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 (ΔG0), enthalpy (ΔH0), and entropy (ΔS0) changes were calculated to predict the nature of adsorption. The estimated values of ΔG0 for the agrowastes used were found to be low (-90.4267 kJ/mol K), thus, indicating spontaneity of the process. The negative value of ΔH0 (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 ΔS0 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.