In this study, we coated a high proton conductive shell on the zero-valent iron (ZVI) surface by mechanically ball-milling ZVI with oxalic acid dihydrate (OX-ZVI), and demonstrated that the generated FeC₂O₄·2H₂O shell dramatically improved the Cr(VI) removal rate of ZVI by about 15-80 times. Owing to a higher proton conductivity of FeC₂O₄·2H₂O shell than that of Fe₂O₃ shell, proton could easily transfer through FeC₂O₄·2H₂O shell into iron core and be reduced to H, accompanying with fast surface-bound Fe²⁺ generation, resulting in high efficiency of Cr(VI) removal in a wide pH range. Meanwhile, the removed Cr(VI) was deposited on OX-ZVI surface in the formation of Fe_xCr_1-x(OH)₃ composites, accompanied by the appearance of typical hollow structure derived from iron core dissolution. This study clarifies the significance of proton transfer on the reactivity of zero-valent iron, and also provides a new strategy to prepare highly active zero-valent iron for Cr(VI) removal.

在这项研究中，我们通过用草酸二水合物（OX-ZVI）机械球磨ZVI，在零价铁（ZVI）表面上涂覆了一个高质子传导壳，并证明了生成的FeC ₂ O ₄ ·2H ₂ O壳显着提高了ZVI的Cr（VI）去除率约15-80倍。由于FeC ₂ O ₄ ·2H ₂ O壳层的质子传导率比Fe ₂ O ₃壳层高，因此质子可以很容易地通过FeC ₂ O ₄ ·2H ₂ O壳层转移到铁核中并还原为H。快速表面结合Fe ²⁺生成，从而在宽的pH范围内高效去除Cr（VI）。同时，去除的Cr（VI）沉积在OX-ZVI表面上，形成Fe _x Cr _1-x（OH）₃复合材料，并伴有典型的由铁芯溶解产生的中空结构。这项研究阐明了质子转移对零价铁反应性的重要性，并提供了一种制备高活性零价铁以去除Cr（VI）的新策略。