Designs of composite photocatalysts for their enhanced performance based on photoinduced charge transfer

Abstract

The author and coworkers focused on the fabrication of composite photocatalysts and charge transfer between composite constituents for increased activity and sensitivity to visible light, aiming at developing materials for environmental preservation through the oxidative decomposition of organic pollutants and clean energy production through water splitting for hydrogen generation. Cu²⁺ ion-grafted titanium dioxide (TiO₂) was designed on the basis of visible-light-induced interfacial charge transfer from the valence band (VB) of TiO₂ to Cu²⁺, generating high oxidative decomposition activity owing to the utilization of photogenerated holes in the VB of TiO₂. Cu⁺ produced by electron injection was converted back to Cu²⁺ by oxygen (O₂) reduction through multi-electron O₂ reduction reaction. As for water splitting, zinc rhodium oxide (ZnRh₂O₄) and bismuth vanadate (Bi₄V₂O₁₁) as H₂ and O₂ evolution photocatalysts, respectively, were connected with silver (Ag), acting as a solid-state electron mediator, to prepare a composite photocatalyst that is sensitive to red light. The key function of the heterojunction photocatalyst is the transfer of photoexcited electrons from the conduction band (CB) of Bi₄V₂O₁₁ to the VB of ZnRh₂O₄ via Ag. Thus, the photoexcited electrons in the CB of ZnRh₂O₄ and the holes in the VB of Bi₄V₂O₁₁ effectively reduced and oxidized water, respectively, thereby splitting water and liberating H₂ and O₂ at a stoichiometric ratio.