Ethanol is widely present in various atmospheres and is the main interfering factor affecting the performance of gas sensors in a wide range of practical applications such as indoor air monitoring, breath analysis, and food freshness monitoring. In fact, most modern gas sensors (such as metal oxides, graphene, carbon nanotubes, and sulfides) are sensitive to ethanol because ethanol has high reactivity in gas sensing reactions. In addition, the concentration of ethanol is usually higher than the concentration of the target gas. Therefore, there is an urgent need for a sensing strategy that can completely eliminate ethanol interference. Significant efforts have been made to mitigate the interference of ethanol gas by doping/loading precious metal or oxide catalysts, adjusting operating temperatures, forming heterogeneous composite materials, and using catalytic filters (Pt loaded Al2O3, WO3 packed bed, Co3O4, SnO2, TiO2, Rh/TiO2, and Au catalytic coating) before using gas sensitive thin films. However, for new applications and high-performance gas sensors, the amount of sensor signals unrelated to ethanol and detectable analyte gases generated through catalytic oxidation are still limited and insufficient. In addition, catalytic oxidation not only reduces the response to ethanol, but also simultaneously reduces the response to the target gas, thereby reducing the selectivity and sensitivity of the analyte to ethanol. Therefore, it is necessary to explore catalytic control strategies from a new perspective, rather than simply using oxide or precious metal catalysts to catalyze the oxidation of ethanol.  

For highly reactive oxidation sensing reactions, selectivity becomes particularly important when detecting small gas molecules containing small amounts of C and H species. For example, as humans spend most of their time indoors, selective detection of sub ppm levels of formaldehyde (HCHO) is crucial for monitoring indoor air quality. HCHO is a potential carcinogen. HCHO is known to come from wooden furniture, paint, and interior decoration materials (such as adhesives). In addition, due to its health risks, the World Health Organization (WHO) has developed guidelines for indoor formaldehyde exposure (80 ppb). Therefore, accurate real-time detection of HCHO is crucial for humans. However, oxide chemical resistance typically exhibits non discriminatory response to ubiquitous ethanol, which may lead to HCHO sensor failure. To overcome this limitation, it has been considered to use molecular sieves to physically filter ethanol molecules with larger kinetic diameters from analyte gases with smaller molecular sizes. However, most gas sensors utilizing molecular sieve layers exhibit low response and slow sensing kinetics towards analyte gases, due to the obstruction of diffusion of analyte gases from the upper part of the sensing layer to the lower part near the sensing electrode. Therefore, using oxide chemical resistance to detect analyte gases with high selectivity, sensitivity, and rapidity in the presence of ethanol remains a challenging task.

Source: Sensor Expert Network