Professor Jeffrey Long – The beauty of chemistry
Story by Veronika Meduna About a tenth of the energy we use globally goes into chemical separations—processes that strip a particular molecule from a gas or liquid. Much of that energy could be saved with a little help from synthetic chemistry. Jeffrey Long is a Professor of Chemistry at the University of California, Berkeley, and in February he visited New Zealand for the first time to attend the MacDiarmid Institute’s AMN-7 meeting in Nelson and to introduce his group’s work in synthesising metal-organic frameworks, or MOFs, to make chemical separations more efficient. Take carbon capture for example. “Currently, if you wanted to separate carbon dioxide from the gas coming out of a power plant you would use amine solution technology. This is very old technology that we’ve had for decades and it’s based on an aqueous solution of organic amines that can effectively remove CO2 emissions from a power plant, but it takes a lot of energy to do that.” Essentially, it means that a power plant has to burn 30% more coal to capture its carbon emissions. But the Long group is developing MOFs with built-in functionality on the surface that allows them to selectively absorb CO2 from the flue gas at about half the energy cost. “The current technologies require heat above 120°C and they use steam that would normally be making electricity in the power plant. Our materials can do it at temperatures as low as 80°, which means that you don’t take high-value steam away from electricity production.” What’s more, the MOF in question is made of cheap components, including magnesium cations and an organic linker connecting them into a three-dimensional network. “Carbon capture from a power plant is about as big-scale in application as you can imagine, so you can’t have a very expensive material to do it.” MOFs are porous, light-weight and tuneable—and in this case the material was coated with carbon-capturing amine groups similar to those used in the current technology. But Long says the results were surprising. “It turns out the mechanism that this material operates by is different from how the amines work in solution. In our material, we use ethylenediamine and one of the two amine groups is bound to a magnesium centre on the surface of the MOF pore. When CO2 bonds, it inserts into the metal-amine bond at one site and actually facilitates CO2 absorption at the next site, and so on down a channel within the material. So we see this unprecedented cooperative CO2 absorption. It was lucky. The way we built it, it just happens that the structure is just right and we can have communication between absorption sites.” Another research project in the Long group is the renewable generation of hydrogen by using solar energy to split water. “If you can do that, then hydrogen cars start making a lot more sense. But they still have a challenge when it comes to storing hydrogen densely in the fuel tank.” To that end, the group has developed a MOF that would reduce the pressure at which the highly volatile gas has to be stored at the moment. “That does two things,” he says. “First of all you don’t have to lose all the energy that goes into compressing hydrogen to put it into the tank, and secondly you can use a cheaper lighter-weight tank and that will take up a lot less volume in the car.” To scale up applications of MOFs, Long formed a company last year together with a former student. “It’s important to recognise that it’s going to be a long time before we can get away from fossil fuels as our energy source,” he says. “The demand is such that there’s no way we can ramp up renewable energy fast enough to keep up. Carbon capture could be an intermediate solution while we figure out how to do renewable energy on a really large scale.” Long says he was originally inspired—and still is—simply by the beauty of chemistry. “My dad’s a chemist. I traveled with him as a kid … and picked up the appreciation for the geometry associated with inorganic materials and for their physical properties.” Molecular structures, colours and crystal shapes still excite him today. “A big part of what we do when we make a new material is to figure out the crystal structure and how the atoms are positioned. There’s always a thrill when you make a new material and see how it’s put together for the first time.” However, beyond the fundamental interest, he says he soon realised the value in designing new materials for environmental applications, and he sees inorganic chemistry as ‘hugely important to tackling these problems’.