Improved Photocatalytic Activity of TiO₂ through MnFe₂O₄/Chitosan–Alginate Doping for Procion red MX-5B Degradation and Ecotoxicity Evaluation

The development of photocatalytic materials for organic pollutant degradation has continued to advance. In this study, a MnFe₂O₄/Chitosan–Alginate@TiO₂ composite was synthesized, in which magnetic MnFe₂O₄ was encapsulated within a chitosan–alginate polymer matrix and doped with TiO₂. The composite’s crystal structure, morphology, elemental composition, optical, and magnetic properties were characterized using XRD, SEM–EDX, UV–DRS, and VSM analyses. Optimization of Procion Red MX-5B (PRD) dye degradation was performed using Response Surface Methodology (RSM), with PRD concentration, pH, and irradiation time as independent variables. The composite exhibited strong magnetic behavior (magnetic moment: 44.63 emu/g) and a narrow band gap (2.20 eV). The photocatalytic degradation followed a quadratic model, with all variables showing significant effects (p-value < 0.05). The predicted optimal conditions, which include a PRD concentration of 45 mg/L, pH 3.3, and 59 min of irradiation time, resulted in a measured degradation efficiency of 99.71%. The composite demonstrated excellent stability after six recycling cycles. TOC removal of 84.30% confirmed substantial mineralization into inorganic compounds, such as CO₂ and H₂O, while ecotoxicity tests using green gram seeds germination indicated that the degradation products were non-toxic.