In2O3 nanosheets array directly grown on Al2O3 ceramic tube and their gas sensing performance

Arrayed In₂O₃ nanosheets were synthesized directly via a two-step solution approach on an Al₂O₃ ceramic tube. Their morphology and structure were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV–Vis absorption spectroscopy, and scanning electron microscopy (SEM). The results reveal that the length of each nanosheet is about 1 µm, the width of the bottom of nanosheet is about 200 nm. Importantly, the In₂O₃ nanosheets with large specific surface area possess highly sensing performance for ethanol detection. The response value to 100 ppm ethanol is about 45 at an operating temperature of 280 °C, and the response and recovery time are extremely short. It is expected that the directly grown In₂O₃ nanosheets with large specific surface area and excellent sensing properties will become a promising functional material in monitoring and detecting ethanol.     

NO2 gas sensing responses of In2O3 nanoparticles decorated on GO nanosheets

Nanomaterials offer a wide range of applications in environmental nanotechnology. Hazardous pollutants in the environment are needed to be detected and controlled effectively to avoid human health risks. In this paper, we described the fine-controlled growth of In₂O₃ nanoparticles embedded on GO nanosheets by a facile precipitation method. The In₂O₃@GO nanocomposites exhibited outstanding gas sensing performance as compared with pure In₂O₃ nanoparticles towards NO₂. At 225 °C, the sensor displayed high selectivity, best response (78) to 40 ppm NO₂, quick response, and recovery times of 106s/42s. The improved sensing performances of the nanocomposite were attributed to large surface area, high gas adsorption-desorption capability, and the formation of p-n heterojunctions between In₂O₃ nanoparticles and GO nanosheets. The excellent gas detecting activities validate In₂O₃@GO nanocomposites as a promising candidate in the NO₂ gas sensor industry.     

In2O3 nanocubes/Ti3C2Tx MXene composites for enhanced methanol gas sensing properties at room temperature

Highly active two-dimensional (2D) nanocomposites, integrating the unique merits of individual components and synergistic effects of composites, have been recently receiving attention for gas sensing. In this work, In₂O₃ nanocubes/Ti₃C₂T_x MXene nanocomposites were synthesized using In₂O₃ nanocubes and layered Ti₃C₂T_x MXene via a facile hydrothermal self-assembly method. Characterization results indicated that the In₂O₃ nanocubes with sizes approximately 20–130 nm in width were well dispersed on the surface of layered Ti₃C₂T_x MXene to form numerous heterostructure interfaces. Based on the synergistic effects of electronic properties and gas-adsorption capabilities, In₂O₃ nanocubes/Ti₃C₂Tx MXene nanocomposites exhibited high response (29.6%–5 ppm) and prominent selectivity to methanol at room temperature. Meanwhile, the low detection concentration could be reduced to ppm-level, the response/recovery times are shortened to 6.5/3.5 s, excellent linearity and outstanding repeatability. The strategy of compositing layered MXene with metal oxide semiconductor provides a novel pathway for the future development of room temperature gas sensors.     

Synthesis and ethanol sensing properties of CuO nanorods coated with In2O3

CuO/In₂O₃ core–shell nanorods were fabricated using thermal evaporation and radio frequency magnetron sputtering. X-ray diffraction and transmission electron microscopy showed that both the cores and shells were crystalline. The multiple networked CuO/In₂O₃ core–shell nanorod sensors showed responses of 382–804%, response times of 36–54 s and recovery times of 144–154 s at ethanol (C₂H₅OH) concentrations ranging from 50 to 250 ppm at 300 °C. These responses were 2.3–2.8 times higher than those of the pristine CuO nanorod sensor over the same C₂H₅OH concentration range. The origin of the enhanced ethanol sensing properties of the core–shell nanorod sensor is discussed.     

Gas sensing properties of multiple networked GaN/WO3 core-shell nanowire sensors

GaN nanowires and GaN-core/WO₃-shell nanowires were synthesized by the thermal evaporation of GaN powders followed by the sputter-deposition of WO₃ and their gas sensing properties were examined. The multiple networked pristine GaN nanowire sensors showed responses of approximately 125%, 140%, 146%, 159%, and 183% to 1, 2, 3, 4, and 5 ppm NO₂ gases, respectively. These responses are comparable to those obtained previously using metal oxide semiconductor one-dimensional nanostructure sensors. The responses of the nanowires to 1, 2, 3, 4, and 5 ppm NO₂ gases were improved 1.3, 1.4, 1.6, 1.7 and 1.8 fold, respectively, further through the encapsulation of GaN nanowires with a WO₃ thin film. The improvement in the response of GaN nanowires to NO₂ gas by encapsulation is attributed to the modulation of electron transport at GaN–WO₃ heterojunction. The electron transport in the core-shell nanowires is modulated by the heterojunction with an adjustable energy barrier height, resulting in an enhanced sensing property of the core-shell nanostructures.     

Gold Sensitized In2O3 nanocubes for ppb level NO2 gas sensing

Hydrothermally synthesized In₂O₃ nanocubes were sensitized with Au and gas sensing performance is analyzed. The Au sensitization was done using sputtering and gas sensing performance is studied as function of different sputtering time. The catalytic activity of Au particles on In₂O₃ films increases with the sputtering time but acquires saturation at high sputtering time. The Au sensitization with sputtering time of 5 s was found to show improved sensor response (R_g/R_a) of 8435 than the sensor response of 6876 for pure In₂O₃ film. The improved sensor response was attributed to the catalytic activity of Au particles on the In₂O₃ film surface. In addition, Au sensitized In₂O₃ also demonstrates the sensor response at 60 ppb.     

In_2O_3纳米陶瓷纤维无纺布的静电纺丝制备及气敏特性研究

采用溶胶-凝胶法结合静电纺丝技术制备了直径20~60 nm的超细氧化铟(In2O3)纳米陶瓷纤维及纳米陶瓷纤维无纺布。采用XRD,IR,SEM,HR-TEM,TGA等分析方法对纳米纤维的形貌和显微结构进行了表征,并研究了其气敏特性。由700℃下煅烧的该超细In2O3纳米纤维所制备的气敏元件具有较好的反应和选择性,对甲醛气体表现出较快的响应和恢复速度。     

A novel ethanol sensor with high response based on one-dimensional YFeO3 nanorods

As the cognition of metal oxide semiconductor becomes deeper and deeper, their excellent sensing ability has also been demonstrated. The gas sensors with metal oxide semiconductor as basis materials have become a hot topic at present. Enhancing the sensitivity and reducing the test limit of the sensor are exceedingly important topic. It is crucial to regulate the morphology of metal oxide semiconductor materials to improve the gas sensing performance. Low-dimensional materials such as quantum dots, one-dimensional nanowires and nanorods usually show the excellent gas-sensitive properties. In this work, one-dimensional YFeO₃ nanorods were synthesized by electrospinning technology. The one-dimensional rod-like structure enables more active sites to be exposed on the surface of materials, which can effectively promote the adsorption process of the YFeO₃ nanorods to the test gases, so as to improve the gas sensing performance. Found by testing the gas sensitivity, YFeO₃ nanorods responds far better to ethanol than other tested gases. The response and recovery time of YFeO₃ nanorods to 100 ppm ethanol at 350 °C was approximately 19 s and 9 s, respectively. It indicates that the response and recovery ability of YFeO₃ nanorods to ethanol were excellent. The study can provide technical reference for subsequent preparation of remarkable performance ethanol sensor and enrich the materials category of gas sensor fields.     

Fabrication of Ti3C2Tx/In2O3 nanocomposites for enhanced ammonia sensing at room temperature

Ti₃C₂T_x, as a novel two-dimensional material, displays promising prospects in NH₃ detection at room temperature. However, the NH₃ detection limit of pristine Ti₃C₂T_x is still a major research concern. Therefore, it is important to explore new Ti₃C₂T_x-based nanocomposites for better NH₃-sensing performance. In the present experiment, Ti₃C₂T_x/In₂O₃ nanocomposites were successfully synthesized by ultrasonication and characterized by XRD, FESEM, TEM, XPS, and BET. The optimal Ti₃C₂T_x/In₂O₃-based sensor had a high response of 63.8% (30.4 times higher than that of pristine Ti₃C₂T_x) to 30 ppm NH₃ at room temperature. In addition, the optimal Ti₃C₂T_x/In₂O₃-based sensor had stable repeatability, excellent selectivity, and long-term stability, while exhibiting excellent potential for NH₃ detection at room temperature.     

Recent progress of Ga2O3-based gas sensors

In recent years, gas sensors fabricated from gallium oxide (Ga₂O₃) materials have aroused intense research interest due to the superior material properties of large dielectric constant, good thermal and chemical stability, excellent electrical properties, and good gas sensing. Over the past decades, Ga₂O₃-based gas sensors experienced rapid development. The long-term stable Ga₂O₃-based gas sensors for detecting oxygen and carbon monoxide have been commercialized and renowned with extremely good gas sensing characteristics. Recent pioneering studies also exhibit that the Ga₂O₃-based gas sensors possess great potentials in applications of detecting nitrogen oxides, hydrogen, volatile organic compounds and ammonia gases. This article presents recent advances in gas sensing mechanism, device performance parameters, influence factors, and applications of Ga₂O₃-based gas sensors. The impacts of influence factors, doping, material structure and device structure on the performance of gas sensors are discussed in detail. Finally, a brief overview of challenges and opportunities for the Ga₂O₃-based gas sensors is presented.     

Ethanol sensing properties of tungsten oxide nanorods prepared by microwave hydrothermal method

Tungsten oxide nanorods have been prepared by a simple microwave hydrothermal (MH) method via Na₂SO₄ as structure-directing agent at 180 °C for 20 min. The structure and morphology of the products are characterized by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). The obtained nanorods are about 20–50 nm in diameter and several micrometers in length. The ethanol sensing property of as-prepared tungsten oxide nanorods is studied at ethanol concentration of 10–1000 ppm and working temperature of 370–500 °C. It was found that the sensitivity depended on the working temperatures and also ethanol concentration. The results show that the tungsten oxide nanorods can be used to fabricate high performance ethanol sensors.     

Mesoporous Fe-doped In2O3 nanorods derived from metal organic frameworks for enhanced nitrogen dioxide detection at low temperature

Mesoporous Fe-doped In₂O₃ nanorods derived from metal-organic frameworks (In/Fe-MIL-68s) were synthesized for NO₂ detection. The morphologies, structures and NO₂ gas-sensing performances of the Fe–In₂O₃ nanorods were systematically investigated. Texture characterizations demonstrate that the as-prepared Fe–In₂O₃ nanorods show rich porous structures, high specific surface areas and reduced grain sizes. Gas-sensing measurements display that the Fe–In₂O₃ nanorods derived from In/Fe-MIL-68s with the Fe(Ⅲ) content of 5 mol.% (Fe(5)-In₂O₃) exhibit high response (82) and short response/recovery time (70/65 s) towards 2 ppm NO₂ at 80 °C compared with their counterparts. Besides, superior selectivity and good stability are observed. The sensing mechanism studies reveal that the improved gas-sensing performances are attributed to the decrease in the gran size, the formation of rich oxygen vacancies and band gaps narrowing caused by Fe(Ⅲ) doping. Therefore, this work indicates that the Fe–In₂O₃ nanorods derived from metal-organic frameworks precursors can be a promising candidate for NO₂ detection.     

Facile fabrication and superior gas sensing properties of spongelike Co-doped ZnO microspheres for ethanol sensors

In this work, a novel strategy has been adopted for the synthesis of hybrid Co-doped ZnO (Co/ZnO) microspheres using the solvothermal method with a synergistic effect of ultrasonic and microwave radiation. The Co/ZnO microspheres were characterized by XRD, FE-SEM, XPS and BET techniques. Sensing tests revealed that the Co/ZnO microspheres exhibited highly better ethanol sensing properties than pure ZnO nanoparticles did, including lower limit of detection (less than 10?ppm), higher response (ca. 120–100?ppm ethanol), lower operating temperature (ca. 220?°C), faster response (10?s) and recovery time (5?s) and better selectivity. The superior gas sensing properties were mainly attributed to the incorporation of Co, which increased the amount of oxygen vacancies and adsorbed oxygen. The sensing mechanism has been explained by oxygen chemisorption on the ZnO surfaces and subsequent reactions of surface adsorbed oxygen species with the ethanol molecules.     

Enhanced gas sensing properties of hierarchical SnO2 nanoflower assembled from nanorods via a one-pot template-free hydrothermal method

Well-defined three-dimensional (3D) hierarchical tin dioxide (SnO₂) nanoflowers with the size of about 200 nm were successfully synthesized by a simple template-free hydrothermal method. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and N₂ adsorption-desorption analyses were used to characterize the structure and morphology of the products. The as-synthesized full crystalline and large specific surface area SnO₂ nanoflowers were assembled by one-dimensional (1D) SnO₂ nanorods with sharp tips. A possible self-assembly mechanism for the formation the SnO₂ nanoflowers was speculated. Moreover, gas sensing investigation showed the sensor based on SnO₂ nanoflowers to exhibit high response and fast response-recovery ability to detect acetone and ethanol at an operating temperature lower than 200 °C. The enhancement of gas sensing properties was attributed to their 3D hierarchical nanostructure, large specific surface area, and small size of the secondary SnO₂ nanorods.     

Synthesis and high sensing properties of a single Pd-doped SnO2 nanoribbon

Monocrystal SnO₂ and Pd-SnO₂ nanoribbons have been successfully synthesized by thermal evaporation, and novel ethanol sensors based on a single Pd-SnO₂ nanoribbon and a single SnO₂ nanoribbon were fabricated. The sensing properties of SnO₂ nanoribbon (SnO₂ NB) and Pd-doped SnO₂ nanoribbon (Pd-SnO₂ NB) sensors were investigated. The results indicated that the SnO₂ NB showed a high sensitivity to ethanol and the Pd-SnO₂ NB has a much higher sensitivity of 4.3 at 1,000 ppm of ethanol at 230°C, which is the highest sensitivity for a SnO₂-based NB. Pd-SnO₂ NB can detect ethanol in a wide range of concentration (1 ~ 1,000 ppm) with a relatively quick response (recovery) time of 8 s (9 s) at a temperature from 100°C to 300°C. In the meantime, the sensing capabilities of the Pd-SnO₂ NB under 1 ppm of ethanol at 230°C will help to promote the sensitivity of a single nanoribbon sensor. Excellent performances of such a sensor make it a promising candidate for a device design toward ever-shrinking dimensions because a single nanoribbon device is easily integrated in the electronic devices.     

Preparation,characterization of 1D ZnO nanorods and their gas sensing properties

The 1D ZnO nanorods (NR's) were grown with Zinc (Zn) ion precursor concentration variation on seed layer glass substrate by the low temperature hydrothermal method and utilized for nitrogen dioxide (NO₂) gas sensing application. Zn ion precursor concentration varied as 0.02, 0.03, 0.04, 0.05 and 0.06 M and thin films were characterized for structural, morphological, optical, electrical, surface defect study and gas sensing properties. All the film showed dominant orientation along the (002) direction, the intensity of the peak vary with the length of the nanorods. SEM cross images confirmed that nanorods had vertical alignment perpendicular to the plane of the substrate surface. The PL intensity of oxygen vacancy related defects for prepared samples was found to be linearly proportional to gas sensing phenomena. This result in good agreement with the theoretical postulation that, oxygen vacancies plays the important role for adsorption sites to NO₂ molecule. The gas sensing performance was studied as a function of operating temperature, Zn ion precursor concentration variation, and gas concentration. The maximum gas response is 113.32–100 ppm NO₂ gas at 150 °C for 0.05 M sample out of all prepared samples. Additionally, ZnO thin film sensor has potential to detect NO₂ as low as 5 ppm.     

Synthesis of few-layered Ti3C2Tx/ WO3 nanorods foam composite material for NO2 gas sensing at low temperature

The few-layered Ti₃C₂T_x/WO₃ nanorods foam composite material was synthesized by electrostatic self-assembly and bidirectional freeze-drying technologies. The phase structure and microstructure of synthesized samples was characterized by XRD, FESEM, TEM and their gas sensing properties estimated via a self-designed equipment with four test channels. The results demonstrate WO₃ nanorods were successfully anchored on the surface and between layers of few-layered Ti₃C₂T_x MXene by electrostatic self-assembly strategy and the composite material simultaneously has a low-density foam morphology by means of bidirectional freeze-drying processes. There exists a typical heterostructure at the interfaces owing to the inseparable contact between the few-layered Ti₃C₂T_x MXene and WO₃ nanorods. Compared with the original WO₃ nanorods, the few-layered Ti₃C₂T_x/WO₃ nanorods foam composite material displays excellent gas sensing properties for NO₂ detection at low temperature, in particular the optimal value of gas sensing response (R_g/R_a) reaches to 89.46 toward 20 ppm NO₂ at 200 °C. The gas sensing mechanism was also discussed. The increase of gas sensitivity is attributed to a fact that during the reaction process of gas sensing, the excellent conductivity of the few-layered Ti₃C₂T_x MXene provided faster transport channels of free carriers, and the heterojunctions formed by few-layered Ti₃C₂T_x MXene and WO₃ nanorods enhanced the carriers separation efficiency. Meanwhile, the low-density layered structure of few-layered Ti₃C₂T_x/WO₃ nanorods foam composite material provides convenient diffusion paths for gas molecules to the surface of WO₃ nanorods.     

Cr_2O_3-Al_2O_3砖中不同组成Cr_2O_3-Al_2O_3电熔颗粒料的抗侵蚀研究

首先以不同比例的铬绿和氧化铝粉电熔制得Cr2O3质量分数分别为15%、40%、50%、60%、85%、99%的6种Cr2O3-Al2O3电熔颗粒料(其编号依次为CR15、CR40、CR50、CR60、CR85和CR99),然后采用回转渣蚀法研究了此电熔颗粒料(4~1 mm)的抗侵蚀性。结果显示:电熔颗粒料的抗侵蚀性随Cr2O3含量的增加及颗粒尺寸的增大而增强;高Cr2O3含量的CR99、CR85颗粒料在渣面层被侵蚀,主要是渣中的FeO和Al2O3对颗粒料的侵蚀,FeO与骨料中的Cr2O3反应,首先形成(Fe,Cr)3O4尖晶石,再与其他物相反应形成了复合尖晶石,当FeO耗尽后,渗入到颗粒内的Al2O3开始和Cr2O3反应,在颗粒表面形成铝铬固溶体;CR60颗粒料在渣面层和渗透层都存在侵蚀,渗透层的侵蚀主要是CaO、SiO2对颗粒料中铝铬固溶体中Al2O3的熔蚀,形成钙长石、钙黄长石以及玻璃相;Cr2O3含量较低的CR50、CR40、CR15颗粒料在渗透层内的侵蚀机制和CR60颗粒料的相同。     

Ultra-high gas sensing properties of porous Cr2O3@SnO2 composite toward NOx based on the p-p heterostructure

In recent years, environmental pollution and industrial accidents caused by the leakage of harmful gas are ever-increasing, and advanced gas sensors have been considered to be one of the main strategies for environmental monitoring and industrial safety control. Herein, Cr₂O₃ film decorated disordered porous SnO₂ (Cr₂O₃@SnO₂) composite was synthesized as an effective gas sensor toward NO_x gas. The response of the Cr₂O₃@SnO₂ gas sensor toward 100 ppm NO_x gas could reach 71 % and the response time is 2.5 s. Meanwhile, the minimum detection level toward NO_x gas is only 0.3 ppm, which is pretty lower compared to other materials reported before. The excellent gas-sensitive performance is attributed to the unique heterostructure formed between the Cr₂O₃ film and the SnO₂ matrix, and electrons in this area can migrate to overcome the barrier with less energy. As a result, O₂ and NO_x gas can draw electrons from the Cr₂O₃@SnO₂ gas sensor easily, thus leading to improved gas-sensitive performance. More importantly, this research provides a new idea to synthesize effective NO_x gas-sensitive materials based on the p-p heterostructure.