A direct Z-scheme heterojunction with boosted transportation of photogenerated charge carriers for highly efficient photodegradation of PFOA: Reaction kinetics and mechanism

Abstract

Z-scheme heterojunction photocatalyst is expected to boost the efficiency for the removal of refractory perfluorooctanoic (PFOA) because of its high carrier separation efficiency and strong redox ability. Here, a direct Z-scheme heterojunction of core-shell CeO2@NiAl-LDHs has been constructed and a high performance for PFOA photodegradation (90.2 % and 36.1 mg g–1 h–1) was observed. By exploring factors affecting the photodegradation performance, including pH, catalyst dosage, light intensity and reaction time, where the kinetics and thermodynamics of the degradation process were investigated in detail. In addition, the reaction order, activation energy, and the detailed form of the rate equation were obtained. In particular, according to the direction of transporation, quantity and rate of photogenerated electron transfer in the heterojunction, we proved the presence of a built-in electric field (BIEF) and confirmed its promoting on photogenerated carriers and the associated enhanced photocatalytic performance of CeO2@NiAl-LDHs. The boosted electron transfer process arises from the difference in the work function of the two phases that constitute the heterojunction. The efficient degradation of PFOA is a result of the synergistic effect between the reduction and defluorination of PFOA and its fluorine-containing intermediates by electrons and the oxidation of active free radicals (associated with the formation of hot electrons and holes).