Influence of Surface and Solution Chemistry on the Aquatic Properties of Multi-Walled Carbon Nanotubes
Thursday, February 16, 2012
William P. Ball, Ph.D.
Department of Geography and Environmental Engineering
Whiting School of Engineering
Johns Hopkins University
Abstract: Multi-walled carbon nanotubes (MWCNTs) are fascinating engineered nanomaterials of high commercial value that are being produced at steadily increasing rates. The behavior of MWCNTs in aquatic systems is of interest in regard to their potential use in treatment technologies and also in the context of their environmental transport and toxicity. In order to develop fundamental understanding of how such particles behave in aquatic settings, we have been investigating the role of surface and solution chemistry in moderating the interactions of MWCNTs with potential dissolved water contaminants (e.g., polycyclic aromatic hydrocarbons and divalent metal cations) and on MWCNT deposition and transport in simple, well-characterized porous media. By providing precise measurements of CNT surface functionality and limiting our focus to simple and well-characterized systems, we hope to provide fundamental data that can complement work by others in more complex systems and provide insights into situations where their unique size and shape will play an important role. This seminar will present data obtained on the sorption, aggregation, deposition, and transport properties of various oxidized MWCNTs that have been prepared by refluxing in different HNO3 solutions. Focus will be on recent work to explore the applicability of filtration theory to the transport of well-dispersed tubes in spherical porous media. We have learned that extreme care must be taken to obtain understandable and reproducible results, but preliminary results suggest that clean-bed filtration theory can apply for properly controlled conditions. Our results to date indicate that the effects of surface functionalization, pH, and ionic strength on MWCNT deposition are qualitatively consistent with DLVO theory, such these materials behave much like other colloids in these regards. On the other hand, preliminary data from the transport experiments suggest, that the extremely high aspect ratio of these materials may make them much more susceptible to interception mechanisms of collision than would be expected on the basis of their hydrodynamic diameter.