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Metal oxide semiconductor (MOS) gas sensor is an effective tool for NO2 detection. However, their performance is seriously influenced by humidity due to water vapor poisoning, and it remains a challenge to develop an anti-humidity NO2 MOS sensor. In this work, a humidity-independent, highly sensitive and selective NO2 sensor based on In2O3 nanoflowers decorated with graphite nanoflakes was fabricated, which exhibited excellent anti-humidity and stability (response fluctuation within 7%) in a wide relative humidity (RH) range of 20% - 90%. The fabricated sensor had a high response of 10 to ppb level NO2 (RH 80%). Besides, the sensor exhibited good selectivity, low operating temperature (75 °C) and rapid response speed (50 s to 5 ppm NO2). The reason for the excellent anti-humidity function was investigated. Large amounts of polar groups were formed on the graphite nanoflakes after hydrothermal treatment, which enhanced the interaction between the graphite and In2O3 and made the surface of the composites have a strong water absorption function. Moreover, the intrinsic hydrophobic property of the graphite can effectively block the interference of water vapor to the moisture-sensitive In2O3. Our work provides a new idea for enhancing the anti-humidity performance of the MOS sensors and can broaden their applications in a variety of complex environments. [ABSTRACT FROM AUTHOR]

In this paper, well-controlled synthesis of In 2 O 3 -reduced graphene oxide (In 2 O 3 –rGO) nanocomposites by hydrothermal method was demonstrated. The structural, morphological, chemical composition studies of the In 2 O 3 –rGO nanocomposites were carried out, evidencing a homogeneous dispersion of In 2 O 3 on the rGO nanosheets. The sensor based on the In 2 O 3 –rGO nanocomposites exhibited excellent selectivity, high response, and relatively short response and recovery time for detection of NO 2 at room temperature. The excellent sensing properties were resulted from the composition and structure advantages of the In 2 O 3 –rGO nanocomposites. [ABSTRACT FROM AUTHOR]

Hierarchical flower-like ZnO nanospheres were synthesized by a facile hydrothermal method using sodium citrate as soft template. The products were characterized by X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray, inductively coupled plasma atomic emissions spectroscopy, and X-ray photoelectron spectroscopy techniques. The SEM and TEM results showed that the 3D ZnO nanospheres were consisted of 2D ZnO nanosheets. The diameter of the nanospheres was 3–4 \mum and the thickness of the nanosheets was 60–70 nm. In order to improve the ethanol-sensing properties, the 3D ZnO nanostructures were functionalized with Au@CuO nanoparticles. Because of the protection of the CuO shell from aggregation, the size of the Au@CuO nanoparticles were smaller than that of the Au nanoparticles after annealing. The sensing response of 0.7% Au@0.3% CuO loaded ZnO was close to that of 1% Au loaded ZnO, and much higher than that of the unfunctionalized ZnO. The good performance was probably attributed to the high intensities of the chemical adsorption oxygen and the active sites of the Au@CuO functionalized ZnO nanostructures. [ABSTRACT FROM PUBLISHER]

The brick-like In 2 O 3 nanomaterials were synthesized by oil bath precipitation and subsequent calcination method without any templates or surfactants. Technologies of X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were carried out to characterize the morphological and structural of the In 2 O 3 samples. Photoluminescence spectra (PL) and X-ray photoelectron spectroscopy (XPS) were used to illustrate the influence of material surface states and internal defects on gas-sensing properties. The In 2 O 3 nanomaterials annealed at 400 °C exhibited a high response (402) toward 500 ppb NO 2 with the fast response/recovery time (114 s/49 s) at rather low operating temperature of 50 °C. Besides, it had a good linear relationship in the range of 100–500 ppb. Such excellent gas sensing properties could be on account of the relative large surface area, abundant adsorbed oxygen and good electrical properties. [ABSTRACT FROM AUTHOR]

A novel NO 2 gas sensing material based on metal-thiourea complex was greenly synthesized via facile mixing of CuCl 2 and thiourea aqueous solution. Its synthesis has advantages, like no need of surfactants, noble metals or other toxic solvents, not necessarily to perform calcination process, thus less time consumed and easy operation. The gas sensing properties of the complex nanowires were investigated to detect NO 2 . The material showed a selective response to NO 2 with a good linear relationship as the concentration of NO 2 varies from 1 to 10 ppm. Compared with different materials, the complex sensor exhibited rapid response with the response/recovery time of 150/200 s even for 100 ppb NO 2 at 60 °C. The reason of the enhanced gas sensing performances by the complex nanowires and the underlying mechanism of the special interaction of the host material (metal-thiourea complex) and the guest molecule (NO 2 ) were studied. [ABSTRACT FROM AUTHOR]

Pd loaded three dimensionally ordered macroporous (3DOM) In 2 O 3 sensors were fabricated by reduction precipitation method with a uniform distribution of Pd nanoparticles (NPs). The response of 0.5 wt% Pd loaded 3DOM In 2 O 3 is 980 for 500 ppb NO 2 which is over 5 times higher than that of pure In 2 O 3 at room temperature. Our work presents a relatively simple but more efficient approach for NO 2 detection without extra heating. Pd inducing surface-modification effectively modulates the thickness of electron depletion layer, which is the dominant sensing mechanism for enhancing NO 2 performance. When Pd NPs are loaded on the surface of 3DOM In 2 O 3 support, not only the amount of surface deficiency and carrier concentration increase, but also electrons flow further from In 2 O 3 to Pd NPs. All of these results in the formation of Pd-In 2 O 3 Schottky contact and eventually widen the depletion layer on the In 2 O 3 support. Apparently, our work presents a relatively simple but more efficient approach for NO 2 detection without extra heating, indicating that Pd loaded 3DOM In 2 O 3 sensors would be more suitable for future applications. [ABSTRACT FROM AUTHOR]

Abstract: Hierarchical flower-like and 1D tube-like ZnO architectures were synthesized by a microemulsion-based solvothermal method. Technologies of XRD, SEM and TEM were used to characterize the morphological and structural properties of the products. The influence of the flower-like and tube-like morphologies on their NO2 sensing properties was investigated. The experimental results showed that high-sensitivity NO2 gas sensors were fabricated. The sensitivity of the tube-like ZnO gas sensor was much higher than that of the flower-like ZnO gas sensor and the tube-like ZnO gas sensor exhibited shorter response time. The in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) technique was employed to investigate the NO2 sensing mechanisms. Free nitrate ions, nitrate and nitrite were the main adsorbed species during the adsorption, and NO also existed in the initial period of surface reoxidation. Furthermore, N2O was formed via NO− and N2O2 − stemmed from NO and increased upon rising temperature. Moreover, the PL spectra and the XPS spectra further proved that the intensity of donors (oxygen vacancy (VO) and zinc interstitial (Zni)) and surface oxygen species (O2 − and O2) involved in the gas sensing mechanism leaded to the different sensitivities. [Copyright &y& Elsevier]