1D rod-like {220}-faceted CeO2/ZnO S-scheme heterojunctions: design, photocatalytic mechanism and DFT calculations

Abstract

Morphological control and heterogeneous combination are two effective strategies to enhance the photodegradation performance of catalysts. In this work, a one-dimensional (1D) rod-like CeO₂/ZnO S-scheme heterojunction was successfully prepared by a facile hydrothermal method. Herein, the CeO₂ nanorod is mainly covered by (220) crystal planes, and the band gap is as low as 2.23 eV. Compared with CeO₂ and ZnO, the formation of the CeO₂/ZnO heterojunction significantly optimizes the photodegradation properties for dyes and antibiotics. By adjusting the loading amount of ZnO nanoparticles on CeO₂ nanorods, the effective active sites and the hydroxyl oxygen content in the CeO₂/ZnO heterojunction can be conveniently regulated. Specifically, the CZ-2 catalyst (CeO₂ : ZnO = 1 : 1) exhibits the best photocatalytic performance, where the degradation efficiencies of Congo red (CR), malachite green (MG) and tetracycline (TC) reach 95.7%, 90.0% and 91.4% at 50 min, respectively. Moreover, the photodegradation rate constants of CZ-2 for CR, MG and TC are 2.7, 5.5 and 2.1 times higher than those of CeO₂. The radical-related experiments, electron spin resonance (ESR) experiments and density functional theory (DFT) calculations verify the formation of an S-scheme heterojunction. The crucial factor in constructing an S-scheme heterojunction instead of a II-scheme configuration is the lower work function of the CeO₂(110) plane than the CeO₂(111) plane, leading to an obvious difference in Fermi levels between CeO₂ and ZnO. The present work provides a feasible solution to the design of efficient S-scheme photocatalysts and the enhancement of the photodegradation ability for dyes and antibiotics.