Correlating surface chemistry and hydrophobicity of sulfidized nanoscale zerovalent iron with its reactivity and selectivity for denitration and dechlorination

Sulfidized nanoscale zerovalent iron (S-nZVI) has been reported to be highly reactive towards lots of contaminants. However, the effects of surface chemistry evolution (e.g. surface S/Fe) and hydrophobicity on its reactivity and selectivity towards the reduction of different functional groups on contaminants are unclear. Here, the reactivity and electron selectivity of aged nZVI and S-nZVI in water for the denitration of chloramphenicol (CAP) and dechlorination of florfenicol (FF) were investigated. The reactivity of nZVI for the denitration of CAP was greatly inhibited after sulfidation, and the kobs, CAP by nZVI decreased along with the aging time. However, the reactivity of nZVI for the dechlorination of FF was significantly improved after sulfidation, and the kobs, FF by S-nZVI firstly increased then decreased with the aging time, which was correlated well with the evolution of S/Fe molar ratio on the surface. S-nZVI with higher hydrophobicity was proved to be more reactive for the dechlorination of FF but less reactive for the denitration of CAP. Interestingly, the electron efficiencies of CAP denitration by nZVI and FF dechlorination by S-nZVI were both maintained >99% no matter the materials were fresh or aged. These results revealed that the sulfidation would change the physicochemical properties and reactivity of nZVI, and it is of great importance to measure the surface chemical composition and hydrophobicity of S-nZVI and apply the materials with appropriate target contaminants to maximum the electron utilization.