Mechanistic role of nitrate anion in TCE dechlorination by ball milled ZVI and sulfidated ZVI: Experimental investigation and theoretical analysis

Recent Advances in Sulfidated Zerovalent Iron for Contaminant Transformation

“…Xu et al found that the iron (Fe 2+ , Fe 3+ ) and sulfur precursors (Na 2 S 2 O 4 , Na 2 S, and K 2 S 6 ) used for synthesis significantly affect the performance of nZVI and S-nZVI for the degradation of TCE, which may contribute to the large variability in reactivity observed among different studies. In addition, ball milling ,− or post synthesis with elemental sulfur seems to be superior sulfidation methods for the degradation of TCE with reported R values larger than 100, albeit with limited data available.…”

“…This may explain the lack of correlation of R with the optimal [S/Fe] dosed of S-(n)­ZVI obtained from the two-step method where relatively limited sulfur loading on the particle is achievable, but significant correlation of R with the optimal [S/Fe] dosed is found for those from one-step synthesis using Na 2 S 2 O 4 ( p < 0.05) where higher extent of sulfur loading is observed (SI Figure S2). Complete transformation of S 0 to FeS was observed during sulfidation of mZVI by ball milling and two-step sulfidation of mZVI with S 0 (i.e., [S/Fe] dosed = [S/Fe] particle = 0.1), ,,− which could partially explain its superior performance for the degradation of TCE (Figure A), because the reported optimal [S/Fe] dosed values from aqueous sulfidation are typically less than 0.1, resulting in even smaller [S/Fe] particle (SI Table S1). Thus, further optimization of S-(n)­ZVI should aim to incorporate higher amount of sulfur or increase the sulfidation ratio in the particle phase to maximize its reactivity for contaminant transformation.…”

“…Precipitation of Fe x S y , especially FeS 2 , after sulfidation increases the hydrophobicity of (n)­ZVI, which makes the reactions with hydrophilic molecules (e.g., H 2 O, NO 3 – ) less favorable as shown experimentally by contact angle analysis and theoretically by DFT calculations, ,,,,,, resulting in improved degradation of hydrophobic TCE. ,, The increased hydrophobicity of S-nZVI has also been shown to be the main reason for the substantially reduced degradation of hydrophilic chloramphenicol (indicated by the octanol–water partition coefficient, log K ow = 0.37) and the increased degradation of the more hydrophobic florfenicol (log K ow = 1.14) compared to nZVI . But the significance of surface hydrophobicity or its contribution to the overall reactivity of S-(n)­ZVI for the transformation of contaminant is still unclear and would likely vary for different type of contaminants.…”

“…161 Both positive and negative effects of common anions in groundwater, including NO 3 − , Cl − , HCO 3 − , CO 3 2− , SO 4 2− , PO 4 3− , and HPO 4 2− , have been observed for the degradation of TCE by S-(n)ZVI, but not to large extent. 73,130,131,162 contaminants other than CHCs under both anoxic and oxic conditions (SI Table S5), which is attributed to the blocking of reactive surface sites by NOM limiting attachment of target compounds. 124 NOM, such as humic acid and rhamonolipid, has been reported to be extensively sorbed to the surface of nZVI, S-nZVI, and Pd-nZVI.…”

Advance of Sulfidated Nanoscale Zero-Valent Iron: Synthesis, Properties and Environmental Application

“…其中天然有机物如腐殖酸等会抑制降解反 应, 这主要是由于这些物质附着于界面上从而屏蔽了用 于吸附和去除目标污染物的活性反应位点 [66] . [58,[67][68][69] . 对于水体中共存的其他重金属离子, 其对降 解反应的影响取决于其与 Fe 0 之间的相互作用形式.…”