(206e) Designer Hybrid Colloids: A Study of Gold Adsorption Onto Polystyrene to Control Morphologies of Reactive Nanoparticles

Colloids are commonly used in groundwater remediation as a tool to mitigate the harmful effects of toxic contaminants in complex porous environments, either via chemical degradation or removal. Many current technologies seek to implement chemically reactive nanomaterials to degrade harmful contaminants in situ and thus prevent them from entering the drinking water supply. However, recent works have shown that many of these nanomaterials are not stable against aggregation, decreasing their reactivity and their resultant ability to treat contaminants effectively. Additional studies have sought to prevent aggregation by applying electrostatic or steric stabilizers on the surfaces of these nanomaterials, which are most commonly catalytic metals, but these solutions do not address a way to easily tune the morphologies, concentrations, or reactivity of injected particles.

We address these shortcomings by developing a framework to control the properties of an inorganic-organic, or hybrid, system comprised of polystyrene colloids that we fabricate via Flash NanoPrecipitation (FNP) and smaller gold nanoparticles. We investigate several parameters, including polymer molecular weight, concentration of charged polymer end groups, gold nanoparticle size, and solvent composition, to determine the mechanism of gold adsorption to polystyrene and control particle morphologies. Interestingly, we find that a high concentration of a good solvent must be present during incubation with gold particles in order for adsorption to occur. We show that the presence of a good solvent results in the development of a mobile surface layer on the polymer colloid, allowing for diffusion and adsorption of gold particles within it. Furthermore, we see that as we increase the molecular weight or concentration of charged end groups, we achieve more uniform dispersal of gold nanoparticles on the surfaces of polymer colloids, which not only prevents their aggregation, but creates a larger surface area over which reactions can take place. Finally, we observe internalization of gold nanoparticles within polymer colloids above a threshold concentration of charged end groups, which presents a unique opportunity for catalytic “activation,” in which internalized gold particles can be selectively drawn to the surface of polymer colloids. For all obtained morphologies, we test the ability of our hybrid colloids to reduce a model contaminant, p-nitrophenol. Taken together, the results of our work provide a systematic approach to control the morphologies of inorganic-organic hybrid colloids and the unique ability to optimize their reactivity for a given application.