The PIs propose a novel approach to the scalable, chiral separation of SWNT in which chirality-determined surface charge is introduced onto the SWNT; subsequently, liquid chromatography techniques are employed to resolve individual SWNT subtypes. The chemical processing procedures which prepare the SWNT for subsequent separation involve the application of functional groups to the nanotubes in a way that exploits differential chiral reactivity. This in turn leads to differential surface acidity/basicity for the functionalized nanotube subtypes as reflected in their different point of zero charge (PZC) values. Professor Pfefferle is an expert in SWNT synthesis and in producing narrow distributions of SWNT identities and functionalizing and characterizing them. She is also developing the concept of using SWNT surface charge as a chirality marker. Functionalized SWNT will be separated on the basis of their surface charge using high-resolution, high-throughput methods involving chromatofocusing that exploit electrostatic interactions. Methods of this type have been under development over the last several years by Dr. Frey at the UMBC for biotechnology applications and will be further adapted here so that they apply specifically to the case of SWNT separations. To accomplish this, the PIs will investigate the use of column packing materials that are likely to enhance the adsorption capacity for SWNT, such as tentacle-type column packings, where the ion-exchange functional groups are located on linear polymer chains extending outward from the particle surface. The PIs will also investigate the use of innovative elution strategies involving chromatofocusing focusing in combination with mobile phase modifiers that optimize the balance between electrostatic and hydrophobic forces during elution. Another line of investigation will be to evaluate novel methods to affect the behavior of SWNT during chromatography, such as the use of microwave radiation.
Broader Impacts: The expected result of the proposed research will be a flexible method that can produce subtypes of purified SWNT from the laboratory scale to the industrial scale. The ability to take a mixed batch of SWNT and, in a scalable manner, obtain a highly selective separation of each component is an important goal in the carbon nanotube field. The current unavailability of inexpensive high purity SWNT is the major reason why SWNT-based electronics have not been practical to-date. By solving this key technical challenge, this project has the potential to be truly transformative. Despite their far-reaching potential, the methods to be investigated here are simple in concept and lend themselves well to projects involving both undergraduate and high school students. Many such students have participated in the past in the PIs? research both at Yale and UMBC. The PIs will expand this effort and include interactions between our groups, and thereby present an exceptional opportunity for students at all levels to participate in an interdisciplinary research program that exploits the complementary capabilities of the PIs.
