Metal–Organic Framework-Derived Ni-Doped Indium Oxide Nanorods for Parts per Billion-Level Nitrogen Dioxide Gas Sensing at High Humidity

Detecting parts per billion (ppb)-level nitrogen dioxide in high-moisture environments at room temperature without reducing sensing performance is a well-recognized significant challenge for metal oxide-based gas sensors. In this study, metal-organic framework-derived nickel-doped indium oxide (Ni-doped In₂O₃) mesoporous nanorods were prepared by a solvothermal method combined with the calcination process. The sensors prepared using the obtained Ni-doped In₂O₃ nanorods showcase an ultrahigh response, low detection limit, and excellent selectivity. Moreover, the abundant active sites triggered by nickel doping and the capillary enhancement effect caused by mesopores endow the sensor with ppb-level (20 ppb) NO₂ detection capability in high-moisture environments (95% RH) at room temperature. With the increase in humidity, the carrier concentration of the sensor increases, and the nitric acid generated by nitrogen dioxide dissolved in water can be completely ionized in water and has high conductivity. Therefore, the gas response of the sensors increases with the increase in humidity. This study establishes a promising approach for the development of trace nitrogen dioxide-sensing devices that are resilient in high-humidity environments.