Infrared hollow waveguide sensors for simultaneous gas phase detection of benzene, toluene, and xylenes in field environments

Simultaneous and molecularly selective parts-per-billion detection of benzene, toluene, and xylenes (BTX) using a thermal desorption (TD)-FTIR hollow waveguide (HWG) trace gas sensor is demonstrated here for the first time combining laboratory calibration with real-world sample analysis in field. A calibration range of 100-1000 ppb analyte/N(2) was developed and applied for predicting the concentration of blinded environmental air samples within the same concentration range, and demonstrate close agreement with the validation method used here, GC-FID. The analyte concentration prediction capability of the TD-FTIR-HWG trace gas sensor also compares well with the industrial standard and other experimental techniques including GC-PID, ultrafast GC-FID, and GC-DMS, which were simultaneously operated in the field. With the advent of a quantum cascade laser with emission frequencies specifically tailored to efficiently overlap benzene absorption as the most relevant analyte, the overall sensor footprint could be considerably reduced to ultimately yield hand-held trace gas sensors facilitating direct and real-time detection of BTX in air down to low ppb levels.     

Real-time monitoring of benzene, toluene, and p-xylene in a photoreaction chamber with a tunable mid-infrared laser and ultraviolet differential optical absorption spectroscopy

We describe the implementation of a mid-infrared laser-based trace gas sensor with a photoreaction chamber, used for reproducing chemical transformations of benzene, toluene, and p-xylene (BTX) gases that may occur in the atmosphere. The system performance was assessed in the presence of photoreaction products including aerosol particles. A mid-infrared external cavity quantum cascade laser (EC-QCL)-tunable from 9.41-9.88?μm (1012-1063?cm(-1))-was used to monitor gas phase concentrations of BTX simultaneously and in real time during chemical processing of these compounds with hydroxyl radicals in a photoreaction chamber. Results are compared to concurrent measurements using ultraviolet differential optical absorption spectroscopy (UV DOAS). The EC-QCL based system provides quantitation limits of approximately 200, 200, and 600 parts in 10(9) (ppb) for benzene, toluene, and p-xylene, respectively, which represents a significant improvement over our previous work with this laser system. Correspondingly, we observe the best agreement between the EC-QCL measurements and the UV DOAS measurements with benzene, followed by toluene, then p-xylene. Although BTX gas-detection limits are not as low for the EC-QCL system as for UV DOAS, an unidentified by-product of the photoreactions was observed with the EC-QCL, but not with the UV DOAS system.     

Thermal desorption solid-phase microextraction inlet for differential mobility spectrometry

A splitless thermal desorber unit that interfaces a differential mobility spectrometry (DMS) sensor has been devised. This device was characterized by the detection of benzene, toluene, and xylene (BTX) in water. The detection of BTX in water is important for environmental monitoring, and ion mobility measurements are traditionally difficult for hydrocarbons in water because water competes for charge and quenches the hydrocarbon signals. This paper reports the use of a DMS with a photoionization source that is directly coupled to a solid-phase microextraction (SPME) desorber. The separation and detection capabilities of the DMS were demonstrated using BTX components. Detection limits for benzene, toluene, and m-xylene were 75, 50, and 5 microg mL(-1), respectively.     

Highly sensitive optical waveguide sensor for SO2 and H2S detection in the parts-per-trillion regime using tetraaminophenyl porphyrin

ABSTRACT

Optical waveguide (OWG) sensors present great potential for detecting trace levels of harmful gases because of their high sensitivity and anti-electromagnetic interference. However, OWG-based SO2 and H2S-detecting sensors in the parts-per-trillion (ppt) range are still lacking. We fabricated 5,10,15,20-(tetra-4-aminophenyl) porphyrin (TAPP) thin film-based OWG sensor devices (TAPP-OWG) to detect SO2 and H2S gases, in which TAPP thin film was immobilized over the surface of a potassium ion exchange glass OWG. These sensors successfully measure extremely low concentrations of SO2 and H2S (detection limit?=?1 ppt), providing good repeatability for SO2 (10 ppt) and H2S (10 ppt) gases, with relative standard deviations of 1.67% and 3.68%, respectively. With fast response (t1) and recovery (t2) times for SO2 (t1=4 s, t2=157 s) and H2S (t1=2 s, t2=117 s) at room temperature, TAPP thin film enhances the potential of OWGs for use in high-sensitivity trace-level gas detection.     

甲苯传感器的制作及特性

采用溶胶-凝胶法制备了NASICON(钠超离子导体)固体电解质材料.利用XRD分析了所制备材料的结构,材料的平均粒径约为22nm.以NASICON为离子导电层,Sm_2O_3为敏感电极制作了具有良好敏感特性的C_7H_8气体传感器.在430℃工作温度下,器件对(5-50)×10~(-6)C_7H_8的灵敏度为-75mV/decade.并且对C_7H_8具有较高的选择性和良好的响应恢复特性,器件对5 × 10~(-6)和50×10~(-6)C_7H_8的响应时间分别为45和35秒,恢复时间分别为8和60秒.对器件的敏感机理做以简要的分析.     

A hybrid humidity sensor using optical waveguides on a quartz crystal microbalance

In this study, slab and ridge optical waveguides (OWGs) made of fluorinated polyimides were deposited on a quartz crystal microbalance (QCM), and hybrid sensors using OWG spectroscopy and the QCM technique were prepared. Polyvinyl alcohol (PVA) film with CoCl₂ was deposited on the OWGs, and the characteristics of humidity sensing were investigated. A prism coupler was used to enter a He–Ne laser beam (λ = 632.8 nm) to the slab OWG. The output light intensity markedly changed due to chromism of the CoCl₂ as a result of humidity sorption, and this change was dependent on the incident angle of the laser beam to the slab OWG. During the measurement of output light, the QCM frequency was simultaneously monitored. The humidity dependence of the sensor with the slab OWG was also investigated in the range from 15 to 85%. For the sensor with the ridge OWG, white light was entered by butt-coupling, and the characteristics of humidity sensing were investigated by observing the output light spectrum and the QCM frequency.     

Screening and optimization of the factors of a detergent admixture preparation

The present research studies the optimization of the preparation of a hydrotrope (mixture of sodium toluenesulfonate and sodium xylenesulfonates) for liquid detergents using experimental designs. The preparation is carried out by selective sulfonation of toluene and xylene present in the BTX fraction of a natural gas. The optimization of five responses has been carried out in two steps. First, we carry out an asymmetrical screening design 2¹3⁶//18 to select from seven factors, those factors which have significant influence on the amount of residual sodium sulfate in the product and on the total conversion of toluene and xylenes. Secondly, we carry out a Box–Behnken design to optimize three retained factors (temperature, molar ratio of acid to toluene plus xylenes, and the amount of desulfation agent), using response surface methodology. In addition, and in order to reach near-optimal sulfonation conditions, we use the desirability functions to optimize the five responses simultaneously. This allows us to determine for the whole process, sulfonation conditions leading to a high yield of toluene and xylene conversion and acceptable amounts of residual sodium sulfates and sodium benzenesulfonate.     

Preparation of SnO2 nanowires by solvent-free method using mesoporous silica template and their gas sensitive properties

In this paper, a facile method was presented to synthesize tin dioxide (SnO2) nanowires by solvent-free method using SnCl2 x 2H2O as precursor and mesoporous silica SBA-15 as the hard template. No solvent was used in the processing. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and N2 adsorption/desorption isotherms. The results indicated that SnO2 nanowires fabricated by this method have a diameter of about 8 nm and a relatively high surface area 73.0 m2/g. The gas sensing properties of SnO2 nanowires were measured. The response and recovery time of this sensor were 6 s and 12 s, respectively. With the concentration of toluene increasing, the response of the sensor doubled increase. Compared with bulk SnO2, SnO2 nanowires showed much higher response to toluene.     

Air monitoring of a coal tar cleanup using a mobile TAGA LPCI-MS/MS

Real-time detection of air toxics is becoming increasingly important in understanding the sources and constituents of air pollution. The detection of low levels of air contaminants requires reliable sampling and calibration techniques, as well as sophisticated analytical instrumentation. Recently, a new low pressure chemical ionization (LPCI) source was developed for ambient air monitoring of benzene, toluene, xylene (BTX) and gas-phase polycyclic aromatic hydrocarbons (PAH) in real-time. This ion source in conjunction with a triple quadrupole (Q1, Q2, Q3) mass spectrometer (trace atmospheric gas analyzer (TAGA IIe)) has been proven highly useful for measuring selected air pollutants. The ion chemistry under LPCI conditions involves charge transfer reactions yielding parent ions which are selected in the first quadrupole, Q1, dissociated in the second quadrupole, Q2, and the resultant daughter ions are then identified by the third quadrupole, Q3. Monitoring of specific parent/daughter (P/D) ion pairs is used to measure concentrations of BTX and selected PAH. The response of the TAGA IIe is characterized through multi-point calibration curves. Detection limits (DL) as low as 0.5 microg/m(3) for BTX and PAH were accomplished by optimizing various TAGA IIe operating parameters. This unique method was applied in November 1999 to monitor emissions released during the cleanup of a historical coal tar site in Kingston, Ontario. This information was used by local officials for enhancing abatement activities or in some cases temporarily halting the excavation when levels of air toxics were higher than allowable provincial guidelines.     

Transient signal analysis using complementary metal oxide semiconductor capacitive chemical microsensors

This work explores the possibility to discriminate analytes based on their nonequilibrium signals in polymer-coated capacitive chemical microsensors. The analyte uptake in the chemically sensitive polymer layers of 3-7-microm thickness has been analyzed using a diffusion model and the dynamic sensor response data. The shapes of the response profiles have been calculated analytically. Despite the simplifications in the model, the observed transient signal profiles could be described accurately. Comparison of the measured diffusion coefficients (on the order of 10(-12) m2/s) with literature values measured at similar concentration levels showed good agreement. Concentration-independent diffusion coefficients for several analyte/polymer combinations (poly(etherurethane)/all analytes; poly(epichlorohydrin)/alcohols) as well as slightly concentration-dependent diffusion coefficients (poly(epichlorohydrin)/toluene or ethyl cellulose/toluene) have been found in the investigated concentration range of tens to hundreds of pascals gas-phase partial pressure. The diffusion times of water and the first aliphatic monohydric alcohols in the polymers are strongly correlated to their molecular size. The discrimination of these substances based on dynamic sensor data of a single sensor could be demonstrated. In particular, the analysis of mixtures of analytes with similar chemical behavior (water/ethanol or methanol/ethanol) by means of analyzing the response profile of single-exposure steps or by applying a series of decreasingly long alternating target gas exposure and carrier gas exposure steps has been performed.     

Preparation of modified MWCNTs-doped PANI nanorods by oxygen plasma and their ammonia-sensing properties

Multi-wall carbon nanotubes (MWCNTs)-doped polyaniline (PANI) nanopowders were prepared by chemical oxidation polymerization. Then, the MWCNTs-doped PANI nanopowders were modified by a radio frequency (RF) oxygen plasma source. The morphology and structure of modified MWCNTs-doped PANI nanorods were analyzed by SEM and FI-IR. Gas sensors were fabricated based on plasma modified MWCNTs-doped PANI nanorods to detect ammonia at room temperature. The response amplitude of the gas sensor based on modified MWCNTs-doped PANI nanorods was much higher than those of MWCNTs-doped PANI nanopowders and pure PANI nanopowders sensors, respectively, in ammonia concentration range of 10–150 ppm. Cross responses of modified MWCNTs-doped PANI nanorods sensor to ammonia, ethanol, formaldehyde, and toluene were tested. The sensor showed good selectivity and stability. The sensing mechanism of modified MWCNTs-doped PANI nanorods gas sensor was analyzed.     

Adaptive K-NN for the detection of air pollutants with a sensor array

The field of air-quality monitoring is gaining increasing interest, with regard to both indoor environment and air-pollution control in open space. This work introduces a pattern recognition technique based on adaptive K-nn applied to a multisensor system, optimized for the recognition of some relevant tracers for air pollution in outdoor environment, namely benzene, toluene, and xylene (BTX), NO/sub 2/, and CO. The pattern-recognition technique employed aims at recognizing the target gases within an air sample of unknown composition and at estimating their concentrations. It is based on PCA and K-nn classification with an adaptive vote technique based on the gas concentrations of the training samples associated to the K-neighbors. The system is tested in a controlled environment composed of synthetic air with a fixed humidity rate (30%) at concentrations in the ppm range for BTX and NO/sub 2/, in the range of 10 ppm for CO. The pattern recognition technique is experimented on a knowledge base composed of a limited number of samples (130), with the adoption of a leave-one-out procedure in order to estimate the classification probability. In these conditions, the system demonstrates the capability to recognize the presence of the target gases in controlled conditions with a high hit-rate. Moreover, the concentrations of the individual components of the test samples are successfully estimated for BTX and NO/sub 2/ in more than 80% of the considered cases, while a lower hit-rate (69%) is reached for CO.     

Performance of BTX degraders under substrate versatility conditions

A microbial consortium acclimatized with benzene, toluene or xylene (BTX) was employed to study the degradation pattern of these compounds individually under aerobic conditions. Batch and continuous experiments were conducted to evaluate the adaptability of the enriched cultures under substrate versatility conditions. The bio-kinetic parameters obtained under substrate versatility conditions were compared with those of a single substrate condition. Similar degradation patterns were observed for all the substrates with inhibition occurring at higher concentration (approximately 150 mg/L for benzene and xylene, and approximately 200 mg/L for toluene). Toluene degradation was highest, followed by benzene and xylene in the aqueous phase. Adaptation to a more toxic compound like benzene and xylene improved the utilization of toluene. On the other hand, microbes grown on a less toxic compound (toluene) grew at a lower rate in the presence of more toxic compounds. Suitable kinetic parameters such as micro(max) (maximum specific growth rate per hour), Ks (half saturation constant, mg/L), and KI (threshold substrate inhibition constant, mg/L) were determined using Haldane and Levenspiel substrate inhibition models. The Haldane equation seems to be an adequate expression for the system. The degradation behavior of pollutants in the gas phase was also evaluated using a toluene acclimatized biotrickling filter operated in continuous mode. The biotrickling filter acclimatized with toluene could degrade benzene and xylene with a lower elimination capacity. But, the system could recover its original efficiency quite fast even after a prolonged shock loading. The degradation was better for toluene, followed by benzene and xylene.     

Treatment of gasoline-contaminated waters by advanced oxidation processes

In this study, the efficiency of advanced oxidative processes (AOPs) was investigated toward the degradation of aqueous solutions containing benzene, toluene and xylenes (BTX) and gasoline-contaminated waters. The results indicated that BTX can be effectively oxidized by near UV-assisted photo-Fenton process. The treatment permits almost total degradation of BTX and removal of more than 80% of the phenolic intermediates at reaction times of about 30 min. Preliminary investigations using water contaminated by gasoline suggest a good potentiality of the process for the treatment of large volumes of aqueous samples containing these polluting species. Heterogeneous photocatalysis and H2O2/UV system show lower degradation efficiency, probably due to the heterogeneous character of the TiO2-mediated system and lost of photonic efficiency of the H2O2/UV system in the presence of highly colored intermediated.     

波导式气体吸收池时间响应特性

波导式光学吸收池在气体浓度测量等领域有广泛的应用前景.本文理论分析了在普通扩散环境和压差环境下波导式光学吸收池的时间响应机理和特性,并搭建了相应的传感系统,优化系统结构进行了实验验证.通过对低浓度的甲烷和甲苯气体的测量实验,验证和修正了响应时间的理论模型.实验结果表明,优化系统在可以大幅降低响应时间的同时,保持较高的灵敏度,为波导式吸收池的设计与优化提供了重要的参考.     

Effects of electrode configuration on polymer carbon-black composite chemical vapor sensor performance

The performance of polymer carbon-black composite chemical vapor sensors as a function of underlying electrode size and geometry has been studied. The sensor performance parameters investigated were sensor response magnitude to a toluene analyte (100, 500, and 1000 ppm), fundamental sensor noise in the presence of air, and two concentrations of toluene (100 and 500 ppm), and signal-to-noise ratio (100 and 500 ppm). An array of sensors with 42 different circular electrode configurations were designed, fabricated, and tested where electrode gap was varied from 10 to 500 /spl mu/m and the diameter of the sensors was varied from 30 to 2000 /spl mu/m. Each array of electrodes was coated with an approximately 1 /spl mu/m-thick layer of conducting polymer carbon-black composite with an insulating poly(alkylacrylate) polymer. The response magnitude, fundamental noise, and signal-to-noise ratio of each sensor was measured and compared to electrode geometry, such as electrode gap, aspect ratio, and overall size. No significant dependence of sensor response magnitude and noise to electrode configuration has been observed to be larger than the variation from sensor to sensor. However, the signal-to-noise ratio tended to decrease for sensors with the smallest scales.     

Improvement of gas-sensing performance of rGO/g-C3N4 nanocomposites by Ag NPs functionalization

The current research presents the effects of Ag nanoparticles (NPs) as a functionalization agent to improve the rGO/g-C₃N₄ nanocomposites as the gas sensor. Existing characterization techniques, including energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS), confirmed the successful synthesis of Ag/rGO/g-C₃N₄ nanocomposites. Besides Ag/rGO/g-C₃N₄ nanocomposites, two other samples, including pristine g-C₃N₄ and rGO/g-C₃N₄ nanocomposites were synthesized, and their performance in sensing acetone, carbon monoxide, methanol, isopropanol, formalin, and toluene at different temperatures, was investigated. The Ag/rGO/g-C₃N₄ nanocomposite-based sensor exhibited good selectivity of 68.77% and a high response of 42.97 to 50 ppm toluene at 100 °C, a significant reduction in operating temperature and a substantial increase in response and selectivity, in comparison to the rGO/g-C₃N₄ nanocomposite-based sensor. Moreover, the Ag/rGO/g-C₃N₄ nanocomposite-based sensor demonstrated excellent long-term stability. The role of Ag NPs and rGO in the improvement of toluene sensing of g-C₃N₄ nanosheets is explained comprehensively.     

酸处理对MWCNTs石英晶振微天平VOCs传感器灵敏度的影响(英文)

为分析酸处理过程对石英晶振型碳纳米管(CNTs)有机(VOCs)气体传感器灵敏度的影响,制作了一种多壁碳纳米管(MWCNTs)石英晶振式VOCs传感器.发现酸处理可以明显提高传感器灵敏度,利用毛细凝聚原理与开尔文公式对上述实验现象进行了分析.另外,比较了传感器对不同有机气体(甲苯、乙醇和丙酮)的灵敏度,研究结果表明传感器灵敏度与气体饱和蒸汽压有关,同样,该实验现象可利用毛细凝聚原理与开尔文公式来解释.     

Cu2+掺杂ZnO纳米棒的制备及气敏性能研究

通过溶剂热法(无水乙醇)制备了Cu2+(0～6mol%)掺杂ZnO纳米棒粉体,采用X射线衍射仪和扫描电镜对掺杂ZnO纳米粉体的晶体结构和微观形貌进行了表征.研究了Cu2+掺杂比例、溶剂热反应温度及时间对材料气敏性能的影响;考察ZnO(120℃,10h)和3mol%Cu2+掺杂ZnO(120℃,10h)粉体对应元件对甲醛、乙酸、甲苯、乙醇、丙酮、三甲胺等六种气体的气敏性能.结果表明:通过溶剂热法制备的ZnO粉体为纳米棒状结构,棒长度和直径随Cu2+掺杂比例不同发生变化;3mol%Cu2+掺杂ZnO(120℃,10h)样品对应元件对低浓度乙醇有很好的选择性,在395℃工作温度下对1×10–3乙醇的灵敏度为380.5,响应和脱附时间分别为5 s和40 s,对1×10–6乙醇的灵敏度可达4.2.     

Effect of hydrometallurgical process parameters on the Mn2O3 nano catalysts derived from spent batteries used in the plasma catalytic oxidation of BTX

Manganese oxide catalysts have been synthesized from the used batteries via hydrometallurgical method and effect of hydrometallurgical parameters such as the effect of acid type (H₂SO₄, HNO₃, HCl), acid concentration (0.5, 1, 1.5, 2 %v/v) and powder to acid ratio (1/50, 1/60, 1/70, 1/80) were in detail investigated. The physico-chemical properties of as-prepared catalysts were characterized by FT-IR, XRD, FESEM, EDX, BET, TEM, and TPR-H₂ analysis. The activity of as-prepared catalysts were investigated towards the oxidation of benzene, toluene, and xylene (BTX) in a plasma-catalytic process. The results show that benzene and toluene conversion were almost constant in the range of 97–98% in case of various acid types, acid concentrations and solid to liquid ratios. However, the xylene conversion were varied in case of different hydrometallurgical factors. The highest xylene conversion was obtained in the presence of MnS0.5–60, which was prepared using H₂SO₄ with concentration of 0.5%v/v and solid to liquid ratio of 1/60. The effect of the input voltage and BTX flow rate on the BTX conversion was also investigated using MnS0.5–60 catalyst in detail.