Photodegradation of 2,4-dichlorophenol and rhodamine B over n-type ZnO/p-type BiFeO3 heterojunctions: detailed reaction pathway and mechanism.

The development of new technologies for efficient degradation of pollutant has been an increasing demand in the globe due to the serious environmental issues. Herein, we report n-type ZnO/p-type BiFeO3 composites as highly efficient visible light nanophotocatalysts prepared via a wet chemical solution method. Based on the measurements of •OH-related fluorescence (FL) spectra, photoluminescence (PL) spectra, photoelectrochemical I-V curves, and electrochemical impedance spectra (EIS), it is demonstrated that the photo-induced charge carrier (electron-hole pairs) in the as-prepared n-type ZnO/p-type BiFeO3 composites with proper amount of the coupled ZnO (10% by mass) exhibits high separation compared with the bare BiFeO3 (BFO) nanoparticles. This is well responsible for the superior visible light photocatalytic performance of the composites for 2,4-dichlorophenol (2,4-DCP) and rhodamine B (RhB) degradation. It is confirmed by means of scavenger test and liquid chromatography-tandem mass spectrometry (LC/MS) analysis of the intermediate products that •OH is the pre-dominant oxidant involved in the degradation of 2,4-DCP. A detailed reaction pathway for 2,4-dichlorophenol degradation over the amount-optimized ZnO/BFO composite is proposed mainly based on the LC/MS product ions. This work will provide a feasible route to design and develop BFO-based highly efficient visible light-active photocatalysts for environmental purification and could be extended to other visible light-active semiconductor materials.