A comparative study on the physicochemical properties, reactivity and long-term performance of sulfidized nanoscale zerovalent iron synthesized with different kinds of sulfur precursors and procedures in simulated groundwater

There are plentiful ways to synthesize sulfidized nanoscale zerovalent iron (S-nZVI), and this study investigated the influence of sulfur reagents (Na 2 S, Na 2 S 2 O 3 , Na 2 S 2 O 4 ) and sulfidation sequence (co-sulfidation and post-sulfidation method) on the physicochemical properties, reactivity, and long-term performance of S-nZVI in simulated groundwater. The results suggested that the co-sulfidized nZVI (S-nZVI co ) has higher reactivity (∼2-fold) than S-nZVI post due to the stronger electron transfer capacity, deriving from the higher content of Fe 0 and reductive sulfur species. However, during aging, the reactivity of S-nZVI co would be lost more rapidly than S-nZVI post , due to the faster corrosion of Fe 0 and more oxidation of reductive sulfur species. S-nZVI post has the superior long-term performance with the degradation rate of trichloroethylene (TCE) remained at 30%∼60% even after 90 d of aging. Sulfur precursors can control the selectivity of S-nZVI by affecting the sulfur speciation on the particle surface. The proportion of reductive sulfur species on S-nZVI post synthesized by Na 2 S was higher than S-nZVI post synthesized by Na 2 S 2 O 3 or Na 2 S 2 O 4 , resulting in a higher selectivity of the former S-nZVI post than the latter S-nZVI post . In addition, sulfidation procedures and sulfur precursors did not affect the degradation pathway of TCE. Nevertheless, the degradation product distribution can be affected by the different physicochemical transformation of various types of S-nZVI with the aging time. These results indicated that sulfur reagents and sulfidation procedures have crucial effects on the reactivity and long-term performance of S-nZVI, which can be designed for the specific application scenarios.