(Ti,Sn) Solid Solution Based Gas Sensors for New Monitoring of Hydraulic Oil Degradation

TiO2-Based Nanostructures, Composites and Hybrid Photocatalysts

The field of materials sciences has always been strongly interconnected with the most significant technological developments in the modern era, and such an interconnection is absolutely evident at least since the 1950s revolution of electronics and microelectronics, driven by advances in the science of semiconductors [...].

Optical Sensing of Molecular Oxygen (O2) via Metal Oxide Photoluminescence: A Comparative Study of TiO2, SnO2 and ZnO

A comparative study is presented on the photoluminescence (PL) response toward molecular oxygen (O2) in tin dioxide (SnO2), zinc oxide (ZnO) and titanium dioxide (TiO2) nanoparticles. The findings show that both PL enhancement and PL quenching can be observed on different materials, arguably depending on the spatial localization of the defects responsible for the PL emission in each different oxide. No significant results are evidenced for SnO2 nanoparticles. ZnO with red/orange emission shown an O2-induced PL enhancement, suggesting that the radiative emission involves holes trapped in surface vacancy oxygen centers. While the ZnO results are scientifically interesting, its performances are inferior to the ones shown by TiO2, which exhibits the most interesting response in terms of sensitivity and versatility of the response. In particular, O2 concentrations in the range of few percent and in the range of a few tenths of a part per million are both detectable through the same mixed-phase TiO2 sample, whose rutile phase gives a reversible and fast response to larger (0.4–2%) O2 concentration while its anatase phase is usable for detection in the 25–75 ppm range. The data for rutile TiO2 suggest that its surfaces host deeply trapped electrons at large densities, allowing good sensitivities and, more notably, a relatively unsaturated response at large concentrations. Future work is expected to improve the understanding and modeling of the photophysical framework that lies behind the observations.

Growth Mechanisms of ZnO Micro-Nanomorphologies and Their Role in Enhancing Gas Sensing Properties

Zinc oxide (ZnO) is one of the main functional materials used to realize chemiresistive gas sensors. In addition, ZnO can be grown through many different methods obtaining the widest family of unique morphologies. However, the relationship between the ZnO morphologies and their gas sensing properties needs more detailed investigations, also with the aim to improve the sensor performances. In this work, seven nanoforms (such as leaves, bisphenoids, flowers, needles, etc.) were prepared through simple wet chemical synthesis. Morphological and structural characterizations were performed to figure out their growth mechanisms. Then, the obtained powders were deposited through screen-printing technique to realize thick film gas sensors. The gas sensing behavior was tested toward some traditional target gases and some volatile organic compounds (acetone, acetaldehyde, etc.) and compared with ZnO morphologies. Results showed a direct correlation between the sensors responses and the powders features (morphology and size), which depend on the specific synthesis process. The sensors can be divided in two behavioral classes, following the two main morphology kinds: aggregates of nanocrystals (leaves and bisphenoids), exhibiting best performances versus all tested gases and monocrystal based (stars, needle, long needles, flowers, and prisms).