Congo Red Dye Degradation and Biotoxicity Elimination by a Novel Hybrid Semimembrane Capacitive Deionization (SM-MCDI) Device Coupled with Peroxymonosulfate (PMS)

A novel hybrid semimembrane capacitive deionization (SM-MCDI) system is proposed for the efficient degradation of anionic dye wastewater. Unlike conventional membrane capacitive deionization (MCDI), the SM-MCDI device employs a single cation exchange membrane (CEM) positioned on the cathode side, enabling the direct enrichment of anionic dyes on the anode surface while maintaining charge efficiency. Iron oxide-loaded carbon felt electrodes were used to enhance dye enrichment and catalytic activity. The SM-MCDI system was coupled with peroxymonosulfate (PMS) to promote the in situ oxidative degradation of Congo Red (CR). The effects of the applied voltage, PMS dosage, pH, dye concentration, and coexisting salt ions on CR removal were systematically evaluated. Under optimal conditions (1.2 V, pH 7, 500 mg/L PMS, flow rate of 3 mL/min), 80.84% of 100 mg/L CR was removed within 15 min. Chloride and dihydrogen phosphate ions slightly inhibited CR removal, whereas bicarbonate promoted degradation. Electron paramagnetic resonance analysis confirmed that sulfate radicals (SO4·–), singlet oxygen (1O2), and hydroxyl radicals (·OH) were the dominant reactive species. This study demonstrates that the SM-MCDI–PMS strategy enables effective dye degradation and simultaneous salt removal, offering a promising approach for treating complex dye wastewater.