Developing novel nanostructures to enhance the efficiency of solar-to-chemical conversion through integrated photocatalytic hydrogen (H₂) evolution and organic transformation holds great promise in addressing pressing energy and environmental crises. Ternary metal sulfides have garnered considerable attention in photocatalytic H₂ production due to their tunable bandgap and excellent visible light response. Among them, Zn_0.5Cd_0.5S stands out as a reduction photocatalyst with a narrow bandgap, a high conduction band level, and excellent resistance to photocorrosion. However, unitary Zn_0.5Cd_0.5S suffers from a high recombination rate of photogenerated electron/hole pairs, resulting in only a small fraction of charge carriers being involved in the photoreactions, leading to a low quantum efficiency that falls short of practical demand. WO₃, a typical oxidation photocatalyst with a lower valence band position and strong oxidization ability, is an ideal candidate for constructing an S-scheme heterojunction with Zn_0.5Cd_0.5S. Herein, a core-shell structured WO₃/Zn_0.5Cd_0.5S heterojunction with Zn_0.5Cd_0.5S nanosheets vertically growing out of WO₃ nanofibers is fabricated through electrospinning and hydrothermal methods. The distinct disparity in work functions leads to the transfer of electrons from Zn_0.5Cd_0.5S to WO₃ upon contact, creating an interfacial electric field (IEF) and simultaneously bending the energy bands at the interface. As a consequence of IEF, bent energy bands, and coulomb attraction, the photogenerated electrons in the conduction band of WO₃ migrate to the valence band of Zn_0.5Cd_0.5S and recombine with its photoinduced holes, signifying the formation of an S-scheme heterojunction between WO₃ and Zn_0.5Cd_0.5S and enabling efficient separation of powerful charge carriers, as evidenced by in situ irradiated X-ray photoelectron spectroscopy, electron paramagnetic resonance, and time-resolved fluorescence spectroscopy analyses. Benefiting from the unique S-scheme photocatalytic mechanism, along with the effective chemisorption and activation of reactants on the catalyst, the optimized WO₃/Zn_0.5Cd_0.5S heterostructures exhibit exceptional photocatalytic performance in H₂ production (715 μmol∙g⁻¹∙h⁻¹) and the transformation from lactic acid to pyruvic acid without the need for any noble metal cocatalyst, achieving the full utilization of photoinduced electrons and holes. In situ diffuse reflectance infrared Fourier transform spectroscopy, as well as density functional theory simulations, reveal the photoreaction mechanism of H₂ production and organic transformation. This work offers valuable insights into the design and investigation of the mechanism behind novel S-scheme heterojunction photocatalysts, enabling high-performance H₂ production and simultaneous organic transformation.

In the pursuit of efficient photocatalytic carbon dioxide (CO₂) conversion, the use of artificial semiconductors powered by solar energy offers great potential for simulating natural carbon cycling. However, the efficiency of photocatalytic CO₂ conversion remains suboptimal, primarily due to inadequate separation of photogenerated charges, which hinders the performance of semiconductor-based CO₂ reduction. Consequently, recent research efforts have focused on identifying ideal materials for CO₂ photocatalytic conversion. Among the candidate materials, the structure of Bi₂MoO₆ consists of alternating layers of (Bi₂O₂)²⁺ and perovskite-like (MoO₄)²⁻ layers with shared oxygen atoms between them. This inherent charge distribution within Bi₂MoO₆ creates an inhomogeneous electric field, facilitating the efficient separation of photogenerated charge carriers. The morphology and structure of a catalyst significantly influence the rate of recombination of photogenerated charge carriers. Research has shown that ultrathin Bi₂MoO₆ nanosheets, compared to other 2D and 3D structures of Bi₂MoO₆ materials, possess longer fluorescence lifetimes, providing more opportunities for the separation of photogenerated charge carriers. However, Bi₂MoO₆ still exhibits relatively low catalytic efficiency due to its insufficiently negative conduction band position (ranging between −0.2 and −0.4 V). To address this limitation, a viable strategy is to load a semiconductor with a more negatively positioned conduction band onto Bi₂MoO₆, creating an S-scheme heterojunction. In this study, Bi₂MoO₆ nanosheets were synthesized through a hydrothermal method, and simultaneously, CeO₂ nanoparticles were grown on their surfaces, forming an S-scheme heterojunction modified with Ce³⁺/Ce⁴⁺ ion bridges. Time-resolved photoluminescence (TRPL) and photoelectrochemical tests demonstrated the enhanced charge separation effect of this heterojunction. In situ X-ray photoelectron spectroscopy (In situ XPS) analysis and theoretical calculations further confirmed that photogenerated electrons follow an S-scheme mechanism, transferring from Bi₂MoO₆ to CeO₂. Experimental results revealed that the photocatalytic CO₂ reduction efficiencies of CeO₂/Bi₂MoO₆, Bi₂MoO₆, and CeO₂ were 65.3, 14.8, and 1.2 μmol∙g⁻¹∙h⁻¹, respectively. Compared to pure Bi₂MoO₆, the catalytic efficiency of the CeO₂/Bi₂MoO₆ composite catalyst for CO₂ photocatalytic reduction to CO improved by a factor of 3.12. This enhancement in photocatalytic CO₂ conversion performance can be attributed to the synergistic interaction between the S-scheme heterojunction and Ce³⁺/Ce⁴⁺ ion bridging, resulting in enhanced light absorption, efficient charge separation, and redox capabilities of the composite catalyst. This study offers valuable insights into the rational design and construction of novel S-scheme heterojunction photocatalysts.

The construct of the internal electric field (IEF) is recognized as an effective driver for promoting charge migration and separation to enhance photocatalytic performance. In this study, one-dimensional nanorods of Mn_0.2Cd_0.8S (MCS) co-doped with interstitial chlorine (Cl_int) and substitutional chlorine (Cl_sub) were designed and synthesized using a one-step solvothermal method. The incorporation of Cl_int and Cl_sub led to an unbalanced charge distribution and the formation of IEF in the MCS nanorods, contributing to the improvement of photogenerated carrier kinetic behavior. Through density functional theory (DFT) calculations, the effect of Cl_int and Cl_sub doping on the activity of the MCS was visually explained by examining differences in electronic structure, charge distribution and H₂ adsorption/desorption balance. Interestingly, the modulation of the energy band structure of MCS primarily resulted from the contribution of Cl_int, while Cl_sub playing a negligible role. Moreover, the Cl_sub further facilitated the optimization of Cl_int concerning the H₂ adsorption-desorption Gibbs free energy (ΔG_H*) of MCS. Ultimately, the ΔG_H* of 0.9 Cl-MCS favored H₂ production (1.14 vs. 0.17 eV), leading to a 9 times increase in photocatalytic H₂ production activity compared to MCS. This investigation presents a valuable approach for constructing IEF in bimetallic sulfide photocatalysts.

The production of renewable fuels through water splitting via photocatalytic hydrogen production holds significant promise. Nonetheless, the sluggish kinetics of hydrogen evolution and the inadequate water adsorption on photocatalysts present notable challenges. In this study, we have devised a straightforward hydrothermal method to synthesize Bi₂O₃ (BO) derived from metal-organic frameworks (MOFs), loaded with flower-like ZnIn₂S₄ (ZIS). This approach substantially enhances water adsorption and surface catalytic reactions, resulting in a remarkable enhancement of photocatalytic activity. By employing triethanolamine (TEOA) as a sacrificial agent, the hydrogen evolution rate achieved with 15% (mass fraction) ZIS loading on BO reached an impressive value of 1610 μmol∙h⁻¹∙g⁻¹, marking a 6.34-fold increase compared to that observed for bare BO. Furthermore, through density functional theory (DFT) and ab initio molecular dynamics (AIMD) calculations, we have identified the reactions occurring at the ZIS/BO S-scheme heterojunction interface, including the identification of active sites for water adsorption and catalytic reactions. This study provides valuable insights into the development of high-performance composite photocatalytic materials with tailored electronic properties and wettability.

Directional electron transfer is an appealing strategy for harnessing photogenerated charge separation kinetics. Herein, a novel 2D/1D SnNb₂O₆/nitrogen-enriched C₃N₅ S-scheme heterojunction with strong internal electric field (IEF) and dipole field (DF) is designed through in situ growth of C₃N₅ nanorods on SnNb₂O₆ nanosheets. The IEF generated at the interface via the formation of the S-scheme heterojunction induces directional charge transfer from SnNb₂O₆ to C₃N₅. Simultaneously, the DF within C₃N₅ provides the impetus to guide photo-excited electrons to the active sites. Consequently, the synergistic effects of IEF and DF facilitate swift directional electron transfer. The optimized SnNb₂O₆/C₃N₅ heterojunction demonstrates a remarkable H₂ production rate of 1090.0 μmol∙g⁻¹∙h⁻¹ with continuous release of H₂ bubbles. This performance surpasses that of SnNb₂O₆ and C₃N₅ by 38.8 and 10.7 times, respectively. Additionally, the SnNb₂O₆/C₃N₅ heterojunction exhibits superior activity in the removal of Rhodamine B, tetracycline, and Cr(Ⅵ). Based on electron paramagnetic resonance (EPR), time-resolved photoluminescence (TPRL) and density functional theory (DFT) calculations, etc., the directional charge transfer mechanism was systematically explored. The research furnishes a plausible approach to construct effective heterojunction photocatalysts for applications in energy and environmental domains.

Cu-Graphdiyne and CoNiWO₄ were synthesized by organic and hydrothermal methods, respectively. The establishment of an S-scheme heterojunction between Cu-Graphdiyne and CoNiWO₄ was achieved by interface engineering design. The efficient separation and transfer of photogenerated carriers are facilitated by the synergistic effect of the built-in electric field and band bending, while maintaining the strong redox capacity of the catalysts. The introduction of Cu-Graphdiyne effectively enhances the photo absorption capacity and conductivity of the composite catalyst, and significantly suppresses the recombination of photogenerated carriers. The unique two-dimensional planar network structure of Cu-Graphdiyne provides abundant active sites for photocatalytic processes, thereby facilitating the photocatalytic reaction. Density functional theory (DFT) calculations demonstrate that hot electrons generated by surface plasmon resonance effects of Cu will transfer to Graphdiyne to promote hydrogen evolution reaction. This study offers insights into potential applications of Cu-Graphdiyne and nickel-cobalt based catalysts in photocatalytic hydrogen evolution.

Transitional metal oxyhydroxides have been demonstrated to be the reliable cocatalysts for water oxidation reaction. However, their insufficient adsorption ability for H₂O and its intermediate products during water oxidation greatly restricts the improvement of water oxidation rate. In this study, a spontaneously improved adsorption of H₂O and its intermediates on the electron-deficient Mn^(3+δ)+ of MnOOH cocatalyst can greatly promote the rapid water oxidation to realize the efficient photocatalytic H₂O₂ production in a pure water system. In this case, amorphous MnOOH is selectively deposited on the (110) facet of AuPd-modified single-crystal BiVO₄ photocatalyst via the directionally photoinduced oxidation approach to produce AuPd/BiVO₄/MnOOH photocatalyst. Photocatalytic experiments exhibit that the as-prepared AuPd/BiVO₄/MnOOH (0.5%) photocatalyst obtains the boosted H₂O₂-evolution rate of 214 μmol∙L⁻¹ as well as exhibits an outstanding stability and reproducibility. Density functional theory calculations and X-ray photoelectron spectroscopy (XPS) characterization reveal that the free electrons of MnOOH can effectively transfer to BiVO₄ to induce the generation of electron-deficient Mn sites (Mn^(3+δ)+), which spontaneously promotes the adsorption of H₂O and its intermediates for enhancing 4-electron water oxidation reaction, resulting in an efficient H₂O₂ production. The present work about the strong interaction between cocatalyst and bulk catalyst provides a fresh idea for the rational design of highly efficient catalytic materials.

Covalent organic frameworks (COFs) represent a kind of novel crystalline porous organic substances with extended π-conjugation framework and tunable structures, which display great promise in photocatalysis. However, unadorned COFs suffer from sluggish reaction kinetics, and a cocatalyst is essentially needed to reduce the activation barrier toward specific surface reaction and accelerate reaction kinetics. In this work, bimetallic alloys serving as co-catalysts were decorated on COFs to enhance the photocatalytic hydrogen evolution performance. By precisely-tuning the ratio of AuCu alloy, the resultant Au₁Cu₅/COF-TpPa displays the highest photocatalytic hydrogen generation rate (8.24 mmol∙g⁻¹∙h⁻¹), even surpassing the Pt modified COF-TpPa (6.51 mmol∙h⁻¹∙g⁻¹). According to the systematic characterizations and theoretical calculation, Au₁Cu₅/COF-TpPa exhibits the significantly enhanced charge carrier separation efficiency and reduced H* formation energy barrier, thus possessing high photocatalytic performance. This work affords a valuable approach to advancing COF-based photocatalysts by employing bimetallic alloy cocatalysts.

Artificial photosynthesis is an appealing approach for generating hydrogen peroxide (H₂O₂) from H₂O and O₂ with solar energy as the sole energy input. However, the current catalyst systems commonly face challenges such as the limited optical absorption, poor electron-hole pair separation efficiency, and restricted surface reactivity, which hinders the overall photoactivity. Here, we immobilize cubic-phase ultrathin In₄SnS₈ nanosheets (E_g = 2.16 eV) with thickness of 5–10 nm on the surface of few-layer Ti₃C₂ to develop a sandwich-like hierarchical structure of Ti₃C₂/In₄SnS₈ nanohybrid via in situ hydrothermal strategy. The enlarged interfacial area and close contact between Ti₃C₂ and In₄SnS₈ benefit for carrier transportation among nanohybrids. Characterization through X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) corroborates the successful construction of Ti₃C₂/In₄SnS₈ nanostructures. Band structures investigation including valence band maximum and Mott-Schottky plots reveals the formation of Schottky junction in this 2D/2D heterostructure, that favors for ultrafast charge carrier separation and transportation from In₄SnS₈ to Ti₃C₂ and preventing the electrons backflow from Ti₃C₂ to In₄SnS₈. Photoluminescene analysis and photo/electrochemical measurements prove that the combination of Ti₃C₂ and In₄SnS₈ accelerates the transportation of photoexcited electron-hole pairs and efficiently suppresses charge carrier recombination. Unsurprisingly, 7 wt% Ti₃C₂/In₄SnS₈ catalysts exhibit the highest visible-light-driven photoreactivity with H₂O₂ production rates of 1.998 µmol∙L⁻¹∙min^‒1 that is 2.2 times larger than that of single In₄SnS₈. Additionally, Ti₃C₂/In₄SnS₈ demonstrates a multifunctional capability in Cr(Ⅵ) reduction with the greatest reaction rates of 19.8 × 10⁻³ min^‒1 that is almost 4-fold larger than that of individual semiconductor. Moreover, the nanohybrids exhibit excellent photostability after 5 cycles testing in both reaction systems. The morphology, crystal structure and composition for Ti₃C₂/In₄SnS₈ remain unaltered after photoreaction. A comprehensive analysis including trapping agents and atmosphere experiments as well as electron paramagnetic resonance demonstrates that the H₂O₂ evolution pathway consists of two channels: a two-step successive 1e^‒ oxygen reduction reaction and a one-step 2e^‒ water oxidation reaction. This work may provide a viable protocol for designing efficient and multifunctional photocatalytic systems for solar-to-chemical energy conversion.