The detection of VOCs in indoor air is investigated by the production of semiconducting metal oxides and mixed metal oxide sensors. Titania, titania borate mixed metal oxides and ceria were successfully synthesized using reverse micelle sol gel synthesis and characterised using scanning electron microscopy coupled with energy dispersive x-ray analysis (SEM-EDAX), x-ray diffraction (XRD), thermogravimetric analysis (TGA) and thermal elemental analysis. The sol-gel structures are utilised due to their formation of characteristically uniform and porous materials that have a high surface area. The XRD results revealed that the titania when calcined under air, has two phase changes from an
amorphous phase to the anatase phase and from the anatase phase to the rutile phase. The samples calcined under nitrogen showed a phase change from amorphous to anatase and then at higher temperatures, 1200 °C, a phase change to an unexpected material; titanium carbide. The XRD results showed that ceria, when calcined under air, showed a cubic system, specifically a fluorite structure in which the crystallinity increased with the calcination temperature.
Titania and titania borate mixed metal oxides were then dip coated onto sensor
elements to produce thin films which were successfully used in preliminary experiments to detect a range of volatile analytes; acetone, ethanol, methanol, propanol, toluene, and cyclohexane. Responses were immediate and to most analytes the response was large. Based on the results obtained it is thought, with further investigation of the responses of specific sensor surfaces to specific analytes, an array could be produced that with the help of pattern recognition software, would allow the determination of specific analytes from the responses of a number of sensor surfaces.