Adsorption studies of methylene blue dye using cellulose based adsorbents of invasive weed plants: optimization and mechanistic insights

Abstract

Water pollution from industrial dye effluents poses a significant environmental challenge, and adsorption has emerged as an efficient and eco-friendly remediation strategy. This study investigated cellulose-derived adsorbents, Cellulose Nanoparticle Dialdehyde (CNPD) and Cellulose Nanoparticles (CNP), synthesized from invasive weed plants, for the removal of methylene blue (MB) from aqueous solutions. Structural characterization using FTIR, SEM, and XRD confirmed functional groups and porous morphologies favorable for adsorption. Batch experiments evaluated the effects of contact time, temperature (25–85 °C), pH (3.0–9.0), and initial dye concentration (10–100 mg/L) on adsorption performance. Equilibrium was reached within 70 min for CNPD and 50 min for CNP, with maximum adsorption capacities of 36.15 mg/g and 30.38 mg/g, respectively. Adsorption increased with temperature, rising to 43.4 mg/g for CNPD and 40.5 mg/g for CNP at 65 °C, and showed strong pH dependence, plateauing at pH 6.0. At low dye concentrations, removal efficiency increased proportionally, while a saturation point was observed at higher concentrations due to site limitation. Kinetic analysis revealed pseudo-second-order behavior (R2 = 0.982 for CNPD, 0.991 for CNP), indicating chemisorption predominance. Thermodynamic parameters confirmed spontaneous and endothermic adsorption, with negative ΔG° values becoming more favorable at elevated temperatures. Equilibrium data fitted the Freundlich isotherm (R2 = 0.991 for CNPD, 0.992 for CNP), suggesting multilayer adsorption on heterogeneous surfaces. Reusability studies showed CNPD retained ∼55% of its initial efficiency after 10 cycles, while CNP maintained ∼50% after six cycles, demonstrating potential for sustainable applications. Overall, CNPD and CNP represented low-cost, environmentally friendly adsorbents with high efficiency for MB removal, providing a dual benefit of wastewater remediation and valorization of invasive plant biomass.