Enhanced reductive degradation of trichloroethylene by ball milled nitridation of bimetallic Ni-ZVI: Combination effect of electron transfer and catalytic hydrogenation

Abstract

The performance optimization of zerovalent iron (ZVI) based materials for reductive dechlorination is critical but remains challenging. Combining the advantages of bimetallic and heteroatomic modification may lead to a novel strategy for reductive dechlorination of chlorinated ethenes (CEs) pollution. In this study, three different types of dual-modified micron ZVI (mZVI) composite particles, namely, pre-bimetallic modified mZVI (Ni/mZVI-N), pre-nitrogen modified mZVI (N/mZVI-Ni), and simultaneously modified mZVI (Ni/N-mZVI), were prepared by adjusting the order of ball milling modification of nickel and melamine, in which ball milling mechanical-chemical interactions contributed to the generation of enriched M-N structures. In terms of combined reactivity and selectivity, Ni/N-mZVI exhibited the best performance, with trichloroethylene (TCE) dechlorination rate (kobs,TCE) and electron efficiency (εe) of 0.14 h−1 and 8.9 %, respectively, which were 10.7 and 7.5 times higher than those of mZVI. The distribution and percentage of degradation products further illustrated the reductive dechlorination of nickel-nitrogen dual-modified mZVI via both electron transfer and atomic hydrogen (H*) pathways. A series of characterization and mechanistic analyses showed that the enhancement of TCE reductive dechlorination performance could be attributed to the combined effect of Fe−N to accelerated electron transfer and Ni-N to enhance catalytic hydrogenation. In addition to decreased H2 accumulation, Ni/N-mZVI reduced leaching ions thus mitigating secondary contamination. This double-modification strategy employed to enhance the optimization of mZVI for groundwater remediation establishes a foundation for ongoing progress in the synthesis of reactive materials.