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The effects of Fe-bearing smectite clays on OH formation and diethyl phthalate degradation with polyphenols and H2O2

Chen, Ning, Fang, Guodong, Liu, Guangxia, Zhou, Dongmei, Gao, Juan, Gu, Cheng
Journal of hazardous materials 2018 v.357 pp. 483-490
anaerobic conditions, cations, clay, diethyl phthalate, electrons, free radicals, hydrogen bonding, hydrogen peroxide, hydroxyl radicals, iron, models, particle size, phthalic acid, polyphenols, smectite
The natural formation of hydroxyl radicals (OH) is important for the attenuation of organic contaminants. In this study, seven model polyphenols were selected to react with four types of smectite clays with varied Fe contents in the presence of H2O2. Diethyl phthalate (DEP) was selected as a model organic contaminant due to its wide distribution in environment. The results show the appearance of Fe-bearing smectite clays can significantly promote ·OH formation with polyphenols and H2O2 under anoxic conditions; clay particle size, the content and location of lattice Fe in smectite clays greatly affect OH formation. Hydrogen bond between phenolic group and smectite surfaces, and cation assisted hydrogen bond between carboxylic group and clay surfaces are important types of complexation. Electrons can be transferred from coordinated polyphenols to structural Fe(III) atoms in tetrahedral layers or at broken edges to form structural Fe(II) and/or semiquinone radicals, both of which can induce H2O2 decomposition to OH. DEP can be degraded by OH attack, and the main products are proposed as phthalic acid, monomethyl phthalate, hydroxyl-diethyl phthalates. Our findings suggest that Fe(III)-bearing smectite clay can be reduced by polyphenol and produce OH in anoxic environments, which can induce organic contaminants transformation.