Ag as Cocatalyst and Electron-Hole Medium in CeO₂ QDs/Ag/Ag₂Se Z-scheme Heterojunction Enhanced the Photo-Electrocatalytic Properties of the Photoelectrode

A recyclable photoelectrode with high degradation capability for organic pollutants is crucial for environmental protection and, in this work, a novel CeO₂ quantum dot (QDs)/Ag₂Se Z-scheme photoelectrode boasting increased visible light absorption and fast separation and transfer of photo-induced carriers is prepared and demonstrated. A higher voltage increases the photocurrent and 95.8% of tetracycline (TC) is degraded by 10% CeO₂ QDs/Ag₂Se in 75 minutes. The degradation rate is superior to that achieved by photocatalysis (92.3% of TC in 90 min) or electrocatalysis (27.7% of TC in 90 min). Oxygen vacancies on the CeO₂ QDs advance the separation and transfer of photogenerated carriers at the interfacial region. Free radical capture tests demonstrate that •O₂^-, •OH, and h⁺ are the principal active substances and, by also considering the bandgaps of CeO₂ QDs and Ag₂Se, the photocatalytic mechanism of CeO₂ QDs/Ag₂Se abides by the Z-scheme rather than the traditional heterojunction scheme. A small amount of metallic Ag formed in the photocatalysis process can form a high-speed charge transfer nano channel, which can greatly inhibit the photogenerated carrier recombination, improve the photocatalytic performance, and help form a steady Z-scheme photocatalysis system. This study would lay a foundation for the design of a Z-scheme solar photocatalytic system.