I.A. Mkhalid / Journal of Alloys and Compounds 631 (2015) 298–302
299
Au/LaTiO3 nanocomposites was studied for synthesis of aniline
from photocatalytic reduction of nitrobenzene.
0.4 wt % Au/LaTiO3 after
0.4 wt % Au/LaTiO3
2. Experimental
0.3 wt % Au/LaTiO3 before
0.2 wt % Au/LaTiO3
2.1. Preparation of photocatalyst
LaTiO3 nanoparticles are prepared by an ultrasonic method. All of the chemicals
were used without further purification. In a typical preparation, 0.3 mol of lantha-
num acetate was added under a nitrogen atmosphere to 16 mol of glacial acetic acid
and stirred for 2 h at room temperature. Then, 5 mol of titanium isoperoxide, was
added to above solution and the resulting mixture was stirred at room temperature
for 6 h. Then, 20 ml of acetone was added to them and the resulting mixture was
put in an apparatus for low frequency ultrasound (Bransonic 42 kHz) for 1 h. The
resulting materials were dried for 24 h at 100 °C, and then the materials were cal-
cined at 550 °C for 5 h in air. A photo-assisted deposition (PAD) route was used to
prepare Au/LaTiO3 samples which contain different wt.% from Au metal (0.1, 0.2,
0.3, and 0.4 wt.%). In this route, Au metal was deposited on LaTiO3 under UV-light
irradiation by using an aqueous solution of HAuCl4. The obtained samples dried
for 24 h at 60 °C.
0.1 wt % Au/LaTiO3
LaTiO3
4
8
12 16 20 24 28 32 36 40 44 48 52 56 60 64 68
2θ, degree
Fig. 1. XRD pattern of LaTiO3 and Au/LaTiO3 nanocomposites.
2.2. Characterization of photocatalysts
Bruker axis D8 with Cu Ka radiation (k = 1.540 Å) is used for X-ray diffraction
(XRD) analysis that was done at room temperature. N2-adsorption measurements
were used for calculating the surface area and for that purpose a Nova 2000 series
Chromatech apparatus at 77 K was used. The samples were treated for 2 h under
vacuum at 100 °C before taking the measurements. A UV–visible diffuse reflectance
spectroscopy (UV–Vis-DRS) is used for displaying the performance of the band-gap
of samples. The spectroscopy is done in air at room temperature using a UV/Vis/NIR
spectrophotometer (V-570, JASCO, Japan) and in the wavelength range of 200–
800 nm. A JEOL-JEM-1230 microscope is used for conducting the transmission elec-
tron microscopy (TEM). The entire samples were set up in a suspension of ethanol
and then for half an hour of ultrasonication are done over the samples. A low
amount of solution is placed on a copper grid coated by carbon and left to dry. Once
the solution is dry, the sample is loaded into the TEM. A Thermo Scientific K-ALPHA,
XPS is used for performing the X-ray photoelectron spectroscopy (XPS). Photolumi-
nescence (Pl) emission spectra was measured by Shimadzu RF-5301 fluorescence
spectrophotometer.
Au 4f7/2
Au 4f5/2
90
88
86
84
82
2.3. Photocatalytic performance
Binding energy /eV
The photocatalytic apparatus consists of two parts: a sealed quartz reactor and
an annular quartz tube. A visible light source is obtained by a 500-W Xenon lamp
(Institute of Electric Light Source, Beijing) with a maximum emission of about
470 nm and cutoff filter to control wavelength of light. The lamp was in an empty
chamber of the annular tube, and running water passed through the tub and con-
tinuous cooling kept the temperature of reaction solution at approximately 30 °C.
The sealed quartz reactor has a diameter of 8.3 cm and is put below the lamp.
50 mg of photocatalyst was dispersed in 10 ml of nitrobenzene-CH3OH mixture
Fig. 2. XPS spectra of Au 4f for 0.3 wt.% Au/LaTiO3 nanocomposites.
TEM images of LaTiO3 and Au/LaTiO3 nanocomposites are shown in Fig. 3. The
results reveal that the gold is well dispersed into LaTiO3 surface, and the diameter
of the gold depend on weight percent of gold. It is clear that the homogeneity of
gold was increased by increase weight percent of gold up to 0.3 wt.%. In addition,
higher weight percent of gold (i.e. 0.4) decreases the homogeneity. This observation
indicated that there is an optimum value for the deposition of gold metal.
(1/99, v/
v
), where 8.13 ꢁ 10ꢀ4 mol/L is initial concentration of nitrobenzene.
11 cm is the distance between the surface of reaction solution and light source.
Before illumination, dissolved oxygen in reaction mixture was removed by passing
nitrogen gas through the reaction mixture for 30 min. At interval times, samples
which were taken from reaction mixture were filtrated to remove any residual par-
ticles and the filtrates were analyzed using a gas chromatography Agilent GC 7890A
model: G3440A Gas Chromatography using 19091J-413 capillary column
2.5. Texture structure
The texture parameters of LaTiO3 and Au/LaTiO3 nanocomposites are demon-
strated in Table 1. The SBET values for LaTiO3, 0.1 wt.% Au/LaTiO3, 0.2 wt.% Au/LaTiO3,
0.3% Au/LaTiO3 and 0.4% Au/LaTiO3 nanocomposites were 19, 18, 15, 13 and 11 m2/g,
respectively. The total pore volume of Au/LaTiO3 is smaller than that of LaTiO3
sample due to the blocking of some pore of Au/LaTiO3 by Au metal deposition.
Presence of mesopores in all samples was confirmed by close values of SBET and St
in most samples as shown in Table 1.
(30 m ꢁ 0.32 lm ꢁ 0.25 lm).
2.4. Structural characterization, morphology and composition
The X-ray diffraction patterns of LaTiO3 and Au/LaTiO3 Au/LaTiO3 nanocompos-
ites are compared in Fig. 1. The structural feature of LaTiO3 and Au/LaTiO3 Au/
LaTiO3 nanocomposites are mainly composed of LaTiO3 (JCPDS card: 75-0267), indi-
cating that the LaTiO3 structure remained after doping of Au into surface of LaTiO3
by PAD method. However, no diffraction peaks for Au or Au2O was appeared, due to
low weight percent of gold or may be Au is well dispersed into surface of LaTiO3.
Also, we noticed that dispersion of Au into surface of LaTiO3 leads to decrease peak
intensity of XRD. The average crystallite size of LaTiO3 was calculated by Scherer
equation using the half-width of the peak in the X-ray diffraction pattern at
2h = 32.07°, which corresponds to the most intense peak. The crystallite size of
LaTiO3, 0.1 wt.% Au/LaTiO3, 0.2 wt.% Au/LaTiO3, 0.3 wt.% Au/LaTiO3, and 0.4 wt.%
Au/LaTiO3 Au/LaTiO3 nanocomposites were 35, 30, 23, 18 and 14 nm, respectively.
Thus, the crystallite size of LaTiO3 was decreased by increase weight percent of
doped gold.
2.6. Optical characterization
UV–Vis diffuse reflectance spectra of LaTiO3 and Au/LaTiO3 nanocomposites is
shown in Fig. 4. The results reveal that the absorption edge of LaTiO3 was shifted
from 427.6 to 539.1 nm by deposition of Au metal into LaTiO3 surface. The results
of UV–Vis spectra’s were used to calculate direct band gap of LaTiO3 and Au/LaTiO3
nanocomposites based on the method which used by Kumar et al. [29]. The band
gap energies were calculated employing the following equation:
Eg ¼ 1239:8=k
where k is wavelength of the absorption edges in the spectrum (nm), and Eg is band
gap (eV). The results are tabulated in Table 2. The results reveal that the band gap
was decreased from 3.4 to 2.4 eV by increase wt.% of Au from 0.1 to 0.3 wt.%, respec-
tively. However, no significant change in the band gap is found by high wt.% of Au
above 0.30. Therefore, band gap was controlled by control wt.% of Au deposited.
XPS spectra of 0.3 wt.% Au/LaTiO3 nanocomposite is shown in Fig. 2. XPS spectra
showed that the peak at 87.7 eV and 84.0 eV attributed to metallic gold, which con-
firm that gold is dispersed above LaTiO3 surface as gold metal.