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MnO2 nanozyme-driven polymerization and decomposition mechanisms of 17β-estradiol: Influence of humic acid

Author:
Sun, Kai, Liu, Qingzhu, Li, Shunyao, Qi, Yongbo, Si, Youbin
Source:
Journal of hazardous materials 2020 v.393 pp. 122393
ISSN:
0304-3894
Subject:
active sites, carbon cycle, catalytic activity, enzymes, estradiol, estrone, humic acids, hydroxylation, manganese dioxide, nanomaterials, oxidation, pH, polymerization, polymers
Abstract:
Nanozymes, which display the bifunctional properties of nanomaterials and natural enzymes, are useful tools for environmental remediation. In this research, nano-MnO₂ was selected for its intrinsic enzyme-like activity to remove 17β-estradiol (E2). Results indicated that nano-MnO₂ exhibited laccase-like activity (7.22 U·mg⁻¹) and removed 97.3 % of E2 at pH 6. Humic acid (HA) impeded E2 removal (only 72.4 %) by competing with E2 for the catalytic sites of the MnO₂ nanozyme surface, and there was a good linear correlation between the kinetic constants and HA concentrations (R² = 0.9489). Notably, the phenolic −OH of E2 interacted with HA to yield various polymeric products via radical-driven covalent coupling, resulting in ablation of phenolic −OH but increase of ether groups in the polymeric structure. Intermediate products, including estrone, E2 homo-/hetero-oligomers, E2 hydroxylated and quinone-like products, as well as aromatic ring-opening species, were identified. Interestingly, HA hindered the extent of E2 oxidation, homo-coupling, and decomposition but accelerated E2 and HA hetero-coupling. A reasonable catalytic pathway of E2 and HA involving MnO₂ nanozyme was proposed. These findings provide novel insights into the influence of HA on MnO₂ nanozyme-driven E2 radical polymerization and decomposition, consequently favoring the ecological water restoration and the global carbon cycle.
Agid:
6851911