Nanostructured Catalytic Filter-Assisted Nanotube Array Sensor for Selective NO2 Detection.

NO2 detection is crucial for protecting the public health and understanding atmospheric chemistry. SnO2-based chemiresistive NO2 gas sensors inherently suffer from poor selectivity because of their inherent non-specific adsorption. While bilayer catalytic filters have improved selectivity for decades, signal crosstalk from the top catalytic filter remains a fundamental limitation. To overcome this, we developed a porous alumina membrane-based nanotube array gas sensor with a vertical top-bottom signal electrode structure. An in situ grown reticulate ZnO nanosheet filter was integrated on the sensor surface. This design provides high catalytic activity while the top-bottom signal electrode configuration effectively insulates the sensing element from the filter-induced signal interference. As a result, the ZnO nanosheet filter-assisted sensor achieves excellent selectivity for NO2, exhibiting negligible responses to ethanol, formaldehyde, toluene, CO, NH3, and NO. The sensor demonstrates high sensitivity (815% to 1 ppm NO2) with the theoretical detection limit of 1.86 ppb (in dry air) at 250 °C. Moreover, the interference of humidity on the sensing response is remarkably inhibited by the ZnO nanosheet filter. Meanwhile, the sensor shows comparable accuracy with a commercial electrochemical (EC) NO2 sensor module. In addition, we demonstrated the sensor's potential miniaturization and mass production using a highly compatible lithography process, resulting in the sensor size down to 10 μm.