A new kinetic and thermodynamic approach to phenol biosorption by chitosan and keratin

Chitosan and keratin were tested as low cost biosorbents to remove phenol from water solutions at variable temperature (20-50°C), initial phenol concentration (10-90 mg L-1) and pH (5.0-10.0), and fixed biosorbent dosage (10 g L-1). The pseudo-second order kinetic model exhibited the best fit to the experimental data and allowed estimating theoretical values of sorption capacity of 4.51 mg g-1 with keratin and 2.87 mg g-1 with chitosan. Equilibrium isotherms, described at best by the Freundlich model, pointed out that keratin (KF = 1.34 mg1-1/n L1/n g-1) was more effective than chitosan (KF = 0.19 mg1-1/n L1/n g-1) in phenol removal, although the sorption intensity was almost coincident (n = 1.18-1.19). The results of tests performed at different temperatures suggested a novel thermodynamic approach based on the occurrence of a sorbent inactivation equilibrium, whose changes of enthalpy and entropy were estimated to be 35.7 kJ mol-1 and 118 J mol-1 K-1 with chitosan, and 256 kJ mol-1 and 845 J mol-1 K-1 with keratin. The main functional groups involved in phenol sorption by both raw and phenol-bound materials were identified by FT-IR spectroscopy