Insight into peroxymonosulfate-assisted photocatalysis over acidified red mud-supported TiO2 composite for highly efficient degradation of metronidazole

An efficient TiO₂/ARM_(2:1) catalyst was prepared by sol-gel method, in which the ratio of TiO₂ to ARM was 2:1, and the prepared TiO₂/ARM_(2:1) catalyst was utilized to activate peroxymonosulfate (PMS) for the degradation of metronidazole (MET). X-ray diffractometry (XRD), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) analyses showed that the pore volume, pore diameter, and specific surface area of RM were significantly increased by acidification. Acidified RM provided more loading space for TiO₂, allowing more TiO₂ to be dispersed on the RM surface and in the pore interstitials. The TiO₂/ARM_(2:1) composite could expose more highly reactive components, thereby increasing the catalytic activity of the catalyst. X-ray photoelectron spectroscopy (XPS) and electrochemical analyses demonstrated the excellent activity of TiO₂/ARM_(2:1) composite in separating and transferring photoinduced electrons and holes. Approximately, 91.0 % of MET (10 mg/L) was decomposed at 60 min under the optimal reaction conditions of the TiO₂/ARM_(2:1) catalyst [TiO₂/ARM_(2:1)] = 0.05 g/L, [PMS] = 3 mM, and the pH of 5.9. The results of the quenching experiments indicated that the •O₂⁻, ¹O₂ and h⁺ were the main reactive species responsible for the degradation of MET in the TiO₂/ARM_(2:1)/PMS/vis system. The possible degradation pathways of MET were proposed through Density-Functional Theory (DFT) calculations and liquid chromatography-mass spectrometry (LC-MS). Results. The prediction results of the Toxicity Evaluation Software Tool (T.E.S.T) suggested that the toxicity of MET was effectively reduced after treatment in the TiO₂/ARM_(2:1)/PMS/vis system. After five cycling experiments, TiO₂/ARM _(2:1) showed excellent stability. This work provided a new perspective on the modification of industrial waste RM applied in the direction of catalysis.