Revelation of ferrate(VI) unimolecular decay under alkaline conditions: Investigation of involvement of Fe(IV) and Fe(V) species
Revelation of ferrate(VI) unimolecular decay under alkaline conditions: Investigation of involvement of Fe(IV) and Fe(V) species
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DOI：
10.1016/j.cej.2020.124134
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发表时间：
2020-05-15
影响因子：
15.1
通讯作者：
Huang, Ching-Hua
中科院分区：
文献类型：
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作者：
Luo, Cong;Feng, Mingbao;Huang, Ching-Hua
需要了解高铁酸盐（VI） (（FeO42-)- o -VI, Fe(VI)）在从酸性到碱性的整个pH范围内的自衰减动力学和机制，以评估Fe（VI）在不同pH值下氧化污染物的能力。对铁（VI）在酸性至中性pH条件下的自腐机理进行了广泛的研究。然而，Fe（VI）在碱性pH（例如，pH 9.0或更高）下的自衰减鲜为人知。本研究对pH为9.0和10.0时Fe（VI）的衰变进行了动力学和建模研究。研究表明，在pH为9.0和10.0时，Fe（VI）的衰变遵循一级动力学（即单分子衰变），而在pH为7.0时，由于Fe（VI）的不同种类（FeO42-和HFeO4-），其顺序改变为3/2级动力学。密度泛函理论（DFT）支持了FeO42-在碱性条件下通过氧偶联（OC）进行二聚化的单分子衰变机制。单体FeO42-的WA之所以被提出，是因为它的激活势垒比OC低。通过Fe(V)和Fe（IV）的动力学模拟，成功预测了不同条件下Fe（VI）的消失和H2O2的生成。FeO42-的衰变与质子化Fe（VI）的二级动力学（H2FeO4和HFeO4-）不同。我们的结果将有助于理解铁（VI）在碱性条件下降解污染物的氧化能力。
The kinetics and mechanisms of self-decay of ferrate(VI) ((FeO42-)-O-VI, Fe(VI)) over the entire pH range from acidic to basic pH range need to be understood to assess the ability of Fe(VI) to oxidize pollutants at different pHs. Mechanism of self-decay of Fe(VI) has been extensively examined under acidic to neutral pH conditions. However, Fe(VI) self-decay at alkaline pH (e.g., pH 9.0 or higher) is poorly understood. This study performed kinetic and modeling studies of the Fe(VI) decay at pH 9.0 and 10.0. Our research reveals that the decay of Fe (VI) follows first-order kinetics (i.e., unimolecular decay) at pH 9.0 and 10.0 and the order changes to 3/2-order at pH 7.0 due to the different species of Fe(VI) (FeO42- versus HFeO4-). Results of unimolecular decay mechanism through water attack (WA) are supported by density functional theory (DFT) calculations, which indicate unfavorable dimerization of FeO42- through oxo-coupling (OC) under alkaline conditions. The WA on the monomeric FeO42- is proposed due to its lower activation barrier compared to OC. Kinetic simulation of Fe(VI) decay involving Fe(V) and Fe(IV) successfully predicts Fe(VI) disappearance and H2O2 generation (a product) under varied conditions. The decay of FeO42- is different from the second-order kinetics of protonated Fe(VI) species (H2FeO4 and HFeO4-). Our results will aid in comprehending oxidation power of Fe(VI) in degrading pollutants under alkaline conditions.