Fig. 5 displays the pore size distribution (PSD) of the raw and
calcined samples with Si-to-Ti of 2.3 as was estimated by the BJH method from the desorption branch. It is evident that the volume
of nitrogen adsorbed by the aerogels increased with increasing
the calcination temperature (200–400 C) due to removal of residual
organic components and –CH3 groups from the aerogels [25].
Further increase of the temperature led to partial collapse of the
walls separating mesopores as a result of crystallization [39]. Interestingly,
these results are congruent with those of previous studies
that investigated the effect of heat-treatment on the silica aerogels
[19,20,25]. Our research group reported [19,20] synthesis of sodium
silicate based hydrophobic silica xerogels and aerogels beads
with specific surface areas up to 920 m2/g. In the present study we
expanded the scope of our previous studies by introducing a modified
sol–gel method to fabricate TiO2–SiO2 aerogel photocatalysts
suitable for heterogeneous catalysis. Subsequently, Bhagat et al.
[21] investigated the effect of surface modification, solvent exchange
and removal of sodium ions in the preparation of superhydrophobic
silica aerogels from sodium silicate. It can be seen that
the average surface area of the aerogels obtained in the present
study are very close to those reported by Bhagat et al. [21]. The
specific surface areas of the samples obtained via this method increased
with increasing Si content but the textural properties of
the TS1 and TS3 samples were smaller than those of TS2. Therefore
in order to form binary TiO2–SiO2 aerogels with desirable properties,
the synthetic methods must be optimized by controlling the
Si-to-Ti. In the present study we found that the Si-to-Ti of 2.3 is
appropriate to yield a product with moderate surface area and
large porosities. Meanwhile, the PSD shows that the composites
exhibited broad average pore diameter ranging from 10 nm to
50 nm (Fig. 5).