Synthesis and Characterization of Tin Oxide Nanoparticles by Solid State Chemical Reaction Method

ORI GIN AL PA PER

Synthesis and Characterization of Tin OxideNanoparticles by Solid State Chemical ReactionMethod

Parvin Sarabadani • Mahdi Sadeghi •

Mohamadreza Ghasemi • Zargham Asadollahi •

Narges Afshari

Received: 23 January 2011 / Published online: 18 February 2011

� Springer Science+Business Media, LLC 2011

Abstract High purity tin oxide nanopowders have been synthesized by using a

solid-state chemical reaction technique with annealing at elevated temperature. The

effects of two parameters, specifically by controlling the annealing temperature and

kind of alkaline chlorides as precursors, the effect on particle size, morphology and

IR spectra of synthesized tin oxide nanopowder were investigated. From the X-ray

pattern, the crystal structure of the synthesized powders was confirmed as a tetragonal

structure. Based on the recorded FTIR spectrum of SnO2, the IR bands due to SnO2

vibrations and its lattice modes were observed at 625 and 690 cm-1, respectively. In

addition, an important characterization peak has been identified at 1,450 cm-1 due to

Sn–O–Sn bridges observed only when LiCl was used as precursor. The formation of

Sn–O–Sn bridges was confirmed by TGA–DTA analysis. According to the SEM

images, it is obvious to notice that the kind of alkaline chlorides as precursors play a

dominant role in controlling the morphology of tin oxide nanopowders.

Keywords Tin oxide � Nano-particles � Solid state � Synthesis

Introduction

Nano-structured materials have attracted increasing interest because of their novel

characteristic properties and potential technological applications [1]. Among such

materials, tin oxide nanoparticles has recently received a great scientific interest

because of their wide range of applications as gas-sensing materials, antistatic films,

thin film resisters and anti reflecting coatings in solar cells [2]. These nanoparticles

are synthesized by several methods such as sol–gel [3], spray pyrolysis [4],

P. Sarabadani � M. Sadeghi (&) � M. Ghasemi � Z. Asadollahi � N. Afshari

Agricultural, Medical and Industrial Research School, Nuclear Science and Technology Research

Institute, Karaj, Iran

e-mail: [email protected]

123

J Clust Sci (2011) 22:131–140

DOI 10.1007/s10876-011-0350-1

sputtering [5] and template method [6]. However, the disadvantages of the reported

methods include the need to use expensive organic precursors as starting materials,

or particle aggregations during high temperature oxidation in the air.

Generally, these methods are complicated and expensive, but mechanochemical

processing is a novel candidate to synthesize nano-structured materials [7]. During the

solid state chemical reaction method which a chemical reaction takes place when solid

precursors are ground together [8]. There are three main advantages in the solid-state

reaction approach. They are (a) simple, cheaper and convenient, (b) involve less

solvent and reduce contamination and (c) give high yields of products.

In this paper, we report the preparation of tin oxide nanoparticles by solid-state

chemical reactions at ambient temperature utilizing different alkaline chlorides as

precursors. Our studies show that this is not only a simple processes but also gives

uniform products similar to other profitable methods. We have also investigated the

effect of varying the annealing temperature and type of alkaline chloride precursors.

Experimental

Materials and Equipments

Tin tetrachloride pentahydrate (SnCl4�5H2O) and other regents were all of analytical

grade and used without purification.

The crystal structures were identified by a powder X-ray diffractometer (XRD,

Philips PW-1840) employing Cu Ka radiation (k = 1.5418 A). The XRD Patterns of

nanoparticles were verified by comparing with the JCPDS (Joint Committee on

Powder Diffraction Standards) data.

The morphology and chemical composition of the synthesized tin oxide

nanoparticles were imaged by scanning electron microscopy (SEM, Philips XL-30).

The combined thermogravimetry and differential thermal analysis (TG–DTA,

Rheometeric STA-1500) was performed at a scan rate of 5 �C min-1 from room

temperature to 1,000 �C.

FTIR spectra were taken with an IR spectrometer in the 4,000–400 cm-1 range.

Preparation of Tin Oxide Nanoparticles

A mixed solid powder of SnCl4�5H2O (0.01 mol, 3.51 g) and KCl was ground for

30 min with a weight ratio of 1:1. Powdered KOH (0.038 mol, 2.13 g) was added to

the system and ground for 30 min at room temperature. The reaction began during

the mixing process, accompanied by the emission of water vapor from the system

due to the reaction being exothermic.

The product was washed with distilled water, treated in an ultrasonic bath for

15 min, and then centrifuged for 15 min (6,000 rpm). This process was repeated

until no Cl- ion could be detected. The detection has done with AgNO3 solution

(0.10 mol l-1).The solution was then dried at 85 �C for 24 h to obtain white SnO2

powder was assigned A sample. Also the produced tin oxide powder was further

sintered in air for 2 h at various temperatures (from 85–1,000 �C).

132 P. Sarabadani et al.

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The synthesis procedure of tin oxide was repeated by using other precursors such

as NaCl and LiCl which named B and C samples, respectively. Figure 1 shows the

synthesis process flowchart.

Results and Discussion

The tin oxide nanoparticles are produced by the following solid-state reaction:

SnCl4 � 5H2O sð Þ þ 4KOH! SnO2 � H2Oþ 4KCl sð Þ þ 6H2O

Often self-initiated and self-sustained reactions started with H2O vapor releasing

after grinding of the precursors mixture. There are four steps in a typical solid-state

of reaction: diffusion, reaction, nucleation and growth [9].

Fig 1 Flowchart of synthesis process of tin oxide nano-particles

Synthesis and Characterization of Tin Oxide Nanoparticles 133

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10 20 30 40 50 60 70 80

0

100

200

300

400

500

600

700

800

900

1000

1100

(202)(112)

(310)(002)

2θ°

10 20 30 40 50 60 70 80

2θ°

10 20 30 40 50 60 70 80

2θ°

++

+

+

++

(301)(220)

(211)(200)

(101)(110)

1000°C

900°C800°C

700°C

600°C

500°C

400°C

300°C200°C

85°C

Inte

nsi

ty(a

rbit

rary

un

it)

-100

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

(202)(310)(002)(111)

XX

+1000°C

900°C

800°C

700°C

600°C

500°C

400°C

300°C

200°C85°C

+ +

+

+

(301)(220)+

(211)

(200)

(101)(110)

Inte

nsi

ty(a

rbit

rary

un

it)

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

(202)(112)

(310)(002)(111) ++

+

+

++

1000°C

900°C

800°C

700°C600°C

500°C400°C

300°C

200°C85°C

Inte

nsi

ty(a

rbit

rary

un

it)

(301)(220)

(211)

(200)

(101)(110)

a

b

c

Fig. 2 XRD patterns of synthesized tin oxide by different precursor a KCl, b NaCl, c LiCl

134 P. Sarabadani et al.

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The hand grinding process can only make the precursor particles mix in the range

of lm. As SnCl4�5H2O is mixed and ground with KOH, they conjunct only at the

border point, where several SnCl4�5H2O atoms or molecules react with KOH first.

Due to the decrease of reaction enthalpy, further reactions are initiated and sustained

[10]. The produced SnO2�H2O and KCl atoms expand to tens or even hundreds.

After that, a barrier core mixed of SnO2�H2O and KCl exits between SnCl4�5H2O

and KOH. To continue the reaction between SnCl4�5H2O and KOH, there are two

ways: transferring along the crust of the products or piercing directly through the

products interior. If the produced SnO2�H2O ? KCl formed a ball between

SnCl4�5H2O and KOH, the comparison of the two ways show that the diffusion

activation energy of piercing is several orders higher than that of interface

transferring and the pathway of the length of transferring is about 1.57 times of that

of piercing, thus transferring is chosen to be the right diffusion path.

As the grinding continues, the further conjunction and reaction are continuing

in the system. More cores are obtained and the sizes of them are determined by

the ratio of nucleation and growth of the products. If growth in a reaction is

quicker than nucleation, the particles will aggregate to bulks; otherwise more

cores are created next to the core, which is still composed of limited number of

particles. The constant formation and precipitation of KCl from KCl shells

surrounding the SnO2�H2O particles, prevents them from aggregating to large

particles [11].

Characterization of Tin Oxide Nanoparticles

The Influence of Heat Treatment and Precursor on Particles Size

From the XRD pattern, the average particle sizes are obtained from the most intense

peaks of (110), (101) and (211) in SnO2 nanoparticles by using the Debye–Scherer

equation. The particles size of synthesized samples were measured from the peak

broadening were in good agreement with the values obtained by SEM. Comparison

of the XRD patterns with the JCPDS data confirms the samples are tin oxide with

tetragonal structure.

The XRD patterns of the obtained samples after heat treatment at various

temperatures are shown in Fig. 2. The observed diffraction peaks at (110), (101),

(200), (211), (220), and (113) agree well with the tetragonal structure of tin oxide

(JCPDS file No. 46-1088).

Only two sharp peaks (X) observed in Fig. 2b at 32 and 45 (2h�) indicate

residual NaCl which was removed after 700 �C due to the melting. The XRD

results reveal that the calcining time obviously influences the crystallization of

the powders. The experiments showed that significant growth of the particles

began at about 400 �C for SnO2. The growth accelerated with increased

temperature.

The average grain size D of tin oxide particles were estimated according to the

Scherrer’s equation [12] where h is the diffraction angle of the peak in the tetragonal

phase, k is the wavelength for the X-ray source (for Cu, k = 1.54 A) and b is the

Synthesis and Characterization of Tin Oxide Nanoparticles 135

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full width at half maximum of the peak (in radian), which is calibrated by high

purity silicon and shown in Fig. 3.

The obtained XRD patterns of these oxide nanoparticles revealed an increase in

the size of the oxide particles at 85–1,000 �C, indicating some crystallization in the

annealing process. The minimum size of the particles is observed at 600 �C, by

increasing the temperature up to 600 �C, both root and terminal hydroxyl groups

condense as grains aggregates and grow but at 600 �C due to the connected

hydroxyl effects, porosity decreases and thus particles became smaller [13].

Inducing hydroxyl-groups condensation by increasing temperature, results on

particles growth back again. In addition, the results reveal that A sample particles

size is smaller than B and C samples. It could be because of smaller size of Li atoms

which would indicate SnO2 is better surrounded by LiCl.

SEM images in Fig. 4 show fine particles with uniform size, which coincide with

the XRD-determined grain size. The SEM images show that using NaCl and KCl as

precursors led to produce morphologically similar tin oxide nano-powders

(spherical particles) whereas LiCl led to formation of smaller SnO2 particles with

a flower structure.

Figure 5 presents the FTIR spectra of SnO2 powders which are heat treated at

400 �C. In all samples, the broad adsorption peak in the range 2,500–4,000 cm-1

was assigned to asymmetric hydroxyl stretching mode. SnO2 vibrations and lattice

modes were observed at 625 and 690 cm-1, respectively. An important character-

ization peak was observed at 1450 cm-1 in Fig. 5c probably an overtone for the

asymmetric stretching mode of a surface bridging oxide formed by condensation of

adjacent surface hydroxyl groups Sn–O–Sn bridges. Dehydration phenomena from

0 200 400 600 800 1000

05

10152025303540455055606570758085

Par

ticl

es s

ize

(nm

)

Temprature(°C )

A B C

Fig. 3 The effect of annealing temperature on particles size of tin oxide powders prepared by differentprecursors: a LiCl, b NaCl, c KCl

136 P. Sarabadani et al.

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Fig. 4 Scanning electron micrograph of SnO2 powders by different precursors a LiCl, b NaCl, c KCl at 400 �C

Synthesis and Characterization of Tin Oxide Nanoparticles 137

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of SnO2 surface occurs via adjacent surface hydroxyl groups condensation on the

[100] and [101] planes. Hydroxyl groups condensation on these planes will leads to

Sn–O–Sn bridges formation at surface [14]. These formed Sn–O–Sn bridges remain

on the surface, reducing the number of gas adsorption active sites, so as a

conclusion, it is not recommended to use of LiCl as precursor for producing SnO2

nano-powder as sensor layers.

Figure 6 shows TG–DTA curves of A, B and C samples in N2. As observed in

Fig. 6a, there is an endothermic peak at 25–100 �C with a 22% weight loss

corresponding to the water physically adsorbed on the tin oxide surface desorption.

A second weight loss step (6%) was observed without any induced thermal event.

As presented in Fig. 6b, there are two endothermic peaks. The first peak observed

around 25–100 �C attributed to desorption of that water physically adsorbed on the

tin oxide surface with a 6% weight loss and a second peak is located between

780–800 �C without any weight loss assigned to residual sodium chloride melting

on tin oxide powder as confirmed by XRD patterns results (Fig. 2b).

As seen in Fig. 6c there is an additional endothermic peak at 50–100 �C with a

8% weight loss attributed to desorption of the water physically adsorbed on the tin

oxide surface. A second weight loss step (8%) was observed without any thermal

event. A third 4% weight loss step is assigned to the surface SnO2 dehydration via

adjacent surface hydroxyl groups condensation [14] and Sn–O–Sn bridges

formation is in good agreement with FTIR spectra (Fig. 4c).

Fig. 5 The FTIR spectra of SnO2 powders by different precursors a KCl, b NaCl, c LiCl (The sampleswere heat treated at 400 �C)

138 P. Sarabadani et al.

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Fig. 6 Thermal analysis of SnO2 powders prepared by using different precursors a KCl, b NaCl, c LiCl

Synthesis and Characterization of Tin Oxide Nanoparticles 139

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Conclusion

High purity tin oxide nanopowders were synthesized by solid state chemical

reaction method successfully. According to our study, increasing the temperature to

600 �C, both root and terminal hydroxyl groups condense as grains aggregate and

grow but at 600 �C due to connected hydroxyl effects, porosity decrease and thus tin

oxide particles became smaller. Inducing hydroxyl-groups condensation by

increasing temperature, results on particles growth back again. The SEM images

show that using of NaCl and KCl as precursors led to produce morphologically

similar tin oxide nanopowders (spherical particles) whereas LiCl led to formation of

smaller SnO2 particles with flower structure. In addition, the Sn–O–Sn bridges

formed on the surface only using of LiCl as precursor.

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