No abstract

No abstract

No abstract

No abstract

No abstract

Among the various chemoresistive gas sensing properties studied so far, the sensing response reproducibility, i.e., the capability to reproduce a device with the same sensing performance, has been poorly investigated. However, the reproducibility of the gas sensing performance is of fundamental importance for the employment of these devices in on-field applications, and to demonstrate the reliability of the process development. This sensor property became crucial for the preparation of medical diagnostic tools, in which the use of specific chemoresistive gas sensors along with a dedicated algorithm can be used for screening diseases. In this work, the reproducibility of SmFeO3 perovskite-based gas sensors has been investigated. A set of four SmFeO3 devices, obtained from the same screen-printing deposition, have been tested in laboratory with both controlled concentrations of CO and biological fecal samples. The fecal samples tested were employed in the clinical validation protocol of a prototype for non-invasive colorectal cancer prescreening. Sensors showed a high reproducibility degree, with an error lower than 2% of the response value for the test with CO and lower than 6% for fecal samples. Finally, the reproducibility of the SmFeO3 sensor response and recovery times for fecal samples was also evaluated.

The crystalline growth kinetics during isothermal sintering of two nanotitania powders synthesized by similar routes, but with and without the presence of chlorine in the synthesis batch) were studied by X-ray powder diffraction and modelled by several grain growth models. Both nanopowders contained anatase as the initial titania phase with similar crystallite dimension. Crystal growth curves at three isotherms per each samples were sampled over a period of time up to 40 h. Temperature steps within different ranges (375, 425, and 475 °C for Cl-free sample; 500, 550, and 600 °C for Cl-containing sample) were chosen. The XRD analysis of samples heated at 900°C revealed that, while the entire Cl-free sample was converted to rutile, only 10% of the Cl-containing sample had transformed to rutile with a very limited crystal growth. Direct comparison of the crystal growth curves show different behaviour which was modelled by different grain growth kinetic equations which include a growth limiting factor. Although the generalized parabolic grain growth model with time-exponent (so called "Höfler-Averback equation") provided good fits for both the Cl-free and Cl-containing nanopowders at all temperature, only the isothermal curve at 500°C of the Cl-containing sample was satisfactorily fitted with a modified KJMA equation. The activation energy of the grain growth are very similar and in line with the previously reported values. We conclude that the crystal size locking phenomenon observed for Cl-bearing anatase can be ascribed to the effects of chlorine ions adsorbed on grain surface as previously suggested. The blocked crystal growth of nanoanatase obtained by the reflux synthesis of organic solvents in the presence of hydrochloric acid as catalyst makes this material very appealing for devices that require a given nanosize and for anatase phase in spite of the high temperature processing.

A deepened investigation on an innovative organic-inorganic hybrid material, referred to as ECS-14 (where ECS = Eni carbon silicates), revealed the possibility to use them as gas sensors. Indeed, among ECS phases, the crystalline state and the hexagonal microplateletlike morphology characteristic of ECS-14 seemed favorable properties to obtain continuous and uniform films. ECS-14 phase was used as functional material in screen-printable compositions and was thus deposited by drop coating for morphological, structural, thermal, and electrical characterizations. Possible operation at room temperature was investigated as technological progress, offering intrinsic safety in sensors working in harsh or industrial environments and avoiding high power consumption of most common sensors based on metal oxide semiconductors. Electrical characterization of the sensors based on ECS-14 versus concentrations of gaseous analytes gave significant results at room temperature in the presence of humidity, thereby demonstrating fundamental properties for a good quality sensor (speed, reversibility, and selectivity) that make them competitive with respect to systems currently in use. Remarkably, we observed functionality reversal of the organic and inorganic components; that is, in contrast to other hybrids, for ECS-14 the functional site has been ascribed to the inorganic phase while the organic component provided structural stability to the material. The sensing mechanism for humidity was also investigated.