Adsorption of Gold Nanoparticles and Humic Acid On Activated Carbon Used In Drinking Water Treatment

Granular activated carbon (GAC) is primarily used in drinking water treatment processes for removing dissolved organic matter comprising of humic and fulvic acids (DOM), and other pollutants. The increasing applications of gold nanoparticles (GNPs) in diagnostic imaging, chemical and biological sensing, also present potential concerns for adsorption and removal of GNPs in water treatment units, following post-clinical discharge. The current study employs spectroscopic separation to evaluate the extent of adsorption of citrate coated GNPs with core size 50 nm (GNPs-50), and HA separately and in mixtures. Modified Freundlich isotherms were used to describe the adsorption behavior of humic acid and gold in mixtures. The novelty of the approach was to examine the adsorption behavior for synergistic or antagonistic effects when all three materials (gold nanoparticles, HA and activated carbon) were present, and to carefully account for the fluorescence of the controls in determining fractional fluorescence prior to establishing the isotherms. The GNPs-50 were completely adsorbed on activated carbon when present individually, however in the presence of HA the adsorption of GNPs-50 decreased significantly. The adsorption of humic acid also decreased in the presence of GNPs-50 showing an antagonistic effect. Therefore, the mixtures of HA/GNPs-50 present significant implications for the fate and removal of GNPs and HA in water processing units.