Achieving High Performance Metal-Organic Framework Materials through Pore Engineering

Achieving high performance functional materials has been a long-term goal for scientists and engineers that can significantly promote science and technology development and thus benefit our society and human beings. As well-known porous materials, metal-organic frameworks (MOFs) are crystalline open frameworks made up of molecular building blocks linked by strong coordination bonds, affording pore space for storing and trapping guest molecules. In terms of porosity, MOFs outperform traditional porous materials including zeolites and activated carbon, showing exceptional porosity with internal surface area up to thousands of square meters per gram of sample and with periodic pore sizes ranging from sub-nanometer to nanometers. Numerous MOFs have been synthesized with potential applications ranging from storing gaseous fuels to separating intractable industrial gas mixtures, sensing physical and chemical stimulus, and transmitting protons for conduction. Compared to traditional porous materials, MOFs are distinguished for their exceptional capability for pore adjustment and interior modification through pore engineering, which have made them a preeminent platform for exploring functional materials with high performance. Rational combinations of rigid building units of different geometry and multibranched organic linkers have provided MOFs with diverse pore structures, ranging from spherical to cylindrical, slit, and tubular ones isolating or interconnecting in different directions, which can be optimized for high-capacity gas storage. Based on the isoreticular principle and building blocks approach in MOF chemistry, the pore adjustment of porous materials can be performed with exquisite precision, making them suitable to address industrially important gas separation. The large pore cavities in MOFs are readily available for encapsulation of different functional guest species, resulting in novel MOF composite materials with various functions. In this Account, we summarize our recent research progress on pore engineering to achieve high-performance MOF materials. We have been able to tune and optimize pore structures, immobilize specific functional sites, and incorporate guest species into target MOF materials for hydrogen storage, methane storage, light-hydrocarbon purification, and proton conduction, especially for various industrially important gas separations including acetylene removal and ethylene and propylene purification. By engineering the porosity and pore chemistry that endows MOFs with multiple functionalities, our research endeavors have brought about the customization of high-performance MOF materials for corresponding application scenarios.