Developing new chemical-based sensors for the detection of volatile compounds

This research project aims to enhance the performance of a series of chemical-based sensor devices. In particular, metal oxide gas sensors. These materials are well known and primarily employed in several applications, thanks to their characteristic of interacting with volatile compounds, giving a response in terms of reversible change in the electrical resistance. Another exciting feature of metal oxide semiconductors, in particular rare earth-dope ones, is represented by their cataluminescence (a type of light emission when they interact with certain volatile compounds). We attempt to register simultaneously and combine the two different sensor responses (electrical resistance and light emission) to enhance sensor sensitivity and selectivity. This mode of operation can be defined as "dual-modality", and it represents a novel approach to sensor technology.For this purpose, the first part of the research project involved the synthesis and the characterisation of metal oxide nanoparticles to be employed in the sensing experiments. Afterwards, the materials obtained were used as sensing elements in in-house made equipment, recording the electrical resistance and the cataluminescence simultaneously. We tested each material under investigation with the following volatile compounds: acetone, ethanol, hydrogen peroxide, nitroglycerine, ethylene glycol dinitrate, 2,3-dimethyl-2,3-dinitrobutane, 2,4-dinitrotoluene and triacetone triperoxide. The experiments were repeated at different sensor temperatures in the range of 150-400°C. These ensured a full screening of the operating conditions and, consequently, the possibility of identifying the best parameters to ensure optimal sensor performance.The results obtained are encouraging in terms of sensor performances. In particular, the europium-doping of the zirconium oxide gas sensor allowed achieving a higher cataluminescence production, especially in the temperature range 250-275°C, and consequently a better sensor sensitivity. Recording the light emission simultaneously with the resistance response was shown to be very promising in terms of selectivity. If two given compounds showed a similar response in terms of resistance, discrimination is still possible thanks to their different cataluminescence response profiles.This thesis work showed for the first time and promisingly the possibility of combining more than one response from a single sensor to enhance its performance. We found out that the dual-modality can increase the sensor's possibility to distinguish among different volatiles. Especially the doping with rare earth metals, such as europium, increased the general response and consequently, they represent a promising material for the employment of dual-modality sensing