Co-catalyst free direct Z–scheme photocatalytic system with simultaneous hydrogen evolution and degradation of organic pollutants

Abstract

Photocatalytic hydrogen evolution coupled with simultaneous pollutant degradation is a promising but challenging strategy for both wastewater treatment and renewable energy production. In this work, a series of direct Z-scheme heterostructural catalysts, denoted as CeO2/Cu–I-bpy, were designed and constructed by in-situ synthesizing CeO2 nanoparticles on the surface of a coordinate polymer, named Cu–I-bpy. The simultaneous photocatalytic evolution of hydrogen and photo-degradation of organic pollutants was successfully achieved with this hybrid catalyst, even without any co-catalyst. The hybrid catalyst exhibited a 6.9 folds higher hydrogen evolution efficiency than the corresponding individual photo-reduction catalyst (Cu–I-bpy here), and 2.5 times degradation rate of the corresponding individual photo-oxidation catalyst (CeO2 here), after optimizing the CeO2 loading. After extensively characterized via XRD, XPS, Raman spectroscopy, UV–Vis absorption spectroscopy, SEM, TEM, BET, photo-electrochemical method and photoluminescence, it was found that the hybrid catalysts show higher charge separation and transfer efficiency than corresponding individual CeO2 and Cu–I-bpy. Further mechanism investigation via active species trapping, EPR and electron flow experiments indicates a direct Z-scheme charge transfer mechanism in the CeO2/Cu–I-bpy, which not only boosts the photogenerated electron-hole separation efficiency, but also retains the high reduction and oxidation ability the corresponding individual catalyst for hydrogen evolution and pollutant degradation, respectively. This work demonstrates the possibilities of turning waste water into energy resources using carefully designed photocatalytic systems.