Carbon dioxide adsorption on nanomaterials

In this study, CO₂ adsorption in the presence and absence of co-adsorbed H₂O was investigated on different nanomaterials including nanocrystalline NaY zeolite (nano NaY), ZnO, MgO and λ-Al₂O₃ nanoparticles as well as mixed phase aluminum nanowhiskers. In the case of nano NaY, FTIR spectra show that a majority of CO₂ adsorbs in the pores of these zeolites in a linear complex with the exchangeable cation. Most interesting is the formation of carbonate and bicarbonate on the external surface of nano NaY zeolites, suggesting unique sites for CO₂ adsorption on the surface of these small nanomaterials. Adsorption of ¹⁸O-labeled carbon dioxide and theoretical quantum chemical calculations confirms the assignment of these different species. For aluminum oxyhydroxide nanowhiskers and gamma alumina in the absence of co-adsorbed water, CO₂ reacts with surface hydroxyl groups to yield adsorbed bicarbonate as well as some carbonate. C¹⁸O₂ adsorption confirms these assignments. In the case of nanoparticulate ZnO, CO₂ adsorption under dry conditions results in formation of carbonate, bicarbonates as well as carboxylates. However, in the presence of co-adsorbed water, only carbonate species is formed. ¹⁸O-labeled carbon dioxide adsorption and theoretical quantum chemical calculations confirm the vibrational assignment for these different species. Mixed isotope studies with H₂¹⁶O + C¹⁸O₂ and H₂¹⁸O + C¹⁶O₂ suggest that there is extensive exchange between oxygen in adsorbed water and oxygen atoms in gas-phase carbon dioxide. CO₂ adsorption on MgO surfaces, under dry conditions results in formation of carbonate and bicarbonates. Implications for the use of these nanomaterials in carbon dioxide uptake and storage are discussed.