This talk will begin with some of the most memorable moments in which Professor Lawler taught me how to be a better researcher, teacher, and mentor. In recent years, I have had the privilege to work on a NSF-funded project together with Professor Lawler. This presentation will focus on highlighting some of our recent findings. The surfaces of nanoparticles (NPs) are continuously evolving as they are exposed to different environments. Partly-sulfidized silver NPs (AgNPs) are suggested to be a prevalent “species” formed under reducing conditions. Under the same sulfidation condition, AgNPs are generally considered to undergo the same surface modifications (i.e., removal of original ligands and formation of a new silver sulfide (Ag2S) shell). This study examined this generalization by studying how different ligands, polyvinylpyrrolidone (PVP) and thiolated polyethylene glycol (PEG), affected 1) the formation of a new Ag2S shell and 2) the subsequent mobility of these transformed AgNPs. The deposition of PEG-AgNPs decreased by a factor of 40 after sulfidation while the deposition of PVP-AgNPs increased by a factor of 15. The decreased deposition of sulfidized PEG-AgNPs was attributed to the removal of PEG and the formation of Ag2S, which created a more negatively charged surface (-15 mV to -30 mV) and consequently greater electrostatic repulsion with the silica substrate. The increased deposition of sulfidized PVP-AgNPs was suggested to be caused by the truncation of PVP, which decreased steric repulsion with the silica substrate. For the first time, this study demonstrates that the formation of Ag2S is ligand-dependent and significantly impacts the consequent mobility and risk of the transformed AgNPs. Because of this Ag2S-dependence, not all sulfidized NPs have the same mobilization potential, and therefore it is important to characterize the continuous evolution of specific NP surfaces for better prediction of NP exposure and toxicity.

Encountering the heterogeneous and evolving surfaces in the transport and transformation of aquatic nanoparticles

255th National Meeting (2018)

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