Development of gas sensors is essential for the protection of environment and work places from harmful and hazardous gases . Due to the increase in the emission of gases from automobiles, there is a sharp rise in air pollution. The alarming increase in the usage of various gases in day today life, either in a domestic kitchen or workplaces or industries especially of explosive or toxic nature has immensely increased the need for reliable gas sensors in the commercial market. The major attributes to look forward in a gas sensor are: (i) high sensing response, (ii) small recovery time, (iii) selectivity . In the present work, focus has been done on the detection of ammonia (NH3). This is because, NH3 , in gaseous form is a highly harmful to human health, commonly produce as animals and human excreta at home, work places and industries in many ways [3, 4]. The lower limit of NH3 perception by smell by human beings is around 5 ppm, thus, it is important to develop efficient gas sensors which can monitor and detect the low concentration of (smaller than ,5 ppm) NH3 leaks . Researchers have put enormous efforts on designing the highly efficient NH3 gas sensors [6, 7].
Semiconductor metal oxides represent an interesting, and a varied class of materials that are suited for gas sensing applications for several types of gases like oxidizing gases, reducing gases, odorous gases etc.. Amongst the various metal oxides exploited for gas sensing, Zinc Oxide (ZnO) is the most suitable metal oxide for gas sensing applications having diverse semiconducting, piezoelectric and pyroelectric properties . Conducting polymers is a new class of sensing material which have arisen interest in due to good electrical and optical properties . Poly pyrrole (PPy) is mostly exploited material due to highly stable nature at high temperatures and ease in synthesis by using chemical methods . Arora et al. have prepared PPy thin films electrochemically for NH3 sensing in the concentrations of 0.01–1% . Another report is on chemically synthesized Ppy films giving show response values 4–8% and response time of 4 min to detect NH3 gas .
Nanocomposite thin films have found enormous applications in the field of gas sensing due to high sensing response at lower operating temperature and selectivity towards a target gas [13, 14]. Wu et al. have observed the improvement in selectivity towards the target NOx gas by making the nanomposites of ZnO and PPy prepared by the simple method of mechanical mixing . Patil et al. designed a highly sensitive NO2 gas sensor using ZnO and PPy nanocomposite thin films . Wang et al. have proposed a highly novel sensing platform of nanofiber composites of PPy/TiO2-ZnO for detecting a small concentration of NH3 .
Hence, the present manuscript focusses on the development of NH3 gas sensor using the composite thin films of ZnO and PPy by varying its compositional percentage.