Strategies of realizing NO2 detections with enhanced selectivity and anti-humidity based on snowflake-like in-situ grown ZIF-8/ZnOHF composites

Realizing nitrogen dioxide (NO2) detections based on semiconductor-based gas sensors with high tolerance to humidity conditions is deemed to be a long-term challenge. To independently acknowledge the physisorbed-water influence mechanism on semiconductor-based sensors, hydrophobic zeolitic imidazolate framework-8 (ZIF-8) covered chemisorbed-oxygen-nonexistence zinc hydroxyfluoride (ZnOHF) snowflake-like nanorod bundles are synthesized for NO2 detections with non-hindrance of interfering gases and high humidity in our work. Gas-sensing testing results display that the 0.6ZIF-8/ZnOHF-based gas sensor provides an optimum NO2 response of 12.1 to 10 ppm NO2 at the operating temperature of 200 ℃ with excellent selectivity. As the relative humidity (RH) increases from 20% RH to 80% RH, the response of the 0.6ZIF-8/ZnOHF sensor shows a marginal fluctuation of only 13%, exhibiting outstanding anti-humidity characteristics towards NO2 detections, the outperformed NO2 selectivity and humidity tolerance of which are greatly attributed to the unique band structures of ZnOHF and the surficial hydrophobic treatment by ZIF-8, which is further validated via In-situ diffuse reflection infrared Fourier transform spectroscopy (In-situ DRIFTS) and electronic structure analyses. Humidity impact on ZnOHF poses persuasive evidence for establishing the separate physisorbed water interfering mechanism on semiconductors. This work endows a perspective on optimizing humidity tolerance for semiconductor-based sensors at low operating temperature.