Final Report Summary - EXONMR (Exploiting 17O NMR Spectroscopy: Atomic-Scale Structure, Disorder and Dynamics in Solids)
The project exploited the largely untapped potential of solid-state 17O NMR spectroscopy. The fundamental importance of oxide-based systems in technology, energy materials, geochemistry and catalysis, and the presence of oxygen in many biomaterials, should have resulted in oxygen NMR spectroscopy emerging as a vital tool for the characterization of solid materials. However, despite the almost ubiquitous presence of oxygen in inorganic solids, oxygen NMR studies have been relatively scarce in comparison to more commonly-studied nuclei, owing primarily to the low natural abundance of the only NMR-active isotope, 17O (0.037%). While enrichment of materials with the isotope is possible, this can be very costly and restricts the synthetic procedures that can be used. Furthermore, the presence of anisotropic quadrupolar broadening in 17O NMR spectra hinders the extraction of accurate structural information. The programme involved:
1. The exploration of novel synthetic approaches for cost-efficient isotopic enrichment of solids with 17O, enablng NMR experiments to be performed on a reasonable timescale with good sensitivity. The methods developed require tiny amounts of high cost enriched reagents, and ensure as much as possible of the enriched material is incorporated into the final product. For example, we have shown that microporous zeolite frameworks (that have applications in catalysis and ion exchange) can be easily enriched at room temperature by wetting with a small amount of enriched water, avoiding the conventional high temperature routes that can modify their structures and affect their reactivity.
2. The development of new solid-state NMR methodology to improve the sensitivity of 17O NMR experiments. Despite isotopic enrichment, the sensitivity of 17O NMR spectroscopy remains poor, particularly for the high-resolution experiments required to remove the broad lines present in NMR spectra of quadrupolar nuclei. As an example, we have replaced the pulses conventionally used in these experiments by trains of pulses designed by automated, high-throughput simulations.
3. The development and application of first-principles calculations of NMR parameters in solids. The complex lineshapes seen for disordered solids provide a significant challenge for the interpretation and assignment of NMR spectra; necessary to validate structural models, and to understand how materials are affected by substitution, hydration, adsorption and chemical reactions. We have tested methods for predicting NMR parameters in solids, including new work visualizing unusual couplings between atoms. We have also investigated different methods for efficiently generating structural models for systems that exhibit disorder (i.e. a variation in the nature or position of atoms in space or time). We have exploited automated computational approaches to efficiently generate 1000s of possible structures, for which predicted NMR parameters can then be compared to experiment.
4. The combined application of new NMR experiments and computational methods to investigate disordered materials. Work has included the study of disordered ceramic materials with applications for the encapsulation of radioactive waste, the hydration of the high-pressure silicate minerals that are found at depths of 400 km in the Earth’s mantle, understanding the host-guest interactions in microporous solids with uses drug delivery and gas storage and investigating the chemical reactivity of zeolite materials, used in catalysis, and understanding how novel zeolites can be made by following this reaction within the NMR spectrometer.
We have shown that the combination of isotopic enrichment, advanced NMR spectroscopy and computation is able to provide detailed information on the local structure, disorder and chemical reactivity of a range of inorganic materials, aiding research in geoscience, materials chemistry and inorganic chemistry. The advances in methodology and new approaches we have introduced are readily transferrable, and the materials studied represent a fraction of the potential future applications of our research.
1. The exploration of novel synthetic approaches for cost-efficient isotopic enrichment of solids with 17O, enablng NMR experiments to be performed on a reasonable timescale with good sensitivity. The methods developed require tiny amounts of high cost enriched reagents, and ensure as much as possible of the enriched material is incorporated into the final product. For example, we have shown that microporous zeolite frameworks (that have applications in catalysis and ion exchange) can be easily enriched at room temperature by wetting with a small amount of enriched water, avoiding the conventional high temperature routes that can modify their structures and affect their reactivity.
2. The development of new solid-state NMR methodology to improve the sensitivity of 17O NMR experiments. Despite isotopic enrichment, the sensitivity of 17O NMR spectroscopy remains poor, particularly for the high-resolution experiments required to remove the broad lines present in NMR spectra of quadrupolar nuclei. As an example, we have replaced the pulses conventionally used in these experiments by trains of pulses designed by automated, high-throughput simulations.
3. The development and application of first-principles calculations of NMR parameters in solids. The complex lineshapes seen for disordered solids provide a significant challenge for the interpretation and assignment of NMR spectra; necessary to validate structural models, and to understand how materials are affected by substitution, hydration, adsorption and chemical reactions. We have tested methods for predicting NMR parameters in solids, including new work visualizing unusual couplings between atoms. We have also investigated different methods for efficiently generating structural models for systems that exhibit disorder (i.e. a variation in the nature or position of atoms in space or time). We have exploited automated computational approaches to efficiently generate 1000s of possible structures, for which predicted NMR parameters can then be compared to experiment.
4. The combined application of new NMR experiments and computational methods to investigate disordered materials. Work has included the study of disordered ceramic materials with applications for the encapsulation of radioactive waste, the hydration of the high-pressure silicate minerals that are found at depths of 400 km in the Earth’s mantle, understanding the host-guest interactions in microporous solids with uses drug delivery and gas storage and investigating the chemical reactivity of zeolite materials, used in catalysis, and understanding how novel zeolites can be made by following this reaction within the NMR spectrometer.
We have shown that the combination of isotopic enrichment, advanced NMR spectroscopy and computation is able to provide detailed information on the local structure, disorder and chemical reactivity of a range of inorganic materials, aiding research in geoscience, materials chemistry and inorganic chemistry. The advances in methodology and new approaches we have introduced are readily transferrable, and the materials studied represent a fraction of the potential future applications of our research.