Adsorption Studies on Carbon Nanotubes

Southern Illinois University At Carbondale, Carbondale IL

Investigators

Abstract

DMR-0089713 Aldo Migone This proposal describes several sets of adsorption isotherm measurements that will be performed to characterize the systems formed by gases physisorbed on carbon nanotubes and on carbon nanohorns: 1) We will search for, and investigate the characteristics of, the one-dimensional (1-D) phases which can be present for gases adsorbed on bundles of single walled nanotubes (SWNTs). Our preliminary data indicate that 1-D phases are, indeed, present for Xe and CH4 on SWNT bundles. We will study further these two systems; 2) we will establish whether or not H2 can adsorb in the interstitial channels (ICs) of nanotube bundles, by comparing the area determined, on the same sample, using H2, and using a larger adsorbate. While this question remains open for H2, our results show that Ne, Xe and CH4 can not penetrate into the ICs; 3) we will determine the binding energies of H2, Ar, Kr and CF4 on close-ended and on open-ended SWNT bundles, and on agglomerations of carbon nanohorns. Our results for Ne, CH4, and Xe indicate that the binding energies on close-ended SWNT bundles are approximately 1.75 times larger than on graphite, in excellent agreement with theory. However, we have very preliminary (and quite intriguing) evidence that suggests that the binding energy for H2 may be considerably higher; and 4) we will investigate the adsorption of Xe, H2 and Ar on carbon nanohorns. We will determine the potential of carbon nanohorns for gas storage applications. All of the proposed experiments will be performed on high-sensitivity, in-house-built, computer-controlled setups, which have already been thoroughly tested in previous adsorption experiments. This work will be done with students who will be prepared to enter the scientific/technical work force of the next few decades. %%% This project deals with the characteristics of the systems formed by gases adsorbed on two new forms of carbon: nanotubes and nanohorns. Nanotubes have diameters which are ten thousand times smaller than a human hair. The walls of the nanotubes we will use in our studies are only one single atom thick (single-wall nanotubes). Gases adsorbed on nanotubes allow the physical realization, in the laboratory, of matter in one dimension. One-dimensional systems behave quite differently from three-dimensional matter; this makes these adsorbed systems interesting from a fundamental perspective. From a practical point of view, adsorption on nanotubes and on nanohorns (a related, form of carbon), has significant potential for applications in gas storage technology. This project consists of several parts: 1) An investigation of the different one-dimensional phases (i.e., the one-dimensional analogs of solids, liquids and gases) that are present in systems formed by gases adsorbed on nanotubes and nanohorns; 2) a determination of how tightly hydrogen, krypton, xenon, argon, and freon are bound to these two new forms of carbon; and 3) a determination of the effective area available for adsorption on carbon nanohorns for different gases. These quantities are determined by measuring, at several fixed temperatures, the amount of gas adsorbed on the carbon substrates, as a function of the pressure of the surrounding vapor. These measurements will be conducted on fully automated, high-sensitivity, adsorption setups. These experiments will be performed with the aid of students who thereby gain valuable experience in an area of current technological importance and who will be prepared for employment by industry, academia, or government. ***