基于非分散红外法的二氧化碳浓度检测综述

二氧化碳(CO₂)是温室气体的重要组分之一,实时检测其浓度变化对缓解温室效应等方面具有非常重要的意义。非分散红外(Non-dispersion infrared, NDIR)法具有稳定性好、响应速度快、测量范围宽等优点,广泛应用于便携式气体检测等领域。首先分析了NDIR法应用在CO₂检测领域的优点,并对NDIR检测原理进行了简单的概述。然后对NDIR气体分析仪的基本结构进行了详细阐述,并对测量系统的经典气体标定方法进行了综述。最后综合分析了NDIR的特点,并展望了未来的发展趋势。     

An optic fiber sensor for multiple gases based on fiber loop ring-down spectroscopy and microring resonator arrays

A high-sensitivity sensor for multiple gases based on microring array filter and fiber loop ring-down spectroscopy system is proposed and demonstrated. The parameters of the resonators are designed so that the filtered signal from a broadband light source can be tuned with an absorption spectral line of gas. Therefore, through adding microring resonators horizontally and vertically, the number of target gases and filter range are increased. In this research, in the broad spectral range of about 0.9 μm, only the absorption spectral lines of target gases are filtered. The simulation results show that three target gases, CH₄, CO₂ and HF, can be simultaneously detected by the sensing system. Owing to the fiber loop ring-down spectroscopy, the whole system is optimized in mini-size and sensitivity, and we can choose different sensing methods to enhance the measurement accuracy for high and low concentration conditions.     

Room-Temperature Hydrogen Sensor with High Sensitivity and Selectivity using Chemically Immobilized Monolayer Single-Walled Carbon Nanotubes

Although semiconducting single-walled carbon nanotubes (sc-SWNTs) exhibit excellent sensing properties for various gases, commercialization is hampered by several obstacles. Among these, the difficulty in reproducibly fabricating sc-SWNT films with uniform density and thickness is the main one. Here, a facile fabrication method for sc-SWNT-based hydrogen (H₂) sensors with excellent reproducibility, high sensitivity, and selectivity against CO, CO₂, and CH₄ is reported. Uniform-density and monolayer sc-SWNT films are fabricated using chemical immobilized through the click reaction between azide-functionalized polymer-wrapped sc-SWNTs and immobilized alkyne polymer on a substrate before decorating with Pd nanoparticles (0.5–3.0 nm). The optimized sc-SWNT sensor has a high room-temperature response of 285 with the response and recovery times of 10 and 3 s, respectively, under 1% H₂ gas in air. In particular, this sensor demonstrates highly selective H₂ detection at room temperature (25 °C), compared to other gases and humidity. Therefore, the chemical immobilization of the monolayer SWNT films with reproducible and uniform density has the potential for large-scale fabrication of robust room-temperature H₂ sensors.     

HgCdTe molecular beam epitaxy material for microcavity light emitters: Application to gas detection in the 2–6 µm range

Most pollution gases, CO, CO₂, NO_x, SO₂, CH₄ …, have fundamental optical absorption in the near infrared range. We report here on microcavity light sources emitting at room temperature between 2 and 6 μm integrated in a gas detection system. HgCdTe has been chosen for this application, among several semiconductor materials. Molecular beam epitaxy (MBE) is very well adapted to grow the suitable HgCdTe heterostructure. The quality of involved HgCdTe layers has to be optimized in order to have a good photoluminescence response at 300 K. For this study, we used the knowledge we acquired in the field of MBE HgCdTe growth for infrared focal plane arrays (IRFPAs). Especially, we took advantage of the substrate preparation before growing and the flux control. We show subsequently several characterization results concerning our material quality. The compact emitting system is formed by this microcavity structure coupled to a 0.8-μm external pumping source. The Fabry-Perot type microcavity is obtained by using two evaporated YF₃/ZnS dielectric multilayered Bragg mirrors. We developed several devices exhibiting emission wavelengths at 3.3 μm, 4.26 μm, and 4.7 μm for CH₄, CO₂, and CO gas measurements, respectively, and 3.7 μm for the reference beam. We measured less than 200 ppm CH₄ in a 1 bar mixed gas along a 10-cm-long cell.     

Terahertz Frequency-Domain Spectroscopy of Low-Pressure Acetonitrile Gas by a Photomixing Terahertz Synthesizer Referenced to Dual Optical Frequency Combs

A terahertz (THz) frequency synthesizer based on photomixing of two near-infrared lasers with a sub-THz to THz frequency offset is a powerful tool for spectroscopy of polar gas molecules due to its broad spectral coverage; however, its frequency accuracy and resolution are relatively low. To tune the output frequency continuously and widely while maintaining its traceability to a frequency standard, we developed a photomixing THz synthesizer phase-locked to dual optical frequency combs (OFCs). While the phase-locking to dual OFCs ensured continuous tuning within a spectral range of 120 GHz, in addition to the traceability to the frequency standard, use of a broadband uni-traveling carrier photodiode for photomixing enabled the generation of CW-THz radiation within a frequency range from 0.2 to 1.5 THz. We demonstrated THz frequency-domain spectroscopy of gas-phase acetonitrile CH₃CN and its isotope CH₃ ¹³CN in the frequency range of 0.600–0.720 THz using this THz synthesizer. Their rotational transitions were assigned with a frequency accuracy of 8.42?×?10^?8 and a frequency resolution of 520 kHz. Furthermore, the concentration of the CH₃CN gas at 20 Pa was determined to be (5.41?±?0.05)?×?10¹⁴ molecules/cm³ by curve fitting analysis of the measured absorbance spectrum, and the mixture ratio of the mixed CH₃CN/CH₃ ¹³CN gas was determined to be 1:2.26 with a gas concentration of 10¹⁴–10¹⁵ molecules/cm³. The developed THz synthesizer is highly promising for high-precision THz-FDS of low-pressure molecular gases and will enable the qualitative and quantitative analyses of multiple gases.     

Enhanced ammonia sensing characteristics of tungsten oxide decorated polyaniline hybrid nanocomposites

Polyaniline (PAni)-tungsten oxide (WO₃) hybrid nanocomposites sensor have been lucratively synthesized by in-situ chemical oxidative polymerization method by entrapping tungsten oxide nanoparticles (10–50%) in the polyaniline matrix on precleaned glass substrate. The structural, morphological and surface composition elucidation of PAni-WO₃ hybrid nanocomposites were explored by X-ray diffraction (XRD) technique, field emission scanning electron microscopy (FESEM) and X-ray photoelectron spectroscopy (XPS). The existence of WO₃ in PAni matrix and interaction between them was confirmed using XRD and Raman spectroscopy. The incorporation of WO₃ nanoparticles into the PAni matrix introduces porosity which enhanced gas sensing properties. The TEM image of PAni-WO₃ hybrid nanocomposite film exploded the average diameter of WO₃ nanoparticles ranging from 40 to 50 nm. Chemical composition of PAni-WO₃ hybrid nanocomposites was characterized by using X-ray photoelectron spectroscopy (XPS). In order to investigate the gas sensing parameter of PAni-WO₃ hybrid nanocomposite, hybrid nanocomposite film was exposed to different oxidizing gases (Cl₂, NO₂) and reducing gases (NH₃, H₂S, CH₃OH, C₂H₅OH) in range 5–100 ppm concentration of gas. It was observed that the sensors of PAni-WO₃ hybrid nanocomposites showed better sensitivity, selectivity, stability and reproducibility compared to pure PAni and pure WO₃. PAni-WO₃ (50%) hybrid nanocomposite sensor operating at room temperature reveals maximum response of 158% towards 100 ppm of NH₃ gas and also capable to respond very little concentration of 5 ppm NH₃ gas with reasonable response of 24%. The gas sensing mechanism of the nanocomposites in presence of air and with target NH₃ gas atmosphere was discussed in detail with the help of energy band diagram. The interaction of NH₃ and NO₂ gas with PAni-WO₃ hybrid nanocomposite sensor was investigated by employing an impedance spectroscopy also.     

Highly CO2 Selective Metal–Organic Framework Membranes with Favorable Coulombic Effect

The topology and chemical functionality of metal–organic frameworks (MOFs) make them promising candidates for membrane gas separation; however, few meet the criteria for industrial applications, that is, selectivity of >30 for CO₂/CH₄ and CO₂/N₂. This paper reports on a dense CAU-10-H MOF membrane that is exceptionally CO₂-selective (ideal selectivity of 42 for CO₂/N₂ and 95 for CO₂/CH₄). The proposed membrane also achieves the highest CO₂ permeability (approximately 500 Barrer) among existing pure MOF membranes with CO₂/CH₄ selectivity exceeding 30. State-of-the-art atomistic simulations provide valuable insights into the outstanding separation performance of CAU-10-H at the molecular level. Adsorbent–adsorbate Coulombic interactions are identified as a crucial factor in the design of CO₂-selective MOF membranes.     

Photocatalytic Coupling of CH4 and CO2 to Ethanol on Asymmetric Ce−O−Zn Sites

Partial oxidation of methane (CH₄) to value-added products is significantly challenging due to the highly inert chemical property of CH₄ at ambient conditions and easy over-oxidation into carbon dioxide (CO₂) or carbon monoxide (CO) at elevated temperatures and pressures. Targeting this challenge, the efficient photocatalytic coupling of CO₂ and CH₄ into ethanol is demonstrated, using a cerium (Ce)-doped zinc oxide (ZnO) photocatalyst with abundant Ce─O─Zn units. Under light illumination, CO₂ is adsorbed on the Ce atoms and photo-reduced to CO, and CH₄ is captured by the Zn atoms and photo-oxidized to hydroperoxymethane (CH₃OOH). The close proximity of Ce and Zn atoms on the Ce─O─Zn units allowed to further efficiently couple the as-formed CO and CH₃OOH into ethanol. Without additional Oxygen (O₂) oxidant or sacrificial regent, the ethanol production rate reached 580 µmol g⁻¹ h⁻¹, substantially exceeding previously reports on photocatalytic CH₄ oxidation. This work features to convert two greenhouse gases into value-added chemicals with adjacent and asymmetric reaction sites, suggesting attractive potentials for CH₄ and CO₂ utilization.     

Electrophoretic Nuclei Assembly for Crystallization of High‐Performance Membranes on Unmodified Supports

Metal–organic framework (MOF) films have recently emerged as highly permselective membranes yielding orders of magnitude higher gas permeance than that from the conventional membranes. However, synthesis of highly intergrown, ultrathin MOF films on porous supports without complex support‐modification has proven to be a challenge. Moreover, there is an urgent need of a generic crystallization route capable of synthesizing a wide range of MOF structures in an intergrown, thin‐film morphology. Herein, a novel electrophoretic nuclei assembly for crystallization of highly intergrown thin‐films (ENACT) approach, that allows synthesis of ultrathin, defect‐free ZIF‐8 on a wide range of unmodified supports (porous polyacrylonitrile, anodized aluminum oxide, metal foil, porous carbon and graphene), is reported. As a result, a remarkably high H₂ permeance of 8.3 × 10^?6 mol m^?2 s^?1 Pa^?1 and ideal gas selectivities of 7.3, 15.5, 16.2, and 2655 for H₂/CO₂, H₂/N₂, H₂/CH₄, and H₂/C₃H₈, respectively, are achieved from an ultrathin (500 nm thick) ZIF‐8 membrane. A high C₃H₆ permeance of 9.9 × 10^?8 mol m^?2 s^?1 Pa^?1 and an attractive C₃H₆/C₃H₈ selectivity of 31.6 are obtained. The ENACT approach is straightforward, reproducible and can be extended to a wide range of nanoporous crystals, and its application in the fabrication of intergrown ZIF‐7 films is demonstrated.     

Repeatability of indium oxide gas sensors for detecting methane at low temperature

A simple method for fabricating methane gas sensor of indium oxide (In₂O₃) transparent film was presented. Indium of 3 mg as a raw material was used to direct deposition of In₂O₃ film through a simplified thermal evaporation method. X-ray diffraction confirmed the cubic polycrystalline structure of the as prepared In₂O₃ film. The transmittance (T) of the film was recorded as high as 96%. The optical band gap (E_g) of the deposited film was found of 3.68 eV. The sensing properties of In₂O₃ film toward methane gas (CH₄) were investigated at various operating temperatures and various gas concentrations. The prepared film highly detected CH₄ gas at concentrations much lower than the explosive limit. Good performance (sensor response and stability) of the film for CH₄ gas was exhibited. The film exhibited a good repeatability with repeating the gas sensing measurements towards CH₄.     

Study of sensitivity and selectivity of α-Fe2O3 thin films for different toxic gases and alcohols

This paper presents a detailed study on the sensitivity and selectivity of α-Fe₂O₃ thin films produced by deposition of Fe and post-deposition annealed at two temperatures of 600 °C and 800 °C with flow of oxygen for application as a sensor for toxic gases including CO, H₂S, NH₃ and NO₂ and alcohols such as C₃H₇OH, CH₃OH, and C₂H₅OH. The crystallographic structure of the samples was studied by X-ray diffraction (XRD) method while an atomic force microscope (AFM) was employed for surface morphology investigation. The electrical response of the films was measured while they were exposed to various toxic gases and alcohols in the temperature range of 50–300 °C. The sample annealed at higher temperature showed higher response for different gases and alcohols tested in this work which can be due to the higher resistance of this sample. Results also indicated that the α-Fe₂O₃ thin films show higher selectivity to NO₂ gas relative to the other gases and alcohols while the best sensitivity is obtained at 200 °C. The α-Fe₂O₃ thin film post-deposition annealed at 800 °C also showed a good stability and reproducibility and a detection limit of 10 ppm for NO₂ gas at the operating temperature of 200 °C.     

非分光红外气体传感器研究进展

介绍了非分光红外气体传感器的工作原理,将非分光红外传感器与常用气体传感器进行了对比分析。综述了非分光红外技术在光源设计、气室设计、探测器设计、信号处理及自组装多气体探测系统等关键技术的研究进展,为进一步提高气体检测精度和响应提供了研究方向。提出了非分光红外气体传感器要朝着小体积、多功能集成、满足复杂应用环境的方向发展。     

Highly efficient Ceramic-SWCNT based free standing films for gas sensing application

This paper presents a method of preparation of ceramic-carbon nanotube nanocomposite films using a gel-cast technique to improve the sensitivity of the carbon nanotubes based gas sensor for toxic gases (NH₃, NO₂) to a sub-ppm levels. A detailed study is presented on nanocompostite synthesis, sensing mechanism and performance of free standing nanocomposites film. The method is simple, low cost, environment friendly and allows batch fabrication process. The film was prepared by a motor driven machine fitted with doctor׳s blade where single wall carbon nanotube(SWCNT) powder dispersed in sol–gel based alumina solution was poured and rolled out on Mylar tape at specific speed to have control on film thickness. Electron microscopy, Energy-dispersive X-ray and Raman Spectroscopy were used to characterize the morphology and composition of prepared material. The proposed free standing nanocomposite film shows excellent and stable sensitivity to NH₃ and NO₂ molecules are 15% and 32% for 1 ppm respectively     

Sol–gel synthesized Titania nanoparticles deposited on porous polycrystalline silicon: Improved carbon dioxide sensor properties

Titania nanoparticles (TNPs) were synthesized by a sol–gel method in our laboratory using titanium tetrachloride as the precursor and isopropanol as the solvent. The particles׳ size distribution histogram was determined using ImageJ software and the size of TNPs was obtained in the range of 7.5–10.5 nm. The nanoparticle with the average size of 8.5 nm was calculated using Scherrer׳s formula. Homogeneous and spherical nanoparticles were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM) and UV–visible spectroscopy (UV–vis). The X-ray powder diffraction analysis showed that the prepared sample (TNPs) has pure anatase phase. TNPs were deposited on porous polycrystalline silicon (PPS) substrate by electron beam evaporation. The TNPs thickness was 23±2 nm at 10⁻⁵ mbar pressure at room temperature. Porosity was performed by an anodization method. Since polycrystalline silicon wafers consist of different grains with different orientations, the pore size distribution in porous layer is non-uniform [1]. Therefore, the average diameter of pores can be reported in PPS layer analysis. Average diameter of pores was estimated in the range of 5 μm which was characterized by FESEM. The nanostructured thin films devices (Al/Si/PPS/TNPs/Al and Al/Si/PPS/Al) were fabricated in the sandwich form by aluminum (Al) electrodes which were also deposited by electron beam evaporation. Electrical measurements (I–V curves) demonstrated the semiconducting behavior of thin film devices. The gas sensitivity was studied on exposure to 10% CO₂ gas. As a result, conductivity of devices increased on exposure to CO₂ gas. The device with TNPs thin film (Al/Si/PPS/TNPs/Al) was more sensitive and, had better response and reversibility in comparison with the device without TNPs thin film (Al/Si/PPS/Al).     

High‐Performance CO2 Capture through Polymer‐Based Ultrathin Membranes

Thin film composite (TFC) membranes have attracted great research interest for a wide range of separation processes owing to their potential to achieve excellent permeance. However, it still remains challenging to fully exploit the superiority of thin selective layers when mitigating the pore intrusion phenomenon. Herein, a facile and generic interface‐decoration‐layer strategy collaborating with molecular‐scale organic–inorganic hybridization in the selective layer to obtain a high‐performance ultrathin film composite (UTFC) membrane for CO₂ capture is reported. The interface‐decoration layer of copper hydroxide nanofibers (CHNs) enables the formation of an ultrathin selective layer (≈100 nm), achieving a 2.5‐fold increase in gas permeance. The organic part in the molecular‐scale hybrid material contributes to facilitating CO₂‐selective adsorption while the inorganic part assists in maintaining robust membrane structure, thus remarkably improving the selectivity toward CO₂. As a result, the as‐prepared membrane shows a high CO₂ permeance of 2860 GPU, superior to state‐of‐the‐art polymer membranes, with a CO₂/N₂ selectivity of 28.2. The synergistic strategy proposed here can be extended to a wide range of polymers, holding great potential to produce high‐efficiency ultrathin membranes for molecular separation.     

New CW FIR laser lines obtained in ammonia pumped by a CO2 laser,using the Stark tuning method

We report fifty seven CW FIR emissions observed in NH₃, by resonant pumping with a CO₂ laser. Exact coincidences between IR absorption lines of the gas and emission lines of the CO₂ laser have been carried out by Stark tuning. IR frequency shifts, up to 30 GHz, have allowed the pumping of forty three NH₃ transitions. These FIR emissions correspond to thirty one different wavelengths in the 50–400 μm range; eighteen ones of them are new emitted wavelengths by pumping with the CO₂ laser.     

An optically-pumped multigas Far-IR laser

We report here the operation of an optically-pumped multigas Far-IR laser. In our experiment, three different gases (CH₃OH, CH₃Br, CH₃I) were simultaneously introduced into the Far-IR cavity. By adjusting the partial pressures of the gases and by tuning the appropriate CO₂ laser pump line, we were able to obtain the laser action for each one of them as efficiently as is observed when the gases are present by themselves.     

Development of highly conducting n-type micro-crystalline silicon oxide thin film and its application in high efficiency amorphous silicon solar cell

Wide band gap and highly conducting n-type nano-crystalline silicon film can have multiple roles in thin film solar cell. We prepared phosphorus doped micro-crystalline silicon oxide films (n-μc-SiO:H) of varying crystalline volume fraction (X_c) and applied some of the selected films in device fabrication, so that it plays the roles of n-layer and back reflector in p-i-n type solar cells. It is generally understood that a higher hydrogen dilution is needed to prepare micro-crystalline silicon, but in case of the n-μc-SiO:H an optimized hydrogen dilution was found suitable for higher X_c. Observed X_c of these films mostly decreased with increased plasma power (for pressure<2.0 Torr), increased gas pressure, flow rate of oxygen source gas and flow rates of PH₃>0.08 sccm. In order to determine deposition conditions for optimized opto-electronic and structural characteristics of the n-μc-SiO:H film, the gas flow rates, plasma power, deposition pressure and substrate temperature were varied. In these films, the X_c, dark conductivity (σ_d) and activation energy (E_a) remained within the range of 0–50%, 3.5×10⁻¹⁰ S/cm to 9.1 S/cm and 0.71 eV to 0.02 eV, respectively. Low power (30 W) and optimized flow rates of H₂ (500 sccm), CO₂ (5 sccm), PH₃ (0.08 sccm) showed the best properties of the n-μc-SiO:H layers and an improved performance of a solar cell. The photovoltaic parameters of one of the cells were as follows, open circuit voltage (V_oc), short circuit current density (J_sc), fill-factor (FF), and photovoltaic conversion efficiency (η) were 950 mV, 15 mA/cm², 64.5% and 9.2% respectively.     

Life‐cycle greenhouse gas effects of introducing nano‐crystalline materials in thin‐film silicon solar cells

Solar PV is widely considered as a “green” technology. This paper, however, investigates the environmental impact of the production of solar modules made from thin‐film silicon. We focus on novel applications of nano‐crystalline Silicon materials (nc‐Si) into current amorphous Silicon (a‐Si) devices. Two nc‐Si specific details concerning the environmental performance can be identified, when we want to compare to a‐Si modules. First, in how far the extra (and thicker) silicon layer (s) affects upstream material requirements and energy use. Second, in how far depositing an extra silicon layer may increase emissions of greenhouse gases as additional emissions of Fluor gases (F‐gases) are associated to this step. The much larger global warming potential of F‐gases (17 200–22 800 times that of CO₂) may lead to higher environmental burdens. To date, no study has yet analyzed the effect of F‐gas usage on the environmental profile of thin‐film silicon solar modules. We performed a life‐cycle assessment (LCA) to investigate the current environmental usefulness of pursuing this novel micromorph concept. The switch to the new micromorph technology will result in a 60–85% increase in greenhouse gas emissions (per generated kWh solar electricity) in case of NF₃ based clean processing, and 15–100% when SF₆ is used. We conclude that F‐gas usage has a substantial environmental impact on both module types, in particular the micromorph one. Also, micromorph module efficiencies need to be improved from the current 8–9% (stabilized efficiency) toward 12–16% (stab. eff.) in order to compensate for the increased environmental impacts. Copyright © 2010 John Wiley & Sons, Ltd.