金属氧化物半导体基三乙胺传感器研究进展

三乙胺是一种应用广泛但对人体有毒副作用的挥发性有机物,需要长期有效的监测,开发一种性能稳定、安全可靠的三乙胺气敏传感器,实现对环境中三乙胺气体浓度实时检测,对于三乙胺的安全储存、运输和使用等环节是至关重要的。金属氧化物半导体基气敏传感器具有制备简单、价格低廉、响应值高等优点,在三乙胺气体的检测中具有不可替代的作用。重点介绍了基于金属氧化物半导体的三乙胺传感器最新研究进展。综述了近年来包括掺杂、异质结、有机金属骨架和氧化还原石墨烯在内的关于金属氧化物半导体基三乙胺气敏材料的制备和性能等方面的研究成果。论述了金属氧化物半导体基复合材料对三乙胺气敏性能的机理。展望了金属氧化物基三乙胺气敏材料的未来研究方向。     

Detection of hazardous volatile organic compounds (VOCs) by metal oxide nanostructures-based gas sensors: A review

Since the sensing capability of semiconducting metal oxides was demonstrated in the 1960s, solid state gas sensors based on these materials have attracted considerable attention from both scientific and practical point of view. Because of the promising characteristics for detecting toxic gases and volatile organic compounds (VOCs) compared to conventional techniques, these devices are expected to play a key role in environmental monitoring, chemical process control, personal safety and so on in the near future. Therefore, in recent years, intensive studies have been conducted to improve their sensing performances, particularly to increase the sensitivity and detection limit of such devices. This can be accomplished by using metal oxide nanostructures with various shapes such as nanoparticles, nanowires, nanorods and nanotubes having sizes in the nanometer range. Owing to the high surface-to-volume ratios and consequently large number of surface sites exposed to target gas, nanostructured metal oxides enable a larger gas-sensing layer interaction and hence a higher sensitivity in comparison with conventional materials.This article extensively reviews recent developments in this field, focusing the attention on the detection of some common VOCs, including acetone (C₃H₆O), acetylene (C₂H₂), benzene (C₆H₆), cyclohexene (C₆H₁₀), ethanol (C₂H₅OH), formaldehyde (HCHO), n-butanol (C₄H₉OH), methanol (CH₃OH) toluene (C₇H₈), and 2-propanol (C₃H₈O), by means of conductometric solid state sensors based on nanostructured semiconducting metal oxides.     

Review of recent progress on graphene-based composite gas sensors

Development of gas sensors for detecting toxic, harmful, flammable, and explosive gases has always been very popular research direction. Graphene is considered potential chemi-resistive gas sensing material owing to its high specific surface area and good conductivity. Recent studies have shown that graphene-based gas sensors doped with metals, polymers, and metal oxides have good sensitivity, selectivity, and repeatability. Moreover, they are superior to traditional gas sensors. In this review, sensing mechanism of such composite sensors is introduced. In addition, research status on various sensors is discussed, and their advantages and disadvantages are summarized. Possible improvement methods are proposed as well. Finally, several common problems characteristic of graphene-based gas sensors are described, together with some critical ideas for improving their performance.     

Zinc ferrite based gas sensors: A review

Flammable, explosive and toxic gases, such as hydrogen, hydrogen sulfide and volatile organic compounds vapor, are major threats to the ecological environment safety and human health. Among the available technologies, gas sensing is a vital component, and has been widely studied in literature for early detection and warning. As a metal oxide semiconductor, zinc ferrite (ZnFe₂O₄) represents a kind of promising gas sensing material with a spinel structure, which also shows a fine gas sensing performance to reducing gases. Due to its great potentials and widespread applications, this article is intended to provide a review on the latest development in zinc ferrite based gas sensors. We first discuss the general gas sensing mechanism of ZnFe₂O₄ sensor. This is followed by a review of the recent progress about zinc ferrite based gas sensors from several aspects: different micro-morphology, element doping and heterostructure materials. In the end, we propose that combining ZnFe₂O₄ which provides unique microstructure (such as the multi-layer porous shells hollow structure), with the semiconductors such as graphene, which provide excellent physical properties. It is expected that the mentioned composites contribute to improving selectivity, long-term stability, and other sensing performance of sensors at room or low temperature.     

Effects of reduction of metal oxide sorbents on reactivity and physical properties during hot gas desulphurization in IGCC

In this study, the changes of physical properties and reactivity of the metal oxide sorbents were investigated under the reducing conditions of coal gas. Metal oxide sorbents are converted into metal sulphides as a result of reaction with H₂S in synthesis gas. This could cause the reduced reactivity of sorbents if the metal oxides were converted into metallic elements due to the reduction by either hydrogen or carbon monoxide. In this experiment, the changes of physical properties and reactivity of the metal oxides were investigated over the temperature range 480-700 °C. It is confirmed that the reactivity of sulphidation and the reduction of metal oxide increased with increasing temperature. Even though the sulphur capacity of the sorbents in the early stage was high, it reduced rapidly due to the progressive reduction of metal oxides as the sulphidation/regeneration process was repeated. The reduction of metal oxide and the extent of reduction were verified by measuring the amount of oxygen consumed and the amount of SO₂ produced during the regeneration of sulphidated sorbents with the aids of a gas analyser. It was concluded that the reactivity of the metal oxide sorbents was influenced by reduction with coal gas at high temperature.     

Semi-conductor metal oxide gas sensors for online monitoring of oak wood VOC emissions during drying

This study presents a semi-conductor metal oxide gas sensor system for the online flue gas monitoring during oak wood drying. Oak wood flakes and solid oak wood were heated on laboratory scale. The emissions were analyzed by gas chromatography–mass spectrometry and monitored by a semi-conductor metal oxide gas sensor setup. The calibrated sensor system was able to detect different drying and degradation stages of the oak wood flakes by online monitoring acetic acid and furans/methoxyphenols at 25–240?°C. The system also allowed a monitoring of acetic acid emission from solid wood at 75?°C. This sensor application has the potential to online monitor the flue gas of oak lumber drying and optimize the drying process.     

Catalytic properties of oxide nanoparticles applied in gas sensors

A series of gas sensing layers based on indium oxide doped with gold were prepared by using the aerosol technology for deposition as the active contact layer in a metal oxide semiconductor capacitive device. The interaction between the measured species and the insulator surface was quantified as the voltage changes at a constant capacitance of the device. The sensor properties were investigated in the presence of H₂, CO, NH₃, NO, NO₂ and C₃H₆ at temperatures between 100–400 °C. Significant differences in the morphology of the layer and its sensitivity were noted for different preparation methods and different gas environments.     

基于MOFs材料的酸性气体传感器应用研究进展

采用化学气体传感器对有害酸性气体进行实时有效的监测具有重要意义.目前的传统材料在灵敏度、选择性和稳定性等方面仍存在很大问题.金属有机框架材料(MOFs)是一种具有多孔结构的有机-无机杂化材料,具有孔隙率结构丰富、孔结构可调节和比表面积大等特点,已成为当今新功能材料研究的热点.MOFs材料的优良特性为解决上述问题提供了很...     

基于金属氧化物的乙醇检测气敏材料的研究进展

金属氧化物型半导体气体传感器是目前常用的乙醇检测手段,深入研究和改进金属氧化物型半导体材料是提升传感器性能的重要方式。本文首先论述了气敏检测的机理和影响因素,并综述了近年来发展的主要金属氧化物型半导体气敏材料,重点介绍了不同微观结构的Co₃O₄、ZnO、SnO₂及掺杂金属氧化物材料、氧化物异质结等的研究和发展情况,对它们的合成方法、结构特点以及结构与乙醇气敏性能之间的关系进行了探讨。分析表明,减小材料颗粒尺寸、构建大比表面积多孔结构、掺杂和复合改性,是提升金属氧化物材料气敏性能的有效措施。此外,基于传感器微小化的趋势,以微机电系统（MEMS）工艺为基础的微型传感器成为气体传感器的发展趋势。然而,目前针对金属氧化物气敏材料的制备依然缺乏一定的理论指导,气体检测缺乏相应的机理研究,亟需物理、化学、材料等多学科的相互结合,促进乙醇等半导体气体传感器的进一步发展。     

Effects of methane and oxygen on decomposition of nitrous oxide over metal oxide catalysts

Catalytic activities of various metal oxides for decomposition of nitrous oxide were compared in the presence and absence of methane and oxygen, and the general rule in the effects of the coexisting gases was discussed. The reaction rates of nitrous oxide were well correlated to the heat of formation of metal oxide, i.e., a V-shaped relationship with a minimum at −ΔH_f⁰ around 450 kJ (O mol)⁻¹ was observed in N₂O decomposition in an inert gas. In the case of metal oxides having the heat of formation lower than 450 kJ (O mol)⁻¹, CuO, Co₃O₄, NiO, Fe₂O₃, SnO₂, In₂O₃, Cr₂O₃, the activities were strongly affected by the presence of methane and oxygen. On the other hand, the activities of TiO₂, Al₂O₃, La₂O₃, MgO and CaO were almost independent. The reaction rate of nitrous oxide was significantly enhanced by methane. The promotion effect of methane was attributed to the reduction of nitrous oxide with methane: 4N₂O+CH₄→2N₂+CO₂+2H₂O. The activity was suppressed in the presence of oxygen on the metal oxides having lower heat of formation. On the basis of Langmuir–Hinshelwood mechanism, the effect of oxygen on nitrous oxide decomposition was rationalized with the strength of metal–oxygen bond.     

Effect of the morphology of solution‐grown ZnO nanostructures on gas‐sensing properties

Despite the great potential of zinc oxide (ZnO) nanostructures as a sensing material for high‐performance gas sensors, the correlation between the morphology of ZnO nanostructure and its gas‐sensing performance has not been systematically investigated yet. In this work, ZnO nanostructures with controlled morphologies were synthesized by low‐temperature solution route and chemical bath deposition method. Thin film gas sensors were fabricated from the nanostructures and the sensor performance such as the response, recovery time, and stability was examined for several gases. It is demonstrated that the gas‐sensing performance of a ZnO nanostructure sensor is strongly influenced by its morphology. One dimensional ZnO nanocones are highly promising for practical application to gas sensors, due to their large surface area per unit mass and unique conical structure.     

Fabrication of patterned nanostructures with various metal species on Si wafer surfaces by maskless and electroless process

Maskless and electroless fabrication was demonstrated to form patterned nanostructures of various metal species, based upon the process previously developed by the authors. In this process, the metallic nanostructures were formed on the surface of clean, hydrogen terminated p-(1 0 0) Si wafer with pre-patterned nanoscopic defects, which were confirmed to possess higher activity for the reductive deposition reaction of the metal ion species. The deposition was achieved spontaneously and selectively at the defect sites on the wafer surface by immersing into dilute aqueous fluoride solution containing trace amount of metal ion species. By optimizing the formation condition of the patterned defects and composition of the solution, fabrication of patterned nanostructures of various metallic species such as Au, Ag, and Co, was achieved. Formation of the patterned nanostructures to 10 μm² in extent, as well as control of the feature size of the deposits by adjusting the formation condition of the patterned defects were also attempted.     

Effect of sintering temperature on the electrical and gas sensing properties of tin oxide powders

Tin oxide is an n-type semiconducting material having superior properties that can be utilized in several applications. The warning and detection of several dangerous gases in the environment are possible by utilizing gas sensors. The comprehensive functionality of these sensors could help to reduce the risk of severe health hazards and unexpected explosion risks. Tin oxide-based gas sensors exhibit reliable gas sensing performances along with respectful sensitivity and selectivity. Tin oxides in micro-and nano-particle forms provide an extremely high surface-to-volume ratio, which is favorable for gas sensors. Processing and synthesis of tin oxide particles accompany high-temperature processes, and this paper focuses on studying the effect of sintering temperatures on the structural and grain size of the commercially available tin oxide particles. The surface morphology of the tin oxide samples sintered at three different temperatures of 1100, 1200, 1300 ^°C shows a clear difference in the grain size and further affecting the dielectric properties of the materials. The gas sensing performances of three tin oxide samples are investigated by fabricating a pellet-type gas sensor. The sensor with the sintering temperature of 1200 ^°C exhibits the best gas-sensing performance with high response and low limit of detection (LOD). Our results suggest that the sintering temperature plays a vital role in deciding the dielectric properties and grain sizes, which are important parameters that affect the gas sensing behavior of tin oxide micro-and nano-particles.     

A review on synthetic strategies and gas sensing approach for polypyrrole-based hybrid nanocomposites

Polypyrrole (PPy)-based hybrid nanocomposites of organic and inorganic hybrid materials are not restricted for academic research, but nowadays, they are useful to design innovative industrial applications such as fuel cell, solar cell, catalysts, sensors, energy, and medical applications. In recent applications, PPy and its hybrid composites have been emerged as promising sensors due to their unique physical and chemical properties. In this article, the role of PPy-based hybrid nanocomposites for the improvement in sensing applications has been discussed in detail. Along with this is the systematic discussion of the synthesis techniques of PPy sensory hybrid nanocomposites that provides a better understanding of this research area. Finally, certain limitations of PPy and its hybrid nanocomposites-based sensor are also discussed for sensing.     

A review of recent developments in tin dioxide nanostructured materials for gas sensors

Gas sensors based on SnO₂ nanostructures have been extensively investigated in recent years. Many recent investigations have focused on synthesizing 0D, 1D, 2D and 3D SnO₂ nanostructures with high sensing capacity. This work presents a review of the recent developments in pure, doped and metal oxide functionalized SnO₂ nanostructured gas sensors, emphasizing the main SnO₂ preparation methods and the working principle of SnO₂ gas sensors. Most studies have shown that doping, coupled with a high surface area, can significantly improve SnO₂ sensing properties. Sensing response, response/recovery times, and operating temperature can be modulated by the synergistic effect between these two factors. In general, fine nanoparticles, mesoporous materials, hollow and 3D nanostructures combined with additives such as Pt, Pd, Cu, Ni, Ag and Al have shown the best improvements in gas sensing.     

Solid state ceramic gas sensors based on interfacing ionic conductors with semiconducting oxides

Solid-state ceramic NO_x sensors based on interfacing an ionic conductor (NASICON) with semiconducting oxides (rare earth perovskite-type oxides) were investigated. NASICON powders were pressed into thimbles 12 mm long with 3 mm inner diameter and 4 mm outer diameter, then sintered at 1270°C in air. A Pt wire was attached to the outer surface of the tubes using a platinum paste. A uniform Au/Pd (60 wt.%) coating, permeable to oxygen but not to NO_x, was sputtered for 40 min on the sensor external surface to allow the exposure of both electrodes to the gas atmosphere without using reference air. Windowless energy-dispersive spectroscopy (EDS) was used to evaluate the chemical composition of the Au–Pd layer before and after the performance of sensing tests. Sodalite powder as an auxiliary phase was tightly packed into the NASICON thimbles with a Pt lead for the electrical contact. To get an in-situ NO conversion to NO₂, a Pt-loaded alumina powder was used as a catalyst and incorporated with the sensor on the top of the auxiliary phase. Nano-sized and chemically-pure rare earth perovskite-type oxide (LaFeO₃, SmFeO₃, NdFeO₃ and LaCoO₃) powders, prepared by the thermal decomposition of the corresponding hexacyanocomplexes, were also used in the electrochemical cells. Each of the tested oxides was packed into the thimbles replacing the sodalite and the Pt-loaded alumina catalyst. Tests were performed also using only the perovskitic oxides. The microstructure of the materials tested was evaluated using scanning electron microscopy (SEM). The NO₂ sensing properties of the prototype sensors were investigated at controlled temperature (in the range 300–600°C) by measuring the electromotive force (EMF) at different NO₂ concentrations (in the range 2–2000 ppm in air). Some measurements were performed at various NO concentrations diluted with Ar. The results obtained showed a promising NO₂ sensing performance when ferrites were used. SmFeO₃ has a lower catalytic effect on NO oxidation than the Pt-loaded alumina catalyst, and has a similar effect to sodalite when used as auxiliary phase. The perovskite-type oxides are more preferable as auxiliary phase than sodalite because they improve the stability of the electrochemical sensor performances.     

Highly sensitive gas sensors on low-cost nanostructured polymer substrates

SnO₂ thin-film gas sensors have been successfully fabricated on nanospiked polyurethane polymer surfaces, which are replicated by a low-cost soft nanolithography method from silicon nanospike structures formed with femtosecond laser irradiations. Measurements revealed significant response to carbon monoxide (CO) gas at room temperature, which is considerably different from the sensors of SnO₂ thin films coated on smooth surfaces that show no response to CO gas at room temperature. The high area/volume ratio and sharp structures of the nanospikes enhance the sensitivity of SnO₂ at room temperature. This will greatly decrease the electrical power consumption of the gas sensor and the cost for calibrations, and has great potential for application in other sensing systems.     

Advanced metal oxide (supported) catalysts: Synthesis and applications

A variety of metal oxides catalysts are used in heterogeneous catalysis for chemical processes and have now been developed for their catalytic performance and durability. The heterogeneous catalysis is the most important technology in chemical industry as well as other environmental, energy applications, etc. This review examines recent advances at the preparation and applications of metal oxide particles, especially pertaining to catalytic enhancements for current and future chemical process such as Fischer–Tropsch process, alkylation, and transesterification and environmental applications such as the oxidation of volatile organic compounds and the reduction of NO_x.     

Seed-mediated electrochemical growth of gold nanostructures on indium tin oxide thin films

Two-dimensional gold nanostructures (Au NSs) were fabricated on amine-terminated indium tin oxide (ITO) thin films using constant potential electrolysis. By controlling the deposition time and by choosing the appropriate ITO surface, Au NSs with different shapes were generated. When Au NSs were formed directly on aminosilane-modified ITO, the surface roughness of the interface was largely enhanced. Modification of such Au NSs with n-tetradecanethiol resulted in a highly hydrophobic interface with a water contact angle of 144°. Aminosilane-modified ITO films further modified with colloidal Au seeds before electrochemical Au NSs formation demonstrated interesting optical properties. Depending on the deposition time, surface colors ranging from pale pink to beatgold-like were observed. The optical properties and the chemical stability of the interfaces were characterized using UV-vis absorption spectroscopy. Well-defined localized surface plasmon resonance signals were recorded on Au-seeded interfaces with λ_max = 675 ± 2 nm (deposition time 180 s). The prepared interfaces exhibited long-term stability in various solvents and responded linearly to changes in the corresponding refractive indices.     

Some kinetic aspects of unsteady-state partial oxidation reactions. Dynamic processes on metal oxide surfaces

It is shown that steady-state kinetic data do not allow the discrimination between the redox and associated mechanisms of the partial oxidation reactions. A discrimination between these mechanisms was performed using transient experiments. The obtained rate expressions are in agreement with experimental kinetic data for catalytic partial oxidation of o-xylene.

An influence of the conjugate oxidation of a catalyst surface on dynamics and kinetics of the heterogeneous catalytic oxidative reactions is considered. Computing simulation of methane oxidative coupling of methane reaction at lowered temperature and elevated pressure has been performed. It showed that the reaction order with respect to oxygen exceeding unity is consistent with the chain branching mechanism of the reaction in the presence of TiSi₂ and TiB₂ and showed the important role of the branching chain cycles in the low-temperature OCM reaction at elevated pressure.