156
G. Compagnini et al.
Fig. 4.14 a Amount of produced hydrogen under UV irradiation for different titania samples before
and after laser irradiation process. b Amount of produced hydrogen under UV and Visible irradiation
versus time for as received P25 and laser modified P25
actions. The induced magnification was long-living and provides a simple and environmentally friendly methodology. Figure 4.14a shows the overall hydrogen evolution as a function of time, comparing as received and irradiated rutile, anatase, and
P25 samples at the maximum fluence. It is important to underline that the increase
of laser fluence had a positive effect on the photocatalytic performance of titania
which could be correlated to higher concentration of defects. The laser irradiation
strongly enhanced the production rate up to a factor of three for P25 that showed the
best performance, but also anatase and rutile samples increased their photocatalytic
activity after laser irradiation. It is also possible to exclude a correlation between
the increased activity and the phase change of titania from anatase to rutile. Indeed
P25, which was the sample with the largest difference in the activity, did not exhibit
any relevant change in the crystalline phase due to irradiation. In agreement with
the theoretical studies reported by Zhao et al. [93] the same figure also evidences a
higher rutile activity with respect to anatase.
Figure 4.14b reports the amount of produced hydrogen versus time of UV or
Visible irradiation for the P25 as received and after laser irradiation. Under UV
irradiation, the curves display an initial induction period lasting less than 10 min due
to stabilization of lamp radiation and the saturation of water with evolved gases; a
linear increment in which there is a maximum in the hydrogen production rate and
finally a moderate decrease of the production rate after about one-hour irradiation
due to a recombination of photo-generated electron/hole pairs or to a fast backward
reaction (recombination of hydrogen and oxygen into water).
G. Compagnini et al.
Fig. 4.14 a Amount of produced hydrogen under UV irradiation for different titania samples before
and after laser irradiation process. b Amount of produced hydrogen under UV and Visible irradiation
versus time for as received P25 and laser modified P25
actions. The induced magnification was long-living and provides a simple and environmentally friendly methodology. Figure 4.14a shows the overall hydrogen evolution as a function of time, comparing as received and irradiated rutile, anatase, and
P25 samples at the maximum fluence. It is important to underline that the increase
of laser fluence had a positive effect on the photocatalytic performance of titania
which could be correlated to higher concentration of defects. The laser irradiation
strongly enhanced the production rate up to a factor of three for P25 that showed the
best performance, but also anatase and rutile samples increased their photocatalytic
activity after laser irradiation. It is also possible to exclude a correlation between
the increased activity and the phase change of titania from anatase to rutile. Indeed
P25, which was the sample with the largest difference in the activity, did not exhibit
any relevant change in the crystalline phase due to irradiation. In agreement with
the theoretical studies reported by Zhao et al. [93] the same figure also evidences a
higher rutile activity with respect to anatase.
Figure 4.14b reports the amount of produced hydrogen versus time of UV or
Visible irradiation for the P25 as received and after laser irradiation. Under UV
irradiation, the curves display an initial induction period lasting less than 10 min due
to stabilization of lamp radiation and the saturation of water with evolved gases; a
linear increment in which there is a maximum in the hydrogen production rate and
finally a moderate decrease of the production rate after about one-hour irradiation
due to a recombination of photo-generated electron/hole pairs or to a fast backward
reaction (recombination of hydrogen and oxygen into water).