Carbon dioxide adsorption on oxide nanoparticle surfaces

In this paper, focused on environmental nanotechnology, we review some recent results for carbon dioxide (CO2) adsorption on hydroxylated Fe2O3, γ-Al2O3, and TiO2 nanoparticle surfaces at 296 K as followed by transmission FTIR spectroscopy. In the absence of water vapor (<1% relative humidity, RH), following exposure to CO2 different species formed on the oxide surface due to the presence of adsorption sites with different basicities. While the majority surface species on Fe2O3, γ-Al2O3 is determined to be adsorbed bicarbonate, on TiO2 nanoparticles bidentate carbonate was more prevalent. A carboxylate species was observed on TiO2 nanoparticles under dry conditions as well. When water is present at 40% RH, the nature of the adsorbed CO2 species changed to that of solvated carbonate formation in the adsorbed water layer. Observed initial adsorption rates were calculated from time–course experiments under dry conditions and in the presence of 40% RH. When initial adsorption rates were compared between dry and wet experiments, a larger value was found for dry experiments suggesting that CO2 molecules have to compete for adsorption sites with water on these nanoparticle surfaces. As discussed here, quantum chemical calculations provide some additional insights into CO2 adsorption on hydroxylated metal oxide surfaces in the presence and absence of molecularly adsorbed water.