Synthesis of Molybdenum Oxide Nanoparticles by Sol-Gel Method for Ammonia Gas Sensing

Molybdenium oxide nanoparticles were prepared by simple sol gel method using aliquat HTA-1 as surfactant for ammonia gas sensing. As synthesized sensor give good sensitivity and very good response. The synthesized MoO3 nanoparticles were characterized by using UV-Visible, XRD, SEM-EDS and TEM analysis techniques. TEM micrograph confirms the particle size is about 25 nm with layered structure. The particle size distribution shows the narrow size distubution which are well matches with calculated from XRD.


Introduction
Last several years much effort has been devoted to the study of molybdenum oxides and its related compound. Molybdenum oxide nanomaterials have attractive catalytic, photochromic and electronic properties, and a lot of potential applications in the areas of electrochemistry and sensing devices [1][2][3][4][5]. Molybdenum is a metal with a wide range of oxidation states from +2 to +7 existing in a variety of oxides. Molybdenum oxide is a potential material because of its wide range of stoichiometry and interesting behaviour which includes structural, chemical, electrical and optical, properties [6][7][8][9]. It exhibits a unique layer structure, which permits ion intercalation/deintercalation. Their properties strongly change as a function of oxygen vacancy concentration & nonstoichiometry. As a wide band gap n type semiconducting materials, MoO 3 has received considerable attention in many technological applications such as erasable optical storage media, optical switching coatings and high density memory devices, gas & chemical sensors catalysis, energy efficient window technology, photochromic & electrochromic devices [10][11][12].To date, molybdenum oxide nanomaterials were mainly synthesized by hydrothermal route ultrasonic, solvothermal and chemical vapour deposition methods [13][14][15][16]. However, in these processes, it took a long time to synthesize molybdenum oxide nanomaterials or the synthesis process required a high temperature. However, the reproducible preparation of small, stable MnO 3 nanoparticles with tight size distribution is of immense importance and still remains a challenging task. Here in we report a simple route for the synthesis of MoO 3 nanoparticles and its application for ammonia gas sensing.    The ammonia gas sensing studies of as synthesized MoO 3 nanoparticles have been carried out and the result is shown in The wire embedded as an electrode for sensing the Gas was used and the sensors were mounted into a specially designed Quartz cell. When the sensor absorbs the gas, the redox reaction takes place and it changes the resistance. The reducing gas used in the present study is ammonia. The concentration of ammonia gas was controlled by adjusting the flow rate ratios of target gases to dry air. The sensitivity of the sensors is expressed as the ratio of the air resistance to gas resistance. i.e. = R air / R gas was measured in the temperature range of 200ºC to 350ºC in a dynamic flow system.

Synthesis and Characterization
The measurements were performed inside a closed chamber at different temperatures. Gas mixtures were obtained by means of mass flow controllers and driven into the test chamber. A known amount of target gas is mixed in air and injected to the measuring cell at a flow rate of 1000 cc per minute of air, which is a carrier gas.
A previous stabilization treatment is performed to reach a stable conductance value before making the test. Ammonia gas was used for the gas sensitivity measurements. For characterization of gas sensing properties the sensor element were placed in a 1000 cc, in a temperature controlled gas chamber. A typical gas measurements sequence containing predetermined intervals, in which the sensors were exposed to gas atmospheres. After completion of one sequence, the sensors and measurement cycle was repeated. The resistance response of each sensor structure was transformed into a sensitivity value using commonly used formula for the gases as

Conclusion
In conclusion, The MoO 3 nanoparticles of narrow size distribution was synthesized and characterized successfully. XRD pattern showed that phase pure MoO 3 nanoparticles are formed.
TEM study showed that the particle size of MoO 3 nanoparticles is about 25 nm. The advantages of this method are simplicity of the process, short duration, energy saving, accessible for auxiliary materials, non-sophisticated equipment and structures with high efficiency. The experimental results confirm that gas sensor based on MnO 3 pellets sensitive layer are of great interest for gas detection.