Elsevier

Synthetic Metals

Volume 204, June 2015, Pages 1-9
Synthetic Metals

Ammonia sensing properties of polyaniline/α-Fe2O3 hybrid nanocomposites

https://doi.org/10.1016/j.synthmet.2015.02.032Get rights and content

Highlights

  • Novel method of fabrication of PAni–Fe2O3 hybrid sensor.

  • PAni–Fe2O3 hybrid sensor showed maximum sensitivity 50% to NH3.

  • PAni–Fe2O3 hybrid sensor operates at room temperature.

  • Sensing mechanism of PAni–Fe2O3 hybrid sensor demonstrated using an impedance spectroscopy.

Abstract

Polyaniline (PAni) films modified by different loading of α-Fe2O3 nanoparticles have been formed by solid state synthesis method and investigated for various oxidizing and reducing gases. We demonstrates that α-Fe2O3 nanoparticles (50%): PAni hybrid nanocomposites films are highly selective to NH3 with high sensitivity (50 at 100 ppm), fast response time (29 s) and highly reproducible response curves. X-ray diffraction analysis, field emission scanning electron microscopy observations, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy analysis revealed that the n-type α-Fe2O3 nanoparticle transfers the electrons to polyaniline forms into a incredibly reduced state. These observations in PAni/α-Fe2O3 hybrid nanocomposites is insensitive to interaction with other gases except ammonia. The sensing mechanism of PAni/α-Fe2O3 hybrid nanocomposites to NH3 was interpreted with the help of proposed energy band diagram. In-addition to this, the interaction mechanism between the NH3 and PAni/α-Fe2O3 hybrid nanocomposite was investigated by an impedance spectroscopy tool.

Introduction

During the last few decades, environmental pollutions have greatly increased. So the detection of polluted gases, especially toxic gases has become increasingly important. A large effort has been done to prepare materials having promising characteristics for sensor applications and to understand their sensing mechanism, with the aim to improve their sensing performances, in terms of stability, selectivity, sensitivity, and soon [1].

The sensing materials including inorganic or organic have been widely investigated [2], [3], [4], [5], [6], [7], [8], [9], [10]. But both of them have specific drawbacks. The significant disadvantages of inorganic sensing materials are their high working temperature, for example, the working temperature of Fe2O3 is about 200–400 °C [11], [12], which increases power consumption and reduces sensor life. Several organic semiconductors, such as polyaniline, polypyrrole, polythiophene and polyacetylene have gas sensitivity at normal temperature, but they have long response time due to the highly ordered structure [13]. In addition, the low selectivity is the most serious problem of organic and inorganic sensing materials.

To complement the characteristics of pure inorganic and organic materials, organic–inorganic sensing hybrids have been developed [14], [15]. Polyaniline/TiO2 had NH3 gas sensitivity [16], polyaniline/tin dioxide [17] had superior selectivity to NH3; polyaniline/SnO2 thin film and pressed pellet [18], [19], [20], [21], [22] were synthesized and studied for the gas sensitivity to volatile organic compounds formaldehyde, ethanol, toluene, benzene, and soon. But the sensitivity research of organic–inorganic hybrids on the toxic gases is few.

However, hybrid nanocomposites of PAni and α-Fe2O3 nanoparticles are not studied, which appears to be a promising work. Therefore, further studies on α-Fe2O3 nanoparticles filled PAni hybrid nanocomposites may offer interesting results. Hence, efforts have been aimed to study inexpensive hybrid nanocomposites with high sensitivity, selectivity, better reproducibility and stability.

Section snippets

Preparation of polyaniline (PAni)

Polyaniline was prepared by polymerization of aniline in the presence of hydrochloric acid as a catalyst and ammonium peroxidisulphate as an oxidant by chemical oxidative polymerization method [23].

Preparation of α-Fe2O3 nanoparticles

Sol–gel method was used for preparation of α-Fe2O3 nanoparticles by use of iron chloride hexahydrate (Cl3Fe·6H2O) as a source of Fe [24].

Preparation of polyaniline/α-Fe2O3 hybrid nanocomposites

Polyaniline/α-Fe2O3 hybrid nanocomposites were prepared by loading α-Fe2O3 nanoparticles in different weight ratios (10–50%) into the PAni matrix. The prepared

X-ray diffraction study

X-ray diffraction patterns of the pure PAni and PAni/α-Fe2O3 (50%) hybrid nanocomposites are shown in Fig. 2(A). The diffraction pattern of pure PAni [Fig. 2A(a)] shows broad diffraction peak at 2θ = 20–30°, which is due to the scattering of X-rays from PAni chain [25]. Fig. 2A(b) shows the X-ray diffraction pattern of PAni/α-Fe2O3 hybrid nanocomposites. The XRD pattern of PAni/α-Fe2O3 (50%) hybrid nanocomposite film was indexed to a wurtzite structure with diffraction peaks of α-Fe2O3 at 2θ = 

Impedance analysis of PAni/α-Fe2O3 hybrid nanocomposite film

As per literature review, there is no report available on the interaction between NH3 gas molecules and PAni/α-Fe2O3 hybrid nanocomposite by impedance spectroscopy. Therefore, in the present study we made an attempt to study the interaction between PAni/α-Fe2O3 film and NH3 gas molecules using impedance spectroscopy. The impedance measurements on PAni/α-Fe2O3 hybrid nanocomposite films were carried out in presence of air and after exposure to 100 ppm of NH3 gas at room temperature and

Conclusions

In the present paper, PAni/α-Fe2O3 (10–50%) hybrid nanocomposites were prepared by solid state synthesis route and their systematic chemiresistive performance toward various gases (i.e., NH3, H2S, NO2, Cl2, CH3OH and C2H5OH) was carried out at room temperature. Among various compositions, PAni/α-Fe2O3 (50%) hybrid nanocomposite films are found to be highly sensitive and selective toward reducing NH3 gas than the other test gases at room temperature with maximum response of 50%. All the gas

Acknowledgments

Authors (V.B. Patil) are grateful to DAE-BRNS, for financial support through the scheme no. 2010/37P/45/BRNS/1442.

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