Preparation of two-dimensional molybdenum disulfide for NO2 detection at room temperature

In this work, the two-dimensional MoS₂ film was prepared by sulfuring the molybdenum atomic layer on SiO₂/Si substrate. The reaction temperature, heating rate, holding time and carrier gas flow rate were investigated comprehensively. The quality of MoS₂ film was characterized by optical microscopy, atomic force microscopy, Raman and photoluminescence spectroscopy. The characterization results showed that the optimum synthesis parameters were heating rate of 25 °C/min, reaction temperature of 750 °C, holding time of 30 min and carrier gas velocity of 100 sccm. The MoS₂ gas sensor was fabricated and its gas sensing performance was tested. The test results indicated that the sensor had a good response to both reducing gas (NH₃) and oxidizing gas (NO₂) at room temperature. The sensitivity to 100 ppm of NO₂ was 31.3%, and the response/recovery times were 4 s and 5 s, respectively. In addition, the limit of detection could be as low as 1 ppm. This work helps us to develop low power and integrable room temperature NO₂ sensors.     

Highly sensitive,humidity-tolerant and flexible NO2 sensors based on nanoplate Bi2Se3 film

Recently, two-dimension (2D) materials have fueled considerable interest in the field of gas sensing to cope urgent demands at specific scenarios. Unfortunately, the susceptibility to ambient humidity, and/or fragile operation stability always frustrate their further practicability. To overcome these drawbacks, we proposed one novel flexible gas sensor based on bismuth selenide (Bi₂Se₃) nanoplates for sensitive NO₂ detection at room temperature. The as-prepared Bi₂Se₃ sensor exhibited favorable sensing performance, including remarkable NO₂ selectivity, high response of 120% and fast response time of 81 s toward 5 ppm NO₂, an ultralow detection limit of 100 ppb, and nice stability. Besides, the excellent humidity tolerance and mechanical flexibility endowed Bi₂Se₃ sensors with admirable reliability under harsh working conditions. The first-principles calculation further revealed the insights of extraordinary NO₂ selectivity and the underlying gas-sensing mechanism.     

Novel NO2 Gas Sensor Based on Cr(III) Complex Thin Film

The results concerning the gas‐sensing characteristics of novel NO₂ gas sensors, fabricated from complex [Cr(bipyO₂)Cl₂]Cl thin films, were first presented. The sensors exhibited high response to NO₂ gas in the concentration range from 1.97% to 6.67% at relative low temperatures (from room temperature to 348 K). No response to H₂S and SO₂ was observed. The maximum response for 6.03% NO₂ was approximately 11.7 at 338 K and 10 V operating voltage. The response time of the sensors was about 4.5 min for NO₂ and the recovery time about 40 s. The effect of the electrical resistance change of the sensors in the presence of NO₂ could be used for gas sensing measurements. The performance and reliability of the sensors showed their potential applications for monitoring and controlling NO₂ component continuously in chemical production.     

Optimization of strontium- doping concentration in BaTiO3 nanostructures for room temperature NH3 and NO2 gas sensing

In this study, we comprehensively present the gas sensing performance of strontium (Sr)-doped barium titanate (BaTiO₃) nanostructures which are synthesized by a low-temperature hydrothermal route. The in-situ doping of strontium in BaTiO₃ nanostructures is achieved with different molar concentrations of Sr, and the sensing performance was evaluated by screen printing process of products to form their thick films. The thick films of as-prepared Sr-doped BaTiO₃ (BaSrTiO₃) were investigated for gas sensing performance for various gases at different operating temperatures where strong response was observed for both nitrogen dioxide (NO₂) and ammonia (NH₃) gases at room temperature. Furthermore, the sensing response at room temperature for NH₃ and NO₂ gases was also studied with respect to Sr doping concentrations in BaTiO₃ nanostructures.     

Solution-Processed p-SnSe/n-SnSe2 Hetero-Structure Layers for Ultrasensitive NO2 Detection

The formation of semiconductor heterostructures is an effective approach to achieve high performance in electrical gas sensing. However, such heterostructures are usually prepared via multi-step procedures. In this contribution, by taking advantage of the crystal phase-dependent electronic property of SnSe_x based materials, we report a one-step colloid method for the preparation of SnSe(x%)/SnSe₂(100−x%) p–n heterostructures, with x ≈30, 50, and 70. The obtained materials with solution processability were successfully fabricated into NO₂ sensors. Among them, the SnSe(50 %)/SnSe₂(50 %) based sensor with an active layer thickness of 2 μm exhibited the highest sensitivity to NO₂ (30 % at 0.1 ppm) with a limit of detection (LOD) down to 69 ppb at room temperature (25 °C). This was mainly attributed to the formation of p–n junctions that allowed for gas-induced modification of the junction barriers. Under 405 nm laser illumination, the sensor performance was further enhanced, exhibiting a 3.5 times increased response toward 0.1 ppm NO₂, along with a recovery time of 4.6 min.     

Nanofibrous polyaniline thin film prepared by plasma‐induced polymerization technique for detection of NO2 gas

A nanofibrous polyaniline (PANI) thin film was fabricated using plasma‐induced polymerization method and explored its application in the fabrication of NO₂ gas sensor. The effects of substrate position, pressure, and the number of plasma pulses on the PANI film growth rate were monitored and an optimum condition for the PANI thin film preparation was established. The resulting PANI film was characterized with UV–visible spectrophotometer, FTIR, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The PANI thin film possessed nanofibers with a diameter ranging from 15 to 20 nm. The NO₂ gas sensing behavior was studied by measuring the change in electrical conductivity of PANI film with respect to NO₂ gas concentration and exposure time. The optimized sensor exhibited a sensitivity factor of 206 with a response time of 23 sec. The NO₂ gas sensor using nanofibrous PANI thin film as sensing probe showed a linear current response to the NO₂ gas concentration in the range of 10–100 ppm. Copyright © 2009 John Wiley & Sons, Ltd.     

Application of Pt@SnO2 nanoparticles for hydrogen gas sensing

We report the fabrication of Pt@SnO₂ nanoparticles using a sol–gel method. These nanoparticles are used as a sensing material. The structural and morphological characterization of the prepared Pt@SnO₂ nanoparticles was performed using ultraviolet–visible spectroscopy, X‐ray diffraction, transmission electron microscopy, and energy‐dispersive X‐ray spectroscopy. The sensor responses of SnO₂ and 1 wt% Pt/SnO₂ to 1% hydrogen gas (H₂) were 1.3 and 1.9, respectively. The sensor response of a Pt@SnO₂ core–shell sensor increased to 5.1 at room temperature; it improved by 3.9 times compared to SnO₂ and by 2.7 times compared to 1% Pt/SnO₂ in sensing 1% H₂. The response time for the prepared Pt@SnO₂ sensor was also shortened by 2.0 and 1.4 times compared to SnO₂ and 1 wt% Pt/SnO₂, respectively. The sensor response increased rapidly from 1.4 to 5.1, with an increase in H₂ concentration from 800 to 10,000 ppm (1%). We investigated the H₂‐sensing mechanism of Pt@SnO₂.     

A high-sensitivity H2S gas sensor based on optimized ZnO-ZnS nano-heterojunction sensing material

This paper reports a high-performance H₂S gas sensing material that is made of ZnO nanowires (NWs) modified by an optimal amount of ZnS to form nano-heterojunctions. Compared with the intrinsic ZnO-NWs, the three differently modified nano-heterostructure material ZnO-ZnS-x (x = 5, 10, 15) shows significant improvement in sensing performance to H₂S at the working temperatures of 100−400 °C, especially in the low temperature range (<300 °C). The chemiresistive sensor with ZnO-ZnS-10 sensing-material exhibits the largest response signal to H₂S among all the other ZnO-ZnS-x (x = 5, 10, 15, 20) sensors. Its response signal to 5 ppm H₂S at 150 °C is about 2.7 times to that of the ZnO-NWs sensor. Besides, the ZnO-ZnS-10 sensor also features satisfactory selectivity and repeatability at 150 °C. With the technical advantage attributed to the reduction of the redesigned band gap at the interface between ZnO and ZnS, the ZnO-ZnS heterostructure sensor rather than the traditional ZnO-NWs sensor can be used for high-sensitivity application at low working temperature.     

Zirconia-based amperometric sensor using La–Sr-based perovskite-type oxide sensing electrode for detection of NO2

An amperometric zirconia-based sensor attached with perovskite-type oxide sensing electrode was examined for monitoring NO₂ in automobile exhaust. The sensor using La_0.6Sr_0.4Co_0.98Mn_0.02O₃ showed high response to NO₂. The response was almost linear to NO₂ concentration in the range between 50 and 800 ppm, and a 90% reaction time to 400 ppm NO₂ was less than 20 s. Though the NO₂ response of the sensor was slightly affected by the changes in O₂ concentrations, it showed still high response in the examined range of 5–21 vol%.     

Enhanced ethanol sensing properties of WO3 modified TiO2 nanorods

Pristine and WO₃ decorated TiO₂ nanorods (NRs) were synthesised to investigate n-n-type heterojunction gas sensing properties. TiO₂ NRs were fabricated via hydrothermal method on fluorine-doped tin oxide coated glass (FTO) substrates. Then, tungsten was sputtered on the TiO₂ NRs and thermally oxidised to obtain WO₃ nanoparticles. The heterostructure was characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) spectroscopy. Fabricated sensor devices were exposed to VOCs such as toluene, xylene, acetone and ethanol, and humidity at different operation temperatures. Experimental results demonstrated that the heterostructure has better sensor response toward ethanol at 200 °C. Enhanced sensing properties are attributed to the heterojunction formation by decorating TiO₂ NRs with WO₃.     

Template Based Synthesis of Porous Graphdiyne Nanosheet for Reversible and Fast NO2 Detection by UV Irradiation

Two-dimensional graphdiyne (GDY) formed by sp and sp² hybridized carbon has been found to be an efficient toxic gas sensing material by density functional theory (DFT). However, little experimental research concerning its gas sensing capability has been reported owing to the complex preparation process and harsh experimental conditions. Herein, porous GDY nanosheets are successfully synthesized through a facile solvothermal synthesis technique by using CuO microspheres (MSs) as both template and source of catalyst. The porous GDY nanosheets exhibit a broadband optical absorption, rendering it suitable for the light-driven optoelectronic gas sensing applications. The GDY-based gas sensor was demonstrated to have excellent reversible to NO₂ behaviors at 25 °C for the first time. More importantly, higher response value and faster response-recovery time once exposed to NO₂ gas molecules are achieved by the illumination of UV light. In this way, our work paves the way for the exploration of GDY-based gas detection experimentally.     

Detection of nitrogen dioxide using mixed tungsten oxide-based thick film semiconductor sensor

The thick film semiconductor sensor for NO₂ gas detection was fabricated by screen-printing method using a mixed WO₃-based as sensing material. The sensing characteristics, such as response time, response linearity, sensitivity, working range, cross sensitivity, and long-term stability were further studied by using a WO₃-based mixed with different metal oxides (SnO₂, TiO₂ and In₂O₃) and doped with noble metals (Au, Pd and Pt) as sensing materials was observed. The highest sensitivity for low concentrations (<16 mg l⁻¹) was observed using WO₃-based mixed with In₂O₃ or TiO₂. The NO₂ gas sensor showing the fastest response and recovery time (both within 2 min), good linearity (Y=0.606X+0.788 R²=0.991) for gas concentrations from 3 to 310 mg l⁻¹, low resistance (3 MΩ), high sensitivity, undesirable cross sensitivity effect and good long-term stability (at least 120 days) using WO₃-SnO₂-Au as sensing material.     

Sensor properties of hybrid SnO2-polysilazane materials

New hybrid materials based on nanocrystalline tin dioxide and two types of surface-immobilized polymer organosilicon structures with hydrocarbon substitutes were synthesized for gas sensors application. The sensing responses of pure SnO₂ and hybrid samples were determined in the presence of NO₂ (ppb range), CO (ppm range) and different humidity (RH = 15 – 95 %). Also the influence of water presence on sensor signal towards NO₂ and CO was analyzed. Strong influence of nature of hydrocarbon substitutes on sensor response value towards NO₂ and H₂O was discovered.     

Resistive-type sensors based on few-layer MXene and SnO2 hollow spheres heterojunctions: Facile synthesis,ethanol sensing performances

High-performance and low-cost gas sensors are highly desirable and involved in industrial production and environmental detection. The combination of highly conductive MXene and metal oxide materials is a promising strategy to further improve the sensing performances. In this study, the hollow SnO₂ nanospheres and few-layer MXene are assembled rationally via facile electrostatic synthesis processes, then the SnO₂/Ti₃C₂T_x nanocomposites were obtained. Compared with that based on either pure SnO₂ nanoparticles or hollow nanospheres of SnO₂, the SnO₂/Ti₃C₂T_x composite-based sensor exhibits much better sensing performances such as higher response (36.979), faster response time (5 s), and much improved selectivity as well as stability (15 days) to 100 ppm C₂H₅OH at low working temperature (200 °C). The improved sensing performances are mainly attributed to the large specific surface area and significantly increased oxygen vacancy concentration, which provides a large number of active sites for gas adsorption and surface catalytic reaction. In addition, the heterostructure interfaces between SnO₂ hollow spheres and MXene layers are beneficial to gas sensing behaviors due to the synergistic effect.     

Lattice engineering route for self-assembled nanohybrids of 2D layered double hydroxide with 0D isopolyoxovanadate: chemiresistive SO2 sensor

Tuning the interior chemical composition of layered double hydroxides (LDHs) via lattice engineering route is a unique approach to enable multifunctional applications of LDHs. In this regard, the exfoliated 2D LDH nanosheets coupled with various guest species lead to the lattice-engineered LDH-based multifunctional self-assembly with precisely tuned chemical composition. This article reports the synthesis and characterization of mesoporous zinc–chromium-LDH (ZC-LDH) hybridized with isopolyoxovanadate nanohybrids (ZCiV) via lattice-engineered self-assembly between delaminated ZC-LDH nanosheets and isopolyoxovanadate (iPOV) anions. Electrostatic self-assembly between 2D ZC-LDH monolayers and 0D iPOV significantly altered structural, morphological, and surface properties of ZC-LDH. The structural and morphological study demonstrated the formation of mesoporous interconnected sheet-like architectures composed of restacked ZCiV nanosheets with expanded surface area and interlayer spacing. In addition, the ZCiV nanohybrid resistive elements were used as a room-temperature gas sensor. The selectivity of ZCiV nanohybrid was tested for various oxidizing (SO₂, Cl₂, and NO₂) gases and reducing (LPG, CO, H₂, H₂S, and NH₃) gases. The optimized ZCiV nanohybrid demonstrated highly selective SO₂ detection with the maximum SO₂ response (72%), the fast response time (20 s), low detection limit (0.1 ppm), and long-term stability at room temperature (27 ± 2 °C). Of prime importance, ZCiV nanohybrids exhibited moderately affected SO₂ sensing responses with high relative humidity conditions (80%–95%). The outstanding SO₂ sensing performance of ZCiV is attributed to the active surface gas adsorptive sites via plenty of mesopores induced by a unique lattice-engineered interconnected sheet-like microstructure and expanded interlayer spacing.     

基于硫堇掺杂的聚乙烯醇薄膜的光波导传感器检测硫化氢气体

采用旋转甩涂法将硫堇掺杂的聚乙烯醇薄膜固定在K⁺交换玻璃光波导表面,研制出一种高灵敏硫化氢气体传感器。 传感膜与硫化氢(H₂S)气体作用时,薄膜颜色从紫色变为无色,从而降低薄膜对倏逝波的吸收,使传感器的输出光强度（信号）增强。 采用流动注射法对H₂S气体进行检测。 实验结果表明,H₂S传感器对浓度在0.14~56 mg/m3范围的H₂S气体具有良好的线性响应（r=0.99667）,检出限为0.11 mg/m³(S/N=3),相对标准偏差为4.0%,响应时间（t90）＜2 s。 该传感器具有灵敏度高、响应快、可逆性和重复性好等特点。     

Ethanol Gas Sensor Based on γ-Fe2O3 Nanoparticles Working at Room Temperature with High Sensitivity

Improving the sensing sensitivity and lowering the working temperature are the critical issues for the practical application of gas sensors. For a gas sensor, the sensing materials play important roles in determining the sensing properties. In the present work, γ-Fe₂O₃ microspheres composed of nanoparticles were successfully fabricated by a typical facile hydrothermal process and a following annealing treatment. Interestingly, the as-synthesized γ-Fe₂O₃ microspheres showed excellent sensing properties for the detection of ethanol gas with high sensitivity, and especially working temperature as low as room temperature. The gas sensing results showed that at the optimal operating temperature (200 °C), the response intensity of γ-Fe₂O₃ microspheres for 1000 ppm ethanol gas could reach 74.6 and the limit of detection (LOD) was about 0.026 ppm. At room temperature, the γ-Fe₂O₃ microspheres still demonstrated a good response to different concentrations of ethanol gas from 1 to 1000 ppm, with a very good selectivity over other gas species and a good stability. This study indicated that the γ-Fe₂O₃ phase could be a type of promising room-temperature gas sensing material for ethanol gas detection.     

常温SnO_2-α-Fe_2O_3气敏元件制备

用a-Fe_2O_3研制成的加热式气敏元件功耗大(约1.5W)。常温SnO_2-a-Fe_2O_3气敏元件功耗低(约0.1W),灵敏度高,响应恢复快,稳定,具有一定选择性。 气敏元件制备方法:按62.5％,6.2％和31.3％称取SnO_2,a-Fe_2O_3和硅胶,加水研磨2小时,使其呈浆糊状,点入模具内,放入一对φ0.05mm铂丝电极,晾干,脱模,在860～890℃空气中烧结95分钟。     

High-Performance Sensor Based on Thin-Film Metallic Glass/Ultra-nanocrystalline Diamond/ZnO Nanorod Heterostructures for Detection of Hydrogen Gas at Room Temperature

This article outlines a novel material to enable the detection of hydrogen gas. The material combines thin-film metallic glass (TFMG), ultra-nanocrystalline diamond (UNCD), and ZnO nanorods (ZNRs) and can be used as a device for effective hydrogen gas sensing. Three sensors were fabricated by using combinations of pure ZNRs (Z), UNCD/ZNRs (DZ), and TFMG/UNCD/ZNRs (MDZ). The MDZ device exhibited a performance superior to the other configurations, with a sensing response of 34 % under very low hydrogen gas concentrations (10 ppm) at room temperature. Remarkably, the MDZ-based sensor exhibits an ultra-high sensitivity of 60.5 % under 500 ppm H₂. The MDZ sensor proved very fast in terms of response time (20 s) and recovery time (35 s). In terms of selectivity, the sensors were particularly suited to hydrogen gas. The sensor achieved the same response performance even after two months, thereby demonstrating the superior stability. It is postulated that the superior performance of MDZ can be attributed to defect-related adsorption as well as charge carrier density. This paper also discusses the respective energy band models of these heterostructures and also the interface effect on the gas sensing enhancements. The results indicate that the proposed hybrid TFMG/UNCD/ZNRs nanostructures could be utilized as high-performance hydrogen gas sensors.     

A SAW gas sensor for NO2. Chemically immobilized phthalocyanines as chemical interface

Summary A surface acoustic wave (SAW) gas sensor for NO₂ has been developed in which a chemically immobilized copper(II)-phthalocyanine layer was applied using 3-aminopropyl triethoxysilane as a spacer instead of a sublimated layer. The response time is shortened and the sensitivity is decreased in this way. It is expected that response time and selectivity will improve even more when true monolayers are obtained instead of the observed layers containing the polymerized spacer.

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SAW-Gassensor fur NO₂. Chemisch immobilisierte Phthalocyanine als chemisches Interface