Nanostructure boosts CO₂ uptake

Jeffrey Urban and his colleagues at the Lawrence Berkeley National Laboratory noticed something surprising during their study of a potential hydrogen-storing material. When they grew magnesium borohydride on reduced graphene oxide, it formed an unusually open and porous crystalline nanostructure. “Working with the playbook of the periodic table, most inorganic crystals are dense,” Urban says. But the gamma form of crystalline magnesium borohydride (shown) is an exception. Contemplating the material’s large surface area and its plethora of exposed, reactive borohydrides, postdoc Sohee Jeong had “a chemical intuition that it would soak up CO₂,” Urban says. She was right. Detailed studies revealed that the material initially works slowly, as the borohydrides first reduce the gas to create formate groups. There is then a stepwise spike in carbon dioxide uptake, forming methoxide groups (Adv. Mater. 2019, DOI: 10.1002/adma.201904252). A version of the material pretreated to create the formate groups works as well as existing CO₂-scrubbing materials, but under much milder conditions. “It’s a massive thermodynamic sink for CO₂,” even at ambient temperature and pressure, Urban says. He expects the material will find use in scuba-diving systems, space stations, and other enclosed spaces. But since it takes high temperatures to regenerate the material and release CO₂, it would be challenging to adapt to industrial carbon capture and storage systems.