Construction of Z-scheme heterojunction between Zn-doped UiO-66-NH2 and CeO2 towards highly selective photoreduction of CO2 to CH4†
Abstract
Constructing mixed-metal nodes and heterojunctions in UiO-66-NH2 (UNH) are two effective strategies to improve the photocatalytic activity and CH4 selectivity in CO2 photoreduction. In this study, ZnO-loaded CeO2 (CeO2/ZnO) was added to the solvothermal synthesis system of UNH, in order to introduce Zn2+ and nano-CeO2 simultaneously into the UNH framework. The XRD, SEM, FT-IR and XPS characterization results proved that Zn2+ partially replaced Zr4+ to form mixed-metal nodes, and the nano-CeO2 was encapsulated in the UNH framework. The optimal catalyst exhibited a CO yield of 22.52 μmol g−1 h−1 and a CH4 yield of 53.18 μmol g−1 h−1 with a CH4 selectivity of 90.42%. The photoelectrochemical characterization and ESR radical trapping experiment results confirmed that Zn-doped UNH was conducive to the enhancement of light utilization, and the direct Z-scheme heterojunction which was constructed between Zn-doped UNH and CeO2 facilitated the separation and migration of photogenerated carriers. The in situ DRIFTS results indicated that the reaction mechanism of CO2 on the catalyst followed the formaldehyde pathway, and the *HCOO species was the key intermediate for CH4 generation.