mixed-phase TiO 2 of anatase/brookite via hydrothermal treatments. Compared with
a reference TiO 2 prepared by conventional sol–gel synthesis, the anatase/brookite
nanocomposites which are obtained by hydrothermal method showed the higher
photocatalytic activity for producing H 2 . Furthermore, they found that the anatase/
brookite ratio in the nanocomposite had a great influence on the photocatalytic
activity in H 2 production.
Apart from the research applying mixed-phase anatase/brookite TiO 2 as the
photocatalyst to produce hydrogen, a great deal of research on the mixed-phase
anatase/rutile TiO 2 has also been done. Li et al. [112] fabricated photocatalysts with
a tuned anatase/rutile structure by calcination of commercial P25 at different temperatures and investigated their photocatalytic activity for hydrogen production
through photocatalytic biomass reforming. Surprisingly, it was found that compared
with P25 without any treatment, the photocatalytic performance of the thermaltreated P25 for hydrogen production is better. The overall photocatalytic activity
for hydrogen production on thermal-treated P25 had a dramatic improvement of
three to five times. It was proposed that the anatase/rutile junction structure was
mainly responsible for the enhanced photocatalytic performance. The research work
implied that the photocatalytic ability of TiO 2 could be further improved by elaborately designing the anatase/rutile structure. Amal et al. [113] obtained the similar
conclusions. They did a systematical study on photocatalytic H 2 evolution using
mixed-phase TiO 2 as a function of anatase and rutile phase compositions with
methanol as hole scavengers. The TiO 2 nanomaterials they prepared contain
4–95 mol % anatase, with the remaining being rutile. Synergistic effects on H 2
evolution were observed for a wide range of anatase contents, from 13 to 79 mol %,
while due to insufficient physical contact, no synergistic effect was observed for the
sample obtained by mixing anatase and rutile particles physically. Recently, in
addition to the above research on particulate TiO 2 (Fig. 6.12a, b), Yu et al. [114]
prepared a kind of anatase/rutile TiO 2 nanofiber photocatalyst (Fig. 6.12b, c). The
enhanced photocatalytic performance for H 2 production was also observed in the
synthesized anatase/rutile composite nanofibers. The product with 45 wt.% rutile
phase and 55 wt.% anatase phase exhibited the highest photocatalytic activity with
the H 2 production rate of 324 mmol h
À1 and the apparent QE of 20.9% at 365 nm.
Though the research on the mixed-phase TiO 2 of anatase/rutile generally demonstrated that the combination of the two phases favored the photocatalytic hydrogen production efficiency, the low utilization rate of visible light still remains as a
big limit for its practical application. The relatively narrow bandgap of rutile extends
some visible light absorption to some extent. However, this is not enough for TiO 2
photocatalyst to apply in the practical applications. Researchers have made great
efforts on to expand the visible light absorption of the mixed-phase TiO 2 crystals.
Keller et al. [115] reported Au-modified anatase/rutile mixed-phase TiO 2
photocatalyst (Fig. 6.13) for hydrogen production. The light absorption of the
sample with and without Au deposition was investigated via UV–vis light absorption
spectra. Before the Au deposition, the catalyst with rutile phase whose content was
higher than that of P25 exhibited more light absorption extended up to 550 nm, but
its intensity is relatively low. After Au deposition, the samples showed an obvious
152
6 Phase Control of TiO 2 Photocatalyst
a reference TiO 2 prepared by conventional sol–gel synthesis, the anatase/brookite
nanocomposites which are obtained by hydrothermal method showed the higher
photocatalytic activity for producing H 2 . Furthermore, they found that the anatase/
brookite ratio in the nanocomposite had a great influence on the photocatalytic
activity in H 2 production.
Apart from the research applying mixed-phase anatase/brookite TiO 2 as the
photocatalyst to produce hydrogen, a great deal of research on the mixed-phase
anatase/rutile TiO 2 has also been done. Li et al. [112] fabricated photocatalysts with
a tuned anatase/rutile structure by calcination of commercial P25 at different temperatures and investigated their photocatalytic activity for hydrogen production
through photocatalytic biomass reforming. Surprisingly, it was found that compared
with P25 without any treatment, the photocatalytic performance of the thermaltreated P25 for hydrogen production is better. The overall photocatalytic activity
for hydrogen production on thermal-treated P25 had a dramatic improvement of
three to five times. It was proposed that the anatase/rutile junction structure was
mainly responsible for the enhanced photocatalytic performance. The research work
implied that the photocatalytic ability of TiO 2 could be further improved by elaborately designing the anatase/rutile structure. Amal et al. [113] obtained the similar
conclusions. They did a systematical study on photocatalytic H 2 evolution using
mixed-phase TiO 2 as a function of anatase and rutile phase compositions with
methanol as hole scavengers. The TiO 2 nanomaterials they prepared contain
4–95 mol % anatase, with the remaining being rutile. Synergistic effects on H 2
evolution were observed for a wide range of anatase contents, from 13 to 79 mol %,
while due to insufficient physical contact, no synergistic effect was observed for the
sample obtained by mixing anatase and rutile particles physically. Recently, in
addition to the above research on particulate TiO 2 (Fig. 6.12a, b), Yu et al. [114]
prepared a kind of anatase/rutile TiO 2 nanofiber photocatalyst (Fig. 6.12b, c). The
enhanced photocatalytic performance for H 2 production was also observed in the
synthesized anatase/rutile composite nanofibers. The product with 45 wt.% rutile
phase and 55 wt.% anatase phase exhibited the highest photocatalytic activity with
the H 2 production rate of 324 mmol h
À1 and the apparent QE of 20.9% at 365 nm.
Though the research on the mixed-phase TiO 2 of anatase/rutile generally demonstrated that the combination of the two phases favored the photocatalytic hydrogen production efficiency, the low utilization rate of visible light still remains as a
big limit for its practical application. The relatively narrow bandgap of rutile extends
some visible light absorption to some extent. However, this is not enough for TiO 2
photocatalyst to apply in the practical applications. Researchers have made great
efforts on to expand the visible light absorption of the mixed-phase TiO 2 crystals.
Keller et al. [115] reported Au-modified anatase/rutile mixed-phase TiO 2
photocatalyst (Fig. 6.13) for hydrogen production. The light absorption of the
sample with and without Au deposition was investigated via UV–vis light absorption
spectra. Before the Au deposition, the catalyst with rutile phase whose content was
higher than that of P25 exhibited more light absorption extended up to 550 nm, but
its intensity is relatively low. After Au deposition, the samples showed an obvious
152
6 Phase Control of TiO 2 Photocatalyst