Dechlorination and defluorination capability of sulfidized nanoscale zerovalent iron with suppressed water reactivity

Recently, sulfidation of nanoscale zerovalent iron (S-nZVI) has become a potential remediation technology. However, the impact of sulfidation methods and actual sulfur content ([S/Fe]particle) on the physicochemical properties and the reactivity of S-nZVI remains unknown. Here, we synthesized S-nZVI via one co-sulfidation and three post-sulfidation methods to determine how different sulfur reagents and addition procedures affect the reactivity of S-nZVI for defluorination. The measured S amounts of co-sulfidized S-nZVI and post-sulfidized S-nZVI was much lower than their dose. Different sulfur reagents and sulfidation approach would affect the amount and speciation of sulfur in the particles. Sulfidation of nZVI improved the reactivity for dechlorination (up to 12-fold) and defluorination (up to 3-fold) of florfenicol (FF), but inhibited the reactivity with water (up to 31-fold). Density functional theory calculations showed that sulfidation increases the hydrophobicity of materials, and the amount and nature of sulfur affect the hydrophobicity and the number of blocked H sites. S-nZVI particles with more S2− and S22− species showed faster dechlorination and defluorination of FF. Up to ~ 45% of FF was defluorinated by S-nZVI after 15 days reaction at room temperature and pressure. The [S/Fe]particle and Fe0 content was responsible for the initial and long-term defluorination, respectively. These results suggest that S-nZVI could be a promising agent for defluorination, and the sulfur reagents and sulfidation approach would affect its properties and reactivity.