Nano-synthesis often involves free energy input that creates material structures that are out-of-equilibrium with the natural environment. These materials may undergo spontaneous chemical transformation at finite rates, and nanorisk management requires knowledge of these transformation pathways, and the toxicity and fate and transport of their end products. Even material classes generally regarded as stable during normal storage and use can undergo such transformations due to several factors: extreme dilution in the natural environment, the presence of a wide variety of natural oxidants and reductants, the action of sunlight, and the nanoscale or atomic scale dimensions of the material, which dramatically reduces time scales for complete transformation relative to familiar bulk materials.<br/><br/>This talk examines the phenomenon of environmental transformation using three case studies: (i) nanometals, (ii) atomically thin carbon forms, and (iii) metal-carbon hybrids. Nanometals are subject to oxidation, dissolution, and sulfidation that are analogous to corrosion reactions in bulk metals, but greatly accelerated by nanoscale dimension. These behaviors will be illustrated by data on Ag and Cu-based nanomaterials. Bulk materials made of elemental carbon materials are all out-of-equilibrium with respect to oxidation when in contact with the atmosphere or oxic waters, but are kinetically stabilized by the low rates of CO/CO<sub>2</sub> desorption at ambient conditions. The talk will show that this situation is altered in certain atomically-thin carbon forms with disrupted graphenic surfaces, namely graphene oxide and certain functionalized single-walled carbon nanotubes. Finally, many nanoproducts are now based on hybrid materials, and the talk will give a case study on nanometal hybridization with graphene materials, showing how the presence of carbon influences the key metal transformation pathways of oxidation and dissolution.

Case studies in the environmental transformations of nonequilibrium nanomaterials

250th National Meeting (2015)

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