16 research outputs found
Visible light driven photocatalysis in chromate(VI)/TiO_2 systems : improving stability of the photocatalyst
Titanium dioxide photosensitization to visible light can be observed in the presence of chromate(VI) ions
adsorbed at the surface of TiO
2
. The resulting materials do not show, however, sufficient stability and
photostability—chromium(VI) species desorb from the surface and can be reduced to chromium(III). The
stability of such systems has been improved by TiO
2
impregnation with fluorochromate(VI), K[CrO
3
F],
instead of K
2
Cr
2
O
7
, yielding yellow F-Cr
VI
@TiO
2
material. Fluorides playing the role of anchors enable
stronger adsorption of chromates at titanium dioxide. Also composites of water insoluble chromates(VI)
with TiO
2
release significantly lower amounts of Cr
VI
ions. Such materials have been synthesized accord-
ing to two main strategies—the first one involves precipitation of water insoluble chromates in the
presence of TiO
2
particles (MCrO
4
@TiO
2
) while the second strategy comprises of TiO
2
synthesis in the
presence of insoluble chromate particles (TiO
2
@MCrO
4
). Visible light induced photocatalytic activity of
synthesized materials was studied in the process of 4-chlorophenol (4-CP) oxidation. A considerable pho-
tocatalytic activity was observed in the case of F-Cr
VI
@TiO
2
and TiO
2
@MCrO
4
type materials (M
n
+
:Ba
2+
,
Co
2+
,Mn
2+
,Cr
3+
). Among the composites the highest photoreactivity was shown by TiO
2
@CoCrO
4
(1.7%
Cr
VI
, mol/mol, calcined at 450
◦
C) and TiO
2
@Cr
2
(CrO
4
)
3
(5% Cr
VI
, mol/mol, calcined at 450
◦
C)
Enhanced UV light emission by core-shell upconverting particles powering up photocatalysis in near-infrared light
The core-shell NaYb0.99F4:Tm0.01@NaYF4 upconverting particles (UCPs) with a high UV emission to apply in NIR-driven photocatalysis were synthesized. The influence of the Yb3+ doping concentration in NaYxF4:Yb0.99−xTm0.01 core particles, and the role of the NaYF4 shell on the upconversion emission intensity of the UCPs were studied. The absorption of NIR light by the obtained UCPs was maximized by increasing the Yb3+ concentration in the core, reaching the maximum for Y3+-free particles (NaYb0.99F4:Tm0.01). Additionally, covering the NaYb0.99F4:Tm0.01 core with a protective layer of NaYF4 minimized the surface luminescence quenching, which significantly improved the efficiency of upconversion emission. The high intensity of the UV light emitted by the NaYb0.99F4:Tm0.01@NaYF4 under NIR irradiation resulted in a high photocatalytic activity of TiO2 (P25) mixed with the synthesized material