Development and characterization of a chitosan/acid-modified lignocellulosic biomass (Eggplant residue, Solanum melongena L.) biocomposite for brilliant green dye removal

This work focuses on the valorization of lignocellulosic biomass, specifically eggplant residue, to contribute to sustainable waste-to-resource strategies. By utilizing this lignocellulosic biomass, the research promotes environmental sustainability through the conversion of waste into valuable materials for water treatment. A novel biocomposite of chitosan and acid-modified lignocellulosic biomass derived from eggplant (Solanum melongena L.) residue was developed to efficiently remove the organic pollutant (brilliant green dye, BG) from aquatic systems. The physicochemical properties of the lignocellulosic biomass-based absorbent (chitosan/eggplant reside-sulfuric (H₂SO₄) acid, CS/ER-SA) were analyzed through various techniques, including elemental analysis (CHNS-O), point of zero charge (pH_pzc), Brunauer–Emmett–Teller surface area analysis (BET), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy with energy dispersive X-ray analysis (SEM–EDX). The Box-Behnken Design (BBD) was used to enhance BG dye adsorption performance by considering dosage (0.03–0.09 g), pH (4–10), and duration (10–50 min). The optimal circumstances for maximum BG dye elimination (98.21%) were identified as a pH of about 9, a CS/ER-SA dosage of 0.057 g, and a contact duration of 49.8 min, as determined by the analysis of the BBD model results. The pseudo-first-order kinetic and Freundlich isotherm models responsibly characterized the adsorption of BG dye. The calculated maximum adsorption capacity for CS/ER-SA was found to be 872.75 mg/g. Thermodynamic analysis confirms that the adsorption process is spontaneous (Gibbs free energy change, ΔG° = −7.811 to −12.728 kJ/mol) and endothermic (enthalpy change, ΔH° = 41.059 kJ/mol), with increased interfacial disorder (entropy change, ΔS° = 0.1639 kJ/mol·K) promoting BG dye uptake onto the CS/ER-SA biocomposite. The synthesized biocomposite exhibited remarkable adsorption efficacy for BG dye, highlighting its considerable potential in the removal of basic dyes. This study highlights the potential of utilizing agricultural residues in developing sustainable and cost-effective adsorbents for dye wastewater treatment applications.