Properties and reactivity of sulfidized nanoscale zero-valent iron prepared with different borohydride amounts

• Published in: Environmental science. Nano 2021-09, Vol.8 (9), p.267-2617
• Main Authors: Cao, Zhen, Li, Hao, Zhang, Shuangyu, Hu, Yunxuan, Xu, Jiang, Xu, Xinhua
• Format: Article
• Language: English
• Subjects: Dechlorination; Electron transfer; Electrons; Iron; Lattice parameters; Liquid phases; Oxidoreductions; Physicochemical processes; Physicochemical properties; Reactivity; Reducing agents; Selectivity; Solvents; Speciation; Trichloroethene; Trichloroethylene
• ISSN: 2051-8153; 2051-8161
• DOI: 10.1039/d1en00364j

The liquid-phase reduction method with NaBH 4 as the reductant is the most widely used method for sulfidized nanoscale zero-valent iron (SNZVI) synthesis. However, it is unclear how the reductant amount ( e.g. , NaBH 4 /Fe ratio) affects the physicochemical properties ( i.e. Fe 0 and S content, surface S speciation, and lattice constant of the Fe BCC structure) and reactivity of SNZVI. Herein, we synthesized SNZVI with different NaBH 4 /Fe ratios to assess how the NaBH 4 /Fe ratio affects their properties, and how these properties correlated to the reactivity and selectivity. The S/Fe molar ratio in the particles of SNZVI decreased from 0.15 to 0.02 when the NaBH 4 /Fe ratio increased from 1.5 to 5, respectively; meanwhile, the yield of SNZVI increased from 20% to 97%. The Fe 0 content and the surface S 2− /S 2 2− molar ratio ([S 2− /S 2 2− ] surface ) increased with the increase of the NaBH 4 /Fe ratio, which enhanced the electron transfer of SNZVI. The trichloroethylene reactivity increased ∼8.5-fold when the [S 2− /S 2 2− ] surface of SNZVI increased from 0.85 to 1.62, while the selectivity decreased from 82.8% to 64.4% accordingly, indicating that [S 2− /S 2 2− ] surface could be an indicator for predicting the reactivity and selectivity of SNZVI. These results indicate that the NaBH 4 /Fe ratio is a possible reason for the lab-to-lab variability of SNZVI reactivity. A higher NaBH 4 /Fe ratio was favorable for the TCE dechlorination reaction while a lower NaBH 4 /Fe ratio could enhance the electron selectivity. A higher NaBH 4 /Fe ratio was favorable for the TCE dechlorination reaction while a lower NaBH 4 /Fe ratio could enhance the electron selectivity.