INTERNATIONAL JOURNAL OF RESEARCH AND INNOVATION IN APPLIED SCIENCE (IJRIAS)
ISSN No. 2454-6194 | DOI: 10.51584/IJRIAS |Volume X Issue IX September 2025
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Page 1001
Study on NH
3
Gas Sensing Properties of PANI-WO
3
Nanocomposites
CholNam Li, NamChol Yu
Kim Chaek University of Technology
DOI: https://dx.doi.org/10.51584/IJRIAS.2025.100900099
Received: 16 August 2025; Accepted: 23 August 2025; Published: 25 October 2025
ABSTRACT
We dispersed WO
3
nanoparticles with average particle size of 20-30 nm into aniline monomers and prepared
PANI-WO
3
nanocomposites by chemical oxidative polymerization. PANI-WO
3
nanocomposites were spin-
coated on substrates with interdigital carbon electrodes to form PANI-WO
3
nanocomposites films and to study
the NH
3
gas sensing properties at room temperature. The gas sensing properties of pure PANI and PANI-WO
3
with different blending ratios were compared and evaluated. The minimum detectable concentration of NH
3
gas of the sensor fabricated from PANI-20%WO
3
nanocomposites is 3 ppm, and the sensitivity of 100 ppm
NH
3
gas is 31, which is five times higher than that of pure PANI. In addition, the response time and recovery
time were faster than pure PANI, especially the recovery characteristics were significantly improved.
INTRODUCTION
Among these conducting polymers, Polyaniline(PANI) with unique electrical and optical properties is
frequently used because of its easy processing capability, flexibility, high electrical conductivity and good
environmental stability[1, 3].
PANI is prepared by oxidative polymerization of aniline monomers by chemical or electrochemical methods
[1,3,5]. The electrical conductivities of PANI vary with doping and the concentration of NH
3
gas. Therefore,
PANI has been widely used as a NH
3
gas sensing material. The gas sensor using PANI is operating at room
temperature, has low power consumption, good environmental stability and long life [7]. On other hand, metal
oxide semiconductor materials such as SnO
2
, TiO
2
, Fe
2
O
3
, ZnO, CeO
2
, and WO
3
are widely used to detect
toxic gases, which have the advantages of high sensitivity, fast response time and recovery time. However,
sensors based on these materials have the disadvantage of high operating temperatures of 300-500℃ and lack
of selectivity. To overcome these drawbacks, hybrid nanocomposites of conductive polymers and metal oxides
can be employed to enhance the gas sensing characteristics such as sensitivity, selectivity and stability[1].
Among the conductive polymers, PANI is used as a material for sensing toxic gases such as NH
3
, NO
x
, H
2
, CO,
CO
2
, H
2
S, etc. [2,4,5,7,8 ].
The gas sensing properties of the hybrid nanocomposites of PANI and metal oxides are much improved over
pure PANI, which might be caused by some chemical interaction between PANI and metal oxides and be also
attributed to the p-n heterojunction formed at the surface between p-type PANI and n-type metal oxides[5].
Especially PANI-WO
3
nanocomposites showed maximum response to NH
3
gas as compared other target gases
because of the strong interaction between the PANI-WO
3
film and adsorbed NH
3
gas molecules, also the rate
of reaction in between the surface of PANI-WO
3
film and NH
3
gas molecules is greater compared to other
target gases, as result PANI-WO
3
film showing higher selectivity to NH
3
gas [1, 14].
In the present study, we report the NH
3
gas sensing characteristics of the sensor fabricated with the PANI-WO
3
nanocomposites film on the interdigital carbon electrodes.
INTERNATIONAL JOURNAL OF RESEARCH AND INNOVATION IN APPLIED SCIENCE (IJRIAS)
ISSN No. 2454-6194 | DOI: 10.51584/IJRIAS |Volume X Issue IX September 2025
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Page 1002
Experiments
Materials and measurement apparatus
WCl
6
(Aldrich Chem.Co.), ethanol (Aldrich Chem.Co.), polyethylene glycol (polyethylene glycol, 99%,
Aldrich Chem.Co.), aniline monomer(Thomas Baker), ammonium persulfate (APS, Thomas Baker),
HCl(Thomas Baker)
In order to evaluate the electrical resistance change of PANI-WO
3
nanocomposites films with the different
NH
3
gas concentration, the thickness and electrical resistance of the films were measured after drying by spin-
coating PANI-WO
3
nanocomposites on a plastic substrate (7×7 mm) with the interdigital carbon electrodes.
Fig. 1 The structure of the interdigital carbon electrodes
The thickness and electrical resistance of PANI-WO
3
nanocomposite films was measured by a thickness meter
(SANKO SDM-mini) and a digital multimeter (Escort EDM 2347).
In the analyses of the samples TEM(FEI - TECNAI G2 20S – TWIN) and XRD(D8, ADVANCED),
SEM(Zeiss model-SUPRA VP/500)were used.
The NH
3
sensing properties of PANI-WO
3
nanocomposites were evaluated by sensitivity S.
S = R
g
/R
a
where R
a
and R
g
are the electrical resistances of the sensor in air and NH
3
gas, respectively.
The response time and recovery time are calculated as the times to reach 90% of the total resistance change in
air or NH
3
gas.
Preparation of WO
3
nanoparticles
0.1g of WCl
6
and 20 mg of polyethylene glycol were dissolved in 2ml of ethanol and stirred for 3 h. The
precursors were dried thoroughly at 40-50℃ and sintered at 500℃ for 1 h to obtain nanocrystalline WO
3
powders.
Preparation of PANI-WO
3
nanocomposites
PANI was prepared by chemical oxidative polymerization from aniline monomers.
To prepare the PANI-WO
3
nanocomposites, the aniline monomer and WO
3
nanopowder were mixed in a
constant ratio and added to 1 mL HCl and stirred for 15 min. In another beaker, a certain amount of ammonium
persulfate(APS) was dissolved in HCl. The two solutions were mixed together at 0-5℃ and the reaction
mixtures were stirred until the color of the mixture turns deep green. After stirring, the sample was left for 24 h,
and the PANI-WO
3
precipitate was filtered and washed with distilled water and acetone. The final product was
dried at 80℃. The PANI-WO
3
nanocomposites was mixed with a certain amount of 10% PVA to prepare a
paste that could be coated on the substrate.
The polymerization of anilineis an exothermic reaction, which is maintained at a constant temperature at the
early stage, and the reaction mixture exhibits a light brown color as a oligomerization intermediate.
1mm 1mm
INTERNATIONAL JOURNAL OF RESEARCH AND INNOVATION IN APPLIED SCIENCE (IJRIAS)
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When the polymerization reaction starts, the temperature increases, the color of the mixture changes to dark
blue and becomes slurry. Also, the surface of the reaction vessel was brown metallic by PANI coating. After a
certain time, the color of the reaction solution changes to dark green, and the surface of the reaction vessel is
colored green.
Fig.2 Preparation of PANI
RESULTS AND DISCUSSION
Grain size and crystal structure of WO
3
nanoparticles
The morphology and microstructure of WO
3
nanoparticles were measured by transmission electron microscope
(TEM, FEI-TECNAI G2 20S-TWIN) (Fig. 3)
As shown in Fig.3, the structure of WO
3
nanoparticles is mostly spherical with uniform grain size and the
average particle size of WO
3
nanoparticles is 20-30 nm.
Fig. 3 TEM image of WO
3
nanoparticles
The crystal structure of WO
3
nanoparticles was determined by XRD measurement (XRD, D8, ADVANCED).
INTERNATIONAL JOURNAL OF RESEARCH AND INNOVATION IN APPLIED SCIENCE (IJRIAS)
ISSN No. 2454-6194 | DOI: 10.51584/IJRIAS |Volume X Issue IX September 2025
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Diffraction peaks were observed at 2θ = 23.05, 23.54, 24.30, 28.83, 34.07, 55.97, 61.66 and 63.2, which
correspond to (002), (020), (200), (202), (420), (422), (413) planes respectively, of monoclinic WO
3
with a
lattice constant of a = 7.319 Å, b = 7.55 Å, c = 7.71 Å.
NH
3
gas sensing properties of PANI-WO
3
nanocomposites
The uniform film was formed by spin-coating PANI-WO
3
-PVA on the substrate with interdigital carbon
electrodes (Fig. 4). As shown in the SEM(Zeiss model-SUPRA VP/500) image of PANI-WO
3
-PVA film, the
surface of the film consists of fibers with porous structure and the diameter of the fibers is uniform. WO
3
nanoparticles are surrounded by a network of PANI-PVA fibers.
Fig. 4 The structure and SEM image of sample
- NH
3
gas sensing characteristics
The NH
3
gas sensing characteristics according to the mixture ratio of PANI-WO
3
nanocomposites at room
temperature are shown in Fig. 5.
The sensitivity of PANI-WO
3
nanocomposites in 100 ppm NH
3
increased with increasing WO
3
percentage,
decreased above 20 wt%, and showed maximum value of 31 at 20 wt%. The NH
3
sensing mechanism in PANI-
WO
3
nanocomposites material can be explained mainly by the depletion layer between PANI and WO
3
.
Generally, after exposure to NH
3
gas, emeraldine salt form of PANI was reduced to emeraldine base resulting
into decrease in density in PANI which causes increase in resistance.
Fig. 5 NH
3
gas sensing characteristics according to the mixture ratio of PANI-WO
3
nanocomposites at room
temperature
In PANI-WO
3
nanocomposites, n-type WO
3
nanoparticles form depletion layers with p-type PANI. When the
sensor was exposed to NH
3
gas, the width of depletion layer increases resulting into increase in resistance.
Thus, in NH
3
gas the electrical resistance of PANI-WO
3
nanocomposites changes more than that of pure PANI.
When the WO
3
percentage exceeds a certain value, the resistance decreases and the sensitivity decreases.
NH
3
100ppm
INTERNATIONAL JOURNAL OF RESEARCH AND INNOVATION IN APPLIED SCIENCE (IJRIAS)
ISSN No. 2454-6194 | DOI: 10.51584/IJRIAS |Volume X Issue IX September 2025
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This might be explained by two factors.
First, the excess addition of WO
3
made PANI insufficient to completely cover the surface of WO
3
and certain
amount of NH
3
was absorbed on the surface of WO
3
which would not improve the sensitive properties to NH
3
.
Second, the large amount of electrons generated by excess WO
3
made the depletion layer thicker at the
heterointerface between PANI and WO
3
, which leads to a higher resistance and a lower resistance change,
leading to a lower sensitivity.
Therefore, the excess addition of WO
3
was unfavorable to improve the sensitivity to NH
3
gas. The sensing
properties of PANI-20 wt% WO
3
nanocomposites to NH
3
gas concentration at room temperature are shown in
Fig. 6.
As shown in Fig. 7, the resistance of PANI-20 wt% WO
3
nanocomposites varies greatly with increasing NH
3
gas concentration and enhances by 31 times at 100 ppm.
The response and recovery times of PANI-20 wt% WO
3
nanocomposites at room temperature are shown in Fig.
7. As shown in Fig. 7, the response time is around 40 s, the recovery time is around 60-70 s, and the recovery
time is about three times faster than that of pure PANI.
Fig. 6 sensing properties of PANI-20 wt% WO
3
nanocomposites to NH
3
gas concentration at room temperature
The resistance of pure PANI increased in the presence of NH
3
gas, recovered very slowly in air, and took a
long time to reach the original resistance value.
PANI-WO
3
nanocomposites have faster recovery times than pure PANI and reach their original resistivity
values.
Fig. 7 Response characteristics of PANI-WO
3
PANI
NH
3
100ppm
PANI-WO
3
INTERNATIONAL JOURNAL OF RESEARCH AND INNOVATION IN APPLIED SCIENCE (IJRIAS)
ISSN No. 2454-6194 | DOI: 10.51584/IJRIAS |Volume X Issue IX September 2025
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Page 1006
CONCLUSIONS
The NH
3
gas sensing properties of sensors fabricated from a mixture of WO
3
nanoparticles prepared by sol-gel
method and PANI prepared by chemical oxidative polymerization were investigated.
TEM, SEM and XRD analysis of PANI-WO
3
nanocomposites showed that the prepared WO
3
particles had the
average size of 20-30 nm and the crystalline phase, and also showed that the PANI-WO
3
nanocomposites film
had a porous structure.
The minimum detectable concentration of NH
3
gas of the sensor fabricated from PANI-20% WO
3
nanocomposites is 3 ppm, and the sensitivity of 100 ppm NH
3
gas is 31, which is five times higher than that of
pure PANI.
In addition, the response time and recovery time were faster than pure PANI, especially the recovery
characteristics were significantly improved.
The fabricated PANI-WO
3
nanocomposites can be used as good sensing material for NH
3
gas at room
temperature, and can be widely used for the fabrication of NH
3
sensors with advantages of low cost,
environmental safety and low power consumption.
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