Nobel Prize in Chemistry: Next-Gen Smart Sorbents

Between 1995 and 1999, this year’s Nobel laureates developed a new chemical technology that makes it possible to use organic and inorganic materials in the building of metal-organic frameworks (MOFs) – special porous materials that can selectively absorb various substances. In these frameworks, metal ions are bound by long organic molecules and organized into crystals with large cavities – pores that are able to absorb all kinds of substances. By combining different metal ions and molecules, chemists can create materials with pores of varying sizes and shapes that can separate or store water, CO2, carbohydrates, toxic metals, and other substances.

“Metal-organic frameworks have enormous potential, bringing previously unforeseen opportunities for custom-made materials with new functions,” states the website of the Nobel Foundation.

For traditional sorbents (activated carbon, zeolites, silica gel), their properties are usually determined by nature – the size and shape of their pores is hard to change, which means that any materials based on them aren’t selective in terms of what they absorb. MOFs, on the other hand, are ordered and changeable structures that can be made for a specific task, such as to catch molecules of CO2 while allowing water through.

“MOFs combine the best properties of compound particles within a single material: the strength of metal-coordination connections and the flexibility and responsiveness of organic molecules. The high specific surface parameters provided by the large share of free space inside the metal-organic architecture enable the frameworks to absorb and store gas, accelerate organic reactions, and purify water. These capacities can help solve modern problems in ecology, biomedicine, and chemical industry,” says Anton Muravev. 

The first attempts to produce ordered, porous molecular structures took place in Japan in 1959, but proved unsuccessful. Richard Robson was the next to try – and was more lucky. In 1989, he connected positively charged copper ions with a four-rayed molecule, creating an ordered crystal. However, the structure was unstable and fragile. A few years later, between 1995 and 1999, Susumu Kitagawa and Omar Yaghi improved this method – independently of each other – and made a number of important discoveries. For instance, Susumu Kitagawa showed that gas can “flow” into MOFs and flow out of them and suggested that these structures can be made flexible. In 1999, Omar Yaghi created MOF-5, a very durable material that doesn’t disintegrate even at 300°C; in his papers for Science and Nature, he demonstrated that MOFs can be modified and imbued with different properties.

Thanks to these discoveries, chemists around the world were able to create tens of thousands of different MOFs that are already used to solve crucial challenges: collect water from air in deserts, purify water and soil from toxic substances, detect and store toxic gases, separate industrial gases for the oil and gas industry, accelerate chemical reactions, and deliver drugs to specific organs.

“This year’s Nobel Prize in Chemistry was awarded for the development of highly efficient and highly selective sorbents. Apart from their direct purpose, these materials have other promising applications: they can replace silicon in logical elements, control chemical reactions, or conduct electricity. I am certain that in the future, MOFs will become an alternative to semiconductors and will be used as memristors – electronic components that participate in the recording, processing, and storage of information,” says Valentin Milichko.

MOFs are developed in Russia, as well. One of the most prominent teams in the field is Vladimir Fedin’s group at the Nikolaev Institute of Inorganic Chemistry of the Siberian Branch of the RAS. In collaboration with the team, ITMO researchers have designed MOF-based polymers for biovisualization that help detect toxic substances in living organisms. At ITMO, MOFs are actively studied by scientists at the School of Physics and Engineering and the Infochemistry Scientific Center. Recently, a team from ITMO has discovered a new family of metal-organic crystals that turn from 3D into 2D structures on their own. These materials can be used in memristors and ReRAM – technologies used for the recording and storage of data.