Designing Bilayer Oxide Chemiresistors Consisting of Rh Nanoparticle Loaded TiO₂ Catalytic Overalyer ans SnO₂ Sensing Layer for Highly Selective and Sensitive Detection of Volatile Aromatic Compounds

Oxide chemiresistors have mostly been used to detect reactive gases such as ethanol, acetone, formaldehyde, nitric dioxide, and carbon monoxide. However, the selective and sensitive detection of volatile aromatic compounds such as benzene, toluene, and xylene (BTX), which are extremely toxic and harmful, using oxide chemiresistors remains challenging because of the molecular stability of benzene rings containing chemicals. Moreover, the performance of the sensing materials is insufficient to detect trace concentration levels of BTX, which lead to harmful effects on human beings. Herein, novel bilayer sensors consisting of a SnO2 sensing layer and three different xRh-TiO2 catalytic overlayers (x = 0.5, 1, and 2 wt%) are designed for the selective detection, discrimination, and analysis of benzene, toluene, and p-xylene. The 2Rh-TiO2/SnO2 bilayer sensor shows a high selectivity and response toward trace concentration of benzene over a wide range of sensing temperatures. An array of three Rh-TiO2/SnO2 sensors can quantitatively discriminate aromatic compounds. The conversion of gases into more active species by gas reforming or into non-reactive forms by excessive catalytic promotion through the reaction with volatile armatic compoudns and nanosize noble metal catalysts are proposed as the reasons behind the enhancement and suppression of analyte gases, respectively. Analysis using proton transfer reaction-quadrupole mass spectrometer (PTR-QMS) is performed to verify the above proposals.