Gas Adsorption in Nanoporous Materials: Molecular Structure and Recognition

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ABSTRACT CTS-0114123Lee, Lloyd L/ U of Oklahoma Nanostructured materials are currently being developed for use in molecular adsorption and molecular recognition. The design and selection of sensor materials [65,66] in commercial use have been mostly done by trial and error and qualitative thinking, rather than with tailor-made specificity and quantitative principles. With the development of the nanostructured materials, such as self-assembled monolayers (SAMs) and dendritic structures, there have been created a vast menu of chemical and physical properties for selection. We need to have a molecular level understanding of the nature and consequence of the molecular interactions at play. This research is aimed at establishing a microscopic framework, using molecular theory and computer simulation, for gas adsorption in three typical nanomaterials: aerogels, zeolites, and starburst dendrimers. This furnishes a quantitative principle rooted in the molecular level that shall aid in the design and development of gas adsorption and molecular recognition devices.There are, broadly speaking, older nanomaterials (e.g., zeolites, membranes, aerogels, activated carbons, etc.) and newer ones (e.g., star polymers, dendrimers, etc.) Whathappens to the gases (fluids) included in these substrates with respect to their molecular distributions, isosteric heats of adsorption, phase behavior, thermodynamic properties, adsorption isotherms, separation efficiency (for mixtures), selective adsorption, and partition coefficients? An accurate molecular theory and well-targeted molecular simulation are needed that give the probabilistic densities of distribution of theconfined gases around the ordered substrates, as well as their theoretical connections to the thermodynamic properties. This is properly the task for our statistical mechanics of adsorption.The principal investigator will develop a new integral equation (IE) theory and perform molecular computer simulation to determine the gas structures (distribution functions) and thermodynamic properties of inclusion gases and gas mixtures around nanostructures. He uses the existing replica Ornsterin-Zernike (ROZ) equations as astarting point. New forms will be developed for the inclusion gas in random as well as regular media, and in rigid as well as deformable adsorbents. The conventional ROZ can treat only inrigidlo matrices. He uses a two-temperature quench procedure to formulate a new equation for responsive systems. In addition, consistency is achieved by designing a new closure relation satisfying a set of exact self-consistency principles. The principal investigator stresses that without this closure relation, a good one at that, no integral equations can achieve high consistency, nor accuracy. Monte Carlo molecular simulations and molecular dynamics will be carried out to determine the mechanism of adsorption and to test the theories.