EPR and DRS evidence for NO2 sensing in Al-doped ZnO

Abstract

Abstract Zinc oxide (ZnO) is a well-known semiconducting multifunctional material wherein properties right from the morphology to gas sensitivity can be tailor-made by doping or surface modification. Aluminum (Al)-incorporated porous zinc oxide (Al:ZnO) exhibits good response towards NO 2 at low-operating temperature. The NO 2 gas concentration as low as 20 ppm exhibits S = 17% for 5 wt.% Al-incorporated ZnO. The NO 2 response increases with operating temperature and concentration and reaches to its maximum at 300 °C without any interference from other gases such as SO 3 , HCl, LPG and alcohol. Physico-chemical characterization likes differential thermogravimetric analysis (TG-DTA) electron paramagnetic resonance (EPR) and diffused reflectance spectroscopy (DRS) have been used to understand the sensing behavior for pure and Al-incorporated ZnO. The TG-DTA depicts formation of ZnO phase at 287 °C. The EPR study reveals distinct variation for O − ( g = 2.003) and Zn interstitial ( g = 1.98) defect sites in pure and Al:ZnO. The DRS studies elucidate signature of adsorbed NO x species in aluminium-incorporated zinc oxide indicating its tendency to adsorb these species even at low temperatures. This paper is an attempt to correlate the gas sensing behavior with the physico-chemical studies such as EPR and DRS.