Eco-Friendly Chitosan/Graphene Oxide Hybrid Nanoparticles as a Dual-Action Platform for Methylene Blue Removal and Antimicrobial Water Treatment

This work reports the synthesis and characterization of sustainable, multifunctional chitosan/graphene oxide hybrid nanoparticles (GOCSNPs) prepared via a low-temperature ionotropic gelation method utilizing sodium tripolyphosphate as a green crosslinker. Combined DLS and TEM analyses confirmed the successful formation of submicron spherical nanoparticles with a mean diameter of 295 ± 15 nm (PDI 0.26), and GOCSNPs were evaluated as a dual-action platform for the adsorption of a model cationic dye, Methylene Blue (MB), and for antimicrobial remediation against Staphylococcus aureus and Escherichia coli. Equilibrium adsorption studies revealed that incorporating GO dramatically increased the maximum monolayer adsorption capacity from 2.78 mg g−1 (for CSNPs) to 37.16 mg g−1 (for GOCSNPs), closely following the Langmuir and Sips models through a pseudo-second order sorption mechanism. Furthermore, desorption investigations demonstrated that the GOCSNPs maintained substantial adsorption performance over multiple adsorption–desorption cycles under controlled conditions. Concurrently, GOCSNPs exhibited a dose-dependent enhancement in antibacterial efficacy, showing greater activity against Gram-negative E. coli (MIC of 1.25 mg mL−1) than against Gram-positive S. Aureus (MIC of 2.50 mg mL−1). Overall, these findings elucidate the structure–property–performance relationships of these carbon–biopolymer hybrid nanocomposites, validating their suitability as an advanced, eco-friendly, and reusable platform for comprehensive and sustainable wastewater remediation.