Development of printed semiconducting gas sensors: industrial, medical and environmental applications

Most common metal-oxide semiconductors featuring chemoresistive effect, such as ZnO, SnO2, TiO2, LaFeO3 and WO3 have been considered as functional materials for gas sensors, adopting wet chemical routes for nano-powder preparation. Electrical, structural and morphological characterizations of the corresponding thick films deposited through screen-printing technique, have been examined, also considering their behavior in on-site applications. Among the functional materials, ZnO has been mainly investigated due to its many and various properties, synthesizing several nanostructures. The correlation between the obtained different morphologies and the electrical and spectroscopic behavior has been examined. It turned out that all sensors based onto different nanomorphologies of ZnO are mainly sensitive to acetone, the films constituted of nanoparticle aggregates detecting acetone concentrations down to few tens of ppb. Thereby, these sensors resulted suitable to be used in breath gas analysis for diagnosis of metabolic diseases. A second concrete implementation in industrial framework of the thick film gas sensors has been concerning the monitoring of the hydraulic oil aging. The oil samples have been characterized by means of gas chromatography and of a laboratory system, based on sensors, specifically prepared for this aim. Both characterizations have shown a lower analytes concentration in the more aged samples. It has been therefore highlighted a correlation between the hydraulic oil aging and the composition of their vapors. For this application, oil samples have been also studied through organic electrochemical liquid sensors (developed at IMEM-CNR), again showing the same correlation. Finally, a portable monitoring station based on the aforementioned sensors has been prepared, including electronics for acquisition, processing and wireless transmission of the data. The in-field experiments performed during this work concerned an industrial zone in Ferrara in addition to a monitoring in Naples at monumental site of “Maschio Angioino” leaning out of an arterial road of heavy traffic close to docklands. The comparison performed between the temporal evolution of the conductivity changes of the sensors with the pollutants’ concentrations, as measured by the analytical instruments located in fixed monitoring stations managed by ARPA resulted in good agreement.