Solid waste-azo dye degradation closed loop: bridging coal gangue recycling and azo dye removal

Abstract

To address the dual challenges of coal gangue utilization and azo dye wastewater treatment, this study developed cobalt-loaded geopolymer microsphere catalysts (Co@CGM) through the resource utilization of coal gangue for peroxymonosulfate (PMS) activation, achieving efficient degradation of azo dyes sunset yellow (SY) and amaranth red (AR). Single-factor experiments demonstrated that Co@CGM exhibited exceptional catalytic performance at ultra-low PMS concentrations (0.25–0.50 mmol/L), achieving degradation efficiencies of 99.38% for SY and 99.91% for AR within 30 min for 100 mL solutions at 50 mg/L concentration. Stability tests revealed that Co@CGM maintained significant PMS activation effectiveness through five degradation cycles, demonstrating strong acid-base resistance (pH=3–9) and excellent anion interference resistance (Cl⁻, NO₃⁻, H₂PO₄⁻, etc.). Quenching experiments and electron paramagnetic resonance spectrometer (EPR) analysis confirmed that singlet oxygen (¹O₂) served as the primary reactive species driving the rapid degradation process in both SY and AR systems. Liquid chromatography-mass spectrometer (LC-MS) analysis identified intermediate products and proposed degradation pathways for both dyes. This work successfully developed an eco-friendly functional material through coal gangue waste recycling, achieving the goal of “treating waste with waste” in azo dye wastewater remediation.

Graphical abstract