CH4 Gas Research Articles

Study of the Effect of Tetrabutylammonium Halide Aqueous Solutions on the Gas Storage of Methane and Carbon Dioxide

In this study, the effect of tetrabutylammonium halide aqueous solutions on the gas storage of CH4 and CO2 gases were studied with molecular dynamics (MD) simulations. The results show that the surface tension and the gas molecules adsorbed at the interface decreases and increases, respectively, in the presence of TBAX (X: Br, Cl, F) in the aqueous phase compared to pure water at similar gas pressures. Both of these factors may facilitate gas uptake into cages during semi-clathrate hydrate formation. CO2 showed a stronger intermolecular interaction with the water molecules since it was preferentially adsorbed at the interface, leading to a higher surface density as compared to CH4. Moreover, the relative increase in CH4 adsorption on the surface was because of the hydrophobic interactions between the CH4 molecules and the n-alkyl chains of the cation. The counter-ions of TBAXs can affect their surface activity. TBAX salts enhance the tetrahedral ordering of water molecules at the interface compared to the bulk, leading to a potential mechanism for forming semi-clathrate hydrates.

Stratospheric-trace-gas-profile retrievals from balloon-borne limb imaging of mid-infrared emission spectra

Abstract. The Limb Imaging Fourier Transform Spectrometer Experiment (LIFE) instrument is a balloon-borne prototype of a satellite instrument designed to take vertical images of atmospheric limb emission spectra in the 700–1400 cm−1 wavenumber range from the upper-troposphere–lower-stratosphere (UTLS) altitude region of the atmosphere. The prototype builds on the success of past and existing instruments while reducing the complexity of the imaging design. This paper details the results of a demonstration flight on a stabilized stratospheric balloon gondola from Timmins, Canada, in August 2019. Retrievals of vertical trace gas profiles for the important greenhouse gases H2O, O3, CH4, and N2O, as well as HNO3, are performed using an optimal estimation approach and the SASKTRAN radiative transfer model. The retrieved profiles are compared to approximately coincident observations made by the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) solar occultation and Microwave Limb Sounder (MLS) instruments. An evaluation of the LIFE measurements is performed, and areas of improvement are identified. This work increases the overall technical readiness of the approach for future balloon, aircraft, and space applications.

Geological control on carbon isotope equilibrium and kinetic fractionation of CH4-CO2-HCO3− in microbial coalbed and shale gas systems

Microbial coalbed gas (CBG) and shale gas (SG), predominately composed of methane (CH4) and carbon dioxide (CO2), are important economic resources and potent greenhouse gases. Although isotopic equilibrium of CH4 and CO2 has been observed in microbial CBG and SG basins, it is difficult to judge under what geological conditions equilibrium is achieved. Moreover, the effects of CO2 dissolution on the isotopic fractionation process need to be considered. We use data from eight microbial CBG and SG basins to discuss the geological conditions in which equilibrium and kinetic isotopic fractionation in CH4-CO2-HCO3− system is achieved. Based on isotopic equilibrium temperatures calculated using computer codes developed in MatLab software, we show that, in deep and closed reservoirs, the CH4-CO2 and CH4-HCO3− are close to carbon isotope equilibrium. In contrast, in shallow and open reservoirs, they are in disequilibrium. The CO2-HCO3− is in disequilibrium in most reservoirs. We propose that both low free energy gradients and long coexisting time of CH4 and CO2/HCO3− are necessary to attain isotopic equilibrium. However, it is difficult to accurately estimate the timescale for attaining isotope equilibrium among them. In general, a closed and deep CBG/SG reservoir is likely to be geologically and geochemically stable over long timescales, favoring isotopic equilibrium of CH4-CO2 and CH4-HCO3−. However, a shallow and open reservoir is unfavourable for their isotopic equilibrium due to shorter timescales for the coexistence of CH4-CO2-HCO3−. Using data from systems close to equilibrium, we estimated the percentage of CO2 in total CH4 and CO2 in CBG reservoirs in various basins to be from 27% to 50%, where methanogenesis is mainly by CO2 reduction. This is significantly higher than the CO2 content (1% to 15%) in gaseous CH4 and CO2 in these basins but is consistent with those (36% to 48%) from culture experiments for coal conversion by methanogenesis. Further study shows that 53–99% of the CO2 formed during CBG generation has dissolved into groundwaters to form dissolved inorganic carbon (DIC) in CBG reservoirs. We propose that CO2 dissolution likely has significantly affect the abundance and isotopic compositions of gaseous CO2 in subsurface.

Risk-assessment of carbon-dioxide recycling in a gas-fired power plant using CVaR-based convex optimization

With the rise of renewable resources’ penetration, the use of clean excessive renewable energy as the primary source of a Power to Gas (PtG) system for the reduction of CO2 pollution is quite advantageous. This paper presents a mixed integer linear formulation for modeling the optimal operation of a gas-fired power plant (GFPP)-PtG system that utilizes an excessive renewable resource, wind power, as the primary mover of the proposed PtG system for capturing and recycling the produced CO2 pollution. CO2 and CH4 gas storages are considered in the proposed PtG system to boost the operational efficiency of the system. Additionally, the scenario generation method models both wind power generation and electrical demand. The effective conditional value at risk (CVaR) method, which is a convex risk modeling approach, models the risks imposed by the generated scenarios for wind power and electrical demand. Due to the convexity of the proposed formulation for the PtG system and the risk modeling method, the ultimate model can be simply solved by using any available LP solver. To evaluate the outcomes of an optimization problem based on CVaR, a comparative analysis is conducted with chance constraints programming, which demonstrates the optimality and computational efficiency of the CVaR results due to convexity. The effectiveness of the proposed model is approved by modeling a test system based on real data, and the obtained numerical results are discussed comprehensively.

CMOS AlN and ScAlN Pyroelectric Detectors with Optical Enhancement for Detection of CO2 and CH4 Gases

AbstractGas sensors are useful for monitoring of greenhouse gases. As the move toward complementary metal‐oxide‐semiconductor (CMOS) compatible pyroelectric room temperature detectors is gaining traction due to its scalability to 8‐in./12‐in. wafer area and integrable with CMOS electronics, CMOS compatible aluminum nitride (AlN)‐ and scandium aluminum nitride (ScAlN)‐based pyroelectric detectors are developed for sensing of CO2and CH4gases, which are two of the greenhouse gases that contribute significantly to global warming. Leveraging gas absorption at respective mid‐infrared (IR) wavelengths, CO2 and CH4 gases are detected at various concentrations with fast response time ≈1 s. A compound parabolic collector (CPC) is designed and integrated into the gas sensor to enhance the optical flux received by the detector, which demonstrates ≈10× signal improvement in its presence. Further factors such as the effect of sensing area reduction and response to random gas concentrations are also tested on AlN‐ and ScAlN‐based pyroelectric detectors respectively to observe the gas sensing behaviors of both detectors. The results obtained provide further understanding of the behavior of CMOS AlN‐ and ScAlN‐based pyroelectric detectors as IR gas sensors, which can potentially inspire new design and design selection for various gas sensing applications.

Adsorption of SF6 gas and insulating oil decomposition gas by CoO-doped SnSe monolayer in various environments: A study of strong adsorption performance

Taking into account that Sulfur hexafluoride (SF6) gas leakage can result in environmental pollution, the insulating oil used in high-voltage equipment can decompose into various detectable dissolved gases, allowing for the monitoring of its operational status. In this study, we use a CoO-doped SnSe (SnSe-CoO) monolayer to achieve strong adsorption of SF6 gas, CO, and C2H2 gas, and highly sensitive monitoring of H2 and CH4. Thus, the SnSe-CoO monolayer can serve as an adsorbent for SF6 gas leakage and a material for monitoring insulating oil-dissolved gas. Furthermore, we also observed that the adsorption energy of each gas on the intrinsic material increases with the solvent dielectric constant, facilitating the control of gas adsorption. Our research provides a significant theoretical foundation for future adsorption and monitoring of insulating gases and insulating oil decomposition gases.

Bituminous Coal Sorption Characteristics and Its Modeling of the Main Coal Seam Gas Component in the Huaibei Coalfield, China

Knowledge of the gas sorption and permeability characteristics of a coal provides an essential basis for the evaluation of coalbed methane reserves and their recoverability. Thus, the gas excess sorption capacities of the main gas component of coal seam gas (CSG) in bituminous coal samples derived from the Xutuan Coal Mine in the Huaibei Coalfield, in the Anhui Province of China, were measured using a volumetric method. The results showed that under the same equilibrium pressure, the order of excess sorption capacity was CO2 > CH4 > N2. Furthermore, the sorption capacity ratios of coal from the Xutuan Mine for CO2, CH4, and N2 were approximately 6.0:2.3:1. It was also demonstrated that the sorption capacity during depressurization was always larger than that of the adsorption process, which is indicative of desorption hysteresis. The behaviors of three adsorption models, Langmuir, BET, and D-R, all of which include two parameters, are considered in this paper. The different gas sorption measurement data were fitted by the three models. For the bituminous coal samples, the fits of the D-R equation of all three different gases are higher than 0.99, the fits of the Langmuir equation are higher than 0.985, while the fits of the BET equation for CH4 and N2 absorption are higher than 0.95. However, the fits of the BET equation for CO2 absorption are only about 0.5. Coal sorption has an apparent influence on coal permeability; the permeability of the same coal sample to N2, CH4, and CO2 gases was tested and analyzed. The result shows that the permeability of CO2 was found to be lower than that of other coal seam gas constituents, CH4 and N2, due to their different adsorption abilities.

Compact optical fiber photoacoustic gas sensor with integrated multi-pass cell

Optical fiber acoustic sensors with miniature size and high sensitivity are attractive to develop compact photoacoustic spectroscopy. Here, a compact photoacoustic gas sensor was demonstrated by utilizing a diaphragm-based fiber-optic Fabry-Perot cavity as both the acoustic sensor and the multipass cell. A nanoscale graphite film was used as the flexible diaphragm to increase the acoustic sensitivity of the Fabry-Perot cavity and the cavity inner surface was coated with highly-reflective Au film to form a multipass cell for amplification of the photoacoustic signal. With a laser power of 20 mW at 1532.8 nm, the sensor demonstrated a low detection limit of ∼ 50 ppb for C2H2 gas with an integration time of ∼ 100 s. The optical fiber photoacoustic gas sensor with a millimeter-scale diameter and ppb-level detection limit is promising for trace gas sensing in various areas including industrial process and environmental monitoring.

Polyvinylidene Fluoride (PVDF) / Poly (Ether Sulfones) (PES) Blend Membrane For CO2/CH4 Separation

In this study, a combination of Polyvinylidene fluoride (PVDF) and Poly (ether sulfones) (PES) blend membrane and DMF as solvent component was developed to evaluate the CO2 and CH4 separation performance. The gas permeation test was thereafter conducted on the membrane produced. The separation through a membrane works on the theory of permeation based on permeability and selectivity. These two important values were estimated using a set of analytical functions. The membranes produced was then characterized using scanning electron microscopy (SEM) and the Fourier Transform Infrared Spectroscopy (FTIR). The result obtained revealed that a higher permeability for the CO2 and CH4 gases when the blending ratio of membrane and solvent of PVDF:PES:DMF/ 5:15:80 were applied. Moreover, the selectivity results showed that the use of the blending ratio of PVDF:PES:DMF/ 20:0:80 produce the highest selectivity (1.3086 GPU) while blending ratio of PVDF:PES:DMF/ 10:10:80 exhibited the least selectivity. In addition, the morphological elucidation revealed the presence of pores for every cross-section composite membrane and this aids the permeability properties of the membrane aggregates at different blending ratio. Also, the FTIR results showed nearly similar functional group characteristics.

Synthesis, characterization, and selective gas adsorption performance of hybrid NH2-MIL-101(Fe)/ZIF-8 metal organic framework (MOF)

In this paper, an efficient NH2-MIL-101(Fe)/ZIF-8 metal organic framework (MOF) with tunable pore architecture was synthesized by an internal extended growth approach, using polyvinylpyrrolidone (PVP) as a regulator. In the resultant structure, the larger-pore MOF (NH2-MIL-101(Fe)) provides the facilitated transport pathways and the smaller-pore MOF (ZIF-8) acts as the shell, enhancing the molecular sieving properties. The synthesized MOFs were characterized by FESEM, EDS, HRTEM, FTIR, XRD, TGA, and BET analyses, and the hybrid structure formation was accordingly approved. Furthermore, the pure gas adsorption measurements were conducted for CO2, N2, CH4, C2H6, and C2H4 gases at 298 and 328 K and equilibrium pressures up to 4 bar. The CO2 adsorption capacity of 3.982 mmol g−1 at 298 K for NH2-MIL-101(Fe)/ZIF-8 was obtained, which is ∼43% and ∼127% higher than the values for the individual MOFs, respectively. This increase is mainly attributed to the favorable CO2 interactions with the unpaired electrons of nitrogen (amine functional groups and imidazole nitrogen) as well as oxygen atoms along with unsaturated metal sites present in the both MOFs. In addition, the beneficial size exclusion effect of the shell MOF, resulted in improved gas adsorption selectivity values. The synthesized hybrid structure displayed considerably higher CO2/N2 and CO2/CH4 adsorption selectivities, which were ∼3.8 and 1.7 times greater than those of the pristine NH2-MIL-101(Fe) MOF, respectively. Furthermore, the C2H6/C2H4 selectivity of NH2-MIL-101(Fe)/ZIF-8 was raised by ∼48%, compared to the NH2-MIL-101(Fe) MOF, owning to the molecular sieving effect of ZIF-8 for C2H6 with larger kinetic diameter compared to C2H4.

A theoretical probe into the separation of CO2/CH4/N2 mixtures with polysulfone/polydimethylsiloxane–nano zinc oxide MMM

In the current investigation, molecular dynamics (MD) and Grand Canonical Monte Carlo (GCMC) simulation as remarkable and competent approaches have been employed for understanding structural and transport properties of MMMs in the realm of gas separation. The two commonly used polymers i.e. polysulfone (Psf) and polydimethylsiloxane (PDMS) as well as zinc oxide (ZnO) nanoparticle (NP) were used to carefully examine the transport properties of three light gasses (CO2, N2 and CH4) through simple Psf, Psf/PDMS composite loaded by different amounts of ZnO NP. Also, the fractional free volume (FFV), X-ray diffraction (XRD), glass transition temperature (Tg), and Equilibrium density were calculated to scrutinize the structural characterizations of the membranes. Moreover, the effect of feed pressure (4–16 bar) on gas separation performance of simulated MMMs was investigated. Results obtained in different experiments showed a clear improvement in the performance of simulated membranes by adding PDMS to PSf matrix. The selectivity of studied MMMs was in the range from 50.91 to 63.05 at pressures varying from 4 to 16 bar for the CO2/N2 gas pair, whereas the corresponding value for CO2/CH4 system was found to be in the range 27.27–46.24. For 6 wt% ZnO in 80%PSf + 20%PDMS membrane, high permeabilities of 78.02, 2.86 and 1.33 barrers were observed for CO2, CH4 and N2 gases, respectively. The 90%PSf + 10%PDMS membrane with 2% ZnO had a highest CO2/N2 selectivity value of 63.05 and its CO2 permeability at 8 bar was 57 barrer.

N-doped sponge-like biochar: A promising CO2 sorbent for CO₂/CH₄ and CO2/N₂ gas separation

Sponge-like biochar sorbents were prepared from the dissolution of chitosan followed by freeze-drying methodology and pyrolysis at three different temperatures (400, 600, and 800 °C) to produce sustainable N-enriched carbon materials with enhanced CO2 uptake from CO2/CH4 and CO2/N2 gas mixtures. The pyrolysis process was reproduced by operando TGA-IR to study the gas evolved from the pyrolysis process. It was found that the pyrolysis temperature highly influences the textural properties of the chitosan sponge-like biochar materials, impacting mainly the amount and type of the N-species on the sample but also at the microporosity. XPS revealed the transformation of the amino groups from chitosan into pyridinic-N, pyrrolic-N, graphitic center-N, and graphitic valley-N or pyridine-N oxide species during the pyrolysis process. Increasing the pyrolysis temperature enhanced the quantity of the latter two N-type species. All sponge-like biochars adsorbed higher amounts of CO2 compared with CH4 and N2 gases, with maximum CO2 uptake (∼1.6 mmol⋅g−1) at 100 kPa and 25 °C for the sample pyrolyzed at 600 °C (named CTO_P600). Biochar produced at 800 °C showed no longer adsorption capacity for CH4 and N2, having the highest selectivity value for CO2/N2 separation under continuous flux conditions among all prepared biochar sorbents. Isobaric CO2 adsorption measurements on the CTO_P600 sorbent revealed that physisorption phenomena predominantly governed the CO2 adsorption process, which was confirmed by its consistent adsorption capacity after 10 consecutive adsorption–desorption cycles. Moreover, the biochar exhibited tolerance to water vapor adsorption, indicating its suitability to work under moisture-rich conditions.

Waste to energy: An experimental study on hydrogen production from food waste gasification

Though food scarcity realizing in many places in the world, food waste generation still shows its increasing trend because of cultural and habitual changes, as well as technological characteristics. However, food waste comprises a large amount of organic material and biodegradable components, showing that it could be a potential source for producing hydrogen (H2) aiming to satisfy the key goals of diversifying the energy supply and reducing environmental pollution. Indeed, this research addresses the potential possibilities to use food waste for the production of H2 by using a water gasification reactor. In this work, food waste was gasified by varying the operating parameters in the H2 production process and the addition of additives. In this investigation, different additives such as HCl, NaCl, and NaHCO3 were considered to investigate at different reactor temperatures like 300, 350, and 400 °C for different reaction durations like 30, 45, and 60 min. The results revealed that the best average yields of CH4, H2, CO2, CO, and total gas were obtained as 1.5, 12.9, 0.2, 0.1, and 13.9 mol/kg, respectively, when the reaction employed with NaHCO3 additive than the other cases (with HCl, NaCl additives and no additive cases). The H2 production efficiency was estimated as 43%, 34%, 27%, and 30% when the use of NaHCO3, NaCl, HCl, and no additives. Hence, it is found that the NaHCO3 catalyst considerably enhances the gasification process through the improvement of the water-gas shift reaction, and thereby H2 production increases.

Hydrogen Production from Gadolinium-Promoted Yttrium-Zirconium-Supported Ni Catalysts through Dry Methane Reforming.

Hydrogen production from dry reforming of methane (DRM) not only concerns with green energy but also involves the consumption of two greenhouse gases CH4 and CO2. The lattice oxygen endowing capacity, thermostability, and efficient anchoring of Ni has brought the attention of the DRM community over the yttria-zirconia-supported Ni system (Ni/Y + Zr). Herein, Gd-promoted Ni/Y + Zr is characterized and investigated for hydrogen production through DRM. The H2-TPR → CO2-TPD → H2-TPR cyclic experiment indicates that most of the catalytic active site (Ni) remains present during the DRM reaction over all catalyst systems. Upon Y addition, the tetragonal zirconia-yttrium oxide phase stabilizes the support. Gadolinium promotional addition up to 4 wt % modifies the surface by formation of the cubic zirconium gadolinium oxide phase, limits the size of NiO, and makes reducible NiO moderately interacted species available over the catalyst surface and resists coke deposition. The 5Ni4Gd/Y + Zr catalyst shows about ∼80% yield of hydrogen constantly up to 24 h at 800 °C.

Investigation of the tribological characteristics of Ta–Zr–Si–B–C–N coatings

Ta–Zr–Si–B–C–N coatings were deposited by magnetron sputtering using a TaSi2–Ta3B4–(Ta, Zr)B2 composite target. Ar, as well as Ar + N2 and Ar + C2H4 gas mixtures, were used as the working gas. The structure and composition of the coatings were studied by scanning electron microscopy, glow-discharge optical emission spectroscopy, and X-ray diffraction. A Calowear tester was used to measure the thickness and abrasion resistance of the coatings. Erosion resistance tests were carried out using a UZDN-2T (Russia) ultrasonic disperser. Tribological tests in the sliding friction mode were carried out on an HT Tribometer (CSM Instruments, Switzerland) automated friction machine. The wear zone after tribological testing was examined using a Veeco Wyko 1100 (Veeco, USA) optical profiler. The results showed that the Ta–Zr–Si–B coating was characterised by a columnar structure with an h-TaSi2 crystallite size of 11 nm. The introduction of nitrogen and carbon into the composition of the coatings led to the suppression of columnar growth and a ~2–4-fold decrease in the size of h-TaSi2 crystallites. Carboncontaining coatings demonstrated the best abrasive resistance. The sliding friction tests showed that the Ta–Zr–Si–B coating is characterised by a stable coefficient of friction of 0.3 at a temperature of 25 °C up to the maximum working temperature of 250 °C. The introduction of nitrogen led to an increase in the coefficient of friction up to 0.8–1.0 at a t = 50÷110 °С. The coating with the minimum carbon concentration showed a stable coefficient of friction of ~0.3 up to a maximum temperature of 250 °C. The best result was demonstrated by the sample containing the maximum amount of carbon, with its coefficient of friction remaining at the 0.25 level up to a temperature of 350 °C.

Effective UV–visible-infrared light-driven photothermocatalytic dry reforming of methane on Ni/Ni-MgO caused by a novel synergetic effect and photoactivation

Light-driven photothermocatalytic dry reforming of methane (DRM) is a promising technology which can efficiently convert two greenhouse gases of CO2 and CH4 into fuels and realize effective solar energy storage simultaneously. It is greatly challenging to achieve high fuel production rate with a relatively low light intensity and restrain the coking side-reactions that cause catalyst deactivation. Herein, a novel nanocomposite of Ni nanoparticles (NPs) loaded on Ni-doped MgO (Ni/Ni-MgO) was prepared. Very high production rate (r) of H2 and CO (82.78 mmol min−1 g−1 and 98.05 mmol min−1 g−1) as well as a light-to-fuel efficiency (η, 28.8%) are obtained with concentrated UV–vis IR irradiation at a relatively low light intensity (78.8 kw m−2). Ni/Ni-MgO displays excellent durability due to its very low coking rate of 2.46 × 10−3 gc h−1 g−1catalyst, reduced by 11.6 times as compared to that of a reference sample of Ni NPs loaded on MgO (Ni/MgO). This is attributed to a synergetic effect between Ni NPs and Ni-MgO, in which the active oxygen of Ni-doped MgO participates in the oxidation of carbon species as one of the rate-determining steps of DRM, thus facilitating DRM on Ni NPs and greatly improving coking resistance. A photoactivation is found to greatly reduce activation energy and thus enhances catalytic activity due to the substantial facilitation of carbon oxidation by light irradiation.

Separation of CH4 - CO2 gas mixture by gas hydrate crystallisation: A parametric study

In the present study a comprehensive experimental study of the CO2 gas hydrate recovery from the CH4 (81.70 mol.%) - CO2 (18.30 mol.%) experimental gas mixture was realised. The effect of the mode, temperature, pressure, and promoter on the CO2 gas hydrate recovery efficiency was investigated. The parametric study will optimise the technology of gas hydrate crystallisation to CO2 remove from natural gas. The gas mixture process separation factor and gas hydrate recovery were studied in SDS (0.30 wt%) aqueous solutions with and without THF (3.80 wt%). The separation simulation was performed for the two modes: pressure-dropping and constant pressure in the temperature range 272.15–283.15 К at the driving forces 1.00 and 2.00 MPa 8 h after the start of the gas hydrate formation. The different temperature dependence is shown for the CH4 and CO2 gas hydrate recovery in depending on the aqueous solution. The CO2 gas hydrate recovery maximum, equal to 63.92% (without THF) and 57.19% (with THF), is observed at the constant pressure separation at 272.15 K and 2.00 MPa. However, THF addition makes it possible to decrease the gas hydrate dissociation pressure of the experimental gas mixture in 7.87 times at 272.15 K. Thus, the choice of the aqueous solution was determined by the aim for the gas hydrate separation – high gas hydrate recovery (without THF) or low process pressure (with THF).

Simultaneous detection of CH4 and CO2 through dual modulation off-axis integrated cavity output spectroscopy

This study established a novel method for the simultaneous detection of two-component gases. Radio frequency (RF) white noise disturbance laser current and wavelength modulation were simultaneously used to improve the off-axis integrated cavity output spectroscopy technique, and a high-precision dual modulation OA-ICOS (RF-WM-OA-ICOS) system was established. The two laser beams were coupled into one laser beam that was applied incident to the cavity of RF-WM-OA-ICOS system. The second harmonic signals of CH4 and CO2 gas simultaneously appeared in the rising or falling edge of a triangular wave. This method was used to measure CH4 and CO2 with different concentrations. The results indicated that the proposed system has high stability and can accurately and simultaneously measure the concentrations of CH4 and CO2, with an optimal integration time of 220 s. The minimum detection limit was 10 ppb for CH4 and 1.5 ppm for CO2. The corresponding noise equivalent absorption sensitivity values were calculated as 2.67 × 10−13 cm−1⋅Hz−1/2 and 5.18 × 10−11 cm−1⋅Hz−1/2, respectively. The proposed dual-component gas simultaneous detection method can also be used for high-precision simultaneous detection of other gases. Therefore, this study may serve as a reference for developing portable multicomponent gas analyzers.

High Sensitivity Low-Temperature Hydrogen Sensors Based on SnO2/κ(ε)-Ga2O3:Sn Heterostructure

The structural and gas-sensitive properties of n-N SnO2/κ(ε)-Ga2O3:Sn heterostructures were investigated in detail for the first time. The κ(ε)-Ga2O3:Sn and SnO2 films were grown by the halide vapor phase epitaxy and the high-frequency magnetron sputtering, respectively. The gas sensor response and speed of operation of the structures under H2 exposure exceeded the corresponding values of single κ(ε)-Ga2O3:Sn and SnO2 films within the temperature range of 25–175 °C. Meanwhile, the investigated heterostructures demonstrated a low response to CO, NH3, and CH4 gases and a high response to NO2, even at low concentrations of 100 ppm. The current responses of the SnO2/κ(ε)-Ga2O3:Sn structure to 104 ppm of H2 and 100 ppm of NO2 were 30–47 arb. un. and 3.7 arb. un., correspondingly, at a temperature of 125 °C. The increase in the sensitivity of heterostructures at low temperatures is explained by a rise of the electron concentration and a change of a microrelief of the SnO2 film surface when depositing on κ(ε)-Ga2O3:Sn. The SnO2/κ(ε)-Ga2O3:Sn heterostructures, having high gas sensitivity over a wide operating temperature range, can find application in various fields.

A novel modeling strategy for the prediction on the concentration of H2 and CH4 in raw coke oven gas

A novel modeling strategy for the prediction on the concentration of H2 and CH4 in raw coke oven gas