Application of SO42–/Fe2O3-CuO solid superacid materials in cyclic compounds from wastewater: Performance and mechanism

In wastewater treatment, the degradation of refractory cyclic compounds by catalytic ozonation using sulfated solid superacid has not been thoroughly investigated. The doped S element alters the electronic activity and drives the ozone oxidation of recalcitrant organic pollutants, potentially leading to an increase in catalytic efficiency. This study aimed to develop a novel iron-copper sulfate (SO42–/Fe2O3-CuO) solid superacid composite to strengthen catalytic reactions. According to the characterization results, the embedding of SO42– enhanced the electron transfer inside the material, leading to more Lewis acid sites, which facilitated the catalytic decomposition of O3. The catalytic degradation and reaction kinetics experiments on quinoline verified the superior catalytic performance of the SO42–/Fe2O3-CuO system compared to other systems. Fluorescence, UV–Vis spectrophotometry, and EPR experiments demonstrated that the hydroxyl radicals (OH), superoxide radicals (O2−), and singlet oxygen (1O2) were generated in the SO42–/Fe2O3-CuO system, and their presence accelerated the redox cycling of Fe(III)/Fe(II) and Cu(II)/Cu(I). In addition, the possible degradation pathways of quinoline were verified by density functional theory (DFT) calculations, and the toxicity of intermediates was assessed by quantitative structure–activity relationship (QSAR) analysis. Finally, the applicability of the SO42–/Fe2O3-CuO catalytic system in bio-treated coking wastewater (BTCW) was validated. GC–MS experiments further confirmed that it was mainly the cyclic compounds that contributed to the removal rate during the catalytic process. In summary, this study demonstrated the significant potential of the SO42–/Fe2O3-CuO catalytic system in degrading refractory cyclic compounds, providing valuable technical support for the field of wastewater treatment.