A Hierarchical Z-Scheme α-Fe₂ O₃ /g-C₃ N₄ Hybrid for Enhanced Photocatalytic CO₂ Reduction.

Abstract

The challenge in the artificial photosynthesis of fossil resources from CO₂ by utilizing solar energy is to achieve stable photocatalysts with effective CO₂ adsorption capacity and high charge-separation efficiency. A hierarchical direct Z-scheme system consisting of urchin-like hematite and carbon nitride provides an enhanced photocatalytic activity of reduction of CO₂ to CO, yielding a CO evolution rate of 27.2 µmol g^-1 h^-1 without cocatalyst and sacrifice reagent, which is >2.2 times higher than that produced by g-C₃ N₄ alone (10.3 µmol g^-1 h^-1 ). The enhanced photocatalytic activity of the Z-scheme hybrid material can be ascribed to its unique characteristics to accelerate the reduction process, including: (i) 3D hierarchical structure of urchin-like hematite and preferable basic sites which promotes the CO₂ adsorption, and (ii) the unique Z-scheme feature efficiently promotes the separation of the electron-hole pairs and enhances the reducibility of electrons in the conduction band of the g-C₃ N₄ . The origin of such an obvious advantage of the hierarchical Z-scheme is not only explained based on the experimental data but also investigated by modeling CO₂ adsorption and CO adsorption on the three different atomic-scale surfaces via density functional theory calculation. The study creates new opportunities for hierarchical hematite and other metal-oxide-based Z-scheme system for solar fuel generation.