In situ bridging nanotwinned all-solid-state Z-scheme g-C3N4/CdCO3/CdS heterojunction photocatalyst by metal oxide for H2 evolution

1D/1D W18O49/Cd0.9Zn0.1S S-scheme heterojunction with spatial charge separation for high-yield photocatalytic H2 evolution

Semiconductor photocatalytic water splitting is a green way to convert solar energy into chemical energy, but the recombination of electron and hole pairs and the low utilization of sunlight restrict the development of photocatalytic technology. By comparing the morphologies and hydrogen production properties of different proportions of solid solutions (Cd_xZn_1-xS), one-dimensional (1D) Cd_0.9Zn_0.1S nanorods (NRs) with the best photocatalytic properties are obtained. In addition, 1D W₁₈O₄₉ nanowires are assembled on the surface of 1D Cd_0.9Zn_0.1S NRs to construct a novel 1D/1D step-scheme (S-scheme) W₁₈O₄₉/Cd_0.9Zn_0.1S heterojunction photocatalyst. The W₁₈O₄₉/Cd_0.9Zn_0.1S heterojunction expands the optical absorption capacity of Cd_0.9Zn_0.1S NRs to provide more energy for the photoexcitation of electrons. The optimal hydrogen production rate of W₁₈O₄₉/Cd_0.9Zn_0.1S NRs with W₁₈O₄₉ content of 9 wt% is as high as 66.3 mmol·h^-1·g^-1, which is 5.7 times and 1.6 times higher than that of Cd_0.9Zn_0.1S NRs and 1 wt% Pt/Cd_0.9Zn_0.1S NRs. The apparent quantum efficiency (AQE) of 9 wt% W₁₈O₄₉/Cd_0.9Zn_0.1S reaches 56.0 % and 25.9 % under light wavelength irradiation at 370 and 456 nm, respectively. After the 20 h cycle stability test, the activity of photocatalytic hydrogen evolution does not decrease, due that the severe photo-corrosion of Cd_0.9Zn_0.1S NRs is efficiently inhibited. This work not only provides a simple and controllable synthesis method for the preparation of heterojunction structure, but also opens up a new way to improve the hydrogen evolution activity and stability of sulfur compounds.

Facilitating charge transfer through an atomic coherent interface of a novel direct Z-scheme BiVO4@Cu3SnS4 heterojunction to boost photocatalytic performance

Direct Z-scheme photocatalytic systems are very promising composite photocatalysts, and their photocatalytic performance is highly associated with the quality of the interface within them. Herein, a novel direct Z-scheme heterojunction with a coherent interface has been presented for the first time. Specifically, the heterojunction was constructed by dispersing pre-prepared BiVO₄ crystals into the reaction system to synthesize Cu₃SnS₄, followed by a hydrothermal reaction. It is shown that Cu₃SnS₄ was deposited on the surface of each pre-prepared BiVO₄ crystal as a thin layer via heterogeneous nucleation to acquire a core-shell heterojunction. The BiVO₄@Cu₃SnS₄ heterojunction was found to possess an atomic coherent interface, which is formed through the bonding between the (121) plane of BiVO₄ and the (112) plane of Cu₃SnS₄, originating from the matching in the crystalline lattice between the two planes. The coherent interface facilitated the charge transfer from Cu₃SnS₄ to BiVO₄ owing to the difference in their Fermi levels, thereby forming a built-in electric field pointing from Cu₃SnS₄ to BiVO₄. Reduced fluorescence emission and a shortened carrier lifetime reveal an obvious reduction in the inter-band charge recombination for the optimal BVO@CTS-0.19 sample. Consequently, BVO@CTS-0.19 shows remarkably enhanced photocatalytic performance in MO degradation, Cr⁶⁺ reduction and oxygen evolution. The Z-scheme charge transfer mechanism for BVO@CTS-0.19 was verified by a suite of techniques. This work provides a universal strategy for building a coherent interface to develop high-performance direct Z-scheme heterojunctions.