Degradation of Chloroform by Zerovalent Iron: Effects of Mechanochemical Sulfidation and Nitridation on the Kinetics and Mechanism

Chloroform(CF) is a widely used chemical reagent and disinfectantand a probable human carcinogen. The extensive literature on halocarbonreduction with zerovalent iron (ZVI) shows that transformation ofCF is slow, even with nano, bimetallic, sulfidated, and other modifiedforms of ZVI. In this study, an alternative method of ZVI modification involvingsimultaneous sulfidation and nitridation through mechanochemical ballmilling was developed and shown to give improved degradationof CF (i.e., higher degradation rate and inhibited H-2 evolutionreaction). The composite material (denoted as S-N(C)-ZVI)gave synergistic effects of nitridation and sulfidation on CF degradation.A complete chemical reaction network (CRN) analysis of CF degradationsuggests that O-nucleophile-mediated transformation pathways may bethe main route for the formation of the terminal nonchlorinated products(formate, CO, and glycolic polymers) that have been used to explainthe undetected products needed for mass balance. Material characterizationsof the ZVI recovered after batch experiments showed that sulfidationand nitridation promoted the formation of Fe3O4 on the S-N(C)-ZVI particles, and the effect of agingon CF degradation rates was minor for S-N(C)-ZVI. Thesynergistic benefits of sulfidation and nitridation on CF degradationwere also observed in experiments performed with groundwater. Nitridated and sulfidated of zerovalentiron (ZVI) altersthe kinetics and mechanisms of chloroform degradation in ways thatare largely beneficial for water treatment.