dc.description.abstract | In this study, TiO2 photocatalyst materials with high surface area
were prepared by grafting a TiO2 thin layer onto SBA-15. Photosentisizer
(2,9-dichloro quinacridone, DCQ) is impregnated to extend
their use of visible light. And metal nanoparticles are immobilized to
promote their photocatalytic activities. These prepared catalysts were
employed in photocatalytic reduction of CO2 for mitigating the
greenhouse gas effect and serving as a new energy source.
We used P123 surfactant as a template to prepare conventional
SBA-15, and used ternary surfactants (C16TMAB/SDS/P123) to prepare
vc-SBA-15 with vertical nanochannels. TiO2/SBA-15 and TiO2/vc-
SBA-15 were prepared by grafting a thin layer of TiO2 onto SBA-15 and
vc-SBA-15 with TBOT as Ti source. HRTEM images showed that
vc-SBA-15 had short and face-up nanochannels, which was extremely
different from SBA-15 of longer parallel channels. The XRD patterns
of SBA-15 and vc-SBA-15 exhibited a characteristic (100) peak,
indicating that they were of highly ordered hexagonal structures. After
grafting with TiO2, there were no significant changes in the morphology
and structure. Meanwhile, the surface area of SBA-15 was decreased
from 725 m2/g to 573 m2/g, and that of vc-SBA-15 was also decreased
from 797 m2/g to 584 m2/g as determined by N2 sorption isotherms.
UV-Visible spectrum showed that a strong absorption band occurred at
the wavelength less than 380 nm, indicating that TiO2 was successfully
grafted onto the mesoporous silica. Photosensitizer DCQ was then
introduced in order to facilitate the TiO2-containing catalysts to extend
the use of visible light. As shown by UV-Visible spectrum, the obtained
catalysts had obvious absorption ranged from 500 to 600 nm. The DCQ
uptake of DCQ/TiO2/SBA-15 and DCQ/TiO2/vc-SBA-15 were 2.0 wt% and 4.6 wt%, respectively, as estimated by TGA. The photoreduction of
CO2 was conducted in NaHCO3(aq) under visible and UV light
illumination. As a result of the short and face-up nanochannels that
permits the higher accessibility for the reactants, the methanol yield of
vc-SBA-15 supported photocatalysts were much higher than those of
SBA-15 supported ones. The methanol yield of DCQ/TiO2/vc-SBA-15
was 0.44 μmole/g-cat./hr under visible light irradiation, whereas that of
TiO2/vc-SBA was 11.5 μmole/g-cat./hr under UV irradiation.
Platinum and/or rhodium nanoparticles were immobilized on the
TiO2/SBA-15 and TiO2/vc-SBA-15 by photochemical deposition method.
The metal particle size of the prepared catalysts were about 2 - 5 nm as
observed by HRTEM. The catalytic activities of were evaluated by
photoreduction of CO2, photodegradation of salicylic acid and CO
oxidation. For photocatalytic reduction of CO2, it was found that the
methanol of TiO2-containing catalysts can be substantially enhanced by
metal modification. For photodegradation of salicylic acid, the activities
were in the order: Pt > Pt-Rh > Rh. For CO oxidation, it was found that
the activity of TiO2/vc-SBA-15 was higher than TiO2/SBA-15. The
catalytic activities of catalysts supported the metal for CO oxidation were
in the order: Pt-Rh > Rh > Pt. | en_US |