Adsorption isotherm, kinetics, and thermodynamic studies of O,O-diethyl-O-(3,5,6-trichloropyridin-2-yl) phosphorothioate (chlorpyrifos) on cinnamon verum-based activated carbon

Cinnamon verum was used as a low-cost precursor to produce microporous-activated carbons with a high surface area (894 m(2)/g) and large total pore volume (0.49 cm(3)/g). Thermogravimetric analysis scanning electron microscopy, Fourier-transform infrared spectroscopy, Brunauer-Emmett-Teller surface area, and pore size analyzer techniques were used to characterize the new sorbent. The new porous carbon's ability to remove chlorpyrifos (CPS), an organo-phosphorus surrogate of ware gases and the active component in most insecticides and pesticides, has been assessed by a batch adsorption procedure. Different sorption factors such as initial CPS concentrations, contact time, pH, solution temperature, and sorbent dosage have been studied. The results show that the new sorbent could remove 100% of CPS at low concentrations of 20 ppm within 20 min of contact time under a favorable sorption process. CPS adsorption was found to be exothermic, and the adsorption capacity decreases with increasing temperature. Equilibrium results were modeled using three isotherm models: Langmuir, Freundlich, and Temkin. The Langmuir isotherm model was found to be the best model to represent the CPS adsorption data. The kinetic results were fitted to pseudo-first-order, pseudo-second-order, and intraparticle diffusion models and thoroughly followed the pseudo-second-order kinetic model. Thermodynamic factors such as enthalpy (Delta H-o), entropy (Delta S-o), and free energy (Delta G(o)) were assessed. The negative values of Delta H-o and Delta G(o) indicate the exothermic and spontaneous nature of the adsorption process. The sorbent from waste cinnamon bark was economically practical and eliminates organophosphorus compounds from aqueous solutions.