Effectiveness of activated carbons developed by different strategies in the removal of diclofenac sodium and salicylic acid from water

Abstract

The adsorption performance of different activated carbons (ACs) developed from Parkinsonia aculeata wood in the removal of two emerging contaminants, sodium diclofenac (SD) and salicylic acid (SA), from model aqueous solutions was comparatively examined. ACs were obtained by chemical activation with H3PO4 solution applying conventional heating (AC-PC) and microwave energy (AC-PM), and by activation with K2CO3 (AC-C) and KOH (AC-H). A thermal post-treatment was additionally carried out (AC-PC-T). The performance of each sample in the adsorption of both contaminants was first determined at equilibrium pre-established conditions and related to its chemical and textural characteristics. The ACs with higher BET surface area, wider pore size, and higher content of acidic surface oxygen functional groups presented better SD removal levels. Instead, the BET surface area had almost no incidence on SA adsorption. The latter was favoured by the presence of basic surface functional groups. AC-PC-T showed a lower SD removal than the untreated sample, but a slightly higher SA adsorption. Kinetic data for the adsorption of SD and SA onto the ACs followed a pseudo-second order model. The adsorption equilibrium isotherms were well described by the Langmuir model. AC-PM and AC-H presented the highest values of maximum adsorption capacities of SA and SD (1.3 and 2.5 mmol g−1), respectively, thus showing potentialities for their use in tertiary treatment of water polluted with this kind of emerging contaminants.