Titanium
dioxide doped with the Pt ion (Pt–TiO
2
) was synthesized
by a sol–gel method using only water as the solvent and conducting
dialysis. The photocatalytic activity for the degradation of 4-chlorophenol
(4-CP) on Pt–TiO
2
was not affected by the Brunauer–Emmett–Teller
specific surface area under visible light (VL) irradiation. X-ray
photoelectron spectroscopy (XPS) and X-ray absorption near-edge structure
measurements revealed that only the Pt(IV) ion existed in the TiO
2
bulk and both Pt(II) and Pt(IV) were present near the Pt–TiO
2
surface. Pt(IV) is most likely substituted in the Ti(IV)
site of the TiO
2
lattice because of their similar ionic
sizes. Quantitative analysis of Pt(II) was performed in the XPS measurements,
indicating that the amount of Pt(II) on the surface increased with
an increase in the doping amount from 0.2 to 1.0 atom %. We synthesized
0.5 atom % Pt–TiO
2
with various Pt(II)/Pt(IV) ratios
by changing the Ti(OC
3
H
7
)
4
concentration
used in the sol–gel synthesis. The 4-CP conversion on Pt–TiO
2
increased linearly with an increase in the Pt(II)/Pt(IV)
ratios. A similar relationship was obtained with Pt–TiO
2
, which was prepared by a conventional sol–gel method
in ethanol–water mixed solvent. Therefore, the Pt(II)/Pt(IV)
ratio is a key factor affecting the photocatalytic activity of Pt–TiO
2
under VL irradiation. Our results indicate that controlling
the mixed valence states of the doped metal ions is a new strategy
to developing highly active metal-ion-doped TiO
2
under
VL irradiation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.