Adsorption of pharmaceutical pollutants onto graphene nanoplatelets

This study explores the removal of aspirin (ASA), acetaminophen (APAP), and caffeine (CAF); as examples of hazardous pharmaceutical pollutants, from aqueous solution by graphene nanoplatelets (GNPs). Characterization of the GNPs showed a transparent, layered structure with a smooth surface and many wrinkles, as well as a specific surface area of 635.2 m(2) g(-1). The effects of adsorption time, GNPs mass, solution pH, ionic strength, and temperature were studied and optimized. The effect of temperature on the adsorption kinetics was investigated using pseudo-first-order, pseudo-second-order kinetic models, and the experimental data were fitted well to the pseudo-second-order kinetic model. Also, the adsorption mechanism was explored using intra-particle diffusion and liquid film diffusion models, and the results revealed that none of these models was the rate-determining steps. The adsorption was studied thermodynamically, and the Gibbs free energy change (Delta G degrees), enthalpy change (Delta H degrees), and entropy change (Delta S degrees), were calculated. The Delta G degrees values were negative at all temperatures indicating the spontaneity of the adsorption of ASA, APAP, and CAF by GNPs from aqueous solution. GNPs showed great efficiency when they were used for the removal of ASA, APAP, and CAF from real environmental samples. (C) 2014 Elsevier B.V. All rights reserved.