The Need

Metal-organic frameworks (MOFs) are porous polymers constructed by self-assembly of organic and inorganic components. They have been extensively studied for gas storage and separation applications, and post-combustion CO2 capture under flue gas conditions has been a particularly intense area of study. However, there has been growing interest in developing porous materials for CO2 directly captured from air. Efficient direct air capture would enable more distributed efforts toward mitigating the effect of CO2 on climate change and perhaps facilitate the greater use of CO2 as a chemical feedstock. In addition, efficient CO2 remediation from air is necessary to maintain habitable atmospheres in confined environments such as submarines and spacecraft. For example, while the concentration of CO2 in Earth’s atmosphere is currently around 415 ppm, NASA requires that CO2 concentrations be maintained at levels < 2630 ppm in the International Space Station (ISS) and other spacecraft. There exists a need to develop a more advanced method for the removal of trace carbon dioxide from air or other gas streams.

The Technology

Researchers at the Ohio State University led by Dr. Casey Wade have conceived a materials design concept and synthetic protocols in which nucleophilic transition metal hydroxide groups are generated at the internal pore surfaces of MOFs to facilitate selective gas-phase CO2 fixation at low pressures via formation of metal bicarbonate species. A novel postsynthetic modification protocol was used to prepare a MOF that contains nucleophilic groups. This solid material reacts with gas-phase CO2 at pressures below 5 mbar and can be fully regenerated by heating at 100 °C. Under specific conditions, single component adsorption isotherms show that 1-ZnOH exhibits a high gravimetric CO2 uptake. The adsorption is reversible, and the MOF sorbent can be fully regenerated by heating to 100 °C under dynamic vacuum. IR spectroscopic studies support the involvement of a Zn–OH/Zn–O2COH interconversion mechanism that is aided by intercluster hydrogen bonding interactions. Preliminary thermal swing adsorption measurements have been carried out on 1-ZnOH to interrogate adsorption-desorption cycling behavior in different gas streams. In preliminary results, only a small decrease in adsorption capacity is observed after 10 adsorption-desorption cycles.

Benefits

• Excellent CO2 uptake
• Use of pressures relevant for direct CO2 capture from air
• Mild regeneration requirement
• Lack of volatile components
• Maintains habitable atmospheres in spacecraft and submarines
• Reduces effect of CO2 on climate change

Commercial Applications

• Chemical feedstock
• Coal gasification
• Ethanol production
• Fertilizer production
• Natural gas processing
• Refinery hydrogen production
• Coal-fired power generation