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NO 2 is an oxidizing gas, which is considered to be the most dangerous and most toxic gas that should be controlled. Because of the advantages of high sensitivity, selectivity, stability and fast response/recovery speed, the chemical resistance sensor is used as a NO 2 gas sensor. This article reviews the NO 2 gas sensor based on metal oxides. Firstly, the hazards of NO 2 and the major disadvantages of chemiresistive sensors based on metal oxides were discussed. Then, different sensitive materials of chemical resistance sensors were discussed, including metal oxides (MO), conductive polymers and carbon-based materials. Finally, the NO 2 gas sensors based on metal oxide (including ZnO, NiO, CuO, SnO 2 , WO 3) were discussed from the aspects of morphology, preparation method, modification, doping and composite. [ABSTRACT FROM AUTHOR]

Here, we reported the synthesis of pure CoSn(OH) 6 and Fe-doped CoSn(OH) 6 nanocubes for gas sensing application by hydrothermal method. The extensive characterizations determined the crystal structure, morphology and chemical composition of the samples, such as, XRD, SEM, XPS, etc. Compared with the pure CoSn(OH) 6 , the gas sensing performance of 5Fe-CoSn(OH) 6 to N-butyl alcohol is improved significantly. The 5Fe-CoSn(OH) 6 based sensor presented high gas response of 60.309 toward 30 ppm N-butyl alcohol at relatively low operating temperature of 200 °C. Moreover, the 5Fe-CoSn(OH) 6 based sensor also exhibited excellent stability, selectivity and humidity resistance to N-butyl alcohol. The gas sensing properties of 5Fe-CoSn(OH) 6 is greatly improved due to the large specific surface area, narrow band gap, sufficient oxygen vacancies and quickly separation efficiency of electrons-hole pairs. The results demonstrate that the doping of Fe3+ is an effective way to improve the gas sensing properties of CoSn(OH) 6 sensors to detect N-butyl alcohol. [Display omitted] • The pure CoSn(OH)6 and Fe-doped CoSn(OH)6 were successfully synthesized by a hydrothermal method. • The sensing properties of the pure CoSn(OH)6 and Fe-doped CoSn(OH)6 to N-butyl alcohol were investigated for the first time. • 5Fe-CoSn(OH)6 exhibits the most remarkable gas sensing performance to N-butyl alcohol at 200 ℃. • The doping of Fe3 + is a promising approach for achieving an excellent gas sensing performance for the development of CoSn(OH)6 gas sensors to detect N-butyl alcohol. [ABSTRACT FROM AUTHOR]

In this work, we designed and prepared CuO-loaded In 2 O 3 /CeO 2 nanofiber heterojunctions, which are promising for trace CO gas detection. We characterized the materials, confirmed the morphology of the nanofibers and structure of the p-n heterojunctions, and analyzed the effect of morphology and structure on the gas sensing performance. In gas sensing tests, the sensor is found to show a low optimum operating temperature of 70 °C, with a limit of detection that reaches as low as 50 ppb. At concentrations ranging from 50 ppb to 10 ppm, the sensor shows a sensitive and linear response for CO gas. In particular, the sensor shows a response (R a /R g) of 11.7–10 ppm CO gas, and a response/recovery time of 125 s/12 s for 2 ppm CO gas. In addition, we tested the selectivity, humidity response and long-term stability of the gas sensors. Finally, based on the structure of the materials, we propose a mechanism for the enhanced CO gas sensing performance. • CuO-loaded In 2 O 3 /CeO 2 nanofibers were synthesized for fabricating superior CO gas sensors. • CuO was loaded onto the surface of nanofibers to form p-n junctions, leading to enhanced sensing properties. • The CO gas sensor shows a low optimum operating temperature of 70 °C, with a limit of detection as low as 50 ppb. • Combined with the experimental results, the mechanism for the enhanced performance of the gas sensor is discussed. [ABSTRACT FROM AUTHOR]

In this work, we designed and prepared CuO-loaded In 2 O 3 /CeO 2 nanofiber heterojunctions, which are promising for trace CO gas detection. We characterized the materials, confirmed the morphology of the nanofibers and structure of the p-n heterojunctions, and analyzed the effect of morphology and structure on the gas sensing performance. In gas sensing tests, the sensor is found to show a low optimum operating temperature of 70 °C, with a limit of detection that reaches as low as 50 ppb. At concentrations ranging from 50 ppb to 10 ppm, the sensor shows a sensitive and linear response for CO gas. In particular, the sensor shows a response (R a /R g) of 11.7–10 ppm CO gas, and a response/recovery time of 125 s/12 s for 2 ppm CO gas. In addition, we tested the selectivity, humidity response and long-term stability of the gas sensors. Finally, based on the structure of the materials, we propose a mechanism for the enhanced CO gas sensing performance. • CuO-loaded In 2 O 3 /CeO 2 nanofibers were synthesized for fabricating superior CO gas sensors. • CuO was loaded onto the surface of nanofibers to form p-n junctions, leading to enhanced sensing properties. • The CO gas sensor shows a low optimum operating temperature of 70 °C, with a limit of detection as low as 50 ppb. • Combined with the experimental results, the mechanism for the enhanced performance of the gas sensor is discussed. [ABSTRACT FROM AUTHOR]

In this work, the pure and Ni-doped Bi 2 WO 6 are successfully synthesized by a one-step hydrothermal method. We apply the various techniques, such as X-ray diffraction (XRD), Scanning Electron Microscope (SEM),Transmission Electron Microscope (TEM), Ultraviolet–visible spectroscopy (UV–vis) and photo luminescence (PL) et al., to characterize the structure, morphology, chemical compositions, optical properties and crystal defects of the prepared samples. Compared with pure Bi 2 WO 6 and other Ni-doped Bi 2 WO 6 , the 4 at% Ni-Bi 2 WO 6 sensor exhibits the highest gas response (31.2), fast response-recovery characteristic, good stability and unique selectivity to 30 ppm n-butanol at 325 ℃. The enhanced gas sensing mechanism could be attributed to its unique hierarchical hydrangea-like structure, the large specific surface area, the low band gap energy, high electron separation efficiency and abundant oxygen vacancies. We have fabricated the pure Bi 2 WO 6 and Ni-doped Bi 2 WO 6 successfully. The as-fabricated 4 at% Ni-doped Bi 2 WO 6 gas sensor shows superior gas-sensing performance toward n-butanol. [Display omitted] • The pure and Ni-doped Bi 2 WO 6 were successfully synthesized by hydrothermal method and the 4 at% Ni-Bi 2 WO 6 exhibits hydrangea-like morphology with hierarchical structures. • The Ni-doped Bi 2 WO 6 gas sensor presented a largely enhanced gas sensing properties to n-butanol. • The 4 at% Ni-doped Bi 2 WO 6 gas sensor showed excellent gas sensing properties to n-butanol. • The introducing Ni into Bi 2 WO 6 can increase oxygen vacancies and improve high electron-hole pairs separation efficiency. [ABSTRACT FROM AUTHOR]