Synergistic Effect of Metal–Organic Frameworks and Metal Oxides for Ultrasensitive and ppb-Level NO ₂ Detection at High Humidity

Efficient NO₂ gas sensors are critical for environmental monitoring and industrial safety. However, the design of reliable NO₂ sensing materials with high activity and moisture resistance remains a challenge, primarily due to limited active sites and interference from high air humidity. In this paper, SnO₂/ZIF-8 nanocomposites were prepared by leveraging the inherent moisture resistance and abundant active sites of ZIF-8 nanoparticles, as well as the good electronic migration capabilities of SnO₂ nanospheres. The synergistic effect between metal-organic frameworks and metal oxides enables the gas sensor to show an impressive response (Rg/Ra = 85.95) to 1 ppm of NO₂ even in high-humidity conditions, with good selectivity. Additionally, the SnO₂/ZIF-8 composite-based chemiresistive sensors exhibit a low limitation of detection (11 ppb), fast response/recovery time (57/75 s), and excellent long-term stability (over 35 days), rendering them highly suitable for practical NO₂ detection. Density functional theory (DFT) calculations have demonstrated that the loading of ZIF-8 nanoparticles can enhance the adsorption effect as well as promote charge transfer between NO₂ molecules and the SnO₂ nanospheres. The synthesis of this composite material provides new ideas for improving the detection ability of NO₂ at high humidity.