Influences of Structural Design on Molecular Accessibility, Kinetics, Adsorption, and Reactivity: Degradation of CWAs by MOFs
Abstract
Military personnel and first responders are faced with increasing uncertainty in a complex battlefield environment in which the presence of chemical warfare agents (CWAs) can significantly affect operations. Advanced protective materials incorporating highly-efficient catalysts that provide rapid adsorption and decomposition of CWAs are needed to mitigate chemical threats. Current protective materials provide high adsorption capacity of liquid and low vapor-pressure CWAs but do not provide adequate chemical decomposition. Metal-organic frameworks (MOFs) offer materials designers the freedom to combine metal centers and organic linkers as structural building blocks to create a wide variety of topologies and structures for desired functionality including decontamination of CWAs. However, despite their open structures with extraordinary internal surface areas and reaction sites, many MOFs contain pore apertures that are either smaller than or comparable to the molecular sizes of CWAs and adequate access of CWAs to the internal surface of micropores in MOFs remains uncertain. Evaluations of micropore accessibility, diffusion and mass transport of CWAs in MOFs are urgently needed along with an understanding of the relevant chemical reaction mechanisms. Here we propose to use unique nuclear magnetic resonance (NMR) approaches including an in situ NMR-detected adsorption/desorption isotherm technique as well as Raman spectroscopy, ab initio density functional theory (DFT) and molecular dynamics (MD) simulations for studies of MOFs with four different ideal framework topologies as well as with carefully controlled and well characterized defects. We intend to establish relationships between key structural elements and optimized functionalities including micropore accessibility, kinetics, and reactivity of CWAs. This study will provide a valuable broad data set for the distillation of MOF design rules for effective decontamination of CWAs. The specific objectives are: 1) Synthesize Zr-based MOFs with different topologies and engineered defects, characterized by thermal analysis, x-ray diffraction, Raman, NMR, and MD simulations. 2) Evaluate micropore accessibilities under both dry and wet conditions by in situ NMR-acquired simulant isotherms as well as new NMR approaches, Raman techniques, and MD validations. 3) Measure reactivities of CWAs and simulants, identify reaction sites and mechanisms including the role of hydration. 4) Identify key characteristics of topology and defects crucial for optimizing accessibility, molecular mass transport, and reactivity, converging on design rules for effective decontamination of CWAs by MOFs. Our goal is to provide fundamental understanding at the molecular level of micropore accessibility, diffusion and mass transport, and chemical activity in MOFs and to shed light on how topological parameters of MOFs affect the overall CWA degradation process and thereby to elucidate design rules based on the role of topology for developing MOF catalysts as a key component for next-generation military and first-responder protective materials against CWAs.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Aug 01, 2019
- Source ID
- HDTRA11910008
Entities
People
- Yue Wu
Organizations
- Defense Threat Reduction Agency
- University of North Carolina at Chapel Hill