Sustainable organic dye remediation using a sulfonated lignocellulosic biomass (banana peel, <i>Musa spp.</i> )/chitosan composite: kinetic, isotherm, and adsorption optimization

The increasing discharge of synthetic dyes into aquatic environments has raised serious environmental concerns, prompting the need for sustainable and cost-effective treatment solutions. Herein, a sustainable biocomposite of sulfonated lignocellulosic biomass (banana peel, <i>Musa spp.</i>)/chitosan polymer composite (CTS/SBP) was produced to be an efficient adsorbent for the removal of crystal violet (CV) dye from water systems. The physicochemical properties of CTS/SBP were investigated by the use of several techniques, including CHNS-O, FTIR, BET, pH_pzc, XRD, EDX, and FESEM measurements. When optimizing the adsorption performance of CTS/SBP, the Box-Behnken Design (BBD) was adopted, considering several elements, including the dosage of CTS/SBP (0.03-0.09 g), the pH (4-10), and the duration (10-70 min). In terms of the experimental data of CV adsorption by CTS/SBP, the Freundlich isotherm and pseudo-first-order models are in good agreement with the obtained results. The negative values of Gibbs free energy (ΔG° = -4.919 to -6.964 kJ/mol) confirm the spontaneity of the CV dye adsorption. Furthermore, the positive enthalpy (ΔH° = 15.403 kJ/mol) and entropy (ΔS° = 0.0681 kJ/molK) changes indicate an endothermic process accompanied by an increase in disorder at the solid-liquid interface. The adsorption of CV dye by CTS/SBP is identified as physisorption, based on its conformity to the pseudo-first-order kinetic model and a Dubinin-Radushkevich adsorption energy of 1.112 kJ/mol, a value characteristic of physical adsorption processes. The adsorption capacity of CTS/SBP was measured to be 667.68 mg/g. One of the primary reasons for the significant adsorption of CV onto CTS/SBP is the presence of electrostatic interaction between the CTS/SBP's acidic groups and the CV's positive group. The obtained data illustrate a sustainable, environmentally friendly, and green method to produce effective adsorbents, opening the door for the development of adsorbents produced from renewable resources as a viable substitute for the removal of cationic dyes from polluted water.