(129b) Uncoated and Polymer Coated Titanium Dioxide (TiO2) Nanoparticles: Differences in Deposition and Charge Characteristics

Authors: 
Powell, T., USEPA National Exposure Research Laboratory
Zepp, R., EPA
Bouchard, D., USEPA National Exposure Research Laboratory



The advent of nanotechnology has opened up several potential avenues starting from the development of advanced manufacturing processes, revolutionary medical treatments, new consumer products, environmental applications, pollution control, etc. The backbone of this new leading-edge technology is the engineered nanomaterials (NMs), which are utilized both in the pure form (un-coated; U-NMs) and those for which the surfaces are modified, using polymers, surfactants, functional groups (coated; C-NMs), to attain certain specific properties in the final product.  The colloidal behavior of U-NMs and C-NMs, even though when composed of the same core-material, can be drastically different and requires a deeper understanding for their optimal usage, in designing effective solid-liquid separation technologies, in minimizing exposure adversaries both to the human and the environment and for the development of reliable predictive models.

In this work, we have investigated the deposition and electro-kinetic behavior of both polymer coated and un-coated TiO2 NMs, which directly impacts their separation and mobility characteristics. The deposition behavior of the NMs was investigated using deep-bed filters made using acid-washed sand columns and 1D convective-dispersive transport models. The effects of different forces (electrostatic, van-der Walls, and electrosteric--both osmotic and elastic) on the attachment & retention kinetics of NMs were analyzed. Predicted attachment efficiencies, using well-established dimensionless models, though matched well with the experimental values for U-NMs but failed for the C-NMs (R2<0.5).  However, an improvised model, which takes into account the effect of steric hinderance, improved the predicted attachment efficiency values for the C-NMs (R2>0.8) and points towards the importance of other non-DLVO (Derjaguin and Landau, Verwey and Overbeek) forces for coated NMs.