Preparation of aniline from photocatalytic reduction of nitrobenzene using Pt/Nd2O3 nanocomposite

Article abstract of DOI:10.1016/j.jallcom.2015.06.217

In this manuscript, a template method was used to synthesis Pt-doped Nd₂O₃ nanostructures with controlled Pt doping contents. The characterizations illustrated that the obtained samples have ultra high surface area (190 m²/g), high crystallinity, small grain size (20 nm) and hollow spherical like morphology. Also, the band gap of the Pt-doped Nd₂O₃ nanostructures can be controlled by controlling the Pt contents. The photocatalytic activity of the Pt-doped Nd₂O₃ nanostructures samples was studied by studying the reduction of nitrobenzene into aniline using visible light irradiation. The photocatalytic performance of Nd₂O₃ was enhanced by Pt doping. This can be attributed to the fact that the trapping effect of the Pt-doped Nd₂O₃ nanostructures and the red shift of absorption edge. The study result provides an effective method to create different photocatalysts with enhanced visible-light-driven photocatalytic performance.

Full text of DOI:10.1016/j.jallcom.2015.06.217

Accepted Manuscript
Preparation of aniline from photocatalytic reduction of nitrobenzene using Pt/ Nd O
2 3
nanocomposite
R.M. Mohamed
PII:
S0925-8388(15)30365-0
10.1016/j.jallcom.2015.06.217
JALCOM 34625
DOI:
Reference:
To appear in: Journal of Alloys and Compounds
Received Date: 8 May 2015
Revised Date: 19 June 2015
Accepted Date: 28 June 2015
Please cite this article as: R.M. Mohamed, Preparation of aniline from photocatalytic reduction of
nitrobenzene using Pt/ Nd O nanocomposite, Journal of Alloys and Compounds (2015), doi: 10.1016/
2 3
j.jallcom.2015.06.217.
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ACCEPTED MANUSCRIPT

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Preparation of aniline from photocatalytic reduction of nitrobenzene using Pt/ Nd2O3 nanocomposite
R. M. Mohamed,1 *
1Chemistry Department, Faculty of Science, King Abdulaziz University, P.O. Box 80203 Jeddah 21589, Saudi Arabia,
*Corresponding author, E-mail: mhmdouf@gmail.com; Tel.: +966-540715648; Fax: +966-2-6952292
Abstract
In this manuscript, a template method was used to synthesis Pt-doped Nd2O3
nanostructures with controlled Pt doping contents. The characterizations illustrated that the
obtained samples have ultra high surface area (190 m2/g), high crystallinity , small grain size (20
nm) and hollow spherical like morphology. Also, the band gap of the Pt-doped Nd2O3
nanostructures can be controlled by controlling the Pt contents. The photocatalytic activity of
the Pt-doped Nd2O3 nanostructures samples was studied by studying the reduction of
nitrobenzene into aniline using visible light irradiation. The photocatalytic performance of
Nd2O3 was enhanced by Pt doping. This can be attributed to the fact that the trapping effect of
the Pt-doped Nd2O3 nanostructures and the red shift of absorption edge. The study result
provides an effective method to create different photocatalysts with enhanced visible-light-
driven photocatalytic performance.
Keywords: Nd2O3; Pt Doping ; Visible absorption; Aniline synthesis
1.Introduction
The intermediates keys in the preparation of agrochemicals, pharmaceuticals and dyes
are aromatic amines[1]. One of the most common method which used for preparation of amines
is a hydrogenation method. The drawback for the hydrogenation method is poor efficiency and
toxicity of metal used for hydrogenation [2]. Thus, from economic and environmental point of
view, an effective method for cheap and cleaner fabrication of amine is remain a challenge in

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synthesis of organic. Recently, the photoreduction method is an effective and clean method for
preparation of amine for organic synthesis[3]. TiO2 is one of the most promising photocatalyst
due to thermal and chemical stability, nontoxicity as well as its low cost. P25 Degussa has high
photocatalytic activity due to separation between electron and hole between rutile (20%) and
anatase (80 %)[4]. The first example of photoreduction of nitroaromatic compounds to aniline
under UV irradiation using P25 Degussa is reported by Li et al [5]. Many researchers were tried
to convert absorption of TiO2 from UV to visible region or design new materials absorb in
visible region. The first examples of photoreduction of nitro compounds using dye-sensitized
TiO2–P25 [6] or PbBiO2X,[7] under LED irradiation were reported by Konig and co-workers.
Ag–TiO2, TiO2 (anatase) and TiO2–P25, and under solar and UV-A light irradiation were used
for preparation of ketones from ketoximes by Swaminathan and co-workers[8]. TiO2–P25, Pt–
TiO2, and Ag–TiO2 nanoparticles under UV and solar light were used for preparation of indazole
and benzimidazoles[9]. Single-crystalline rutile TiO2 nanorods was used for preparation of
benzaldehyde from photocatalytic oxidation of benzyl alcohol under visible light[10]. Synthesis
of aldehydes and ketones from the corresponding oximes using sunlight irradiation were
reported by activated amorphous TiO2 incorporated into periodic mesoporous organosilicas [11].
From the green chemistry point view, still need to develop methods for preparing organic
compounds using solar energy[12]. Therefore, the aim of this work is preparation of a new
visible photocatalyst for synthesis of aniline from reduction of nitrobenzene.

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2. Experimental
2.1. Materials synthesis
The hydrothermal method which was reported by Li et al [13] was used to prepare
carbon spheres. To prepare the Pt-doped Nd2O3 nanostructures, 1 mmol of Neodymium(III)
nitrate hexahydrate and stoichiometric amount of Platinum (II) chloride were dissolved in100
mL of N,N-dimethylformamide. 50 mg of as-synthesized carbon spheres was added to above
mixture and the resulting mixture was sonicated for 40 min, then the resulting mixture was
stirred for 24 h at room temperature. The resulting mixture was filtered many times by distilled
water and ethanol. The obtained Pt-doped Nd2O3 nanostructures was dried at 80 ◦C for 24 h,
◦
then calcined at 400 C in air for 5 h. The changeable concentrations of Pt in Pt-doped Nd2O3
nanostructures could be attempted by controlling the ratio of Neodymium(III) nitrate
hexahydrate and Platinum (II) chloride (1:0, 1:0.01, 1:0.02, 1:0.03, 1:0.04, 1:0.05) in the
solution. The contents of Pt in Nd2O3 were 0, 1, 2, 3, 4 and 5 % by molar ratio. The
corresponding products were marked as 1N, 2 N, 3 N, 4 N, 5 N and 6 N, respectively.
2.2. Photocatalyst characterization
A Bruker Axis D8 using Cu Kα radiation (λ = 1.540 Å) was used to determine the X-ray
diffraction patterns of the Nd2O3 and Pt-doped Nd2O3 nanostructures. A Nova 2000 series
Chromatech apparatus was used to measure the BET surface area of the Nd2O3 and Pt-doped
Nd2O3 nanostructures. Before measurement, the samples were heated under vacuum for 3 h at
200 °C. A UV/Vis/NIR spectrophotometer (V-570, JASCO, Japan) was used to measure the
band gap energy of the Nd2O3 and Pt-doped Nd2O3 nanostructures. A JEOL-JEM-1230
microscope was used to determine the shape and particle size of the Nd2O3 and Pt-doped Nd2O3
nanostructures. Before measurement, the samples were dispersed in ethanol for 30 min. Then, a

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small portion of the samples were placed on a carbon-coated copper grid. A Thermo Scientific
K-ALPHA, X-ray photoelectron spectroscope (XPS), England, was used to determine the
elemental nature of the sample. The photoluminescence emission spectra of Before
measurement, were measured using a Shimadzu RF-5301 fluorescence spectrophotometer.
2.3. Photocatalytic activity
Photocatalytic device consists of two parts was used to study photocatalytic application
The first part is an annular quartz tube. For visible light source, Xenon lamp(500 W)covered by
◦
UV cut-off filter was used. It laid in annular tube and it temperature kept at about 30 C by
cooling by water. The second part is laid below the Xenon lamp and it consist of sealed quartz
reactor with a diameter of 8.3 cm and The distance between the light source and the surface of
the reaction solution is 11 cm. Before each photocatalytic reaction, definite weight of
photocatalyst sample was dispersed ultrasonically into 10 ml of mixture of nitrobenzene-
methanol(1:99, volume per volume). 8.13 × 10−4 mol/l is initial concentration of nitrobenzene.
Before start of irradiation, to remove dissolved oxygen from reaction medium, N2 gas was
passed through reaction medium for 30 min. During reaction time, samples were taken for
analysis using gas chromatography Agilent GC 7890A model: G3440A Gas Chromatography
using 19091J-413 capillary column (30 m× 0.32 µm×0.25 µm) and chromatographic conditions
applied for photocatalytic reduction of nitrobenzene are summarized in Table 1

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3. Results and discussions
3.1. Characterization of photocatalyst
3.1.1. X-ray diffraction study
X-ray diffraction (XRD) was used for characterization the crystallographic structure of
the products. Fig.1. shows XRD patterns of the Nd2O3 and Pt-doped Nd2O3 nanostructures. The
results demonstrated that XRD pattern of Nd2O3 was in readily agreement with XRD pattern of
Nd2O3 phase (PDF#74- 2139). Also, with increasing Pt contents, there is no peaks of platinum
oxide or other phases could be detected in the Pt-doped Nd2O3 nanostructures samples,
suggesting that the doping of platinum does not effect on the crystallization properties of Nd2O3.
Because, the platinum concentrations were a little low and the radius of Pt 2+ (94 pm) is smaller
2+
than that of Nd3+ (112 pm) and, so Pt
may be doped into the crystal lattice of Nd2O3 as
shown in XRD patterns as shifting of main peak. of Nd2O3 at 2- theta = 30.8 which inset of
Fig.1 to high value , forming a platinum- neodymium oxide finite solid solution.
3.1.2. SEM and TEM examination
Fig.2. shows SEM images of Nd2O3 with different Pt contents. The results reveal that
addition of Pt does not change the morphology of the Nd2O3. The shape of all samples is
spherical with diameter ranging from 100 to 200 nm. Also, we noticed that the shell of the
spheres was composed of nanoparticles with small size. Fig.3. shows TEM image for 5 N
sample. The result demonstrates that the thickness of the shell was about 8 nm and large numbers
of pores were existed in the shell.

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3.1.3. XPS analysis
Fig.4. shows the XPS spectra of 5 N sample in Pt 4f. The results reveal that platinum
2+
present as Pt ion due to the
present of Pt 4 f 7/2 peak as 72.4 eV, which confirm the
2+
doping of Pt ion into the crystal lattice of Nd2O3 as shown before in XRD patterns as
shifting of main peak.
3.1.4. BET surface areas and pore distributions
Fig.5. shows nitrogen adsorption–desorption isotherms of 5 N sample. The results reveal
that the category of nitrogen adsorption–desorption isotherms of Pt- doped Nd2O3 nanostructure
is type IV with distinct hysteresis loops observed in the relative pressure range of 0.6–0.90. It
was clearly indicated that the products were mesoporous materials, which agreed well with the
morphologies and microstructures of porous Nd2O3 products (Fig. 3). Also, the other samples
have similar isotherm and pore diameter. BET surface area of as- prepared samples are listed in
Table 2. The results demonstrated that the value of BET surface areas of Pt- doped Nd2O3
nanostructure is higher than that of Nd2O3 due to the introduce of Pt 2+ ion into lattice of Nd2O3.
3.1.5. Optical properties measurements
Fig.6. shows the UV–Vis spectra of Nd2O3 and Pt- doped Nd2O3 nanostructures. The
results reveal that the red shift of absorption edge from 362 to 466 nm was occurred by doing
of Pt into crystal lattice of Nd2O3 . The band gap of Nd2O3 and Pt- doped Nd2O3 nanostructures
was calculated from their UV-Vis spectra and was tabulated in Table 3. The values of band
gap are 3.42, 3.15, 2.98, 2.87, 2.73 and 2.66 eV, for 1 N, 2 N,3 N , 4 N , 5 N and 6 N samples,
respectively, which means the band gap was decreased from 3.42 to 2.66 , eV by increased wt
% of Pt doped into Nd2O3 nanostructures from 0 to 5 wt %, respectively.

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Pl spectra of Nd2O3 and Pt- doped Nd2O3 nanostructures is shown in Fig.7. The results
reveal that Pl intensity was decreased as wt % of Pt doped Nd2O3 nanostructures increased. This
means Pt can capture electron from a conduction band of Nd2O3. Therefore, this leads to an
increase in the life time required for e-h pair recombination and an increase of photocatalytic
activity, as shown in photocatalytic activity part.
3.2. Photocatalytic reduction of nitrobenzene
3.2.1. Effect of the type of photocatalyst
Fig.8. shows effect of type of photocatalyst on photocatalytic reduction of nitrobenzene.
Nitrosobenzene and aniline are the main compounds, which are detected by gas chromatography
(GC). There is no detection by GC for aniline or nitrosobenzene in the absence of light or
catalyst. The results reveal that the photocatalytic activity of 1 N and 2 N is very small ( about 5
%) due Nd2O3 and 1 wt % Pt doped Nd2O3 absorb in UV region and photocatalytic was
carried out under visible region. Also, increase wt % of Pt from 2 to 4 % increase
photocatalytic activity from 53 to 98 %, respectively. Above 4 wt % of Pt has no significant
effect on photocatalytic activity. Therefore, 4 wt % of Pt is an optimum condition for doping at
which photocatalytic reduction of nitrobenzene reach to 98 % after 60 min reaction time. The
reaction kinetics and rate constants for the effect of type of photocatalyst on reduction of
nitrobenzene were studied and calculated as shown in Fig.9. and Table 4. The results show that
the order of reaction is first order with respect to [nitrobenzene].

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3.2.2. Effect of the amount of the photocatalyst
The effect of the loading of 4 wt % Pt doped Nd2O3 photocatalyst on photocatalytic reduction
of nitrobenzene is shown in Fig. 10. The results reveal that the photocatalytic activity increased
from 83 to 100 % after 60 min by increasing the weight of 4 wt % Pt doped Nd2O3
photocatalyst from 0.3 to 0.6 g/l. The reaction time decreased from 60 to 40 min by increasing
the weight of 4 wt % Pt doped Nd2O3 photocatalyst from 0.6 to 0.9 g/l due to the increase in
available active sites for the photocatalytic reaction. Additionally, we noticed that the
photocatalytic activity decreased by increasing weight of 4 wt % Pt doped Nd2O3
photocatalyst above 0.9 g/l because the high weight of the photocatalyst will hinder the
penetration of light during the reaction and decrease the available active sites for the
photocatalytic reaction, decreasing the overall photocatalytic activity. The reaction kinetics and
rate constants for the effect of amount of photocatalyst on reduction of nitrobenzene were
studied and calculated as shown in Fig.11. and Table 5. The results show that the order of
reaction is first order with respect to [nitrobenzene].
3.2.3. Recycling the photocatalyst
Testing the photocatalyst multiple times is an important factor for the commercial use of the
photocatalyst. Fig. 10 shows the activity of 4 wt % Pt doped Nd2O3 photocatalyst that was
recycled five times. The results demonstrate that the photocatalytic activity remained unchanged
after being recycled five times. The results demonstrate that 4 wt % Pt doped Nd2O3
photocatalyst was stable after being recycled five times. Therefore, the 4 wt % Pt doped Nd2O3
photocatalyst can be recycled and separated easily.

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3.3. Mechanisms
Noble metal-semiconductor nanocomposites, such as Pd-TiO2 [14], Ag-TiO2 [15], can be
highly active photocatalysts due to synergy between the basis material and the surface plasmon
resonance effect of noble metals. A similar effect was considered responsible for the
photocatalytic reduction of nitrobenzene on Pt/Nd2O3. Visible-light irradiation excited Pt/Nd2O3
due to the surface plasmon resonance of Pt nanoparticles and electron-hole pairs on the surface
of Pt nanoparticles. Nd2O3 excellent electron mobility could increase Pt/Nd2O3 charge transport
rate, inhibit charge recombination and promote photocatalytic activity. GC results showed that
the main products were nitrosobenzene and aniline. The mechanisms of photocatalytic reduction
of NB over are as follows:
(1) Light generates hole-electron pairs. When photons with energy equal to or larger than the
band gap irradiate Pt/Nd2O3, electrons transfer from the valence band to conduction band,
producing oxidative photogenerated valence holes (h+) and reductive conduction
electrons (e_) (Eq. 1).
(2) Photogenerated holes and electrons without recombination move to photocatalyst’s
surface.
(3) Photogenerated carriers react with adsorbents. CH3OH solvent captures the holes,
producing HCHO oxide and reductive H. (Eqs. 2 and 3). Photogenerated electrons and H.
reduce NB, producing more nitrosobenzene and aniline (Eq. 4).

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Pt/Nd2O3 (e - + h+)
Pt/Nd2O3 Visible light
(1)
(2)
+
. .
CH3OH + h+
CH3O + CH2OH
. .
.
CH3O + CH2OH
2H + 2HCHO
(3)
HO
OH
N
2e-, 2H+
NO2
.
2H
-H2O
OH
NO
NH
2e-, 2H+
.
2H
2e-, 2H+
-H2O
.
2H
NH2
(4)

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4. Conclusion
We have prepared the Pt doped Nd2O3 nanostructures with controlled Pt doping contents
using a template method . The band gap of the Pt doped Nd2O3 could be tuned by controlling Fe
doping contents. We found that increasing of Pt doping content, increasing the shift of
absorption edge to visible region. Also, the separation and transformation of the photo-excited
electrons and holes could be enhanced with appropriate Pt2+ ions doping contents. Therefore, the
4 wt % Pt doped Nd2O3 nanostructures have the highest photocatalytic efficiency under visible
light.
We can synthesize different photocatalysts with enhanced visible-light-driven
photocatalytic performance using a template method.
Acknowledgement
This work was funded by the Deanship of Scientific Research (DSR), King Abdulaziz
University, Jeddah, under grant number (130-521-D1435). The authors, therefore, acknowledge
with thanks DSR technical and financial support.
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Figures Caption
Fig. 1. XRD patterns of the as-prepared samples.
Fig.2. SEM images of the as-prepared samples.
Fig.3. TEM image of 5 N sample.
Fig.4. XPS spectra of 5 N sample in Pt 4f.
Fig.5. nitrogen adsorption–desorption isotherms and corresponding pore diameter distribution
curve( insets) of 5 N sample.
Fig.6. UV-Vis spectra of Nd2O3 and Pt- doped Nd2O3 nanostructures.
Fig.7. Pl spectra of Nd2O3 and Pt- doped Nd2O3 nanostructures.
Fig. 8. Effect of type of photocatalyst on the photocatalytic reduction of nitrobenzene.
Fig.9. Rate constant of reaction kinetic for photocatalytic reduction of nitrobenzene by different
photocatalyst
Fig.10.Effect of amount of 4 wt % Pt doped Nd2O3 photocatalyst on the photocatalytic reduction
of nitrobenzene.
Fig.11. Rate constant of reaction kinetic for effect of catalyst amount on reduction of
nitrobenzene
Fig. 12. Recycling and reuse of 4 wt % Pt doped Nd2O3 photocatalysts for the photocatalytic
reduction of nitrobenzene.

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Table 1: Chromatographic conditions applied for photocatalytic reduction of nitrobenzene.
Item
Reduction of nitrobenzene
50°C for 5 min →200 °C
50→ 200 °C 10 °C/min
Oven
Detector
Injection
Column
Type: FID
Heater: 300 °C
H2 flow: 30 ml/min
Air flow: 400 ml/min
Makeup flow: 25 ml/min
Heater: 250 °C
Pressure:13.762 psi
Total flow: 41.384 ml/min
Septum purge flow: 3 ml/min
Mode: split with ratio (10:1)
(30 m× 0.32 µm×0.25 µm)

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Table 2. Texture parameters of Nd2O3 and Pt- doped Nd2O3 nanostructure.
SBET
St
Smicro
Sext
Vp
r
Sample
(m2/g)
(m2/g)
(cm2/g)
(cm2/g)
(cm3/g)
(Å)
190 .00
192.00
105.00
85.00
95.00
0.200
0.210
40.00
1 N
2 N
205.00
211.00
215.00
206.00
212.00
217.00
110.00
112.00
115.00
35.00
32.00
28.00
98.00
0.225
0.235
3 N
4 N
100.00
220.00
225.00
223.00
226.00
118.00
120.00
0.240
0.244
24.00
22.00
5 N
6 N
102.00
105.00

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Table 3 : Band gap energy of Nd2O3 and Pt- doped Nd2O3 nanostructure.
Sample
Band gap energy, eV
3.42
3.15
2.98
2.87
2.73
2.66
1 N
2 N
3 N
4 N
5 N
6 N

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Table 3: Rate constant of reaction kinetic for photocatalytic reduction of nitrobenzene by
different photocatalyst
Sample
k x 10-5, min-1.
1 N
2 N
3 N
4 N
5 N
6 N
365
448
5237
13208
13498
14613

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Table 4 : Rate constant of reaction kinetic for effect of catalyst amount on reduction of
nitrobenzene
Sample
k x 10-5, min-1.
0.3 g/l
0.6 g/l
0.9 g/l
1.2 g/l
1.5 g/l
13208
13498
20316
18517
1281

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1N
2N
3 N
4 N
5 N
6 N
28
30
32
1N
2N
3N
4N
2-Theta, degree
5N
6N
20
30
40
50
60
70
80
2-Theta, degree
Fig.1.

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1 N
2 N
3 N
4 N
5 N
6 N
Fig.2.

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Fig.3.

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Pt 4 f 7/2
Pt 4 f 5/2
65
70
75
80
85
Binding energy, eV
Fig.4.

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Adsorption
Desorption
2.5
2.0
1.5
1.0
0.5
0.0
0
2
4
6
8
10 12 14 16 18 20 22 24 26 28
Pore Size (nm)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
P/P0
Fig.5.

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6 N
5 N
4 N
3 N
2 N
1 N
200
300
400
500
600
700
800
Wavelength, nm
Fig.6.

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1 N
2 N
3 N
4 N
5 N
6 N
420
440
460
480
500
520
540
560
580
600
620
Wavelength (nm)
Fig.7.

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100
80
60
40
20
0
1 N
2 N
3 N
4 N
5 N
6 N
0
10
20
30
40
50
60
Reaction time, min
Fig.8.

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1 N
2 N
3 N
4 N
5 N
6 N
0
5
10
15
20
25
30
Reaction time, min
Fig.9.

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100
80
60
40
20
0
0.3 g/l
0.6 g/l
0.9 g/l
1.2 g/l
1.5 g/l
0
5
10
15
20
25
30
35
40
45
50
55
60
Reaction time, min
Fig.10.