Characterisation of porous silica. 2. CPG-10 (VYCOR)

Interaction of Ethanol Vapour with Silane-Modified Surface of Corning Porous Glass CPG-10

“…The BET ethanol specific surface area for the untreated CPG-10 sample of pore diameter 12.5 nm is 100 m 2 g −1 . This is larger than, but in reasonable agreement with, the value of 85 m 2 g −1 obtained using benzene as the adsorptive [24] (see Table 1). It seems that, in spite of fewer ethanol potential adsorption sites, more ethanol molecules are adsorbed in a monolayer than benzene probably because they have easier access to the internal pore network due to their smaller cross-sectional area.…”

“…Ethanol was chosen as an adsorbate because of its polar-organic nature so that it can gain easier access to residual hidden silanols in the modified silica samples than benzene through its stronger specific interactions with the silanols through hydrogen bonding, which is intermediate between physisorption and chemisorption. The potential complications expected here in the interpretation of BET surface area results, compared to the case of benzene [20,24], will be avoided by using the results obtained for comparative purposes only.…”

“…The Gurvitsch volume given on the sample bottle by the manufacturer for CPG-10 of pore-diameter of 12.5 nm is 0.59 cm 3 g −1 ; implying that modification hardly affects the volume of the pores. The small difference observed could probably be attributed to the decrease in multilayer adsorption (Figures 5 and 7), with contributions from the decrease in pore volume due to blocking of smaller pores and narrowing of the pore size distribution (as shown by a more asymptotic capillary condensation branch of the adsorption isotherm at an earlier relative pressure P/P 0 = 0.9, and a sudden upward turn of the cross-plot in Figure 7) just as in the case of benzene [24].…”

“…However, modification of CPG-10 with TES results in a type II ethanol adsorption isotherm (see Figure 3). The pores are definitely not blocked by chemisorption of the TES groups at the entrances, because benzene adsorption in this region exhibits hysteresis effects in which a loop of type H1 is observed [24]. The Gurvitsch volume, in benzene adsorption, is only slightly affected by the TES groups (for CPG-10 pore diameter 17.5 nm from 1.01 cm 3 unmodified to 0.93 cm 3 TES-modified).…”