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.