COLL 350 |
| A nanomaterial's surface chemistry will influence its behavior in the environment, dispersion properties in polar and nonpolar solvents, and utility in medical and engineering applications. In the case of carbon nanotubes (CNTs), the concentration and distribution of surface oxides are one of the most important aspects affecting the surface properties and, consequently, behavior in aquatic environments. Oxygen containing functional groups permit the long hydrophobic CNTs to separate and form stable suspensions in aqueous environments. To understand the influence of oxides on CNTs, we have treated the CNTs' surface with different concentrations of nitric acid as well as with varying equivalents of permanganate; we have found that the gross level of surface oxides measureed with X-ray Photoelectron Spectroscopy (XPS) systematically increases with the amount of oxidant. In lieu of Boehm titrations, a traditional and difficult method for determining oxide distribution, we have developed a spectroscopic technique using XPS in conjunction with specific chemical derivatization reactions to selectively tag oxide groups (hydroxyl, carbonyl, and carboxyl) with fluorine containing reagents in stoichiometric quantities. Using this technique, we have accounted for over 90% of the surface oxides present on our oxidized CNTs. Information obtained from these studies has been crucial in understanding the behavior of CNTs in aqueous environments and highlights the fact that oxide distribution as well as oxygen concentration control the macroscopic behavior of CNTs. We have also developed methods to modify oxide distributions and tailor the CNTs surface properties using selected chemical treatments and thermal annealing. |
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The Physical Chemistry of Environmental Interfaces
8:30 AM-12:40 PM, Wednesday, April 9, 2008 Morial Convention Center -- Rm. 225, Oral
Division of Colloid & Surface Chemistry |