Fabrication of chitosan-MnOX composites based on structure-performance relationship and mechanistic insights into efficient photocatalytic PMS activation for dye degradation.

Natural polymer chitosan (CS) was employed as a modifier to fabricate CS-MnOₓ composite photocatalysts via oil-bath (CS-AM, 80 °C) and hydrothermal (CS-CM, 160 °C) methods for visible-light-driven peroxymonosulfate (PMS) activation toward the degradation of cationic dyes. The oil-bath condition preserves the structural integrity of CS, allowing its steric hindrance effect to effectively suppress MnOₓ agglomeration. Meanwhile, the strong interfacial chemical interactions between CS and MnOₓ establish efficient charge transport pathways that substantially enhance photogenerated carrier separation. The resulting bimodal mesoporous architecture provides ample active sites and facilitates rapid mass transfer. Consequently, the optimal CS-AM catalyst achieves 94.5% degradation of methylene blue (MB) and 92.2% of toluidine blue (TB) within 120 min under visible light, retains over 82% activity after five consecutive cycles, and exhibits robust performance across a wide pH range and in the presence of common inorganic anions. Mechanistic investigations identify 1O₂ as the dominant reactive species. Photogenerated electrons continuously drive the Mn(IV)/Mn(III) redox cycle, as confirmed by post-reaction XPS showing a decrease in Mn(III) from 37.5% to 34.67%, thereby sustaining efficient PMS activation. LC-MS and ECOSAR analyses reveal the cleavage of the phenothiazine ring and a marked reduction in intermediate toxicity. This work establishes a clear preparation-microstructure-performance relationship for CS-MnOₓ composites, offering a cost-effective and environmentally benign photocatalytic/PMS synergistic strategy for dye wastewater remediation.