An ultrasensitive NO2 gas sensor based on a NiO-SnO2 composite with a sub-ppb detection limit at room temperature

The highly sensitive detection of ppb-level NO2 at room temperature (RT, 25 degrees C) remains a challenge hindering the detection of metal oxides due to their chemical inactivity. Herein, a strategy for constructing mixed metal oxides with high specific surface areas and highly active surfaces is proposed. In this work, we synthesized NiOSnO2 using the solvothermal and calcination methods with Ni/Sn bimetallic organic frameworks (Ni/Sn-BTC MOFs, BTC: benzene-1,3,5-tricarboxylic) as sacrificial templates. The characterization shows that NiO-SnO2 has a high porosity (0.343 m3/g) and a large specific surface area (74.73 m2/g), which can produce abundant permeability pathways for NO2, maximize the number of active sites, and enhance the capacity for NO2 capture. The sensing test results indicate that the NiO-SnO2 sensor exhibits an excellent sensing response of 693.1% (Delta R/ Ra) to 150 ppb NO2, a fast response/recovery time (86.8/29.4 s), a distinct selectivity, a lower detection limit (25 ppb) and good long-term stability at RT and 60% RH (RH: relative humidity). The outstanding sensing performance can be attributed to the microstructure characteristics, oxygen vacancies and p-n heterojunctions formed between NiO and SnO2. The current work provides a versatile platform for designing sensitive materials with heterogeneous structures and opens up a new pathway for the development of room temperature gas sensors based on metal oxide.