Semiconducting Oxide Gas Sensors: from Powder Design to Monitoring Devices in Real Applications

Gas sensors are essential in many areas, from environmental monitoring to quality and safety control of industrial processes, food and healthcare. Those based on metal oxides semiconductor (MOX) provide a versatile solution to detect many different gases with low costs, small dimensions, easy to install and use. On the other hand, sensor performances depend on many factors, first of all the selection and the design of the nanostructured functional material. The most used oxides are SnO2, TiO2, ZnO and WO3, although many strategies could be introduced to increase sensing performances of the functional materials such as the use of solid solutions characterized by higher performances with respect to the single oxides. The system TixSn1-xO2, with Ti molar ratio x = 0.1, 0.2, 0.25, 0.3, 0.5, 0.7, 0.9), is very attractive because the two pristine oxides, SnO2 and TiO2, show several similarities in crystalline structure as well as in electronic properties and thus can easily form a solid solution. On the other hand, they exhibit some differences, such as electrical transport properties and gas sensing behavior. This work represents a complete study in the field of MOX gas sensing. It starts from the design of the sensitive material, then the study of their properties from a fundamental point of view, concluding with two real successful real applications (CO detection in air quality monitoring and analytes concentrations monitoring in hydraulic fluid headspace).