Mechanistic insights into methomyl adsorption from aqueous solutions by Ficus nitida biochar: kinetic and isotherm modeling

Methomyl is one of the pesticides that have already been found in the environment. It is a broad-spectrum systemic pesticide, classified as a very toxic and dangerous pesticide. The removal efficiency of biochar produced from the residues of the Ficus nitida tree at a pyrolysis temperature of 300 °C was investigated in this study to remove the carbamate pesticide, Methomyl, from aqueous media. The adsorption parameters were studied. Different kinetic and isotherm models were used to describe experimental data. Thermodynamic parameters were determined to study the nature of the adsorption process of Methomyl. The results indicated that the highly efficient Ficus nitida biochar was able to remove Methomyl from aqueous media with qe = 30.8 mg/g, the adsorption increased with increasing temperature, pH, adsorbent dose, and contact time. Pseudo-second-order and the Freundlich models successfully described the experimental data (R2= 0.9977 and 0.9971) for both models, respectively. The negative thermodynamic parameter, ΔG, indicated spontaneous adsorption; the positive values of ΔH and ΔS confirm the endothermic nature and a random process. The values of ΔG and E (mean free energy) indicate physisorption, while the value of ΔH refers to the occurrence of chemisorption, meaning that both types occur for Methomyl adsorption onto FNB.