The scattering intensity (arb. units) over a range of d-spacing values during clay based CO2 capture

https://doi.org/10.1038/srep08775

“The layered nature of smectite clays gives rise to well-defined (00l) diffraction peaks and the angular position of these peaks is a direct measure of the interlayer repetition distance (the d-spacing). Figure 1 displays how the intensity of the (001) diffraction peak grows with time as the samples are exposed to CO₂ at −20°C and 20 bar. All the samples were pre-dried before the measurements (see Methods section below). Intercalation of CO₂ in the interlayer space manifests itself as the growth of an intercalation peak at a lower scattering angle (higher d-spacing) than the peak of dry, non-intercalated clay. As the intercalation progresses, the intensity of the CO₂-intercalation peaks increase whereas the scattering from non-intercalated part of the sample decreases and eventually vanishes. LiFh and NaFh show similar intercalation behaviors in the X-ray diffractogram (XRD). The (001) peaks develop to d-spacings of 1.196 nm and 1.240 nm, for LiFh and NaFh respectively. This could correspond to a monolayer of intercalated CO₂, in analogy to what occurs for H₂O. For the NiFh sample we observe a similar intercalation state with d-spacing of 1.219 nm and in addition the development of another state with a larger d-spacing of 1.311 nm. To our knowledge, this is the first time such a complex CO₂ intercalation state has been observed in a clay mineral, although other authors have found evidence of multiple intercalated layer type^9,37. One may note that the secondary low-angle peak is at a d-spacing of ca. 1.3 nm, which is distinct from the ≈1.25 and ≈1.55 nm spacings of the one (1WL) and two water layer (2WL) smectite states as reported by Ferrage et al^38,39. Other XRD studies have generally observed only blurred peaks in this region and have interpreted them as mixtures of peaks with the 1WL and 2WL spacings.”

“Figure 1 The scattering intensity (arb. units) over a range of d-spacing values at different times (hours), for LiFh, NaFh and NiFh, respectively. In all cases the CO₂ adsorption conditions were −20°C and 20 bar. The red line (∇) shows the time at saturation. Experiment performed at NTNU.”