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Undoped and fluorine (F)-doped nanostructured zinc oxide (ZnO) thin films were deposited over glass substrates by spray pyrolysis technique using zinc acetate dihydrate with and without ammonium fluoride as dopant in precursor solution respectively. The deposition conditions and the concentration of the dopant were optimized to obtain nanostructured ZnO thin films. The film obtained from 0.05 M of zinc acetate aqueous solution and 20% F sprayed at the rate of 3 ml/min on preheated substrate kept at 503 K yielded spherical shape well-connected grains, which has large surface to volume ratio. The structural and morphological studies of the films were investigated by using X-ray diffraction (XRD) and scanning electron microscope (SEM) respectively. The diffraction peak positions in XRD confirmed the formation of highly crystalline ZnO film with hexagonal wurtzite phase. Further sensing behavior of the films towards various concentrations of volatile organic compounds (VOCs) such as ethanol and trimethyl amine (TMA) has been investigated at an optimized operating temperature of 373 K and reported.

In this paper, a hybrid electronic noses' system (HENS) based on MOS-SAW detection units intended for lung cancer diagnosis is proposed. The MOS gas sensors are used to detect the VOC molecules with low molecular weight (LMW), and the SAW sensors are adopted for the detection of VOC with high molecular weight (HMW). Thus, the novel combination of these two kinds of gas sensors provides higher sensitivities to more of VOC species in breath than that of using only a single kind of sensor. The signals from MOS-SAW detection units are then recognized by a multi-model diagnosis method. Applying four algorithms, six models were established for diagnosis and tested by leave-one-out cross-validation method. The model by artificial neural network (ANN) was selected as the best model to analyze breath samples. 89 clinical samples were tested with MOS-SAW ANN diagnostic model, which takes the features derived from both the MOS and SAW sensors. It shows the highest sensitivity of 93.62%, and the highest selectivity of 83.37%. The study shows that, promisingly, our HENS is effective during screening of lung cancer patients, especially among the people of high risk.

The effective utilisation of solar radiation requires the development of novel photocatalysts activated by visible-light. Activity tests of toluene decomposition were carried out in the presence of modified titanium dioxide photocatalysts in which some oxygen ions were substituted by sulfur. The elimination of toluene after 1 hour irradiation of the photocatalysts by a pulsed blue LED yielded 44 percent elimination. Pretreatment in which S-doped TiO₂ was irradiated by UV for 1 hour prior to the activity test was effective in decomposing acetaldehyde, even under a pulsed green LED irradiation.

Dielectric barrier discharge plasma was used to oxidize trichloroethylene (TCE) in 21% of O₂ in carriers of N₂ and He. The degradation products of TCE were analyzed using gas chromatography mass spectrometry. TCE was decomposed completely at optimum energy density of 260 and 300 J/l for He and N₂, respectively and its conversion followed zero order reaction. The TCE removal efficiency is decreased in humid air due to interception of reactive intermediates by OH radicals.

Tropospheric ozone (O₃) is nowadays recognized as the most important widespread air pollutant, deteriorating materials and causing adverse effects to living organisms. It occurs at levels potentially phytotoxic, thus influencing cultivated plants and natural ecosystems. In this chapter, we describe the mechanisms of O₃ formation in the stratosphere and the troposphere, its spatial (longitudinal and latitudinal) distribution, its trends, as well as the diurnal and seasonal patterns of its concentrations. Furthermore, the role of plants as indirect “sources” (through the biogenic volatile organic compounds emissions) and “sinks” (through wet and dry deposition) are discussed.

This chapter aims to illustrate the research that was conducted in Portugal or in collaboration with Portuguese research groups in the 2011–2022 period on the oxidative conversion of volatile organic compounds (VOCs) to useful building blocks. It concerns the selective oxidation under mild catalytic oxidations of some VOCs (toluene, xylene, ethylbenzene, styrene and n-hexane), which are hazardous to human health and the environment. Both homogeneous and heterogeneous catalysts are discussed.