The kinetic and thermodynamic studies of phenol-sorption onto three agro-based carbons

Abstract

In the present investigation, adsorption kinetics of phenol from aqueous media onto three agro-based adsorbents, namely Black Gram Husk (BGH), Green Gram Husk (GGH) and Rice Husk (RH), were carried out. The pseudo-first-order, Bhattacharya and Venkobachar, Natarajan and Khalaf, power function model, second-order kinetic model and intraparticle diffusion model were used to describe the kinetic data to estimate the rate constants. Free energy of adsorption (Δ G 0), enthalpy (Δ H 0), and entropy (Δ S 0) changes were calculated to predict the nature of adsorption. The estimated values of Δ G 0 for the agrowastes used were found to be low (–90.4267 kJ/mol K), thus, indicating spontaneity of the process. The negative value of Δ H 0 (lowest BGH –42.36 kJ/mol and highest for RH – 34.31 kJ/ mol) will indicate the process is exothermic and the sorption behavior may be physio-sorption in nature. The positive values of Δ S 0 of all the three agro-based adsorbents (range 0.11–0.14 J/mol K) shows the increased randomness at the solid/solution interface during the adsorption process.