Key Laboratory for City Cluster Environmental Safety and Green Development of the Ministry of Education, School of Ecology, Environment and Resources, Guangdong University of Technology, Guangzhou 510006, China; Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou 511458, China.
Key Laboratory for City Cluster Environmental Safety and Green Development of the Ministry of Education, School of Ecology, Environment and Resources, Guangdong University of Technology, Guangzhou 510006, China; Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou 511458, China.
Water Res. 2022 Sep 1;223:119014. doi: 10.1016/j.watres.2022.119014. Epub 2022 Aug 22.
Multiple reactive intermediates have been proposed to be involved in peroxydisulfate (PDS) activation by zerovalent iron (ZVI), including sulfate radical (SO) produced via iron-oxide shell mediated electron transfer, ferryl ion species (Fe(IV)) formed from Fe(II)-PDS interaction, and hydroxyl radical (OH) generated by ZVI aerobic oxygenation. In this study, evolution of the relative role of these intermediates in microscale and nanoscale ZVI (mZVI vs. nZVI) activated PDS processes is comparatively investigated by using a methyl phenyl sulfoxide (PMSO) probe that selectively reacts with Fe(IV) to produce methyl phenyl sulfone (PMSO). Interestingly, during PMSO transformation by mZVI/PDS process, yields of PMSO (η(PMSO)) exhibit three-stage behavior that they first increase to a maximum (∼80% but lower than 100%) (Stage I) and then plateau for a period (Stage II) followed by a decrease phase (Stage III). Accordingly, the relative role of Fe(IV) in PMSO transformation is unceasingly improved in Stage I and subsequently reaches equilibrium with that of free radicals in Stage II, while it finally decreases in Stage III. Similar η(PMSO) evolution trends are obtained in nZVI/PDS process, except that the η(PMSO) increase in Stage I is negligible, possibly due to the exceptional fast nZVI dissolution. It was further clarified by tert-butyl alcohol scavenging assay that, in addition to Fe(IV), the free radical involved in Stages I and II is SO, while OH was dominant in Stage III. Moreover, studies on O effect reveal that ZVI aerobic oxygenation participates in mZVI corrosion during the entire process, while it is only involved in nZVI corrosion when PDS content is reduced to a low concentration, indicating that the reactivities of PDS and O are similar in mZVI corrosion, but differ greatly in nZVI corrosion. Additionally, effects of reactant dose and pH on η(PMSO) evolution are also explored. Dynamics of the relative role of different reactive oxidants should be taken into account in further applications of ZVI/PDS in situ chemical remediation technology considering their different chemistries.
多种活性中间体被认为参与了零价铁（ZVI）活化过二硫酸盐（PDS）的过程，包括通过氧化铁壳介导的电子转移产生的硫酸根自由基（SO）、Fe(II)-PDS 相互作用形成的高铁离子物种（Fe(IV)）以及 ZVI 有氧氧化产生的羟基自由基（OH）。在这项研究中，通过使用对 Fe(IV)具有选择性反应性的甲基苯基砜（PMSO）探针，比较研究了这些中间体在微尺度和纳米尺度 ZVI（mZVI 与 nZVI）活化 PDS 过程中的相对作用的演变。有趣的是，在 mZVI/PDS 过程中，PMSO 的转化（η（PMSO））表现出三阶段行为，即首先增加到最大值（约 80%但低于 100%）（阶段 I），然后在一段时间内达到平台（阶段 II），随后进入下降阶段（阶段 III）。因此，在阶段 I 中，Fe(IV)在 PMSO 转化中的相对作用不断提高，随后在阶段 II 中与自由基达到平衡，而在阶段 III 中最终降低。在 nZVI/PDS 过程中也得到了类似的 η（PMSO）演变趋势，只是在阶段 I 中 η（PMSO）的增加可以忽略不计，这可能是由于 nZVI 的异常快速溶解。通过叔丁醇清除试验进一步澄清，除了 Fe(IV)之外，阶段 I 和 II 中涉及的自由基是 SO，而 OH 在阶段 III 中占主导地位。此外，对 O 效应的研究表明，ZVI 有氧氧化在整个过程中参与了 mZVI 的腐蚀，而当 PDS 含量降低到低浓度时，它仅参与了 nZVI 的腐蚀，这表明在 mZVI 腐蚀中，PDS 和 O 的反应性相似，但在 nZVI 腐蚀中差异很大。此外，还探索了反应物剂量和 pH 对 η（PMSO）演变的影响。考虑到 ZVI/PDS 原位化学修复技术中不同氧化剂的化学性质不同，应考虑不同活性氧化剂相对作用的动力学，以进一步应用于该技术。
