The area of nanomaterials research has witnessed tremendous growth due to their unusual physical and chemical properties and their small size exhibit novel material properties that largely differ from the bulk properties. Nanoparticles of noble metals are of great interest today because of their possible applications in microelectronics, anti coating, antimicrobial, biomedical field etc.

The global awareness about environment pollution and human safety is increasing with the technological development. With the drastic growth in industrial development and population, the natural atmospheric environment has become polluted and is rapidly deteriorating. To prevent environmental disasters, before it is too late, it is imperative that such pollutants be monitored and controlled. Therefore the urge for developing potential sensors has been increasing in fields of technological importance.

Gas sensors play an important role with regards to safety of residential and commercial places. They can easily detect toxic gases, oxygen deficiency and explosive atmosphere that may leak into the air and thereby save us from unexpected accident that may cause loss of life and property. This is the reason why gas detector is absolutely required for industrial areas and domestic purposes. The function of this sensor is to rapidly alert the people about gas leakage by producing high pitch sound/flashing light. Among various toxic gases CO₂ is one of the most important green house gases with high toxicity. Hence, as a safety concern, it is necessary to develop a sensor for CO₂

In the present study the design and synthesis of a novel p-n type semiconducting MoO₃: NiO (MN) nanocomposite and the effect of noble metal on Sensitivity and Selectivity towards CO₂ gas was under taken. The details of which will be presented and discussed.