Journal of University of Science and Technology Beijing
Volume 14, Number 6, December 2007, Page 1
Corresponding author: Changchun Ge, E-mail: ustbgcc@163.com Also available online at www.sciencedirect.com
Materials
Enhanced photocatalytic activity of (La, N) Co-doped TiO
2
by
novel TiCl
4
sol-gel autoigniting synthesis
Zhongqing Liu, Yanping Zhou, Zhenghua Li, Yichao Wang, and Changchun Ge
Materials Science and Engineering School, University of Science and Technology Beijing, Beijing 100083, China
(Received 2006-12-07)
Abstract: (La, N) co-doped TiO
2
photocatalysts were synthesized using novel TiCl
4
sol-gel autoigniting synthesis (SAS) starting
from a complex compound system of TiCl
4
-La(NO
3
)
3
-citric acid-NH
4
NO
3
-NH
3
H
2
O, in which the (La, N) co-doped process was ac-
complished in the formation of TiO
2
nanocrystals. The prepared samples were characterized by using X-ray diffractometer (XRD),
X-ray photoemission spectroscopy (XPS) and UV-vis diffuse reflectance spectra. The results indicated that nitrogen and lanthanum
were incorporated into lattice and interstices of tiania nanocrystals, which resulted in narrowing of the band gap and promoting the
separation of photoexcited hole-electron pairs, respectively, and showing expected red-shifts and enhanced the photocatalytic activity
under visible light. The mechanism on doping nitrogen and enhancement of the photocatalytic activity of (La, N) co-doped titania by
SAS has been discussed in detail.
Key words: (La, N) Co-doped TiO
2
; sol-gel autoigniting synthesis; photocatalytic activity
1. Introduction
Titanium dioxide, which is well known as a cheap,
nontoxic, efficient, and the most promising photoca-
talyst, has attracted much attention for past decades.
Unfortunately, the photocatalytic activity of pure tita-
nia, because of relatively broad band gap that is ex-
cited only by irradiation with ultraviolet (UV) light, is
not high enough for practical application. Several in-
vestigations focused on introducing foreign species
are in progress for the improvement of the catalytic
activity and broadening the absorption to the solar
spectrum of TiO
2
. Among them, titania doped with
metals or metallic cations as photocatalyst, such as
transition metallic cations, rare metal cations, and
n
oble metal, have been widely and deeply investigated
to broaden the photoabsorption region and improve
the photocatalytic activity of titania. However, these
doped metallic cations, efficient acceptors of electrons,
tend to serve as recombination centers. As a result, in
most cases, photoexcited charges are recombined by
the sites of doping metallic cations [1-2].
Recently, titania doped with nonmetallic anions,
such as carbon [3-4], sulfur [5-6], fluorine [7-8],
phosphorus [9], and especially nitrogen [10-16], has
been synthesized because Asahi and coworkers suc-
cessfully prepared titanium dioxide doped with nitro-
gen to broaden the wavelength of optical response of
titania from the UV to the visible light region. Nitro-
gen-doped titanium dioxide powders have been pro-
duced using hydrolysis and other methods such as
thermal treatment for the precursor of titanium [17],
direct thermal treatment for nano-TiO
2
in NH
3
[11],
homogeneous precipitation-solvothermal synthesis,
and decomposition of Ti-based metal organic [18-19]
have also been reported. However, there are few re-
ports on the synthesis of (metal, N) co-doped titania
[20-21], and the disadvantages of these methods are
complicated procedures, the requirement of special
atmosphere, and costly reagents and raw materials.
As shown in this article, titania photocatalysts
co-doped with lanthanum and nitrogen have been
synthesized by sol-gel autoigniting synthesis (SAS)
with the complex sol of TiCl
4
-La(NO
3
)
3
-citric ac-
id-NH
4
NO
3
-NH
3
H
2
O as the precursor. The SAS has
the advantage of using inexpensive raw materials of
inorganic titanium, mixing of compositions at the lev-
el of atoms or molecules, producing ultrafine and
highly homogeneous powders, having simple proce-
dure [22], and co-doping lanthanum and nitrogen in
the formation of TiO2 nanocrystals, with enhanced
visible light activity, simple process(与上面重复？删
除？
), and lower cost.
2. Experimental
The photocatalysts were prepared by SAS starting
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