Available online at www.sciencedirect.com
Sensors and Actuators B 130 (2008) 882–888
Room temperature synthesis of ␥-Fe2O3 by sonochemical
route and its response towards butane
I. Ray a , S. Chakraborty a , A. Chowdhury b , S. Majumdar a ,
A. Prakash a , Ram Pyare b , A. Sen a,∗
a
Sensor and Actuator Division, Central Glass and Ceramic Research Institute, 196 Raja S.C. Mullick Road, Kolkata 32, India
b Department of Ceramic Engineering, Institute of Technology, Banaras Hindu University, Varanasi 221005, India
Received 27 March 2007; received in revised form 26 October 2007; accepted 29 October 2007
Available online 6 November 2007
Abstract
Nanocrystalline gamma iron oxide (␥-Fe2 O3 ) has been synthesized at room temperature through sonication-assisted precipitation technique.
The key in obtaining ␥-Fe2 O3 at room temperature lies in exploiting high-power ultrasound (600 W). The gas-sensing properties to n-butane of
pure ␥-Fe2 O3 were investigated by studying the electrical properties of the sensor elements fabricated from the synthesized powder. The maximum
response (∼90%) of the sensor to 1000 ppm n-butane at 300 ◦ C can be explained on the basis of catalytic activity of the nanocrystallites. The
response and recovery time of the sensor to 1000 ppm n-butane were less than 12 s and 120 s, respectively.
© 2008 Published by Elsevier B.V.
Keywords: Gamma iron oxide; Sonochemical; Gas sensor; Butane; Room temperature
1. Introduction
Gamma iron oxide (␥-Fe2 O3 ) is a ferrimagnetic material that
is widely used in audio and video recording [1] as a magnetic
storage medium, magnetic refrigeration [2], bioprocess [3], etc.
Recently, it has been studied as a gas-sensitive material because
␥-Fe2 O3 does not require costly noble metal catalyst to perform
as a good sensor [4–8].
In gas-sensing applications nanosized powders have shown
outstanding properties, especially sensors made with them
showed low operating temperature, high sensitivity and high
selectivity [9,10] because of their large surface to volume
ratio and the criterion imposed by the Debye length. ␥-Fe2 O3
nanoparticles have previously been prepared by different routes
[11–15], such as vapour deposition (280 ◦ C), sol–gel processing
(300 ◦ C), combustion processing (250 ◦ C) and co-precipitation
(400 ◦ C). Currently, sonochemical technique has emerged as a
cheap, simple and alternative route of nanopowder preparation
[16]. The chemical effects of ultrasound arise from acoustic cav-
∗
Corresponding author.
E-mail address: [email protected] (A. Sen).
0925-4005/$ – see front matter © 2008 Published by Elsevier B.V.
doi:10.1016/j.snb.2007.10.057
itation, which is the formation, growth and implosive collapse
of bubbles in a liquid [17,18]. The cavitation can generate a temperature of around 5000 ◦ C and a pressure over 1800 kPa, which
enable many unusual chemical reactions to occur easily [19].
In this study, nanosized ␥-Fe2 O3 powder has been prepared
by a sonication-assisted precipitation route at around room temperature (∼70 ◦ C). The gas-sensing characteristics of ␥-Fe2 O3
in the presence of n-butane have been investigated in detail keeping in view the presence of butane in LPG, the latter being used
as a fuel in domestic, industrial and automobile sectors.
2. Experimental
2.1. Synthesis
Ferric nitrate nanohydrate [Fe(NO3 )3 ·9H2 O] and hydrazine
monohydrate [(NH2 )2 ·H2 O] were used as starting materials.
First, 0.01 M ferric nitrate was prepared by dissolving a required
amount of Fe(NO3 )3 ·9H2 O (Merck, 99 % purity) in distilled
water. The solution was sonicated (ultrasonic processor, Sonics,
600 W, 20 kHz, probe length 25 cm, diameter 20 mm, titanium
alloy TI-6AL-4V) for 15 min at a time in a 250 mL container
I. Ray et al. / Sensors and Actuators B 130 (2008) 882–888
(probe dipping length in the solution was 4 cm), followed by
a rest period of 15 min [20]. Hydrazine monohydrate (0.5 M)
(Qualigens, 99 % purity) was then added dropwise to the nitrate
solution under sonication. The whole procedure was carried out
for 5 h (total sonication time was 2 h) until the resulting suspension reached pH of 5. The solution was allowed to cool and at the
end of the reaction, a black precipitate was obtained. The precipitate was centrifuged, washed with distilled water and acetone
in sequence. The filtrate was dried at 70 ◦ C for 5 h in air.
The particle morphology of the dried powder was observed
in a high resolution transmission electron microscope (HRTEM,
JEOL) after ultrasonically dispersing the powder in acetone.
The phase identification of the calcined powder was carried out
by X-ray diffraction (XRD; Philips, PW 1710; Cu K␣ radiation). The specific surface area, SBET , of the dried powder
was determined from N2 adsorption–desorption experiments
using the BET method. The measurement was performed with
Micromeritics Gemini II 2370 equipment.
Fig. 1. XRD patterns of synthesized iron oxide powders after drying at 70 ◦ C for
5 h: (a) without sonication, (b) sonication under 300 W for 2 h and (c) sonication
under 600 W for 2 h.
tation route) no crystalline phase was clearly identified after
drying.
The mean crystalline size of the powder was calculated using
Scherrer formula [22],
2.2. Sensor fabrication
D=
For fabricating sensors from the synthesized powder, thick
paste of the powder was prepared in an aqueous medium containing a small amount (3 wt%) of polyvinyl alcohol (PVA) binder.
The paste was painted on the outer surface of thin alumina tubes
(length 3 mm, outer diameter 2 mm and thickness 0.5 mm). Gold
electrode and platinum lead wires were attached to the end of
the tubes (by curing at a high temperature) before applying the
paste. The consistency of the paste and the processing variables
were optimized to get final coatings of around 100 ␮m thickness.
After painting, the coated alumina tubes were fired at 400 ◦ C for
10 min. Kanthal heating coils were then placed inside the tubes.
The details of sensor packaging arrangement have been given
elsewhere [20,21]. The impedance studies of the sensors were
made using a Solartron impedance analyzer (model-SI 1260)
in the frequency range 1 Hz to 8 MHz. The electrical resistance,
percent response, response time and recovery time of the sensors
were measured at different temperatures (from 275 ◦ C to 425 ◦ C
in an ambience of 50–60% relative humidity) by using a digital multimeter (Solartron) and a constant voltage/current source
(Keithley 228A). The sensors were initially aged at 300 ◦ C for
72 h to achieve the desired stability before the measurements.
883
0.9λ
β cos θ
(1)
3. Results and discussions
where D is the average
crystallite size, λ = 1.541 Å (X-ray wave√
length) and β = B2 − b2 , B being the width of the diffraction
peak at half maximum for the diffraction angle 2θ and b is the
same for very large crystallites. The value of b was determined
from the XRD of a large grained sample prepared by calcining
the powder at a high temperature. The crystallite sizes of the
powders have been furnished in Table 1. From the XRD plots,
the cubic lattice parameter of the sonochemically prepared powder (dried at 70 ◦ C) was found to be a = 8.3504 Å, whereas those
of standard ␥-Fe2 O3 was a = 8.350 Å (JCPDF File no. 24-0081).
Hence, as the lattice parameters match well, the broadening of
the XRD peaks [Fig. 1(a)] arises primarily due to the fine particle size of the powder. After heat treatment of the powder at
400 ◦ C for 10 min, which was required for curing the coating
on the sensor substrates, the ␥-Fe2 O3 peak positions remained
unchanged (Fig. 2) and only the crystallite size of the powder
increased slightly due to the heat treatment (Table 1).
The TEM images of the ␥-Fe2 O3 powders (a) dried at 70 ◦ C
for 5 h and (b) heat treated at 400 ◦ C for 10 min indicate the
presence of agglomerates and the average particle sizes of the
powders are around 40 nm and 70 nm, respectively (Fig. 3a and
b).
3.1. Structural characterization
3.2. Sensor characterization
The XRD patterns of the iron oxide powders prepared by
a conventional precipitation route (without sonication) and a
sonochemical route (using varying ultrasonic power, i.e., 300 W
and 600 W) are shown in Fig. 1. The XRD patterns indicate
that the powder synthesized under high ultrasonic power rating (i.e., 600 W) showed pure ␥-Fe2 O3 phase after drying at
70 ◦ C for 5 h, while the powder synthesized under low ultrasonic power rating (i.e., 300 W) showed mixed-phase powder
(␥-Fe2 O3 and ␣-Fe2 O3 ) after drying at 70 ◦ C for 5 h. It can
also be noted that without sonication (conventional precipi-
The percent response (S) of the sensors fabricated from the
synthesized ␥-Fe2 O3 powder in 1000 ppm n-butane was calcuTable 1
Crystallite size of sonochemically prepared (600 W) ␥-Fe2 O3 powders
Condition
Crystallite
size (nm)
Surface area
SBET (m2 /g)
Dried at 70 ◦ C for 5 h
Heat treated at 400 ◦ C for10 min
12
21
44.7
38.9
884
I. Ray et al. / Sensors and Actuators B 130 (2008) 882–888
Fig. 2. XRD patterns of ␥-Fe2 O3 powder: (a) dried at 70 ◦ C for 5 h and (b) heat
treated at 400 ◦ C for 10 min.
Fig. 4. Percent response vs. temperature plots of a ␥-Fe2 O3 sensor.
lated from the following relation:
RA − RG
S(%) =
× 100
RA
(2)
where RA is the sensor resistance in air at a particular temperature and RG is the sensor resistance in 1000 ppm n-butane at
the same temperature. Fig. 4 shows the percent response of ␥Fe2 O3 with temperature. The maximum response to n-butane
is obtained at around 300 ◦ C. To understand this behaviour of
our samples, we have to consider that, as a first step, an alkane
Cn H2n+2 is adsorbed (also desorbed depending on temperature)
on the sensor surface as given below:
Cn H2n+2 (gas) ⇔ Cn H2n+2 (physisorbed)
(3)
The response of the sensor goes down drastically above 325 ◦ C.
Fig. 3. TEM images of the ␥-Fe2 O3 powder prepared by a sonication-assisted
precipitation method: (a) dried at 70 ◦ C for 5 h (the inset shows higher magnification of the image) and (b) heat treated at 400 ◦ C for 10 min.
Such behaviour can be understood by considering the role of
desorption of gas molecules (Eq. (3)) at higher temperatures.
For real-life applications of the sensors, the response time
(the time required for a sensor to respond to a step increase
in the analyte gas) should be low so that the buzzer of a gas
alarm rings during gas leak without delay. Similarly, the buzzer
should not go on ringing for a long time (i.e., quick recovery, the time required for a sensor to return to the baseline
after a response to an analyte) after the gas is withdrawn. In
the present case, the response and recovery time (Fig. 5(a) and
(b)) of the sensor (both normal ambient (RH = 55%) and humid
condition (RH = 100%)) decrease with an increase in operating
temperature due to faster adsorption–desorption of the gas at
higher temperatures. Under humid condition (RH = 100%), the
response and recovery time of the sensor are slightly slower
than under normal ambient condition, and this is caused by the
concentration change of adsorbed surface hydroxyl groups due
to variation in ambient humidity [23]. The resistance change
of the sensor during the short aging time [24] may be due to
adsorption, desorption and transformation of various species
of oxygen, as well as slow growth of particles and diffusion
between grain boundaries. This behaviour is well known and
hence all commercial sensors are aged for a week before reallife applications. Figs. 6 and 7 show the variations of electrical
I. Ray et al. / Sensors and Actuators B 130 (2008) 882–888
885
Fig. 7. Long-term stability (in terms of percent response) of a ␥-Fe2 O3 sensor
under normal ambient (55% RH) and humid (100% RH) condition at operating
temperature 300 ◦ C.
Fig. 5. Response and recovery time vs. temperature plots of a ␥-Fe2 O3 sensor
under (a) normal ambient and (b) 100% RH humid condition.
resistance and percent response of the sensor with time, respectively, under normal ambient (RH = 55%) and humid condition
(RH = 100%). It is well known that the mechanisms associated
with the detection of water vapour involve chemical and physical
adsorption [25]. Physisorbed water requires low temperatures,
∼150 ◦ C, to be removed, but the chemisorption of water (OH−
groups adsorbed) onto oxides is very strong, requiring high temperatures to remove it. It is found that the ␥-Fe2 O3 material is
not much sensitive to the concentration change of adsorbed surface hydroxyl groups at 300 ◦ C and above because of the faster
dehydroxylation kinetic process at higher temperatures. Fig. 8(a)
and (b) shows the actual sensing curves to various concentrations (250–1000 ppm) of n-butane. It is found that the percent
responses towards 1000 ppm, 750 ppm, 500 ppm and 250 ppm
n-butane are around 93, 88, 85 and 80, respectively. It is also
observed (Fig. 8(b)) that the percent response increases almost
linearly as the n-butane concentration increases from 250 ppm to
1000 ppm. The linear relationship between the percent response
and the n-butane concentration may be attributed to the availability of a sufficient number of sensing sites on the film to act
upon the n-butane sensing. The low gas concentration implies
a lower surface coverage of gas molecules, resulting in lower
surface reaction between the surface adsorbed oxygen species
and the gas molecules. The increase in the gas concentration
increases the surface reaction due to a large surface coverage.
A further increase in the surface reaction will be gradual when
saturation of the surface coverage of gas molecules is reached.
Incidentally, a novel way to understand the quality of a sensor
is through impedance analysis [20]. The frequency-dependent
properties of an insulator are generally described by complex
impedance plots, where the impedance Z* is given by
Z∗ = Z − Z
Fig. 6. Long-term stability (in terms of resistance in air) of a ␥-Fe2 O3 sensor under normal ambient (55% RH) and humid (100% RH) condition at an
operating temperature of 300 ◦ C.
(4)
where Z and Z being the real and imaginary parts of the
impedance, respectively.
Fig. 9 shows a plot of the real part of the complex impedance
versus the imaginary part (Argand plot) for the ␥-Fe2 O3 gas
sensor at 300 ◦ C. The equivalent circuit for the impedance plot
in the present case is given in Fig. 10, where Rg and Rgb are the
grain and grain boundary resistances, and Cg and Cgb are the
grain and grain boundary capacitances, respectively.
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I. Ray et al. / Sensors and Actuators B 130 (2008) 882–888
Fig. 10. Equivalent circuit used for analysis of the impedance plots.
Fig. 11. Schematic diagram showing formation of a potential barrier at a grain
boundary on adsorption of oxygen on polycrystalline ␥-Fe2 O3 . Here EF is the
Fermi energy, and EC1 and EC2 are the conduction band edges of the material
exposed to normal air and a reducing gas, respectively.
Fig. 8. Typical sensing curves to n-butane of various concentrations
(250–1000 ppm).
Fig. 9. Two-probe ac impedance spectra of a ␥-Fe2 O3 gas sensor in air and in
1000 ppm n-butane (working temperature 300 ◦ C).
The optimum values of resistance (Rg , Rgb ) and capacitance
(Cg , Cgb ) obtained for the sensor under different conditions are
given in Table 2.
It is seen that while the sample resistance falls on exposure to
gas, the capacitance increases [26]. We attribute this to the barriers at grain boundaries as shown in Fig. 11. The adsorbed oxygen
at grain boundaries traps electrons from grains of ␥-Fe2 O3 ,
reducing carrier density in the n-type material and forming a
barrier to electron transport. On interaction with n-butane this
adsorbed oxygen is removed, forming gaseous species and H2 O.
Consequently, the film resistance is reduced. The increase in
capacitance values on exposure to gas is attributed to a reduction
in the width of depletion region after exposure to gas. Incidentally, nearly smooth semicircles in the impedance plots vindicate
[20] the high quality of the present sensor.
To understand the typical gas-sensing behaviour of ␥-Fe2 O3 ,
we have to consider that, as a first step, an alkane Cn H2n+2 is
adsorbed (also desorbed depending on the operating temperature) on the sensor surface. Though the final oxidation products
of alkanes are CO2 , CO and H2 O, the reactions may proceed through intermediate steps [27], e.g., the decomposition
of butane may proceed via the formation of fragment groups
Table 2
Values of resistance (Rg , Rgb ) and capacitance (Cg , Cgb ) of the ␥-Fe2 O3 sensor in air and in 1000 ppm n-butane
Sensor
Condition
Rg (M)
Cg (pF)
Rgb (M)
Cgb (pF)
Sonochemically prepared ␥-Fe2 O3
Air
n-Butane
7.23
0.88
1.98
2.41
34.23
2.89
8.87
8.91
I. Ray et al. / Sensors and Actuators B 130 (2008) 882–888
such as butyl, acetyl, formate, etc. Incidentally, transition metal
oxides like Fe2 O3 are primarily used as a redox catalyst and their
acid–base properties are also of significant importance [28].
We envisage the following chemical reaction for the formation of ␥-Fe2 O3 in aqueous solution under sonication:
N2 H5 + + Fe3+ → NH4 + + (1/2)N2 + H+ + Fe2+
)))))
Fe2+ −→Fe3+ (␥-Fe2 O3 )
Air
(5)
(6)
Suslick [29] reported that there are three regions of sonochemical activity: (i) the inside of the collapsing bubble
(T > 5000◦ ), (ii) the interface between the bubble and liquid
(T ∼ 1900◦ ), and (iii) the bulk solution which is at ambient temperature. During cavitational collapse, intense heating of the
bubbles occurs. Shock waves from cavitation in liquid produce
high-velocity interparticle collisions, the impact of which is sufficient to form nanosized particles at the interfacial region. It is
also well known that H2 O2 can be generated from the evaporation and pyrolysis of water in the gas phase of the collapsing
bubbles [30–32]. It is possible that Fe2+ (aq) ions are oxidized
to Fe3+ (aq) with H2 O2 . Subsequently, Fe3+ ions hydrolyze to
Fe(OH)3 and the sonication causes the dehydration and the formation of ␥-Fe2 O3 nanoparticles. In the present case, the powder
synthesized at low ultrasonic power shows the formation of a
mixed phase. We found that the key to synthesize phase-pure
␥-Fe2 O3 lies in exploitating high power ultrasonics. ␥-Fe2 O3 is
a defect oxide of spinel structure and can be represented as 3/4
[Fe3+ (Fe3+ 5/3 2+ 1/3 )O4 ]. The small difference in the satellite
structures between ␣-Fe2 O3 and ␥-Fe2 O3 results mainly from
the changes in the Fe–O hybridization parameters, suggesting an
increased covalency in ␥-Fe2 O3 compared to ␣-Fe2 O3 [33–38].
In ␥-Fe2 O3 , Lewis acid sites (Fe3+ ) are the active positions where
adsorption or oxidation takes place. The conversion and selectivity of a particular reaction are influenced not only by the nature
of the active sites but also by their number, strength and the
size of the particle [39–41]. Here the enhancement of the gassensing performance for sonochemically prepared ␥-Fe2 O3 may
be attributed to the formation of nanosized ␥-Fe2 O3 powder,
resulting in a large specific surface area. However, further work
is needed to find out the nature and concentration of active sites
on the sonochemically prepared nanosized ␥-Fe2 O3 powder.
4. Conclusion
Nanocrystalline ␥-Fe2 O3 can be directly synthesized
through high-power-sonication-assisted precipitation technique
at around room temperature without any further heat treatment.
High power (600 W) ultrasound is necessary to get the desired
phase. It has been found that such nanocrystalline ␥-Fe2 O3
shows maximum response to 1000 ppm n-butane at around
300 ◦ C and the response and recovery of the sensor are also
very fast.
887
Acknowledgements
The authors are thankful to the Department of Science and
Technology, Government of India for financial assistance and
also to Dr. H.S. Maiti, Director of Central Glass and Ceramic
Research Institute, Kolkata for his kind permission to publish
the research work.
References
[1] P. Kiemle, J. Wiese, G. Buxbaum, Process for the production of iron oxides
epitaxially coated with cobalt, the coated oxides and their cue, US Patent
No. 652214.
[2] R.D. Mcmichael, R.D. Schull, L.J. Swartzendruber, Magnetocaloric effect
in superparamagnets, J. Magn. Magn. Mater. 111 (1992) 29–33.
[3] N.M. Pope, R.C. Alsop, Y.A. Chang, A.K. Smith, Evaluation of magnetic
alginate beads as a solid support for positive selection of CD34+ cells, J.
Biomed. Mater. Res. 28 (1994) 449–457.
[4] M. Liao, D. Chen, Preparation and characterization of a novel magnetic
nano-adsorbent, J. Mater. Chem. 12 (2002) 3654–3659.
[5] Z. Jing, S. Wu, Synthesis, characterization and gas sensing properties of
undoped and Co-doped ␥-Fe2 O3 -based gas sensors, Mater. Lett. 60 (2006)
952–956.
[6] Y. Liu, W. Zhu, O.K. Tan, Y. Shen, Structural and gas sensing properties of
ultrafine Fe2 O3 prepared by plasma enhanced chemical vapor deposition,
Mater. Sci. Eng. B 47 (1997) 171–176.
[7] I.S. Lim, G.E. Jang, C.K. Kim, D.H. Yoon, Fabrication and gas sensing
characteristics of pure and Pt-doped ␥-Fe2 O3 thin film, Sens. Actuators B
77 (2001) 215–220.
[8] J. Wang, M. Tong, X. Wang, Y. Ma, D. Liu, J. Wu, D. Gao, G. Du, Preparation of H2 and LPG gas sensor, Sens. Actuators B 84 (2002) 95–97.
[9] N. Yamazoe, N. Miura, T. Seiyama (ed.), Chem. Sen. Technol. vol. 4,
Kohanha, Japan, Elsevier, Amsterdam, 1992, p. 30.
[10] N. Sergent, P. Gelin, L.P. Camby, H. Praliaud, G. Thomas, Preparation and
characterization of high surface area stannic oxides: structural, textural and
semiconducting properties, Sens. Actuators B 84 (2002) 176–188.
[11] Z. Jing, Preparation and magnetic properties of fibrous gamma iron oxide
nanoparticles via a nonaqueous medium, Mater. Lett. 60 (2006) 2217–2221.
[12] V. Chhabra, P. Ayyub, S. Chattopadhyay, A.N. Maitra, Preparation of acicular ␥-Fe2 O3 particles from a microemulsion-mediated reaction, Mater.
Lett. 26 (1996) 21–26.
[13] Z. Jing, S. Wu, Synthesis, characterization and magnetic properties of ␥Fe2 O3 nanoparticles via a non-aqueous medium, J. Solid State Chem. 177
(2004) 1213–1218.
[14] K. Sureshu, K.C. Patil, A combustion process for the instant synthesis of
␥-iron oxide, J. Mater. Sci. Lett. 12 (1993) 572–574.
[15] S. Tao, X. Liu, X. Chu, Y. Shen, Preparation and properties of ␥-Fe2 O3 and
Y2 O3 doped ␥-Fe2 O3 by a sol–gel process, Sens. Actuators B 61 (1999)
33–38.
[16] R. Vijaykumar, Y. Kottypin, I. Felner, A. Gedanken, Sonochemical synthesis and characterization of pure nanometer-sized Fe3 O4 particles, Mater.
Sci. Eng. A 286 (2000) 101–105.
[17] A. Tuulmets, Ultrasound and polar homogeneous reactions, Ultrason.
Sonochem. 4 (1997) 189–193.
[18] J.M. Loning, C. Horst, U. Hoffmann, Investigations on the energy conversion in sonochemical processes, Ultrason. Sonochem. 9 (2002) 169–179.
[19] E.B. Flint, K.S. Suslick, The temperature of cavitation, Science 253 (1991)
1397–1399.
[20] S. Chakraborty, A. Sen, H.S. Maiti, Complex plane impedance plot as a
figure of merit for tin dioxide based methane sensors, Sens. Actuators B
119 (2006) 431–434.
[21] S. Chakraborty, A. Sen, H.S. Maiti, Selective detection of methane and
butane by temperature modulation in iron doped tin dioxide sensors, Sens.
Actuators B 115 (2006) 610–613.
[22] A. Taylor, X-ray Metallography, John Wiley, New York, 1961, p. 678, 686.
888
I. Ray et al. / Sensors and Actuators B 130 (2008) 882–888
[23] K. Ihokura, J. Watson, The Stannic Oxide Gas Sensors—Principles and
Application, CRC Press, Boca Raton, FL, 1994.
[24] X.Q. Liu, S.W. Tao, Y.S. Shen, Preparation and characterization of
nanocrystalline ␣-Fe2 O3 by a sol–gel process, Sens. Actuators B 40 (1997)
161–165.
[25] J.G. Fagan, V.R.W. Amarakoon, Reliability and reproducibility of ceramic
sensors (part III), Am. Ceram. Soc. Bull. 72 (1993) 119–130.
[26] W. Gőpel, K.D. Schierbaum, SnO2 sensors: current status and future
prospects, Sens. Actuators B 26 (1995) 1–12.
[27] D. Kohl, Function and applications of gas sensors, J. Phys. D: Appl. Phys.
34 (2001) R125–R149.
[28] M.H. Kheder, M.S. Sobhy, A. Tawfik, Physicochemical properties of
solid–solid interactions in nanosized NiO-substituted Fe2 O3 /TiO2 system
at 1200 ◦ C, Mater. Res. Bull. 42 (2007) 213–220.
[29] K.S. Suslick, Sonochemistry, Science 247 (1990) 1439–1445.
[30] L. Yin, Y. Wang, G. Pang, Y. Koltypin, A. Gedanken, Sonochemical synthesis of cerium oxide nanoparticles—effect of additives and quantum size
effect, J. Colloid Interf. Sci. 246 (2002) 78–84.
[31] B. Djuricic, S. Pickering, Nanostructured cerium oxide: preparation and
properties of weakly-agglomerated powders, J. Eur. Ceram. Soc. 19 (1999)
1925–1934.
[32] K.S. Suslik, Ultrosound: Its Chemical, Physical and Biological Effects,
VCH Publisher, Weinheim, 1998.
[33] C. Cantalini, H.T. Sun, M. Faccio, G. Ferri, M. Pelino, Niobium-doped, ␣Fe2 O3 semiconductor ceramic sensors for the measurement of nitric oxide
gases, Sens. Actuators B 24/25 (1995) 673–677.
[34] H.T. Sun, C. Cantalini, M. Faccio, M. Pelino, NO2 gas sensitivity of sol–gelderived ␣-Fe2 O3 thin films, Thin Solid Films 269 (1995) 97–101.
[35] J.S. Han, T. Bredow, D.E. Davey, A.B. Yu, D.E. Mulcahy, The effect of
Al addition on the gas sensing properties of Fe2 O3 -based sensors, Sens.
Actuators B 75 (2001) 18–23.
[36] G. Neri, A. Bonavita, S. Ipsale, G. Rizzo, C. Baratto, G. Faglia, G. Sberveglieri, Pd and Ca-doped iron oxide for ethanol vapor sensing, Mater. Sci. Eng.
B 139 (2007) 41–47.
[37] W. Weiss, W. Ranke, Surface chemistry and catalysis on well-defined epitaxial iron-oxide layers, Prog. Surf. Sci. 70 (2002) 1–151.
[38] J.E. Huheey, E.A. Keiter, R.L. Keiter, Inorganic Chemistry: Principles of
Structure and Reactivity, fourth ed., Harper Collins, 1993.
[39] A. Auroux, A. Gervasini, Microcalorimetric study of the acidity
and basicity of metal oxide surfaces, J. Phys. Chem. 94 (1990)
6371–6379.
[40] N. Lopez, T.V.W. Janssens, B.S. Clausen, Y. Xu, M. Mavrikakis, T.
Bligaard, J.K. Nørskov, On the origin of the catalytic activity of gold
nanoparticles for low-temperature CO oxidation, J. Catal. 223 (2004)
232–235.
[41] P. Li, D.E. Miser, S. Rabiei, R.T. Yadav, M.R. Hajaligol, The removal of
carbon monoxide by iron oxide nanoparticles, Appl. Catal. B 43 (2003)
151–162.
Biographies
Indrani Ray received an MTech in Ceramic Engineering from Calcutta University in 1988. Presently, she has been working as a scientist (under D.S.T.
sponsored scheme) at Sensor and Actuator Division, Central Glass and Ceramic
Research Institute, Kolkata, India. Her current research interest is in preparing semiconducting oxide-based sensor compositions for detection of VOC and
combustible gases.
Shirshendu Chakraborty received an MTech in Ceramic Engineering from
Banaras Hindu University in 2003. Presently, he has been working as a scientist
at Sensor and Actuator Division, Central Glass and Ceramic Research Institute,
Kolkata, India. His current research interest is in developing semiconducting
oxide-based sensors for detection of toxic and combustible gases.
Arun Chowdhury received a BTech in Ceramic Technology from Calcutta
University in 2005. Presently, he is doing MTech in Ceramic Engineering from
Banaras Hindu University. His current research interest is in preparing and characterization of semiconducting oxide-based material for gas sensor application.
Sanhita Majumdar received an MSc in environment science from Bardwan
University in 2005. Presently, she has been working as a research intern at Sensor
and Actuator Division, Central Glass and Ceramic Research Institute, Kolkata,
India. Her current research interest is in preparing semiconducting oxide-based
sensor compositions for detection of toxic and combustible gases.
Amit Prakash received a MTech in Nanoscience and Technology from Jadavpur
University in 2007. Presently, he is working as a research scholar at Sensor and
Actuator Division, Central Glass and Ceramic Research Institute, Kolkata, India.
His current research interest is in preparing and characterization of semiconducting oxide-based material for gas sensor application.
Ram Pyare obtained a PhD in Ceramic Engineering from Banaras Hindu University in 1981. Currently, he is the assistant professor of Ceramic Engineering
Department, BHU. His current research interests are in processing and characterization of glass, glass ceramic and electronic materials.
Amarnath Sen obtained a PhD in Materials Science from Indian Institute of
Technology, Kanpur in 1986. Currently, he is the Head of Sensor and Actuator
Division, Central Glass and Ceramic Research Institute, Kolkata, India. His
current research interests are in processing and characterization of electronic
ceramic materials like gas sensors and piezoelectric materials.