Photochemical behavior of ferrihydrite-oxalate system: Interfacial reaction mechanism and charge transfer process
Photochemical behavior of ferrihydrite-oxalate system: Interfacial reaction mechanism and charge transfer process
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水铁矿-草酸盐体系的光化学行为：界面反应机理和电荷转移过程
DOI：
10.1016/j.watres.2019.04.055
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发表时间：
2019
期刊：
影响因子：
12.8
通讯作者：
Zhang Lizhi
中科院分区：
文献类型：
--
作者：
Xu Tianyuan;Zhu Runliang;Shang Huan;Xia Yabei;Liu Xiao;Zhang Lizhi
天然铁（氢）氧化物和草酸的非均相光化学反应在有机污染物降解应用中引起了广泛的科学关注。然而，由于复杂的铁循环和活性氧（ROS）的产生，反应机理仍然不清楚。采用原位衰减全反射-傅里叶变换红外光谱法研究草酸在水铁矿表面的吸附过程及光化学行为。从电荷转移过程的角度，详细阐述了一个全面的反应机制，包括非均相铁循环和活性氧的产生。我们发现，草酸首先吸附在水铁矿表面的单核双齿结合几何。有趣的是，在可见光照射下，在水铁矿表面的单核双齿配合物是稳定的。随后，整个络合物以Fe（C2 O 4）+的形式通过非还原溶解离开水铁矿表面。在溶液中，Fe（C2 O 4）+络合物会迅速转化为Fe（C2 O 4）2−络合物。在可见光照射下，Fe（C2 O 4）2−络合物光解产生的电子与O2反应生成O2·−/·OOH。同时，Fe（III）被还原为Fe（II）。最后，生成的O2·−/·OOH可以与Fe（II）一步反应生成·OH，比以H2 O2为中间体的两步反应具有更高的·OH生成效率。该研究有助于我们理解铁矾-草酸体系的原位光化学反应机理，为有效利用自然环境中广泛存在的铁（氢）氧化物和有机酸开发水处理工程系统提供指导。
Heterogeneous photochemical reactions associated with natural iron (hydr)oxides and oxalic acid have attracted a great deal of scientific attention in the application of organic pollutants degradation. However, the reaction mechanism is still unclear due to the complicated iron cycles and reactive oxygen species (ROS) generation. In this study, thein situattenuated total reflectance-Fourier transform infrared spectroscopy was implemented to investigate the adsorption process and photochemical behavior of oxalic acid on the surface of ferrihydrite. A comprehensive reaction mechanism from the perspective of charge transfer process, including homogeneous-heterogeneous iron cycling and ROS generation, was illustrated in detail. We found that oxalic acid was first adsorbed on the surface of ferrihydrite with a mononuclear bidentate binding geometry. Interestingly, this mononuclear bidentate complex on the surface of ferrihydrite was stable under visible light irradiation. Subsequently, the whole complex departed from ferrihydrite surface through non-reduction dissolution with the form of Fe(C2O4)+. In the solution, the Fe(C2O4)+complexes would quickly convert to Fe(C2O4)2−complexes. Under visible light irradiation, the electrons generated from the photolysis of Fe(C2O4)2−complex reacted with O2to form O2•−/•OOH. Meanwhile, Fe(III) was reduced to Fe(II). Finally, the produced O2•−/•OOH could react with Fe(II) through a one-step way to generate •OH, which possessed higher •OH formation efficiency than that through the two-step way of H2O2as the intermediates. This study helps us with understanding ofin-situphotochemical reaction mechanism of ferrihydrite-oxalic acid system, and also provides guidance to effectively utilize widespread iron (hydr)oxides and organic acids in natural environment to develop engineered systems for water treatment.