Construction of a reusable Ce-Fe bimetallic oxide flocculant featuring coordinately unsaturated Fe3+ Lewis acid sites for highly efficient and selective removal of Congo Red

Abstract

Numerous flocculants have been developed to target the removal of Congo Red (CR), a non-degradable and carcinogenic dye. However, challenges such as non-reusability and potential adverse effects limit their widespread application. To address this, a novel cerium oxide-iron (III) oxide (CeO2-Fe2O3, denoted as CeFe) flocculant featuring coordinatively unsaturated Fe3+ Lewis acid sites was synthesized for selective CR removal. Unlike many counterparts, CeFe maintains its efficiency over repeated uses and showcases exceptional stability. The pronounced interaction between CeO2 and Fe2O3 enhances the coordination unsaturation in CeFe, amplifying the electrophilicity of Fe3+ species and creating more Lewis acid sites. According to the results of characterizations and DFT studies, these sites effectively chelate the −NH3 and −N = N − groups on CR molecules, leading to efficient flocculation. Under optimized conditions (pH=6, initial CR concentration of 400 mg/L, and CeFe dosage of 50 mg/L), CeFe achieved a CR removal efficiency of 95.60 ± 0.90%. This research positions CeFe as a promising, reusable flocculant for efficient CR removal, suggesting a new direction in flocculant design.