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

Abstract

The highly sensitive detection of ppb-level NO2 at room temperature (RT, 25 °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 NiO-SnO2 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% (ΔR/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.