Solvent selection critically influences the aggregation and crystal growth of suspended metal oxide nanoparticles. We use ReaxFF molecular dynamics simulations to study the aggregation of various titanium dioxide (anatase) nanocrystals suspended in the following non-aqueous solvents; methanol, ethanol, propanol, iso-propanol and ethylene glycol. The nanocrystals are in the 2-6 nm size range and they generally possess shapes dictated by the Wulff construction. Wulff-shaped nanocrystals are terminated by {101} and {001} facets. To mimic the effects of HCl in the hydrothermal synthesis of anatase1, we also create {112} facets on the surfaces of some of the particles. We find that methanol and ethylene glyocol can facilitate aggregation by oriented attachment (OA) giving rise to single crystals. We observe that alignment of nanocrystals along a specific crystallographic direction is a necessary precursor to aggregation by OA. Alignment is accomplished by the creation of a hydrogen-bonding network by the adsorbed solvent species at the particle-particle interface. Organic solvents with shorter hydrocarbon chains or with higher concentration of hydrogen bonding species like ethylene glycol are conducive to the formation of this hydrogen-bonding network and thus can facilitate OA. Organic solvents with longer hydrocarbon chains like ethanol, propanol and iso-propanol inhibit the formation of this hydrogen-bonding network and gives rise to the formation of polycrystalline material. This indicates the important role that solvent plays in nanocrystal aggregation and how solvent can be a powerful tool for directing and controlling nanocrystal growth to fabricate nanostructures with desired shapes and sizes. (1). Penn, R. L.; Banfield, J. F., Morphology development and crystal growth in nanocrystalline aggregates under hydrothermal conditions: Insights from titania. Geochimica Et Cosmochimica Acta 1999, 63.

Reaxff reactive force field study of oriented attachment of TiO2 nanocrystals in non-aqueous solvents

251st National Meeting (2016)

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