Two-dimensional-layered heterojunctions have attracted extensive interest recently due to their exciting behaviours in electronic/optoelectronic devices as well as solar energy conversion systems. However, layered heterojunction materials, especially those made by stacking different monolayers together by strong chemical bonds rather than by weak van der Waal interactions, are still challenging to fabricate. Here the monolayer Bi₂WO₆ with a sandwich substructure of [BiO]⁺–[WO₄]²⁻–[BiO]⁺ is reported. This material may be characterized as a layered heterojunction with different monolayer oxides held together by chemical bonds. Coordinatively unsaturated Bi atoms are present as active sites on the surface. On irradiation, holes are generated directly on the active surface layer and electrons in the middle layer, which leads to the outstanding performances of the monolayer material in solar energy conversion. Our work provides a general bottom-up route for designing and preparing novel monolayer materials with ultrafast charge separation and active surface.

The stoichiometric photocatalytic reaction of CO₂ with H₂O is one of the great challenges in photocatalysis. Here, we construct a Cu₂O-Pt/SiC/IrO_x composite by a controlled photodeposition and then an artificial photosynthetic system with Nafion membrane as diaphragm separating reduction and oxidation half-reactions. The artificial system exhibits excellent photocatalytic performance for CO₂ reduction to HCOOH and H₂O oxidation to O₂ under visible light irradiation. The yields of HCOOH and O₂ meet almost stoichiometric ratio and are as high as 896.7 and 440.7 μmol g⁻¹ h⁻¹, respectively. The high efficiencies of CO₂ reduction and H₂O oxidation in the artificial system are attributed to both the direct Z-scheme electronic structure of Cu₂O-Pt/SiC/IrO_x and the indirect Z-scheme spatially separated reduction and oxidation units, which greatly prolong lifetime of photogenerated electrons and holes and prevent the backward reaction of products. This work provides an effective and feasible strategy to increase the efficiency of artificial photosynthesis.

This work shows the solar-driven dehydrogenative coupling of methane to ethane at room temperature. A solar-to-C₂H₆ energy conversion efficiency of 0.08% was achieved on the polar surface of Au/ZnO porous nanosheets (NSs), where methane C–H bonds are polarized and dissociated by the local electric field normal to the polar {001} plane, and finally converted into ethane and hydrogen through a radical coupling pathway. Mechanistic studies suggest that the Au-plasmon-induced resonance energy transfer modulates charge carrier energetics to trigger the stoichiometric conversion. Hot electrons reduce protons to H₂, which is the rate-determining step of methane coupling.

The active center for the adsorption and activation of carbon dioxide plays a vital role in the conversion and product selectivity of photocatalytic CO₂ reduction. Here, we find multiple metal sulfides CuInSnS₄ octahedral nanocrystal with exposed (1 1 1) plane for the selectively photocatalytic CO₂ reduction to methane. Still, the product is switched to carbon monoxide on the corresponding individual metal sulfides In₂S₃, SnS₂, and Cu₂S. Unlike the common metal or defects as active sites, the non-metal sulfur atom in CuInSnS₄ is revealed to be the adsorption center for responding to the selectivity of CH₄ products. The carbon atom of CO₂ adsorbed on the electron-poor sulfur atom of CuInSnS₄ is favorable for stabilizing the intermediates and thus promotes the conversion of CO₂ to CH₄. Both the activity and selectivity of CH₄ products over the pristine CuInSnS₄ nanocrystal can be further improved by the modification of with various co-catalysts to enhance the separation of the photogenerated charge carrier. This work provides a non-metal active site to determine the conversion and selectivity of photocatalytic CO₂ reduction.