NO<sub>2</sub> sensing properties of porous Fe-doped indium oxide

It is of great significance to study the characteristics and working mechanism of NO₂ sensor material for monitoring air pollution and protecting human health. As a metal oxide semiconductor material with simple preparation, low cost and good long-term stability, In₂O₃ has been widely studied in the detection of NO₂. In order to explore the influence of Fe content on the gas sensing properties of porous In₂O₃ material, porous Fe-doped In₂O₃ nanoparticles are synthesized by the hydrothermal method, and the NO₂ sensor is fabricated by using the above nanoparticles. The X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy and specific surface area measurement are used to characterize the micro morphology of the prepared nanoparticles in this paper, while the sensor performance is studied, including temperature, response recovery, selectivity and stability. In most samples, Fe atoms are completely doped into the In₂O₃ lattice as indicated by the XRD results. The SEM results show that the Fe-doped In₂O₃ nanoparticles prepared with Span-40 as activators are square in size of 50–200 nm, and a large number of small pores are distributed in it, which are also observed in the N₂ adsorption/desorption experiment, this is one of the main reasons for the large specific surface area and high sensitivity of the nano materials. Studying the performance of the sensor, we find that when the molar ratio of In∶Fe is 9∶1, the sensor made of porous Fe-doped In₂O₃ nanoparticles has an excellent selectivity and short response recovery time for NO₂ gas. The sensitivity of the sensor to 50-ppm-concentration (1 ppm = 1 mg/L) NO₂ can reach 960.5 at 260 ℃, and the response time and recovery time are 5 s and 6 s respectively. Based on the theory of space charge and the knowledge of built-in barrier and energy band change before and after doping, the mechanism of the sensor is analyzed.