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Realizing nitrogen dioxide (NO 2) detections based on semiconductor-based gas sensors with high tolerance to humidity conditions is deemed to be a long-term challenge. To independently acknowledge the physiosorbed-water influence mechanism on semiconductor-based sensors, hydrophobic zeolitic imidazolate framework-8 (ZIF-8) covered chemisorbed-oxygen-nonexistence zinc hydroxyfluoride (ZnOHF) snowflake-like nanorod bundles are synthesized for NO 2 detections with non-hindrance of interfering gases and high humidity in our work. Gas-sensing testing results display that the 0.6ZIF-8/ZnOHF-based gas sensor provides an optimum NO 2 response of 12.1–10 ppm NO 2 at the operating temperature of 200 ℃ with excellent NO 2 selectivity. As the relative humidity (RH) increases from 20% RH to 80% RH, the response of the 0.6ZIF-8/ZnOHF sensor shows a marginal fluctuation of only 13%, exhibiting outstanding anti-humidity characteristics towards NO 2 detections, the outperformed NO 2 selectivity and humidity tolerance of which are greatly attributed to the unique band structures of ZnOHF and the surficial hydrophobic treatment by ZIF-8, which is further validated via In-situ diffuse reflection infrared Fourier transform spectroscopy (In-situ DRIFTS) and electronic structure analyses. Humidity impact on ZnOHF poses a persuasive evidence for establishing the separate physiosorbed water interfering mechanism on semiconductors. This work endows a perspective on optimizing humidity tolerance for semiconductor-based sensors at low operating temperature. • Snowflake-like ZIF-8/ZnOHF was synthesized via an in-situ chemical process. • Hydroxyl-independent humidity-interfered behaviors were identified of ZnOHF. • Optimized ZIF-8/ZnOHF sensor exhibits excellent anti-humidity NO 2 sensitivity. • In-situ Fourier Transform infrared spectra verify the anti-humidity mechanism. [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]

• The porous In 2 O 3-x nanospheres were synthesized via metallic aluminum reduction for the first time. • The correlation between the electronic structure of In 2 O 3 and the gas-sensing performance to NO 2 was further investigated. • The In 2 O 3-x nanospheres obtained at 300 °C exhibits improved sensitivity and superior selectivity at 80 °C. • The gas mechanism was further studied via the calculated density of states (DOS) of In 2 O 3 and In 2 O 3-x. Investigating the correlation between the electronic structure of indium oxide materials with oxygen vacancy defects and their sensing property to nitrogen dioxide is important for future development of high-efficient sensing materials. For the first time, the defective structure of porous In 2 O 3 nanospheres was introduced in a two-zone tube furnace using metallic Al as reducing agent. Texture characterizations show that In 2 O 3 and In 2 O 3-x are porous nanospheres assembled by small particles with the size of ca. 10–20 nm. The surface oxygen vacancy defects and electronic structure of samples were characterized by X-ray power diffraction, X-ray photoelectron spectroscopy, electron paramagnetic resonance, photoluminescence, ultraviolet-visible spectrophotometer and Hall analysis, and the sensing performance of samples to NO 2 gas was evaluated. The results display that the porous In 2 O 3-x nanospheres prepared at the reducing temperature of 300 °C (Vo-In 2 O 3 -300) exhibits improved response of 130 to 3 ppm NO 2 at 80 °C, which is almost 2.5-folds as high as the response (55) of the porous In 2 O 3 nanospheres. The sensing mechanism study carried out using DFT indicates that oxygen vacancies on the surface of In 2 O 3 as donor level optimize the electron structure and electrical properties of materials, such as supplying more free-electrons in the conduction band, narrowing the band gap and improving the mobility of electrons, which result in the low energy barrier for the adsorption of NO 2 molecules on the surface and in turn enhance the gas-sensing performance of In 2 O 3. Therefore, this work can provide some instructive thoughts for constructing In 2 O 3 -based sensing materials for high-efficient nitrogen dioxide detection. [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]