RUI: New Ultrastable Crystalline Porous Materials

NON-TECHNICAL SUMMARY

Metal-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 SUMMARY

With 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.