Multi-heterointerface charge transfer in amine-functionalized cadmium sulfide-copper sulfide@titanium dioxide hollow spheres with rich oxygen vacancies for carbon dioxide photoreduction.

Photocatalytically reducing CO₂ into high-value-added chemical materials has surfaced as a viable strategy for harnessing solar energy and mitigating the greenhouse effect. But the inadequate separation of the photogenerated electron-hole pair remains a major obstacle to CO₂ photoreduction. Constructing heterostructure photocatalysts with efficient interface charge transfer is a promising approach to solving the above problems. Herein, a straightforward synthetic strategy is developed to fabricate amine-functionalized cadmium sulfide-copper sulfide@titanium dioxide (CdS-CuS@TiO₂) hollow spheres with rich oxygen vacancies for CO₂ photoreduction. The synthetic route involves successive steps of the coating of CdS nanolayer on the prepared SiO₂ solid nanospheres, transformation of CdS into CdS-CuS through cation exchange reaction, the coating of amorphous TiO₂ nanoparticle layer on the SiO₂@CdS-CuS solid nanospheres, and the simultaneous transformations of solid nanospheres to hollow nanospheres and amorphous TiO₂ nanoparticle layer to amine-functionalized anatase TiO₂ nanosheets with rich oxygen vacancies via the hydrothermal reaction process in the presence of ethylenediamine. In the composite catalyst, the formed multi-heterointerfaces among the different components accelerate charge separation and transport. Moreover, the formed hollow spherical structure covered with amine-functionalized TiO₂ ultrathin nanosheets with rich oxygen vacancies exposes a greater number of active sites for CO₂ adsorption and increases incident light absorption and utilization. As anticipated, the optimal composite catalyst demonstrates much higher CO₂ reduction properties with a considerable CO yield (115.66 μmol g^-1 h^-1), surpassing that of the control catalysts (single component and bicomponent). This research offers a versatile synthetic method to synthesize excellent catalysts aimed at the production of solar fuels.