Stacking Engineering of Semiconductor Heterojunctions on Hollow Carbon Spheres for Boosting Photocatalytic CO2 Reduction

Fabrication of semiconductor heterojunctions into hollow nanostructures holds multiple intrinsic advantages in enhancing the photocatalytic performance but still faces lots of challenges. To overcome the obstacles, herein, we report an alternative stacking design of semiconductor heterojunctions on hollow carbon spheres for significantly improved photocatalytic activity, selectivity, and stability in CO2-to-CO conversion. In the smart design, CdS nanoparticles are first deposited on the hollow carbon and then selectively coated with ZnIn2S4 outer layers, producing a ternary C/CdS@ZnIn2S4 photocatalyst. The photocatalytic enhancements are attributed to the prominent features and merits of hollow carbon: (i) multiple light reflection and scattering in improving light harvesting; (ii) electron collection behavior in promoting charge separation; (iii) large surface area in increasing CO2 adsorption; (iv) highly active and selective sites for targeted reduction reaction; (v) porous shell in spatially separating reduction and oxidation half reactions; (vi) protective layer in preserving CdS from photocorrosion; and (vii) ideal architecture for the deposition of spatially separated redox cocatalysts. It is expected that the emerging design would be extended to other semiconductor heterojunctions if only the two semiconductors would be integrated into the core–shell nanostructure with a hole-accumulated shell and an electron-accumulated core.