GOALI: Molecular Modeling of Confined Nano-Phases and Nano-Porous Materials

North Carolina State University, Raleigh NC

Investigators

Abstract

ABSTRACT CTS-9908535 Gubbins, K./N. C. State Activated carbons are the most widely used of all industrial adsorbents. They have two main advantages: (a) they are cheap, since they are made from readily available materials (wood, lignite, etc.), (b) they adsorb a wide range of fluids and materials very strongly, and are highly selective. The latter property derives from the fact that the carbon atoms are very high. Despite these advantages, activated carbons have proved very difficult to characterize because of their complex and amorphous structure. In general they possess both micropores (less than 2 nm in width) and also some mesopores (larger than 2 nm) linked in a complex pore structure. Some information on this structure can be obtained from small angle x-ray or neutron scattering (SAXS and SANS), and from high resolution transmission electron microscopy (HRTEM). However, the picture of the structure is incomplete from experiment. A realistic structural model of the carbon, at the molecular level, is needed in order to interpret other experiment on these materials, to determine pore size distributions, and to predict selective adsorption and pore phase transitions for the wide range of chemical systems used in industry. The current models used for this purpose (arrays of independent slit pores) are known to be much over simplified, and are too crude for industrial needs. We have recently developed protocols based on molecular simulation to construct much more realistic models of carbons at the atomic level. These are based on Reverse Monte Carlo, which matches the structure of the model to the structure factor (SAXS or SANS) and HRTEM data from experiment. The resulting models agree well with other experimental measures of the carbons, and there is good reason to believe that they are quite accurate representations of the real materials, A long range goal is to use these simulation methods to construct a data bank of materials which could be used to match data for particular industrial carbons. Such a data bank can be used for characterization of a wide range of carbons, and subsequent prediction of their adsorption and separation behavior. Most of the expertise for synthesizing these carbons, and in addition most of the characterization and adsorption data, resides in industry. We need access to samples of these materials, and particularly advice on future directions for the modeling, in order to ensure that our research follows directions that are most relevant and useful for industry. Westvaco is a major world producer of these carbons. Westvaco's Charleston Technical Center has a number of leading experts in synthesis and characterization of activated carbons, particularly: Dr. Jacek Jagiello, Research Chemist