Highly microporous sorbents from lignocellulosic biomass: Different activation routes and their application to dyes adsorption

Abstract

Highly microporous carbons were produced from two abundant agricultural residues, olive tree pruning and coffee husk. Different activation routes were tested to obtain the adsorbents, choosing experimental conditions that allowed the comparison between methods. Chemical activations were performed using K2CO3 and KOH, and physical activation using steam. The influence of the activation route on the yields and on textural and chemical properties of the activated carbons were analyzed. Highly microporous carbons were obtained through the chemical route, reaching surfaces areas over 2500 m2. g-1, while physical activation gave adsorbents with areas around 1500 m2. g-1 when applied to coffee husks. The porous materials were tested as adsorbents for the removal of methylene blue. The kinetic data were well represented by the pseudo-second order model for adsorption onto all carbons. The experimental isotherm data were analyzed by Langmuir, Freundlich and Temkin models. Maximum adsorption capacities were between 312.5 and 1000 mg.g-1, respectively. The activated carbons obtained from both lignocellulosic precursors exhibited an excellent methylene blue adsorption capacity, indicating their potential textile effluents treatment.