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The online monitoring of GIS equipment can be realized through detecting SF6 decomposition gasses. Metal oxide heterojunctions are widely used as gas-sensing materials. In this study, the structural and electrical properties of In2O3-ZnO and TiO2-ZnO heterojunctions were analyzed based on density functional theory calculations. After heterojunction structural optimization, the electrical conductivity of these two heterojunctions was enhanced compared to each intrinsic model, and the electrical conductivity is ranked as follows: In2O3-ZnO heterojunction > TiO2-ZnO heterojunction. The gas-sensing response of these two heterojunctions to four SF6 decomposition gasses, H2S, SO2, SOF2, and SO2F2, was investigated. For gas adsorption systems, the adsorption energy, charge transfer, density of states, charge difference density, and frontier molecular orbitals were calculated to analyze the adsorption and gas-sensing performance. For gas adsorption on the In2O3-ZnO heterojunction surface, the induced conductivity changes are in the following order: H2S > SO2F2 > SOF2 > SO2. For gas adsorption on the TiO2-ZnO heterojunction surface, H2S and SOF2 increase conductivity, and SO2 and SO2F2 decrease conductivity. [ABSTRACT FROM AUTHOR]

From the past decade, there is a demand for the development of highly sensitive and selective, operating at low temperature, and stable gas-sensing materials used to monitor hazardous gases. The discovery of graphene has led to the implication of the same as gas sensor as it possesses large value of surface to volume ratio and high value of electron mobility at room temperature. Few researchers have fabricated reduced graphene oxide–metal oxide composite gas sensors exhibiting good electrical and gas-sensing properties. But still, it is a very less explored area. This article provides an overview of electrical and gas-sensing properties of reduced graphene oxide–metal oxide nanocomposites with improved sensitivity, selectivity, stability, and other sensing performances. This review is mainly focuses on reduced graphene oxide–metal oxide nanocomposite-based gas sensors which are cost-effective and sensitive to the various gases/vapors. [ABSTRACT FROM AUTHOR]

The online monitoring of GIS equipment can be realized through detecting SF6 decomposition gasses. Metal oxide heterojunctions are widely used as gas-sensing materials. In this study, the structural and electrical properties of In2O3-ZnO and TiO2-ZnO heterojunctions were analyzed based on density functional theory calculations. After heterojunction structural optimization, the electrical conductivity of these two heterojunctions was enhanced compared to each intrinsic model, and the electrical conductivity is ranked as follows: In2O3-ZnO heterojunction > TiO2-ZnO heterojunction. The gas-sensing response of these two heterojunctions to four SF6 decomposition gasses, H2S, SO2, SOF2, and SO2F2, was investigated. For gas adsorption systems, the adsorption energy, charge transfer, density of states, charge difference density, and frontier molecular orbitals were calculated to analyze the adsorption and gas-sensing performance. For gas adsorption on the In2O3-ZnO heterojunction surface, the induced conductivity changes are in the following order: H2S > SO2F2 > SOF2 > SO2. For gas adsorption on the TiO2-ZnO heterojunction surface, H2S and SOF2 increase conductivity, and SO2 and SO2F2 decrease conductivity.

The bismuth vanadate (BiVO4) powder material was successfully fabricated by a simple one-step hydrothermal method. The structure and morphology of BiVO4 were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The gas-sensing properties of the obtained materials were analyzed for ammonia, formaldehyde, methanol and ethanol. It is shown that the BiVO4 samples obtained in the experiment are anomalous microspheres with an average size of 800 to 900 nm. When the experimental temperature is 460 °C, the response value of the gas sensor to 500 x 10-6 ethanol gas is about 5.50, and it shows good sensitivity and selectivity to ethanol. The experiment has the advantages of simple operation, comprehensive knowledge and novel themes. The synthesis, characterization and analysis of the gas-sensitive components of BiVO4 through comprehensive experimental teaching could further stimulate the interest of students in scientific research on materials. Meanwhile, it will help consolidate the foundation of scientific research and enhance the scientific literacy and innovation capabilities of students. [ABSTRACT FROM AUTHOR]

• Enhanced gas sensing performance: the study demonstrates that the SnO 2 -graphene sensor exhibits improved gas sensing properties compared to a pure SnO 2 sensor. This suggests that the incorporation of graphene into the SnO 2 sensor enhances its sensitivity and detection capabilities for SF 6 decomposition products. • Improved selectivity towards SF 6 decomposition products: The SnO 2 -graphene sensor shows enhanced selectivity towards SF 6 decomposition products. This means that it can effectively distinguish and detect specific gases or compounds associated with SF 6 decomposition, making it a promising sensor for monitoring SF 6 gas in various applications. • Lower operating temperature requirement: The research findings indicate that the SnO 2 -graphene sensor requires a lower operating temperature for gas sensing. This is significant as it reduces the energy consumption and potential safety risks associated with high-temperature operation, making the sensor more practical and efficient for real-world applications. Based on theoretical calculation and experimental detection, SnO 2 -modified graphene (SnO 2 -graphene) was proposed as a gas-sensing material for the SF 6 characteristic decomposition products (SO 2 , H 2 S, SOF 2 , SO 2 F 2) in SF 6 -insulated equipment. Based on density functional theory calculations, the most stable modifying structure of single and double SnO 2 on the surface of graphene is optimized. The adsorption structure, adsorption energy, and charge transfer of four gas molecules on the surface of SnO 2 -graphene are calculated and analyzed. Then the total density of states (DOS) and partial density of states (PDOS) of the system before and after gas adsorption were compared and analyzed to explore the interaction mechanism between different gases and SnO 2 -graphene. In experimental study, graphene was prepared by the modified Hummers oxidation–reduction method in the laboratory. four concentration gradients of SnO 2 modified on the surface of graphene, and then specific gas sensing experiments were carried out with 10, 25, 50, 100 ppm of the SF 6 characteristic decomposition products. The gap between simulation and experiment is compared and analyzed, which lays a theoretical and experimental foundation for the development of new specific sensors. [Display omitted] [ABSTRACT FROM AUTHOR]

Using SnCl2·2H2O and SnCl4·5H2O as tin source and polyvinylpyrrolidone (PVP) as polymer matrix, fibril was prepared by using simple and controllable electrostatic spinning technology, and SnO2 nanofibers were obtained after calcination. Scanning electron microscope (SEM), X-ray diffractometer (XRD) etc. were used to investigate the effect of PVP molecular weight and different tin sources on the morphological properties of SnO2 nanofibers, and the specific surface area and gas-sensing characteristics of SnO2 nanofibers were tested. The results show that the fiber precursor prepared by electrospinning can remove the polymer matrix and solvent after calcination, and obtain pure tetragonal rutile SnO2 nanofibers, which show the characteristics of large specific surface area, high sensitivity and fast response speed. When PVP-K30 is used as high molecular matrix and SnCl4 · 5H2O is used as tin source, the prepared SnO2 nanofibers have uniform diameter, clear fiber, good orientation and better gas sensing characteristics.

The urchin-like core-shell In2O3/ZnO nanocomposites were prepared via a facile solvothermal method which In2O3 nanowires were grown on the ZnO microspheres. The nanocomposite microspheres had mesoporous structure, whose large specific surface area was 58.5 m2/g and pore size was 14.0 nm. The influence of initial reactant In3+ content on the morphology, component and structure of composites was systemically investigated. The sensor based on In2O3-ZnO-0.1 (the addition amount of indium nitrate was 0.1 g) displayed more excellent gas-sensing performance to triethylamine (TEA) than other samples, such as higher response (221), lower working temperature (100 °C). The outstanding gas-sensing performance of urchin-like In2O3/ZnO nanocomposites could be attributed to the special urchin-like structure with mesoporous and high specific surface area, plentiful oxygen vacancies and the formation of n-n heterojunction. [ABSTRACT FROM AUTHOR]

The application of carbyne-enriched nanomaterials opens unique possibilities for enhancing the functional properties of several nanomaterials and unlocking their full potential for practical applications in high-end devices. We studied the ethanol-vapor-sensing performance of a carbyne-enriched nanocoating deposited onto surface acoustic wave (SAW) composite substrates with various electrode topologies. The carbyne-enriched nanocoating was grown using the ion-assisted pulse-plasma deposition technique. Such carbon nanostructured metamaterials were named 2D-ordered linear-chain carbon, where they represented a two-dimensionally packed hexagonal array of carbon chains held by the van der Waals forces, with the interchain spacing approximately being between 4.8 and 5.03 Å. The main characteristics of the sensing device, such as dynamic range, linearity, sensitivity, and response and recovery times, were measured as a function of the ethanol concentration. To the authors' knowledge, this was the first time demonstration of the detection ability of carbyne-enriched material to ethanol vapors. The results may pave the path for optimization of these sensor architectures for the precise detection of volatile organic compounds, with applications in the fields of medicine, healthcare, and air composition monitoring. [ABSTRACT FROM AUTHOR]

Nanocrystalline and amorphous nanostructured tellurium (Te) thin films were grown and their gas-sensing properties were investigated at different operating temperatures with respect to scanning electron microscopy and X-ray diffraction analyses. It was shown that both types of films interacted with nitrogen dioxide, which resulted in a decrease of electrical conductivity. The gas sensitivity, as well as the response and recovery times, differed between these two nanostructured films. It is worth mentioning that these properties also depend on the operating temperature and the applied gas concentration on the films. An increase in the operating temperature decreased not only the response and recovery times but also the gas sensitivity of the nanocrystalline films. This shortcoming could be solved by using the amorphous nanostructured Te films which, even at 22 °C, exhibited higher gas sensitivity and shorter response and recovery times by more than one order of magnitude in comparison to the nanocrystalline Te films. These results were interpreted in terms of an increase in disorder (amorphization), leading to an increase in the surface chemical activity of chalcogenides, as well as an increase in the active surface area due to substrate porosity.

Using SnCl2 • 2H2O and SnCL • 5H2O as tin source and polyvinylpyrrolidone (PVP) as polymer matrix, fibril was prepared by using simple and controllable electrostatic spinning technology, and SnO2 nanofibers were obtained after calcination. Scanning electron microscope (SEM), X-ray diffractometer (XRD) etc. were used to investigate the effect of PVP molecular weight and different tin sources on the morphological properties of SnO2 nanofibers, and the specific surface area and gas-sensing characteristics of SnO2 nanofibers were tested. The results show that the fiber precursor prepared by electrospinning can remove the polymer matrix and solvent after ca lei nation, and obtain pure tetragonal rutile SnO2 nanofibers, which show the characteristics of large specific surface area, high sensitivity and fast response speed. When PVP-K30 is used as high molecular matrix and SnCL4 • 5H2O is used as tin source, the prepared SnO2 nanofibers have uniform diameter, clear fiber, good orientation and better gas sensing characteristics. [ABSTRACT FROM AUTHOR]

[Display omitted] • We modify the black phosphorene (BP) monolayer by adsorption or doping Au atoms. • The Au-adsorbed/doped BP sensor can detect and remove the NO x mixtures with ultra-sensitivity. • The Au-doped BP sensor shows highly sensitive and recyclable detection for H 2 at room temperature. Effective detecting toxic gases and the clean energy hydrogen is urgently necessary in industrial production and our daily life. Here, the sensing properties of Au-adsorbed/doped black phosphorene monolayer towards six different gases (CO, H 2 , H 2 S, NO, NO 2 , and SO 2) are theoretically investigated through density functional theory in combination with the non-equilibrium Green's function approach. The calculated adsorption energy, the charge transfer, the electron localization function, the band structure, and the density of states reveal that the Au-adsorbed/doped black phosphorene exhibits sensitive chemisorption to NO x gases, and, surprisingly, the Au-doped black phosphorene exhibits sensitive physisorption towards H 2 molecules. The calculated recovery time and current–voltage curves show that the Au-adsorbed/doped black phosphorene device acts as an ultra-sensitive (71%–100% sensitivity) remover of NO x molecules, and, importantly, the Au-doped black phosphorene sensor achieves a highly sensitive (85% sensitivity), selective, and reusable (0.01 ns recovery time) detection of H 2 at room temperature. Our results provide a theoretical basis for the potential applications of the Au-adsorbed/doped black phosphorene in gas-sensing, especially in the desirable NO x remover and H 2 sensor. [ABSTRACT FROM AUTHOR]

The application of carbyne-enriched nanomaterials opens unique possibilities for enhancing the functional properties of several nanomaterials and unlocking their full potential for practical applications in high-end devices. We studied the ethanol-vapor-sensing performance of a carbyne-enriched nanocoating deposited onto surface acoustic wave (SAW) composite substrates with various electrode topologies. The carbyne-enriched nanocoating was grown using the ion-assisted pulse-plasma deposition technique. Such carbon nanostructured metamaterials were named 2D-ordered linear-chain carbon, where they represented a two-dimensionally packed hexagonal array of carbon chains held by the van der Waals forces, with the interchain spacing approximately being between 4.8 and 5.03 Å. The main characteristics of the sensing device, such as dynamic range, linearity, sensitivity, and response and recovery times, were measured as a function of the ethanol concentration. To the authors’ knowledge, this was the first time demonstration of the detection ability of carbyne-enriched material to ethanol vapors. The results may pave the path for optimization of these sensor architectures for the precise detection of volatile organic compounds, with applications in the fields of medicine, healthcare, and air composition monitoring.

Abstract Wormhole-like mesoporous tin oxide was synthesized via a facile evaporation-induced self-assembly (EISA) method, and the gas-sensing properties were evaluated for different target gases. The effect of calcination temperature on gas-sensing properties of mesoporous tin oxide was investigated. The results demonstrate that the mesoporous tin oxide sensor calcined at 400 °C exhibits remarkable selectivity to ethanol vapors comparison with other target gases and has a good performance in the operating temperature and response/recovery time. This might be attributed to their high specific surface area and porous structure, which can provide more active sites and generate more chemisorbed oxygen spices to promote the diffusion and adsorption of gas molecules on the surface of the gas-sensing material. A possible formation mechanism of the mesoporous tin oxide and the enhanced gas-sensing mechanism are proposed. The mesoporous tin oxide shows prospective detecting application in the gas sensor fields.

This paper investigates the physicochemical characteristics and gas-sensitivity mechanisms of nickel oxide (NiO) and nickel ferrite (NiFe2O4) obtained by levitation-jet synthesis LJS). Properties of synthesized materials were examined using various spectroscopic methods. XPS showed that the presence of Ni3+ ions in samples reduced significantly with an increase in the specific surface area of the powders and a decrease in the average diameter of their particles. In this regard, it can be concluded that the number of uncompensated Ni2+ vacancies in such samples also decreases and the concentration of O2– vacancies, on the contrary, increases significantly. The Raman spectra of nanoscale NiO lacked a magnon band, which is usually observed at v = 1500 cm–1, whereas the spectrum of nanoferrite sample had a pronounced 2M band, which indicates an increase in spin correlation. According to the analysis of UV spectra of the samples, there is an increase in reflectivity values with an increase in wavelength for large nanoparticles when compared to the corresponding values for small particles. In this regard, we suggested that Ni-based oxide nanoparticles are semiconductors with an indirect transition to band-gap energy, and this is in sharp contrast to the data obtained earlier by other researchers. The gas sensitivity of nanoscale powders was investigated in relation to carbon monoxide and nitrogen dioxide at operating temperatures of 350–500°C. An evaluation of the results made it possible to conclude that the operating characteristics of the sensors that we propose are superior in a number of parameters to the similar characteristics of sensors made of commercial powders, as well as of powders obtained by other synthetic methods. [ABSTRACT FROM AUTHOR]

In this paper, NiO/In2O3 nanocomposites were prepared by hydrothermal and water bath method. The nanocomposites were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray diffraction (XRD). Characterization results show that the NiO nanosheets were uniformly grown on the surface of In2O3 nanospheres with the diameter of 200-300 nm, and the thickness of NiO nanosheets was about 20 nm. Gas-sensing tests exhibit that the sensor response to 10×10-6 formaldehyde was about 20 at 220 oC with the fast response time (about 4 s) and recovery time (about 16 s), and good reproducibility and selectivity. Some possible mechanisms were further discussed based on the hierarchical structure and p-n heterojunction. [ABSTRACT FROM AUTHOR]

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In this work, we prepared rose-like MoS 2 microspheres by using a simple hydrothermal route. It is found that synthesis temperature is a decisive factor influencing the morphology of MoS 2 products. The rose-like MoS 2 microspheres were obtained at 210 ℃. To enhance the gas-sensing properties, noble metal Pt was employed to decorate MoS 2 microspheres. Compared to the bare MoS 2 , the 0.10Pt-MoS 2 sensors show higher sensitivity, better repeatability, and more excellent selectivity towards NO 2 at the optimal operating temperature of as low as 150 ℃. The 0.10Pt-MoS 2 sensors also exhibit a fast response and recovery time of 21 s/173 s to 32 ppm NO 2. The enhanced sensing properties are primarily due to the strong spill-over effect of Pt and modulated Schottky barrier between Pt and MoS 2. Our results indicate that the Pt-MoS 2 sensors are a promising candidate for detecting toxic and harmful gases in practical use. [Display omitted] • Novel 3D rose-like MoS 2 microspheres were successfully synthesized. • The optimal synthesis temperature for rose-like microspheres is 210 ℃. • Enhanced gas responses induced by the unique nanostructure and Pt modification. • 0.10Pt-MoS 2 sensors have a low detection limit of 100 ppb. • 0.10Pt-MoS 2 exhibits a fast response/recovery time to 32 ppm NO 2 at 150 ℃. [ABSTRACT FROM AUTHOR]

In order to solve issues of air pollution, to monitor human health, and to promote agricultural production, gas sensors have been used widely. Metal oxide semiconductor (MOS) gas sensors have become an important area of research in the field of gas sensing due to their high sensitivity, quick response time, and short recovery time for NO2, CO2, acetone, etc. In our article, we mainly focus on the gas-sensing properties of MOS gas sensors and summarize the methods that are based on the interface effect of MOS materials and micro–nanostructures to improve their performance. These methods include noble metal modification, doping, and core-shell (C-S) nanostructure. Moreover, we also describe the mechanism of these methods to analyze the advantages and disadvantages of energy barrier modulation and electron transfer for gas adsorption. Finally, we put forward a variety of research ideas based on the above methods to improve the gas-sensing properties. Some perspectives for the development of MOS gas sensors are also discussed.

The influence of Sc3+ ion content on the microstructure, electrical, and gas-sensing properties of Ni0.5Co0.5ScxFe2–xO4 (x = 0.0, 0.05, 0.1 and 0.2) ferrites synthesized by a novel self-combustion method using polyvinyl alcohol as the colloidal medium, was studied. X-ray diffraction, X-ray photon spectroscopy (XPS), Brunauer–Emmett–Teller (BET) surface area, scanning electron microscopy (SEM), and energy-dispersive X-ray analysis (EDX) were employed to characterize the structure and morphology properties of these ferrites. The gas-sensing properties of hydrogen, methane, ethanol, methylene chloride, and benzene were investigated. The samples show p-type semiconducting properties for the studied gases within the temperature range of 100–380 °C. The results revealed that the partial substitution of Fe3+ by Sc3+ ions on the octahedral sites of the spinel structure of Ni0.5Co0.5Fe2O4 ferrite has a favorable effect on the sensing activity of this ferrite. The increase of the degree of Fe3+ ion substitution by Sc3+ ions up to x = 0.2 in the basic composition (Ni0.5Co0.5Fe2O4) results in the increase of the response and the decrease of the optimal operating temperature for all the studied gases. The sensor element Ni0.5Co0.5Sc0.2Fe1.8O4 (x = 0.2) has the best response to benzene (2.57) and to methylene chloride (2.10) at the operating temperature of 175 °C for a gas concentration of 500 ppm and a relative humidity of 50%. Highlights: The Ni0.5Co0.5ScxFe2–xO4 (0 < x < 0.2) ferrites have been prepared by self-combustion method. The porosity is amplified by a system with open pores distributed along the grain agglomerations. The increase of substitution by Sc results in the increase of sensor response to the studied gases. The substitution with Sc ions has the effect of decreasing the optimal operating temperature. The Ni0.5Co0.5Sc0.2Fe1.8O4 sensors have the best response to benzene and methylene chloride gas. [ABSTRACT FROM AUTHOR]

Hierarchical porous α-Fe 2 O 3 /TiO 2 nanorod@core-shell microspheres were synthesized by a facile one-step hydrothermal approach without templates or surfactants. The as-obtained α-Fe 2 O 3 /TiO 2 nanorod@core-shell microspheres had an average diameter of 3.5 μm. Porous nanorods, with an average length of 1.5 μm, were randomly grown on the core-shell microsphere surfaces. The morphology, microstructure, and composition of the α-Fe 2 O 3 /TiO 2 heterostructures were characterized by various analytical techniques. Changes in the morphology and composition of the microspheres had an effect on the final gas sensing performance. Gas sensors based on the porous nanorod@core-shell α-Fe 2 O 3 /TiO 2 microspheres exhibited an excellent gas-sensing performance, with markedly enhanced responses in comparison with the pristine α-Fe 2 O 3 sensor. The response of the porous nanorod@core-shell α-Fe 2 O 3 /TiO 2 microspheres to 20 ppm acetone was approximately 34, which was 2.7 times higher than that of pure α-Fe 2 O 3 at 220 °C. Furthermore, the sensor could be easily recovered to its initial state following a short exposure to fresh air. The remarkably enhanced acetone-sensing performance was attributed to the unique porous nanorod@core-shell microsphere morphology, the strong interfacial interaction between TiO 2 and α-Fe 2 O 3 , and the presence of α-Fe 2 O 3 /TiO 2 heterojunctions. Thus, the prepared porous nanorod@core-shell α-Fe 2 O 3 /TiO 2 microspheres sensors showed an outstanding performance in acetone detection. • Novel sphere/rod-like α-Fe 2 O 3 /TiO 2 were synthesized using a facile hydrothermal method without templates or surfactants. • Gas sensors based on α-Fe 2 O 3 /TiO 2 microspheres exhibited excellent gas sensitivity comparison with the pristine α-Fe 2 O 3 sensor. • The strong interfacial interaction between TiO 2 and α-Fe 2 O 3 can enhance acetone-sensing performance. [ABSTRACT FROM AUTHOR]

–The gas-sensing properties of nickel ferrite (NiFe2O4) and nickel oxide (NiO) nanoparticles prepared by a self-sustaining levitation-jet synthesis (LJS) method are reported. These have been compared to the gas-sensing properties of a NiO sensor prepared using a commercially sourced powder. The microstructure, surface area, particle size, and morphology varied widely across the sensors fabricated. It was anticipated that these contrasting properties would play a key role in either enhancing or worsening the sensing capabilities of the materials. Gases of interest included ethanol, toluene, and carbon monoxide as well as the gas response of the sensors was investigated at different operating temperatures. In general, the sensors responded to gases with different degrees of sensitivity. Among the sensors with higher surface areas, one provided noticeable enhancements in sensitivity towards gases when compared, for instance, to the sensitivity of the commercially based NiO sensor. The NiFe2O4 sensor presented most promise as a gas sensor to ethanol and, to a greater or lesser degree, towards toluene gas. In general, sensors were poorly responsive to the carbon monoxide concentrations tested. This study is one of the first reports of using LJS-based powders for gas sensing applications and it highlights the suitability of the method to fabricate size- and shape-controlled nanomaterials for the detection of environmentally relevant gases. [ABSTRACT FROM AUTHOR]

• Size and shape controlled nanopowders production by levitation-jet synthesis (LJS). • First report of using LJS-based nanopowders for gas sensing application. • The sensing performance of the LJS- fabricated sensors was typically enhanced in relation to that of the sensor fabricated with the commercial NiO powder. The gas sensing properties of nickel ferrite (NiFe 2 O 4) and nickel oxide (NiO) nanoparticles prepared by a levitation-jet synthesis (LJS) method are reported. These have been compared to the gas sensing properties of a NiO sensor, prepared using a commercially-sourced powder. The microstructure, surface area, particle size and morphology varied widely across the sensors fabricated. Gases included ethanol, acetone, carbon monoxide, toluene and nitrogen dioxide and the gas response of the sensors was investigated at different operating temperatures. The NiFe 2 O 4 sensor presented most promise as a gas sensor, with outstanding sensor sensitivity towards ppb concentrations of NO 2. This sensor was also remarkably sensitive to ethanol and, to a greater or lesser degree, towards acetone and toluene gases. In general, sensors were poorly responsive to the carbon monoxide concentrations tested. This study is one of the first reports of using LJS-based powders for gas sensing applications for the detection of environmentally-relevant gases. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Fe-doped In 2 O 3 nanospheres were synthesized via one-step impregnation. • Suitable Fe doping could increase sensing performance of In 2 O 3 nanospheres. • The effect of doping amount of Fe on sensing performance was discussed. Abstract Here we demonstrate high-performance ethanol sensors based on Fe-doped In 2 O 3 mesoporous nanospheres. By using FDU-12 as template via a facile one-step impregnation method Fe-doped In 2 O 3 were synthesized, which display high surface area, uniform shape, ordered mesoporous structure and small particle size. The Fe-doped In 2 O 3 exhibited a larger response to ethanol gases than pure In 2 O 3 under all measured concentrations. Furthermore, the effect of Fe/In molecular ratio on sensing property was investigated by comparing their response. The enhanced sensing properties could result from the unique mesoporous structure and the synergic electronic interaction between the guest Fe dopant and the host In 2 O 3 material. [ABSTRACT FROM AUTHOR]

The phase and structural transformations that Pd–Ru(7 at %) solid solution thin films undergo during thermal oxidation in oxygen in the temperature range 570–1070 K are studied by transmission electron microscopy, high-energy electron diffraction, and reflection high-energy electron diffraction. With increasing oxidation temperature, the phase composition is found to change in the order: Pd–Ru(7 at %) solid solution → Pd–Ru(7 at %) + PdO + RuO2 → PdO + RuO2 → PdO–RuO2 solid solution. We show that the complete oxidation of Pd–Ru(7 at.%) thin films to form single-phase films of the PdO–RuO2 solid solution takes place at a temperature of 100 K higher compared to pure palladium films. The resistance sensor response of the prepared PdO−RuO2 oxide films to ozone in air is studied for the first time. The results suggest that this is a promising material for use in gas-sensing applications. [ABSTRACT FROM AUTHOR]

Enhanced physical and chemical properties of materials through bimetallic synergistic effects remain a challenging problem because it is difficult to construct well-defined bimetallic synergies. Here, a series of bimetallic (Co, Mn)-codoped SnO 2 nanobelts were synthesized through the chemical vapor deposition (CVD) method by precisely controlling Co and Mn contents. The results show that the interaction between Co and Mn sites not only affects the chemical coordination environment of SnO 2 nanobelts and promotes the activity of an electronic catalytic reduction reaction but also greatly improves the gas-sensing properties. At the working temperature of 300 °C, the response value of the gas sensor to 200 ppm ethanol reaches an amazing 311.9. The amount of oxygen adsorbed on the surface of the sensitive material plays a crucial role in the gas-sensing response of the material. X-ray photoelectron spectroscopic analysis (XPS) spectra of the O 1s region of the sensor show that the adsorption oxygen content is 37.96%, which is higher than that of pure SnO 2 (27.41%). The increase of adsorbed oxygen content can be attributed to the synergistic effect of Co and Mn bimetal, which leads to electron enrichment on the surface of SnO 2 and promotes the activation of SnO 2 , and helps to improve the gas-sensitive characteristics of SnO 2 .

Mesoporous indium (In)-doped hematite (α-Fe 2 O 3 ) nanowires were synthesized with mesoporous SBA-15 silica as a hard template, and then the influence of In dopant on the microstructure and gas-sensing performance was investigated in detail. With characterization by transmission electron microscopy, X-ray diffraction, UV–vis spectroscopy, and nitrogen physisorption experiments, it was shown that the average grain size increased for up to 1 mol% In dopant and then decreased with increasing In dopant content, while the surface area changed in the inverse manner. Because of the low melting point of In, In acted as a fluxing agent and entered the α-Fe 2 O 3 lattice when the In content was low, and the average grain size increased. With higher In content, In precipitated out the lattice and existed at the grain boundary, and the grain size decreased. It is concluded that In in the lattice increased lattice distortion and In at the boundary increased the surface area and oxygen vacancies, which were both beneficial for improving the gas-sensing performance. The response of In-doped α-Fe 2 O 3 nanowires increased by about 30%–50% as compared with that of pure α-Fe 2 O 3 nanowires. The gas sensor based on 3 mol% In–doped α-Fe 2 O 3 nanowires exhibited the best gas response and a rapid response-recovery time toward ethanol at the optimum temperature. Owing to the same valence, In dopant affected only the microstructure and components of the α-Fe 2 O 3 lattice, which was necessary to improve the gas-sensing behavior. [ABSTRACT FROM AUTHOR]

A novel hollow carbon@SnO 2 nanocomposite has been developed via a high cost-effective and facile in-situ etching technique. The as-prepared C@SnO 2 product has a high surface area of about 115 m 2  g −1 and a hollow carbon core, where a lot of SnO 2 nanosheets grow onto the carbon shell. Particularly, the silica core as the sacrificial template can be fully removed by hydrofluoric acid (HF) byproduct during the reaction process. Moreover, the deposition of SnO 2 sheets and the removal of the silica template can be synchronously performed by a simple one-step process. When applied as the gas-sensing material, the C@SnO 2 product manifests highly sensitive and selective to n-butanol. The large surface area, hollow nanostructure and the perfect combination of SnO 2 nanosheets and carbon layer contribute to the enhanced gas-sensing performances. The method described in our work can also be employed to design other hollow metal oxides@carbon hybrids for energy storage and catalysis. [ABSTRACT FROM AUTHOR]

Wormhole-like mesoporous tin oxide was synthesized via a facile evaporation-induced self-assembly (EISA) method, and the gas-sensing properties were evaluated for different target gases. The effect of calcination temperature on gas-sensing properties of mesoporous tin oxide was investigated. The results demonstrate that the mesoporous tin oxide sensor calcined at 400 °C exhibits remarkable selectivity to ethanol vapors comparison with other target gases and has a good performance in the operating temperature and response/recovery time. This might be attributed to their high specific surface area and porous structure, which can provide more active sites and generate more chemisorbed oxygen spices to promote the diffusion and adsorption of gas molecules on the surface of the gas-sensing material. A possible formation mechanism of the mesoporous tin oxide and the enhanced gas-sensing mechanism are proposed. The mesoporous tin oxide shows prospective detecting application in the gas sensor fields. [ABSTRACT FROM AUTHOR]

In this paper, nickel oxides (NiO) and iron (Fe)-doped NiO nanowires (NWs) with the various doping content (from 1 to 9 at%) were synthesized by using SBA-15 templates with the nanocasting method. All samples were synthesized in the same conditions and exhibited the same mesoporous-structures, uniform diameter, and defects. Mesoporous-structures with high surface area created more active sites for the adsorption of oxygen on the surface of all samples, resulting in the smaller surface resistance in air. The impurity energy levels from the donor Fe-doping provided electrons to neutralize the holes of p-type Fe-doped NiO NWs, which greatly enhanced the total resistance. The comparative gas-sensing study between NiO NWs and Fe-doped NiO NWs indicated that the high-valence donor Fe-doping obviously improved the ethanol sensitivity and selectivity for Fe-doped NiO NWs. And NiFeO NWs sensor presented the highest sensitivity of 14.30 toward ethanol gas at 320 °C for the high-valence metal-doping. [ABSTRACT FROM AUTHOR]

In this paper, the mesoporous NiO nanowires (NWs) were synthesized by using SBA-15 silica as the hard templates with the nanocasting method, and then calcined from 550 to 750 °C. X-ray diffraction, transmission electron microscopy (TEM), nitrogen adsorption/desorption isotherm and UV-vis spectrum were used to characterize the morphology, phase structure and microstructure of the as-prepared samples. All results indicated that the calcination temperature greatly affected crystallization degree and specific surface area of the as-prepared NiO NWs. And the crystallization degree increased and specific surface area decreased with the calcination temperature. The higher specific surface area created more active sites for the surface redox reaction, while the higher crystallization degree led to the wider bandgap and made the charge carriers transport easily. It was concluded that the calcination temperature of NiO NWs greatly affected the gas-sensing performance. The optimized results from the gas-sensing behavior indicated that NiO NWs-650 based sensor exhibited the highest sensitivity to ethanol for the suitable calcination temperature. Furthermore, NiO NWs-650 sensor exhibited a better selectivity to ethanol than n-hexane, methanol, acetone and formaldehyde. [ABSTRACT FROM AUTHOR]

The mesoporous α-Fe 2 O 3 nanowires (NWs) were successfully synthesized by changing the calcination temperature from 550 to 750 °C (marked NWs-550, NWs-650 and NWs-750) via using SBA-15 silica as the hard templates with the nanocasting method. The characterization results indicated that the bandgap of the as-prepared samples hardly changed and the high BET surface areas changed a little with the calcination temperature from 550 to 750 °C. Mesoporous α-Fe 2 O 3 NWs had been found to possess the remarkable gas-sensing performance to ethanol gas. The gas-sensing behavior indicated that α-Fe 2 O 3 NWs-650 exhibited the higher response than that of α-Fe 2 O 3 NWs-550 and α-Fe 2 O 3 NWs-750. The calcination-temperature-dependent gas-sensing properties were mainly attributed to the competition of surface defects and body defects by the crystallization temperature. The lower calcination temperature could create more surface defects to improve the gas-sensing response, while the higher temperature would reduce the body defect and make the charge carriers transport easily. As the result, the suitable calcination temperature was desired to optimize the defects of nanostructures to improve the gas sensitivity. [ABSTRACT FROM AUTHOR]

Nickel oxides (NiO) nanowires were synthesized using the ordered mesoporous silica SBA-15 as hard templates with the nanocasting method, and then mesoporous NiO nanowires (NiO MNWs) were separated from the dispersed NiO nanowires (NiO DNWs) by the centrifugation technique. XRD, TEM, nitrogen adsorption/desorption isotherm and UV–vis spectrum were used to characterize the phase structure and microstructure. Both samples existed in bundles with the different grain size and NiO MNWs with the larger grain size presented the higher mesopores percent. The specific surface area (92.61 m 2 /g) and bandgap (3.31 eV) of NiO MNWs were higher than those of NiO DNWs for the higher mesoporous-structure. Therefore, the NiO MNWs based sensor exhibited the good sensitivity and fast response-recovery to ethanol at 340 °C. The gas-sensing properties of NiO MNWs were better than those of the NiO DNWs, which should be attributed to the higher surface area and wider bandgap. [ABSTRACT FROM AUTHOR]

The single-walled carbon nanotube (SWCNT)-molecularly imprinted powder (MIP) composites in this paper were prepared by mixing SWCNTs with MIPs. The structure and micrograph of the as-prepared SWCNTs-MIPs samples were characterized by XRD and TEM. The gas-sensing properties were tested through indirect-heating sensors based on SWCNT-MIP composites fabricating on an alumina tube with Au electrodes and Pt wires. The results showed that the structure of SWCNTs-MIPs is of orthogonal perovskite and the average particle size of the SWCNTs-MIPs was in the range of 10-30 nm. SWCNTs-MIPs exhibit good methanol gas-sensitive properties. At 90 °C, the response to 1 ppm methanol is 19.7, and the response to the interferent is lower than 5 to the other interferent gases (ethanol, formaldehyde, toluene, acetone, ammonia, and gasoline). The response time and recovery time are 50 and 58 s, respectively. Graphical Abstract: The as prepared SWCNTs-MIPs possesses good selectivity and high response to low concentrationmethanol [ABSTRACT FROM AUTHOR]

The novel sensors based on TiO2 nanotubes-supported MS (TiO2@MS, M = Cd, Zn) are synthesized via a simple wet chemical method at room temperature. The products are characterized with transmission electron microscopy (TEM), X-ray diffraction (XRD), and photoluminescence spectrum (PL). Their optical and morphological properties indicate the interaction between the TiO2 nanotube and MS nanoparticle. The gas-sensing properties of the obtained samples are studied. Sensors based on the TiO2@MS core/shell heterostructures all show improved gas-sensing properties. The results reveal that the improved performance of the nanocomposites strongly depends on the specific interaction between MS and support.

SnO nanoparticles have been successfully synthesized by a facile hydrothermal method from SnCl·2HO, hexamethylenetetramine, and trisodium citrate in water at 120 °C for 12 h. The effects of surfactant and precipitant on SnO synthesis were investigated. SnO nanoparticles can be synthesized in the temperature range of 120-180 °C with long reaction time in the presence of trisodium citrate. When NaOH was used as precipitant instead of hexamethylenetetramine, it is difficult to obtain SnO nanoparticles at 120 °C in the presence of trisodium citrate. SnO nanoparticles with an average size of about 5 nm show good crystallinity and excellent sensitivity to ethanol and acetaldehyde in about 55% relative humidity. [ABSTRACT FROM AUTHOR]

The zinc oxide (ZnO) nanorods with different aspect ratio (length/diameter) were grown directly on the porous silicon (PS) substrate through electrochemical synthesis. The obtained ZnO nanorods/PS products were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and gas-sensing test. Comparative study shows that the addition of nonionic polymer polyvinylpyrrolidone (PVP) into oxygenated zinc chloride electrolyte can modulate the crystal growth and the aspect ratio of ZnO nanorods from electrodeposition, thus, influence the gas-sensing properties of ZnO nanorods/PS composites. With appropriate amount of PVP in the electrolyte, the product possessing high-density and large aspect ratio ZnO nanorods has an obvious improvement of the NO-sensing performances with high sensitivity, fast response-recovery characteristic, and good repeatability and selectivity. The gas-sensing mechanism was discussed in the paper. The result indicated that the heterojunction effect of ZnO nanorods and PS may be responsible for the excellent gas-sensing properties. [ABSTRACT FROM AUTHOR]

Co 3 O 4 nanowires (NWs) arrays with the different valence metal-cations-doping (Zn, In and Sn) were synthesized by nanocasting method. The cations-doping hardly affects the morphology and mesoporous-structures, and all samples in bundles are composed of nanowires with the same diameter. Mesoporous-structures of all cations-doped Co 3 O 4 NWs results in a higher response to toluene gas. The different valence metal-cations-doping greatly affects the gas-sensing performance of Co 3 O 4 NWs sensors, which the response increases with the metal valence. Co 2.841 Sn 0.106 O 4 NWs sensor possesses the highest response (7.28) to 100 ppm toluene gas for the highest surface area and high-valence Sn-doping. Mesoporous-structure absorbs more oxygen to form O- and the thicker hole accumulation lay in air, while Sn-doping supplies electrons to combine holes in E V and increases the resistance in toluene gas. The high response is dominated with mesoporous-structures of all Co 3 O 4 NWs, while the gas-sensing performance could be further improved with Sn-doping. [ABSTRACT FROM AUTHOR]

Novel twin-layered SnO 2 well-oriented nanorods arrays have been synthesized by a substrate-free hydrothermal route of using sodium stannate and sodium hydroxide at 190 °C for 48 h. The characteristic results of the morphology and structure show that the synthesized nanoarray can be well indexed to tetragonal phase SnO 2 nanorods with a diameter of 20 nm and length of several hundred nanometers. The twin-layered SnO 2 nanorods array was tightly combined together by two layers of nanrods array with an apparent interface in the center. The results of the gas-sensing characteristics for various volatile organic compounds show that the sensor based on layered SnO 2 nanoarray exhibits the highest gas sensitivity, very fast response and recovery to isopropanol at the operating temperature of 250 °C, and good gas-sensing performances to ethanol and acetone have also been found at the operating temperature of 278 and 300 °C, respectively. The enhanced response is attributed to the numbers of the gas transport channels increasement leading to more effective surface areas and the additional modulation of the sensor resistance due to the potential barrier at nanorod/nanorod junctions of twin-layered SnO 2 well-oriented nanorods array. [ABSTRACT FROM AUTHOR]

As a promising gas-sensing material, tungsten tri-oxide with a wide band gap has attracted much attention. However, the preparation of tungsten tri-oxide nanomaterials in alkaline solution faces difficulties because of the weak solubility of the tungsten source. Here, the influence of pH values on the final products was investigated in detail. The results showed that pH value played no role in the phase for the final product. However, it had an obvious impact on the morphology evolution. Gas-sensing properties showed that the sensitivity increased with the increase of synthesised time because of improved crystallinity. Moreover, the sensitivity of the product synthesised in an alkaline environment was obviously higher than that of the product synthesised in an acid environment . [ABSTRACT FROM AUTHOR]

Porous corundum-type In 2 O 3 (rhombohedra In 2 O 3 , rh-In 2 O 3 ) nanosheets with unique shoeprint morphology are fabricated successfully by a facile, template-free solvent-thermal method. The products are characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), photoluminescence (PL) and N 2 adsorption–desorption. The response of the porous rh-In 2 O 3 nanosheets sensor to 50 ppm NO 2 is about 164, and the response/recovery times are not exceeding 5 s and 14 s, respectively. Porous lamellar structure could increase the number of the active sites and speed up the gas transportation, which is helpful for the enhancement of the response and rapid adsorption/desorption. The effect of morphology on the gas sensing responses is investigated. Compared with the nonporous rh-In 2 O 3 nanosheets sensor, the porous rh-In 2 O 3 nanosheets sensor exhibits significantly enhanced sensing performances toward NO 2 . Porous rh-In 2 O 3 nanosheets sensors show a long-term stability, which might be ascribed to the avoidance of aggregation of the nanostructures. [ABSTRACT FROM AUTHOR]