Fate and transformation of gold nanoparticles in surface water conditions

The inevitable release of man-made gold nanoparticles (GNPs) (due to a poised array of commercial applications) into surface water will result in simultaneous interactions with aquatic organisms and environmental entities such as humic acid (HA). The current research aims at understanding the fate and transformation of gold nanoparticles as emerging pollutants in surface water. The specific goals of this research are to develop fundamental understanding of the role of critical physico-chemical features of gold nanoparticles such as stabilizer coating and nanoparticle core size and external factors including solution pH in determining aggregation behavior in the presence of humic acid. The current body of work employs UV-visible absorbance and fluorescence spectroscopy and dynamic light scattering techniques to investigate the interactions of commercial humic acid (HA) and gold nanoparticles. The current aggregation mechanism model available for gold nanoparticles mainly addresses the aggregation behavior of nanoparticles with a given core size at various pHs and low ionic strength. This model is very specific and the current body of work will provide more generalized models for such aggregation mechanisms. Also in the literature often UV-Vis data is the basis for proposed mechanisms. The current research additionally relies on fluorescence spectroscopy as a probe for the nanoscale effects happening at the nanoparticle/fluid interface.;The aggregation behavior of gold nanoparticles with different core sizes has not been studied before, therefore this research provides important new information relevant to fate and transport in the environment taking into account the complexities in spectroscopic properties of GNPs as a function of size. Additionally, the current research involves evaluation of the role of solution pH on the colloidal and surface charge characteristics of gold nanoparticles and humic acid. Different colloidal models for aggregation mechanisms are discussed with relevance to previously predicted dispersible states for nanoparticles under varying pH conditions.;Finally, the research extends to inform the engineering community about fate of GNPs and HA in the presence of activated carbon mainly used in drinking water treatment. Application of spectroscopic separation to evaluate the extent of adsorption of HA and gold nanoparticles on activated carbon (when present individually and as well as in a mixture) exhibits new information concerning nanoparticles partitioning in filtration systems.