Deciphering the Role of Heavy Metals in Zero-Valent Iron-Driven Dechlorination of PVC Microplastics under Mild Condition

Traditional nanoscale zerovalent iron (nZVI) plays a crucial role in combating solid emerging pollutants. This study demonstrates that nZVI can effectively facilitate the aging and dechlorination of polyvinyl chloride (PVC) microplastics under mild anaerobic conditions. The effects of common heavy metals on the dechlorination aging process showed a dechlorination efficiency ranking of Ni > Cu > Co > Cr. Ni2+ and Cu2+ promote electron transfer and the formation of active iron phases by generating active metallic sites, while the catalytic efficiency of Cu is regulated by the redox cycle between Cu+ and Cu2+. In contrast, Cr6+ significantly inhibits dechlorination due to the formation of passivation layers. Electron transfer capacity was identified as the critical driving force for dechlorination, with Ni2+ exhibiting the highest electron donor and acceptor capacity. The dechlorination process was accompanied by C-Cl bond cleavage and the formation of C═C groups, indicating that chain scission and carbon backbone rearrangement are key reactions. However, the sequence of bond cleavage and formation varied among different metals. Additionally, in high-efficiency aging systems, more short-chain compounds were produced alongside long-chain compounds, indicating that synergistic effects between metals and nZVI promoted the molecular transformation of PVC chains.