Ti-containing porous silica thin film [86, 88, 89]. Figure 3.11a shows the yields of
products with the change of reaction time. The yields of CH 4 and CH 3 OH in the
photocatalytic reduction of CO 2 and H 2 O on the Ti-oxides containing various porous
materials are shown in Fig. 3.11b. They found that it is possible to determine a real
quantum yield of the photocatalytic reduction of CO 2 with H 2 O on tetrahedrally
coordinated Ti-oxides. Ti-oxide was constructed within porous silica material, and
its quantum yield could to be 0.3% at room temperature by the total number of
photons absorbed by the catalyst.
3.5.2.2 NO/NO 2 Photoreduction
In 1985, Anpo et al. [77] carried out a research on photoluminescence studies of
titanium oxide anchored onto porous Vycor glass. It is proposed that the
photoluminescence quenching is closely associated with the electron transfer from
the excited states of the catalyst to the added O 2 or N 2 O molecules. In Fig. 3.12, it
shows the comparison between the reduction of NO and the decomposition of CO 2 .
The structure of Ti-oxide single-site is presented on the left top of this picture.
Similarly, the structure of TiO 2 particles is presented on the right bottom of this
picture. The quantum yield of CO 2 + H 2 O ! CH 3 OH + CH 4 is much smaller than
the decomposition of NO, due to its demanding of more configurations of
co-adsorbed reactants involving six participating atoms [90]. In 1997, titanium
oxide catalysts prepared within the Y-zeolite cavities via an ion-exchange method
were reported by Anpo et al. [79], which exhibited high and unique photocatalytic
reactivities for the decomposition of NO into N 2 and O 2 . It was also found that the
charge-transfer excited state of the titanium oxide species, (Ti
3+ -O
À )*, plays a vital
role in these unique photocatalytic reactions. Table 3.1 revealed the yields of the
photo-formed N 2 and N 2 O and its selectivity in the photocatalytic decomposition of
NO. It is obvious that the efficiency and selectivity of the formation of N 2 strongly
depend on the type of catalysts.
In 2000, Masato Takeuchi et al. [76] prepared transparent TiO 2 thin film
photocatalysts on transparent porous Vycor glass (PVG) by an ionized cluster
beam (ICB) method. These thin films worked with high efficiency as photocatalysts
for the decomposition of NO into N 2 , O 2 , and N 2 O under UV light irradiation at
275 K. When the film thickness increases, the photocatalytic reactivity decreases
gradually. In 2004, Yamashita and Anpo [80] proposed a new concept of an ion
beam technology using accelerated metal ions, a metal ion implantation, and an
ionized cluster beam (ICB) (detailed schematic diagram is shown in Fig. 3.13a). The
decomposition of NO into N 2 , O 2 , and N 2 O can be occurred not only under UV light
but also visible light, realizing the efficient use of solar beam energy. The samples
were also characterized by XANES (as shown in Fig. 3.13b). It revealed the XAFS
(XANES and FTEXAFS) spectra of the Cr ion–implanted TiO 2 powder catalyst. By
analyzing on these spectra, we can tell that in the Cr ion–implanted TiO 2 , the Cr ions
are highly dispersed in the lattice of TiO 2 possessing octahedral coordination. These
Cr ions are isolated and substitute the Ti
4+ ions in the lattice positions of TiO 2 .
3.5 The Development of Mesoporous Ti–SiO 2 Materials in Photocatalysis
65
products with the change of reaction time. The yields of CH 4 and CH 3 OH in the
photocatalytic reduction of CO 2 and H 2 O on the Ti-oxides containing various porous
materials are shown in Fig. 3.11b. They found that it is possible to determine a real
quantum yield of the photocatalytic reduction of CO 2 with H 2 O on tetrahedrally
coordinated Ti-oxides. Ti-oxide was constructed within porous silica material, and
its quantum yield could to be 0.3% at room temperature by the total number of
photons absorbed by the catalyst.
3.5.2.2 NO/NO 2 Photoreduction
In 1985, Anpo et al. [77] carried out a research on photoluminescence studies of
titanium oxide anchored onto porous Vycor glass. It is proposed that the
photoluminescence quenching is closely associated with the electron transfer from
the excited states of the catalyst to the added O 2 or N 2 O molecules. In Fig. 3.12, it
shows the comparison between the reduction of NO and the decomposition of CO 2 .
The structure of Ti-oxide single-site is presented on the left top of this picture.
Similarly, the structure of TiO 2 particles is presented on the right bottom of this
picture. The quantum yield of CO 2 + H 2 O ! CH 3 OH + CH 4 is much smaller than
the decomposition of NO, due to its demanding of more configurations of
co-adsorbed reactants involving six participating atoms [90]. In 1997, titanium
oxide catalysts prepared within the Y-zeolite cavities via an ion-exchange method
were reported by Anpo et al. [79], which exhibited high and unique photocatalytic
reactivities for the decomposition of NO into N 2 and O 2 . It was also found that the
charge-transfer excited state of the titanium oxide species, (Ti
3+ -O
À )*, plays a vital
role in these unique photocatalytic reactions. Table 3.1 revealed the yields of the
photo-formed N 2 and N 2 O and its selectivity in the photocatalytic decomposition of
NO. It is obvious that the efficiency and selectivity of the formation of N 2 strongly
depend on the type of catalysts.
In 2000, Masato Takeuchi et al. [76] prepared transparent TiO 2 thin film
photocatalysts on transparent porous Vycor glass (PVG) by an ionized cluster
beam (ICB) method. These thin films worked with high efficiency as photocatalysts
for the decomposition of NO into N 2 , O 2 , and N 2 O under UV light irradiation at
275 K. When the film thickness increases, the photocatalytic reactivity decreases
gradually. In 2004, Yamashita and Anpo [80] proposed a new concept of an ion
beam technology using accelerated metal ions, a metal ion implantation, and an
ionized cluster beam (ICB) (detailed schematic diagram is shown in Fig. 3.13a). The
decomposition of NO into N 2 , O 2 , and N 2 O can be occurred not only under UV light
but also visible light, realizing the efficient use of solar beam energy. The samples
were also characterized by XANES (as shown in Fig. 3.13b). It revealed the XAFS
(XANES and FTEXAFS) spectra of the Cr ion–implanted TiO 2 powder catalyst. By
analyzing on these spectra, we can tell that in the Cr ion–implanted TiO 2 , the Cr ions
are highly dispersed in the lattice of TiO 2 possessing octahedral coordination. These
Cr ions are isolated and substitute the Ti
4+ ions in the lattice positions of TiO 2 .
3.5 The Development of Mesoporous Ti–SiO 2 Materials in Photocatalysis
65