Wang Zhenzhen, Jia Xiaolei, Sun Wei, Wang Jianfei, Li Chen, Zhao Qun, Li Yingjie, Tian Senlin
Faculty of Environmental Science and Engineering, Kunming University of Science and Technology, Kunming, Yunnan Province 650500, China.
Faculty of Environmental Science and Engineering, Kunming University of Science and Technology, Kunming, Yunnan Province 650500, China.
Sci Total Environ. 2023 Dec 20;905:167177. doi: 10.1016/j.scitotenv.2023.167177. Epub 2023 Sep 19.
The use of persulfate (PDS) for in-situ chemical oxidation of organic contaminants in soils has garnered significant interest. However, the presence of naturally occurring iron-containing substances and humic acid (HA) in environmental compartments can potentially influence the effectiveness of soil remediation. Thus, this study aimed to investigate the role of key functional groups (adjacent phenolic hydroxyl (Ar-OH) and carboxyl groups (-COOH)) in HA that interact with iron. Modified HAs were used to confirm the significance of these moieties in iron interaction. Additionally, the mechanism by which specific functional groups affect Fe complexation and redox was explored through contaminant degradation experiments, pH-dependent investigations, HA by-products analysis, and theoretical calculations using six specific hydroxybenzoic acids as HA model compounds. The results showed a strong positive correlation between accessible Ar-OH and -COOH groups and Fe/Fe redox. This was attributed to HA undergoing a conversion process to a semiquinone-containing radical form, followed by a quinone-containing intermediate, while Fe acted as an electron shuttle between HA and PDS, with Fe leaching facilitated by generated H ions. Although the stability of HA-Fe complexes with -COOH as the primary binding sites was slightly higher at neutral/alkaline conditions compared to acidic conditions, the buffering properties of the soil and acidification of the PDS solution played a greater role in determining the Ar-OH groups as the primary binding site in most cases. Therefore, the availability of Ar-OH groups on HA created a trade-off between accelerated Fe/Fe redox and quenching reactions. Appropriate HA and iron contents were found to favor PDS activation, while excessive HA could lead to intense competition for reactive oxygen species (ROS), inhibiting pollutant degradation in soil. The findings provide valuable insights into the interaction of HA and Fe-containing substances in persulfate oxidation, offering useful information for the development of in-situ remediation strategies for organic-contaminated soil.
过硫酸盐（PDS）用于土壤中有机污染物的原位化学氧化已引起广泛关注。然而，环境介质中天然存在的含铁物质和腐殖酸（HA）的存在可能会影响土壤修复的效果。因此，本研究旨在探讨HA中与铁相互作用的关键官能团（邻位酚羟基（Ar-OH）和羧基（-COOH））的作用。使用改性HA来证实这些部分在铁相互作用中的重要性。此外，通过污染物降解实验、pH依赖性研究、HA副产物分析以及使用六种特定羟基苯甲酸作为HA模型化合物的理论计算，探索了特定官能团影响铁络合和氧化还原的机制。结果表明，可及的Ar-OH和-COOH基团与Fe/Fe氧化还原之间存在强正相关。这归因于HA经历了向含半醌自由基形式的转化过程，随后是含醌中间体，而Fe作为HA和PDS之间的电子穿梭体，生成的H离子促进了Fe的浸出。尽管以-COOH为主要结合位点的HA-Fe络合物在中性/碱性条件下的稳定性略高于酸性条件，但在大多数情况下，土壤的缓冲特性和PDS溶液的酸化在确定Ar-OH基团为主要结合位点方面发挥了更大作用。因此，HA上Ar-OH基团的可用性在加速Fe/Fe氧化还原和猝灭反应之间产生了权衡。发现适当的HA和铁含量有利于PDS的活化，而过量的HA可能导致对活性氧（ROS）的激烈竞争，抑制土壤中污染物的降解。这些发现为过硫酸盐氧化中HA与含铁物质的相互作用提供了有价值的见解，为有机污染土壤原位修复策略的开发提供了有用信息。
