Capacity of activated carbon in the removal of acid dyes subsequent to its thermal treatment

A commercial activated carbon (Prolabo) was subjected to thermal treatment at 400 and 600 °C for 2 h. Characterization of the parent, and heated products, was carried out by determining the N2/77 K adsorption isotherms, FTIR spectra, acidic/basic sites, and adsorption of iodine, Acid Blue 74 (AB), Acid Red 73 (AR) and Acid Yellow 23 (AY) from aqueous solution. Thermal treatment resulted in some enhancement in the porosity characteristics (specific area and pore volume) particularly in micropores, although insignificant changes appear in the surface chemical properties. Two liquid-phase adsorption models are applied, the Langmuir and Dubinin–Radushkevich linear equations, which showed satisfactory fit to the adsorption data. Evaluated capacity and affinity parameters demonstrated that the uptake of the acid dyes decrease in the order of AB > AR >> AY, which may be ascribed to chemical structure differences in substituents and side chains leading to unavailable accessibility. Heated carbons exhibit a reduction in uptake of AB, and an increase in case of AY and AR dyes. Changes in surface chemical groups, under action of heat probably influence the adsorbate/adsorbent, adsorbate/liquid and adsorbent/liquid relationships leading to the apparent differences.