Fabrication and characterization of a novel magnetic nanocomposite based on chitosan hydrogel modified with mesoporous silica and copper-based MOF as an effective and antibacterial adsorbent for the removal of methylene blue from water.

The contamination of water bodies by methylene blue (MB), a persistent cationic dye, necessitates the development of efficient adsorbents for wastewater treatment. This study introduces a novel magnetic nanocomposite, MCM-48 -Cu(BDC-NH2)/CS hydrogel@Fe3O4, designed for enhanced MB adsorption. The nanocomposite integrates mesoporous MCM-48 for high surface area, Cu(BDC-NH2) for selective pollutant capture, chitosan (CS) crosslinked with glutaraldehyde (GA) for structural stability, and Fe3O4 for magnetic separability. Response surface methodology (RSM) was employed to optimize adsorption parameters including pH, adsorbent dosage, contact time, and initial dye concentration to achieve maximum adsorption efficiency (98.32 %). Adsorption behavior was analyzed using isotherm models, and the Freundlich model provided the best fit to the experimental data, indicating heterogeneous surface adsorption with multilayer formation and favorable adsorption intensity. Kinetic studies revealed a double-exponential (DE) mechanism as the best fit, indicating biphasic adsorption with an initial rapid surface-controlled stage followed by a slower pore-diffusion stage, while intraparticle diffusion analysis highlighted additional pore diffusion contributions. Thermodynamic parameters (ΔG° < 0, ΔH° < 0, ΔS° < 0) confirmed a spontaneous, exothermic process with reduced system entropy due to ordered adsorption. The nanocomposite exhibited excellent reusability, retaining 83.64 % efficiency after eight cycles, facilitated by magnetic separation. Additionally, the material demonstrated significant antibacterial activity against Escherichia coli and Staphylococcus aureus, attributed to Cu(BDC-NH2) and chitosan, enhancing its applicability for dual-purpose wastewater treatment. This comprehensive study underscores the nanocomposite's potential as a sustainable, high-performance adsorbent, addressing both chemical and biological contaminants in environmental remediation.