Enhanced degradation of 1,2,4-trichlorobenzene by Pd-loaded biochar-supported nZVI: Through a reduction-oxidation coupling process.

Advanced oxidation processes (AOPs) utilizing hydrogen peroxide (H2O2) have been extensively employed for the degradation of organic contaminants in groundwater. However, conventional advanced oxidation processes and dechlorination processes often generate toxic by-products. This study innovatively synthesized a Pd-loaded biochar-supported nano zero-valent iron (Pd-nZVI/BC) material and employed it to degrade and even mineralize 1,2,4-TCB through a coupled reductive-oxidative process. During the reduction phase, 1,2,4-TCB was degraded via electrophilic substitution and removed within 12 h. Subsequently, benzene was oxidized within 3.5 h after H2O2 addition. Compared to AOPs, the reduction-oxidation coupling process reduced chlorinated by-product formation significantly, with a dechlorination efficiency 1.51 times higher. Radical scavenging experiments, cyclic voltammetry (CV) curves, and electron spin resonance (ESR) spectroscopy revealed that atomic hydrogen (H∗) and hydroxyl radicals (·OH) were the key reactive species during the reduction and oxidation stages, respectively. Based on density functional theory (DFT) calculations and GC-MS identification of intermediate products, 1,2,4-TCB underwent either simultaneous or sequential dechlorination under anoxic conditions, followed by ring-opening and mineralization in the subsequent aerobic oxidation stage. This study demonstrates that the novel Pd-nZVI/BC material, combined with the reductive-oxidative coupling process, represents a highly promising and effective approach for the complete removal of 1,2,4-TCB from water.