Evidence of Isotope Selective Diffusion of Ambient CO2 Gas in WO3 Nanostructures

We report the isotope selective diffusion of carbon dioxide (CO2) gas through large aspect ratio (length/diameter = 20:1) and porous one-dimensional nanostructure of tungsten oxide (WO3). This novel effect was demonstrated in an ensemble of binary oxide, WO3 nanostructures with large surface area. When atmospheric CO2, which has two major stable isotopes ((CO2)-C-12 and (CO2)-C-13), flows through such an ensemble of nanotubes, it allows only the (CO2)-C-12 isotopes to diffuse through it and hinders diffusion of the (CO2)-C-13 isotopes. The selective diffusion leads to different isotopic fractionations of ambient CO2 (C-12:C-13), in other words, generating different isotope-enriched CO2 gases as established through high-precision cavity-enhanced absorption spectroscopy technique. The phenomena are strongly dependent on the surface morphology of nanostructures of binary oxide, and the surface-induced diffusion process is most likely to be the effects of physical processes enabling the Knudsen diffusion, but is not related to any chemical activities.