Development of high sensitivity ethanol gas sensor based on Co-doped SnO2 nanoparticles by microwave irradiation technique

We have successfully synthesized Co doped SnO2 nanoparticles by a simple microwave irradiation technique. Powder X-ray diffraction results reveal that the SnO2 doped with cobalt concentration from 0 to 5 wt % crystallizes in tetragonal rutile-type structure. The products were annealed at 600 °C for 5 h in ambient atmosphere in order to improve crystallinity and structural perfection. Transmission electron microscopy (TEM) studies illustrate that both the undoped and Co doped SnO2 crystallites form in spherical shapes with an average diameter of 30–15 nm, which is in good agreement with the average crystallite sizes calculated by Scherrerʹs formula. A considerable red shift in the absorbing band edge was observed with increasing of Co content (0–5 wt %) by using UV–Vis diffuse reflectance spectroscopy (DRS). Oxygen-vacancies, tin interstitial and structural defects were analyzed using photoluminescence (PL) spectroscopy. Electron paramagnetic resonance (EPR) spectroscopic studies clearly showed that the Co2+ was incorporated into the SnO2 host lattice. Ethanol gas sensitivity of pure and Co-doped (5 wt %) SnO2 nanoparticles were experimented at ambient temperature using optical fiber based on clad-modified method. By modifying the clad exposure to ethanol vapor, the sensitivities were estimated to be 18 and 30 counts/100 ppm for undoped and Co-doped SnO2 nanoparticles, respectively. These results show that the Co doping into SnO2 enhances its ethanol gas sensitivity significantly.