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.     

CuO–ZnO Micro/Nanoporous Array‐Film‐Based Chemosensors: New Sensing Properties to H2S

CuO–ZnO micro/nanoporous array‐films are synthesized by transferring a solution‐dipped self‐organized colloidal template onto a device substrate and sequent heat treatment. Their morphologies and structures are characterized by X‐ray diffraction, field‐emission scanning electron microscopy, transmission electron microscopy, and X‐ray photoelectron spectrum analysis. Based on the sensing measurement, it is found that the CuO–ZnO films prepared with the composition of [Cu²⁺]/[Zn²⁺]=0.005, 0.01, and 0.05 all show a nice sensitivity to 10 ppm H₂S. Interestingly, three different zones exist in the patterns of gas responses versus H₂S concentrations: a platform zone, a rapidly increasing zone, and a slowly increasing zone. Further experiments show that the hybrid CuO–ZnO porous film sensor exhibits shorter recovery time and better selectivity to H₂S gas against other interfering gases at a concentration of 10 ppm. These new sensing properties may be due to a depletion layer induced by p–n junction between p‐type CuO and n‐type ZnO and high chemical activity of CuO to H₂S. This work will provide a new construction route of ZnO‐based sensing materials, which can be used as H₂S sensors with high performances.     

Gas sensing performance of polyaniline/ZnO organic-inorganic hybrids for detecting VOCs at low temperature

Polyaniline (PANI) was prepared by the chemical oxidative polymerization of aniline, and ZnO, with the mean particle size of 28 nm, was synthesized by a non-aqueous solvent method. The organic-inorganic PANI/ZnO hybrids with different mass fractions of PANI were obtained by mechanically mixing the prepared PANI and ZnO. The gas sensing properties of PANI/ZnO hybrids to different volatile organic compounds (VOCs) including methanol, ethanol and acetone were investigated at a low operating temperature of 90°C. Compared with the pure PANI and ZnO, the PANI/ZnO hybrids presented much higher response to VOCs. Meanwhile, the PANI/ZnO hybrid exhibited a good reversibility and a short response-recovery time, implying its potential application for gas sensors. The sensing mechanism was suggested to be related to the existence of p-n heterojunctions in the PANI/ZnO hybrids.     

Reduced graphene oxide-porous In2O3 nanocubes hybrid nanocomposites for room-temperature NH3 sensing

Metal oxide semiconductors (MOS)-reduced graphene oxide (rGO) nanocomposites have attracted great attention for room-temperature gas sensing applications. The development of novel sensing materials is the key issue for the effective detection of ammoniagas at room temperature. In the present work, the novel reduced graphene oxide (rGO)-In₂O₃ nanocubes hybrid materials have been prepared via a simple electrostatic self-assembly strategy. Characterization results exhibit that the intimate interfacial contact between In₂O₃ nanocubes and the rGO sheets are achieved. Particularly, the as-prepared rGO/In₂O₃ nanocomposites displayed high sensitivity, fast response and excellent selectivity towards ammonia (NH₃) at room-temperature, which clearly uncovers the merit of structural design and rational integration with rGO sheets. The superior gas sensing performance of the rGO/In₂O₃ nanocomposites can be attributed to the synergetic effects of rGO sheets and porous In₂O₃ nanocubes. The reported synthesis offers a general approach to rGO/MOS-based semiconductor composites for room-temperature gas sensing applications.     

NiO@ZnO heterostructured nanotubes: coelectrospinning fabrication, characterization, and highly enhanced gas sensing properties

Novel NiO@ZnO heterostructured nanotubes (NTs) were fabricated by the coelectrospinning method, consisting of external hexagonal ZnO shell and internal cubic NiO NTs. They are carefully investigated by scanning electron microscopy, transmission electron microscopy, scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy mapping, X-ray diffraction, and X-ray photoelectron spectroscopy techniques. A reasonable formation mechanism of the hierarchical NiO@ZnO NTs is proposed, which is discussed from the view of degradation temperature of different polymers and the amount of inorganic salts. They were then explored for fabrication of H(2)S gas sensors. The gas sensing test reveals that compared with the pure ZnO, NiO, and the ZnO-NiO mixed gas sensors, hierarchical gas sensor exhibits highly improved sensing performances to dilute hydrogen sulfide (H(2)S) gas. The response of the optimum NiO@ZnO NTs sensor to 50 ppm H(2)S increases as high as 2.7-23.7 times compared to the other sensors, whereas the response and recovery times also become shorter considerably. These enhanced gas sensing properties are closely related to the change of nanostructure and activity of ZnO and NiO nanocrystals as well as combination of homo- and heterointerfaces in the optimum gas sensor, which are confirmed by a series of well-designed experiments.     

NiO-WO3纳米立方块的制备及在甲醛检测中的应用

采用一步水热合成法合成NiO-WO₃纳米立方块,以WO₃为主体,引入p型半导体NiO构建NiO-WO₃ p-n异质结。通过扫描电子显微镜(SEM)和X射线衍射仪(XRD)对相应的微观结构进行了分析表征,表明产物为单斜相WO₃,由尺寸大小均匀的纳米立方块组成,平均粒径100 nm左右,引入NiO后WO₃纳米立方块的形貌基本保持不变。 将NiO-WO₃纳米立方块制成气敏元件并测验了其对甲醛气体的敏感特性。 气敏测试结果表明,构建NiO-WO₃异质结可显著地提高WO₃传感器对甲醛气体的敏感特性。 特别是5％NiO-WO₃异质结纳米立方块结构传感器,其在200 ℃下对0.134 mg/L甲醛的灵敏度达到18.5,且具有快速响应-恢复特性、良好的稳定性及对甲醛的良好选择性。 传感器性能提升的原因主是界面处p-n异质结的形成和NiO的高催化活性。     

Zinc Oxide-Based Acetone Gas Sensors for Breath Analysis: A Review

Acetone is one of the toxic, explosive, and harmful gases. It may cause several health hazard issues such as narcosis and headache. Acetone is also regarded as a key biomarker to diagnose several diseases as well as monitor the disorders in human health. Based on clinical findings, acetone concentration in human breath is correlated with many diseases such as asthma, halitosis, lung cancer, and diabetes. Thus, its investigation can become a new approach for health monitoring. Better management at the early stages of such diseases has the potential not only to reduce deaths associated with the disease but also to reduce medical costs. ZnO−based sensors show great potential for acetone gas due to their high chemical stability, simple synthesis process, and low cost. The findings suggested that the acetone sensing performance of such sensors can be significantly improved by manipulating the microstructure (surface area, porosity, etc.), composition, and morphology of ZnO nanomaterials. This article provides a comprehensive review of the state-of-the-art research activities, published during the last five years (2016 to 2020), related to acetone gas sensing using nanostructured ZnO (nanowires, nanoparticles, nanorods, thin films, etc). It focuses on different types of nanostructured ZnO-based acetone gas sensors. Furthermore, several factors such as relative humidity, acetone concentrations, and operating temperature that affects the acetone gas sensing properties- sensitivity, long-term stability, selectivity as well as response and recovery time are discussed in this review. We hope that this work will inspire the development of high-performance acetone gas sensors using nanostructured materials.     

Morphosynthesis of hierarchical hydrozincite with tunable surface architectures and hollow zinc oxide

Hydrozincite (Zn5(CO3)2(OH)6) microspheres with a tunable surface architecture have been successfully synthesized via a homogeneous precipitation method under solvothermal conditions. For a smooth hydrozincite microsphere, various building blocks such as nanocubes, nanorods, and nanosheets are arranged to cover a spherical surface by concisely controlling reaction time and the volume of ethylene glycol. Hexagonal Zn5(CO3)2(OH)6 with nanostep structures are also prepared without any additives. The hollow ZnO microspheres with a porous surface have been successfully fabricated via a solution-based method by the room-temperature treatment of filled Zn5(CO3)2(OH)6 microspheres composed of nanocubes. A possible growth mechanism of these hollow ZnO microspheres is proposed. The similar filled ZnO microspheres can also be obtained by a direct pyrolysis of Zn5(CO3)2(OH)6 microspheres composed of nanocubes at 450 degrees C.     

Preparation of homogeneous porous Zn-CoOx and its response to alcohols under relative low operating temperature

A homogeneous porous Co₃O₄-ZnO nanomaterial (Zn-CoO_x) was successfully fabricated by precipitation-annealing route. The as-prepared Zn-CoO_x exhibited good response, reliable reversibility and good selectivity towards alcohols, which attributed to the porous structure and p-n heterojunction formed between Co₃O₄ and ZnO. In particular, the different Fermi levels of Co₃O₄ and ZnO leaded to a further increase the depth of the space charge layer, which improved the gas sensitivity of the material from 10% to 480%. Besides, the continuous Co₃O₄ leaded to a relatively lower operating temperature and resistance. This material preparation method and bimetallic oxides could be widely used in the research and development of metal oxide gas sensitive materials and sensors.     

Examining the use of oxide particles to enhance the sensitivity of polymer\carbon black nanocomposite gas sensors

This paper investigates the use of NiO particles to enhance the vapour sensing properties of polyethylene adipate (PEA)\carbon black (CB) composite materials. Four PEA\CB suspensions were prepared with 0, 10, 20 and 30 w/w% NiO, respectively. Hypermer PS3 surfactant was shear mixed into each of the suspensions for 300 s to achieve a homogenous dispersion and to prevent reagglommeration of both the CB and NiO particles. A 0.1 μl drop of each composite was deposited between Cu electrodes on a printed circuit board (PCB) substrate using a microlitre syringe. The samples were allowed to dry for 24 h in an oven at 333 K to remove any remaining solvent. After preparation, the sensors were exposed to propanol and butanol at concentrations ranging from 0 to 25 000 ppm in steps of 5000 ppm. The response of the PEA\CB sensors improved significantly as the concentration of NiO particles in the material increased and maximum relative differential responses as high as 37% and 92.8% were recorded after exposure to 25 000 ppm propanol and butanol, respectively. This high response can be explained using the Flory–Huggins interaction parameter along with structural changes in the polymer composite caused by the addition of NiO. This paper concludes that NiO particles can be used as a method to increase the sensitivity of existing conducting polymer composite gas sensing materials.     

中空多壳层结构材料的制备及气体传感应用研究进展

先进气体传感器技术在现代社会安全生产生活中扮演着极为重要的角色,而高效敏感材料的设计与开发是其中的关键.中空多壳层结构材料因其独特的层层嵌套的多壳层与多腔体结构而表现出特别的物理化学性质,在气体传感领域显现出巨大的应用潜力.传统的硬模板法、软模板法以及基于奥斯特瓦尔德熟化和柯肯德尔效应的无模板法在中空多壳层纳米结构材料的普适制备及壳层结构的精确调控等方面存在诸多限制.次序模板法的出现突破了上述限制,促进了该领域的迅速发展.本文简要回顾了中空多壳层结构材料制备方法的发展历程,介绍了其在甲醛、乙醇、丙酮、甲苯及二氧化氮等有害气体检测中的具体应用,分析了其在气体传感领域的独特优势,最后对该领域面临的挑战和发展前景进行了总结与展望.     

Hydrothermal synthesis of hierarchical SnO2 nanomaterials for high-efficiency detection of pesticide residue

Acephate pesticide contamination in agricultural production has caused serious human health problems. Metal oxide semiconductor (MOS) gas sensor can be used as a portable and promising alternative tool for efficiently detection of acephate. In this study, hierarchical assembled SnO₂ nanosphere, SnO₂ hollow nanosphere and SnO₂ nanoflower were synthesized respectively as high efficiency sensing materials to build rapid and selective acephate pesticide residues sensors. The morphologies of different SnO₂ 3D nanostructures were characterized by various material characterization technology. The sensitive performance test results of the 3D SnO₂ nanomaterials towards acephate show that hollow nanosphere SnO₂ based sensor displayed preferable sensitivity, selectivity, and rapid response (9 s) properties toward acephate at the optimal working temperature (300 °C). This SnO₂ hollow nanosphere based gas sensor represents a useful tool for simple and highly effective monitoring of acephate pesticide residues in food and environment. According to the characterization results, particularly Brunauer-Emmett-Teller (BET) and Ultraviolet-Visible Spectroscopy (UV–vis), the obvious and fast response can be attributed to the mesoporous hollow nanosphere structure and appropriate band gap of SnO₂ hollow nanosphere.     

Facile synthesis of Pd-decorated ZnO nanoparticles for acetone sensors with enhanced performance

ZnO and Pd nanoparticles (NPs) with average diameter of 38 and 10 nm were prepared in advance through a chemical solution method. Pd-functionalized ZnO nanoparticles (Pd@ZnO) were simply synthesized by adding ethanol solution of Pd NPs into ZnO powder, and annealing in argon atmosphere at 500 °C for 1 h after grinding for 30 min. The morphology and structure of the materials were systemically analyzed using Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM) techniques. A weak peak in the XRD pattern of Pd@ZnO belonging to the (111) plane of elemental Pd indicated successfully loading of Pd. EDS and TEM results further confirmed successfully coating of Pd NPs onto the surface of ZnO. Sensors using ZnO NPs decorated with Pd (1 wt%) on the surface of exhibited highly elevated sensitivity of 76 in comparing with the response of 36 when based on pure ZnO NPs. In addition, such modification also resulted in a decrease in the operating temperature from 370 to 340 °C for 100 ppm acetone vapor. The sensing mechanism of the sensor based on Pd@ZnO NPs is discussed. Addition of Pd NPs can play an important role in improving the performance of gas sensors, including high sensitivity, good selectivity, and short response/recovery times.     

Y掺杂的ZnO纳米纤维材料的制备及其气敏传感器作用机理

采用静电纺丝法成功制备了Y掺杂的ZnO纳米纤维.并通过X射线衍射(XRD),扫描电子显微镜(SEM),能量色散X射线(EDX),透射电子显微镜(TEM)以及热重差热分析(TG-DTA)等手段对样品的结构和形貌进行了表征分析.同时用纯的ZnO和Y掺杂的ZnO纳米纤维制备了传感器,对浓度为(1-200)×10^-6 (体积分数)丙酮的气敏特性进行了测试分析.测试结果表明,可以通过简单控制纳米纤维中Y的含量,来微调该传感器的气敏特性.同时也发现通过Y掺杂, ZnO纳米纤维对丙酮的气敏特性有所改善,表现出很高的响应.纯ZnO和Y掺杂ZnO制成的传感器对几种潜在干扰气体表现出良好的选择性,比如氨气、苯、甲醛、甲苯以及甲醇.本文最后也讨论了该传感器的气敏作用机理.     

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.     

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.     

A facile construction of heterostructured ZnO/Co_3O_4 mesoporous spheres and superior acetone sensing performance

The rapid development of internet and internet of things brings new opportunities for the expansion of intelligent sensors,and acetone as a major disease detection indicator(i.e.,diabetes) making it become extremely important clinical indicator.Herein,uniform mesoporous ZnO spheres were successfully synthesized via novel formaldehyde-assisted metal-ligand crosslinking strategy.In order to adjust the pore structure of mesoporous ZnO,various mesoporous ZnO spheres were synthesized by changing weight percentage of Zn(NO_3)_2·6 H_2 O to tannic acid(TA).Moreover,highly active heterojunction mesoporous ZnO/Co_3 O_4 has been fabricated based on as-prepared ultra-small Co_3 O_4 nanocrystals(ca.3 nm) and mesoporous ZnO spheres by flexible impregnation technique.Profit from nano-size effect and synergistic effect of p-n heterojunction,mesoporous ZnO/Co_3 O_4 exhibited excellent acetone sensing performance with high selectivity,superior sensitivity and responsiveness.Typically,5 wt% Co_3 O_4 embedded mesoporous ZnO sphere showed prominent acetone response(ca.46 for 50 ppm),which was about 11.5 times higher than that in pure ZnO sensing device,and it was also endowed high cyclic stability.The nanocrystals embedded hybrid material is expected to be used as promising efficient material in the field of catalysis and gas sensing.     

碳纳米管基气体传感器研究进展

碳纳米管具有灵敏度高、响应快和工作温度低等优异的气敏特性,近年来碳纳米管基气体传感器的研究成为研究热点.概述了碳纳米管基气体传感器的种类、结构特点、气敏性能和未来的发展方向,着重介绍了纯的碳纳米管包括单壁碳纳米管、多壁碳纳米管和碳纳米管阵列的气敏特性,以及碳纳米管的修饰或碳纳米管与高分子材料、氧化物等复合对其气敏性能的影响.     

Ordered porous metal oxide semiconductors for gas sensing

This review gives a comprehensive summary about the porous metal oxides with focus on the synthesis methods, structure related properties, as well as the modification strategies for gas sensing improved performances.     

ZnO掺杂的SnO_2纳米纤维的制备、表征及气敏机理(英文)

以二水氯化亚锡(SnCl2·2H2O)为盐原料,采用静电纺丝的方法制备了SnO2纳米纤维.为了研究ZnO掺杂对SnO2形貌、结构及化学成分的影响,分别制备了不同含量ZnO掺杂的SnO2/ZnO复合材料.利用热重-差热分析(TG-DTA)、X射线衍射(XRD)、傅里叶变换红外(FTIR)光谱仪、扫描电镜(SEM)及能量色散X射线(EDX)光谱对材料的结晶学特性及微结构进行了表征.制备的SnO2/ZnO复合材料是由纳米量级的小颗粒构成的分级结构材料.ZnO含量不同,对应的SnO2/ZnO复合材料结构不同.表征结果表明ZnO的掺杂量对SnO2材料的形貌及结构均起着重要作用.将制备的不同ZnO含量的SnO2/ZnO复合材料进行气敏测试,测试结果表明,Sn:Zn摩尔比为1:1制作的气敏元件对甲醇的灵敏度优于其它摩尔比的气敏元件.讨论了SnO2/ZnO复合材料气敏元件的敏感机理.同时针对Sn:Zn摩尔比为1:1时表现出最好的气敏响应,分析了其原因,包括Zn的替位式掺杂行为、ZnO的催化作用、过量ZnO对SnO2生长的抑制作用以及SnO2与ZnO晶粒界面处的异质结.