Reusable CS-Ca@PEI/CuMnO₂ Hydrogel Beads for Peroxymonosulfate-Activated Degradation of Congo Red

Metal oxides can activate peroxymonosulfate (PMS) for the catalytic degradation of organic dyes. However, achieving high catalytic efficiency, structural stability, ease of recovery, and recyclability remains challenging for both research and practical applications. To address these requirements, a bimetallic oxide, CuMnO₂, was synthesized using a simple hydrothermal approach and was encapsulated to create hydrogel beads, CS-Ca@PEI/CuMnO₂. Subsequently, CS-Ca@PEI/CuMnO₂ was used to activate PMS and establish a solid–liquid heterogeneous oxidation system (CS-Ca@PEI/CuMnO₂/PMS) for the degradation of Congo red (CR). The effects of various parameters such as different systems, catalyst dosages, initial pH values, PMS concentrations, temperatures, and anion types on the catalytic degradation properties of CS-Ca@PEI/CuMnO₂ for CR were systematically evaluated. The results indicated that CS-Ca@PEI/CuMnO₂ has exceptional degradation capacity, achieving 91.0% degradation of CR at pH 7. After three degradation cycles, the catalyst maintained an 86.9% degradation efficiency compared to its original performance, highlighting its robust structural stability. The presence of reactive radicals, specifically ¹O₂ and ^•O₂^–, were confirmed through quenching experiments, X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance spectroscopy (EPR). Liquid chromatography-tandem mass spectrometry (LC-MS) revealed ten proposed intermediates in the catalytic degradation process. Due to its exceptional catalytic performance, structural durability, recyclability, and ease of retrieval, the catalyst shows great potential for effectively removing organic pollutants from industrial wastewater.