Sulfide-modified NZVI (S-NZVI): Synthesis, characterization, and reactivity

Abstract

Sulfide-modified nanoscale zerovalent iron (S-NZVI) is attracting more and more attention due to its ease of production, improved reactivity with various pollutants (e.g., trichloroethene, diclofenac, cadmium, chromate), and most importantly, the selectivity to pollutants over water. Although there are some microstructural differences between nanoparticles derived from one-pot and two-step synthesis methods, with optimal S/Fe molar ratio (during preparation), both types of S-NZVI can achieve much higher pollutant removal efficacy than unmodified NZVI. For dechlorination, sulfidation not only inhibits the reaction between Fe (0) and H2O but creates a nucleophilic zone on the particle surface which is favorable for β-elimination. The latter change endows S-NZVI with capacity to degrade particular pollutants which previously cannot be removed by NZVI. For metal ion removal, besides the increased metal removal capacity, the chemical stability of metal-NZVI is also enhanced through sulfidation. Further, sulfidation is beneficial to heterogeneous Fenton-like reactions. With the presence of dissolved oxygen, S-NZVI generates much more hydroxyl radicals for pollutant degradation through a one-electron transfer pathway than NZVI. Although results from lab-scale studies are very encouraging, there is still lack of pilot-scale field test demonstrating the efficacy of S-NZVI in the field. Fate and transport of S-NZVI in subsurface and how S-NZVI (with pollutants) affects microbial community are still largely missing.