Recently, carbon nanotube membranes attracted attention because of experiments and simulations indicating extremely high fluxes. If selective separations can also be demonstrated, these membranes will be a major breakthrough in efficient gas, liquid and vapor separations with tremendous implications in energy efficiency, especially in hydrocarbon separations, water purification and microdevices for hydrogen purification and storage. The currently used multi-step microfabrication procedures, although appropriate for laboratory scale measurements, do not allow for efficient and economic production of the large membrane areas (e.g., hundred square meters) needed for membrane based purification applications nor they provide means for precisely controlling nanotube size and structure that may be desirable for highly selective separations. We propose to undertake the challenge to develop practical selective nanotube membranes by growing submicron thick, densely-packed, subnanometer diameter carbon nanotubes in the interior of the pores of oriented aluminophoshate (AlPO4) molecular sieve films. The proposed use of AlPO4 films as hosts of carbon nanotubes is motivated by previous studies that demonstrate carbon nanotube synthesis inside the micropores of AlPO4 crystalline powders and builds on our ability to grow well-intergrown and appropriately oriented AlPO4 films. If successful, we expect to form high concentration of oriented and uniformly sized carbon nanotubes extending throughout the molecular sieve channels. It is possible that membranes with unprecedented performance (high selectivity and extremely high flux) will be the ultimate outcome of this work. Moreover, the growth technique that we propose to develop and the resulting oriented carbon nanotube films may be of interest for electronic and electrochemical applications.
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