Comprehensive evaluation and Mechanistic comparison of Cr-Catalyzed homogeneous Fenton-Like reactions for coexisting organics degradation

Chromium, as a widely utilized transition metal, presents wastewater with high toxicity and challenging treatment. To date, there has been limited exploration regarding the application of chromium in homogeneous Fenton-like reactions. This study aims to explore the potential of Cr(VI) and Cr(III) to activate hydrogen peroxide (H₂O₂) and permonosulfate (PMS) for degrading coexisting pollutants in homogeneous solutions. The Cr(VI)/PMS system was found to be the most effective, with a 95.58 % removal efficiency for the azo dye Acid Red 73 (AR73). The Cr(VI)/H₂O₂ system followed with 72.35 %, while the Cr(III)/H₂O₂ and Cr(III)/PMS systems showed lower efficiencies at 25.65 % and 16.95 %, respectively. Various techniques were employed to delve into the mechanisms underlying chromium activation. The results indicate that both Cr(VI) and Cr(III) can activate H₂O₂ to generate hydroxyl radical (HO^•). Moreover, Cr(VI) can activate PMS in the pH range of 3 ∼ 11, producing HO^•, sulfate radical (SO•- 4), and singlet oxygen (¹O₂), while Cr(III) engages in chelation with PMS, causing the reaction to cease. Additionally, this study reveals that the chelating agent EDTA, upon complexing with Cr(III), efficiently activates PMS to generate ¹O₂, and the mechanism behind EDTA-Cr(III) activation of PMS was elucidated through DFT calculations. An integrated evaluation of Cr performance in the Fenton-like reaction provides new research directions for the removal of pollutants from chromium-containing wastewater.