Background of clay and the related CO2 capture

https://doi.org/10.1038/srep08775

“Clay minerals are materials based on two-dimensional stacks of inorganic layers⁵. In some clay minerals (smectites), non-equivalent substitutions of atoms generate a negative charge on each layer surface which is balanced by exchangeable interlayer cations. These cations are responsible for the differences in the physico-chemical behavior of smectites such as water adsorption and retention, plasticity, swelling etc^6,7. Smectite clay mineral particles typically consist of approximately hundred layers. Smectites have the ability to intercalate additional molecules into the interlayer space, thereby changing the repetition distance along the layer normal (z-direction), a process which is known as swelling^8,9. Intercalation of water can also occur, since H₂O is a polar molecule and this has been extensively studied with a wide range of techniques, such as neutron^8,10,11 and X-ray scattering^9,12,13, NMR spectroscopy^14,15,16 tracer experiments¹⁷ or numerical modeling^14,18.

Experiments^{19,20,21,22,23,24,25,26,27,28} and simulations^{18,29,30,31,32} have also shown that CO₂ intercalates in some smectite clays, both in supercritical and in gaseous/liquid form. We have recently demonstrated that CO₂ is able to intercalate in Na-fluorohectorite (NaFh) smectite clay mineral at conditions close to ambient (−20°C, 5 bar)²². In that work we also showed that under the same conditions neither H₂O vapor nor N₂ gas intercalates. These are not the typical conditions found in geological storage sites, but the conditions are relevant if clays are considered as a potential material for the capture or sequestration of CO₂ and it is also of interest to study CO₂ capture and retention under these conditions for the purpose of understanding the underlying molecular mechanisms. Several porous materials are currently being assessed for the purpose of CO₂ capture and retention^33,34,35. In this context, clay-containing materials could have a distinct advantage in that they are both cheap and ubiquitous³¹ and also because they generally provide a very large accessible effective surface area that arises from nanolayered stacked structures embedded in a mesoporous powder matrix.”