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Zinc hydroxyfluoride (ZnOHF) is a newly found resistive semiconductor used as a gas-sensing material with excellent selectivity to NO2 because of its unique energy band structure. In this paper, Al3+ doping and UV radiation were used to further improve the gas-sensing performance of ZnOHF. The optimized 0.5 at.% Al-ZnOHF sample exhibits improved sensitivity to 10 ppm NO2 at a lower temperature (100 °C) under UV assistance, as well as a short response/recovery time (35 s/96 s). The gas-sensing mechanism demonstrates that Al3+ doping increases electron concentration and promotes electron transfer of the nanorods by reducing the bandgap of ZnOHF, and the photogenerated electrons and holes with high activity under UV irradiation provide new reaction routes in the gas adsorption and desorption process, effectively promoting the gas-sensing process. The synergistic effect of Al3+ and UV radiation contribute to the enhanced performance of Al-ZnOHF. [ABSTRACT FROM AUTHOR]

Abstract: Alpha-Fe2O3 nanotubes and alpha-Fe2O3@ZnO heterostructured nanotubes have been synthesized through a hydrothermal method and a sol–gel route, respectively. Electronic microscopy examinations demonstrate that the alpha-Fe2O3 nanotubes with lengths ranging from 200 to 300nm and width around 150nm have a hollow feature and the thickness of the wall is about 30nm. After a sol–gel process, a layer of ZnO with a thickness of 20nm formed on the surface. X-ray diffraction patterns show that the obtained products are well crystallized and have high purity. The synthesized alpha-Fe2O3 nanotubes and alpha-Fe2O3@ZnO heterostructured nanotubes have specific surface area of 26.5m2g−1 and 35m2g−1, respectively. The gas sensing test reveals that the heterostructured nanotubes can get a high sensitivity (32) to acetone at the temperature of 642K. [Copyright &y& Elsevier]

We report for the first time using pure cobaltous tungstate (CoWO 4) as an efficient ethanol sensor by controlling the Co3+-Co2+ redox couple in CoWO 4. The prepared Co x WO 4 has a flower-like structure self-assembled by a mesoporous microbelt. Moreover, the Co x WO 4 sensor with a Co3+/Co2+ ratio of 38.9% exhibits a high response (42.9–100 ppm ethanol), fast response/recovery time (11/13 s), low detection limit (0.42 ppm), as well as remarkable short-term and long-term repeatability. Notably, the Co x WO 4 sample maintains a constant response value over a wide range of humidity (30–90 RH%), manifesting its good anti-humidity properties. The outstanding sensing performance is owing to the Co3+-Co2+ redox couple, high surface area and moderate porosity of the obtained samples. The self-transforming of the Co3+-Co2+ redox couple contributes to the formation of absorbed oxygen (O 2 -), oxygen vacancies and the reduction of the band gap, which is a crucial factor in improving the sensing properties of Co x WO 4. • Pure cobalt tungstate was used for the first time as an efficient ethanol sensor. • The sensor shows a fast response/recovery time and low detection limit. • The self-transforming of Co3+-Co2+ redox on the surface is also a crucial factor. [ABSTRACT FROM AUTHOR]

Water vapor greatly interferes with gas sensing characteristics of metal oxide semiconductors (MOS). Consequently, for the first time, Nd 2 O 3 -loaded In 2 O 3 porous nanorods were synthesized which exhibited excellent H 2 S sensitivity along with prominent humidity-independent characteristics, whereas pristine In 2 O 3 without Nd 2 O 3 showed deteriorated H 2 S sensing features under increasing ambient humid conditions in a wide operating temperature range. The mechanism of humidity-independent H 2 S sensing properties was researched via X-ray photoelectrons spectroscopy (XPS), in-situ Fourier Transform infrared spectroscopy (in-situ DRIFTS) and the corresponding gas sensing measurements, which is in close relations with the inhibition of chemisorbed oxygen and scavenging hydroxyl groups on In 2 O 3 surface induced by surficial Nd 2 O 3 component. This strategy poses a cutting-edge comprehending of temperature-dependent humidity-interference on MOS, paves a novel route for fabricating H 2 S sensors with exceptional sensitivity, selectivity and anti-humidity properties, which will be quite conducive for real-time exhaled breath analyses in disease diagnosis. [Display omitted] • Nd 2 O 3 -loaded In 2 O 3 porous nanorods were prepared for anti-humidity H 2 S detections. • Temperature-dependent anti-humidity behaviors of Nd 2 O 3 -loaded In 2 O 3 are identified. • The optimized H 2 S sensor exhibits well selectivity, sensitivity and low detection limit. • In-situ Fourier Transform infrared spectra verifies the anti-humidity mechanism. [ABSTRACT FROM AUTHOR]

Regulation based on the crystalline structure modulations is capable of optimizing the band gap and chemisorbed oxygen components thus adjusting the gas sensing characteristics of sensing materials. Herein, In 2 O 3 hierarchical-assembled microspheres with diverse crystalline structures were synthesized via a simple hydrothermal method combined with calcinating procedure under different temperatures. The gas sensor based on rhombohedral In 2 O 3 (rh-In 2 O 3) microspheres assembled by pine needle shaped nanorods annealed at 350 ℃ (350-In 2 O 3) exhibited superior H 2 S sensing performances at relative low operating temperature of 100 ℃ with low detection limit (50 ppb) and optimized stability compared with cubic In 2 O 3 (c-In 2 O 3). Notably, H 2 S sensing characteristics of In 2 O 3 samples with different crystalline structures certificated that crystal structures can dominate the H 2 S sensing reactions with different mechanisms. This work enlightened a novel prospect for designing rh-In 2 O 3 based sensors and provides an innovative pathway for analyzing the feasible H 2 S sensing mechanisms. [Display omitted] • In 2 O 3 materials with diverse crystalline structures were prepared for H 2 S detections. • Rhombohedral In 2 O 3 microspheres is composed of nanorods (diameter of 8 nm). • Rhombohedral In 2 O 3 based sensor displayed the optimized H 2 S sensitivity. • Crystalline structure controls H 2 S sensing mechanism. [ABSTRACT FROM AUTHOR]

Due to the intrinsic properties of wide band gap and the 5d shell being vacant, WO 3 still has the disadvantages of low response dynamics, slow response/recovery speed and high detection limit for real-time gas monitoring. To address such issues, the Ni3+ doped WO 3 hierarchical hollow structure composed of irregular nanosheets was achieved and the content of adsorbed oxygen was adjusted by Ni3+ doping to further improve the gas sensing performance of WO 3. In comparison to pure WO 3 , the 3 wt%Ni-WO 3 sensor exhibited remarkable response value (396), short response/recovery speed (13 s/6 s) and low detection limit (510 ppt) at 160 ℃. The impressive gas properties could be attributed to the reduced band gap and oxygen inhibiting effect of Ni3+ doping, which provides more NO 2 adsorption sites and making it easier for NO 2 to capture more electrons in the conduction band by restraining the oxygen ions chemisorbed on the surface. The unique sensing characteristics of the Ni3+ doped WO 3 suggest its wonderful potential applications in environmental pollution gas detection. The mechanism of oxygen inhibiting effect induced by Ni3+ doping was also discussed in detail [Display omitted] • The Ni3+ doped WO 3 was synthesized via soaking and oil bath evaporation. • The sensor based on Ni3+ doped WO 3 presented rapid response/recovery speed and low detection limit. • The superior sensing characteristic can be attributed to the oxygen inhibiting effect. [ABSTRACT FROM AUTHOR]

Triethylamine (TEA) is a typical pollution in chemical industry and Corrupt markers of aquatic products. TEA emissions have a serious impact on human health, industrial production and food safety. In this study, hierarchical flower-like Pt-loaded/Ce-doped In 2 O 3 microspheres are synthesized via simple hydrothermal and in-situ reduction methods. The triethylamine (TEA) sensing measurements display the 0.5Pt-3CeIn gas sensor exhibits high sensitivity (R a /R g = 900–100 ppm triethylamine), ultra-low optimal working temperature (100 ℃), enhanced responding and recovering speed (158/45 s) and excellent selectivity towards different target gases (ethanol, acetone, xylene, methanol, nitrogen dioxide and methane) including amine (response towards 50 ppm NH 3 is lower than 10). The TEA detection limit is as low as 5 ppb and the sensor exhibits a wide TEA detection range. The introduction of Pt and Ce components into In 2 O 3 effectively reduces the operating temperature, promotes the chemisorbed oxygen content (18.14 %) and wildly decreases the band gap (2.97 eV). The gas sensing mechanism of Pt/Ce-In 2 O 3 , which is dominated by electronic and chemical sensitization of Pt, catalytic function of Ce dopants and the functional interface between Pt nanoparticles and Ce-doped In 2 O 3 microspheres, is proposed. This work as well testifies the feasibility for multi-components cooperative optimization of MOS in gas sensing applications. [Display omitted] [ABSTRACT FROM AUTHOR]

In this work, Ni-doped In 2 O 3 nanoparticles were successfully fabricated via a simple metal-organic framework-derived solvothermal method. The synthesized Ni-In 2 O 3 exhibited as ultrafine nanoparticles with an average size of 13 nm. Gas sensing test results demonstrated that the sensor composed of Ni-doped In 2 O 3 (2 mol%) nanoparticles showed fast response/recovery properties, and the response and recovery speeds toward 10 ppm NO 2 were 2 and 2 s, respectively. Furthermore, the response value to 10 ppm NO 2 was about 70 at the optimum working temperature of 200 °C exhibiting high sensitivity of the sensors. Additionally, the sensor indicated a superior low detection limit of 5 ppb. These characteristics make Ni-doped In 2 O 3 nanoparticles a desiring candidate for rapid detection of NO 2. The possible mechanism of enhanced sensing properties was discussed in detail. The Debye-scale nanoparticles furnish abundant adsorption sites. High oxygen vacancies content provides more electrons to accelerate NO 2 excitation. Furthermore, the catalytic action of Ni2+ improved the response/recovery speed. The Ni-doped In 2 O 3 nanoparticles are reasonable to be an ideal substitution for fabricating rapid NO 2 detection devices in the future. • Ni-In 2 O 3 nanoparticles have been prepared by a solvothermal method. • The average size of Ni-doped In 2 O 3 nanoparticles are only ∼13 nm. • The NO 2 sensor exhibits ultra-fast response/recovery and low detection limit. • Abundant oxygen vacancies and catalytic functions of Ni2+ enhance the sensitivity. [ABSTRACT FROM AUTHOR]

In this paper, Ni 0.9 Zn 0.1 O/ZnO composite fibers were prepared by a combined approach of electrospinning and hydrothermal method for enhanced H 2 S gas sensing performance. The composite fibers have a diameter of 2 µm and are densely and vertically covered with irregularly shaped nanosheets with a thickness of about 20 nm. When the operating temperature is 100 °C, the maximum response (Ra/Rg) of the Ni 0.9 Zn 0.1 O/ZnO sample to 5 ppm H 2 S is about 450, which is about 15 times of pure ZnO nanofibers gas sensor (∼ 30). Moreover, Ni 0.9 Zn 0.1 O/ZnO based gas sensors showed good selectivity and low detection limit (10 ppb) to H 2 S. The nanosheets structure of Ni 0.9 Zn 0.1 O/ZnO composite fibers, as well as the proper energy band structure alignment between Ni 0.9 Zn 0.1 O and ZnO, have improved its gas sensing performance. • A novel nanosheets covered fiber with large specific surface area synthesized by electrospinning and hydrothermal method. • Ni 0.9 Zn 0.1 O/ZnO composite show high response and low detection limits for the first time as H 2 S detection materials. • Excellent properties is attributed to the interconversion of p-n heterojunctions and metal-n type semiconductor contacts. [ABSTRACT FROM AUTHOR]