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

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 (Delta G(0)), enthalpy (Delta H-0), and entropy (Delta S-0) changes were calculated to predict the nature of adsorption. The estimated values of Delta 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 Delta 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 Delta 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.