Efficient removal of methylene blue dye from textile wastewater using modified grass ( <i>Cynodon dactylon</i> )

This study investigates the sustainable valorization of grass (Cynodon dactylon), an abundant lignocellulosic agricultural waste, as an eco-friendly adsorbent for the removal of synthetic dyes from aqueous systems. Both untreated grass (UGS) and treated grass with acetic acid (AAGS) and sodium hydroxide (SHGS) were prepared at varying concentrations (10% and 5%, respectively) to enhance surface functionality. Comprehensive characterization using FTIR, SEM, EDS, XRD, and BET analysis elucidated the physicochemical changes induced by acid and alkali treatment. Adsorption studies targeting Methylene Blue (MB), a cationic dye commonly found in textile effluents, were conducted under varying operational parameters, including dye concentration (5–60 mg/L), adsorbent dosage (0.25–1.25 gm), contact time (1–6 h), pH (2–12), and temperature dependence (30–70 °C). The 5% alkali-modified grass (5% SHGS) demonstrated superior adsorption efficiency, achieving 76.20% dye removal at pH 8 for an initial dye concentration of 5 mg/L. Kinetic data followed a pseudo-second-order model, suggesting physical adsorption as the dominant mechanism. In contrast, equilibrium data were best described by the Freundlich isotherm for MB (R2=0.99), indicating multilayer adsorption on a heterogeneous surface. The thermodynamic study mainly demonstrated the spontaneous and endothermic nature of MB adsorption. The process was found to be more effective at 50 °C temperature, highlighting its feasibility for low-energy wastewater treatment applications. This study advocates for the circular utilization of agricultural byproducts in environmentally sustainable remediation approaches for industrial dye contamination.