Copper and iron co-loaded biochar (CuFe-BC) activated peroxydisulfate (PDS): A novel non-radical system for 4-chlorophenol removal through electron-transfer-induced polymerization.

4-Chlorophenol (4-CP), a widespread and highly toxic pollutant, poses significant environmental risks. In this study, we developed a copper-iron co-loaded biochar (CuFe-BC) as an efficient peroxydisulfate (PDS) activator for 4-CP removal. Under low chemical inputs (0.1 g/L catalyst, PDS/4-CP molar ratio = 5:1), the CuFe-BC/PDS system achieved 93.6% 4-CP removal and 61.1% total organic carbon (TOC) removal within 6 h. Comprehensive mechanism investigations revealed that pollutant removal was primarily governed by an electron transfer pathway (ETP), wherein PDS is activated via outer-sphere interactions with Fe(III)/Cu(II) sites to form a surface CuFe-BC-PDS∗ complex. Simultaneously, synergistic valence cycling between Fe and Cu sustains catalytic activity, while the defective carbon matrix promotes both interfacial adsorption and efficient electron shuttling. Notably, product analyses further demonstrated the formation of phenoxy radicals, which subsequently coupled into polymers, establishing a distinctive polymerization-driven removal pathway. The CuFe-BC/PDS system exhibited robust performance across diverse water matrices and pH conditions, broad-spectrum efficacy toward phenolic contaminants, outstanding reusability, and stable continuous-flow operation. This work establishes a bimetallic-biochar platform that enables non-radical persulfate activation to drive pollutant polymerization, providing a sustainable strategy for treating refractory organic contaminants beyond mineralization-based approaches.