RUI: New Ultrastable Crystalline Porous Materials

非技术概述金属-有机骨架是由与有机配体配位的金属中心组成的分子级筛，其产生具有均匀孔径的三维结构。它们可以实现或改善大规模的能源，健康和国防应用，如气体储存和分离，水和其他化学品净化，直接水收集和从空气中捕获二氧化碳，以及核废物处理。然而，目前很少有金属-有机骨架材料具有孔隙率和化学稳定性的合适组合以满足这些应用的需求。开发化学稳定和孔径可调的金属有机框架是最重要的科学挑战之一，也是该项目的目标，该项目由材料研究部的固态和材料化学项目支持。该项目旨在通过同时创建高度连接的结构构建块和刚性框架来赋予高化学稳定性，这些结构构建块和刚性框架不易被常见分子和分子片段（如水和氢氧离子）分解。这些新材料的孔几何形状可以使用不同的组合结构构建块和有机配体进行调整。 通过开发这些新的合成途径，创造了金属有机框架材料中具有最高化学稳定性的新材料，这些材料可以在现实世界应用中经常遇到的苛刻化学条件下使用。此外，该项目还能开展各种研究活动，并为加州州立大学-长滩的不同人群的本科生和研究生提供丰富的培训机会。Xianhui Bu教授和他的研究小组开发合成途径，以创建一个新的超稳定和超不稳定的金属有机框架材料家族。该结构平台在金属-配体键类型（例如，金属-羧酸盐、金属-唑盐、金属-吡啶基），这允许在相同的等网格系列材料内对孔隙率、官能度和稳定性进行高水平的控制。为了扩大金属有机框架的酸碱稳定性的界限，研究人员合成了具有高连接（大于6）三聚体构建块的铬三聚体框架。在该项目之前仅已知低连接的铬金属有机框架（6个或更少），并且在该项目中具有混合的Cr-O和Cr-N交联的高连接框架材料的产生进一步增加了三价金属离子的动力学惰性，并且还保护金属节点免受配位物质的化学攻击。研究人员还系统地探索了关键的实验参数，如反应温度、溶剂类型和调制剂，与大多数金属有机框架中的不稳定离子相比，所有这些参数在该项目中对非不稳定金属离子的作用都要大得多。在该项目中实现的综合成分和结构特征同时在低pH和高pH方向上增加了酸碱稳定性。这些材料的特殊化学稳定性可以实现广泛的应用，特别是那些在苛刻的化学条件下运行的应用，如核废料处理。此外，该项目还能开展各种研究活动，并为加州州立大学-长滩分校的本科生和研究生提供丰富的培训机会。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL SUMMARYMetal-organic frameworks are molecular-scale sieves composed of metal centers coordinated to organic ligands, which results in three-dimensional structures with uniform pore size. They can enable or improve large-scale energy, health, and defense applications such as gas storage and separation, water and other chemical decontamination, direct water harvesting and carbon dioxide capture from air, and nuclear waste treatment. However, currently few metal-organic framework materials have a suitable combination of porosity and chemical stability to meet the demands of these applications. Developing chemically stable and pore-size-tunable metal-organic frameworks is among the most important scientific challenges and is the objective of this project, which is supported by the Solid State and Materials Chemistry program in the Division of Materials Research. The project aims to impart high chemical stability by simultaneously creating highly connected structural building blocks and rigid frameworks that are not easily broken down by common molecules and molecular fragments, such as water and hydroxide ions. The pore geometry of these new materials can be tuned using different combinations structural building blocks and organic ligands. By developing these new synthesis pathways new materials with the highest chemical stability among metal-organic framework materials are created that can be used under harsh chemical conditions commonly encountered in real-world applications. In addition, this project enables a variety of research activities and provides rich training opportunities for a diverse population of undergraduate and graduate students at California State University – Long Beach.TECHNICAL SUMMARYWith this project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research, Prof. Xianhui Bu and his research group develop synthetic pathways to create a family of new ultrastable and ultratunable metal-organic framework materials. The structural platform has an extraordinary flexibility in metal-ligand bond type (e.g., metal-carboxylate, metal-azolate, metal-pyridyl), which allows a high level of control over porosity, functionality, and stability within the same isoreticular series of materials. To expand the boundaries in acid-base stability of metal-organic frameworks, the researchers synthesize chromium-trimer-based frameworks with the high-connected (higher than 6) trimer building block. Only low-connected chromium metal-organic frameworks (6 or less) were known prior to this project, and the creation of high-connected framework materials in this project with mixed Cr-O and Cr-N crosslinks further increases the kinetic inertness of trivalent metal ions and also shields the metal nodes from chemical attacks by coordinating species. The researchers also systematically explore key experimental parameters such as reaction temperature, solvent type, and modulators, all of which play a far greater role for nonlabile metal ions in this project, compared to labile ions in most metal-organic frameworks. The integrated compositional and structural features to be achieved in this project increase acid-base stability simultaneously in both low- and high-pH directions. The exceptional chemical stability of these materials can enable a broad range of applications, especially those that operate under harsh chemical conditions such as nuclear waste treatment. In addition, this project enables a variety of research activities and provides rich training opportunities for a diverse population of undergraduate and graduate students at California State University – Long Beach.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.