DNP enhanced solid state NMR of green and sustainable materials

项目背景(查明问题及其对可持续性的重要性和相关性)为了开发绿色和可持续材料，更好地了解结构与性能的关系将有助于简化其设计和合成，从而能够进行更有效的过程。为了获得这种深入的理解，需要先进的分析技术。固体核磁共振是研究复杂和非均质材料分子水平细节的强大技术。然而，即使在今天的高磁场下，固态核磁共振也存在灵敏度低的问题，因为涉及到小的核自旋极化，因此需要长时间的采集或大样本。值得庆幸的是，在低温(~100K)下，通过动态核极化(DNP)可以增强微弱的核磁共振信号。动态核极化是指注入自由基的大电子自旋极化转移到附近的原子核。高功率微波源(回旋管)的进步使在现代核磁共振光谱仪中发现的高场DNP成为可能。冷冻生物分子的大信号增强(高达300倍)已经实现，相当于实验时间减少了100,000倍。最近，在介观结构杂化二氧化硅材料中，使用从浸渍到孔中的溶液中注入的自由基，记录了孔表面官能团的DNP增强的核磁共振信号。尽管略有提高(20倍)，但结构细节，如官能化基团的构象及其分布，是从13C和29Si核磁共振谱中建立的。这一研究引发了材料核磁共振领域的一场革命，使许多新的应用首次成为可能。DNP有可能将固态核磁共振转变为表征绿色和可持续材料的首选技术。目前，大多数这种类型的DNP研究涉及用特殊设计的双自由基溶液浸渍样品，并将其极化转移到感兴趣的原子核，然后通过溶剂基质进行极化转移。这一过程是一个关键因素，溶剂、自由基浓度、样品形态和表面积等的变化需要经验优化才能最大限度地提高效率。样品制备步骤代表了DNP增强固态核磁共振的一个问题，因为由此产生的增强是不可重现的，并且浸渍溶液可能与感兴趣的材料不相容。为了提高DNP增强固态核磁共振的适用性，该项目将开发新的样品制备技术。这些新技术将用于分析从CDT正在进行的研究中选择的各种绿色和可持续材料，包括聚合物、金属有机骨架材料和催化剂。提出的新样品制备技术有：1)超临界二氧化碳作为浸渍溶剂。2)以DNP为基质的介孔泡沫塑料(可根据要求提供每种技术的详细信息)领域：分析科学、催化、储能、功能陶瓷和无机物、能源应用材料、聚合物材料和表面科学

Project background (identification of the problem and its importance and relevance to sustainability)For the development of green and sustainable materials, greater understanding of structure-property relationships will help to streamline their design and synthesis allowing for more efficient processes. To gain this deep understanding, advanced analytical techniques are required.Solid-state NMR is a powerful technique for studying the molecular-level detail of complex and heterogeneous materials. However, even with the high magnetic fields available today, solid-state NMR suffers from low sensitivity, because of the small nuclear spin polarizations involved, so that long acquisitions or large samples are required. Fortunately, weak NMR signals can be enhanced at low temperatures (~100 K) by dynamic nuclear polarization (DNP) in which the large electron spin polarization from an implanted radical is transferred to nearby nuclei. Progress with high-power microwave sources (gyrotrons) has made DNP possible at the high fields found in modern NMR spectrometers. Large signal enhancements (up to 300-fold) have been achieved for frozen biomolecules, corresponding to a reduction by a factor of 100,000 in experiment time.More recently, DNP-enhanced NMR signals have been recorded for the functionalizing groups at the pore surfaces in meso-structured hybrid silica materials using radicals implanted from a solution impregnated into the pores. Despite the modest (20-fold) enhancement, structural details, such as the conformation of the functionalizing groups and their distribution were established from 13C and 29Si NMR spectra. This study triggered a revolution in materials NMR, making many new applications feasible for the first time.DNP has the potential to transform solid-state NMR into the technique of choice for the characterization of green and sustainable materials. Currently, most DNP studies of this type involve impregnating the sample with a solution of a specially designed biradical with polarization transfer to the nuclei of interest, followed by polarization transport through the solvent matrix. This process is a critical factor, with changes in solvent, radical concentration, sample morphology and surface area etc. requiring empirical optimization to maximize the enhancement. The sample preparation step represents a problem for DNP-enhanced solid-state NMR, since the resulting enhancement is not reproducible, and the impregnating solution may not be compatible with the material of interest.To improve the applicability of DNP-enhanced solid-state NMR this project will develop new sample preparation techniques. These new techniques will be used to analyse a variety of green and sustainable materials, chosen from research ongoing in the CDT, including polymers, metal organic framework materials and catalysts. The new sample preparation techniques proposed are:1) Supercritical carbon dioxide as an impregnation solvent. 2) Mesocellular foams as DNP matrices(details about each technique available on request)Areas: Analytical Science, Catalysis, Energy Storage, Functional Ceramics and Inorganics, Materials for Energy Applications, Polymer Materials and Surface Science