CO2 photoreduction.
SampleLight SourceSacrificial AgentEvolution Rate μmol/g (4 h)Ref.
MoS2/In2S3300 W Xe-lamp (Beijing Zhongjiao Jinyuan CEL-HXF300, Beijing, China)WithoutCO: 40.36[31]
Atomic strain In2S3300 W Xe-lamp (Chengdu Lihang PLS-SXE300D), AM 1.5 G filter, Chengdu, ChinaWithoutCO: 20.64[32]
Cu7S4@Cu2O300 W Xe Arc lamp (Beijing Bofeilai, Beijing, China)WithoutCO: 24.76[33]
ZnIn2S4/MOF-808OFR Xe-lamp (Beijing Education Au-light, Beijing, China)WithoutCO: 32.84[34]
CDs/CdS300 W Xe-lamp, AM 1.5 G filter.
(Xi’an TopTION Instrument Co., Ltd., Xi’an, China)		TriethanolamineCO: 48.16[35]
MgCr2O4/MgIn2S4300 W Xe-lamp (Chengdu Lihang PLS-SXE 300+, Chengdu, China)WithoutCO: 32.12[36]
ZnIn2S4/Cu2S300 W Xe-lamp (Beijing China Education Au-light, Beijing, China)WithoutCO: 13.35/CH4: 34.81[37]
NiTiO3/CdS300 W Xe-lamp (Beijing China Education Au-light, Beijing, China)Triethanolamine CO: 20.8[38]
CuInSnS4300 W Xe-lamp, 420 nm cut-off wavelength filter
(Beijing China Education Au-light, Beijing, China)		WithoutCH4: 23.32[39]
WO3/In2S3300W Xe-lamp (Beijing China Education Au-light, Beijing, China)WithoutCO: 55.2 This work
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Wang, Y.; Xu, A.; Lang, J.; Zuo, B.; Yu, Z.; Cui, K.; Li, X.; Zhang, K.; Li, X.; Wei, M.; et al. Interfacial Engineering of S-Scheme WO3/In2S3 Heterojunction for Efficient Solar-Driven CO2 Photoreduction. Catalysts 2025, 15, 460. https://doi.org/10.3390/catal15050460

AMA Style

Wang Y, Xu A, Lang J, Zuo B, Yu Z, Cui K, Li X, Zhang K, Li X, Wei M, et al. Interfacial Engineering of S-Scheme WO3/In2S3 Heterojunction for Efficient Solar-Driven CO2 Photoreduction. Catalysts. 2025; 15(5):460. https://doi.org/10.3390/catal15050460

Chicago/Turabian Style

Wang, Yameng, Ao Xu, Jihui Lang, Bin Zuo, Zihan Yu, Keyu Cui, Xuefei Li, Kewei Zhang, Xin Li, Maobin Wei, and et al. 2025. "Interfacial Engineering of S-Scheme WO3/In2S3 Heterojunction for Efficient Solar-Driven CO2 Photoreduction" Catalysts 15, no. 5: 460. https://doi.org/10.3390/catal15050460

APA Style

Wang, Y., Xu, A., Lang, J., Zuo, B., Yu, Z., Cui, K., Li, X., Zhang, K., Li, X., Wei, M., & Cao, J. (2025). Interfacial Engineering of S-Scheme WO3/In2S3 Heterojunction for Efficient Solar-Driven CO2 Photoreduction. Catalysts, 15(5), 460. https://doi.org/10.3390/catal15050460

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