For the past decade and a half, Seth Cohen has been working with metal-organic frameworks (MOFs), creatively designing new structures with unique properties. His biggest hope for the decade ahead is that current vibrancy surrounding MOF development carries through to the marketplace. He sees a potentially growing disconnect between enthusiasm for MOFs in academic labs and the pace of their broader commercialization and application in the real world.
Material Insights spoke with Cohen, who is professor in the Department of Chemistry and Biochemistry at the University of California, San Diego (UCSD), about his pioneering work in postsynthetic modification of MOFs and MOF-polymer hybrids, exciting future applications of the technology, and continuing misconceptions that may make industry reluctant to embrace MOFs.
Insights: What drives your work with MOFs?
Cohen: I get really excited about molecular design and new structures and synthesis. I appreciate the creative side of designing a new molecule, coming up with a design, seeing it come to fruition and actually work. It’s the fun and joy of doing new chemistry.
Insights: When did you first learn about MOFs and start working with them?
Cohen: I heard Omar Yaghi from Berkeley give talks in grad school but really didn’t start working with them until I was an assistant professor here at UCSD. We were working to make molecules that I thought would be interesting building blocks for liquid crystals but then realized their design made them suitable as building blocks for MOFs. The liquid crystal chemistry was going slowly, and I saw the potential for MOFs, so I shifted gears. This was in 2005, when interest in MOFs was really starting to take off, so my lab made the pivot.
Insights: What are you most proud of in terms of your contributions to the field so far?
Cohen: Probably what my lab and I are best known for is in two areas: 1) postsynthetic modification of MOFs, and 2) MOF-polymer hybrids. The first area, postsynthetic modification, is not an area we started but I think we’ve played a large role in moving it forward. The idea is that you synthesize a MOF and then chemically modify the framework to introduce new properties or add new features. We had all these MOFs and they were really simple; they didn’t have any of the rich functionality of organic chemistry as part of their structure, and we wanted to change that. That is something where my lab has had a substantial impact over the last 10 years.
The second area is more recent. We had been working on the postsynthetic modification for a decade and wanted to have a greater impact. We started looking at the interface between MOFs and polymers. MOFs are rigid crystalline materials, which is perfectly suitable for many applications, but we wanted to see if there was a way to make a hard, solid MOF behave more like a plastic, so that we could manipulate and process it better. It was a growing field when we started, but we came at it from a slightly different angle. We really wanted to develop a material that mechanically behaved like a plastic but chemically behaved like a MOF. And over the past 4 years, we have developed what we think is a potentially new class of materials we have called polyMOFs.
Insights: How has that changed the MOF field?
Cohen: Most people thought MOF ligands had to be rigid, small and directional, otherwise you wouldn’t get a MOF; it wouldn’t self-assemble. We’re making the polyMOFs out of a really flexible, large organic polymers, which most people didn’t think would work. To our great excitement, it has worked, and we are still working to understand why it does work and what makes it a unique material
Insights: What might be potential applications of polyMOFs?
Cohen: Much of the motivation for polyMOFs was the idea of making form factors that are more useful. I always joke that at the end of the day, we’ll call the project a success if we can make “MOF spandex.” Spandex is a very useful material; it is stretchy but snaps back into shape. My goal has been to similarly create a MOF that is really stretchy but connected by rigid blocks with nice mechanical properties and porosity. You could create a new type of apparel line, like a new Lulu Lemon, that uses “MOF spandex” that absorbs odors and other chemicals.
Insights: For MOFs as a whole, what applications are you most excited to see come to fruition and why?
Cohen: In the long term, I really like the bigger applications that some of the groups are going for. They may still be far away but they are important. For example, CO2 separation to capture and sequester the carbon is one area where MOFs are making real headway. My favorite is probably the moisture capture work coming out of Omar Yaghi’s lab and out of some of the MIT groups. They are using MOFs to condense and capture moisture from the atmosphere to provide sources of freshwater to populations that don’t have good access to water. It’s such a fascinating, high-impact application for the whole world. From what I can tell, the literature is encouraging for MOFs as a material to do that.
Insights: What do you think are the leading misconceptions about MOFs right now, especially in industry?
Cohen: Stability and cost. The stability myth has plagued MOFs for a long time because early MOFs were fragile. New designs are becoming more stable all the time, including through coordination structures and polymers that make them more robust. Similarly, for cost, many people still think MOFs are too expensive and out of reach. But when companies find a good application, they can scale up and find new ways to bring down costs. The starting materials are relatively simple, but we just need more industries willing to scale them up for the right applications. Both of these myths, I believe, have biased industry against using the material.
Insights: Along those lines, where do you see the biggest commercialization challenges for MOFs right now?
Cohen: It’s about finding the right applications where you can get immediate capability with an existing industrial process. It’s much more difficult to go after the massive scale applications where there are no existing processes or technology to support MOFs. So, the winning strategy right now is finding places where MOFs can be compatible within perhaps smaller, but very high-value applications.
Insights: What is the outlook you have for the next 10 years?
Cohen: I think we are going to see more applications. At the conference MOF 2018, Bo Wang (BIT)I told me about Chinese industry looking at MOFs as coatings for air filters, using new strategies for integrating MOFs with polymers, for example. It will be interesting to see how that might scale up for use in buildings and vehicles.
In general, I hope to see that the field is still vibrant. There is a lot of excitement in the academic world around MOFs. I hope it will continue but I have some concern that it could flame out unless we have more commercialization; we need more applications showing their value in the real world. We need to see more synergy between the industrial application side and the academic development side.