The effects of organic acids on hexavalent chromium (Cr(VI)) removal by reduced iron-based materials have been extensively studied. Nevertheless, the promotion mechanism from the perspective of the electron transfer process is still unclear. Herein, sulfidated nanoscale zero-valent iron (S-nZVI) and the selected organic acids, citric acid (containing both -OH and −COOH groups) and oxalic acid (containing only −COOH groups), showed significant synergistic promotion effects in Cr(VI) removal. The FeS and FeS₂ on S-nZVI surface could enhance the Cr(VI) reduction as the reductive entity and electron conductor. Furthermore, even though the reactivity of FeS with Cr(VI) is higher than that with FeS₂, the Cr(VI) removal efficiency by FeS₂ was much higher than that by FeS with organic acids. Under neutral and alkaline conditions (pH 6.0-8.0), organic acids promoted the diffusion, adsorption and complexation of Cr(VI) on S-nZVI surface, thus enhancing the electron selectivity towards Cr(VI). However, when the solution pH changed to acidic conditions (pH 4.0), organic acids facilitated the dissolution of Fe(II) ions from S-nZVI and enhanced the electron utilization towards Cr(VI) via the fast Fe(III) reduction process. This study provided a new insight into the Cr(VI) removal, which was beneficial to understand the application boundaries of S-nZVI for Cr(VI) remediation.

有机酸对还原铁基材料去除六价铬 (Cr(VI)) 的影响已被广泛研究。尽管如此，从电子转移过程的角度来看，促进机制仍不清楚。在此，硫化纳米级零价铁 (S-nZVI) 和选定的有机酸柠檬酸（同时含有 -OH 和 -COOH 基团）和草酸（仅含有 -COOH 基团）在 Cr(六）去除。S-nZVI表面上的FeS和FeS ₂作为还原实体和电子导体可以增强Cr(VI)的还原。此外，尽管 FeS 与 Cr(VI) 的反应性高于与 FeS _{2的反应性，但 FeS 2}的 Cr(VI) 去除效率远高于 FeS 与有机酸的比值。在中性和碱性条件下(pH 6.0-8.0)，有机酸促进了Cr(VI)在S-nZVI表面的扩散、吸附和络合，从而增强了对Cr(VI)的电子选择性。然而，当溶液 pH 值变为酸性条件（pH 4.0）时，有机酸促进了 Fe(II) 离子从 S-nZVI 中的溶解，并通过快速 Fe(III) 还原过程增强了对 Cr(VI) 的电子利用。本研究提供了对 Cr(VI) 去除的新见解，有助于了解 S-nZVI 在 Cr(VI) 修复中的应用范围。