Abstract
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.