Cluster of Interfacial Processes Against Pollution (CIPAP), Department of Environmental Science and Engineering, Fudan University, Shanghai200438, China.
Shanghai Institute of Pollution Control and Ecological Security, Shanghai200092, China.
Environ Sci Technol. 2022 Oct 4;56(19):14188-14197. doi: 10.1021/acs.est.2c04594. Epub 2022 Sep 13.
Fe(II)-catalyzed ferrihydrite transformation under anoxic conditions has been intensively studied, while such mechanisms are insufficient to be applied in oxic environments with depleted Fe(II). Here, we investigated expanded pathways of sunlight-driven ferrihydrite transformation in the presence of dissolved oxygen, without initial addition of dissolved Fe(II). We found that sunlight significantly facilitated the transformation of ferrihydrite to goethite compared to that under dark conditions. Redox active species (hole-electron pairs, reactive radicals, and Fe(II)) were produced from the ferrihydrite interface via the photoinduced electron transfer processes. Experiments with systematically varied wet chemistry conditions probed the relative contributions of three pathways for the production of hydroxyl radicals: (1) oxidation of water (5.0%); (2) reduction of dissolved oxygen (40.9%); and (3) photolysis of Fe(III)-hydroxyl complexes (54.1%). Results also showed superoxide radicals as the main oxidant for Fe(II) reoxidation under acidic conditions, thus promoting the ferrihydrite transformation. The presence of inorganic ions (chloride, sulfate, and nitrate) did not only affect the hydrolysis and precipitation of Fe(III) but also the generation of radicals via photoinduced charge transfer reactions. The involvement of redox active species and the accompanying mineral transformations would exert a profound effect on the fate of multivalent elements and organic contaminants in aquatic environments.
在缺氧条件下，Fe(II)催化的水铁矿转化已得到深入研究，而在 Fe(II)耗尽的有氧环境中，这些机制还不足以应用。在这里，我们研究了在有氧条件下，无需初始添加溶解态 Fe(II)的情况下，太阳光驱动水铁矿转化的扩展途径。我们发现，与黑暗条件相比，太阳光显著促进了水铁矿向针铁矿的转化。氧化还原活性物质（空穴-电子对、反应性自由基和 Fe(II)）通过光诱导电子转移过程从水铁矿界面产生。通过系统改变湿化学条件的实验，探究了三种产生羟基自由基的途径的相对贡献：（1）水的氧化（5.0%）；（2）溶解氧的还原（40.9%）；和（3）Fe(III)-羟基配合物的光解（54.1%）。结果还表明，在酸性条件下，超氧自由基是 Fe(II)再氧化的主要氧化剂，从而促进了水铁矿的转化。无机离子（氯离子、硫酸根离子和硝酸根离子）的存在不仅影响 Fe(III)的水解和沉淀，而且还通过光诱导电荷转移反应产生自由基。氧化还原活性物质的参与以及伴随的矿物转化将对水生环境中多价元素和有机污染物的命运产生深远影响。
