Highly Selective Detection of Benzene and Discrimination of Volatile Aromatic Compounds Using Oxide Chemiresistors with Tunable Rh-TiO₂ Catalytic Overlayers

Volatile aromatic compounds are major air pollutants, and their health impacts should be assessed accurately based on the concentration and composition of gas mixtures. 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 new functionalities such as 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 ppm- and sub-ppm-levels of benzene over a wide range of sensing temperatures (325–425 °C). An array of 0.5Rh-, 1Rh-, and 2Rh-TiO₂/SnO₂ sensors exhibits discrimination and composition analyses of aromatic compounds. The conversion of gases into more active species at moderate catalytic activation and the complete oxidation of gases into non-reactive forms by excessive catalytic promotion 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. Although the sensing characteristics exhibit mild moisture interference, bilayer sensors with systematic and tailored control of gas selectivity and response provide new pathways for monitoring aromatic air pollutants and evaluating their health impacts.