Optimal Design of Sulfidated Nanoscale Zerovalent Iron for Enhanced Trichloroethene Degradation

Sulfidated nanoscale zerovalent iron (S-nZVI) has the potential to be a cost-effective remediation agent for a wide range of environmental pollutants, including chlorinated solvents. Various synthesis approaches have yielded S-nZVI consisting of a Fe⁰ (or Fe⁰/S⁰) core and FeS shell, which are significantly more reactive to trichloroethene (TCE) than nZVI. However, their reactivity is not as high as palladium-doped nZVI (Pd-nZVI). We synthesized S-nZVI by the co-precipitation of FeS and Fe⁰ by using Na₂S during the borohydride reduction of FeSO₄ (S-nZVI_co). This resulted in FeS structures bridging the nZVI core and the surface, as confirmed by electron microscopy and X-ray analyses. The TCE degradation capacity of up to 0.46 mol TCE/mol Fe⁰ was obtained for S-nZVI_co at a high S loading and was comparable to Pd-nZVI but 60% higher than the currently most reactive S-nZVI, in which FeS only coats the nZVI (S-nZVI_post). The high TCE degradation was due to complete utilization of Fe⁰ (2 e^-/mol Fe⁰) toward the formation of acetylene. Although Pd-nZVI yielded 3 e^-/mol Fe⁰, TCE degradation was comparable because it reduced acetylene further to ethene and ethane. Under Fe⁰-limited conditions, the S-nZVI_co TCE degradation rate was 16 times higher than that of Pd-nZVI (0.5 wt % Pd) and 90 times higher than that of S-nZVI_post.