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Abstract Incorporation of the dimeric phthalocyanine into sandwich phthalocyaninato europium framework extends the conjugated electronic molecular structure and optimizes the ambipolar semiconducting properties of the QLS thin film-based OFET device, resulting in a significant increase in the hole and electron mobilities from 4.30 × 10−7 and 0.70 × 10−7 cm2 V−1 s−1 for monomeric phthalocyanine-containing triple-decker Eu 2 [Pc(SC 6 H 13) 8 ] 3 (1) to 0.07 and 0.06 cm2 V−1 s−1 for the dimeric phthalocyanine-containing quintuple-decker [Pc(SC 6 H 13) 8 ] 2 Eu 2 [BiPc(SC 6 H 13) 12 ]Eu 2 [Pc(SC 6 H 13) 8 ] 2 (2). This in turn induces an enhanced gas sensing detection performance for NO 2 with the sensitivity increasing from 23.4% for 1 to 46.7% ppm−1 for 2. The present result appears interesting in terms of improving the gas-sensing properties of phthalocyanine-based molecular materials via molecular design and synthesis rather than tuning the film morphology. Graphical abstract Image 1 Highlights • Incorporation of the dimeric phthalocyanine into sandwich phthalocyaninato europium framework extend the conjugated electronic molecular structure. • Fusing phthalocyaninato europium triple-decker into quintuple-decker resulted in an optimized semiconducting nature and enhanced NO 2 gas sensing performance. • The improved performance was achieved for the dimeric phthalocyanine-containing quintuple-decker with hole and electron mobilities of 0.07 and 0.06 cm2 V−1 s−1 and NO 2 detection sensitivity to 46.7% ppm−1. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Vertically aligned MoS 2 nanosheets on the surface of mesoporous In 2 O 3 nanocubes. • The interfacial transfer of electrons from In 2 O 3 to MoS 2 nanosheets. • Highly exposed edge sites of the MoS 2 to enhanced gas sensing properties of the sensor. • The sensor revealed excellent response to NO x at room temperature. Abstract The coupling of MoS 2 with In 2 O 3 is a well-known challenge due to the lower stability of MoS 2 in the presence of oxygen at high temperature. In the present work, stable mesoporous MoS 2 @In 2 O 3 composites were designed by a sonochemical reaction and a low temperature hydrothermal method, in which MoS 2 nanosheets (NSs) were vertically planted on highly mesoporous In 2 O 3 nanocubes. The mesoporous MoS 2 @In 2 O 3 -II nanocomposite with a MoS 2 and In 2 O 3 mass ratio of 1:1 exhibited a high response of 10.3–100 ppm NO x , and ultrafast response time of 1–9 s from 100 to 0.1 ppm. The enhance gas response of MoS 2 @In 2 O 3 -II reveals the synergistic effect of the interfacial transfer of electrons from In 2 O 3 nanocubes to MoS 2 NSs, and the highly exposed active edges of vertically aligned MoS 2 NSs. The MoS 2 @In 2 O 3 -II sensor is a promising candidate as a gas sensing material due to its excellent structure and outstanding properties at room temperature (RT). [ABSTRACT FROM AUTHOR]

Natural gas is known as the main source of energy and also contains significant and noble gases. Numerous researches have been performed to present novel methods for the detection and analysis of natural gas. In this study, Direct Simulation Monte Carlo (DSMC) method is used to evaluate the performance of a new micro gas sensor (MIKRA) for detection of helium in CH4/He gas mixture. In this sensor, the temperature difference of two arms inside a rectangular domain at low-pressure condition induces a Knudsen force which is proportional to physical properties of the gas. In order to define flow feature of a low-pressure gas inside the micro gas actuator, high order equation of Boltzmann is used to attain high precision results. To solve these equations, DSMC approach is used as a robust method for the non-equilibrium flow field. The effects of main factors such as length and gap of arms are comprehensively investigated in different ambient pressures. Furthermore, the effect of various concentrations of the CH4/He gas mixture on force generation is comprehensively studied. Our findings show that value of generated Knudsen force significantly different when the fraction of He in CH4/He gas mixture is varied. This indicates that this micro gas sensor could precisely detect the concentration of Helium gas inside a low-pressure CH4/He gas mixture. [ABSTRACT FROM AUTHOR]

Abstract A high-performance methanol gas sensor based on Co-Fe 2 O 3 /SmFeO 3 p-n heterojunction composite was prepared by sol-gel method with molecular imprinting technology (MIT). The composites were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), respectively. The results indicate that the Co2+/Co3+ entered Fe 2 O 3 by replacing Fe3+ which formed Co-Fe 2 O 3 , and constituted p-n heterojunction with SmFeO 3. The methanol gas sensing properties of Co-Fe 2 O 3 /SmFeO 3 were investigated. The formation of Co-Fe 2 O 3 /SmFeO 3 with MIT exhibited ultrahigh response, quick sensitivity and significant selectivity. The sensor based on Co-Fe 2 O 3 /SmFeO 3 with MIT to 5 ppm methanol gas at 155°C was 19.7 while the response to other test gases lower than 9. The superior sensing performance of composites attributes to the different Fermi levels of Co-Fe 2 O 3 and SmFeO 3 so that the electron delivered across the Co-Fe 2 O 3 /SmFeO 3 interfaces through band. The results reveal that Co-Fe 2 O 3 /SmFeO 3 would be a promising methanol gas sensing materials. Highlights • The enhanced response of Co-Fe 2 O 3 /SmFeO 3 is due to the doping and p-n heterojunction. • Good selectivity is attribute to the molecular imprinting technology. • The detection limit of the sensor for methanol is extremely low. • The optimal operating temperature (155 °C) is extremely low. [ABSTRACT FROM AUTHOR]

Abstract Large-scale fabrication, sensitivity and selectivity are important considerations for the practical applications of metal-oxide nanowire (NW) gas sensors fabricated by thermal evaporation. This paper reports the effect of the distance between the source and the microelectronic chips on the gas-sensing properties of ZnO and Zn 2 SnO 4 NW sensors fabricated by on-chip growth via thermal evaporation. Results indicate that the placement of the microelectrode chips in the range of 2–6 cm results in a similar response for ZnO NW sensors but an order of magnitude difference in response for Zn 2 SnO 4 NW sensors as measured at 10 ppm NO 2. The response of Zn 2 SnO 4 NW sensors is significantly higher than that of ZnO NW sensors. Similar to that of ZnO NW sensors, the NW–NW junction density of Zn 2 SnO 4 NW sensors strongly affects their NO 2 gas-sensing performance. The selectivity of Zn 2 SnO 4 NW sensors is much better than that of ZnO NW sensors under testing with interference gases, such as CO, H 2 , H 2 S and NH 3. Highlights • The gas-sensing performance of ZnO and Zn 2 SnO 4 nanowires were systematically compared. • The distance between source and chip strongly affected on gas response of Zn 2 SnO 4 nanowires. • The gas response of Zn 2 SnO 4 nanowires were strongly affected by the density of the nanowires. • The Zn 2 SnO 4 nanowire sensors exhibited a better selectivity to NO 2 gas as compared to ZnO nanowire sensors. [ABSTRACT FROM AUTHOR]

Emissions in pellet storages caused by the autooxidation of lipids have a negative impact on human health and lead to unpleasant odors. This study investigates (1) the emissions of softwood flakes during temperature treatments (150°C-240 °C), (2) the online monitoring of these emissions with gas sensors, (3) the impact of the thermal treatments on the lipid content in the flakes and (4) the correlation between the lipid content and the storage emissions. The results show a correlation between the temperature during the treatment, the α-pinene, furfural, and 2-methoxyphenol emissions, and the gas sensor response. The decrease of the lipid content is correlated to a decrease in storage emissions, especially hexanal and carbon monoxide. It is discussed if higher drying temperatures during pellet production can reduce the storage emissions of the pellets. The increasing fire risk in the dryer could be controlled by the gas sensors. [ABSTRACT FROM AUTHOR]

PDMS-PU (polydimethylsiloxane-polyurethane) sponge decorated with In(OH)3 (indium hydroxide) and BCP (bromocresol purple) particles is shown to be a room-temperature ammonia sensor with high sensitivity and excellent reproducibility; it can accomplish real-time detection and monitoring of ammonia in the surrounding environment. The superhydrophobic and yellowish In(OH)3-BCP-TiO2-based ammonia-responsive (IBT-AR) sponge changes to a purple superhydrophilic one when exposed to ammonia. Notably, after reacting with ammonia, the sponge can recover its original wettability and color after heating in air. The wettability, color and absorption signal of IBT-AR sponge have been measured for sensing ammonia using the water contact angle, macroscopic observation and UV-vis absorption spectrometry, respectively. The minimum ammonia concentrations that can be detected by the sponge wettability, color and absorption signal are 0.5%, 1.4 ppm and 50 ppb, respectively. This kind of sponge with smart wettability and color is a promising new ammonia detector. [ABSTRACT FROM AUTHOR]

ZnO nanoparticles, nanorods and nanosheets were in-situ deposited on the interdigitated gold electrodes by hydrothermal treatment of electrospun nanofibers containing zinc salt precursors and seed-induced solution growth of ZnO. The nanostructured ZnO was further covered with polyaniline (PANI) via vapor phase polymerization of aniline or dip-coating with water-dispersible PANI to prepare ZnO/PANI nanocomposites. The morphology and structure of the nanocomposites were investigated by scanning electron microscopy, X-ray diffraction patterns and Fourier transform infrared spectroscopy. The electrical responses of the nanocomposites toward NH 3 have been examined at room temperature, and the nanocomposite revealed much better gas sensing properties than ZnO or PANI alone. The morphology of the nanocomposites had a great effect on their sensing properties. Specifically, the composite of ZnO nanosheets covered with vapor phase polymerized aniline demonstrated optimal sensing performance, featuring high response magnitude (relevant resistance change of ∼2150% towards NH 3 as low as 10 ppm), ultralow limit of detection (∼5 ppb), good repeatability and excellent selectivity. It is proposed that the morphology and the interactions between p-type PANI and n-type ZnO are responsible for the highly desirable sensing properties of the nanocomposites. [ABSTRACT FROM AUTHOR]

In this paper, a nitrogen dioxide (NO2) gas sensor using nitrogen‐doped double‐walled carbon nanotubes (N‐DWCNTs) with different types of nitrogen is demonstrated, and the sensor performance to the pyridinic nitrogen is related. The ratio of nitrogen is controlled by the temperature applied for the synthesis. It is found that the fabricated sensor from N‐DWCNTs enable an approximately threefold improvement in NO2 detection compared to the sensor from DWCNTs. Also, the improvement of sensor response of N‐DWCNTs more depends on the pyridinic site than the other types of nitrogen, because it can strongly interact with the NO2 molecule. The sensing mechanism is attributed to the charge transfer between the NO2 molecule and the sensing materials (especially with pyridinic site), which shifts the Fermi level, resulting in a decrease of the electrical resistance. Furthermore, the relation between the sensor response and the concentration of NO2 is derived based on Langmuir adsorption isotherm, and the calculated detection limit can be down to 0.14 ppm, which suggests that the N‐DWCNTs‐based sensor is a promising approach for low concentration NO2 detection at room temperature. [ABSTRACT FROM AUTHOR]

Well-oriented Sm-doped SnO 2 nanoarrays were synthesized by a one-pot substrate-free hydrothermal route. The surface defect of the SnO 2 nanorods caused by the Sm ions doped into the SnO 2 lattice was investigated. The gas-sensing properties indicated that the Sm-doped SnO 2 nanoarrays with optimized doping level of 1.50 at% exhibited an excellent sensing response toward isopropanol at a lower temperature. The enhancement response of the Sm-doped SnO 2 nanoarrays was discussed. [ABSTRACT FROM AUTHOR]

We present resonant tunneling diode-photodetectors (RTD-PDs) with GaAs0.15Sb0.85/AlAs0.1Sb0.9 double barrier structures combined with an additional quaternary Ga0.64In0.36As0.33Sb0.67 absorption layer covering the fingerprint absorption lines of various gases in the mid-infrared wavelength spectral region. The absorption layer cut-off wavelength is determined to be 3.5 μm, and the RTD-PDs show peak-to-valley current ratios up to 4.3 with a peak current density of 12 A/cm−2. The incorporation of the quaternary absorption layer enables the RTD-PDs to be sensitive to illumination with light up to the absorption lines of HCl at 3395 nm. At this wavelength, the detector shows a responsivity of 6.3 mA/W. At the absorption lines of CO2 and CO at 2004 nm and 2330 nm, respectively, the RTD-PDs reach responsivities up to 0.97 A/W. Thus, RTD-PDs pave the way towards high sensitive mid-infrared detectors that can be utilized in tunable laser absorption spectroscopy. [ABSTRACT FROM AUTHOR]

We report a self-powered active gas sensor that can detect acetylene (C 2 H 2 ) reliably and accurately by measuring the output voltages generated during contact electrification between bimetallic Al/Ag-carbon nanofiber (CNF) network and porous PDMS friction surfaces. Upon exposure to certain concentrations of C 2 H 2 , the triboelectric charging behavior of the sensor is altered due to a surface reaction between C 2 H 2 molecules and the Al/Ag-CNF friction layer. The sensor exhibits excellent sensitivity of 83% and a quick response time of 88 s to C 2 H 2 gas at a concentration of 1000 ppm. Importantly, the friction surfaces exhibit high hydrophobicity, which preferentially minimizes the influence of humidity and provides superior sensing performance even in a high humidity atmosphere (∼87% relative humidity). We believe that the proposed approach for harvesting energy and sensing can be advantageous in practical applications and will stimulate new research for the development of high performance, precise, reliable, and durable self-powered active gas sensors that can operate in hostile environments. [ABSTRACT FROM AUTHOR]

A facile and cost-effective preparation process for Ag nanoparticles modified Si nanowires (Ag NPs@RNWs) was first developed based on the metal-assisted chemical etching (MACE)-produced Ag dendrites. Partial removal of the wrapped Ag dendrites and a crucial tetramethylammonium hydroxide (TMAH) post-etching treatment are sequentially involved in the process. The crucial step of TMAH-etching induces a loose array of needle-like SiNWs with highly rough surface (RNWs), and causes redistribution of the attached Ag NPs. HRTEM observations reveal that numerous tiny Ag NPs with size of 2–6 nm are firmly inlaid on the concave-convex surface of RNWs. Comparative investigations of NO 2 -sensing properties among the bare-SiNWs, RNWs and Ag NPs@RNWs were carried out at room temperature. The Ag NPs@RNWs sensor exhibits considerably enhanced response (about five times higher) compared with bare-SiNWs and can rapidly response ultrararefied NO 2 with deep ppb level. Above results demonstrate the considerable effect of the Ag NPs modification process developed here; the resulted rough and loose array promotes the response speed of the SiNWs sensors and the formed tiny Ag NPs contributes dramatic enhancement in response sensitivity. The enhanced response of Ag NPs@RNWs is analyzed based on Ag modification-induced electronic sensitization and TMAH etching-induced structural modulation. [ABSTRACT FROM AUTHOR]

Based on the electrochemical properties of a series of metallophthalocyanines this article shows that the phthalocyanine bearing four alkoxy groups and twelve fluorine atoms behaves approximately as those with eight fluorine atoms. This indicates that the electron-donating effect of one alkoxy group balances the electro-withdrawing effect of one fluorine atom. We engaged three metallophthalocyanines, namely the octafluoro copper phthalocyanine, Cu(F 8 Pc), an octaester metallophthalocyanine and a phthalocyanine bearing four alkoxy groups and twelve fluorine atoms, Zn(T 4 F 12 Pc), in building original conductometric transducers that are Molecular Semiconductor – Doped Insulator heterojunctions (MSDIs) in association with the highly conductive lutetium bisphthalocyanine, LuPc 2 . Whereas the octaester derivative and Zn(T 4 F 12 Pc) exhibited a negative response to ammonia, as expected for p-type materials, Cu(F 8 Pc) exhibited a particular behavior. At low humidity levels, 30 and 10% rh, the current of the Cu(F 8 Pc)/LuPc 2 MSDI decreases, similarly to p-type devices, but at higher relative humidity values, 70% rh, the current increases under ammonia, which is the signature of a n-type behavior. This ambipolar behavior is unique amongst semiconducting sensing materials. This work opens the way to the study of ambipolar materials as sensing materials for the development of a new type of conductometric gas sensors. [ABSTRACT FROM AUTHOR]

One of the most important issues in the development of gas sensors for monitoring gaseous pollutants, such as ozone (O 3 ) and nitrogen dioxide (NO 2 ), is the fabrication of sensor arrays that possess different responses for recognizing patterns of different analytes. Here, we develop a chemiresistive sensor array with a tailoring response by using Zn 2+ doping tailored molybdenum disulfide (MoS 2 ). Compared with the sensor of pure MoS 2 , the responses of the sensor of MoS 2 with 5% Zn 2+ toward five analytes, including O 3 and NO 2 , are improved by more than 160%, indicating that Zn 2+ doping successfully tailor the sensing performances of MoS 2 matrix. Thus, this will be a promising approach to constructing a versatile sensor array, by doping a wide variety of metallic ions and tailoring the doping amounts in the MoS 2 matrix. Furthermore, the sensor of MoS 2 with 5% Zn 2+ exhibits the detection limits of 17 and 215 ppb for O 3 and NO 2 , respectively. The sensor array can identify O 3 , NO 2 and other analytes within 14 s in the real-world detection. This approach to fabricating a tunable and discriminative sensor array may lead to a valuable real-world application for the continuous and low-cost monitoring of gaseous pollutants. [ABSTRACT FROM AUTHOR]

The potential sensor materials of scroll-like dodecylamine-templated vanadium oxide VO x nanotubes doped with Co 2+ or Fe 3+ have been prepared using a sol-gel technique followed by the hydrothermal treatment. The resultant samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning and transmission electron microscopies, thermal and elemental analysis. The gas sensing properties of the metal cations doped VO x nanotubes have been tested in the wide range of working temperatures and targets’ concentrations towards ammonia, ethanol, methanol, toluene and acetone. The highest sensor activity was revealed for ethanol. Stability and electronic properties of pristine and metal doped VO x layers as well as their ad-complexes with O 2 as intermediates during the working process of a sensor were studied by DFT calculations. The study suggests two different mechanisms of cations' action on sensing properties of a VO x compound. In absence of steric obstacles, Co 2+ doing is predicted to be the most efficient dopants for beneficial activation of VO x sensing properties. [ABSTRACT FROM AUTHOR]

This work reports the air-annealing effect on the structure, optical and electrical properties of tin sulfides (SnS) thin films and the capability of using these films for gas sensing application. The X-ray diffraction investigation shows that the predominant phase SnS (040) plane for the as-deposited film changes into Sn 2 S 3 (201) plane after annealing. Furthermore, the annealed films at high temperatures (533 and 553 K) are partially oxidized leading to the formation of mixed tin sulfide oxides-Sn 2 S 3 (MTO-Sn 2 S 3 ) heterostructure thin film. The optical constants and thickness of films are calculated using Swanpole's method. Both optical band gap and electrical activation energy increased after annealing in the range (493–553 K) for 0.5 h in ambient air. Optical and electrical results indicate the existence of mixed phase characteristics of studied films. The gas sensing properties of MTO-Sn 2 S 3 composite are investigated for methane gas detection. The fabricated sensor exhibits a weak sensitivity at low operating temperatures (50 and 100 °C). The sensitivity improves at high temperatures reaching its maximum at 250 °C. At 250 °C the response and recovery times are 250 and 82 s, respectively. [ABSTRACT FROM AUTHOR]

Nitrogen dioxide (NO 2 ) detection is critical because NO 2 is a typical toxic gas that is harmful to humans as well as the environment. Over the last few decades, various nanomaterials such as nanowires, nanoparticles, carbon nanotubes, and graphene have been widely utilized to construct the platform (i.e., supporting material) of NO 2 gas sensors. Among these materials, carbon nanomaterials (e.g., graphene and carbon nanotubes) have received increasing attention owing to their outstanding physical and electrical properties required for NO 2 detection. Recently, many attempts have been made to blend the carbon nanomaterials with other materials, resulting in the creation of composite materials with enhanced electrical conductivity and physical properties for highly sensitive and selective detection of NO 2 gas. As such, blended or stacked carbon composite materials offer higher efficiency (i.e., improved sensitivity and response/recovery time) for detecting NO 2 gas in comparison with pristine carbon nanomaterials. In this review, we consider state-of-the-art amperometric NO 2 gas sensors based on carbon nanomaterials with respect to their dimensionalities, and we discuss the enhanced gas-sensing performance achieved by using composite materials. [ABSTRACT FROM AUTHOR]

Pecan-kernel-like TiO 2 hierarchical architectures and Au-loaded TiO 2 were successfully synthesized via facile hydrothermal synthesis method and simple precipitation route. A series of material characterization methods were employed to characterize the structure, morphology of as-synthesized materials. Characterization indicate that uniform and independent pecan-kernel-like TiO 2 hierarchical architectures consisted by nanorods stacking were formed, and Au nanoparticles were distributed uniformly on the surface of TiO 2 materials. In addition, The gas sensing performance of the sensors based on pure TiO 2 and different amounts of Au-loaded TiO 2 were systematically investigated. The noble metal Au improved the catalytic efficiency which played crucial role in enhancing the performance of the gas sensor. The results indicated that the sensor with 5 wt% Au-loaded TiO 2 exhibited the highest response, short response/recovery time, excellent repeatability and stability to toluene. [ABSTRACT FROM AUTHOR]

The large number of electronics channels has become an issue to the further applications of micropattern gas detectors (MPGDs) and poses a big challenge for the integration, power consumption, cooling, and cost. Induced position encoding readout technique provides an attractive way to significantly reduce the number of readout channels. In this paper, we present an extensible induced position encoding readout method for MPGDs. The method is demonstrated by the Eulerian path of the graph theory. A standard encoding rule is provided, and a general formula of encoding and decoding for n channels is derived. Under the premise of such method, a 1-D induced position encoding readout prototyping board is designed on a $5\times 5$ cm2 thick gas electron multiplier, where 47 anode strips are readout by 15 encoded multiplexing channels. Verification tests are carried out on an 8-keV Cu X-ray source with 100- \mu \text{m} slit. The test results show a robust feasibility of the method and have a good spatial resolution and linearity in its position response. This method can dramatically reduce the number of readout channels, has potential to build large-area detectors, and can be easily adapted to other detectors like MPGDs. [ABSTRACT FROM PUBLISHER]

The hierarchical carpet-like WO 3 microflowers were synthesized via a facile one-step hydrothermal method by using oleic acid as a oriented growth reagent. The as-synthesized WO 3 microflowers show a triclinic crystal structure and are basically hierarchical assemblies of carpet-like nanosheets made up of the subunit of bundle-like nanowires. Based on the morphology evolution process, a possible crystal growth and nanostructure assembling mechanism were proposed. The prepared WO 3 microflower sensor exhibits a gas sensing response of about 228 when exposed to 10 ppm of toxic NO 2 gas at 200 °C. [ABSTRACT FROM AUTHOR]

ZnO and its composites in various morphologies have been shown promising properties in a wide spectrum of applications. Herein, ZnO nanotubes and ZnO/ZnCo 2 O 4 nanotubes have successfully synthesized by single capillary electrospinning, a heat treatment process was followed to obtain the tubular morphology. The structure of as-prepared nanotubes was confirmed by XRD and EDX analyses. The tubular morphology and its dimensions were identified by SEM and TEM microscopes. The specific surface area and porous structure of ZnO and ZnO/ZnCo 2 O 4 nanotubes were characterized by N 2 -absorption-desorption isothermal analysis (BET). Excellent improvement in the gas sensing performance has recorded of composite ZnO/ZnCo 2 O 4 nanotubes with n-p heterojunction in comparison with pristine ZnO nanotubes. High response (34) with rapid response (3.2 s) and recovery (3.4 s) behaviours have clearly observed of as-prepared nanocomposite ZnO/ZnCo 2 O 4 nanotubes toward 100 ppm acetone at an optimal temperature of 175 °C. The tubular morphology and heterojunction could be the reasons of as-reported improvements of ZnO/ZnCo 2 O 4 nanotubes. The gas sensing properties and mechanism of the as obtain materials in the air and acetone ambient are carefully illustrated and discussed. These finding could provide a potential material for gas sensing application and suggested to test in other fields. [ABSTRACT FROM AUTHOR]

Ag-doped hollow urchin-like spheres In 2 O 3 hierarchical nanostructures are developed for NO 2 detection. Such unique architectures are synthesized by a facile and efficient solvothermal route combined with the subsequent thermal treatment. Various techniques, including X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM) were employed to acquire the crystalline and morphological information of the as-obtained samples. Gas sensing performances of the sensor devices fabricated from pure and Ag-doped In 2 O 3 were systematically investigated. The results indicate that the sensors based on Ag-doped In 2 O 3 in certain molar ratio of AgNO 3 to In 2 O 3 (1:100) exhibit the largest response toward 1 ppm NO 2 , which is almost 23 times higher than that of the sensor based on pure In 2 O 3 at the optimum operating temperature. It demonstrates that the Ag-doping can significantly improve the response to NO 2 . The excellent and enhanced NO 2 sensing performances of Ag-doped In 2 O 3 can be attributed to its novel hierarchical structure and the catalytic activity of Ag nanoparticles. [ABSTRACT FROM AUTHOR]

The application of conventional tin oxide thin film sensors is limited by its low response. In this study, a heterojunction thin film composed of nickel oxide deposited by electron beam evaporation and tin oxide prepared by radio-frequency (RF) magnetron sputtering has enhanced gaseous ethanol sensing properties. The 5 nm NiO/100 nm SnO 2 gas sensor shows the excellent response 7.9 at 250 °C for 100 ppm gaseous ethanol, good reproducibility, as well as good linearity. In addition, this sensor can measure the ultra-low concentration of gaseous ethanol, and the concentration can be as low as 100 ppb. The gas sensitive properties is related to the thickness of nickel oxide and the mechanism is discussed. [ABSTRACT FROM AUTHOR]

Amorphous double-shell Fe 2 O 3 hollow nanospheres decorated with PdO nanoparticles were synthesized via a template-free hydrothermal method combined with subsequent annealing process. The chemical composition and microstructure evolution were examined using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), and transmission electron microscope (TEM). Interestingly, the internal structure of hollow spheres could be controlled by varying the reaction time. The formation of such structures was attributed to the combined effect of ripening and hydrogen ions etching process. The sensing properties of Fe 2 O 3 hollow nanospheres before and after functionalization with PdO nanoparticles were investigated. The PdO-loaded Fe 2 O 3 sensor exhibited obviously enhanced response to acetone compared with their unloaded counterparts. The improvement may arise from unique structure and catalytic effect of PdO in promoting the dissociation of gas molecules. [ABSTRACT FROM AUTHOR]

This study reports a facile but efficient synthesis method for the preparation of titanium oxide coated vanadium oxide (V 2 O 5 @TiO 2 ) core-shell nanostructures in water bath at mild temperatures (≤100 °C). This method is featured as short reaction time, no requirement of high temperature calcination (>500 °C) for TiO 2 crystallization, easily tunable TiO 2 shell thickness, high yield, and good reproducibility. The as-prepared V 2 O 5 @TiO 2 nanocomposites can exhibit a large surface area, and good stability. The gas-sensing properties of V 2 O 5 @TiO 2 core-shell nanoparticles were investigated, it was found that the core-shell materials exhibit superior sensing performance (high response, good selectivity, and short response time) toward ammonia than pure TiO 2 or V 2 O 5 sensor materials. Besides experimental studies, theoretical simulations using Density Functional Theory (DFT) method were conducted to fundamentally understand the adsorption behavior of different target gases, such as ammonia, ethanol, methanol, acetone and n -butylamine on the anatase TiO 2 (101) surface. The results show that the ammonia is of the lowest adsorption energy (−1.04 eV), which can help explain why the V 2 O 5 @TiO 2 core-shell sensor exhibits excellent response toward ammonia. These findings may bring a new insight into the designing of TiO 2 -based nanocomposites with diverse functions; meanwhile, provide a better understanding on interactions, at atomic scale, between the TiO 2 crystalline surface and the reducing gases. [ABSTRACT FROM AUTHOR]

Nanocomposites CoO x /SnO 2 based on tin oxide powders with different crystallinity have been prepared by wet chemical synthesis and characterized in detail by ICP-MS, XPS, EPR, XRD, HAADF-STEM imaging and EDX-STEM mapping. It was shown that cobalt is distributed differently between the bulk and surface of SnO 2 nanocrystals, which depends on the crystallinity of the SnO 2 matrix. The measurements of gas sensor properties have been carried out during exposure to CO (10 ppm), and H 2 S (2 ppm) in dry air. The decrease of sensor signal toward CO was attributed to high catalytic activity of Co 3 O 4 leading to oxidation of carbon monoxide entirely on the surface of catalyst particles. The formation of a p -CoO x / n -SnO 2 heterojunction results in high sensitivity of nanocomposites in H 2 S detection. The conductance significantly changed in the presence of H 2 S, which was attributed to the formation of metallic cobalt sulfide and removal of the p – n junction. [ABSTRACT FROM AUTHOR]

Hierarchical MoO 3 microboxes were successfully prepared via a facile hydrothermal method and use MnCO 3 microcubes as the templates. The morphology and structure of as-obtained product were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption-desorption measurement (BET). The results show that hierarchical MoO 3 microboxes possess regular size and morphology, and the size is about 2–3 μm, the hierarchical shell of MoO 3 microboxes with a thickness of about 150 nm. The response value of sensor based on hierarchical MoO 3 microboxes to 100 ppm ethanol is 78 at an operating temperature of 260 °C, and the response and recovery time are less than 15 and 5 s, respectively. It is expected that the hierarchical MoO 3 microboxes with the advantages of hierarchical structure and hollow structure will become a promising functional material in monitoring and detecting of ethanol. [ABSTRACT FROM AUTHOR]

Sn x Ti 1-x O 2 nanofilms deposited at 500 °C heated glass substrate by automated nebulizer spray pyrolysis method. Stabilized anatase phase of polycrystalline nature with decremented intensity were observed in XRD study, correspondingly precursor materials (Ti, Sn, O) were confirmed by XPS, EDS. The surface profilometer shows a coated films thickness and the surface morphology illustrates a various structure such as granular spherical shape, micro grain petal-like structure, a granular structure with wider petals (stripe likes) and void, crack less agglomerated grain particles were acquired with respect to Sn concentration. An optical study shows the maximum oscillating nature of transmittance is 66.8% (at = 524.4 nm) for Sn = 10.00% and the resultant transmittance values were enhanced and their sharp absorption edge shows blue shift by increase Sn concentration. Similarly, band gap values (E g = 3.20 eV–3.56 eV) were increased due to Moss-Burstein shift. Notably, gas sensing performance of Sn x Ti 1-x O 2 shows the highest sensitivity behaviour to Sn = 5.00% (Y 0.05 Ti 0.95 O 2 ) for reducing gas of C 2 H 6 O at 150 °C with 300 ppm gas concentration. All coated films exhibit the better sensitivity for ethanol (C 2 H 6 O) gas against other gases (CH 4 O, C 3 H 8 O, NH 3 , and C 3 H 6 O). [ABSTRACT FROM AUTHOR]

We report a novel method to significantly improve the C 6 H 6 -sensing performance of Si nanowires through the combination of TeO 2 branches and Pd sensitization. The morphological investigation revealed that TeO 2 branches were densely formed on the stem nanowires (NWs). The sensor responses of the Pd-functionalized branched NWs exhibited superior sensor responses of 55.19 to C 6 H 6 gas. In particular, Pd nanoparticles enhanced the sensor response to C 6 H 6 gas most efficiently, increasing the sensor response by 173.5%. Possible mechanisms for the sensing of the Pd-decorated branched nanowires will be associated with resistance modulation along the branch TeO 2 nanowires (including catalytic Pd effects), at the networked homojunctions between the branch TeO 2 nanowires, at the boundaries of the TeO 2 nanograins, and at the Pd/TeO 2 heterojunctions. [ABSTRACT FROM AUTHOR]

The features of conductometric gas sensors based on metal oxide composites are considered. The methods of the composites forming and the advantages of their using in the development of gas sensors are discussed. It is given the analysis of the factors that reduce the effectiveness of the composite using in conductometric gas sensors and can restrict application of nanocomposites in these devices. Technology features of composite synthesis and device fabrication, which should be taken into account while designing and fabricating sensors based on metal oxide composites, are considered. The mechanisms explaining the operation of conductometric gas sensors based on metal oxide composites are also discussed. [ABSTRACT FROM AUTHOR]

Eight different types of nanostructured perovskites based on YCoO3 with different chemical compositions are prepared as gas sensor materials, and they are studied with two target gases NO2 and CO. Moreover, a statistical approach is adopted to optimize their performance. The innovative contribution is carried out through a split-plot design planning and modeling, also involving random effects, for studying Metal Oxide Semiconductors (MOX) sensors in a robust design context. The statistical results prove the validity of the proposed approach; in fact, for each material type, the variation of the electrical resistance achieves a satisfactory optimized value conditional to the working temperature and by controlling for the gas concentration variability. Just to mention some results, the sensing material YCo0.9Pd0.1O3 (Mt1) achieved excellent solutions during the optimization procedure. In particular, Mt1 resulted in being useful and feasible for the detection of both gases, with optimal response equal to +10.23% and working temperature at 312 °C for CO (284 ppm, from design) and response equal to -14.17% at 185 °C for NO2 (16 ppm, from design). Analogously, for NO2 (16 ppm, from design), the material type YCo0.9O2.85 + 1%Pd (Mt8) allows for optimizing the response value at -15.39% with a working temperature at 181.0 °C, whereas for YCo0.95Pd0.05O3 (Mt3), the best response value is achieved at -15.40% with the temperature equal to 204 °C. [ABSTRACT FROM AUTHOR]

Nanocomposites constructed by combining graphene (G) with oxide semiconductors have gained tremendous recent attentions in the field of gas sensors. In this work, we present a facile, green, and low-cost solvothermal process to synthesize the G-W 18 O 49 nanocomposites with different G contents. The gas-sensing properties of the G-W 18 O 49 nanocomposites towards ethanol and acetone vapors were systematically studied. Results showed that the amount of G had obvious influence on both the morphologies and the gas-sensing behaviors of the G-W 18 O 49 nanocomposites. With low amount of 0.5 wt% G, the G-W 18 O 49 nanocomposites exhibited significantly enhanced gas-sensing properties compared to pure W 18 O 49 nanorods, which can be attributed to high yield and uniform distribution of the W 18 O 49 nanorods decorated on the G surfaces as well as the synergistic effects between the G and W 18 O 49 nanorods. The G-W 18 O 49 nanocomposites are more sensitive to acetone than to ethanol, making them promising candidates for novel acetone sensors. This work shed light on the relationship between the G content and the gas-sensing performance of the G-W 18 O 49 nanocomposites and could be extended to the development of other hybrid materials for gas-sensing applications. [ABSTRACT FROM AUTHOR]

By developing a new in-situ surface modification route, P3HT-SnO 2 composite gas sensor with strikingly improved performance was fabricated via modifying the surface of SnO 2 porous nanosolid (SnO 2 PNS). The experimental results indicate that the sensor fabricated from pristine SnO 2 PNS exhibited quite poor sensing performance to NO 2 gas. In contrast, when the adsorbed impurity molecules were removed from the surface of SnO 2 PNS, followed by introducing P3HT into the pores in-situ way, P3HT-SnO 2 composite gas sensors with greatly improved performance were fabricated, namely, lower working temperature, higher sensor response, much faster response-recovery speed and excellent selectivity. This phenomenon was explained by the appearance and disappearance of “synergetic effect” between P3HT and SnO 2 , which was resulted from the forward electron transfer process from P3HT to SnO 2 and the backward process. [ABSTRACT FROM AUTHOR]

Porous NiO/SnO 2 microspheres and microcubes were obtained using a facile chemical solution route combined with a subsequent calcination process. The morphologies and crystal structures of the products were comprehensively characterized via X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, thermogravimetric-differential thermal analysis, and Brunauer–Emmett–Teller N 2 adsorption-desorption analyses. The process of inducing porosity began with the NiSn(OH) 6 precursors formed by the co-precipitation of the metal ions from the aqueous solution. Thermal decomposition of the precursors led to an intimate mixture of cubic phase NiO and tetragonal phase SnO 2 and formed the porous NiO/SnO 2 microspheres and microcubes. The gas-sensing properties of the as-prepared porous NiO/SnO 2 microspheres and microcubes for toxic volatile organic compounds (VOCs), such as formaldehyde, ethanol, benzene, methanol, acetone, and toluene, were investigated. Compared with other VOCs gases, the porous NiO/SnO 2 microsphere and microcube sensors exhibited a high response to formaldehyde. As for the porous NiO/SnO 2 microsphere sensor, the detection limit of formaldehyde was approximately 0.13 ppm (signal-to-noise ratio, S/N = 3). The relationship between the gas-sensing performance and the microstructure of the porous NiO/SnO 2 micro/nanomaterials was also discussed. [ABSTRACT FROM AUTHOR]

A high-sensitivity ammonia gas sensor based on molybdenum disulfide/zinc oxide (MoS 2 /ZnO) nanocomposite film was reported in this paper. The multilayered film of MoS 2 /ZnO was fabricated on a PCB substrate with interdigital electrodes (IDE) via layer-by-layer self-assembly technique. The surface morphology, nanostructure and elemental composition of the MoS 2 /ZnO nanocomposite were described by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results showed that ZnO and MoS 2 had good contact in terms of electric and structure. Ammonia-sensing properties of the sensor were investigated by exposing it to various concentrations of ammonia at room temperature. The experimental results revealed that the MoS 2 /ZnO nanocomposite film sensor exhibited ultra-high sensitivity, good repeatability, excellent stability, outstanding selectivity and fast response/recovery characteristics. Moreover, the sensing device exhibited significantly enhancement in ammonia gas sensing compared to the drop-casted pure ZnO and layer-by-layer self-assembled MoS 2 /polymer sensors. These results render the MoS 2 /ZnO nanocomposite a promising candidate for high-performance ammonia sensing at room temperature. The underlying sensing mechanisms of the MoS 2 /ZnO sensing device towards ammonia gas were ascribed to the excellent electrochemical properties and special nanostructure of the nanocomposite. [ABSTRACT FROM AUTHOR]

WO 3 -based gas sensors have received considerable attention in breath acetone analysis for their great potential in the clinical diagnosis of diabetes. However, several key challenges, especially sensitivity, selectivity and stability, should be further addressed before WO 3 -based materials are capable of applying for acetone analysis. Herein, C-doped WO 3 sensing materials were synthesized by coupling carbon sphere templates with post-heat treatment method. The resulting materials are composed mainly of ε -WO 3 , a phase with high selectivity to acetone, and featured with porous hollow sphere structure. The as-fabricated sensors based on the C-doped WO 3 materials show high sensitivity to acetone down to 0.2 ppm. By contrast, the sensors show substantially lower response to other gases including ethanol, methanol, toluene, NH 3 , NO and CO. In addition, the effect of the relative humidity ( RH ) on the sensing property was studied and it was found that the response distinction to acetone even at 90% RH was sufficient to separate diabetics from healthy people. More attractively, the ε -phase WO 3 could maintain its acetone sensing activity at 350 °C over 3 months, suggesting excellent long-term stability. The results gained herein may be useful for rational design of new types of highly selective and stable acetone sensing materials. [ABSTRACT FROM AUTHOR]

Chromium oxide (Cr 2 O 3 ) micro/nanospheres are skillfully designed and successfully synthesized by a facile route without any templates or surfactants. Morphology and structure characterizations reveal that Cr 2 O 3 micro/nanospheres are assembled by irregular nanoparticles as primary building blocks and present loose hierarchical architecture. The Cr 2 O 3 micro/nanospheres sensors exhibit rapid response and recovery kinetics (5 s and 6 s), good selectivity and remarkable repeatability to ethanol gas at 220 °C, and the sensitivity to 100 ppm ethanol is about 4 times higher than that of the collapsed Cr 2 O 3 micro/nanospheres based sensors. The enhanced gas sensing performances are predominantly attributed to the synergistic effect of the unique sphere-like architecture and highly loose structure, thus providing beneficial conditions to greatly improve gas diffusion, adsorption and surface reaction. [ABSTRACT FROM AUTHOR]

Nanocrystalline Al-doped ZnO (AZO) thin films were deposited on glass substrates at room temperature by Mather-type plasma focus device using a ZnO target with an Al content of 3 wt%. The effect of number of focus shots on the microstructure, elemental composition, surface morphology and H 2 gas sensor performance of AZO deposited thin films were investigated. X-ray diffraction (XRD) analysis confirmed the polycrystalline nature of the all deposited AZO thin films. XRD results also indicated strong dependence of crystallinity and crystallite size of deposited thin films on number of focus shots. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses led to the conclusion that the size of grains/clusters on the surface of thin films and the surface roughness of deposited samples enhance with increasing of focus shots. The experiments and measurements involving the AZO deposited thin films towards hydrogen were carried out at different operating temperatures within 150–400 °C for various concentrations of hydrogen in air. The H 2 sensing response enhanced with concentration and operating temperature, and reached its maximum at 300 °C–1000 ppm concentration of hydrogen gas. The results also indicated shorter response times for samples deposited with less focus shots. [ABSTRACT FROM AUTHOR]

In this present study, TiO 2 nanofilms were deposited at 773 K by using titanium tetra isopropoxide as precursor and ethanol as solvent with the variation of pH for x = 2.50, 6.50, and 10.50 through automated nebulizer spray pyrolysis (ANSP) technique. The properties of Structural (XRD), Topography (AFM) and surface morphology (FESEM) of the film shows the average particle size, average roughness and particle shape were drastically changed with respect to electrolyte pH parameter. Anatase phase of polycrystalline tetragonal structure was revealed by structural (XRD) and X-ray photoelectron study (XPS). The XPS study confirms the films that not detected with the other trace of impurity except carbon. The optical transmittance decreased at higher pH and their band gap energy in the range of 3.29–3.43 eV was obtained with the change in electrolyte pH parameter for all the TiO 2 film. The electrical study of dielectric constant, tan δ is continue to decrease with increase the frequency and the maximum dielectric constant and tan δ value observed as ∼41.73 and ∼03.62 for pH = 6.50. The adsorption and desorption of various gas sensing performance of TiO 2 film were analysed with the function of temperature and the high sensing response of NH 3 where noted. [ABSTRACT FROM AUTHOR]

In this work, 0–1.00 wt% Ru-loaded nickel oxide nanoparticles were synthesized by the chemical precipitation/impregnation methods and systematically characterized for gas-sensing applications. Characterizations by electron microscopy, X-ray diffractometry, X-ray photoemission spectroscopy showed that primary particles were face-centered-cubic structure of NiO and RuO 2 nanoparticles were dispersed within larger NiO NPs. Nitrogen adsorption studies also revealed that specific surface area of RuO 2 /NiO nanoparticles increased with increasing Ru content. Gas-sensing measurement showed that increasing Ru loading content considerably improved C 2 H 5 OH response and selectivity against H 2 S, NO 2 , SO 2 , H 2 , and NH 3 at an operating temperature of 350 °C. In particular, the NiO sensor with the highest Ru content of 1.00 wt% showed a high p-type sensor response of 35.9–2000 ppm C 2 H 5 OH at 350 °C, which was about three times as high as that of unloaded one. Therefore, RuO 2 loading by impregnation is an effective mean to improve the gas-sensing performances of p -type NiO-based gas sensors. [ABSTRACT FROM AUTHOR]

A series of nanocrystalline nickel-copper ferrites having chemical composition NiCuFeO (x = 0.0, 0.2, 0.4, 0.6 and 0.8) has been synthesized via sol-gel method to investigate their surface morphological, nanostructural, optical and thermal properties. The synthesized nanostructures have been fabricated by spin coating method in order to examine the potential applicability of the films for the leakage detection of harmful gases such as liquefied petroleum gas (LPG) and carbon dioxide gas. The leakage detection of the gases has been tested at room temperature (25 °C) as it provides good life time and stability to the sensor without any power consumption. The effect of various compositions of nanostructured nickel-copper ferrites on the gas sensing properties (sensitivity, reproducibility, stability, and response and recovery times) has been investigated in detail in order to examine the capability of the investigated sensor for leakage detection of the gases. The best LPG sensing performance has been observed for nanostructured NiCuFeO thin film as evinced by high value of sensitivity and stability as well as small value of response and recovery times. [ABSTRACT FROM AUTHOR]

In this paper we report on how to increase the selectivity of gas sensors by using fluoropolymer membranes. The mass transport of polar and non-polar gases through a polymer membrane matrix was studied by systematic selection of polymers with different degrees of fluorination, as well as polymers whose monomers have ether groups (-O-) in addition to fluorine groups (-F). For the study, a set of application-relevant gases including H2, CO, CO2, NO2, methane, ethanol, acetone, and acetaldehyde as well as various concentrations of relative humidity were used. These gases have different functional groups and polarities, yet have a similar kinetic diameter and are therefore typically difficult to separate. The concentrations of the gases were chosen according to international indicative limit values (TWA, STEL). To measure the concentration in the feed and permeate, we used tin-dioxide-based metal oxide gas sensors with palladium catalyst (SnO2:Pd), catalytic sensors (also SnO2:Pd-based) and thermal conductivity sensors. This allows a close examination of the interdependence of diffusion and physicochemical operating principle of the sensor. Our goal is to increase the selectivity of gas sensors by using inexpensive fluoropolymer membranes. The measurements showed that through membranes with low polarity, preferably non-polar gases are transported. Furthermore, the degree of crystallization influences the permeability and selectivity of a polymer membrane. Basically the polar polymers showed a higher permeability to water vapor and polar substances than non-polar polymer membranes. [ABSTRACT FROM AUTHOR]

Tin oxide-based thin films are deposited by ultrasonic spray pyrolysis technology, in which Cu addition is introduced to enhance the gas sensing performance by H2S detection. The thin films are porous and comprise nano-sized crystallites. One of the Cu-containing thin film sensors demonstrates a fast and significant response to H2S gas. The values of power law exponent n are calculated to discuss the sensitivity of the sensors, which is significantly promoted by Cu additive. The sensitivity of Cu-doped SnO2 gas sensors is determined by two mechanisms. One is the normal gas sensing mechanism of SnO2 grains, and the other is the promoted mechanism caused by the transformation between CuO and CuS in the H2S detection. [ABSTRACT FROM AUTHOR]

Development of high-performance p-type semiconductor based gas sensors exhibiting fast-response/recovery times with ultra-high response are of major importance for gas sensing applications. Recent reports demonstrated the excellent properties of p-type semiconducting oxide for various practical applications, especially for selective oxidation of volatile organic compounds (VOCs). In this work, sensors based on CuO nanowire (NW) networks have been successfully fabricated via a simple thermal oxidation process on pre-patterned Au/Cr pads. Our investigation demonstrates high impact of the process temperature on aspect ratio and density of copper oxide NWs. An optimal temperature for growth of thin and densely packed NWs was found to be at 425 °C. The fabricated sensors demonstrated ultra-high gas response by a factor of 313 to ethanol vapour (100 ppm) at an operating temperature of 250 °C. High stability and repeatability of these sensors indicate the efficiency of p-type oxide based gas sensors for selective detection of VOCs. A high-performance nanodevice was fabricated in a FIB-SEM system using a single CuO NW, demonstrating an ethanol response of 202 and rapid response and recovery of ∼198 ms at room temperature. The involved gas sensing mechanism of CuO NW networks has been described. We consider that the presented results will be of a great interest for the development of higher-performance p-type semiconductor based sensors and bottom-up nanotechnologies. (© 2016 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

A study on the propane gas-sensing properties of Cu-doped ZnO thin films is presented in this work. The films were deposited on glass substrates by sol-gel and dip coating methods, using zinc acetate as a zinc precursor, copper acetate and copper chloride as precursors for doping. For higher sensitivity values, two film thickness values are controlled by the six and eight dippings, whereas for doping, three dippings were used, irrespective of the Cu precursor. The film structure was analyzed by X-ray diffractometry, and the analysis of the surface morphology and film composition was made through scanning electron microscopy (SEM) and secondary ion mass spectroscopy (SIMS), respectively. The sensing properties of Cu-doped ZnO thin films were then characterized in a propane atmosphere, C3H8, at different concentration levels and different operation temperatures of 100, 200 and 300 °C. Cu-doped ZnO films doped with copper chloride presented the highest sensitivity of approximately 6 x 104, confirming a strong dependence on the dopant precursor type. The results obtained in this work show that the use of Cu as a dopant in ZnO films processed by sol-gel produces excellent catalysts for sensing C3H8 gas. [ABSTRACT FROM AUTHOR]

Mesoporous In 2 O 3 nanospheres were successfully synthesized by a simple solvothermal route, which was performed without the assistance of any additives or templates. The obtained mesoporous In 2 O 3 nanospheres show high monodispersity with average size about 90 nm and pore size about 2–4 nm. The optical absorption property of the In 2 O 3 mesoporous spheres was investigated by UV–vis spectroscopy, which indicates that the In 2 O 3 mesoporous spheres are semiconducting with a direct band gap of 3.1 eV. The gas sensing performance of the as-prepared In 2 O 3 mesoporous nanospheres was investigated towards a series of typical organic solvents and fuels. For 100 ppm of butanol and ethanol, the mesoporous In 2 O 3 demonstrates sensing responses of 59.6 and 29.6, respectively. These values are much higher than those of the reported In 2 O 3 -based gas sensors and the In 2 O 3 powder sample with similar size, indicating the highly enhanced gas sensing performance of In 2 O 3 mesoporous nanospheres. The obtained In 2 O 3 mesoporous nanospheres appear to be a promising sensing material for environmental detection application and would also find applications in catalyst, electrode, or related fields. [ABSTRACT FROM AUTHOR]

Porous small-sized ZnO nanoparticles (NPs) are synthesized by the method combination of precipitation and hydrothermal and applied as acetone sensor. Cetyltrimethyl ammonium bromide (CTAB) of different amounts is used as a surface-active agent to obtain Zinc Oxide (ZnO) NPs of unique and smaller size morphologies which lead to larger specific surface areas and private more space for target gases molecules. These sensors of acetone gas exhibit lower operating temperature (290 °C), higher response and shorter response time (about 9 s and 7 s). The most probable reasons for this higher performance of gas sensing can be attributed to the unique morphology, the higher crystallinity degree, smaller particle size and larger surface areas. [ABSTRACT FROM AUTHOR]

Herein, we describe a facile surfactant-freemethod to preparethe ZnO–Ag hybrids at room temperature for improving gas-sensingperformance toward ethanol. Characterizations indicate that Ag nanoparticlesare well deposited on the surface of ZnO nanorods. It is interestingto note that the introduction of only 1 wt % Ag in ZnO–Ag hybridsleads to the impressive enhancement in gas-sensing properties of ZnO.Notably, the ZnO–Ag hybrids can offer a gas response valueof 884.7 toward 1000 ppm of ethanol (approximately 12.6 times higherthan pure ZnO nanorods). Meanwhile, the hybrids exhibit excellentstability with only ±5% fluctuation of the gas response valueover a period of 480 cycles. Moreover, the above-mentioned hybridsalso exhibit good selectivity (about 4.7–52.9 times greaterthan that of other tested vapors). The high sensitivity, good selectivityand excellent stability presented by ZnO–Ag hybrids make ita potential material for developing an excellent gas-sensing sensortoward ethanol. [ABSTRACT FROM AUTHOR]