Omar M. Yaghi is a Jordanian chemist celebrated in the scientific communities for his outstanding contributions in the field of material science. Yaghi worked for long years on the development of new substances that have extremely high surface area and very low crystalline densities.
Omar Yaghi, has successfully produced classes of compounds known as Metal-Organic Frameworks (MOFs), Zeolitic Imidazolate Frameworks (ZIFs), and Covalent Organic Frameworks (COFs). He developed these materials from basic science to extensive applications in clean energy technologies, including hydrogen and methane storage, as well as carbon dioxide capture and storage.
To have an understanding of the nature of the materials Yaghi developed, one needs first to grasp a specific concept in material science. For starters, a metal microscopic structure consists of a crystalline arrangement of atoms, ions, or molecules. Let us think of this crystalline structure as a large box that is built of an array of smaller boxes, while each one of the smaller boxes in turn consists of much smaller boxes, infinitely repeating in all three spatial directions.
Such a unit cell is the smallest unit of volume that contains all of the structural and symmetry information to build-up the macroscopic structure of the metal lattice. The atoms or molecules are linearly connected to each other by bonds to form chains of molecules. The chains, in turn, are cross-link connected to each other forming the overall structure of the material. The nature of these bonds has a great influence on the physical properties of the material.
Yaghi developed a new material, Metal-Organic Frameworks, which is a compound that consists of metal ions coordinated to organic molecules to form dimensional structures that have high porosity. This material was made by linking inorganic and organic units by strong bonds. The flexibility with which the constituents’ geometry, size, and functionality can vary has led to more than 20,000 different MOFs that Yaghi reported and studied within the past decade.
The organic units are usually negatively charged molecules, which, when linked to metal-containing units, yield architecturally robust crystalline MOF structures with a typical porosity of greater than 50% of the MOF crystal volume. The surface area values of such MOFs typically range from 1000 m2/g to 10,000 m2/g; thus, exceeding those of traditional porous materials, such as zeolites and carbons.
Today, Yaghi’s Metal-Organic Frameworks with permanent porosity are more extensive in their variety and multiplicity than any other class of porous materials known. These aspects have made MOFs ideal materials for storage of fuels—hydrogen and methane—capture of carbon dioxide and catalysis applications to mention a few.
After successfully developing his Metal-Organic Frameworks, Yaghi decided to zoom-in his work in developing a subclass of MOFs that can be employed in energy-intensive industries and produce tangible energy and cost saving. This was the Zeolitic Imidazolate Frameworks.
Industrial separation processes comprise approximately 10 % of the global energy demand, driven largely by the utilization of thermal separation methods; for example, distillation. Yaghi studied these processes and realized that significant energy and cost savings can be realized through advanced separation techniques, such as membranes and sorbents.
One of the major barriers to acceptance of these techniques remains creating materials that are efficient and productive in the presence of aggressive industrial feeds. This is where Yaghi decided to employ his Zeolitic Imidazolate Frameworks as a thermally and chemically stable subclass of metal organic framework. The porous structures of ZIFs can be heated to high temperatures without decomposing, and can be boiled in water or solvents for a week and remain stable, making them suitable for use in hot, energy-producing environments such as power plants.
He did not stop there. Yaghi continued in upgrading the design and synthesis of crystalline extended organic structures and developed another subclass of metal organic frameworks in which the lattice building blocks are linked by strong covalent bonds. The upgraded materials were porous crystalline solids consisting of secondary building units that assemble to form a periodic and highly porous framework.
An almost infinite number of frameworks can be formed through various secondary building unit combinations, leading to unique material properties for applications in separations, storage, and heterogeneous catalysis. These are the Covalent Organic Frameworks (COFs). They are porous, crystalline, and made entirely from light elements—H, B, C, N, and O—that are known to form strong covalent bonds in well-established and useful materials such as diamond, graphite, and boron nitride.
The successful realization of covalent organic framework materials through molecular building blocks provided unique frameworks that could be functionalized into lightweight materials optimized for gas storage, photonic, and catalytic applications.
In 2006, Omar Yaghi’s work on methane and hydrogen storage was recognized by several publications, which listed him among the “most brilliant 10 scientists and engineers in the USA”. In 2010, Science Watch published a list of the “top 100 chemists in the world”; in this list Omar Yaghi was the second name.
References
Yaghi, Omar M. et al., “Effects of functionalization, catenation, and variation of the metal oxide and organic linking units on the low-pressure hydrogen adsorption properties of metal-organic frameworks”, 2006.
Yaghi, Omar M. et al., “Exceptional chemical and thermal stability of zeolitic imidazolate frameworks”, 2006.
Yaghi, O. M. et al., “Reticular synthesis and the design of new materials”, 2003.
http://yaghi.berkeley.edu
www.sciencedaily.com
www.sciencemag.org