photodegradation of rhodamine B under UV light irradiation than the one of
commercial P25 (Wang et al. 2014a, b). However, the correlation between crystalline structures and mesoporous porous structure with photocatalytical activity when
molar ratio Ti/Sn is varied was not clearly evidenced.
Concerning TiO 2 nanoparticles, they are highly photocatalytically active for the
photodegradation of organic pollutant in solution. However, their morphology
makes them difficult for handling and for recovering. To overcome these problems,
various strategies to synthesize TiO 2 nanoparticles supported composites as
photocatalysts for dye degradation have been developed. Two series of TiO 2 –SiO 2
composites have been prepared by post-synthesis impregnation of a TiO 2 precursor
onto SBA-15 silica matrices and a subsequent thermal treatment at 400
C under air
(Besançon et al. 2016). The influence of the textural properties (pore size from 4 to
8 nm) of the SBA-15 and the TiO 2 content (20–80 wt%) on the dispersion of TiO 2
and its crystallization in anatase were evaluated. For TiO 2 content superior to 25 wt
% and mesopores smaller than 8 nm, the impregnation occurred inside and outside
the porosity of the hosts and TiO 2 crystallized as anatase nanoparticles on the
SBA-15 particle surface. The quantity of crystallized anatase was determined by
XRD using an internal standard when crystalline particles were detected. Their
photocatalytic activity was evaluated by following the degradation of methyl orange
and compared to commercial TiO 2 references (P25 from Degussa and pure anatase
10 nm from Alfa Aesar). While P25 reference appeared to be the best photocatalyst
for the degradation of methyl orange in the used conditions, the photoactivity of the
composites containing crystallized anatase was similar to that of Alfa Aesar commercial fully crystallized anatase with a particle size of the same order of magnitude.
It clearly appeared that comparing the composites, the one with 44 wt% of crystallized anatase (experimental 80 wt% TiO 2 ), so more than twice less than commercial
anatase references, exhibit the highest methyl orange degradation rate, very closed to
the one observed for P25. The presence of the amorphous SiO 2 support has led to a
well dispersion of 20 nm well-crystallized anatase particles and assured a high
density of hydroxyl groups that consequently improved the catalytic performance
of TiO 2 -SBA15 composite.
Supported TiO 2 on silica SBA-15 have been also prepared with varied 30–80 wt
% TiO 2 loading by a post-synthesis step based on Ti-alkoxide hydrolysis in a
support/isopropanol suspension and subsequent calcination 500–900
C (Yang
et al. 2006). The presence of mesoporous SiO 2 amorphous support allowed having
high specific area and delaying anatase-to-rutile transformation (only the anatase
phase was detected by XRD for calcination temperature up to 800
C) and
controlled-size anatase nanocrystals. As a consequence, the TiO 2 -supported
SBA-15 composites were found to be more active for the photodegradation under
UV irradiation of methylene blue in aqueous solution than the commercial P25.
Mesoporous aluminosilicate Al-SBA-15 prepared in supercritical carbon dioxide
(Sc-CO 2 ) was also considered for supporting TiO 2 nanoparticles (Chang et al. 2013).
It was observed that TiO 2 /Al-SBA-15 composites showed good methylene blue
decolorization in aqueous solutions that was much higher than those of TiO 2 /
SBA-15 and commercial P25 TiO 2 . The photocatalytic activity can be mainly related
58
B. Lebeau et al.
commercial P25 (Wang et al. 2014a, b). However, the correlation between crystalline structures and mesoporous porous structure with photocatalytical activity when
molar ratio Ti/Sn is varied was not clearly evidenced.
Concerning TiO 2 nanoparticles, they are highly photocatalytically active for the
photodegradation of organic pollutant in solution. However, their morphology
makes them difficult for handling and for recovering. To overcome these problems,
various strategies to synthesize TiO 2 nanoparticles supported composites as
photocatalysts for dye degradation have been developed. Two series of TiO 2 –SiO 2
composites have been prepared by post-synthesis impregnation of a TiO 2 precursor
onto SBA-15 silica matrices and a subsequent thermal treatment at 400
C under air
(Besançon et al. 2016). The influence of the textural properties (pore size from 4 to
8 nm) of the SBA-15 and the TiO 2 content (20–80 wt%) on the dispersion of TiO 2
and its crystallization in anatase were evaluated. For TiO 2 content superior to 25 wt
% and mesopores smaller than 8 nm, the impregnation occurred inside and outside
the porosity of the hosts and TiO 2 crystallized as anatase nanoparticles on the
SBA-15 particle surface. The quantity of crystallized anatase was determined by
XRD using an internal standard when crystalline particles were detected. Their
photocatalytic activity was evaluated by following the degradation of methyl orange
and compared to commercial TiO 2 references (P25 from Degussa and pure anatase
10 nm from Alfa Aesar). While P25 reference appeared to be the best photocatalyst
for the degradation of methyl orange in the used conditions, the photoactivity of the
composites containing crystallized anatase was similar to that of Alfa Aesar commercial fully crystallized anatase with a particle size of the same order of magnitude.
It clearly appeared that comparing the composites, the one with 44 wt% of crystallized anatase (experimental 80 wt% TiO 2 ), so more than twice less than commercial
anatase references, exhibit the highest methyl orange degradation rate, very closed to
the one observed for P25. The presence of the amorphous SiO 2 support has led to a
well dispersion of 20 nm well-crystallized anatase particles and assured a high
density of hydroxyl groups that consequently improved the catalytic performance
of TiO 2 -SBA15 composite.
Supported TiO 2 on silica SBA-15 have been also prepared with varied 30–80 wt
% TiO 2 loading by a post-synthesis step based on Ti-alkoxide hydrolysis in a
support/isopropanol suspension and subsequent calcination 500–900
C (Yang
et al. 2006). The presence of mesoporous SiO 2 amorphous support allowed having
high specific area and delaying anatase-to-rutile transformation (only the anatase
phase was detected by XRD for calcination temperature up to 800
C) and
controlled-size anatase nanocrystals. As a consequence, the TiO 2 -supported
SBA-15 composites were found to be more active for the photodegradation under
UV irradiation of methylene blue in aqueous solution than the commercial P25.
Mesoporous aluminosilicate Al-SBA-15 prepared in supercritical carbon dioxide
(Sc-CO 2 ) was also considered for supporting TiO 2 nanoparticles (Chang et al. 2013).
It was observed that TiO 2 /Al-SBA-15 composites showed good methylene blue
decolorization in aqueous solutions that was much higher than those of TiO 2 /
SBA-15 and commercial P25 TiO 2 . The photocatalytic activity can be mainly related
58
B. Lebeau et al.