Sol-Gel Films containing Metal and Semiconductor Nanoparticles for Gas Sensing

Nanotechnology is an exciting modern research field encompassing the traditionally specialist disciplines of chemistry, physics and engineering. Optics and catalysis are two areas of application that will continue to benefit from the recent improvements in control of materials morphology at the nano-scale. The work presented in this thesis is focussed on the application of the Sol-Gel technique in the realization of thin inorganic layers containing metal and semiconductor nanoparticles that are capable of reversibly of detecting gas phase analytes. Three synthetic approaches were adopted, each of them characterized by a systematic increase of the final materials morphology, structure and micro-structure control. This materials engineering was essential in order for nanocomposites with the desired optical and chemical properties applicable to gas sensing devices to be obtained. The synthesized layers comprised of an inorganic porous matrix (SiO2, TiO2 and NiO) containing nanosized metal (Au, Pt) or semiconductor crystals (NiO), and were shown to be active materials for chemical recognition of H2 and CO. The films were readily deposited onto different sensing supports, leading to successful gas detection via optical, conductometric and surface acoustic wave interfaces. SiO2-NiO-Au systems are capable to selectively detect H2 using an optical interface thanks to a marked wavelength dependence of its sensitivity toward this specie. However, if a peculiar NiO-Au morphology is obtained inside the SiO2 support CO is more likely to be detected. TiO2-Au thin films are shown to be excellent conductometric sensors for H2 detection, and ideal gas-sensing dynamics have been observed in this case. This class of layers demonstrated to be effective also for H2 detection through a Surface Acoustic Wave (SAW) interface. Monolayers of Au nanoparticles covered by a thin NiO layer showed promising sensing dynamics in the optical recognition of H2. In this case the material synthesis allows for a detailed control of the single nanocomposite constituents, thus opening the possibility for a finer tuning of the sensor sensitivity.