Interfacial reaction between organic acids and iron-containing clay minerals: Hydroxyl radical generation and phenolic compounds degradation

摘要

Reactive oxygen species, especially hydroxyl radicals ('OH), exert a distinguished role in the transformation of contaminants, and their in-situ generation attracts wide attentions in environmental and geochemical areas. The present work explored the potential formation of ·OH during the interactions between iron-containing clay minerals and environmentally prevalent organic acids in dark environments. The results demonstrated that the accumulative OH concentrations were related to the solution pH, the types of clay minerals, and the nature of organic acid species. At pH 5.5,1.2- 152 times of ·OH were generated from the reduction of Na-nontronite-2 (Na-NAu-2) compared with other clay minerals in the presence of ascorbic acid (AA) at 144 h. X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FT1R) analyses indicated that Fe(Ⅲ) was reduced to Fe(Ⅱ) by AA during ·OH formation. Meanwhile, chemical probe tests coupled with quenching experiments confirmed the generation of H_2O_2 and superoxide radical (O_2~(·-)), which participated in the formation of ·OH. The produced ·OH/O_2~(·- ) can transform 68.4%, 86.4%, and 50.1% of phenol, p-nitrophenol, and 2,4-dichlorophenol within 168 h in AA-Na-NAu-2 suspension, respectively. This work provides valuable insights into ·OH production in the mutual interaction between organic acids and iron-bearing clays, which is helpful for the development of a new method for removing organic pollutants from contaminated water and soil environments.