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Using sunlight to convert CO2 into solar fuel is an ideal solution to both global warming and the energy crisis. The construction of direct Z-scheme heterojunctions is an effective method to overcome the shortcomings of single-component or conventional heterogeneous photocatalysts for photocatalytic CO2 (carbon dioxide) reduction. In this work, a composite photocatalyst of narrow-gap SnS2 and stable oxide Bi2WO6 were prepared by a simple hydrothermal method. The combination of Bi2WO6 and SnS2 narrows the bandgap, thereby broadening the absorption edge and increasing the absorption intensity of visible light. Photoluminescence, transient photocurrent, and electrochemical impedance showed that the coupling of SnS2 and Bi2WO6 enhanced the efficiency of photogenerated charge separation. The experimental results show that the electron transfer in the Z-scheme heterojunction of SnS2/Bi2WO6 enables the CO2 reduction reactions to take place. The photocatalytic reduction of CO2 is carried out in pure water phase without electron donor, and the products are only methanol and ethanol. By constructing a Z-scheme heterojunction, the photocatalytic activity of the SnS2/Bi2WO6 composite was improved to 3.3 times that of pure SnS2.

In today's society, mankind is confronted with two major problems: the energy crisis and the greenhouse effect. The artificial photosynthesis can use solar energy to convert greenhouse gas CO2 into high-value compounds, which is an ideal solution to alleviate the energy crisis and solve the problem of global warming. The combination of ZnO and polythiophenes (PTh) can make up for each other's drawbacks, thus improving the photoresponse behavior and separation efficiency of photogenerated carriers. PTh layer can transfer photogenerated electrons to ZnO, thereby extending the lifetime of photogenerated charges. The production rate of CH4 from photoreduction of CO2 with ZnO/PTh10 is 4.3 times that of pure ZnO, and the selectivity of CH4 is increased from 70.2% to 92.2%. The conductive PTh can absorb photons to induce π–π* transition, the photogenerated electrons can transfer from LUMO to the conduction band (CB) of ZnO, thus more electrons involve in the reduction of CO2.

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