Chitin as biosorbent for phenol removal from aqueous solution: Equilibrium, kinetic and thermodynamic 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 architecture 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.