Influence of Alkali Metals (Na, K, and Cs) on CO2 Adsorption by Layered Double Oxides Supported on Graphene Oxide

The CO2 adsorption capacities, isotherms, and thermal stability of sodium, potassium, and cesium impregnated layered double oxides (LDOs) supported on graphene oxide (GO) are reported. Alkali cations were found to modify the distribution and density of chemisorption sites resulting in higher CO2 adsorption capacities at 573 K (0.56–0.69 molCO2/kg) compared to the unpromoted adsorbents (0.29 molCO2/kg) (LDO and LDO/GO hybrids). The improved thermal stability imparted by incorporation of GO in the LDO was not compromised by the addition of any of the alkali species. Potassium produced the most marked enhancement in CO2 capacity (0.47 molCO2/mol alkali) due to its relatively strong Lewis basicity and even distribution on the surface of the adsorbents. Cesium was found to have a tendency to agglomerate that reduced the effectiveness of promotion. The CO2 adsorption equilibrium of the fresh calcined materials is described by the Freundlich model. After thermal adsorption–desorption cycles the isotherms fit closer to the Langmuir isotherm.