Capture of CO2 from ambient air by sodium manganate and CO2 recovery at low temperatures

Sodium manganate (Na0.66MnO2, NMO) was synthesized by a liquid method using NaOH, Mn(NO3)2, and ethylenediaminetetraacetate. The absorption of CO2 from air by NMO was investigated at room temperature. The CO2 absorption by NMO was promoted at high relative humidity (RH) and accompanied by the formation of birnessite and sodium carbonate hydrate phases. NMO efficiently absorbed CO2 from air when the RH was greater than 60 % because adsorption of water vapor to NMO readily occurred above 60 % RH. Thus, NMO absorbed CO2 together with H2O adsorbed from the air. The regeneration of NMO, was accompanied by the release of CO2 from sodium carbonate hydrates and occurred at temperatures as low as 150 degrees C. This behavior was attributed the similar structural features of NMO and birnessite, which both incorporate layered structures composed of MnO6 octahedra.