Adsorption of Gases in Nanoporous Materials: Equilibrium and Kinetics

Dr. Maria Calbi
Department of Physics
Southern Illinois University Carbondale

ABSTRACT
Adsorption phenomena on surfaces have been extensively investigated based on the presence of thermodynamic equilibrium between the external gas in contact with the surface and the adsorbed film. In nanoporous structures, however, the actual observation of the expected equilibrium properties (such as the total gas uptake for example) may strongly depend on how and how fast that equilibrium is reached, generally referred to as adsorption kinetics. Exploring the interplay between equilibrium and kinetics in a nanoporous structure is essential to fully understand and take advantage of its adsorption capacity, and to design nanomaterials tailored to provide specific applications. In particular, the investigation of the kinetics of adsorption (including the adsorption rates of different species) has always been the leading step to assess the separation efficiency of a sorbent for potential applications.

We present here a series of results concerning the kinetics of adsorption of different gases and mixtures on different regions of a carbon nanotube bundle. Carbon nanotubes have recently emerged as promising materials for separation and membrane applications, and assessing their properties for such purposes has become an imperative need. In addition, since these nanostructures have several kinds of adsorbing surfaces (including pores and inhomogeneous external surfaces) our results are also relevant to many other sorbents that typically have only one type of these surfaces. By implementing a Kinetic Monte Carlo algorithm to follow the time evolution of the gas uptake we are able to explore an interesting variety of kinetic phenomena, identifying the elemental processes responsible for the observed behavior. As a result, we have provided useful insight on long-standing controversies on the adsorption behavior of these structures (including direct explanation of several adsorption kinetics experiments), and also identified a new potential mechanism for gas separation.

BIO
Born and raised in Argentina, Prof. Calbi earned her PhD degree in physics at the University of Buenos Aires in 2000. She then completed her training in condensed matter physics at the Pennsylvania State University where she made her first contributions in the theory of gas adsorption on solid surfaces. In 2003, she joined the Physics Department at Southern Illinois University Carbondale where she was recently promoted to Associate Professor. One of her main interests lies on determining the ability of a variety of nanostructures to act as adsorbents by developing models and methods that can provide a basic understanding of the adsorption processes and phenomena (equilibrium and kinetics) in nanoporous materials. From a practical perspective, the goal is to provide a rational basis for assessing the performance of a nanostructure for specific adsorption applications that can be used, at the same time, to guide the design of new materials for such uses. Prof. Calbi’s research projects have been continuously funded by external agencies since 2005 and are currently supported by the National Science Foundation.  She is the recipient of a CAREER award from that agency, and was also recently honored with the “Presidential Early Career Award for Scientists and Engineers” (PECASE).