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

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.