Growing concerns about the environment and terrorist attacks prompt a search for effective adsorbents for removal of small molecule toxic gases, such as ammonia and hydrogen sulfide, under ambient conditions in the presence of moisture, where physical adsorption is not adequate. We use graphene oxide and CuBTC metal-organic framework as the adsorbents to explore toxic gas removal by reactive adsorption. Using ab initio density functional theory, atomistic reactive molecular dynamics and Monte Carlo simulation strategies, theoretical understanding of the underlying reaction and adsorption mechanisms of ammonia and hydrogen sulfide on graphene oxide and CuBTC metal-organic framework have been gained.
The ab initio calculation results show that ammonia and hydrogen sulfide decompose on carboxyl and epoxy functional groups and vacancy defects of graphene oxide. The existence of water molecules substantially reduces the adsorption/dissociation of ammonia or hydrogen sulfide on graphene oxide because the water molecules either form hydrogen bonds with the functional groups or adsorb more easily on the vacancy defects. Reactive molecular dynamics calculations by the ReaxFF method have been performed to propose realistic graphene oxide models for theoretical calculations. We also use reactive molecular dynamics simulation to study the thermal and hydrostatic stabilities of the CuBTC metal-organic framework and its application for ammonia removal. We predict the collapse temperature for CuBTC crystal structure and observe the partial collapse of CuBTC at lower temperatures upon ammonia adsorption. The results agree well with experiment data and provide insights on the reaction mechanism involved in such an ammonia removal process.
The research in this thesis can provide fundamental understanding, at the electronic and atomistic levels, of the roles of surface defects and functionalities for reactive adsorption of toxic gas molecules. In addition to developing experimental and theoretical algorithms to design effective adsorbents, the results are expected to find applications in air cleaning, energy storage, fuel cell technology and other scientific challenges where the separation of reactive molecules is involved.
|Advisor:||Gubbins, Keith E., Westmoreland, Phillip R.|
|Commitee:||Brenner, Donald W., Hall, Carol K.|
|School:||North Carolina State University|
|School Location:||United States -- North Carolina|
|Source:||DAI-B 74/07(E), Dissertation Abstracts International|
|Subjects:||Toxicology, Surgery, Chemical engineering, Materials science|
|Keywords:||Graphene oxide, Metal-organic frameworks, Reactive adsorption, Reactive molecular dynamics, Toxic gas removal|
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