Microwave synthesis of a photocatalytically active SnO-based material

Article abstract of DOI:10.1134/S0020168514040086

Tin(II) oxide nanopowder has been prepared through microwave processing of an ammoniacal Sn₆O₄(OH)₄ suspension, and the effect of synthesis duration on the surface morphology, acid-base properties, and photocatalytic activity of the SnO has been examined. The results demonstrate that the surface morphology plays a key role in determining the photocatalytic activity of powder SnO for methyl orange photo-degradation.

Full text of DOI:10.1134/S0020168514040086

ISSN 0020ꢀ1685, Inorganic Materials, 2014, Vol. 50, No. 4, pp. 387–391. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © S.A. Kuznetsova, A.A. Pichugina, V.V. Kozik, 2014, published in Neorganicheskie Materialy, 2014, Vol. 50, No. 4, pp. 418–422.
Microwave Synthesis of a Photocatalytically
Active SnOꢀBased Material
S. A. Kuznetsova, A. A. Pichugina, and V. V. Kozik
Tomsk State University, pr. Lenina 36, Tomsk, 634050 Russia
eꢀmail: alina.com@mail.ru
Received September 19, 2013
Abstract—Tin(II) oxide nanopowder has been prepared through microwave processing of an ammoniacal
Sn O (OH) suspension, and the effect of synthesis duration on the surface morphology, acid–base properꢀ
6
4
4
ties, and photocatalytic activity of the SnO has been examined. The results demonstrate that the surface morꢀ
phology plays a key role in determining the photocatalytic activity of powder SnO for methyl orange photoꢀ
degradation.
DOI: 10.1134/S0020168514040086
INTRODUCTION
ing in a 539ꢀW oven (2450 MHz) for 3, 5, 7, and
5 min (series 1, 2, 3, and 4, respectively). The samꢀ
ples were then washed with distilled water, centriꢀ
fuged, and dried at 90
1
Microwave processing is a promising method
widely used to prepare oxide materials [1–4]. In conꢀ
trast to conventional heatꢀtreatment processes,
microwave processing considerably reduces the time
°С.
The solid phase in the suspension and the final synꢀ
needed for the dehydration and decomposition of thesis products (oxides) were characterized by Xꢀray
materials and, when conducted in air, may lead to the diffraction (XRD) on a Rigaku Miniflex 600 diffractoꢀ
formation of oxides with unstable oxidation states [5]. meter (Cu
K
radiation,
2
θ
=
10 –90°, scan step of
°
α
A number of studies [4–6] were concerned with the 0.02°, scan rate of 5 deg/min). JCPDS PDF data were
preparation of tin(II) oxide through the decomposiꢀ used to index diffraction peaks, evaluate the crystallite
tion of tin(II) hydroxy compounds by microwave proꢀ size, and determine the quantitative phase composiꢀ
cessing in air. The lack of SnO oxidation to SnO2 was tion of the samples. The specific surface area of the
attributed by DienꢀShe Wu et al. [6] to the different synthesized tin(II) oxide powders was determined by
microwave absorption intensities in the oxides (SnO BET analysis of lowꢀtemperature nitrogen sorption
has stronger microwave absorption). Available experiꢀ isotherms obtained using a TriStar II automatic gas
mental data on SnO preparation are insufficient for adsorption analyzer (relative uncertainty Δ ± 10%).
assessing the effect of microwave radiation on the surꢀ Surface morphologies were examined by scanning
face morphology and properties of SnO.
electron microscopy on a Hitachi TMꢀ3000 operated
at an accelerating voltage of 15 kV with surface charge
Among the many properties of semiconducting
oxides, particular attention has recently been paid to
their photocatalytic activity, which contributes to the
decomposition of organic contaminants in waste water
2
elimination (electron gun:
5
×
10 Pa; sample chamꢀ
ber: 30–50 Pa), using a QUANTAX 70 energy disperꢀ
sive spectrometer system. The uncertainty in quantitaꢀ
tive elemental analysis was 5%. The acid–base propꢀ
±
[
7, 8], where methyl orange photodegradation in
erties of the synthesized oxides were studied using a
Multitest pH meter by a procedure described elseꢀ
where [9].
aqueous oxide suspensions is used mainly as a model
system.
In connection with this, the purpose of this work
was to study the effect of microwave synthesis time on
The photocatalytic activity of the SnO powders was
the surface morphology and photocatalytic activity of assessed for methyl orange azo dye photodegradation.
SnO.
The SnO powders were mixed with an aqueous soluꢀ
tion of the dye. To reach sorption–desorption equilibꢀ
rium, the mixture was stirred in the dark, then placed
under an I2 excimer ultraviolet lamp (I2_BD_P
EXPERIMENTAL
The starting suspension (precursor) was prepared Model) with
λ
max
= 342 nm, and exposed to ultraviolet
by dissolving metallic tin in concentrated hydrochloric (UV) radiation for 60 min with constant stirring. The
2+
acid, followed by Sn precipitation with 25% aqueous absorbance of the samples was measured at 10ꢀmin
ammonia at pH 10–12. Next, four series of samples of intervals (0, 10, 20, 30, 40, 50, and 60 min). After the
the suspension were subjected to microwave processꢀ beginning of an experiment, we took aliquots, which
387

388
KUZNETSOVA et al.
Sn O (OH) powder (PDF no. 01ꢀ084ꢀ2157) with a
1
01
01
6
4
4
1
500
000
(
e)
tetragonal structure and lattice parameters
7.962151 nm and = 9.142758 nm. Microwave proꢀ
cessing of the solution for 3 min in a 539ꢀW oven led to
the onset of Sn O (OH) decomposition and the forꢀ
a = b =
1
c
0
02
5
00
0
01
6
4
4
mation of a mixture of 17 wt % tetragonal SnO (PDF
no. 01ꢀ072ꢀ101, = 0.3809703 nm,
.4849768 nm) and 83 wt % Sn O (OH) (
0
a
=
b
c =
a =
3
2
1
000
000
000
1
(
d)
c)
0
6
4
4
0
02
b = 8.005666 nm, c = 9.152423 nm) (Fig. 1b).
Increasing the microwave processing time of the
001
001
ammoniacal Sn O (OH) solution led to the formaꢀ
6
4
4
0
000
tion of a singleꢀphase product, which was identified by
XRD (Fig. 1c) as SnO, with a crystallite size of 46 nm
in the (101) plane and 40 nm along (002). It can be
seen from Figs. 1d and 1e that increasing the microꢀ
wave processing time of the starting suspension had no
effect on the composition of the final product but
increased the crystallite size to 49 nm in both growth
directions of SnO. Moreover, it can be seen from the
XRD patterns in Fig. 1 that the intensity of the peaks
corresponding to the growth of the SnO crystal along
3
2
1
1
01
(
000
000
0
002
3
2
1
00
00
00
(
b)
а)
the z axis (in an hkl plane (001, 002)) decreases with an
0
4
3
2
1
00
increase in the microwave processing time of the susꢀ
pension. Therefore, after nucleation accompanying
the Sn O (OH) decomposition, the SnO crystallites
(
00
00
00
0
6
4
4
Precursor
60 80
grew predominantly in the direction of the hkl plane
001, 002), whereas increasing the processing time led
(
to the growth of the crystallites in the direction of the
hkl plane (101). In this process, the anisotropy coeffiꢀ
cient, calculated as the ratio of the crystallite size in
the (002) plane to that along (101), varied from
20
40
2θ, deg
Fig. 1. XRD patterns of (a) the precursor and samples
b) , (c) , (d) , and (e)
0.86 to 1.
(
1
2
3
4.
As seen in Fig. 2, the microwave processing time of
the precursor had little effect on the surface morpholꢀ
were centrifuged to separate the precipitate. From the ogy of the SnO samples. Qualitative and quantitative
variation in absorbance, we assessed the extent of surface morphology analysis data are supported by
methyl orange decomposition. The methyl orange XRD results. Microwave processing for 3 min led to
concentration was determined spectrophotometriꢀ partial formation of tin(II) oxide agglomerates
cally on a PEꢀ5400UF spectrophotometer using the (Fig. 2a), which had the form of tetragonal plates. Sinꢀ
QA5400 quantitative analysis program and was evaluꢀ gleꢀphase SnO was formed after microwave processing
ated from the height of the absorption peak at
61 nm.
The composition of the methyl orange decomposiꢀ
tion products after UV exposure was determined using
a Surveyor highꢀperformance liquid chromatography (series
λ
=
4
(
HPLC) system equipped with an autosampler and an layered structure, ranging in size from 100 to 200 nm.
LCQ Advantage MAX mass spectrometric detector. Their specific surface area and average pore size were
2
Components were separated in a HyperSil Gold colꢀ 3.0 m /g and 18 nm, respectively.
umn packed with a reversed phase sorbent (C18)
grafted on silica gel with a particle size of 5 m. The
eluents used were aqueous formic acid (0.1 wt %) and
acetonitrile (100 wt %). The eluent flow rate was
Even though the samples were identical in specific
surface area and crystallite geometry, they differed in
µ
acid–base properties. The pH of the aqueous susꢀ
eq
pension was 3.86 for samples
4, 5.80 for samples 3, and
0.5 mL/min.
6
.1 for samples . These results indicate that all of the
2
SnO samples were solid Lewis acids but differed in the
surface density of Lewis acid centers [9]. This can be
accounted for in terms of different surface defect denꢀ
RESULTS AND DISCUSSION
According to XRD data (Fig. 1a), the precursor sities [9], for example, because of the formation of difꢀ
had the form of an ammoniacal solution based on ferent types of pores in the tin(II) oxide, as evidenced
INORGANIC MATERIALS Vol. 50
No. 4 2014

MICROWAVE SYNTHESIS OF A PHOTOCATALYTICALLY
389
SnO
Sn O (OH)
4
6
4
50
μ
m
50 μm
(
а)
(b)
50
μ
m
50 μm
(c)
(d)
Fig. 2. Micrographs of samples (a)
1, (b)
2, (c)
3
, and (d) 4.
by the shape of the nitrogen adsorption–desorption
isotherms of our samples (Fig. 3). According to data in
the literature [10, 11], the shape of the sorption–desꢀ
(b)
0.6
orption hysteresis loop for samples
4 (Fig. 3b) correꢀ
sponds to a mesoporous adsorbent nonuniform in
pore size and shape. The shape of the hysteresis loop
0.4
for samples
2 suggests the presence of slit pores in the
SnO powder.
The present results on the photocatalytic activity of
SnO for methyl orange decomposition demonstrate
that, among the samples studied, the highest photoꢀ
0.2
0
catalytic activity was exhibited by samples 4. In particꢀ
ular, after holding these samples in an azo dye soluꢀ
tion, the tin(II) oxide surface sorbed up to 50 wt % of
the methyl orange. According to spectrophotometry
data, subsequent UV exposure led to methyl orange
decomposition. After 60 min of exposure in the presꢀ
(a)
0.6
0.4
0.2
ence of samples
decomposition was as high as 95%. In the presence of
samples and , the degree of azo dye decomposition
4, the degree of methyl orange
2
3
in 60 min was 45 and 73%, respectively (Fig. 4). A
comparative analysis of HPLC/MS spectra of the
methyl orange before photocatalysis (Fig. 5) and mass
Fig. 3. Adsorption–desorption isotherms of samples (a)
and (b)
2
0
0.2
0.4
0.6
0.8
1.0
0
4
.
p/p
INORGANIC MATERIALS Vol. 50 No. 4 2014

390
KUZNETSOVA et al.
α
.60
.55
.50
.45
.40
.35
.30
.25
.20
.15
.10
.05
0
0
0
0
0
0
0
0
0
0
0
0
2
3
4
0
10
20
30
40
50
60
Time, min
Fig. 4. Degree of conversion as a function of time for the photocatalytic decomposition of methyl orange in the presence of samꢀ
ples 2–4
.
spectra of the positively charged species formed after pension influences its acid–base properties and phoꢀ
tocatalytic activity.
the photocatalysis (Fig. 6) showed that, after 50 min,
the major methyl orange decomposition products were
positively charged species with molecular weights from
CONCLUSIONS
224 to 154. The structures of some of them are preꢀ
sented in Fig. 6.
The present results demonstrate that the duration
of the microwave synthesis of SnO determines its surꢀ
face morphology through an increase in anisotropy
Our findings indicate that, all other factors being
the same, the duration of the microwave synthesis of coefficient. At a given specific surface area and pore
tin(II) oxide from an ammoniacal Sn O (OH) susꢀ size, the main factor influencing the photocatalytic
6
4
4
1
5.27
1
1
800000
600000
4
00000
00000
0
2
800000
600000
400000
200000
0
.49 1.22 1.86 1.93
3.97 4.36 5.25 6.15 6.82
8.26 8.69
9.89 10.65 11.44
12.74 13.50 13.82
16.05
16.28 17.23 18.27
1
9.18 19.97 21.30
0
1
2
3
4
5
6
7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
Time, min
3
04.03
H C
3
1
000000
–
N
N
N
SO3
800000
600000
400000
200000
H C
3
349.32
3
05.03
3
06.08
350.41
371.63 392.29
1
72.86 183.79
248.78
287.79
347.12
429.76 441.61 468.83 478.28 490.73
4
08.44
0
160 180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 500
m/z
Fig. 5. HPLC/MS data for methyl orange.
INORGANIC MATERIALS Vol. 50
No. 4 2014

MICROWAVE SYNTHESIS OF A PHOTOCATALYTICALLY
391
212.50
3
3
2
2
1
1
50000
00000
50000
00000 151.49
50000
00000
⊕
HO
N
N
NH2
H
2
07.39
184.49
2
53.36
1
61.51
1
2
25.64
189.56
2
52.09
79.63
2
57.62
5
0000
286.43 320.55 341.20
2
77.37
360.76
3
62.86 403.40 421.86 443.05 471.84 482.48
4
98.22
0
1
60 180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 500
m/z
182.75
⊕
1
1
200000
000000
N
N
H
8
6
4
2
00000
00000 154.83
00000
291.58
1
84.74
2
10.70
2
90.66
00000 158.77
288.74
284.76
318.84
372.61
344.59
368.14 381.15
2
09.70 212.67
2
32.57
245.68
402.47
481.58
294.44
421.62
430.38
454.49
2
78.62
0
160 180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 500
m/z
2
24.66
H C
⊕
3
2
1
1
000000
500000
000000
N
N
N
H C
3
H
186.64
5
00000 1
225.75
226.76 252.96 282.16 282.57308.97 338.23 347.35
52.00
156.88
95.68
197.71
1
375.41 392.38 408.34 427.80
453.25
0
160 180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 500
m/z
Fig. 6. Mass spectra of positively charged species after UVꢀinduced methyl orange decomposition.
activity of SnO is the pore shape. It is worth noting that
the acid properties of the surface of powder SnO are
related to its photocatalytic activity for methyl orange
azo dye photodegradation.
5. Krishnakumar, T., Pinna, N., Prasanna Kumari, K.,
et al., Microwaveꢀassisted synthesis and characterizaꢀ
tion of tin oxide nanoparticles, Mater. Lett., 2008,
vol. 62, p. 3437.
6
. DienꢀShe Wu, ChinꢀYu Han, ShiꢀYu Wang, et al.,
Microwaveꢀassisted solution synthesis of SnO nanocꢀ
rystallites, Mater. Lett., 2002, vol. 53, p. 155.
REFERENCES
1
. Karimov, O.Kh., Daminev, R.R., Kas’yanova, L.Z.,
et al., Application of microwave radiation in the fabriꢀ
cation of metal oxide catalysts, Fundam. Issled., 2013,
no. 4, p. 801.
7. Shaporev, A.S., Ivanov, V.K., Lebedev, V.A., et al., Phoꢀ
tocatalytic activity of nanodispersed zinc oxide syntheꢀ
sized by hydrothermal microwave route, Dokl. Chem.
2010, vol. 434, no. 1, p. 223.
,
2
. Balakhonov, S.V., Ivanov, V.K., Baranchikov, A.E.,
et al., A comparative analysis of the physicochemical
properties of vanadiumꢀoxideꢀbased nanomaterials
prepared by hydrothermal and microwaveꢀassisted
8. Yuanhua He, Franz Grieser, and Muthupandian
Ashokkumar, The mechanism of sonophotocatalytic
degradation of methyl orange and its products in aqueꢀ
ous solution, Ultrason. Sonochem., 2011, vol. 18, p. 974.
hydrothermal processes, Nanosist.: Fiz., Khim., Mat.
012, vol. 3, no. 4, p. 66.
,
9
. Minakova, T.S., Adsorbtsionnye protsessy na poverkhꢀ
nosti tverdykh tel (Adsorption Processes on the Surface
of Solids), Tomsk: Tomsk. Univ., 2007.
2
3
. Vanetsev, A.S., Ketsko, V.A., and Tret’yakov, Yu.D.,
Microwaveꢀinduced microstructural evolution of indiꢀ
vidual metal oxides, Kondens. Sredy Mezhfaznye Granꢀ
itsy, 2009, vol. 11, no. 4, p. 280.
10. Gregg, S.J. and Sing, K.S.W., Adsorption, Surface Area,
and Porosity, New York: Academic, 1982.
1
1. Krylov, O.V., Geterogennyi kataliz (Heterogeneous
4
. Pires, F.I., Joanni, E., Savu, R., et al., Microwaveꢀ
assisted hydrothermal synthesis of nanocrystalline SnO
powders, Mater. Lett., 2008, vol. 62, p. 239.
Catalysis), Moscow: Akademkniga, 2004, pp. 40–45.
Translated by O. Tsarev
INORGANIC MATERIALS Vol. 50 No. 4 2014