Evaluation of Ageratum conyzoides Derived Bioadsorbent for the Removal of Cationic and Anionic Dyes: Kinetic, Isotherm, and Thermodynamic Analysis

Abstract

This research addresses the pressing issue of water pollution caused by dye discharge from industrial sources worldwide. The study focuses on the development of a bioadsorbent derived from Ageratum conyzoides, an invasive plant, with the aim of mitigating contamination by dyes, specifically Methylene Blue (MB) and Congo Red (CR). Structural and functional changes were analyzed through FTIR, XRD, and SEM analyses, providing compelling evidence of the successful transformation of raw material into an effective adsorbent. Adsorption evaluations demonstrated the bioadsorbent’s effectiveness, achieving an ∼80% removal efficiency for MB at ambient temperature, whereas removal of CR was negligible. Kinetic analysis revealed that MB adsorption followed pseudo-second-order kinetics, while isotherm studies indicated Freundlich behavior, suggesting spontaneous adsorption. Further investigations into the effect of contact time demonstrated that adsorption stabilizes at 60 min, with an MB capacity of 40.63 mg/g. Temperature studies indicate increased MB adsorption with rising temperatures, reaching a maximum capacity of 48.10 mg/g at 55 °C. Experimental values closely align with those predicted by the pseudo-second-order model at all concentrations, 30 mg/L (qe = 29.75 mg/g), 50 mg/L (qe = 41.11 mg/g), 70 mg/L (qe = 59.07 mg/g), 100 mg/L (qe = 85.803 mg/g), and the Freundlich isotherm model fits better than the Langmuir model. Moreover, the bioadsorbent exhibits high reusability over 15 cycles, with a total uptake of 976.45 mg/g. These findings underscore the promising potential of Ageratum conyzoides-derived bioadsorbents in mitigating dye-induced water pollution, offering insights into their kinetic, isotherm, and reusability properties.