Fig. 7 shows the pore size distributions (PSD) for the silica
membrane materials; they were calculated by applying the NLDFT
model to the nitrogen adsorption data at 196 C based on a cylindrical
pore model. Although the PSD determined by BJH (Barrett,
Joyner and Halenda) method is more accurate than other method
such as HK (Horváth–Kawazoe) method [14], the NLDFT adsorption
kernels recently developed by Neimark et al. [55] describe the position
of the pore condensation (i.e. adsorption branch) by taking
into account the pressure range of metastable pore fluid prior to
condensation. Hence, the application of this NLDFT adsorption
branch kernel allows obtaining a correct pore size distribution
curve also from the adsorption branch. As it can be seen, the novel
silica membrane material, Hyd–Co–Si, exhibit a narrow pore size
distribution centered at 1.1 nm suggesting that the novel material
can be used for molecular sieving applications. Similar results were