Removal of endrin from aqueous medium using Accacia wood biochar: kinetics and thermodynamic studies

Abstract

Biochar is a potential sorbent for the removal of frequently detected pesticides in water. In the present study, the thermodynamic application and the kinetic models of endrin adsorption from the aqueous medium onto the biochar derived from the acacia wood produced at 500 °C were evaluated. Biochar was characterized using proximate, ultimate, and surface characterization methods. Batch experiments were conducted at 25, 30, and 35 °C for a series of endrin solutions ranging from 100 to 500 ppb using adsorbent water in the following ratios 0.5 g/L, 1 g/L, 2 g/L, and 3 /L. The negative Gibbs free energy change (ΔG) value indicated the feasibility of endrin adsorption on the Acacia wood biochar (ACBC500). The decrease in the Gibbs free energy change (ΔG) with rise in temperature indicated the high favourability of endrin adsorption at lower temperature. The ΔG value proposed that the adsorption proceeded through physisorption by van der Waals force, London dispersion forces, hydrophobic interactions, and hydrogen bonding. The entropy and the enthalpy changes (∆S > 0, ∆H < 0) indicated that the electrostatic forces contribute substantially in the adsorption of endrin onto the ACBC500. The equilibrium adsorption capacities (qe) of ACBC500 predicted by the pseudo-first-order and pseudo-second-order models for endrin were 245.65 μg/g and 200.02 μg/g, respectively. The experimental equilibrium adsorption capacity value of ACBC500 for endrin was very much closer to pseudo-second-order value. The study result indicated that the Acacia wood biochar (ACBC500) can be highlighted as a promising low-cost adsorbent for aqueous endrin removal. The calculated thermodynamic parameters also indicated that the adsorption was feasible, spontaneous, and exothermic in nature.