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

We report the isotope selective diffusion of carbon dioxide (CO 2 ) gas through large aspect ratio (length/diameter = 20:1) and porous one-dimensional nanostructure of tungsten oxide (WO 3 ). This novel effect was demonstrated in an ensemble of binary oxide, WO 3 nanostructures with large surface area. When atmospheric CO 2, which has two major stable isotopes ( 12 CO 2 and 13 CO 2 ), flows through such an ensemble of nanotubes, it allows only the 12 CO 2 isotopes to diffuse through it and hinders diffusion of the 13 CO 2 isotopes. The selective diffusion leads to different isotopic fractionations of ambient CO 2 ( 12 C: 13 C), in other words, generating different isotope-enriched CO 2 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.