Chitin as biosorbent for phenol removal from aqueous solution: equilibrium, kinetic and themodynamic studies

Phenol removal from aqueous solution was studied employing chitin as low cost biosorbent. Initial biosorption tests carried out in the pH range 2-10 pointed out an optimum pH of 2. Temperature and initial phenol concentration were then varied in the ranges 15 <T<50°C and 10.4 <C0<90.8 mg L-1, respectively. The good applicability of Langmuir, Freundlich and Temkin models (R2 = 0.990-0.993) to describe equilibrium isotherms suggested an intermediate mono- /multilayer biosorption mechanism along with a semi-homogeneous arquitecture of biosorbent surface. Biosorption capacity progressively increased from 3.56 to 12.7 mg g-1 when starting phenol concentration was raised from 10.4 to 90.8 mg L-1, and the related sorption kinetics was investigated by pseudo-first-order, pseudo-second order and intraparticle diffusion models. The pseudo second-order model, which showed the best fit of experimental data (R2 = 0.999), allowed estimating a second order rate constant of 0.151 g mg-1 h-1 and a theoretical sorption capacity of 7.63 mg g-1. Phenol biosorption capacity increased with temperature up to a maximum value, beyond which it decreased, suggesting the occurrence of a thermoinactivation equilibrium. Finally, to identify the main functional groups involved in phenol biosorption, both raw and phenol-bound materials were explored by FT-IR spectroscopy.