Detection of organic gases using TiO2 nanotube-based gas sensors

We fabricated porous gas sensing films composed of TiO₂ nanotubes prepared by a hydrothermal treatment for the detection of organic gases, such as alcohol and toluene. The morphology of the sensing films was controlled with a ball-milling treatment and calcination at high temperature to improve the sensitivity of the films. The sensor using nanotubes with the ball-milling treatment exhibited the improved sensor responses to toluene at 500oC. The results obtained indicated the importance of the microstructure control of sensing layers in terms of particle packing density, pore size distribution, and particle size and shape for detecting large sized organic gas molecules.     

Configuration and optimization of semiconductor gas sensors as gas chromatographic detectors

A tin oxide, gas-sensitive semiconductor sensor was configured as a gas chromatographic detector and its performance was optimized. Two sensor housings were compared but little difference was found in performance. The flow rate and temperature of the column and the internal heater voltage of the sensor affected both the sensitivity and peak shape. The temperature of the sensor surface was the most critical parameter. Optimal conditions for the gas chromatographic detection of a mixture of alkanes (C₁–C₅) and hydrogen were identified by using the simplex technique. The detection limit for hydrogen was improved by a factor of five to 20 ppb (v/v), illustrating the value of optimization and the excellent sensitivity of the detector. It is concluded that semiconductor gas sensors offer significant advantages as gas chromatographic detectors for the determination of reducing gases.     

Measurement of toxic volatile organic compounds in indoor air of semiconductor foundries using multisorbent adsorption/thermal desorption coupled with gas chromatography-mass spectrometry

A method for the qualitative and quantitative analysis of volatile organic compounds (VOCs) in the air of class-100 clean rooms at semiconductor fabrication facilities was developed. Air samples from two semiconductor factories were collected each hour on multisorbent tubes (including Carbopack B, Carbopack C, and Carbosieve SIII) with a 24-h automatic active sampling system and analyzed using adsorption/thermal desorption coupled with gas chromatography-mass spectrometry. Experimental parameters, including thermal desorption temperature, desorption time, and cryofocusing temperature, were optimized. The average recoveries and the method detection limits for the target compounds were in the range 94-101% and 0.31-0.89 ppb, respectively, under the conditions of a 1 L sampling volume and 80% relative humidity. VOCs such as acetone, isopropyl alcohol, 2-heptanone, and toluene, which are commonly used in the semiconductor and electronics industries, were detected and accurately quantified with the established method. Temporal variations of the analyte concentrations observed were attributed to the improper use of organic solvents during operation.     

Elemental composition determination of organophosphorus compounds using gas chromatography and atomic emission spectrometric detection

The elemental responses for a series of alkylated and arylated phosphates evaluated were measured on an atomic emission spectrometric detector. The signals for carbon, hydrogen, chlorine, phosphorus and oxygen were used to determine the specifity of elemental response ratios to a particular compound structure and the dependence of response ratios on the amounts of the analytes. Variations of the response ratios, as well as the accuracy and variations of the stoichiometric values of the calculated empirical formulae, were evaluated. For this purpose, a test mixture with reference compounds was used. Determination of empirical formulae with acceptable errors of a few percent is possible if the calibrating reference substance is closely related — by structure, elemental composition, molecular weight and amount — to the compounds to be identified. Analyte amounts of at least 30 ng are required for efficient calibration.     

Determination of acetone and ethanol vapors using semiconductor sensors

Sensors with gas-sensing layers based on tin dioxide with nanosized catalytic additives of palladium, platinum, antimony, and lanthanum have been used to determine ethanol and acetone vapors in air. The use of nonstationary temperature modes, allowed us to reach record-breaking low detection limits for acetone (∼0.1 ppm). For the first time ethanol and acetone have been selectively determined with a single sensor.     

Detection of liquid petroleum gas using mixed nanosized tungsten oxide-based thick-film semiconductor sensor

The thick-film semiconductor sensor for liquid petroleum gas (LPG) detection was fabricated using a mixed WO₃-based sensor. We present the characterization of both their structural properties by means of XRD measurements and the electrical characteristics by using gas-sensing properties. The sensing characteristics such as sensitivity, working range, cross-sensitivity and response time were studied by using nanosized WO₃-based mixed with different metal oxides (SnO₂, TiO₂ and In₂O₃) and doped with noble metals (Au, Pd and Pt). The WO₃-based mixed with 5 wt.% In₂O₃ and 0.5 wt.% Pd showed the higher sensing characteristic at low concentration of LPG sensor at an operating temperature 225 °C.     

Metal oxide semiconductor sensors for determination of reactive gas impurities in air

Characteristics of metal oxide semiconductor sensors intended for measuring O₃, NO _x , Cl₂, C1O₂, and HCl microconcentrations were discussed. Specific features of detection of these microimpurities with semiconductor sensors were determined. The size of signal generated by sensors with WO₃-, ZnO-, and In₂O₃-based sensing layers was examined in relation to the O₃, NO _x , Cl₂, C1O₂, and HCl concentration. The sensitivities exhibited by the semiconductor sensors with respect to target impurities make them suitable for measuring their maximum permissible concentrations in sanitary zones and for monitoring background ozone level in atmosphere. Examples of application of gas analyzers based on semiconductor sensors in determination of gas impurities in the open atmosphere were given.     

Cross-sensitive rare-earth metal sensors based on bidentate neutral organophosphorus compounds and chlorinated cobalt dicarbollide

A new carbon composite electrode material, based on dispersing glassy carbon (GC) microparticles into methyltrimethoxysilane-derived sol, is described in the present paper. The resulting glassy carbon ceramic composite electrodes (GCCEs) combine the electrochemical properties of GC with the advantages of composite electrodes, and thus offer high electrochemical reactivity, low background current and are easy to prepare, modify and renew. The new material has a low double-layer capacitance and a wide potential window. Scanning electron microscopy (SEM) images indicate significant difference in the structure of GCCE and carbon ceramic composite electrode (CCE). The electrochemical properties and advantages of GCCE should find broad utility in electroanalysis.     

Detection of chlorinated methanes by tin oxide gas sensors

Tin oxide thin films prepared by thermal oxidation of Sn films were used for the detection of chlorinated methanes (CH2Cl2, CHCl3 and CCl4). This resulted in better chemical selectivity, sensitivity, response speed and detection limit than seen with previous detectors. The temperature dependence of the sensing of 1% CCl4 gas was studied and the best sensing behavior was observed at 300 degrees C. The films showed different chemical selectivity in both speed and direction of sensing response to each gas and were stable for more than 3 weeks under operating conditions. The films showed rapid gas sensing (<40 s to reach 90% of full response) and low detection limits (< 4 ppm CCl4). The role of oxygen in the detection of chlorinated methanes and in resistance changes without chlorinated methanes was also studied. The changes at the surface of the film after gas sensing were examined using scanning electron microscopy with energy-dispersive X-ray spectrometry.     

Feasibility studies for the detection of volatile organic compounds in the gas phase using microelectrode sensors

The use of microelectrode sensors to detect volatile organic compounds (VOCs) in air is demonstrated. In general, VOCs that oxidize easily to form protons gave a larger electrochemical response. The use of voltammetry for speciation and the effect of electrode size on the electrochemical response are discussed. We demonstrate that surface enhanced Raman spectroscopy (SERS) can be used to monitor the electrochemical reactions in situ and discuss its applicability in identifying the electroactive species.     

Selective dehalogenation and hydrogenation of compounds in adsorption layers with tritium gas

Selective dehalogenation and hydrogenation were observed in treating the corresponding precursors supported on a heterogeneous carrier with tritium gas. This technique was used to obtain tritium-labeled 3′,3,5-triiodothyronine, dihydrofusicoccin terpenoid (DHF), and 3-(piperidine-4-yl)-1,4-dihydroquinazoline-2-on with a molar radioactivity of 0.76, 2.3, and 6.5 PBq/mol, respectively.     

Chlorine gas sensors using one-dimensional tellurium nanostructures

Tellurium nanotubes have been grown by physical vapor deposition under inert environment at atmospheric pressure as well as under vacuum conditions. Different techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and optical absorption have been utilized for characterization of grown structures. Films prepared using both types of tellurium nanotubes were characterized for sensitivity to oxidizing and reducing gases and it was found that the relative response to gases depends on the microstructure. Nanotubes prepared at atmospheric pressure (of argon) showed high sensitivity and better selectivity to chlorine gas. Impedance spectroscopy studies showed that the response to chlorine is mainly contributed by grain boundaries and is therefore enhanced for nanotubes prepared under argon atmosphere.     

Reaction of keto alcohols with organophosphorus compounds

Conclusions Trialkyl(aryl) phosphites and phosphonites react with 3-ketobutanol to give, respectively,-ketobutylphosphonic and phosphinic acids, while the phosphinites react to give the oxides of tertiary phosphines.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimieheskaya, No. 5, pp. 1087–1092, May, 1970.