Heterogeneous Catalytic Reactions Of Phenolic Compounds Mediated By Fe³⁺-Montmorillonite

Montmorillonite,a widely distributed clay mineral in the natural environment,has been considered as an important factor in affecting the persistence,migration,and transformation of organic pollutants in the environment in consideration of its unique layered structure,high swelling capacity,large surface area,and strong cation exchange capacity.Transition metals saturated montmorillonite can dramatically enhance the reactivity of montmorillonite,which has attracted extensive attention.Phenolics are a class of aromatic compounds with the substitution of the hydroxy group on the benzene ring,which are widely used in industrial production and human life along with their different derivatives.Studies demonstrated that phenolics are easily losing electrons to form radicals,especially in the presence of various natural minerals.Thus,the aim of this study is to explore the heterogeneous reactions of several representative phenolics with Fe3+-montmorillonite in both gas and liquid phase reaction system.In view that mineral dusts often contain a high amount of Fe3+-montmorillonite,the interactions of Fe3+-montmorillonite with volatile organic pollutants in the atmosphere are highly possible.Thus we constructed a reactor in which Fe3+-montmorillonite particles can directly interact with gaseous 2-chlorophenol,the reaction products and the toxicity of the reacted clay to human lung cell were investigated.Subsequently,Fe3+-montmorillonite was used to react with acetaminophen in aqueous solution to explore the potential solid-liquid heterogenous reactions mediated by clay mineral.Finally,Fe3+-montmorillonite catalyzed the photodegradation of 2,4-dinitrophenol in the presence of mineral salts were systematically examined as well.Overall,the results obtained in this study demonstrate that Fe3+-montmorillonite mediated reactions with phenolic pollutants should be incorporated into the risk assessment for accurate evaluation of environmental risks of phenolics.The main research contents and the corresponding results are as follows:(1)The wide usage of acetaminophen as human medicine has resulted in its ubiquitous occurrence in various environmental compartments.In this study,oxidative coupling of acetaminophen in bulk solution mediated by Fe3+-montmorillonite was observed under different environmental conditions.In the absence of natural phenolic acids,acetaminophen could be fully eliminated from the solution within 72 h at pH 3.5,acetaminophen dimer was identified as the major reaction product.Reduction of montmorillonite associated Fe3+coupled with the oxidation of acetaminophen was considered as the main mechanism for acetaminophen transformation on Fe3+-montmorillonite.The clay associated Fe3+showed higher reactivity than Fe3+in solution due to the strong complexation between surface Fe3+and acetaminophen.The cross-coupling reactiol between acetaminophen and phenolic acids was also observed when phenolic acids were present in the system.While with the increase of phenolic acid concentration,the competition for the reactive sites between acetaminophen and phenolic acids significantly suppressed acetaminophen removal.(2)2,4-dinitrophenol is a common persistent organic pollutant in the environment.In this part,the interaction mechanism between Fe3+-montmorillonite and a 2,4-dinitrophenol solution containing high concentrations of halid salts under nature light irradiation condition was investigated.Results show that although 2,4-dinitrophenol is relatively stable in the presence of a certain amount of Fe3-montmorillonite alone,the co-existence of Fe3+-montmorillonite and NaCl can significantly enhance the 2,4-dinitrophenol removal.Increased 2,4-dinitrophenol removal rate in the presence of Fe3+-montmorillonite and NaCl can be described as the cation exchange process occurred between the clay associated ferric and the sodium ions lead to the release of free ferric ion into the solution,then the light irradiated the free ferric ion in the solution or the Fe3+-montmorillonite surface absorbed ferric to induce the production of hydroxyl radicals(·OH),which can highly destroy 2,4-dinitrophenol molecule.Otherwise,the reaction of certain halide ions with produced-OH to create reactive halide radicals,which also promote the removal of 2,4-dinitrophenol.(3)The interactions of gaseous 2-chlorophenol with Fe3+-montmorillonite particles in a gas-solid system was investigated to simulate the reactions of mineral dusts with volatile organic pollutants in the atmosphere.Results suggested that Fe3+-montmorillonite mediated the dimerization of gaseous 2-chlorophenol to form hydroxylated polychlorinated biphenyls,hydroxylated polychlorinated diphenyl ethers,and hydroxylated polychlorinated dibenzofurans.The toxicity of Fe3+-montmorillonite particles to A549 human lung epithelial cells before and after interaction with 2-chlorophenol was examined to explore their adverse impact on human health.Based on cell morphological analysis,cytotoxicity tests and Fourier-transform infrared imaging spectra,surface-catalyzed reactions of Fe3+-montmorillonite with 2-chlorophenol increased the toxicity of montmorillonite particle on A549 cells.This was supported by increased cellular membrane permeability,the release of extracellular lactate dehydrogenase,and cell damages on cellular DNA,proteins and lipids.