The liquid-phase reduction method with NaBH₄ 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., NaBH₄/Fe ratio) affects the physicochemical properties (i.e. Fe⁰ and S content, surface S speciation, and lattice constant of the Fe BCC structure) and reactivity of SNZVI. Herein, we synthesized SNZVI with different NaBH₄/Fe ratios to assess how the NaBH₄/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 NaBH₄/Fe ratio increased from 1.5 to 5, respectively; meanwhile, the yield of SNZVI increased from 20% to 97%. The Fe⁰ content and the surface S²⁻/S₂²⁻ molar ratio ([S²⁻/S₂²⁻]_surface) increased with the increase of the NaBH₄/Fe ratio, which enhanced the electron transfer of SNZVI. The trichloroethylene reactivity increased ∼8.5-fold when the [S²⁻/S₂²⁻]_surface of SNZVI increased from 0.85 to 1.62, while the selectivity decreased from 82.8% to 64.4% accordingly, indicating that [S²⁻/S₂²⁻]_surface could be an indicator for predicting the reactivity and selectivity of SNZVI. These results indicate that the NaBH₄/Fe ratio is a possible reason for the lab-to-lab variability of SNZVI reactivity. A higher NaBH₄/Fe ratio was favorable for the TCE dechlorination reaction while a lower NaBH₄/Fe ratio could enhance the electron selectivity.

中文翻译：

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不同硼氢化物用量制备的硫化纳米零价铁的性质和反应性

以NaBH ₄为还原剂的液相还原法是目前应用最广泛的硫化纳米级零价铁（SNZVI）合成方法。然而，目前还不清楚还原剂的量（例如，NaBH ₄ /Fe 比率）如何影响SNZVI的物理化学性质（即Fe ⁰和 S 含量、表面 S 形态和 Fe BCC 结构的晶格常数）和反应性。在此，我们合成了具有不同 NaBH ₄ /Fe 比率的SNZVI，以评估 NaBH ₄ /Fe 比率如何影响其性质，以及这些性质如何与反应性和选择性相关。当 NaBH 加入时，SNZVI 颗粒中的 S/Fe 摩尔比从 0.15 降低到 0.02₄ /Fe比分别从1.5提高到5；同时，SNZVI的产率从20%提高到97%。Fe ⁰含量和表面S ^2- /S ₂ ^2-摩尔比（[S ^2- /S ₂ ^2- ]_表面）随着NaBH ₄ /Fe 比的增加而增加，这增强了SNZVI 的电子转移。当 SNZVI 的 [S ²⁻ /S ₂ ²⁻ ]_表面从 0.85 增加到 1.62 时，三氯乙烯的反应性增加了~8.5 倍，而选择性相应地从 82.8% 减少到 64.4%，表明 [S ²⁻ /S ₂^2- ]_表面可以作为预测 SNZVI 反应性和选择性的指标。这些结果表明，NaBH ₄ /Fe 比率是 SNZVI 反应性的实验室间可变性的可能原因。较高的 NaBH ₄ /Fe 比有利于 TCE 脱氯反应，而较低的 NaBH ₄ /Fe 比可提高电子选择性。