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 reported for Hyd–Si with the same pore size distribution [15]. The
PDS for Co–Si is centered at 1.4 nm; Darmawan et al. [26] have
obtained a metal oxide silica derived from sol–gel method with
an average pore radius of 1 nm and 1.2 nm. There are distinctive
peaks over 2 nm, this could be attributed to the fact that silica
materials possess wider micropores and mesopores (see Table 3).
In fact the actual values of the pore widths for the unsupported
silica or modified silica membrane may differ somehow in the supported
membrane one. Therefore, this could explain why Hyd–Si
showed lower selectivity and the contrary for Co–Si [16,17,25].
Fig. 7 shows the pore size distributions (PSD) for the silicamembrane materials; they were calculated by applying the NLDFTmodel to the nitrogen adsorption data at 196 C based on a cylindricalpore model. Although the PSD determined by BJH (Barrett,Joyner and Halenda) method is more accurate than other methodsuch as HK (Horváth–Kawazoe) method [14], the NLDFT adsorptionkernels recently developed by Neimark et al. [55] describe the positionof the pore condensation (i.e. adsorption branch) by takinginto account the pressure range of metastable pore fluid prior tocondensation. Hence, the application of this NLDFT adsorptionbranch kernel allows obtaining a correct pore size distributioncurve also from the adsorption branch. As it can be seen, the novelsilica membrane material, Hyd–Co–Si, exhibit a narrow pore sizedistribution centered at 1.1 nm suggesting that the novel materialcan be used for molecular sieving applications. Similar results were reported for Hyd–Si with the same pore size distribution [15]. ThePDS for Co–Si is centered at 1.4 nm; Darmawan et al. [26] haveobtained a metal oxide silica derived from sol–gel method withan average pore radius of 1 nm and 1.2 nm. There are distinctivepeaks over 2 nm, this could be attributed to the fact that silicamaterials possess wider micropores and mesopores (see Table 3).In fact the actual values of the pore widths for the unsupportedsilica or modified silica membrane may differ somehow in the supportedmembrane one. Therefore, this could explain why Hyd–Sishowed lower selectivity and the contrary for Co–Si [16,17,25].
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