The transformation of contaminants by photocatalysts under light illumination has been extensively studied in engineered water systems. However, the interfacial photoreaction mechanism for the reduction of chromium (Cr(VI)) on natural iron (Fe) oxides in acidic and oxic surface waters associated with soil remain unclear. Herein, the photochemical behavior of Cr(VI) and oxalate on lepidocrocite surfaces was investigated to disclose the natural detoxification process of Cr(VI). Kinetic results showed that Cr(VI) was quickly reduced in the system with lepidocrocite and oxalate under light illumination, while no Cr(VI) reduction was observed in the dark. No obvious secondary Fe oxides and Cr-containing precipitates were found, but the newly generated Cr(III) was evenly distributed on the lepidocrocite surface or entered into the lepidocrocite defects. Cr(VI) and oxalate can form ternary complexes with lepidocrocite, and Cr(VI) reduction and the oxidation of oxalate to carbon dioxide occurred simultaneously on the lepidocrocite surface. Amongst the reactions involving lepidocrocite, oxalate, and Cr(VI), the oxidation of oxalate was attributed to reactive oxygen species such as H₂O₂, OH, and ·O₂⁻, while Cr(VI) reduction was mainly caused by photogenerated electrons, CO₂⁻, H₂O₂, Fe(II), and through the direct electron transfer in the Cr(VI)-oxalate complex. The findings of the Cr(VI) molecular-scale photoreduction mechanism on mineral surfaces would have implications for interpreting the natural attenuation of Cr(VI) toxicity in natural surface waters associated with soil.

已在工程水系统中广泛研究了光催化剂在光照下对污染物的转化。然而，在与土壤相关的酸性和含氧地表水中，在天然铁 (Fe) 氧化物上还原铬 (Cr(VI)) 的界面光反应机制仍不清楚。在此，研究了 Cr(VI) 和草酸盐在纤铁矿表面上的光化学行为，以揭示 Cr(VI) 的自然解毒过程。动力学结果表明，在光照条件下，纤铁矿和草酸盐体系中 Cr(VI) 迅速还原，而在黑暗中未观察到 Cr(VI) 还原。未发现明显的二次Fe氧化物和含Cr析出物，但新生成的Cr(III)均匀分布在纤铁矿表面或进入纤铁矿缺陷。Cr(VI)和草酸盐可与纤铁矿形成三元络合物，在纤铁矿表面同时发生Cr(VI)还原和草酸盐氧化成二氧化碳。在涉及纤铁矿、草酸盐和 Cr(VI) 的反应中，草酸盐的氧化归因于活性氧物质，如 H₂ O ₂、OH 和·O ₂ ^-，而 Cr(VI) 的还原主要由光生电子、CO ₂ ^-、H ₂ O ₂、Fe(II) 和通过 Cr(VI) 中的直接电子转移引起)-草酸盐复合物。矿物表面上 Cr(VI) 分子级光还原机制的发现将对解释与土壤相关的天然地表水中 Cr(VI) 毒性的自然衰减产生影响。