| Summary: | The nanometer size Cu<sub>2</sub>O@WO<sub>3</sub>·H<sub>2</sub>O composite material has been prepared by the direct hydrolysis of mesitylcopper (I) on WO<sub>3</sub>·2H<sub>2</sub>O nanoleaves. The synthesis has been performed in toluene without the addition of any ancillary ligands. The prepared nanocomposite has been deposited as a gas-sensitive layer on miniaturized silicon devices and heated up gradually to 500 °C in the ambient air. During the heating, the CuWO<sub>4</sub> phase is formed upon the reaction of Cu<sub>2</sub>O with the WO<sub>3</sub> support as revealed by the XRD analyses. The as-prepared CuWO<sub>4</sub>@WO<sub>3</sub> sensors have been exposed to 10 ppm of CO or 0.4 ppm of NO<sub>2</sub> (RH = 50%). At the operating temperature of 445 °C, a normalized response of 620% towards NO<sub>2</sub> is obtained whereas the response to CO is significantly lower (S = 30%). Under these conditions, the sensors prepared either with pristine CuO or WO<sub>3</sub> nanostructures are sensitive to only one of the two investigated gases, i.e., CO and NO<sub>2</sub>, respectively. Interestingly, when the CuWO<sub>4</sub>@WO<sub>3</sub> sensitive layer is exposed to UV light emitted from a 365 nm Schottky diode, its sensitivity towards CO vanishes whereas the response towards NO<sub>2</sub> remains high. Thus, the application of UV illumination allowed us to modify the selectivity of the device. This new nanocomposite sensor is a versatile sensitive layer that will be integrated into a gas sensor array dedicated to electronic nose platforms.
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