Environment Research Institute, Shandong University, Qingdao 266237, China.
School of Environmental and Materials Engineering, Yantai University, Yantai 264005, China.
J Environ Sci (China). 2022 May;115:392-402. doi: 10.1016/j.jes.2021.08.011. Epub 2021 Aug 27.
Catechol pollutants (CATPs) serving as chelating agents could coordinate with many metal ions to form various CATPs-metal complexes. Little information is available on the effects of complexation of metal ions on CATPs degradation. This work presents a systematical study of •OH-mediated degradation of catechol and catechol-metal complexes over the whole pH range in advanced oxidation processes (AOPs). Results show that the pH-dependent complexation of metal ions (Zn, Cu, Ti and Fe) promotes the deprotonation of catechol under neutral and even acidic conditions. The radical adduct formation (RAF) reactions are both thermodynamically and kinetically favorable for all dissociation and complexation species, and OH/O group-containing C positions are more vulnerable to •OH attack. The kinetic results show that the complexation of the four metal ions offers a wide pH range of effectiveness for catechol degradation. At pH 7, the apparent rate constant (k) values for different systems follow the order of catechol+Ti ≈ catechol+Zn > catechol+Cu > catechol+Fe > catechol. The mechanistic and kinetic results would greatly improve our understanding of the degradation of CATPs-metal and other organics-metal complexes in AOPs. The toxicity assessment indicates that the •OH-based AOPs have the ability for decreasing the toxicity and increasing the biodegradability during the processes of catechol degradation.
儿茶酚污染物 (CATPs) 作为螯合剂可以与许多金属离子配位，形成各种 CATPs-金属配合物。关于金属离子配合对 CATPs 降解的影响，目前的信息还很少。本工作系统研究了•OH 介导的 CATPs 和 CATPs-金属配合物在整个 pH 范围内的降解。结果表明，金属离子（Zn、Cu、Ti 和 Fe）的 pH 依赖性络合作用促进了中性甚至酸性条件下儿茶酚的去质子化。自由基加合物形成（RAF）反应在热力学和动力学上都有利于所有的离解和络合物种，并且含有 OH/O 基团的 C 位更容易受到•OH 的攻击。动力学结果表明，四种金属离子的络合作用为儿茶酚的降解提供了广泛的 pH 有效性范围。在 pH 7 时，不同体系的表观速率常数 (k) 值的顺序为儿茶酚+Ti≈儿茶酚+Zn＞儿茶酚+Cu＞儿茶酚+Fe＞儿茶酚。该研究的机理和动力学结果将极大地提高我们对 AOPs 中 CATPs-金属和其他有机金属配合物降解的理解。毒性评估表明，基于•OH 的 AOPs 具有在儿茶酚降解过程中降低毒性和提高可生物降解性的能力。
