Conversion of cow dung into high-performance biochar for efficient adsorptive removal of methyl red from aqueous solutions: Kinetic, isotherm, and mechanistic insights

Abstract

This study aimed to evaluate the effectiveness of biochar derived from cow dung in removing methyl red (MR) from aqueous solutions. The prepared biochar was alkaline in nature with a carbon content of 58.34 % and a specific surface area of 455.5 m² g⁻¹. Adsorption behavior of MR onto cow dung derived biochar was examined under varying experimental conditions, including contact time, adsorbent dosage, initial pH, and initial dye concentration. The results demonstrated that an equilibration time of 40 min, an adsorbent dose of 0.5 g, and an initial pH of 3 constituted the optimal conditions for MR removal. Increasing the initial dye concentrations from 25 mg L⁻¹ to 200 mg L⁻¹ led to a decrease in removal efficiency. Equilibrium data were best described by the Freundlich isotherm model (r² = 0.958), indicating heterogeneous surface characteristics and multilayer adsorption. The pseudo-second-order kinetic model provided the best fit across all tested concentrations (r² > 0.986), suggesting that chemisorption governs the adsorption process. The adsorption intensity (1/n = 0.18) and the dimensionless constant parameter (R_L = 0) further confirmed the favorability of the adsorption. Additionally, the D–R isotherm-derived free energy value (E = 60 kJ mol⁻¹) supports the predominance of chemical adsorption mechanisms. Overall, the cow-dung-based biochar proved to be a cost-effective and efficient adsorbent for MR dye removal. Its performance indicates strong potential for application in the treatment of textile dye-contaminated wastewater in industrial settings.