Clay minerals can adsorb large amounts of CO2 and are present in anthropogenic storage sites for CO2. Nanoscale functionalization of smectite clay minerals is essential for developing technologies for carbon sequestration based on these materials and for safe-guarding relevant long-term carbon storage sites. We investigate the adsorption mechanisms of CO2 in dried and hydrated synthetic Ni-exchanged fluorohectorite clay-using a combination of powder X-ray diffraction, Raman spectroscopy, and inelastic neutron scattering. Both dried and hydrated Ni-exchanged fluorohectorite show crystalline swelling and spectroscopic changes in response to CO2 exposure. These changes can be attributed to interactions with [Ni(OH)(0.)(83)(H2O)(1.)(17)](0.)(1.17+)(37)-interlayer species, and swelling occurs solely in the interlayers where this condensed species is present. The experimental conclusions are supported by density functional theory simulations. This work demonstrates a hitherto overlooked important mechanism, where a hydrogenous species present in the nanospace of a clay mineral creates sorption sites for CO2.