Activated carbon from peanut shells: 2,4-D desorption kinetics study for application as a green material for analytical purposes

Abstract

The desorption kinetic of 2,4 Dichlorophenoxyacetic acid (2,4-D) herbicide initially adsorbed on activated carbon from peanut shells (PSAC) was studied. The herbicide was adsorbed at pH 3.0 and desorbed in aqueous solutions at pH 6.0 and 10.0, in acetonitrile (MeCN) and methanol (MeOH). The determined desorption rate constants ( k_d) were 0.362 s-1, 0.530 s-1, 0.638 s-1, and 0.876 s-1, respectively. The activation energy of desorption (Ea) was determined as 7.4 kJ/mol at pH 6.0 and 11.5 kJ/mol at pH 10.0 using the Arrhenius equation. Adsorption isotherms in aqueous solution at different pH and different solvents showed that the affinity of 2,4-D on the surface of PSAC is higher in aqueous solvents than in organic solvents. PSAC was successfully applied as a low-cost carbonaceous material to be packed in columns for analytical purposes as solid-phase extraction procedure (SPE). The results obtained allowed MeOH to be chosen as the right solvent for this analytical application. In addition, the knowledge of this process could be extremely helpful to avoid a new solid waste after retaining the contaminants in water purification processes and even recovering the carbonaceous material and the solvent in a simple way. The desorption kinetic of 2,4-D in several solvents including water a different pH and 2,4-D adsorption isotherms in organic solvents have not been reported so far.