Presence Of Different Gases Research Articles

Design and testing of a device for the characterization of gas transfer through soap films and measurement protocol based on color matching

Soap films are interesting for their potential utilization as soft, self-assembled, self-healing and possibly recyclable membranes. The intrinsic possibility of tuning their properties, such as e.g. surface and bulk elasticity or permeability, via tailored chemistry makes them flexible enough for a wide range of physical-chemical applications. Here we introduce a novel device that can serve as a research platform for the detailed experimental characterization of the soap film permeability to gases. The design and manufacturing of the novel platform are discussed, along with a sample characterization protocol based on a color-matching procedure for dioxygen diffusion through typical soap films. The experimental data is compared with the results obtained from a numerical model, specifically developed for the problem, and good agreement is found. In perspective, the proposed platform can serve for the precise characterization of gas transfer properties of soap films made from different surfactant mixtures and in the presence of different gases.

Effective Reinforcement of Visible Light Photocatalytic and Gas Sensing Characteristics of Nanocrystalline TiO2: Gd-Based Nb and Mo Dopants

Efficient compositions for the selective detection of ethanol gas and the removal of organic contaminants were realized by codoping of (Gd, Nb) and (Gd, Mo) ions into TiO2. TiO2, Ti0.96Gd0.01Nb0.03O2, and Ti0.96Gd0.01Mo0.03O2 samples were prepared by a coprecipitation method. For all compositions, a crystalline anatase phase of TiO2 was detected. Compared to pure TiO2, the absorption edges of Ti0.96Gd0.01Nb0.03O2 and Ti0.96Gd0.01Mo0.03O2 samples were red-shifted, further broadening towards visible light. The morphological studies demonstrate that the grains of TiO2 were more refined after (Gd, Nb) and (Gd, Mo) codoping. The photocatalytic efficiency of the Ti0.96Gd0.01Mo0.03O2 catalyst for degrading 20 mg/L reactive yellow 145, brilliant green, and amoxicillin was 98, 95, and 93% in 90 min, respectively. The reusability experiments indicate that the Ti0.96Gd0.01Mo0.03O2 catalyst had high stability during reuse. The high photocatalytic activity of the Ti0.96Gd0.01Mo0.03O2 catalyst was correlated to the broad visible-light absorption and effective separation of electron–hole pairs by Gd3+ and Mo6+ cations. The gas sensing characteristic is reflected by the high sensitivity of the Ti0.96Gd0.01Nb0.03O2 sensor to ethanol gas in the presence of different gases at 275 °C. The obtained results indicated that the (Gd, Mo) mixture could more effectively induce the photocatalytic properties of TiO2 while (Gd, Nb) dopants were the best for reinforcing its sensing characteristics.

Calculation of IFT in porous media in the presence of different gas and normal alkanes using the modified EoS

Gas injection can increase oil recovery because the gas–oil interfacial tension is less than the water–oil interfacial tension (IFT) and tends to zero in the miscibility state. However, little information has been provided on the gas–oil movement and penetration mechanisms in the fracture system at the porosity scale. The IFT of oil and gas in the porous medium changes and can control oil recovery. In this study, the IFT and the minimum miscibility pressure (MMP) are calculated using the cubic Peng-Robinson equation of state that has been modified using the mean pore radius and capillary pressure. The calculated IFT and MMP change with the pore radius and capillary pressure. To investigate the effect of a porous medium on the IFT during the injection of CH4, CO2, and N2 in the presence of n-alkanes and for validation, measured experimental values in references have been used. According to the results of this paper, changes in IFT vary in terms of pressure in the presence of different gases and, the proposed model has good accuracy for measuring the IFT and the MMP during the injection of hydrocarbon gases and CO2. In addition, as the average radius of the pores gets smaller, the interfacial tension tends to lower values. This effect is different with increasing the mean size of interstice in two different intervals. In the first interval, i.e. the Rp from 10 to 5000 nm, the IFT changes from 3 to 10.78 mN/m and in the second interval, i.e. the Rp from 5000 nm to infinity, the IFT changes from 10.78 to 10.85 mN/m. In other words, increasing the diameter of the porous medium to a certain threshold (i.e. 5000 nm) increases the IFT. As a rule, changes in IFT affected by exposure to a porous medium affect the values of the MMP. In general, IFT decreases in very fine porous media, causing miscibility at lower pressures.

Influence of gas environment on the dynamics of wetting transition of laser-textured stainless steel meshes

We analyze the role of surrounding gas and aging in ambient air in the wettability behavior of laser-processed stainless steel meshes. Laser texturing of meshes was carried out in the presence of different gases (N2, O2, CO2, Ar, and SF6) in ambient atmospheric air and under different vacuum conditions. The influence of each gas on the evolution of the wettability properties after aging in ambient air is analyzed. The effects of low-pressure and vacuum aging allowed transforming the initial superhydrophilic characteristics of the laser-structured meshes to an almost superhydrophobic state.

The Effect of Gas Solubility on the Secondary Sorption in a Portland Cement Mortar Observed by X-ray CT

In this study, we investigate the secondary sorption in an air-entrained Portland cement mortar that is purged with different gases— $$\hbox {CO}_{2}, \hbox {CH}_{4}$$ , or $$\hbox {N}_{2}$$ . By altering the gas phase present in the void space, we are able to evaluate how gas solubility influences the secondary sorption. The rate of water sorption in the presence of different gases in the entrained voids was captured using successive 30 min X-ray micro-computed tomography scans for 24 h after water-specimen contact. The results show the higher the solubility of the gas, the faster the mortar reaches saturation. The air voids in the $$\hbox {CO}_{2}$$ -purged specimen begin to absorb water within 30 min and reach a critical degree of saturation within hours, while the air voids of $$\hbox {N}_{2}$$ and $$\hbox {CH}_{4}$$ -purged specimens show a significantly slower water absorption over 24 h. The high solubility of $$\hbox {CO}_{2}$$ was found to alter the X-ray mass attenuation value of the water as the water becomes $$\hbox {CO}_{2}$$ saturated. These tests reveal the gas type present in the void space significantly influences secondary sorption of Portland cement mortars. The findings of this study have implications on predicting mass transport in cement-based materials used in below ground carbon sequestration structures.

AC characterization of three-dimensional reduced graphene oxide/molybdenum disulfide nanorose hybrids for ethanol vapor detection

A novel AC impedance study on three-dimensional hybrid structures of graphene sheets/MoS2 nanorose (GMS) toward ethanol vapor detection is presented in this work. These defective 3D hybrid porous structures are sensitive to the presence of different gases as a result of charge transfer with gas species, as well as a change in the effective capacitance of the system. The sensing behavior of the samples is investigated throughout time-dependent impedance measurement and electrochemical impedance spectroscopy (EIS). The sensor response is estimated at about 20% to 10 ppm ethanol vapor, with the response and recovery times about 3.2 s and 0.8 s, respectively. Sensing mechanism proposed to describe the EIS impedance spectra involves three different procedures: charge transfer, double layer formation and diffusion process. Moreover, these processes are probed using equivalent circuits modeled by the impedance spectra curves.

Detection of Emanated Light at the Modified Clad Region (Sno2) of the Optical Fiber for Methanol Gas Sensing

A leakage detecting sensor (radiation mode (or) double fiber mode) is proposed to monitor the light rays propagates from the surface of the modified clad region (SnO2) of the optical fiber. The output intensity increases and decreases for the varying gas concentration (0-500 ppm) with the presence of different gases (methanol, ethanol, acetone and ammonia) at room temperature. The received output intensity from the clad modified surface increases for ammonia and methanol, whereas, it decreases for acetone and ethanol gases for the increase in the gas concentration. However, in the transmitting mode (single fiber mode) the output light intensity decreases for all the gases with varying gas concentration. The output gas sensitivity of the proposed sensor (double fiber mode) is compared with the transmitting mode sensor and the sensor shows superior response for methanol over other gases. The dynamic characteristics of the sensor are reported.

Selective gas sensor based on one single SnO2 nanowire

Nowadays the analysis of ambient atmosphere in order to monitor the presence of dangerous gases and volatile compounds is more and more important. For this reason, a network of tiny sensors capable to discriminate the presence of pollutants and distinguish them is crucial. We present here a resistive sensor based on a single tin oxide nanowire (60 nm in diameter and 3.5 μm long) that can detect the presence of different gases and estimate their concentration in the range of 1–50 ppm. The SnO2 nanowire (NW) is grown by chemical vapor deposition and then used to bridge to metal electrodes. Under a temperature gradient, 5 signals can be extracted, forming the thermal fingerprint of each specific gas that can be present in the measuring chamber. Applying machine learning algorithms to these thermal fingerprints, the system can recognize which gas is present in the chamber (with an 94.3% accuracy) and estimate the concentration of the gas (with an average error of 24.5%). The limit of detection has been found to be under 1 part per million for all the gases tested.

(Invited) In Situ XPS and Aes Characterization of Cathode Surface Chemistry Evolution and Its Effect on Cycle Life

Lithium ion battery cycle life varies significantly with cathode chemistry, structure, and properties. However, it is well known that deconstructing cycled and faded full cells and reassembling them as half cells can retrieve much of the lost capacity. Therefore, cathode chemistry must play a role in exacerbating other side reactions that induce capacity fade without significantly degrading themselves.(1, 2) A well known example in the literature is the effect of Mn(II) dissolution from the cathode in degrading the anode.(3) However, analogous fade mechanisms resulting from interactions between cathode and anode side reactions are not as well understood in other systems. Since such ‘cross-talk’ interactions can have multiple complex steps and inherently have surface reaction contributions, they can be difficult to characterize and identify. The complex nature of degradation reactions motivates the development of in situ and operando characterization techniques. Of particular value for understanding associated mechanisms are surface sensitive in situ characterization techniques such as x-ray photoelectron spectroscopy (XPS), auger electron spectroscopy (AES), etc. Such methods require specialized electrochemical cells that function in vacuum. Ideally, we seek to relate such information to associated changes occurring in the bulk of the electrode particles, in the physical properties of the underlying material, and in the commercially relevant battery environments. We will describe the development of novel Li ion cells suitable for in situ and operando characterization via a variety of electron, optical, and x-ray based methods.(4-7) In situ surface spectroscopy is revealing new insights into the importance of cathode solid electrolyte interphase (SEI) stability during cycling in affecting cycle life. We compare cells based on LiCoO2, LiMn2O4, LiNiO2, Li[Ni1/3Mn1/3Co1/3]O2, and LiFePO4. In particular, we find that gaseous products produced during SEI formation and SEI decomposition drive degradation at the counter electrode. This has motivated ongoing work to investigate the role of gas in affecting capacity fade in traditional battery configurations, as well as model studies employing in situ characterization during cycling in gaseous environments. We find that the presence of different gases commonly evolved during cycling have varying effects on the rate of capacity fade. The effect is non-linear and the gases have different effects in full cells based on different cathode chemistries. This presentation will highlight the relationships between surface reactions observed in situ during model experiments, gas phase evolution in full cells, and the effects of subsequent reactions on capacity fade. The results provide a reasonable basis for understanding capacity fade associated with several commercially relevant cathode systems and can be extended to provide insights into designing next-generation intercalation cathodes. B. Ziv, V. Borgel, D. Aurbach, J.-H. Kim, X. Xiao and B. R. Powell, Journal of The Electrochemical Society, 161, A1672 (2014).J.-H. Kim, N. P. W. Pieczonka, Z. Li, Y. Wu, S. Harris and B. R. Powell, Electrochimica Acta, 90, 556 (2013).D. H. Jang, Y. J. Shin and S. M. Oh, J. Electrochem. Soc., 143, 2204 (1996).C.-Y. Tang and S. J. Dillon, J. Electrochem. Soc., 163, A1660 (2016).C.-Y. Tang, R. T. Haasch and S. J. Dillon, Chem. Commun. (Cambridge, U. K.), 52, 13257 (2016).C.-Y. Tang, K. Leung, R. T. Haasch and S. J. Dillon, ACS Appl. Mater. Interfaces, 9, 33968 (2017).C.-Y. Tang, Y. Ma, R. T. Haasch, J.-H. Ouyang and S. J. Dillon, J. Phys. Chem. Lett., 8, 6226 (2017).

Mycelial Extracts as Sensitive Element for Acoustoelectronic Gas Sensor

The main problem in development of the acoustoelectronic gas sensors is the search of the elements which are sensitive to the presence of different gases. In this paper we suggest to use for this purpose the piezoelectric quartz resonators with the mycelium films of mushroom Lentinula edodes strain F-249, which was cultivated in synthetic medium. The extract of mycelium was deposited on the surface of the resonator. The measurements of the frequency dependencies of the real and imaginary parts of electrical impedance of the resonator allowed finding the density, elastic constants and viscosity of the films under study. The influence of various gases (ammonia, formaldehyde, ethylacetate) and volatile liquids (acetone, acetic acid, chloroform) on physical properties of the extracts of mushroom Lentinula edodes mycelium has been investigated. It has been found that it is possible to use the mycelium films of mushroom Lentinula edodes prepared by different ways as sensitive film to ammonia, formaldehyde and ethyl acetate.

Acousto-electronic gas sensor based on mushroom mycelial extracts

The main problem in the development of acousto-electronic gas sensors is the search for materials which are sensitive to the presence of different gases. For this purpose in this paper we suggest the use of piezoelectric quartz resonators coated by the mycelium-origin films of the mushroom Lentinula edodes strain F-249, which were cultivated in a synthetic medium. The extract of mycelium was deposited on the surface of the resonator. Measurement of the frequency dependence of the complex electrical impedance of the resonator allowed us to evaluate the density, elastic constants, and mass of the films under test. The influence of different gases, such as ammonia, formaldehyde, ethylacetate, and volatile liquids: acetone, acetic acid, chloroform on the physical properties of the extracts of Lentinula edodes mushroom mycelium was investigated. The results have shown that this material prepared according to different technological procedures is suitable as a sensitive layer for development of gas sensors for detection of ammonia, formaldehyde, and ethylacetate.

A novel gas sensor based on Ag/Fe2O3 core-shell nanocomposites

In this communication, Ag/Fe2O3 nanocomposites were successfully synthesized by reduction of silver nitrate with NaBH4 and subsequent coating of Fe2O3 by a simple Pechini sol-gel method. Synthesized powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Gas sensing properties of Ag/Fe2O3 nanocomposites and pristine Fe2O3 were studied at different temperature and in the presence of different gases. It was found that Ag/Fe2O3 sensor even can detect 500 ppb NO2 gas at 150°C, whereas pristine Fe2O3 sensor showed no significant response to NO2. The possible mechanisms of NO2 sensing by Ag/Fe2O3 are discussed in detail.

A density functional theory study for the adsorption of various gases on a caesium-exchanged trapdoor chabazite

Rational design and development of porous materials for adsorptive gas separation gains ever-increasing attention as industrial applications, such as carbon capture and natural gas purification, always require more energy-efficient processes with adsorbents providing high selectivity. Zeolite molecular sieves represent a class of such desirable adsorbents. Our recently discovered molecular trapdoor mechanism in zeolites allows for unprecedented high selectivity and affords designability for versatile adsorbents. In this work, we presented a route for identifying the molecular trapdoor mechanism and predicting the gas separation feasibility using density functional theory calculations, based on a typical molecule trapdoor zeolite – caesium-exchanged chabazite with silicon to aluminium ratio of 3. We established criteria to assess the viability for “door-open” process by examining the dependence of energy barriers for the movement of “door-keeping” cation in the presence of different gases. Calculations at the standard PBE level and the van der Waals DFT levels were carried out. This theoretical route could serve as a standard method to study and develop other molecular trapdoor zeolites.

Experimental study of asphaltene precipitation prediction during gas injection to oil reservoirs by interfacial tension measurement

• Asphaltene precipitation occurs after the surface coverage beat a threshold value. • Bond number (Bo) versus pressure is a tool for determining asphaltene precipitation. • Three distinct regions could be identified in Bo curve for the CO 2 –oil system. • In the Bo versus pressure for the CH 4 –oil, no major slope change is observed. • There is no asphaltene precipitation when injecting CH 4 to the asphaltenic oil. The worldwide increase in energy demand dictates use of enhanced oil recovery (EOR) methods to recover more oil from depleted reservoirs. Displacement of oil by gas injection process is one of these methods. Carbon dioxide (CO 2 ) and methane (CH 4 ) are gases that are mostly used to inject into oil reservoirs. These gases under different reservoir conditions fulfill either miscible or immiscible displacement conditions. Asphaltene precipitation, which could take place during gas injection, would increase the minimum miscible pressure (MMP) of an oil–gas system. Hence, this could affect the economical aspect of the injection process. In this paper, prediction of asphaltene precipitation is studied by measuring the interfacial tension (IFT) between CO 2 or CH 4 (as the displacing gas) and various oil types with different asphaltene content. Also, the mechanism of CH 4 solubility in oil containing asphaltene is analyzed. A proper tool, which is Bond number data versus pressure curve, is introduced to investigate asphaltene precipitation process in presence of different gases. When plotting Bond number against pressure for the CO 2 –oil system, three distinct intervals could be recognized. In the first interval, the oil-swelling occurs at a low pressure, in the second interval, because asphaltene accumulation happens at the gas–liquid interface, Bond number increases with a gentle slope as pressure increases; and in the third interval, more asphaltene accumulation happens when the surface coverage of the particles surpassed a threshold value (e.g., +60% surface coverage) and the rate of change in Bond number is much slower compared to the ones in the other two intervals. However, in the case of CH 4 –oil system, the Bond number increases linearly with pressure, and no significant slope change is observed.

Label-free molecular detection with capped carbon nanotubes

We present a theoretical proof-of-principle analysis of a device composed of mutually faced capped carbon nanotubes for the selective detection of hardly distinguishable gas molecules in binary mixtures (methanol/formaldehyde and H2O/H2S). Selectivity arises, on one side, from I–V responses of the sensor in the presence of different gases trapped between the nanotube caps. On the other side, the different dipole moments and polarizabilities of the molecules lead to different population probabilities in the sensing region, acting as a highly selective electrostatic trapping device. The selectivity can be tuned by the bias voltage and by the gap distance between the nanotubes.

Pressure-broadening of water transitions near 7180 cm−1 by helium isotopes

In this study, pressure-broadening parameters for several H2O transitions near 7180cm−1 are obtained which describe collisions with 3He and 4He. The sensitivity of those parameters to choice of theoretical line profile (Galatry vs. Voigt) is investigated. H2O is an important species in atmospheric chemistry and astronomy. Because of this, basic fundamental research, which explores the nature of the H2O spectrum in the presence of different gases of varying physical properties, can provide useful reference data which can be applied in the fields of atmospheric and planetary remote sensing. Measurements were made using an intensity-modulated laser photoacoustic spectrometer. Results from the present work show that Galatry line profiles, with a constrained narrowing parameter, more accurately describe experimental spectra than Voigt profiles over a wide range of experimental pressure conditions. Average pressure-broadening parameters were found to be 0.0216cm−1/atm and 0.0209cm−1/atm for H2O in 3He and 4He, respectively, and were compared to a literature model for the mass-dependence of line broadening. Specific values were obtained for each transition with nominal combined uncertainties of 2–6%.

Investigation on creeping discharges propagating over epoxy resin and glass insulators in the presence of different gases and mixtures

This paper deals with the experimental characterization of discharges propagating over insulators of epoxy and glass, immersed in a gas or a gaseous mixture, under lightning impulse voltages (1.2/50 μs), using a point-plane electrode arrangement. The gases and mixtures we considered are SF6, N2, CO2, SF6-N2 and SF6-CO2. The morphology of creeping discharges and their final lengths are investigated versus the kind of insulator material, the amplitude and polarity of the voltage, the type of the gas (resp. mixture) and its pressure. It is shown that the shape of discharges and their final (stopping) lengths Lf depend significantly on the solid insulator and the type of gas. For given solid and gas, Lf increases quasi-linearly with the voltage and decreases when the gas pressure increases. The discharges do not always present a radial structure as reported in the literature. For given voltage and pressure, Lf is longer when the point electrode is positive than when it is negative while the initiation voltage of discharges is higher with a negative point than with a positive one; and Lf is longer with glass than with epoxy. Lf is shorter in SF6 than in CO2 or N2. On the other hand, the increase of SF6 content in SF6-CO2 mixture leads to a significant decrease of Lf. Therefore, the addition of small concentration of SF6 in a given gas mixture improves the dielectric strength of insulating structure.

Free radical formation from sonolysis of water in the presence of different gases

In the present study by applying electron spin resonance-spin trapping method, when a high frequency (1650 kHz) ultrasound was irradiated to water dissolved with different gas molecules (O2, N2, Ar, Ne, He, and H2) at 25°C of water bulk temperature, free radical generation pattern differed dependently on the dissolved gas molecules. Only •OH was detected in the O2-dissolved water sample, and the amount of the radical was much greater than that determined in any of other gas-dissolved water samples. One of the possible reasons to explain why the •H radical was not detected in the O2-dissolved water is that the •H reacts with O2 to form •OOH. However, no electron spin resonance signals related to the adduct of not only 5,5-dimethyl-1-pyrroline-N-oxide but 5-(2,2-Dimethyl-1,3-propoxy cyclophosphoryl)-5-methyl-1-pyrroline N-oxide and •OOH were observed. In the H2-dissolved water, only •H was detected, suggesting that H2 reduces or neutralizes •OH. In the N2-disolved water, both •OH and •H were detected at comparable level. In the water samples dissolved with rare gases (Ar, Ne, and He), the amount of •H was almost double as compared with that of •OH, and both •OH and •H yields increased in the order Ar > Ne > He.

Chemical Degradation of Nafion Membranes under Mimic Fuel Cell Conditions as Investigated by Solid-State NMR Spectroscopy

A new ex situ method has been developed to mimic the degradation of the polymer membranes in polymer electrolyte membrane fuel cells (PEMFCs), caused by the cross-leakage of H2 and O2. In this ex situ setup, it is possible to expose membranes to flows of different gases with a controlled temperature and humidity. H+-form Nafion films with and without an electrode layer (Pt) have been treated in the presence of different gases in order to simulate the anode and cathode side of a PEMFC. The changes of the chemical structure occurring during the degradation tests were primarily examined by solid-state 19F NMR spectroscopy. For completion, liquid-state NMR studies and ion-exchange capacity measurements were performed. The molecular mobility changes of the ionomer membrane upon degradation were examined for the first time by variable-temperature 19F NMR line-shape, T1 and T1ρ relaxation experiments. It was found that degradation occurs only when both H2 and O2 are present (condition of gas cross-leakage) and when the membrane is coated with a Pt catalyst. The chemical degradation rate is found to be highest for H2-rich mixtures of H2 and O2, which corresponds to the anode under OCV conditions. It is further shown that side-chain disintegration is very important for chemical degradation, although backbone decomposition also takes place. The temperature-dependent line-width and spectral anisotropy alterations were explained by the reduction of static disorder in the Nafion membrane. From the relaxation data, there is evidence for structural annealing, which is independent of the chemical degradation. Chemical degradation is considered to reduce the chain flexibility, as expressed by smaller motional amplitudes, most probably due to chain cross-linking.

Bidimensional versus tridimensional oxygen vacancy diffusion in SnO2−x under different gas environments

Metal oxides present oxygen defects that induce different chemical and physical properties. Experiments performed in SnO(2-x) sensors show that the dynamics of these vacancies are strongly affected by the presence of different gases in the environment. Experimentally, the electrical resistance of individual metal oxide SnO(2-x) nanowires shows modulation: when the environment is oxygen rich long term drifts (hours) are observed indicating extended vacancy dynamics. Instead, if CO is present, drifts disappear in minutes. Density functional theory indicates that changes in resistance follow the extension of reoxidation. For oxygen-poor environments, oxygen vacancy excorporation and healing are confined to the near-surface layer of SnO(2-x) (bidimensional or near-surface diffusion), and completed in short times. Under oxygen-rich conditions, tridimensional diffusion of oxygen vacancies towards the surface takes place at room temperature. In this case, a push-pull mechanism allows bulk-to-surface diffusion and as a consequence resistance drifts are longer and the vacancy quenching is more extensive.