Tailoring Single-Walled Carbon Nanotubes with Structure-Selective Photochemistry

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Professor Robert B. Weisman of William Marsh Rice University is supported by the Macromolecular, Supramolecular and Nanochemistry Program of the Division of Chemistry to develop new methods to control and manipulate the optical and chemical properties of single-wall carbon nanotubes using laser light sources of specific wavelengths. Carbon nanotubes are an exciting class of nanomaterials that are technologically important for their unique physical and chemical properties and their many potential real-world applications, including uses in energy, health care, and the environment. Current carbon nanotube preparation methods result in mixtures with many structural forms and properties. Separation and sorting of these mixed components are often needed to obtain samples suitable for specific applications. The project selectively alters the surface chemistry of targeted nanotube species to allow them to be physically separated with greater ease and scalability than is currently possible. The aim is to generate samples with tailored optical properties and compositions, enabling advanced and deeper understanding of carbon nanotube reactions, interactions with light, and potential practical applications. In addition to training students in the advanced spectroscopy and analytical chemistry of nanomaterials, high school teachers and a professional visual artist are involved in the project. The teachers are hosted in the laboratory to conduct summer research, thereby gaining knowledge and perspective to enrich their teaching. The artist is incorporating fluorescent carbon nanotubes into his artwork to engage and educate the public about nanotechnology.In this project, optical transitions at short-wave infrared wavelengths are used as a tool to control the composition of single-wall carbon nanotube mixtures. Samples containing nanotubes of many different diameters and chiralities are irradiated with lasers at specific short-wave infrared wavelengths chosen to selectively excite the S11 transitions of targeted nanotubes within the sample. In the presence of appropriate reactants, those excited nanotubes become chemically functionalized. The resulting selectively functionalized nanotube structures exhibit altered physico-chemical properties and suppressed fluorescence yields. In this way, targeted portions of the sample's emission spectrum are "carved out" to generate customized spectral profiles suited for use in basic research and applications development. Subsequent processing of the sample using methods such as aqueous two-phase partitioning or controlled centrifugation isolates the functionalized targeted structure from the rest of the sample. The isolated fraction is then defunctionalized using thermal and chemical methods to recover the physically separated structure in its pristine form. The ultimate goal is to generate structurally sorted carbon nanotube samples with tailored optical properties and compositions. These are investigated to arrive at a deeper understanding of carbon nanotube spectroscopy, photo-processes, and reactions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.