A Quantitative Study of the Interactions between Organic Functionalities and the Surface of Silver Nanoparticles in Aqueous Systems

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Goines, Sondrica
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As nanoparticles become increasingly commonplace in many consumer products, the release of nanomaterials into natural waters is inevitable and potentially harmful. Silver nanoparticles (Ag NPs), the most widely used type of nanomaterial, is of special concern due to the toxicity of silver to many aquatic organisms. Recent laboratory studies examining the behavior of Ag NPs in various conditions have demonstrated the importance of nanoparticle surface chemistry in the potential transformations of Ag NPs such as dissolution and aggregation. However, specific interactions between Ag NPs and organic compounds are usually not quantified. Furthermore, most studies to date have used large, poorly characterized natural organic material (NOM) standards, making it difficult to achieve a molecular-level understanding of relevant NOM-NP interactions that control NP behavior. We have investigated a method by which Ag NPs are allowed to react with various organic compounds and, following a size-based separation, the amount of compound that remains unadsorbed is determined by HPLC or voltammetry. Preliminary results indicate adsorption of benzoic acid derivatives bearing carboxylate groups are negligible under the conditions examined, but adsorption of thiol derivatives was significant. The extent of adsorption varied based on the adsorbate molecule as well as the separation method used, ultrafiltration or centrifugation. Additionally, the sensitivity for thiols with voltammetry allowed for experiments at lower, more environmentally relevant concentrations. Complementary SERS spectra were used to provide a qualitative understanding of the interactions between various organic functionalities and the surface of Ag NPs in aqueous systems, and UV-vis spectra provided evidence of adsorbate induced NP dissolution and aggregation.
silver nanoparticles, surface chemistry