A photo-switch for peroxydisulfate non-radical/radical activation over layered CuFe oxide: Rational degradation pathway choice for pollutants

Abstract

This work presents a novel strategy for peroxydisulfate (PDS) activation under controlled non-radical/radical mechanism, which is based on a photo-switch over layered CuFe oxide (CFO). The non-radical mechanism is attained by CFO under dark environment, and the radical mechanism is achieved through the visible light irradiation. Electron paramagnetic resonance (EPR) and density functional theory (DFT) studies demonstrate the non-radical activation mechanism is conducted by the polarization effect of CFO to PDS molecule. The radical mechanism could be elucidated by the one-electron reduction of the PDS by excited electrons on conduction band of CFO. Products analyses based on HPLC-MS and Fukui functions suggest that the non-radical degradation pathway could decrease the generation of halide intermediates, whereas the radical pathway may not be observed with this property. Quantitative structure-activity relationships (QSARs) were established between the observed pseudo-first-order rates of various phenolic pollutants and the classical descriptors (i.e., Hammett constant, Pka, EHOMO and ELUMO) in the non-radical and radical systems, respectively, to give instructions of pathway choice for different pollutants. Considering the non-radical/radical pathway both have their own unique strengths (e.g., non-radical pathway has high selectivity to pollutants and high utilization efficiency of oxidant, and radical pathway has considerable degradation rate and strong mineralization ability), these pathways should be chosen wisely for pollutant degradation according to reality conditions.