Synthesis of large surface area LaFeO3 nanoparticles by SBA-16 ...

J Nanopart Res
photocatalysts for water splitting such as SrTiO 3 ,
NaTaO 3 , etc. (Subramanian et al. 2006; Kato and Kudo
2003; Maeda and Domen 2007; Penä and Fierro 2001),
and the photocatalytic decompositions of organic
compounds have been widely studied, but all the
performance need to be advanced.
The specific surface area and crystal structure are
the most important two factors influencing catalytic
activity. During several conventional synthetic processes
of perovskites, such as citrate method and
solid state reactions, the high-temperature thermal
treatments needed usually lead to the sintering of the
resulting particles, consequently decreasing greatly
the specific surface area, which will largely influence
the performance of the resulting perovskites and
hinder their widespread use as catalysts. Thus, novel
synthetic methods to obtain materials with large
specific surface area are greatly desired.
Among various preparation methods of nanosized
materials, the template method, which provides a
good choice for the synthesis of nanoparticles with
controllable size and shape because of being in a
confined three-dimensional (3D) space, has recently
sparked great research interests (Lu and Schüth 2006;
Schüth 2003). Unlike conventional surfactant templates,
the hard template could effectively maintain
the local strain caused by the crystallization of
precursors. Zhao et al. synthesized highly dispersed
TiO 2 nanoparticles using SBA-15 as hard template
(Zhao and Yu 2006). Valdés-Solís et al. prepared
nanosized perovskites and spinels through a silica
xerogel template route (Valdés-Solís et al. 2005).
However, so far the articles on the use of the SBA-16
as hard template to synthesize nanosized solid
materials are seldom reported. SBA-16 is a kind of
3D, ‘‘cage-like’’ mesoporous silica, and its pores are
connected by some mesoporous windows, so as to be
beneficial for the substance transportation. Thus, it
can be deduced that its negative replica is 3D
connected structure (Shi et al. 2005a, b; Schüth and
Schmid 2002; Kärger and Freude 2002), so that the
SBA-16 as template to prepare porous solid materials
with large surface area is feasible. It has been
demonstrated that mesoporous structure is highly
desirable for effective photocatalysis, since such
structures enable more light to be harvested and also
possess continuous pore channels that facilitate the
transfer of reactant molecules.
As a kind of important functional material, LaFeO 3
with a typical ABO 3 -type perovskite structure has
many applications, such as catalytic oxidation, electrode
materials, and chemical sensors for the humidity
and alcohols, and it also is an ideal potential semiconductor
material for visible photocatalyst because of its
small band gap energy (Wang et al. 2006; Li et al.
2007). Herein, nanosized LaFeO 3 with large surface
area was synthesized with mesoporous silica SBA-16
as hard template for the first time. The as-prepared
LaFeO 3 exhibits excellent visible-light photocatalytic
activity, which is attributed to the large surface area, as
well as to the high photoinduced charge separation rate
mainly based on the SPS responses. This should be
valuable for the practical application of LaFeO 3 and
also provides a new strategy to prepare other highperformance
nanostructured oxide composite materials
with large surface area.
Experimental
Preparation of the template SBA-16
The SBA-16 was synthesized by a sol–gel process as
described elsewhere (Shi et al. 2005a, b). The F127
(EO 106 PO 70 EO 106 , BASF) and Ethyl silicate
(C 8 H 20 O 4 Si) were used as surfactant and silicon
sources, respectively. After the resulting xerogel was
calcined at 550 °C with a heating rate of 1 °C min -1
and ground, the mesoporous silica SBA-16 was
obtained eventually.
Synthesis of the samples
Nanosized LaFeO 3 was synthesized according to the
flowchart shown in Fig. 1. First, 1 g of freshly
as-synthesized SBA-16 was dispersed in 2 mL of
ethanol solution, containing 0.0041 mol of La(NO 3 ) 3
6H 2 O and 0.0041 mol of Fe(NO 3 ) 3 9H 2 O. After
ultrasonication for 10 min, the mixture obtained was
kept at 60 °C under stirring until the solvent was
evaporated completely. Subsequently, the LaFeO 3 –
SBA-16 composite was obtained after the above
mixture was dried in a vacuum at 80 °C and calcined
in air at needed temperature for 2 h. Finally, the
template-free LaFeO 3 nanopowder was gained by
washing, drying, grinding, and heat-treatment at
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