Abstract: Spinel structure Zn 2 SnO 4 was successfully synthesized by microwave-assisted hydrothermal process. The effects of the microwave power on the formation and physical properties of the Zn 2 SnO 4 particles are discussed. The products were characterized by X-ray diffraction, atomic force microscopy, infrared spectroscopy, and N 2 adsorption. The results indicated that the microwave power had important influence on the formation of the spinel phase. The results also revealed that the physical properties of Zn 2 SnO 4 particles did not change with the increase of the microwave power above 600 W, with 20 min of reaction time. Furthermore, the photocatalytic activity of the Zn 2 SnO 4 particles for the phenol degradation under sunlight was also investigated

Adriano Cancelier

André Gündel

Edson Irineu Muller

Edson Luiz Foletto

Erico Marlon De Moraes Flores

Fagundes Pereira

Letícia Severo

Marcio Antonio Mazutti

Osvaldo Chiavone-Filho

CiteSeerX

J. Chem. Chem. Eng. 8 (2014) 794-799 
 
Effect of Microwave Power on the Zn2SnO4 Synthesis 
and Its Use for Photodegradation of Phenol 
Edson Luiz Foletto1*, Marcio Antonio Mazutti1, Adriano Cancelier1, Erico Marlon de Moraes Flores2, Edson 
Irineu Muller2, Letícia Severo Fagundes Pereira2, Osvaldo Chiavone-Filho3 and André Gündel4 
1. Department of Chemical Engineering, Federal University of Santa Maria, Santa Maria 97105-900, Brazil 
2. Department of Chemistry, Federal University of Santa Maria, Santa Maria 97105-900, Brazil 
3. Department of Chemical Engineering, Federal University of Rio Grande do Norte, Natal 59066-800, Brazil 
4. Department of Physics, Federal University of Pampa, Bagé 96413-170, Brazil 
 
Abstract: Spinel structure Zn2SnO4 was successfully synthesized by microwave-assisted hydrothermal process. The effects of the 
microwave power on the formation and physical properties of the Zn2SnO4 particles are discussed. The products were 
characterized by X-ray diffraction, atomic force microscopy, infrared spectroscopy, and N2 adsorption. The results indicated that 
the microwave power had important influence on the formation of the spinel phase. The results also revealed that the physical 
properties of Zn2SnO4 particles did not change with the increase of the microwave power above 600 W, with 20 min of reaction 
time. Furthermore, the photocatalytic activity of the Zn2SnO4 particles for the phenol degradation under sunlight was also 
investigated. 
 
Key words: Zn2SnO4, zinc stannate, synthesis, microwave, porous material, photocatalysis. 
 
1. Introduction  
Zn2SnO4 ternary oxide is an important 
semiconductor material with a typical inverse spinel 
structure and has attracted much more attention in 
recent years. Zn2SnO4 has potential applications in 
advanced technologies, such as gas sensors [1], 
electrode material for Li-ion batteries [2], synergistic 
flame retardants [3], dye-sensitized solar cells [4], 
photoluminescence material [5], and photovoltaic 
material [6]. In addition, a few available works of the 
application of Zn2SnO4 as photocatalyst are mostly on 
degrading of water-soluble organic pollutants such as 
dyes [7-10]. However, works concerning use of 
Zn2SnO4 for the degradation of phenol molecules are 
scarce. Recently, Zn2SnO4 particles synthesized by 
hydrothermal route have been tested as photocatalyst 
in the degradation of phenol under sunlight [11]. In 
                                                          
*Corresponding author: Edson Luiz Foletto, Dr., research 
fields: materials science, synthesis, oxides and catalysts. E-mail: 
efoletto@gmail.com. 
recent years, various routes have been developed to 
prepare Zn2SnO4 spinel, such as chemical vapor 
deposition [5], thermal evaporation [12], ball-milling [13], 
solid-state [14], coprecipitation followed by 
calcination in air [15], thermal plasma [16], 
hydrothermal reaction [17-19] and microwave [20, 21]. 
Among these methods, the microwave method has 
proved to be a simple and rapid way to prepare highly 
crystalline Zn2SnO4 particles. Nevertheless, works 
approaching the Zn2SnO4 synthesis by microwave 
route are scarce yet in Refs. [20, 21]. Phase-selective 
microwave synthesis and inkjet printing applications 
of Zn2SnO4 quantum dots have been realized [21]. 
Recently, the influence of reaction time on the 
synthesis of particles at a constant irradiation power 
(1,000 W) has been investigated [20]. In this work, 
Zn2SnO4 sample has been obtained in a short time 
(20 min). Thus, the microwave route demonstrates to 
be a rapid and efficient synthesis method. 
In this context, the aim of this work was to verify 
the effect of microwave power on the Zn2SnO4 
D 
DAVID  PUBLISHING 
Effect of Microwave Power on the Zn2SnO4 Synthesis and Its Use for Photodegradation of Phenol 
 
795
synthesis by microwave-assisted hydrothermal 
method. Its physical properties were investigated by 
the characterization techniques XRD (X-ray 
diffraction), FTIR (infrared spectroscopy), N2 
adsorption-desorption isotherms and AFM (atomic 
force microscopy). In addition, the synthesized 
samples were evaluated as catalysts in the phenol 
photodegradation. 
2. Materials and Methods 
2.1 Synthesis and Characterization of the Catalyst 
Tin tetrachloride (SnCl4·5H2O) and zinc acetate 
(ZnAc2·2H2O) were used for the synthesis of Zn2SnO4 
powders. The aqueous solution of zinc acetate (25.7 g 
in 115 mL) was added into aqueous solution of tin 
tetrachloride (17.6 g in 100 mL) slowly. Aqueous 
solution of NaOH (5 M) was added dropwise into the 
mixture under magnetic stirring, resulting in a final 
pH of 7.5. The final mixture was charged into a 
microwave oven (multiwave 3,000 microwave system, 
Anton Paar, Graz, Austria). The microwave-heating 
program was started by applying (1) 400 W with a 
ramp of 5 min, (2) 400 W for 20 min and (3) 0 W for 
20 min (cooling step). The procedure was similar for 
the microwave powers of 600, 800 and 1000 W. The 
formed solids were filtered, washed with distilled 
water and dried at 110 oC for 24 h. 
Zn2SnO4 powders were characterized by XRD 
(equipment Bruker D8 Advance, with Cu Kα 
radiation). The average size of the Zn2SnO4 crystallite 
was determined through the Scherrer equation [22]:  
D = K·λ / (h1/2·cosθ)             (1) 
where, D is the average crystallite size, K is the 
Scherrer constant (0.9), λ is the wavelength of incident 
X-rays (0.15405 nm), h1/2 is the width at half height of 
the most intense diffraction peak and θ corresponds to 
the peak position (in this work, 2θ = 34.43°). N2 
adsorption-desorption isotherm measurements were 
carried out at 77 K using an ASAP 2,020 apparatus, at 
a relative pressure (P/P0) from 0 to 0.99. FTIR spectra 
were recorded on a PerkinElmer FTIR spectrum 
spectrophotometer in the region of 375-4,000 cm-1, 
using KBr pellets. The image of particles was 
obtained by AFM (Agilent Technologies 5,500 
equipment). 
2.2 Photocatalytic Essays 
The photocatalytic essays were carried out in the 
same apparatus presented in a Ref. [23]. The reaction 
system consists of a transparent vessel (Øint. = 10 cm) 
of 200 mL capacity and a magnetic agitator. The 
experiments were carried out under solar irradiation 
between 9:00 a.m. and 15:00 p.m. during the month of 
July 2013 (winter season) at Natal city (05o47'42'' S 
and 35o12'34'' W), located in a northeastern state of 
Brazil. For the photocatalytic tests, 100 mL of 
aqueous solution of phenol at an initial concentration 
of 20 mg·L-1 and 0.15 g of catalyst were prepared. 
This suspension was then irradiated under sunlight 
using continuous stirring. Samples were taken at 
pre-determined times, and filtered before being 
subjected to a TOC (total organic carbon) analyzer 
(Shimadzu 5,000A, Japan). Thus, the photodestruction 
performance of phenol was expressed in terms of TOC 
removal. 
3. Results and Discussion 
Fig. 1 shows the XRD patterns of the prepared 
samples at different microwave powers. As shown in 
Fig. 1, all main diffraction peaks of the samples 
prepared at powers above 600 W are consistent with 
the JCPDS (Joint Committee on Powder Diffraction 
Standards) (74-2184) data of the pure inverse-spinel 
Zn2SnO4. The main characteristic peaks at 2θ  values 
of 29.25o, 34.43o, 35.96o, 41.79o, 45.67o, 51.74o, 
55.14o and 60.49o are corresponding to (220), (311), 
(222), (400), (331), (422), (511) and (440) diffraction 
planes of the Zn2SnO4 spinel, respectively. No 
additional peak of the other phase was observed in the 
XRD patterns for these samples. In addition, at a low 
power (400 W), a less crystalline Zn2SnO4 phase was 
observed. It indicates that a well crystallized Zn2SnO4 
Effect of Microwave Power on the Zn2SnO4 Synthesis and Its Use for Photodegradation of Phenol 
 
796
30 40 50 60 70
(4
40
)
(5
11
)
(3
31
)
(4
22
)
(4
00
)
(2
22
)
(3
11
)
30 40 50 60 70
In
te
ns
ity
2θ
Reference
1000 W
800 W
600 W
In
te
ns
ity
2Θ
400 W
(2
20
)
 
Fig. 1  XRD patterns of synthesized Zn2SnO4 samples at 
different microwave powers (the insert figure shows a 
reference JCPDS 74-2184 card). 
 
single phase could be obtained when a power above 
600 W is applied, at 20 min of reaction time. 
Compared to the conventional hydrothermal method, 
the synthesis time by microwave route is very short. 
Zn2SnO4 has been prepared by conventional 
hydrothermal method at different reaction times such 
as 10 h [11], 20 h [24], 24 h [25] and 48 h [26]. 
Fig. 2 shows the FTIR spectra of spinel prepared at 
different microwave powers. Two main bands can be 
observed in the range 420-580 cm-1 for all spectra of 
the samples prepared above 600 W. The band at 420 cm-1 
corresponds to interaction between metal and oxygen 
in the octahedral site in the crystal lattice, and the 
band around 580 cm-1 corresponds to interaction 
between metal and oxygen in the tetrahedral site [11]. 
Thus, the band observed at 420 cm-1 involves the 
Sn-O bonds in octahedral site, and the band observed 
at 580 cm-1 can be assigned to Zn-O bonds at the 
tetrahedral site. Yet for sample prepared at 400 W, 
there is not the presence of the band at 420 cm-1, 
indicating that this power is inefficient for the 
formation of a single-phase Zn2SnO4 spinel. The 
results obtained in the analysis of FTIR confirm the 
formation of spinel structures for the samples prepared 
at powers above 600 W, and corroborate the results 
obtained in the XRD analysis. 
3500 3000 2500 2000 1500 1000 500
1000 W
800 W
600 W
Tr
an
sm
itt
an
ce
 (%
)
Wavenumber (cm-1)
400 W
 
Fig. 2  FTIR spectra of synthesized samples at different 
microwave powers. 
 
Fig. 3 illustrates the nitrogen adsorption/desorption 
isotherms and pore size distribution curves of the 
Zn2SnO4 samples prepared at 600, 800 and 1,000 W. 
The nitrogen adsorption-desorption isotherms (Fig. 3a) 
and pore size distribution curves (Fig. 3b) presented 
similar behavior for all samples, indicating that the 
microwave power did not influenced the physical 
characteristics of Zn2SnO4 particles produced. The 
isotherms can be classified as type IV in the IUPAC 
(International Union of Pure and Applied Chemistry) 
classification [27], which are characteristic of porous 
materials. Pore parameters of Zn2SnO4 particles as 
well as surface area are shown in Table 1. 
The specific surface area of the samples was about 
60 m2·g-1. The pore size distribution plots showed that 
the Zn2SnO4 particles possessed pores with a mean 
diameter around 70 Å. Table 1 also presents the 
crystallite size estimated from XRD patterns, which 
was found to be about 18 nm for all Zn2SnO4 samples. 
AFM images illustrated in Fig. 4 showed a Zn2SnO4 
particle prepared at 600 W, with average size of 0.8 µm, 
formed by an agglomeration of crystallites with size 
smaller than 50 nm. AFM images indicate that the 
Zn2SnO4 crystallites are reasonably uniform in size. 
The crystallites size obtained by AFM micrograph is 
reasonably consistent with the crystalline size 
estimated from XRD analysis (Table 1). 
 
2θ (o) Wavenumber (cm
-1) 
2θ 
Effec
 
 
Fig. 3  (a) N
Zn2SnO4 sam
 
Table 1  Cry
Power (W) 
600 
800 
1,000 
 
Fig. 4  AFM
 
Before s
Zn2SnO4 po
establishing 
degradation 
solar irradia
phenol mo
simultaneou
powders. 
V
ol
um
e 
(c
m
3 ·g
-1
) 
t of Microwa
R
itrogen adsorp
ples at differe
stallite size, su
Cr
18
17
18
 of (a) Zn2SnO
unlight expo
wders and 
the adsorpt
was negligib
tion only). 
lecules was
s presence 
Fig. 5 
ve Power on
elative pressure
(a)    
tion-desorptio
nt microwave 
rface area an
ystallite size (n
.5 
.8 
.2 
(a)   
4 particle prep
sure, the 
phenol we
ion equilibri
le by direct 
Thus, a deg
 only obse
of sunlight
illustrates 
 the Zn2SnO
 (P/P0)      
            
n isotherms a
powers. 
d pore parame
m) Surfa
61 
60 
61 
           
ared at 600 W
suspension w
re stirred u
um. The ph
photolysis (w
radation of
rved with
 and Zn2S
the ph
4 Synthesis a
            
            
nd (b) the cor
ters of Zn2SnO
ce area (m2·g-1)
      
            
 and (b) their
ith 
ntil 
enol 
ith 
the 
the 
nO4 
enol 
pho
redu
1,00
acti
sam
T
abo
exp
D
v/
dr
 P
or
e 
vo
lu
m
e 
(c
m
3 ·g
-1
 Å
-1
) 
nd Its Use fo
           
            
responding po
4 powders sy
 Total po
0.175 
0.170 
0.186 
            
 crystallites.
todegradatio
ction for th
0 W. As obs
vities for T
ples. 
he results sh
ut 85% of T
osure for all
r Photodegr
   Pore diame
         (b) 
re size distrib
nthesized at di
re volume (cm3
         (b) 
n expressed
e prepared s
erved in Fig
OC remova
owed the hig
OC removed
samples. Th
adation of Ph
ter (Å) 
ution curves 
fferent power
·g-1) Pore si
70.56 
69.87 
69.16 
 in terms
amples at 6
. 5, similar p
l were obta
hest TOC re
 at 360 min
e similar resu
enol 797
 
of synthesized
s. 
ze (Å) 
 
 of TOC
00, 800 and
hotocatalytic
ined for all
duction with
 of sunlight
lts could be
 
 
 
 
 
 
 
 
Effect of Microwave Power on the Zn2SnO4 Synthesis and Its Use for Photodegradation of Phenol 
 
798
0 60 120 180 240 300 360
0.0
0.2
0.4
0.6
0.8
1.0
0 60 120 180 240 300 360
-2.0
-1.5
-1.0
-0.5
0.0
 600 W
 800 W
 1000 W
ln
 (T
O
C
/T
C
O o
)
Time (min)
 600 W
 800 W
 1000 W
TO
C
/T
O
C
o
Time (min)
 
Fig. 5  Decrease of the TOC concentration and kinetics of 
TOC reduction (figure inside) for the synthesized samples 
at 600, 800 and 1,000 W. 
 
attributed to the same physical characteristics 
presented by all samples, as shown in Table 1. The 
correlation coefficients (R2) for all samples were 
superior at 0.99. Various organic pollutants 
degradation reactions follow first-order kinetics [10, 
28, 29]. Here, the reaction kinetic was determined 
according to Eq. (2): 
ln(TOCt / TOC0) = -k·t          (2) 
where, TOC0 is the initial TOC of the phenol solution 
and TOCt is its concentration at reaction time t. 
The straight line (Fig. 5) indicates first-order 
kinetics and the slope of the line corresponds to the 
rate constant of reaction (k), which was found to be 
similar for all photocatalysts, i.e., k = 5.0 × 10-3 min-1 
(600 W), k = 5.1 × 10-3 min-1 (800 W) and k = 5.4 × 10-3 
min-1 (1,000 W). 
The correlation coefficients (R2) for all samples 
were close to 0.99. For comparison purposes, 
photoelectrocatalytic degradation of phenol with 
simulated sunlight by TiO2-film electrodes resulted in 
a rate constant of 6.0 × 10-3 min-1 for the TOC 
reduction [30]. 
4. Conclusions 
Spinel-type Zn2SnO4 was synthesized by the 
hydrothermal process using microwave irradiation as 
energy source. The microwave power plays an 
important role on the formation of well-defined 
structures at short time. When a microwave power 
above 600 W is applied, the resulting product is 
characteristic of single-phase Zn2SnO4. The crystals 
synthesized by microwave-hydrothermal method 
showed similar physical properties when treated at 
power above 600 W, with a high surface area and 
porous structure. In addition, all synthesized Zn2SnO4 
samples showed to be active for photodegradation of 
phenol. 
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Effect of Microwave Power on the Zn 2 SnO 4 Synthesis and Its Use for Photodegradation of Phenol

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Effect of Microwave Power on the Zn 2 SnO 4 Synthesis and Its Use for Photodegradation of Phenol

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