Mitigating global climate change by reducing greenhouse gas emissions and removing legacy greenhouse gases are urgent societal goals. International policies have spurred innovation and discoveries in carbon dioxide removal (CDR) reactions and technologies, including both point-source and direct air capture (DAC). We are currently investigating chemisorption of CO2 using solids and aqueous solutions featuring high oxidation state metals, originally discovered with uranium (VI), and then translated to group IV, V and VI transition metals. Uranyl triperoxide, vanadium, titanium and niobium tetraperoxide are reactive anionic DAC molecules, capturing up to three CO2 molecules as bound carbonate, per metal center. Experimental studies using single-crystal X-ray diffraction, vibrational spectroscopies, thermogravimetry-mass spectrometry, CHN analysis, and scanning and transmission electron microscopies evidence direct metal-carbonate bonding in the most reactive materials, leading to low-temperature regeneration of spent materials. The role of the alkali counter cations is also important, but poorly understood. For example, the lithium uranyl triperoxide converts to uranyl tricarbonate via DAC over the course of months, while the same reaction of cesium uranyl triperoxide can be complete in 30 minutes. For both uranyl peroxide and niobium peroxide materials, we detect reduction of the metal center as an intermediate to carbon capture, which stabilizes via DAC reactions. We have also exploited simple orthovanadate to detect the transition of linear gaseous CO2 to aqueous CO32- at the water-air interface, using sum frequency generation (SFG spectroscopy). Finally, we demonstrated the use of niobium polyoxometalate (Nb-POMs) solutions for point-source CDR, where infusion of these solution drive fragmentation and Nb-carbonate bonding, leading to the assembly of new Nb-POMs.
May Nyman is the Terence Bradshaw Professor of Chemistry at Oregon State University, where she has been employed since 2012. From 1998 to 2012, May was a staff scientist at Sandia National Laboratories in Albuquerque, NM. May’s interdisciplinary educational journey included a BSc in Geology, an MSc in Materials Science and Engineering and a PhD in Chemistry. Through federally and privately funded research, May has nearly three decades of experience in materials design and discovery for both fundamental understand and addressing challenges related to energy and the environment. The latter includes nuclear waste treatment and management, downconverters for solid-state lighting, lithographic materials for microelectronics, critical material separations, carbon capture molecules, and water purification reagents and processes. May’s research group also specializes in small-angle X-ray scattering to understand solution speciation and evolution for bottoms-up materials design. May’s work has been recognized internationally through Alexander von Humboldt Research Award (Humboldt Foundation, Deutschland) and the F. Albert Cotton Award in Synthetic Inorganic Chemistry (American Chemical Society).