Effect of Doping at TiO2-Nanotubular Gas Sensors

Abstract

Last years, atmospheric pollution in urban areas has achieved to critical levels. Processes involving combustion in airplane, energy, power production and automobile engines or industrial settlement are the main source of the pollution. In order to determine the gas emission, developments on chemical gas sensors have increased to remarkable levels in the last decades . It is known that oxides of the transition metals like like SnO2, TiO2, WO3, MoO3, Ga2O3 and Nb2O5 were using such a chemical gas sensors due to their electrochemical properties . TiO2 has excellent chemical stability, semi-conductive properties, non-toxicity and low cost hence it is one of the most important transition metal oxides . For high-temperature sensitivity, better stability or efficiency, TiO2 based gas sensors still need improvements. One of the methods to improve the performance of the TiO2-based gas sensor devices is increase the surface area by structuring of sensors. When a gas species such as oxidizing or reducing gas reaches the semi-conductive metal oxide surface, a reaction occurs on the surface. Thus, the more surface area the metal oxide has, the more reactions on the surface the metal oxide has. Second solution for higher efficiency, selectivity or sensitivity of the TiO2-based gas sensor devices is doping of TiO2 with other elements such as Cr-doping of TiO2. It is known that Cr doping in to the TiO2 causes a change in semi-conductivity properties. These changes improve the NO2-gas sensing activity of TiO2-based gas sensors .