Binding interaction between chlorine and powder activated carbon driving nonradical oxidation toward diclofenac abatement: surface-bound complexes generating on diverse sites performing diverse duties

Abstract

Photolysis of chlorine by UV irradiation is commonly used as an advanced oxidation process for the abatement of micropollutants, but suffers from the energy-extensive consumption and potential risk, e.g., formation of disinfection byproduct and use of fragile mercury-containing lamps. This study demonstrates powder activated carbon (PAC) catalysis-mediated chlorine activation to significantly promote the degradation of diclofenac (DCF), a representative emerging contaminant, via nonradical oxidation pathways, thus reconsidering the interaction between PAC and chlorine in depth which are widely applied in actual water treatment. The chlorine/PAC process produces reactive metastable surface-bound complexes, i.e., PAC-HOCl*, via the cleavage of O–Cl bond in chlorine and formation of C–Cl by interfacial binding interaction, to regulate the charge distribution and electron density configuration. Carbonyl groups and structural defects of PAC are determined as the active sites via functional group derivatization and defect engineering for PAC modification, and performed diverse duties in the chlorine activation, producing PAC-C=O-HOCl* and PAC-D-HOCl*, responsible for the oxidation ability improvement and electron transfer acceleration, respectively. Of particular significance is that the chlorine/PAC process performs high efficiencies in the degradation of diverse micropollutants and is scarcely affected by water matrices, exhibiting a high potential of practical application for the decontamination of emerging micropollutants without the requirement of external energy input.