Semiconductor sensors are widely used in gas monitoring of living and industrial environment in the Internet of Things, but humidity interference affects the detection accuracy. The virtual array is proposed as a novel measurement method. It has the advantages of humidity suppression, low-power consumption, and simple structure, which is conducive to further research and development of intelligent sensing device with integrated sensing, memory, and computing in the Internet of Things. This method adopts the heating mode of cyclic variable temperature and extracts the stable conductance values at different temperatures as the response. In the design of a virtual array, the response difference between reducing gas and humidity at different temperatures is used to overcome humidity interference. The output information is expanded from the perspective of measurement so that the humidity interference quantity is characterized simultaneously. Cyclic variable heating voltage is applied to the sensor to obtain the response value under different heating conditions. The response values under high and low levels are displayed as coordinates in the 2-D plane. Samples with reducing gas and humidity are satisfied by the law of the approximate vector sum of their one-component responses. This method was not only confirmed in the main experiment of toluene detection but also in the detection of butanone and the detection of toluene by multiple sensors.

Ammonia is harmful to human health, however, the detection limit of the sensor based on traditional semiconductor gas sensors is high and the speed is slow. Constructing heterostructure is an effective method to improve the performance of sensors. In this article, 1-D MoO ₃ nanorods and SnO ₂ nanoparticles are successfully combined to obtain MoO ₃ /SnO ₂ nanocomposite. The 1-D structure can increase the speed of electron transport, while the nanoparticles on the surface increase the specific surface area, more importantly, the structure maximizes the interface area between the two materials which can transfer electronic more efficiently. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), energy dispersive spectrometer (EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), and Barrett–Joyner–Halenda (BJH) are used to analyze the microstructure and elemental composition of MoO ₃ /SnO ₂ . The diameter of MoO ₃ /SnO ₂ nanocomposite is approximately 200 nm and the distribution is uniform. The response of MoO ₃ /SnO ₂ nanocomposite to 100-ppm NH ₃ is 12.7 at 280 °C, and the response/recovery time is 13/2 s. The detection limit for NH ₃ can reach 10 ppb (response 1.3), which enables rapid detection of NH ₃ at low concentration. Electron transport requires more energy to overcome the contact barrier between pure SnO ₂ nanoparticles, which can also lead to electron emission and noise increase. However, the sensitive electrons of MoO ₃ /SnO ₂ nanocomposite can transmit electrons along the 1-D rod-like structure of MoO ₃ , which undoubtedly accelerates the efficiency of electron transmission. Moreover, n-n heterojunction formed between MoO ₃ and SnO ₂ to bend the SnO ₂ band and show better sensitivity to NH ₃ . Therefore, MoO ₃ /SnO ₂ nanocomposite shows a low detection limit and a rapid response/recovery speed. Nevertheless, the nanoparticles on the surface of MoO ₃ /SnO ₂ nanocomposite begin to agglomerate with the increase of SnO ₂ content, which leads to the decrease of gas-sensitive response. The formation process of MoO ₃ /SnO ₂ composites is also discussed in this article. The excellent gas sensing results show that MoO ₃ /SnO ₂ composites are a promising gas sensing material.

Triethylamine is a toxic gas that strongly stimulates the respiratory tract, resulting in even death after inhalation. However, conventional gas sensors can not detect the ppb levels of triethylamine gas and can not achieve the purpose of environmental detection in life. Therefore, developing ppb-level triethylamine gas sensors is indispensable. In this article, rGO/In ₂ O ₃ /Pd nanocomposites were prepared by the one-step hydrothermal method. The morphology and structure were fully characterized by transmission electron microscopy etc., which demonstrated that the microstructure of palladium nanoparticles modified flower-like In ₂ O ₃ grown on rGO nanosheets was successfully synthesized. The gas sensor based on rGO/In ₂ O ₃ /Pd nanocomposites was then tested for its gas sensitivity. According to the experimental data, the sensitivity of rGO/In ₂ O ₃ /Pd to triethylamine gas was better than that of pure In ₂ O ₃ , In ₂ O ₃ /Pd, and rGO/In ₂ O ₃ , and the optimal working temperature of rGO/In ₂ O ₃ /Pd to triethylamine was 175. Besides, the gas sensor based on rGO/In ₂ O ₃ /Pd could detect 1 ppb triethylamine. The response value of rGO/In ₂ O ₃ /Pd to 1 ppb triethylamine at the optimal working temperature can reach 1.27. Finally, the gas sensitivity mechanism of the rGO/In ₂ O ₃ /Pd composite was analyzed.

Perovskite LaFeO ₃ materials have received increasing attention in volatile organic compound (VOC) gas detection due to their unique crystal structure and excellent physicochemical properties. However, achieving high sensitivity with a low limit of detection at low temperature is still an important research topic. In this work, p-LaFeO ₃ /n-Fe ₂ O ₃ composites were prepared by a simple one-step hydrothermal method for the detection of acetone gas. Various characterizations showed that the LaFeO ₃ /Fe ₂ O ₃ composites were successfully synthesized. The test results showed that the LaFeO ₃ /Fe ₂ O ₃ composites have more excellent gas sensing properties than acetone compared with pure LaFeO ₃ material. The response of the LaFeO ₃ /Fe ₂ O ₃ sensor to 10 ppm acetone (23.5) at 210 °C is almost five times larger than that of the pure LaFeO ₃ material. In addition, the LaFeO ₃ /Fe ₂ O ₃ sensor has a low limit of detection (100 ppb), good long-term stability, and selectivity. The enhanced acetone sensing performance can be ascribed to changes in the electronic structure and surface properties caused by heterojunctions, as well as to the synergistic effect formed between the two components. This work provides a simple synthetic strategy to enhance the acetone gas sensing performance of perovskite-type LaFeO ₃ , which has promising applications in industrial production and healthcare.

This study synthesizes Ni-doped perovskite-structured LaFeO₃ composite materials via a one-step hydrothermal method, characterizes the morphology and structure of the materials, and tests their gas sensing performance. The test results show that compared to pure LaFeO₃ material, the gas sensing performance of Ni-doped LaFeO₃ material is improved in all aspects. Specifically, LFO-Ni2% exhibits a response as high as 102 towards 100 ppm of triethylamine at 190 °C, along with better selectivity and stability. Furthermore, the gas sensing mechanism is investigated. On one hand, doping with an appropriate proportion of Ni can lead to the formation of more-complete and smaller-sized microsphere structures with pores. This is beneficial for the adsorption of oxygen from the air onto the material surface, as well as for the diffusion of the target gas to the surface of the material, thereby enhancing gas sensitivity performance. On the other hand, the doped Ni enters the interior of the LaFeO₃ crystal, replacing some of the cations in LaFeO₃, increasing the concentration of charge carriers in the material, and reducing the material’s resistance. The sample can adsorb more oxygen, promoting the reaction between adsorbed oxygen and the target gas, and thereby improving the gas sensitivity performance of the sample.