Theoretical study of the herbicide parachlorophenoxyacetic acid molecule and its removal by activated carbon prepared from pine cone

This study focuses on the conversion of pine cones into activated carbon using potassium hydroxide as a chemical activator with a 1:1 impregnation ratio. The resulting material was characterized for volatile matter, ash and moisture content, apparent density, iodine index, Methylene Blue value, Bohem titration, and pHzpc. BET, FTIR, XRD and SEM-EDS analyses were also performed on the activated carbon for specific surface area determination, surface functional groups analysis, crystallographic strucure and morphology study, respectively. The prepared activated carbon had a BET specific surface area of 430 m2 g−1 and a Langmuir surface area of 313.7 m² g−1 with a yield of 72.25 %), carbon content of 67.25 %, and an apparent density of 0.451 g cm3, a moisture content of 2 %, an ash content of 3 %. and a heterogeneous structure. Iodine number, Methylene blue index, and pHzpc reached 666.38 mg g−1, 72.76 mg g−1, and 7.6, respectively. Batch adsorption tests revealed a remarkable ability of the prepared activated carbon to remove the herbicide para-chlorophenoxyacetic acid (P-CPA) from its aqueous solution at an optimized pH of 3.75. Kinetic and thermodynamic studies showed that the pseudo-second-order kinetic model fitted the experimental data and that the adsorption process was spontaneous and endothermic. The models of Langmuir, Freundlich, Temkin, Dubinin Radushkevich, and Redlish Peterson were found to describe the adsorption process with a removal capacity of 266.5 mg g−1. Monte Carlo calculations highlighted the stability, nucleophilic nature, and strong interactions of P-CPA (C8H7O3Cl) with molecules having a dipole moment (μ) of 3.202 Debye.