Methane Gas Sensor Research Articles

Facile fabrication of ZnO nanocrystalline-modified graphene hybrid nanocomposite toward methane gas sensing application

In this paper, we synthetized a hybrid composite of zinc oxide (ZnO) nanocrystalline-decorated reduced graphene oxide (rGO) via a facile hydrothermal process, and fabricated a methane gas sensor by using the ZnO–rGO hybrid composite as sensing film coated on a ceramic tube with Ni–Cr heater. The presence of nanorod-shaped ZnO nanocrystalline and rGO nanosheets was characterized by scanning electron microscopy, X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy, UV–Vis diffuse reflectance and photoluminescence spectra measurement. The sensing properties of the ZnO–rGO film sensor were investigated by exposing to various concentration of methane gas at different temperature. It was found that the presented sensor exhibited unique advantages in methane gas sensing with concentration spanning from 100 to 4000 ppm, such as outstanding repeatability, fast response-recovery time as well as good selectivity, at an optimal operating temperature of 190 °C. The gas response of the ZnO–rGO hybrid composite was superior to that of the pure ZnO and rGO counterpart in methane gas sensing. The possible and proposed sensing mechanism for the sensor is mainly attributed to its nano-hybrid structure and special interactions at p–n heterojunction. This observed results highlight the ZnO–rGO hybrid composite as a candidate material for constructing methane gas sensors.

SnO2 Hollow Hemisphere Array for Methane Gas Sensing

We developed a high-performance methane gas sensor based on a <TEX>$SnO_2$</TEX> hollow hemisphere array structure of nano-thickness. The sensor structures were fabricated by sputter deposition of Sn metal over an array of polystyrene spheres distributed on a planar substrate, followed by an oxidation process to oxidize the Sn to <TEX>$SnO_2$</TEX> while removing the polystyrene template cores. The surface morphology and structural properties were examined by scanning electron microscopy. An optimization of the structure for methane sensing was also carried out. The effects of oxidation temperature, film thickness, gold doping, and morphology were examined. An impressive response of ~220% was observed for a 200 ppm concentration of <TEX>$CH_4$</TEX> gas at an operating temperature of <TEX>$400^{\circ}C$</TEX> for a sample fabricated by 30 sec sputtering of Sn, and oxidation at <TEX>$800^{\circ}C$</TEX> for 2 hr in air. This high response was enabled by the open structure of the hemisphere array thin films.

Ni2O3-decorated SnO2 particulate films for methane gas sensors

High-performance methane gas sensors were developed from Ni2O3-decorated SnO2 semiconducting films. The SnO2 film was fabricated by the sputter deposition of Sn metal followed by oxidation. Ni nanoparticles were then deposited onto the SnO2 film by the arc discharge deposition of single-wall carbon nanotubes followed by the burning out of carbon nanotubes. The catalytic Ni nanoparticles distributed in the carbon nanotubes were oxidized to Ni2O3. The surface morphology and structural properties were examined by scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The methane gas sensing properties were examined at different operation temperatures with SnO2 thickness and Ni2O3 quantity as variables. The synergetic effects induced by the Ni2O3-decoration including enhanced response and lowered operation temperature were observed. We also report very high sensor responses. The sensing mechanism of the hybrid sensor structure was also discussed.

BACK PROPAGATION NEURAL NETWORK MODEL FOR TEMPERATURE AND HUMIDITY COMPENSATION OF A NON DISPERSIVE INFRARED METHANE SENSOR

The infrared absorption gas sensor detects CH4, CO, CO2, and other gases accurately and rapidly. However, temperature and humidity have a great impact on the gas sensor's performance. This article studied the response of an infrared methane gas sensor under different temperatures and humidity conditions. After analyzing the compensation methods, a back propagation neural network was chosen to compensate the nonlinear error caused by temperature and humidity. The optimal parameters of the neural network are reported in this article. After the compensation, the mean error of the gas sensor's output was between 0.02–0.08 vol %, and the maximum relative error dropped to 8.33% of the relative error before compensation. The results demonstrated that the back propagation neural network is an effective method to eliminate the influence of temperature and humidity on infrared methane gas sensors.

Synthesize of polyaniline–multi walled carbon nanotubes composite on the glass and silicon substrates and methane gas sensing behavior of them at room temperature

In this study, fabrication of methane gas sensor using composites of multi-walled carbon nanotubes (MWCNT) and polyaniline (PANI) on glass and silicon substrates is reported. In this respect, 8wt% of purified MWCNT by acid washing procedure, was combined with PANI by solution mixing method. The MWCNT–PANI composite was deposited on the surface of glass and Si substrates using spin coating technique. The methane gas sensing of composite films were evaluated by measuring the change of electrical resistance in the presence of methane gas at room temperature. It is observed that the MWCNT–PANI film on the Si substrate shows a higher sensitivity to methane gas in comparison to pure PANI on the glass substrate. The characterization of samples has also been investigated by Fourier transform infrared, transmission electron microscopy and scanning electron microscopy analyses.

A trace methane gas sensor using mid-infrared quantum cascaded laser at 7.5 μm

Presented is a compact instrument developed for in situ high-stable and sensitive continuous measurement of trace gases in air, with results shown for ambient methane (CH4) concentration accurate, real-time and in-situ. This instrument takes advantage of recent technology in thermoelectrically cooling (TEC) pulsed Fabry-Perot (FP) quantum cascaded laser (QCL) driving in a pulse mode operating at 7.5 microm ambient temperature to cover a fundamental spectral absorption band near v4 of CH4. A high quality Liquid Nitrogen (LN) cooled Mercury Cadmium Telluride (HgCdTe) mid-infrared (MIR) detector is used along with a total reflection coated gold ellipsoid mirror offering 20 cm single pass optical absorption in an open-path cell to achieve stability of 5.2 x 10(-3) under experimental condition of 200 micromol x mol(-1) measured ambient CH4. The instrument integrated software via time discriminating electronics technology to control QCL provides continuous quantitative trace gas measurements without calibration. The results show that the instrument can be applied to field measurements of gases of environmental concern. Additional, operator could substitute a QCL operating at a different wavelength to measure other gases.

Characterization of Pt-doped SnO2 catalyst for a high-performance micro gas sensor

The atomic scale structure and its dependence on Pt concentration of a Pt-doped SnO2 (Pt-SnO2) thin film produced by a sputter-deposition method was investigated, which showed high-performance as a methane gas sensor. Extended X-ray absorption fine structure (EXAFS) and X-ray diffraction (XRD) analyses showed that Pt-SnO2 has a rutile structure similar to SnO2 crystals at less than 10 at% Pt where the Pt ion was located at the Sn position in the rutile structure. There was no evidence that Pt metal clusters were formed in the Pt-SnO2 films. The Pt-SnO2 structure became amorphous at greater than 11 at% Pt. We found a good correlation between the methane activity and local structure of Pt.

ZnO/Ti Thin Film: Synthesis, Characterization and Methane Gas Sensing Property

Thin films of ZnO were synthesised on glass substrate by dc sputtering technique at a system pressure of 10−4 Torr. A layer of TiO2 was deposited onto the above ZnO films by high pressure sputtering technique. The composite structure was then subjected to rapid thermal annealing at a pressure of 10−2 Torr in argon ambience. Microstructural and compositional analyses were carried out by SEM, EADX and XRD studies. The optical band gap pure ZnO (∼3.45 eV) was found to shift to higher energy (∼3.54 eV) for the ZnO/Ti structures. FTIR measurement indicated the presence of a prominent absorption peak at ∼490 cm−1 due to ZnO stretching mode. Methane gas sensing measurement was carried out at 353K, indicated that the highest sensitivity was nearly 60% with a response time ∼52 min when the film were exposed to 10 % vol. of methane gas.

Comb Filter-Based Fiber-Optic Methane Sensor System With Mitigation of Cross Gas Sensitivity

A remote fiber-optic methane gas sensor system is proposed and demonstrated with accurate gas concentration measurement and good mitigation of cross gas sensitivity. We use a polarization-maintaining photonic crystal fiber (PM-PCF)-based Sagnac loop filter to slice the spectrum of a broadband light source so as to precisely match several absorption lines of the methane gas within the near-infrared band. Meanwhile, a compact and cost-effective gas cell with multiple reflections is designed to enhance the interaction between the light beam and the methane gas to be detected, which also subsequently increase the system sensitivity. Due to the insensitive temperature dependence of the PM-PCF-based comb filter, we can obtain gas concentration measurement with a sensitivity of ~410 ppm. Moreover, by intentionally pumping the acetylene gas into the gas cell during the methane gas concentration measurement, the power variation caused by the interfering gas with 100% concentration is only equals to 0.7% of the power variation induced by the 100% concentration methane gas. Thus, effective mitigation of cross gas sensitivity is experimentally verified. The proposed fiber-optic methane gas sensor system is verified with low cost, compact size, potential capability of multipoint detection, and high sensitivity.

A One ppm NDIR Methane Gas Sensor with Single Frequency Filter Denoising Algorithm

A non-dispersive infrared (NDIR) methane gas sensor prototype has achieved a minimum detection limit of 1 parts per million by volume (ppm). The central idea of the design of the sensor is to decrease the detection limit by increasing the signal to noise ratio (SNR) of the system. In order to decrease the noise level, a single frequency filter algorithm based on fast Fourier transform (FFT) is adopted for signal processing. Through simulation and experiment, it is found that the full width at half maximum (FWHM) of the filter narrows with the extension of sampling period and the increase of lamp modulation frequency, and at some optimum sampling period and modulation frequency, the filtered signal maintains a noise to signal ratio of below 1/10,000. The sensor prototype provides the key techniques for a hand-held methane detector that has a low cost and a high resolution. Such a detector may facilitate the detection of leakage of city natural gas pipelines buried underground, the monitoring of landfill gas, the monitoring of air quality and so on.

Methane Gas Sensing Properties of the Zinc Oxide Nanowhisker-derived Gas Sensor

A low power methane gas sensor with microheater was fabricated by silicon bulk micromachining technology. In order to heat up the sensing layer to operating temperature, a platinum (Pt) micro heater was embedded in the gas sensor. The line width and gap of the microheater was 20 <TEX>${\mu}m$</TEX> and 4.5 <TEX>${\mu}m$</TEX>, respectively. Zinc oxide (ZnO) nanowhisker arrays were grown on a sensor from a ZnO seed layer using a hydrothermal method. A 200 ml aqueous solution of 0.1 mol zinc nitrate hexahydrate, 0.1 mol hexamethylenetetramine, and 0.02 mol polyethylenimine was used for growing ZnO nanowhiskers. Temperature distribution of the sensor was analyzed by infrared thermal camera. The optimum temperature for highest sensitivity was found to be <TEX>$250^{\circ}C$</TEX> although relatively high (64%) sensitivity was obtained even at as low a temperature as <TEX>$150^{\circ}C$</TEX>. The power consumption was 72 mW at <TEX>$250^{\circ}C$</TEX>, and only 25 mW at <TEX>$150^{\circ}C$</TEX>.

ANFIS Modeling for Synthesis and Characterization of Cu Doped Cobalt Oxide Nanocrystals for Methane Gas Sensor

In this paper, Nano-sized copper-cobalt compound oxide powders have been prepared by sol-gel technique with different mole ratios of Cu/Co (from 0.00 to 0.15); Detection of the methane gas, the most chemically stable hydrocarbon, is done. The structural properties and morphology of powders were studied by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Transmission electron microscopy (TEM). XRD analysis confirms that Co3O4 and (CuO0.3CO0.7) Co2O4 phases have been formed and mean grain size were decreased with increasing dopant (from 28 to 24nm). According to TEM images it was found that the particles have cubic morphologies with nearly uniform distribution. Then an adaptive neuro-fuzzy inference system (ANFIS) models have been utilized for prediction of sensitivity values of the corresponded sensor. The results of ANFIS model show that the independent predicted Sensitivity values (S) compared to the measured target values have a good agreement. And also, high coefficient were found (R2 > 0.98) for the response.

Nanocomposite carbon-PDMS membranes for gas separation

Polydimethylsiloxane (PDMS) composites containing variable weight amounts of carbon black (CB) have been synthesized as membranes to evaluate the effect of CB concentration on gas selectivity and separation. The membranes were used in conjunction with a commercial semiconducting methane (CH 4) gas sensor that had a strong cross-talk with hydrogen (H 2) gas. The selectivity of the CB-PDMS composite membranes for gas separation was tested using CH 4 and H 2. It was found that at 6 wt% of CB in PDMS, the permeability of CH 4 was significantly and selectively attenuated through the composite membrane. This work demonstrates that CB is an effective additive for tuning H 2/CH 4 gas selectivity of the composite membranes. The selectivity is attributed to a chemical transition occurring with increasing CB doping, which was observed by vibrational spectroscopy measurements.

Study on a Methane and Acetylene Spectrum Absorption Mode Gas Sensor with Optical Fiber

The gas monitor with optical fiber is developed in this paper based on the principle that the absorption light changes with gas intensity under absorptive peak wavelength. The LED of driving light source is selected by the absorptive peak wavelength of measured gas. The light source driving circuit with the different frequency is used to detect the varied gas in real time. The techniques of phase-sensitive detected and ratio between measured signal and reference signal is used to ensure measurement accuracy. The examination system chooses low loss 50cm-long quartz optical fiber as long distance transmitting channel. The light source adopts low power pulse modulation semiconductor LED. 50cm-long absorption gas room is used to ensure measurement sensitivity. The system adopts the technique to carry out scheme combining optical fiber sensing technique with computer data handling technique. Uniting sensing light signal and stimulating light power transfer and measured parameter sensing, the advantages of optical fiber system, micro-electron electric circuit and computer compatibility can be sufficiently realized. The entire measurement system can attain light, the engine and electricity integration, and realize multi-parameter and multi-function. The experiment result of methane and acetylene intensity indicates that the system has higher detected sensitivity and detected accuracy. The system is not only used to detect the methane and acetylene intensity, but also to detect other gas intensity under a little structure parameter change.

Spectrum Absorption Methane Gas Sensor with Optical Fiber Based on Frequency Harmonic Detection Mechanism

Methane is an easily burning and exploding gas. It is the primary component of many gas fuels such as mine gas and natural gas and so on. In the coal mine accidences of our country, the casualties caused by gas explosion covers over 50% in all great casualties, and it becomes the largest obstruction of safe production. Incident online detecting methane gas density has important significance for mine and plant safe production and personal safety. Based on the near infrared spectral absorption of methane, a system using absorption type optical fiber for high sensitivity methane detection is demonstrated in this paper. DFB LD is adopted as light source in this paper. Modulating the light source, methane gas is detected by second harmonic. The ratio of the fundamental and second harmonic signal can be used for eliminating the interference owing to light power changing. The mathematical model of gas concentration harmonic measurement is built up. The result of methane concentration is also shown. The system overcomes the defect of great interference of available instruments by light route. It has advantages such as high sensitivity, quick response speed, large dynamic range, preventing electromagnetic interference, preventing burning and explosion, not easily being poisoned and so on. The probe can be put in condition of easily burning and exploding, being poisonous being high temperature and so on that man and instrument can not easily enter. It can realize online continuous telecontrol and telemeter.

비분산 적외선 가스센서의 온도보상 알고리즘

본 논문에서는 써모파일을 사용한 비분산 적외선 메탄가스센서의 온도보상 알고리즘을 제시하였다. 가스측정을 위해 적외선 감지부에 내장된 써미스터의 출력전압과 분위기 온도와의 상관성을 도출하고, 협 대역통과 필터 특성과 온도 변화에 따른 센서모듈(광 공동과 적외선램프)의 출력전압 특성 및 메탄가스의 흡수계수와 광 경로에 따른 출력특성 해석을 통하여 가스센서 모듈의 온도보상 알고리즘을 도출하였다.온도보상 전 약 <TEX>$\pm$</TEX> 1,500 ppm 이상의 오차를 갖는 센서는 온도보상 알고리즘을 적용함으로써 <TEX>$20^{\circ}C$</TEX>온도변화 구간에서 최대 약 180 ppm 이하의 정밀한 센서모듈을 제작하였다. This paper describes the temperature compensation algorithm using thermopile detector for nondispersive infrared methane gas sensor. From the output voltage of thermistor that is attached onto the infrared detector, the ambient temperature was extracted. The effects of temperatures on the properties of sensor module (the characteristics of narrow bandpass filter, optical cavity and infrared lamp, and gas absorption coefficient times optical path length) have been introduced in order to implement the temperature compensation algorithm. Even though the measurement error of developed sensor module was in the range of <TEX>$\pm$</TEX> 1,500 ppm, after programming the temperature compensation algorithm, the developed sensor module shows a high accuracy less than +180 ppm error within <TEX>$20^{\circ}C$</TEX> temperature variation.

Synthesis and characterization of Cu doped cobalt oxide nanocrystals as methane gas sensors

In this paper, nanoparticles of copper–cobalt compound oxide have been prepared by the sol–gel technique with different mole ratios of Cu/Co (ranging from 0.05 to 0.15) for the detection of methane gas, which is chemically a very stable hydrocarbon. The structural properties and morphology of the powders were studied by x-ray diffraction (XRD), Fourier transform infrared spectroscopy and transmission electron microscopy (TEM). By XRD analysis, we confirm that Co3O4 and (CuO0.3CoO0.7) Co2O4 phases are formed and mean grain size is decreased with increasing Cu doping (from 28 to 24 nm). On the basis of TEM images, it is found that these particles possess a cubic structure with nearly uniform distribution. Also, gas-sensing measurements reveal that the optimal operating temperature is 300 °C, that the use of Cu as a dopant improved the sensing properties of cobalt oxide and that the sensitivity increased considerably with Cu concentration. The best sensitivity properties of nanosensors have been found at the mole ratios of Cu/Co of 0.125 and 0.15.

光学式低浓度甲烷气体传感器的研究

To the methane gas with the concentration lower than 0.5%VOL,an optical methane gas sensor was designed based on near infrared tunable diode laser absorption spectroscopy.The methane gas absorption spectroscopy of 1 653.72 nm was scanned by tunable laser,and the gas concentration was measured by using the first harmonic PAPR.The proposed can effectively eliminate the influences caused by light intensity fluctuation of the laser and other kindred light power fluctuations,and the test results show that the precision of this kind of sensor can be 0.02%VOL.

Improving the Performance of Catalytic Combustion Type Methane Gas Sensors Using Nanostructure Elements Doped with Rare Earth Cocatalysts

Conventional methane gas sensors based on catalytic combustion have the drawbacks of high working temperature, low thermal stability and small measurement range. To improve their performance, cerium, which possesses high oxygen storage and release ability, was introduced via nanotechnology to prepare Ce-contained nanostructure elements. Three kinds of elements with different carriers: Al2O3, n-Al2O3 and n-Ce-Al2O3 were prepared and separately fabricated (Pt-Pd/Al, Pt-Pd/n-Al, Pt-Pd/n-Ce-Al). The performances of Wheatstone Bridges with three different catalytic elements were tested and compared. The results indicated that the cerium-containing element exhibited better performance than other elements regarding activity, anti-sulfur ability and thermal stability. Moreover, a constant temperature circuit was also applied in this system. The measurement range was extended from 4% to 10% by automatically decreasing the working current in a reasonable range. The maximum error for 0%–10% CH4 was controlled below 5%, which fully meets the measurement requirements.

Design of a methane monitoring system based on wireless sensor networks

Wireless sensor prototypes have varying hardware architectures and distinctive sensing principles. In this study, a prototype is developed for the purpose of monitoring leaks of methane (CH4), which has explosive properties and is the main constituent of the natural gas, in the refineries or buildings and work places heating. The prototype can be mounted on the walls as well as it is portable. System is composed of the integration of methane gas sensor module NGM2611 to MicaZ mote. The sensor module is pre-calibrated and is a product of FIGARO firm. The MICAz is a 2.4 GHz, IEEE/ZigBee 802.15.4; board used for low-power, wireless and sensor networks. By means of the designed sensor prototypes, wireless sensor networks are established indoors; hence, methane gas leaks are detected and sent to the base stations. Data received by base station is monitored by the software on a computer connected to the base station. This study explains the system structure, parts of hardware and software design in detail. The aim of the system is to implement a wireless methane gas platform. This platform can be used to real time monitoring of the methane leaks which would be crucial for critical conditions and helpful to decrease risk of death due to those leaks. Key words: Wireless sensor network, methane sensing system.