Activated carbons possess high surface area (typically 1,000-2,000 m2g-1) and are powerful physical adsorbents, but have little catalytic activity except at high temperatures. Metal-organic framework (MOF) materials are generally effective catalysts, but are less effective as adsorbents. Recently, in a proof of concept, we have succeeded in synthesizing a GO/MOF nanocomposite material, and shown that it is very effective in removing toxic gases (ammonia, hydrogen sulfide) from gas streams through a combination of surface reaction and adsorption. The capacity of the nanocomposites to remove toxic gases significantly exceeds that of either the MOF or graphite oxide alone, and preliminary results for ammonia suggest that these nanocomposites can achieve a 300% or more increase in adsorption capacity over conventional activated carbons.
This project will be a joint experimental-theoretical study of such graphene/MOF and GO/MOF (collectively, G/MOF) nanocomposites, with the aim of determining their formation mechanism, atomic structure, pore structure and catalytic and adsorption properties, with the practical goal of designing materials with optimal adsorption and catalytic properties for the removal of toxic gases. As grapheme-based components graphite, graphite oxide and exfoliated graphite will be used. Syntheses will be followed by characterization. The interactions of NH3 and H2S, separately and mixed with methane, with the nanocomposites will then be investigated. These systems are chosen based on the properties and differences in the chemical nature of the adsorbates, the need for reactive adsorption under ambient conditions, and the potential detection capabilities of graphene-based nanocomposites. For the latter the changes in electrical conductivity can be employed. MOFs chosen for the study will include water stable materials with potentially active Cu, Cr and Fe sites, such as Cu-BT or MIL-100.
In parallel with the experimental program, dual scale theoretical studies using molecular simulation (Monte Carlo, Hybrid Reverse Monte Carlo and Molecular Dynamics) and (ab initio) density functional theory will be carried out to determine details of the atomic structure of the materials, the reaction mechanism, reactive adsorption capacity and heats of adsorption. These theoretical results will help direct the experimental program towards promising materials and conditions.
This research project will provide fundamental understanding of the relation between synthesis conditions, atomic structure and pore morphology, and separations performance for a new class of G/MOF nanocomposites that are designed for toxic gas removal. These novel materials may find application in other separations and in sensing devices. The broad spectrum of surface characterization and theoretical methods applied will lead to a better understanding of the surface chemistry of adsorbents and catalysts in general.
The research is directly relevant to developing new strategies to design effective materials for removal of toxic gases from air at ambient conditions through reactive adsorption. Another important technical aspect is the possibility of applications of these materials as gas sensors. If small molecule gases are intercalated within the graphite interlayer space the electrical conductivity is expected to change, and this phenomenon can be used to detect toxic gases at low concentration range. A preliminary exploratory study of ammonia on a GO/MOF nanocomposite showed an approximately threefold increase in adsorption capacity over conventional activated carbons. Thus, the proposed research is potentially transformative. The project will involve two graduate students, two undergraduate researchers and one high school student from an inner city science-oriented high school. CCNY is a minority serving institution, and the project would provide the possibility for a member of an under-represented group to perform research and to earn the Ph.D. NCSU?s AGEP/Opt-Ed and ORNL?s Research Alliance in Math and Science (RAMS) summer program will also provide opportunities to recruit students from under-represented populations. The whole education experience of the students will be based on the integration of research and education.