480605 Stability of MnO2 and MoO3 Nanomaterials in Biological and Environmental Media

Monday, November 14, 2016
Grand Ballroom B (Hilton San Francisco Union Square)
Kyle Gion, Evan Gray and Robert Hurt, School of Engineering, Brown University, Providence, RI

2D nanomaterials (NM), atomically thin sheet-like solids, are a promising group of materials with widespread applications due to their planar structure and high surface area to mass ratio. These NMs have found uses in fields ranging from drug delivery to energy storage in lithium batteries, and as a result are expected to be encountered in human and environmental exposure scenarios. The fates of these materials in biological and environmental systems are not fully understood, and many are expected to undergo transformations, creating multiple potential modes of toxicity. This work investigates the stability of MnO2 and MoO3 NMs in four different media types; nanopure water, phosphate buffered saline (PBS), Roswell Park Memorial Institute medium (RPMI), and EPA standard moderate-hard water. PBS and RPMI were chosen as PBS mimics the pH and ion concentration of bodily fluids and RPMI is a commonly used culture cell media. EPA moderate-hard water mimics fresh water, and nanopure water is a common reference solution. Using Dynamic Light Scattering (DLS), changes in the size (Z-average) of the NMs were tracked over time as a way to identify changes in stability, with a decrease in the observed size distribution implying NM dissolution. Over the course of an hour, DLS indicated a reduction in size of MoO3 NMs in PBS and RPMI. However, in EPA moderate-hard and nanopure water, no changes in size were observed over the course of an hour. These results indicate that MoO3 is unstable in PBS and RPMI, ultimately resulting in dissolution. This result was confirmed in a filtration study employing Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) analysis. The mixtures of MoO3 and media were passed through a 0.02µm Anatop filter to remove any solids. Over the course of an hour in PBS, RPMI, and EPA Moderate-hard water, the total dissolved molybdenum concentration increased, indicating that MoO3 NMs readily dissolves. In nanopure water, MoO3 was not observed to dissolve, consistent with the DLS results. Similar conditions will be used to test the stability of MnO2, where, based on preliminary results, we predict that MnO2 will be relatively stable in all solutions.

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