Ethanol sensing using CuO/MWNT thin film

Copper (II) oxide (CuO)/multiwall carbon nanotube (MWNT) thin film based ethanol-sensors were fabricated by dispersing CVD-prepared MWNTs in varying concentration over DC magnetron sputtered-CuO films. The responses of these sensors as a function of MWNT concentrations and temperatures were measured, and compared. The sensing response was the maximum at an operating temperature near 400 °C for all the samples irrespective of the MWNTs dispersed over them. At optimum operating temperature (T_opt) of 407 ± 1 °C, the response is linear for 100-700 ppm range and tends to saturate at higher concentrations. In comparison with bare CuO sample, the response of CuO/MWNT sensing films increased up to 50% in the linear range. The response improvement for 2500 ppm of ethanol was up to 90% compared to bare CuO sample. In addition, the sensing response time also reduced to around 23% for lowest ethanol concentration at T_opt. However, a decrease in the sensor response was observed on films with very high concentrations of MWNTs.     

Robust model predictive control of a pilot plant distillation column

In this paper, the development and application of a robust MPC to a pilot plant ethanol–water distillation column is described. It is shown through experimental tests in the pilot plant, how the linear model can change depending on the operating point. The obtained model has time delays and repeated poles. For this kind of system, the development of an MPC, based on the step response model that is robust to multi-model uncertainty, is presented. The experimental results that confirm the good performance of the proposed controller are also shown.     

Optical alcohol sensor based on dye–Chitosan polyelectrolyte multilayers

The layer-by-layer deposition technique was used to prepare polyelectrolyte multilayer (PEM) thin films that are sensitive to ethanol content in water. Cationic Chitosan was assembled with anionic acid dye, (phenyl amino)-5-[[4-(3-sulphonatophenyl) azo]-(1-naphthalenyl) azo]-1-naphthalenesulfonic acid disodium salt (Nylosan) on glass slide and characterized using UV–vis spectroscopy. The layer-by-layer deposition of Chitosan–Nylosan into PEM was studied by monitoring the increase in absorbance in the visible region (500–600 nm). The typical linear relationship between increase in absorbance and number of layers was found. The PEM thin films responded to increasing concentrations of ethanol in water with a shift of maximum absorbance (λ_max) from 540 to 580 nm. This shift was also characterized by an increase in absorbance at 600 nm which was used to monitor the response of the thin film to ethanol content in water. The characteristic color shift of the Nylosan dye occurred at a higher ethanol concentration (from 10% to 45%) in the PEM compared to its usual shift in aqueous solution (from 0% to 30%). The Chitosan–Nylosan thin films response to ethanol content was found to be linear from 10% to 45% ethanol content, which renders them useful as ethanol sensing thin films.     

Application of sulfuric acid doped poly (m-aminophenol) as aliphatic alcohol vapor sensor material

Chemically synthesized processable poly (m-aminophenol) (PmAP) film was cast from dimethyl sulfoxide solution and doped with sulfuric acid by solution doping technique. This sulfuric acid doped PmAP film shows a good electrical conductivity. The response of doped film under continuous flow of various aliphatic alcohols vapor and air mixture was examined at room temperature (30 °C) and humidity (65% RH). The doped polymer only showed good result for methanol and ethanol vapor and some week response for the isopropanol vapor. A decrease in resistivity of the doped PmAP film was separately observed in air–alcohol vapor at different concentrations. The response of the film increases as the concentration of the alcohol vapor increases in air–alcohols vapor mixture. The kinetics of the response with respect to the alcohol concentration was studied for methanol and ethanol. Sulfuric acid doped and methanol vapor absorbed doped films were characterized by ultraviolet–visible spectroscopic, attenuated total reflectance Fourier transformed infrared spectroscopic and X-ray diffraction analyses. The mechanism of alcohol vapor sensing by sulfuric acid doped PmAP film has been explained on the basis of the above characterizations. All the above facts are trying to explain from the proposed mechanistic point of view.     

Microstructure, electrical and ethanol-sensing properties of perovskite-type SmFe0.7Co0.3O3

Ultrafine SmFe_0.7Co_0.3O₃ powder, prepared by a sol–gel method, shows a single-phase orthogonal perovskite structure. The influence of annealing temperature upon its crystal cell volume, microstructure, electrical and ethanol-sensing properties was investigated in detail. When the annealing temperature increases from 600 to 950 °C, the unit cell volume of the SmFe_0.7Co_0.3O₃ sample reduces, and its average grain size increases. When the annealing temperature increases from 600 to 850 °C, the optimal working temperature and response to ethanol of the SmFe_0.7Co_0.3O₃ sensor increase, and the response–recovery time shortens. But when the annealing temperature further increases from 850 to 950 °C, there are decreases of the optimal working temperature and sensor response, and the response–recovery time is prolonged. The results indicate that, as for sensor response, its optimal annealing temperature is about 850 °C, and the sensor based on SmFe_0.7Co_0.3O₃ annealed at 850 °C shows the highest response S = 80.8 to 300 ppm ethanol gas, and it has the best response–recovery and selectivity characteristics. When the ethanol concentration is as low as 500 ppm, the curve of its optimal response versus concentration is nearly linear. Meanwhile, the influence mechanisms of annealing temperature upon the conductance, the optimal working temperature and sensor response for SmFe_0.7Co_0.3O₃ were studied.     

A selective room temperature formaldehyde gas sensor using TiO2 nanotube arrays

A new gas sensor using TiO₂ nanotube arrays was fabricated and explored for formaldehyde detection at room temperature. Highly ordered vertically grown TiO₂ nanotube arrays were synthesized by using the conventional electrochemical anodization process. The sensor using the fabricated nanotube arrays as the sensing elements demonstrated a good response to different concentrations of formaldehyde from 10 to 50 ppm and a very good selectivity over other reducing gas species such as ethanol and ammonia at room temperature. While the exact sensing mechanism is unclear, some possibilities are briefly discussed.     

Ultrahigh ethanol response of SnO2 nanorods at low working temperature arising from La2O3 loading

The influences of La₂O₃ loading on the ethanol sensing properties of SnO₂ nanorods were investigated. An obvious enhancement of response was obtained. The response of 5 wt% La₂O₃ loaded SnO₂ nanorods was up to 213 for 100 ppm ethanol at low working temperature of 200 °C, while that of pure SnO₂ nanorods is 45.1. The improvement in response might be attributed to the presence of basic sites, which facilitated the dehydrogenation process. While the working temperature was increased to 300 °C, the sensor response decreased to 16 for 100 ppm ethanol. Additionally, the La₂O₃ loaded SnO₂ nanorods sensors showed good selectivity to ethanol over methane and hydrogen. Our results demonstrated that the La₂O₃ loaded SnO₂ nanorods were promising in fabricating high performance ethanol sensors which could work at low temperature.     

Fabrication of N-type Fe2O3 and P-type LaFeO3 nanobelts by electrospinning and determination of gas-sensing properties

N-type Fe₂O₃ nanobelts and P-type LaFeO₃ nanobelts were prepared by electrospinning. The structure and micro-morphology of the materials were characterized by X-ray diffraction (XRD) and scanning of electron microscopy (SEM). The gas sensing properties of the materials were investigated. The results show that the optimum operating temperature of the gas sensors fabricated from Fe₂O₃ nanobelts is 285 °C, whereas that from LaFeO₃ nanobelts is 170 °C. Under optimum operating temperatures at 500 ppm ethanol, the response of the gas sensors based on these two materials is 4.9 and 8.9, respectively. The response of LaFeO₃-based gas sensors behaves linearly with the ethanol concentration at 10-200 ppm. Sensitivities to different gases were examined, and the results show that LaFeO₃ nanobelts exhibit good selectivity to ethanol, making them promising candidates as practical detectors of ethanol.     

High sensitivity ethanol gas sensor integrated with a solid-state heater and thermal isolation improvement structure for legal drink-drive limit detecting

The paper reports the successful fabrication of ethanol gas sensors with tin-dioxide (SnO₂) thin films integrated with a solid-state heater, which is realized with technologies of micro-electro-mechanical systems (MEMS), and are compatible with VLSI processes. The main sensing part with dimensions of 450×400 μm² in this developed device is composed of a sensing SnO₂ film, which is fabricated by electron-gun evaporation with proper annealing in ambient oxygen gas to yield fine particles and good structure. An integrated solid-state heater with a 4.5 μm-thick cantilever bridge (1000×500 μm²) structure is made of silicon carbide (SiC) material by MEMS technologies. The sensitivity for 1000 ppm ethanol gas reaches as high as 90 with 10 s and 2 min for the response and recovery time, respectively, at an operating temperature of 300°C. Those experimental results also exhibit a much superior performance to that of a popular commercial ethanol gas sensor TGS-822. Therefore, the developed sensor with high performance is a good candidate for some specific application in automobile to detect drink-drive limit and allows an array integration available with various films for controlling each element at separate resistance.     

PVF膜光导纤维乙醇传感器

以聚偏氟乙烯（ＰＶＦ）膜为敏感膜研制的光导纤维乙醇传感器，具有响应迅速可逆、稳定性好、使用寿命长的优点，对酒中乙醇的快速测定以及酒类生产过程中乙醇浓度的连续在线监测有一定的实用价值。     

基于多壁碳纳米管-铂纳米颗粒纳米复合材料的乙醇生物传感器

采用超声法制备了多壁碳纳米管－铂纳米颗粒( MWCNTs￣PtNPs)纳米复合材料,并将其修饰于乙醇生物传感器,表现出良好的检测性能。实验结果表明：传感器最低检测限为0.02 mmol/L,线性范围为0.25 mmol/L~3.00 mmol/L,灵敏度为0.92332μA/( mmol/L),并且具有高稳定性和良好的重现性。     

Surface plasmon resonance study on the optical sensing properties of nanometric polyimide films to volatile organic vapours

The optical sensing properties of nanometric polyimide films towards ethanol and methanol vapours have been investigated by surface plasmon resonance technique. To this purpose polyimide sensing layers have been deposited onto gold/glass substrates by glow-discharge-induced vapour deposition polymerization technique. The sensible layer shows reversible and stable responses to different concentrations of methanol and ethanol vapours. A linear dependence between the change in reflectivity and the vapours concentration is observed being the sensitivity to both vapours similar, however, the response is larger in presence of ethanol vapours. Numerical fitting routines on surface plasmon resonance curves indicate that optical changes are motivated by an absorption process of the analyte. This produces a detectable increase of the real refractive index and a swelling process in the polyimide layer.     

Determining quadratic weighting matrices to locate poles in a specified region

A new procedure of selecting weighting matrices in linear quadratic optimal control problems (LQ-problems) is proposed. In LQ-problems, the quadratic weights are usually decided on trial and error to get good responses. But using the proposed method, the quadratic weights are decided in such a way that all poles of the closed loop system are located in the desired region for good response as well as for stability. As the system constructed by this method has merits of an LQ-problem as well as a pole-assignment problem, this procedure will be useful for designing a linear feedback system.     

Biomorphic synthesis of ZnSnO3 hollow fibers for gas sensing application

Biomorphic ZnSnO₃ hollow fibers have been fabricated using cotton as biotemplates. Cotton fibers are infiltrated with zinc nitrate and stannic chloride solution and subsequently sintered in air at high temperatures to produce the final ZnSnO₃ hollow fibers. The samples have further distinctions in structure and morphology by X-ray diffraction and scanning electron microscopy. It showed that all the samples present an orthorhombic structure of high crystallinity, and the hollow fibers were composed of numerous ZnSnO₃ nanorods. Furthermore, gas sensors were fabricated and an investigation of ethanol sensing properties has been conducted. The sensor, based on ZnSnO₃ hollow fibers calcined at 500 °C, shows highly sensitive to ethanol with fast response, good selectivity and stability, indicating its potential applications for environment and food or the drinking status of drivers.     

An amperometric ethanol sensor based on a Pd–Ni/SiNWs electrode

A new amperometric ethanol sensor has been developed. The sensor uses the silicon nanowires covered with co-deposited palladium–nickel (Pd–Ni/SiNWs) as the working electrode. The detection of ethanol concentration is based on the response currents resulted from the electro-catalytic oxidation of ethanol. The performance of the sensor was characterized by cyclic voltammetry and fixed potential amperometry techniques. In 1 M KOH solution containing different ethanol concentrations, the sensor shows a good sensitivity of 7.48 mA mM⁻¹ cm⁻² and the corresponding detection limit (signal-to-noise ratio = 3) of 6 μM for cyclic voltammetry. Meanwhile, it also displays a sensitivity of 0.76 mA mM⁻¹ cm⁻² and the corresponding detection limit of 10 μM for fixed potential amperometry. The results demonstrate that the Pd–Ni/SiNWs electrodes are potential as the electrochemical integrated sensors for ethanol detection.     

氧化锌基乙醇气体传感器研制及特性研究

利用水热法合成了不同形貌的ZnO基纳米结构气敏材料,利用X射线衍射仪(XRD)和扫描电子显微镜 (SEM)对其进行了结构表征和分析。制备成旁热式气体传感器,测试了其对乙醇(C2H5OH)的气敏特性。实验结果表明：基于ZnO纳米花制作出的传感器比纳米球状传感器对C2H5OH具有更高的灵敏度,在200oC下对50ppm的C2H5OH灵敏度为34.7,是球状ZnO基传感器的1.7倍;两种ZnO基传感器对C2H5OH均表现出较好的重复性,在最佳工作温度下对C2H5OH的响应恢复时间均在15秒以内;最后对ZnO基C2H5OH气体传感器的气敏机理进行了讨论。     

Improving the ethanol sensing of ZnO nano-particle thin films—The correlation between the grain size and the sensing mechanism

ZnO and Sn doped ZnO (ZnO:Sn) thin films at various doping concentrations from 1 to 10 at.% were prepared by the sol-gel method for an ethanol sensing application. The Sn doping significantly influenced the film growth, grain size and response of the films. The XRD patterns showed that the hexagonal wurtzite structure of the ZnO film was retained even after the Sn doping. The crystallite grain sizes of the ZnO:Sn thin films at 0, 2 and 4 at.% were estimated by using the typical Scherrer's equation. The crystalline quality of the films at 6, 8 and 10 at.% of Sn was degenerated. Typical FESEM images demonstrated the different morphologies for the ZnO:Sn thin films at various Sn concentrations; many pores of various dimensions were observed depending on the doping level. A TEM analysis of the ZnO:Sn thin films at 0, 2 and 4 at.% was performed to verify the grain size. The optimum Sn doping level of ZnO:Sn thin film for ethanol sensing was estimated to be 4 at.%. The 4 at.% sample obtained the highest response to ethanol vapor in the 10-400 ppm level range at a low operating temperature of 250 °C. The sensing mechanism was explained by a variation in the sensitivity model from a neck-grain-boundary controlled sensitivity to a neck-controlled sensitivity. Our work demonstrates the ability to reduce the working temperature as well as to increase the response of ZnO thin film based gas sensors to detect ethanol, which would be of great merit for commercialized applications.     

Dispersive SnO2 nanosheets: Hydrothermal synthesis and gas-sensing properties

SnO₂ nanosheets with the thickness of 10 nm were successfully synthesized by a simple hydrothermal process at 180 °C for 12 h. The samples were characterized by X-ray power diffraction, scanning electron microscopy, transmission electron microscopy, and high-resolution transmission electron microscopy. The sensor performance of the as-prepared SnO₂ nanosheets for ethanol and carbon monoxide was measured. The results indicate that the sensor exhibited high response, quick response-recovery kinetics, and good repeatability.     

酒精五塔蒸馏工艺过程模拟

针对典型的酒精蒸馏五塔工艺流程及蒸馏过程各物流的组成、压力、温度等工艺条件,分析模拟计算的热力学方法和热力学数据,结果表明,本文所选用的热力学方法SRKM、IDEAL、NRTL及物流组分交互作用参数均适用于酒精蒸馏五塔工艺流程,各工艺物流的模拟数据与设计数据最大误差均小于4.5%,模拟值与设计值比较吻合,不超出设计误差(10%)的限度.     

Sensitivity to alcohols of a planar waveguide ring resonator fabricated by a sol–gel method

A planar waveguide ring resonator was fabricated by organic–inorganic hybrid sol–gel materials; its sensitivity to ethanol vapor was experimentally investigated. It was found that dips in the transmission spectrum of the device shifted to longer wavelengths with increasing the ethanol concentration, and its sensitivity showed a linear relation with the ethanol concentration, showing a coefficient of 1.13 pm/ppm. In addition, the transmission loss of the ring resonator decreased with increasing the ethanol concentration. The measured characteristics suggest that the device may be considered as one of the candidates of alcohol vapor sensors.