Synthesis of Chitosan-Agar immobilized NiO-MgO bionanocomposites and their photocatalytic application towards toxic azo dye

[Display omitted] •A bionanocomposite (BNC) was synthesized by incorporating NiO-MgO NPs into a chitosan and agar agar biopolymer matrix.•The synthesized CTAG@NiMg BNC exhibited 99.52% photocatalytic degradation of methyl orange (MO).•The CTAG@NiMg BNC demonstrated excellent reusability across four consecutive cycles without significant loss of activity.•Integration of NiO and MgO NPs with CTS-AA matrix increased the material’s surface area to better dye degradation rates. In this study, NiO-MgO nanoparticles (NiMg NPs) were synthesized and incorporated into a biopolymer blend of chitosan (CTS) and agar agar gum (AA), forming the novel CTAG@NiMg bionanocomposite (BNC). Structural analysis revealed a crystal size of 19 nm and a direct band gap of 2.75 eV, indicating strong potential as a UV-active photocatalyst. TEM images confirmed uniform nanoparticle distribution with an average size of 25 nm. The elemental composition, verified by EDX spectra, showed weight percentages of C (21.32 %), O (31.47 %), Ni (35.39 %), and Mg (11.82 %). The CTAG@NiMg BNC demonstrated outstanding photocatalytic degradation of methyl orange (MO) dye, achieving 99.52 % degradation at pH 4 with 20-ppm concentration after 60 min under UV irradiation. The degradation followed pseudo-first-order kinetics, with rate constants (k1) ranging from 0.011 to 0.030 min−1, and a minimum half-life of 25.8 min at 15 ppm. Hydroxyl radicals (•OH) were identified as the primary reactive species driving the photocatalytic process. The material exhibited excellent reusability, retaining high degradation efficiency over four cycles. Compared to similar photocatalysts, CTAG@NiMg BNC demonstrated superior performance, faster degradation rates, and greater stability. Its enhanced surface area and porosity, as confirmed by BET analysis, contributed to better dye adsorption and faster reaction times. These properties make the CTAG@NiMg BNC a highly efficient, sustainable, and recyclable photocatalyst for environmental remediation, particularly in treating organic pollutants like methyl orange from aqueous solutions.