Roles of Catalyst Structure and Gas Surface Reaction in the Generation of Hydroxyl Radicals for Photocatalytic Oxidation

Abstract

Photocatalysis is one of the promising purification technologies for organic degradation due to a potent driving force of hydroxyl radicals (HO• ). Unfortunately, HO• evolution from dissolved oxygen in traditional photocatalysis is a three-electron-reduction process via H2O2 and suffers from the low utilization efficiency of photoexcited electrons. A change of surface processes in direct HO• formation will induce rapid surface redox reactions and improve the utilization of conduction band electrons (CB-e−) for HO• production. In this work, we couple photocatalyst engineering using defect-engineered S-scheme WO3/g-C3N4 nanocomposites with ozonation to analyze the relative contributions of catalyst structure and surface reaction to the improved HO• generation and quantum efficiency. We revealed that the strategies of catalyst engineering via defect structure and S-scheme heterojunction improved CB-e− generation and enrichment but played a minor role in HO• evolution while a change of oxygen to ozone exerted a dominant effect on the surface reaction of HO• evolution pathway into a more efficient single-electron-transfer process. The synergy of catalyst engineering with ozone resulted in a 44-fold increase in rate constant compared with benchmark gC3N4-based photocatalysis and catalytic ozonation. This work advances the mechanistic principles for a kinetic boost in photocatalysis in terms of catalyst design and surface reaction for micropollutant elimination and provides insights into photocatalyst modification and reaction routes in advanced oxidation processes.