UV-laser-light-controlled photoluminescence of metal oxide nanoparticles in different gas atmospheres: BaTiO3, SrTiO3 and HfO2

The photoluminescence (PL) enhancement has been studied at room temperature using various specimen atmospheres (O₂ gas, CO₂ gas, CO₂–H₂ mixture gas, Ar–H₂ mixture gas and vacuum) under 325 nm laser light irradiation on various metal oxides. Of them, the results obtained for BaTiO₃ nanocrystals, SrTiO₃ ones and HfO₂ powder crystal are given in the present paper. Their PL were considerably increased in intensity by irradiation of 325 nm laser light in CO₂ gas and CO₂–H₂ mixture gas. The cause of the PL intensity enhancements is discussed in the light of the exciton theory, the defect chemistry and the photocatalytic theory. The results may be applied for the utilization of greenhouse gas (CO₂) and the optical sensor for CO₂ gas.     

Application of Notched Long-Period Fiber Grating Based Sensor for CO2 Gas Sensing

An inductively coupled plasma etching process to fabricate notched long-period fiber gratings for CO₂ gas sensing is proposed in this article. In the gas sensing test, the 15% mixed CO₂ gas was used for characterization of CO₂ adsorption by the amine-modified nanoporous silica foams of the notched long-period fiber grating sensor. The results shows the spectra were changed with the CO₂ gas flow within 13 min. During the absorption process, the transmission of the resonant dip was decreased by 2.884?dB. Therefore, the proposed notched long-period fiber grating gas sensor shows good performance and is suitable as a gas sensor for monitoring the CO₂ adsorption process.     

Bifunctional Au-nanorod@Fe3O4 nanocomposites: synthesis, characterization, and their use as bioprobes

Membrane gas separation technology has been rapidly growing for industrial applications such as air separation, carbon dioxide (CO₂) separation from natural gas production, hydrogen separation, etc. Needs for CO₂ separation are increasing as carbon capture technology has been recognized as an essential part when combating the global warming issue. Membrane gas separation technology deals with mass transport phenomena through the membrane engineered on a sub-nanoscale controlling transport properties of small gas molecules such as CO₂, N₂, O₂, H₂, etc. In this review, we will report on the recent developments in capture technologies utilizing various membranes including nano-engineered thermally rearranged (TR) polymers. TR polymer membranes show high gas permeability as well as good separation properties, especially in CO₂ separation processes such as from post-combustion flue gas and natural gas sweetening.     

Estimating the density of carbon atoms on a Ni catalyst surface in equilibrium with a carbonaceous gas

The amount of carbon adsorbed on the surface of Ni in contact with carbonaceous gas mixtures such as CH₄/H₂ and CO/CO₂, is estimated from equilibrium segregation data. The results are displayed on “gas composition versus temperature” plots for the above two gas mixtures. These plots provide basic thermodynamic information relevant to reactions such as steam reforming of hydrocarbons on supported Ni catalysts. For example, the plot for CO/CO₂ gas mixtures represents the Boudouard equilibrium on a single crystal Ni catalyst, whilst the plot for CH₄/H₂ gas mixtures provides information relevant to the equilibrium hydrogenation of adsorbed C to CH₄.     

Effects of gas saturation and sparging on sonochemical oxidation activity in open and closed systems,Part I: H2O2 generation

Cavitational/sonochemical activity can be significantly enhanced or reduced depending on the gases dissolved in the liquid. Although many researchers have suggested the order of importance of dissolved gas conditions that affect the degree of sonoluminescence (SL), sonochemiluminescence (SCL), and compound degradation, the most suitable gas condition for sonochemical oxidation reactions is currently unknown. In this study (Part I), the effects of gas saturation and sparging on the generation of H₂O₂ were investigated in a 28-kHz sonoreactor system. Four gas modes, saturation/closed, saturation/open, sparging/closed, and sparging/open, were applied to Ar, O₂, N₂, and binary gas mixtures. The change in dissolved oxygen (DO) concentration during ultrasonic irradiation was measured and was used as an indicator of whether the gaseous exchange between liquid and air altered the gas content of the liquid. Considerable difference in the DO concentration was observed for the gas saturation/open mode, ranging from –11.5 mg/L (O₂ 100 %) to +4.3 mg/L (N₂ 100 %), while no significant difference was observed in the other gas modes. The change in the gas content significantly reduced the linearity for H₂O₂ generation, which followed pseudo-zero-order kinetics, and either positively or negatively affected H₂O₂ generation. Ar:O₂ (75:25) and Ar:O₂ (50:50) resulted in the highest and second-highest H₂O₂ generation for both gas saturation and sparging, respectively. In addition, gas sparging resulted in much higher H₂O₂ generation for all gas conditions compared to gas saturation; this was because of the significant change in the cavitational active zone and concentrated ultrasonic energy, which formed a bulb-shaped active zone, especially for the Ar/O₂ mixtures adjacent to the transducer at the bottom. The sparging flow rate and position also significantly affected H₂O₂ generation; the highest H₂O₂ generation was obtained when the sparger was placed at the bottom adjacent to the transducer, with a flow rate of 3 L/min.In Part II, the generation of nitrogen oxides, including nitrite (NO₂^–) and nitrate (NO₃^–), was investigated using the same ultrasonic system with three gas modes: saturation/open, saturation/closed, and sparging/closed.     

A photonic crystal fiber sensor based on differential optical absorption spectroscopy for mixed gases detection

A photonic crystal fiber sensor based on differential optical absorption spectroscopy for mixed gas detection is presented. In such sensor, hollow core photonic crystal fiber is utilized as gas cell and the feasibility for gas detection is verified by experiment. The components concentration of mixed gas NH₃ and C₂H₂ are measured and the detection sensitivity is 143 ppmv.     

Adsorption behaviour of SO2 and SOF2 gas on Rh-doped BNNT: a DFT study

Abstract

As the insulating medium, SF₆ is widely used in gas insulation equipment. Partial discharge and local overheating can cause the decomposition of SF₆, resulting in a decrease in insulation strength of the equipment. The detection of SF₆ decomposition gas can be used for on-line insulation detection of gas insulation equipment in electric power industry. In order to develop a new sensor gas sensing material for gas detecting. In this work, based on the first-principles density functional calculation (DFT) method of DMol³, the adsorption of SF₆ decomposition gas on (5,0) Z-type Rh-BNNT in different ways was explored. The adsorption energy, adsorption distance, charge transfer as well as density of states were discussed. The results show that the adsorption strength between SO₂ molecule with Rh-BNNT is larger than with SOF₂ molecule, combined with desorption time, theoretically predicts Rh -BNNT have the potential to be a material for SO₂ gas sensors.     

Numerical investigation of a fast-axial-flow CW CO2 laser

This paper presents the results of the calculation of the parameters of the active medium of a fast-axial-flow CO₂ laser using numerical methods in the framework of a one-dimensional approximation of the set of continuity equations, Bernoulli equation, equation of gas state, energy equation and multi-temperature rate equations with regard to diffusion for the gas flow in the cylindrical discharge tube. The spatial distribution of the small-signal gain and gas temperature along the gas flow direction have been calculated for a given set of initial conditions, namely, gas flow velocity, gas pressure and the tube diameter. In addition, the dependence of small-signal gain, the asymmetric stretch vibrational temperature of CO₂ (T₃) and the gas temperature on the discharge current were studied.     

Numerical solution of Boltzmann tranport equation for TEA CO2 laser having nitrogen-lean gas mixtures to predict laser characteristics and gas lifetime

Selective laser isotope separation by TEA CO₂ laser often needs short tail-free pulses. Using laser mixtures having very little nitrogen almost tail free laser pulses can be generated. The laser pulse characteristics and its gas lifetime is an important issue for long-term laser operation. Boltzmann transport equation is therefore solved numerically for TEA CO₂ laser gas mixtures having very little nitrogen to predict electron energy distribution function (EEDF). The distribution function is used to calculate various excitation and dissociation rate of CO₂ to predict laser pulse characteristics and laser gas lifetime, respectively.Laser rate equations have been solved with the calculated excitation rates for numerically evaluated discharge current and voltage profiles to calculate laser pulse shape. The calculated laser pulse shape and duration are in good agreement with the measured laser characteristics. The gas lifetime is estimated by integrating the equation governing the dissociation of CO₂. An experimental study of gas lifetime was carried out using quadrapole mass analyzer for such mixtures to estimate the O₂ being produced due to dissociation of CO₂ in the pulse discharge. The theoretically calculated O₂ concentration in the laser gas mixture matches with experimentally observed value. In the present TEA CO₂ laser system, for stable discharge the O₂ concentration should be below 0.2%.     

Highly sensitive and selective trimethylamine sensors based on WO3 nanorods decorated with Au nanoparticles

One-dimensional tungsten oxide (WO₃) gas sensing materials have been widely used for the detection of trimethylamine (TMA) gas. Furthermore, it is believed that an effective method to improve the gas sensing performance is to introduce noble metals into sensing materials. In this work, a novel gas sensing material was prepared by decorating Au nanoparticles on WO₃ nanorods. Based on field emission scanning electron microscopy (FESEM/EDS), X-ray diffraction (XRD), and transmission electron microscopy (TEM), the morphology and microstructure of as-prepared samples were characterized. Results show that Au nanoparticles with diameter of 13–15 nm are loaded on the surface of WO₃ nanorods with length of about 1–2 µm and width of 50–80 nm. Gas sensing tests reveal that the Au@WO₃ sensor has remarkably enhanced response to TMA gas compared with pure WO₃ nanorods. In addition, and the gas sensing mechanism has been investigated based on the experimental results. The superior sensing features indicate the present Au@WO₃ nanocomposites are promising for gas sensors, which can be used in the detection of the trimethylamine gas and this work provides insights and strategies for the fabrication of sensing materials.     

A first-principle investigation of NO2 adsorption behavior on Co,Rh, and Ir-embedded graphitic carbon nitride: Looking for highly sensitive gas sensor

First-principle calculations were performed to investigate the adsorption behavior of NO₂ gas on the pristine graphitic carbon nitride (gCN) and transition metals (TM)-embedded gCN systems (TM = Co, Rh, and Ir elements) in order to explore the sensing capabilities of gCN systems as toxic gas sensor. The results of adsorption energy revealed that NO₂ gas was physisorbed on the pristine gCN, whereas this gas was strongly chemisorbed on the TM-embedded gCN. Additionally, it was found that the interaction of NO₂ gas with Ir-embedded gCN (−4.47 eV) is much higher than those of the Co and Rh-embedded systems, alluding to its suitability as a highly sensitive gas sensor. The obtained results displayed that the electronic and magnetic properties of the gCN systems remarkably modulated by chemisorption of NO₂ gas. The strong interactions between the TM-embedded gCN and NO₂ gas induced dramatic changes on the conductivity of the systems and led a large reduction in the band gap energy. The results of spin-polarized band structure and density of states indicated that with adsorption of NO₂ gas over the Rh- and Ir-embedded gCN, the magnetic moment of these systems remarkably reduced from 0.10 to 0.07 and 0.01 μB, respectively. Additionally, the results of partial density of states indicated that with adsorption of NO₂ gas over the pristine and TM-embedded gCN systems, the sharp peaks close to the Fermi energy levels of TM-embedded gCN were significantly increased in comparison with the pristine gCN, thanks to the large charge transfer from d-orbitals of the TM atoms to p-orbitals of NO₂ gas. Furthermore, the results of optimized structure showed that with embedding Co-, Rh-, and Ir-elements and also adsorption of NO₂ gas on the gCN, the initial planar structure of the pristine gCN automatically became wrinkle. Finally, based on the obtained results, it can be concluded that the high adsorption energy and considerable charge transfer between NO₂ gas and Ir-embedded gCN make this system as an excellent candidate for NO₂ gas sensor applications.     

Nanocrystalline cerium oxide coated fiber optic gas sensor

A clad-modified fiber optic sensor with nanocrystalline CeO₂ is proposed for gas detection. As-prepared and annealed CeO₂ (500 °C) samples have been used as gas sensing media. The spectral characteristics of the fiber optic gas sensor are studied for various concentrations of ammonia, ethanol and methanol gases (0–500 ppm). The sensor exhibits linear variation in the spectral peak intensity with the gas concentration. The characteristics of the sensor are also studied for gas selectivity. The time response characteristics of the sensor are reported.     

Calibration method at the N K‐edge using interstitial nitrogen gas in solid‐state nitrogen‐containing inorganic compounds

The standard method of soft X‐ray beamline calibration at the N K‐edge uses the ν = 0 peak transition of gas‐phase N₂. Interstitial N₂ gas trapped or formed within widely available solid‐state ammonium‐ and amine‐containing salts can be used for this purpose, bypassing gas‐phase measurements. Evidence from non‐nitrogen‐containing compounds (KH₂PO₄) and from He‐purged ammonium salts suggest that production of N₂ gas is through beam‐induced decomposition. Compounds with nitrate or nitrite as anions produce coincident features and are not suitable for this calibration method.     

Spectroscopic detection of aircraft wake gases

Using the technique of limiting information-metric scales, the potential of laser IR absorption spectroscopy for detecting small gas components of aircraft wake was quantitatively analyzed. Formulas for minimum distinguishable and minimum detectable gas concentrations were derived. Calculation was carried out for SO₂, NO, and NO₂ under typical conditions near the Boeing 707 aircraft engine nozzle at altitude H = 12.2 km. Alternative IR laser spectroscopy methods for detecting various gas components in the near wake were considered. Two possibilities to improve the concentration measurement sensitivity were analyzed: (i) a decrease in the background absorption of CO₂ and H₂O and (ii) an increase in the absorption cross section of detected gas.     

羟基碳纳米管吸附SF6放电分解组分的DFT计算

本文根据密度泛函理论(density functional theory , DFT), 采用MS分子动力学仿真软件对羟基修饰的单壁碳纳米管(SWNT-OH) 吸附SF₆局部放电分解的四种主要组分SOF₂, SO₂F₂, SO₂和CF₄进行了详细的理论计算, 通过分析气体分子和SWNT-OH的前线轨道, 吸附过程中吸附能、电荷转移量和电子态密度的情况, 以及吸附前后SWNT-OH能隙的变化, 评判了SWNT-OH对气体分子的敏感性和选择性, 给出了SWNT-OH是否可以制备气体传感器检测SF₆局部放电分解组分的理论依据.     

Synthesis and gas sensing properties of perovskite CdSnO<Subscript>3</Subscript> nanoparticles

The CdSnO₃ semiconducting oxide that can be used as a gas-sensitive material for detecting ethanol gas is reported in this paper. CdSnO₃ nanoparticles were prepared by a chemical co-precipitation synthesis method, in which the preparation conditions were carefully controlled. The n-type gas-sensing semiconductors were obtained from the as-synthesized powders calcined at 600°C for 1 h. The phase and microstructure of the obtained nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and Brunauer–Emmett–Teller (BET) method with a gas adsorption analyzer. CdSnO₃ has a small particle size range of 30–50 nm and a high surface area of 9.12 m²/g, and a uniformity global shape. The gas sensitivity and operating temperature, and selectivity of CdSnO₃-based sensors were measured in detail. The gas sensors fabricated by CdSnO₃ nanoparticles had good sensitivity and selectivity to vapor of C₂H₅OH when working temperature at 267°C, the value of gas sensitivity at 100 ppm of C₂H₅OH gas can reach 11.2 times. Furthermore, gas-sensing mechanism was studied by using chromatographic analysis.     

AlNxOy thin films deposited by DC reactive magnetron sputtering

AlN_xO_y thin films were produced by DC reactive magnetron sputtering, using an atmosphere of argon and a reactive gas mixture of nitrogen and oxygen, for a wide range of partial pressures of reactive gas. During the deposition, the discharge current was kept constant and the discharge parameters were monitored. The deposition rate, chemical composition, morphology, structure and electrical resistivity of the coatings are strongly correlated with discharge parameters. Varying the reactive gas mixture partial pressure, the film properties change gradually from metallic-like films, for low reactive gas partial pressures, to stoichiometric amorphous Al₂O₃ insulator films, at high pressures. For intermediate reactive gas pressures, sub-stoichiometric AlN_xO_y films were obtained, with the electrical resistivity of the films increasing with the non-metallic/metallic ratio.     

Measurement of radiative gas and particle emissions in biomass flames

Radiation is the dominant mode of heat transfer near the burner of coal and biomass-fired boilers. Predicting and measuring heat transfer is critical to the design and operation of new boiler concepts. The individual contributions of gas and particle phases are dependent on gas and particle concentration, particle size, and gas and particle temperature which vary with location relative to the flame. A method for measuring the contributions of both gas and particle radiation capable of being applied in harsh high temperature and pressure environments has been demonstrated using emission from particles and water vapor using an optical fiber probe transmitting a signal to a Fourier Transform Infrared (FTIR) spectrometer. The method was demonstrated in four environments of varying gas and particle loading using natural gas and pulverized wood flames in a down-fired 130?kW_th cylindrical reactor. The method generates a gas and particle temperature, gas concentrations (H₂O and CO₂), total gas and particle intensities, and gas and particle total effective emissivity from line-of-sight emission measurements. For the conditions measured, downstream of the luminous flame zone, water vapor and CO₂ radiation were the dominant modes of heat transfer (effective emissivity 0.13–0.19) with particles making a minor contribution (effective emissivity 0.01–0.02). Within a lean natural gas flame, soot emission was low (effective emissivity 0.02) compared to gas (0.14) but within a luminous flame of burning wood particles (500?µm mean diameter) the particles (soot and burning wood) produced a higher effective emissivity (0.17) than the gas (0.12). The measurement technique was therefore found to be effective for several types of combustion environments.     

Real-time measurement of nitrogen dioxide in vehicle exhaust gas by mid-infrared cavity ring-down spectroscopy

The application of pulsed cavity ring-down spectroscopy (CRDS) was demonstrated for the measurement of nitrogen dioxide (NO₂) in automotive exhaust gas. The transition of the ν ₃ vibrational band assigned to the antisymmetric stretching mode of NO₂ was probed with a thermoelectrically cooled, pulsed, mid-infrared, distributed feedback, quantum cascade laser (QCL) at 6.13 μm. The measurement of NO₂ in the exhaust gas from two diesel vehicles equipped with different aftertreatment devices was demonstrated using a CRDS-based NO₂ sensor, which employs a HEPA filter and a membrane gas dryer to remove interference from water as well as particulates in the exhaust gas. Stable and sensitive measurement of NO₂ in the exhaust gas was achieved for more than 30 minutes with a time resolution of 1 s.     

Numerical study of the effect of gas flow in low pressure inductively coupled Ar/N<Subscript>2</Subscript> plasmas

The effect of gas flow in low pressure inductively coupled Ar/N₂ plasmas operating at the rf frequency of 13.56 MHz and the total gas pressure of 20 mTorr is studied at the gas flows of 5–700 sccm by coupling the plasma simulation with the calculation of flow dynamics. The gas temperature is 300 K and input power is 300 W. The Ar fractions are varied from 0% to 95%. The species taken into account include electrons, Ar atoms and their excited levels, N₂ molecules and their seven different excited levels, N atoms, and Ar⁺, N⁺, N₂ ⁺, N₄ ⁺ ions. 51 chemical reactions are considered. It is found that the electron densities increase and electron temperatures decrease with a rise in gas flow rate for the different Ar fractions. The densities of all the plasma species for the different Ar fractions and gas flow rates are obtained. The collisional power losses in plasma discharges are presented and the effect of gas flow is investigated.