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One-step hydrothermal synthesis of tin dioxide nanoparticlesand its photocatalytic degradation of methylene blue

Morteza Vatanparast1 Mohammad Taghi Taghizadeh1

Received: 28 July 2015 / Accepted: 28 August 2015/ Published online: 3 September 2015

Springer Science+Business Media New York 2015

Abstract A simple hydrothermal method was developed

for the size-controlled synthesis of tin dioxide (SnO2)nanoparticles, using SnCl45H2O, ethylenediamine and

hydrazine. The molar ratio of the reactants, temperature,

reaction time and the surfactant were changed in order to

investigate the effect of preparation parameters on the mor-

phology and particle size of SnO2. According to scanning

electron microscopy (SEM) results, ethylenediamine and

hydrazine can control the particle growth and play an

important role in formation of SnO2 nanostructures. The

prepared SnO2nanoparticles were characterized extensively

by means of X-ray diffraction, energy-dispersive X-ray

spectroscopy, SEM, transmission electron microscopy,

Fourier transform infrared spectroscopy and diffuse reflec-

tance spectroscopy. Besides, the photocatalytic properties of

as-synthesized SnO2 nanoparticles have been evaluated for

the degradation of methylene blue under UV light irradiation.

1 Introduction

Semiconductor metal oxides have been widely investigated

because of their potential applications as battery materials,

photocatalysts, sensors, and optoelectronic devices [16].As

an important n-type semiconductor metal oxide, tin dioxide

(SnO2) with the wide direct energy band gap (Eg = 3.6 eVat

300 K) has attracted vast interests due to its potential

applications in many fields, such as photocatalysts [7], solar

cells [8], gas sensor [9,10], optoelectronic devices [11,12]

and electrode materials [13]. In general, in most of the

applications, the performance significantly depends onmorphology of the structures [14]. In recent years, various

morphologies of SnO2 nanostructures have been synthe-

sized, such as nanoparticles [15,16], nanorods [17], nano-

wires [18], nanotubes [19], nanocube [20], nanobelts [21],

nanoribbons [22] and hollow spheres [23].

Various approaches have been developed to prepare SnO2nanomaterials, such as microemulsion [24], template-based

[25], solgel [26], controlled precipitation [27], microwave

[28], sonochemical [29], solvothermal [30, 31], and

hydrothermal [32, 33] methods. Among these synthesis

methods, the hydrothermal method is a simple and inex-

pensive technique for large scale production [34]. It is not

only a low temperature preparation method, but also has the

ability of controlling the size and shape of the final product

[35, 36]. In the present work, we report the hydrothermal

synthesis of SnO2 nanoparticles using SnCl45H2O,

ethylenediamine, and hydrazine as precursors. The factors

affecting the morphologies and particle sizes of SnO2crys-

tals, including the molar ratio of the reactants, the

hydrothermal reaction temperature and time, have been

systematically investigated. Furthermore, the photocatalytic

performance of the synthesized SnO2 nanoparticles was

evaluated by monitoring the photodegradation of methylene

blue (MB) under UV light irradiation.

2 Experimental

2.1 Preparation method

All the chemicals reagents (purchased from Aldrich) used

in our experiments were of analytical grade and were used

as received without further purification.

& Morteza Vatanparast

MVatanparast@yahoo.com

1 Department of Physical Chemistry, Faculty of Chemistry,

University of Tabriz, Tabriz, Iran

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J Mater Sci: Mater Electron (2016) 27:5463

DOI 10.1007/s10854-015-3716-6

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In a typical experiment, 0.5 g of SnCl45H2O was dis-solved in 40 ml of distilled water. Then, 0.8 ml of

ethylenediamine and 0.4 ml hydrazine hydrate were added

drop wise to the solution under stirring and ultimately the

clear solution was transferred into the Teflon lined auto-

clave. The autoclave was sealed and maintained at 160 C

for 5 h (sample 1), then cooled naturally to room temper-

ature. The obtained white precipitate was centrifuged andwashed with distilled water and ethanol several times and

was dried at 70 C for 3 h. Finally, it was calcined at

400 C for 2 h. Some parameters including the molar ratio

of the reactants, reaction temperature and time were

changed for reaching the optimized condition. Reaction

conditions are listed in Table 1.

2.2 Characterization

The X-ray diffraction (XRD) study was done by Italstracture

X-ray diffractometer model MPD 3000 with a radiation

source from Cu Ka at scan range of 10\ 2h\80. Energydispersive X-ray (EDX) spectrum and scanning electron

micrographs (SEM) were obtained using a field-emission

scanning electron microscopy (MIRA3 FEG-SEM, Tescan

Brno, Czech Republic). Transmission electron microscope

(TEM) images were obtained on a Philips EM208 trans-

mission electron microscope with an accelerating voltage of

100 kV. Fourier transform infrared (FT-IR) spectra were

recorded on Tensor 27 (Bruker) spectrophotometer in KBr

pellets. TheUVVis diffused reflectance spectra(DRS)were

obtained from UVVis Scinco 4100 spectrometer. UVVis

absorption spectra were recorded on a Perkin-Elmer Lambda

2S UVVis spectrophotometer.

2.3 Photocatalytic experiment

The photocatalytic activities of the samples were deter-

mined by the degradation of aqueous MB under UV light.

In a typical photocatalytic test performed at room tem-

perature, 20 mg of photocatalyst nanoparticles was added

into 150 ml MB aqueous solution (5 mg/l), and then dis-

persed by stirring in a dark condition for 30 min to

establish adsorption/desorption equilibrium. Later, a series

of UV lamps (4 9 15 W, Philips) was switched on a 20 cm

distance over the suspension surface. Then, the changes of

MB concentration were monitored on the basis of its UVvisible absorption peak at 664 nm.

3 Results and discussion

Figure1 shows the XRD patterns of the sample 1 before

and after the calcination process. The XRD pattern of

sample 1 before calcination appears to be amorphous-like

with sharp peak at 31.74, 34.36, 36.22, 47.50, 56.58. It

should be mentioned that we were not able to find any

standard XRD data that match this XRD pattern. However,

the diffraction pattern of sample 1 after calcination can beindexed to a pure tetragonal phase of SnO2 with space

group P42/mnm (JCDPS No. 41-1445) including the lattice

constants of a, b = 4.7382 and c = 3.1871. The crystallite

size of the as-synthesized SnO2, D, was calculated from the

major diffraction peaks using Scherrer equation [37]:

D Kk

b cos h 1

where K is the so-called shape factor, which usually takes a

value of about 0.9,k is the X-ray wavelength used in XRD,

h is the Bragg angle; b is the breadth of the observed

diffraction line at its half-intensity maximum. The esti-mated particle size of SnO2 by the Scherrer equation is

about 10 nm. The purity of the nanostructures was inves-

tigated by means of EDX analysis. EDX analysis of SnO2nanoparticles (sample 1) is shown in Fig. 2. Peaks asso-

ciated with Sn and O are obviously observed. Au peaks are

Table 1 Reaction conditions

for SnO2 nanoparticles Sample no. Hydrazine (ml) Ethylenediamine (ml) Temperature (C) Time (h) Surfactant

1 0.4 0.8 160 5

2 0.4 0.05 160 5

3 0.4 0.2 160 5

4 0.4 1.6 160 5

5 0 0 160 5

6 NH3 160 5

7 NaOH 160 5

8 0.4 0.8 120 5

9 0.4 0.8 200 5

10 0.4 0.8 160 10

11 0.4 0.8 160 15

12 0.4 0.8 160 5 PEG

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detected because the samples were gold coated for con-

duction. Moreover, no impurity peaks are observed, which

indicates a high level of purity in the product.

Figure3a, b show SEM images of obtained products

before and after calcination of sample 1, respectively, in

the presence of 0.8 ml hydrazine and 0.4 ml ethylenedi-

amine. As can be seen, in both of them, spherical

nanoparticles were obtained and after calcination, the

particle size of them was increased (Fig. 3b). For investi-

gation of ethylenediamine effect, several experiments with

different concentration of ethylenediamine including 0.05,

0.2 and 1.6 ml (sample 24, respectively) were performed.

As shown in Fig. 4a, b, by decreasing the ethylenediamine

concentration, products with finer and more homogenous

particle size were obtained. By increasing the concentra-

tion to 1.6 ml (sample 4), increasing and nonuniformity of

particle size is obvious (Fig. 4c). Therefore, for obtaining

finer and more uniform structure, an optimum amount ofethylenediamine is required. In the presence of ethylene-

diamine and hydrazine, releasing of ions is controllable and

so nucleation and growing mechanism in different con-

centration can be controlled and by adjusting conditions,

appropriate nanostructures can be achievable. Ethylenedi-

amine is able to form a complex with metal ions. Thus,

releasing of metal ions is strongly influenced by

ethylenediamine concentration. On the other hand, the high

amount of ethylenediamine concentration cant be useful

because presence of high concentration of ethylenediamine

leads to aggregation of nanoparticles due to carbon burning

while annealing. Also, hydrazine hydrate compared toNaOH and NH3, can release hydroxide ion slower and

more controllable. According to the above description,

mechanism of SnO2 nanoparticles formation can be as

follow:

Coordination: Sn4 nen $ Sn en n 4

2

Hydrolyzation: NH2CH2CH2NH2 2H2O! NH3 CH2CH2NH

3 2OH

3

N2H4 H2O ! N2H5 OH

4

Precipitation: Sn en n 4

4OH annealing

400 C 2 h SnO2

2H2O nenen ethylenediamine5

For direct studying the ethylenediamine and hydrazine

effect and comparison with NaOH and NH3, three experi-

ments were done (Fig.5) in absence of hydrazine and

ethylenediamine (sample 5), in presence of NH3and NaOH

(sample 6 and 7, respectively). As can be seen, in absence

of hydrazine and ethylenediamine, larger particles were

obtained in comparison with sample 1 prepared in the

presence of 0.4 ml ethylenediamine and 0.8 ml hydrazine

and in many parts, aggregation and agglomeration can be

seen (Fig. 5a). In other words, with simple hydrolyze thatthe concentration of hydroxide ion is very low, fine and

uniform nanoparticles of SnO2 cant be obtained. In low

concentration, nucleation rate is low and as a result, large

particles will be achieved. In the presence of NH3 and

NaOH which the concentration of hydroxide ion is high,

larger particle with less uniformity can be synthesized. At

high concentration, the nucleation rate is high and too fine

particles were obtained. Being the particle so fine leads to

instability of particles and as a result, the particles can be

Fig. 1 XRD patterns of sample 1 before (a) and after (b) calcination

Fig. 2 EDX pattern of SnO2 nanoparticles (sample 1)

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aggregated together (Fig. 5b, c, respectively). Figure6a, b

shows SEM images of samples 8 and 9 formed at 120 and

200 C, respectively. As shown, by decreasing the tem-

perature from 160 to 120 C and by increasing temperature

from 160 to 200 C, the particle size got larger and smaller,

respectively. Indeed, by increasing temperature, the parti-

cles became finer and the finest and the most uniform

particles with size of 1015 nm were obtained at 200 C.

An increase of the reaction temperature always results in an

increase of the rate of reaction; therefore at relatively high

temperatures more SnO2nuclei will form before the growthprocess, which causes the formation of more particles with

smaller diameters. For more investigation, TEM analysis

was used to observe the morphology and size of the SnO2nanoparticles. Figure7 shows the TEM images of sample 9

in different scale scopes. The sizes of nanoparticles

obtained from the TEM images are in close agreement with

the XRD diffraction patterns, which show sizes of

1015 nm. For evaluating of time effect, in addition to 5 h

(sample 1), two experiments were performed for 10 and

15 h (samples 10 and 11, respectively). By increasing the

time till 10 h, finer and more uniform structures can be

synthesized (Fig.8a) compared to products obtained for

5 h (sample 1). But, by increasing the time to 15 h (sample

11), the particles got larger and the uniformity was

decreased (Fig.8b). In other words, for achieving fine and

uniform nanoparticles in hydrothermal method, the opti-

mum amount of time is required and this optimum time in

our study for formation of SnO2 is 10 h. For investigating

of surfactant effect, an experiment was done in the pres-

ence of PEG (sample 12) and related SEM image ofobtained product is shown in Fig. 9. As can be seen, in the

presence of surfactant, finer and more uniform particles

were prepared in comparison with products prepared in the

absence of surfactant (sample 1). However, as noted ear-

lier, by adjusting conditions, so fine and uniform

nanoparticles can be obtained (see Fig. 6b). In other words,

by adjusting ethylenediamine concentration, time and

temperature, the surfactant can be eliminated from the

reaction.

Fig. 3 SEM images of sample 1 before (a) and after (b) calcination

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Figure10 represents FT-IR spectra of the sample 1

before and after the calcination. The broad bands around

3440 and 1650 cm-1 in Fig.10a correspond to stretching

and bending vibrations of absorbed water molecules

respectively [38], which can identify the presence of

physisorbed water molecules linked to the SnO2 nanopar-

ticles. The peaks at 2930 cm-1 are attributed to the CH2

asymmetric vibrations [39]. The peak at 1550 cm-1 is

associated with the bending mode of NH [40]. After

calcination, these bands disappear because of the pyrolysis

Fig. 4 SEM images of SnO2 nanoparticles a sample 2, b sample 3, c sample 4

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of the organic precursor. The peaks in the region

8501350 cm-1 are assigned to hydroxyl bending mode of

different types of surface hydroxyl groups [29]. The peaks

at 665 and 550 cm-1 are assigned to the SnOSn

antisymmetric vibrations [29], where after calcination

broad band appear in this region. From the FT-IR results, it

is concluded that further heat treatment is necessary to

remove the residual water and organic precursor.

The UVVis diffuse reflectance spectroscopy (DRS) of

SnO2 nanoparticles (sample 1) are shown in Fig.11. The

Fig. 5 SEM images of SnO2 nanoparticles a sample 5, b sample 6, c sample 7

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fundamental absorption edge in most semiconductors fol-

lows the exponential law. Using the absorption data, the

direct band gap (Eg) for SnO2 nanoparticles can be esti-

mated by Taucs relationship (6):

ahm Bhm Eg1=2 6

where hm, B and a are incident photon energy, a constant

related to the material and the absorption coefficient,

Fig. 6 SEM images of SnO2 nanoparticles a sample 8, b sample 9

Fig. 7 TEM images of sample 9 in different scale

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Fig. 8 SEM images of SnO2 nanoparticles a sample 10, b sample 11

Fig. 9 SEM images of SnO2 nanoparticles (sample 12)

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respectively [41]. The Eg value is calculated as 3.8 eV

(326 nm) for the SnO2nanoparticles (the sample 1), which

shows a blue shift compared with SnO2 bulk (3.6 eV).

To demonstrate the potential applicability of as-syn-

thesized SnO2 nanoparticles, we investigated the photo-

catalytic decomposition of MB as the test reaction.

Moreover, the photocatalytic decomposition was per-

formed under UV-light illumination, and the degradation

rate for the decomposition of MB was estimated by

observing the changes in absorbance (absorption intensity

vs. irradiation time) obtained by UVVis spectra. Fig-

ure12a shows the absorption spectrum of an aqueous

solution of MB in the presence of the sample 1. As can be

seen, the intensity of the characteristic absorption peak

decreased monotonously with the increase in the exposure

time. Figure12b indicated that in the absence of SnO2

nanoparticles, nearly no change in the absorption spectrais observable, while in the presence of SnO2 nanoparti-

cles, more than 90 % of MB was decolorized after

120 min.

4 Conclusions

In summary, SnO2 nanoparticles were successfully syn-

thesized by hydrothermal method using SnCl45H2O,

ethylenediamine and hydrazine. Besides, the effects of

molar ratio of the reactants, temperature, reaction time and

surfactant on the morphology and particle size of thenanoparticles were investigated. The results show that the

ethylenediamine concentration plays a key role in con-

trolling the particle size of the final products. Hydrazine

hydrate compared to NaOH and NH3, can release

hydroxide ion slower and more controllable, which leads to

formation of finer and more homogenous nanoparticles.

SnO2 nanoparticles were characterized by XRD, EDX,

SEM, TEM, FT-IR and DRS techniques. Moreover, the as-

synthesized SnO2 nanoparticles showed the excellent

Fig. 10 FT-IR spectrums of sample 1 before (a) and after

(b) calcination

Fig. 11 The UVVis diffusereflectance spectroscopy (DRS)

of SnO2 nanoparticles (sample

1). The insetshows the plots of

(ahm)2 versus the energy of light

(hm)

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photocatalytic ability for the degradation of MB as a model

of pollutant.

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Fig. 12 The photocatalytic performance of SnO2 nanoparticles (sample 1). a Absorption spectra of MB solution photocatalyzed by SnO2nanoparticles.b MB concentration dependence on irradiation time

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