Krista S. Walton
Assistant Professor
Contact Information
Building: Ford ES&T
Office:
2220
Phone:404.894.5254
Fax: 404.894.2866
email
Mailing Address
Georgia Institute of Technology
School of Chemical &
Biomolecular Engineering
311 Ferst Drive, N.W.
Atlanta, GA 30332-0100
Links
Krista S. Walton
Education
B.S.E., University of Alabama (Huntsville), 2000
Ph.D., Vanderbilt University, 2005
Research Interests
Metal-Organic Frameworks for Adsorption Separations
Microporous metal-organic frameworks (MOFs) have emerged over the past decade as an important new class of materials possessing permanent porosities, uniform pore structures, high surface areas, and low crystal densities. These materials are synthesized under mild conditions from metal ions and organic bridging ligands. The level of design inherent to MOF synthesis has important implications for the development of “smart” materials and has led to much speculation on their ability to be tailored and functionalized for use in applications such as selective sensors, hydrogen storage, and highly selective separations. The development of MOFs for these applications hinges upon a fundamental understanding of adsorption phenomena in these unique host-guest systems, and due to the diverse nature of MOF structures, their adsorption behavior can be quite complex. An incredible number of new MOFs have been synthesized since the late 1990s, but the number of detailed adsorption studies in these new materials is lacking. In particular, multicomponent adsorption equilibria in MOFs is relatively unexplored, but this information is vital to the development of these materials for adsorption applications. The main goal of this project is to examine MOFs as potential adsorbents for gas separations. We are particularly interested in studying mixtures such as CO2 and methane. MOFs have the potential to separate molecules based on differences in polarities, in addition to size and shape preferences. Our lab performs MOF syntheses, adsorption equilibrium measurements, and molecular modeling studies. Cu-BTC (shown in the first figure at left) is a MOF of current focus.
This material is based upon work supported by the National Science Foundation under Grant No. 0700489. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.
Nanostructured Media for Air Purification
One of the biggest challenges in designing or identifying novel porous materials for adsorption applications is developing an in-depth understanding of structure-property relations and host-guest interactions. This information is critical because if we understand the adsorption mechanisms, i.e., how, where, and why a molecule adsorbs in a certain material, we can then exploit this knowledge to design structures that interact more effectively with the molecule of interest. Thus, it is insufficient to focus only on synthesizing materials with permanent porosity. It is essential to also have a good understanding of adsorption science and technology to enable the identification of materials properties that are conducive for use in adsorption applications. This can then provide direction for synthesis efforts. Metal sites in zeolites and impregnated carbons are known to give rise to special adsorption and catalytic behavior. However, the tailoring of these materials for selective interaction with target compounds is limited by the inherent disorder of such sites, large pore size distributions, and rigid structures that are not amenable to chemical modification. The building-block approach to metal-organic framework design provides tremendous flexibility in tailoring these porous materials to have specific physical characteristics and chemical functionalities. A particular focus of this project is the design/identification of novel materials that provide effect removal of high vapor pressure compounds from air.
Multifunctional Structures for Reactive Adsorption
Thousands of new metal-organic frameworks have been synthesized over the past several years, but adsorption and catalytic properties of MOFs are just beginning to be explored in detail relative to traditional porous materials such as activated carbons and zeolites. The focus of this project is to perform a detailed, systematic adsorption study of CO in several MOFs with open metal sites by employing a well-rounded approach combining adsorption equilibrium measurements, X-ray photoelectron spectroscopy, FTIR, and molecular modeling. The results of this thorough investigation will provide much needed predictive information regarding host-guest interactions that will allow us to assess the effectiveness of open metal sites in inducing Lewis acidity for selective adsorption and catalytic behavior.This research will establish a well-characterized baseline system from which improved structures may be developed. The ability to control the physical structure and chemical functionality of porous materials will be an invaluable tool that has important implications for advancing the state-of-the-art in general adsorption-based applications ranging from hydrogen storage and adsorptive separations, to drug delivery devices and smart coatings.
Porous Materials for Controlled Storage and Release
Over the past decade, the development of nitric oxide-releasing materials for implantable biomedical devices has become an intense area of research, and it is now generally accepted that controlled release of NO can prevent thrombus formation at artificial surfaces. The majority of these efforts have centered on doping polymers such as poly(vinyl chloride) with NO-generating secondary amines. After implantation, the NO molecules are then released from the material upon contact with moisture. This method has proven to be effective in preventing thrombus formation. However, it was found by later studies that the water-soluble NO-generating amines would leach from the polymer matrices. This resulted in measurable quantities of carcinogenic nitrosamines in the surrounding media. Efforts to prevent leaching included the use of more lipophilic NO donors that prefer to stay in the polymer phase, and covalent tethering of the donors to the polymer backbone or to embedded nanoparticles. However, donors such as these provide a limited reservoir of NO, and modification of the polymer matrix to include more NO is difficult due to lack of specificity for NO binding. To address these impotant issues, the focus of this research project is the development of porous materials with specificity for NO adsorption (storage) and controlled desorption (release) by exposure to water. Successful development of these types of systems could lead to significant advances in therapeutic coatings.