Physicochemical and adsorption characteristics of activated carbons from cellulose, xylan and lignin

Activated carbons (AC) were prepared from the three major components (cellulose, xylan, and lignin) of lignocellulosic biomass by H3PO4 activation. Physicochemical characterizations reveal that as compared with AC from lignin (AC-L), AC from carbohydrates, especially AC from xylan (AC-X), have higher-developed porous structure, more disordered carbon, and more active O-containing and P-containing functional groups. The adsorption of methylene blue (MB) on all ACs followed Langmuir isotherm and pseudo-second-order kinetic models. Primarily due to its superior porosity, AC-X possessed the highest adsorption capacity for MB of 666 mg/ g. AC from cellulose (AC-C) and AC-L followed with the adsorption capacities of 498 mg/g and 395 mg/g. The adsorption of MB was endothermic and AC-X had the highest feasibility and spontaneity. AC-X also exhibited superior adsorption capacities for the adsorption of typical heavy metals, although the superiority is much weaker as compared with that for MB. This research suggests the positive impact of carbohydrates, especially hemicellulose, in the precursors of the ACs on their adsorption performances.