Adsorption of Methyl Orange Using Modified Chitosan/Graphene Oxide Gel Beads in Wastewater

The development of efficient and environmentally sustainable adsorbents for dye removal from wastewater remains a significant environmental challenge. Azo dyes, such as methyl orange (MO), persist in aquatic environments due to their high chemical stability and resistance to biodegradation. Although chitosan-based materials have been extensively studied for dye adsorption, their low solubility, poor mechanical stability, and limited adsorption capacity restrict large-scale applications. In this study, sulfonated chitosan/graphene oxide (SCSGO) and N,O-carboxymethyl chitosan/graphene oxide (N,O-CMCSGO) were synthesized and evaluated for MO adsorption. SCSGO and N,O-CMCSGO exhibit high MO adsorption capacities (265.67 and 239.60 mg/g, respectively), with Freundlich isotherm modeling confirming multilayer adsorption on heterogeneous surfaces via combined electrostatic, hydrogen bonding, and π–π interactions. Kinetic analysis indicates nonspontaneous adsorption controlled by external and intraparticle diffusion. FTIR and XPS analyses confirm that functionalization alters the surface chemistry, enhancing the MO affinity. Notably, after five consecutive adsorption–desorption cycles, SCSGO maintains over 90% of its original adsorption efficiency.