Synthesis of nanorods and mixed shaped copper ferrite and their applications as liquefied petroleum gas sensor
Highlights
► Mixed shaped (nanocubes/nanospheres) and nanorods of copper ferrite were synthesized by co-precipitation method. ► The influence of surface morphology on the LPG sensing properties of copper ferrite was investigated. ► The role of PEG in the synthesis for obtaining uniform sphericals/nanocubes like surface morphology has been demonstrated. ► Mixed shaped copper ferrite shows an improved sensing performance in comparison with that of the CuFe2O4 nanorods. ► The maximum sensor response obtained with mixed shaped CuFe2O4 to LPG is 57.
Introduction
Liquefied petroleum gas (LPG) is a flammable gas which presents many hazards to both the humans and environment. LPG is being used as fuel for domestic and industrial purposes. Increasing usage of LPG has increased the frequency of accidental explosions due to leakage, because combustion accidents might be caused when it leaks out accidentally or by mistake. Thus the requirements for reliable and sensitive gas detecting instruments have increased for safety at home as well as industries. Therefore, LPG sensor has become the subject of intense research today in view of fundamental research as well as industrial applications. In spite of considerable efforts, good sensors for LPG have not been found till now, the problem being of crucial importance for industrial as well as domestic purposes. LPG sensing at room temperature is of great interest as various LPG sensors reported basically work at higher temperature such as 250 °C, but it is not convenient for commercial point of view. To realize this goal, much attention has been focused on the study of LPG sensors [1], [2], [3]. Semiconductor gas sensors in the form of thin or thick films, based on metal oxides such as SnO2, ZnO, TiO2 and p–n hetrojunctions, have been widely reported in the literature [4], [5], [6], [7]. Current years have been seen the increased interest in searching new semiconducting materials for gas sensor application. Some well known materials for LPG sensing are ZnO [8], modified-ZnO (viz., CoO–ZnO, zinc–gallate, zinc–titanate, cobalt–zincate), SnO2, WO3 and doped materials etc. [9], [10], [11].
Spinels of the type M2+M23+O4 attract the research interest because of their versatile practical applications [12], [13], [14], [15]. In the case of M3+ (M = Fe), the resulting spinel ferrites having a general chemical composition of MFe2O4 (M = Cu, Mn, Mg, Co, Zn, Ni, Cd, etc.) are widely used as magnetic materials [16], [17], [18]. Reddy et al. studied the ferrites prepared by wet chemical precipitation as gas sensing materials [19]. They reported the response of zinc ferrite for H2S and that of nickel ferrite for Cl2. Tianshu et al. reported the response of cadmium ferrite for ethanol sensor [20]. Currently it is a topic of increasing interest to study the gas sensing properties of ferrites [21], [22], [23], [24], [25], [26], [27], [28], [29].
The LPG sensing mechanism of such type of sensors involves the chemisorptions of oxygen on the surface of sensing material, followed by charge transfer during the reaction of oxygen with LPG molecules, which will cause a resistance change on the surface of sensing elements [30]. The adsorption of gas on the surface of a semiconductor is responsible for significant change in the electrical resistance of the materials; there have been a sustained and successful effort to make use of this change for purpose of gas detection.
In our previous papers, we have reported spherical- and nanonails-shaped ferric oxide nanoparticles and studied its LPG sensing properties [31], [32]. Here mixed shaped (nanocubes/nanospheres) and nanorods of copper ferrite were prepared by co-precipitation method using cupric and ferric chlorides with and without PEG, respectively. The influence of the surface morphology on the LPG sensing properties of copper ferrite was investigated. The role of PEG polymer in the synthesis for obtaining uniform sphericals/nanocubes like surface morphology was also demonstrated.
The objective of our research is to determine the best sensing material for the LPG detection. Here we have synthesized copper ferrite with different surface morphologies and its LPG sensing properties were investigated. The sensitivity of these sensing elements to LPG is found better than our previously reported work [31], [32], [33], [34].
Section snippets
Synthesis of CuFe2O4
A chemical co-precipitation method was used for the synthesis of nanocrystalline CuFe2O4. The stoichiometric amount of starting materials, such as cupric chloride (CuCl2·2H2O) and ferric chloride (FeCl3·6H2O) were taken and dissolved in required amount of ethanol. In addition to this, some drops of poly-ethylene glycol was added for synthesis of copper ferrite nanocubes/nanospheres, while nanorods were prepared without PEG. Both solutions (cupric and ferric chlorides) were magnetically stirred
Scanning electron microscopy analysis
Fig. 1(a) and (b) shows SEM images of copper ferrite with PEG, at different magnifications. These images show mixed shaped (nanocubes/cuboids/nanospheres) surface morphology. It is clearly seen from the micrographs that the particles of the CuFe2O4 are at nanoscale. This is very advantageous for gas sensing applications as smaller particles have a large specific surface area and as a result an elevated response to LPG. Fig. 2(a) and (b) shows SEM images of copper ferrite without PEG, at two
Conclusions
Copper ferrite was successfully synthesized via co-precipitation method and characterized for their structural and surface morphological properties. From SEM images we observed that, for mixed shaped copper ferrite, few particles agglomerated and leaving vacant spaces among them; however, for nanorods, the uniform sized and relatively dense and compact structure is seen. The XRD patterns show nanocrystalline nature of the materials with spinel phase. The minimum crystallite size of copper
Acknowledgements
Mr. Satyendra Singh is thankful to CSIR; India, for senior research fellowship vides award number 09/107(0331)2008-EMR.
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