mZVI-GO composites as high-efficiency persulfate activators for trichloroethylene degradation: Unraveling dual radical/nonradical pathways and a sequential system boosting mineralization.

Trichloroethylene (TCE) is a prevalent chlorinated solvent frequently detected in groundwater, necessitating the development of robust remediation strategies. Although microscale zero-valent iron (mZVI) has been extensively used, its effectiveness is hindered by particle agglomeration, surface passivation, and low electron transfer. In this study, ball-milled graphene oxide-supported microscale zero-valent iron (mZVI-GO) was synthesized and applied to activate persulfate (PS) for TCE degradation. A two-stage reduction-oxidation sequential system was then constructed to achieve deep dechlorination and mineralization. Results showed that mZVI-GO exhibited excellent catalytic performance, achieving nearly 99% TCE removal within 60 min, with a pseudo-first-order rate constant 22 times higher than that of pure mZVI. The system maintained high reactivity over a wide pH range (3-9) and showed good resistance to groundwater matrices (HCO3-, NO3-, Mg2+, and Cu2+). Mechanistic investigations revealed that TCE degradation was dominated by a dual-pathway including active species (SO4·-, ·OH, O2·-, and 1O2), non-radical interfacial electron transfer, while Fe2+/Fe3+ cycling and surface hydroxyl groups accelerated PS activation. Notably, the reduction-oxidation sequential system enhanced total organic carbon (TOC) removal from 50.5% to 61.7% and completely eliminated toxic vinyl chloride intermediates. This work provides an efficient and green strategy for enhanced degradation and deep mineralization of TCE-contaminated groundwater.