Low Gas Concentrations Research Articles

Research on the business model of Financing of Capitalized Carbon Quota based on blockchain intelligent integrated energy management and control system

The carbon emission trading in China is mainly managed by a centralized system, with too much administrative intervention and a lack transparent trading information. This has led to the inactivity of the carbon trading market. To innovate the carbon market in China and help small and medium-sized carbon reduction enterprises to achieve the “dual carbon” target, the essay firstly launches a research on the intelligent integrated energy control system (including data uploaded to blockchain, data capitalization and carbon pool bank) based on the low-concentration gas treatment project of Shizuishan abandoned coalmine. The system solves the problems of non-transparent data utilization of abandoned coalmine gas and launches the full life circle carbon trace management mechanism for carbon emission and trading. Secondly, based on the energy control system, the Financing of Capitalized Carbon Quota by Blockchain (FCCQB) business model has been proposed for the first time in China to solve the problem of financing difficulties, lack of financing channels and inadequate policy support for small and medium-sized carbon reduction enterprises. The carbon trading market has achieved interconnectivity and high efficiency by the traceable and indispensable characteristics of blockchain. Besides, the FCCQB business model can be promoted in various industrial parks and enterprise gathering areas across the country.

Preparation and characterization of Titanium oxide-composite polymers

Two types of monomers polyindole and poly m-aminophenol were used to prepare conducting copolymer with use FeCl3 as an initiator by using chemical polymerization. The prepared polymers were characterized using infrared spectroscopy, X-ray scattering, scanning electron microscope (SEM) and thermal analysis TGA. This study was included preparation of copolymers from both monomers in various ratios (1:1, 1:2, 2:1, 1:3, and 3:1) to study the effect of ratios on chemical and physical properties. Moreover, nano-metal oxide (TiO2) (10%) of the weight of the monomers was added to copolymers to synthesis composite polymers. Results of FTIR, SEM and EDX were proved the prepared compounds. TGA findings were showed that composites have remarkably increased of thermal stability. Finally, nano-composite polymers have applied as electrochemical sensor for (NH3) gas. Further, results display that the best sensitivity value is (24.12%) by using copolymer (1mA:3In) (without nano) with response time (7 seconds) and recovery time (3 seconds). Furthermore, results show that prepared nanocomposites have highly sensitive features with fast responses time even within a low concentration of ammonia gas at 25° C. The highest sensitivity value (79.14%), response time (3 seconds) and recovery time (3 seconds) was recorded when used nanocomposite titanium oxide (TiO2) at the ratio (1mA:3In).

Low-cost NO2 trace concentration measuring device using a broadband diode laser and a customized cavity

A low-cost NO2 trace concentration measuring device based on a cavity ring-down spectroscopy (CRDS) technique is presented. We theoretically and experimentally demonstrate that, if the nonresonant direct reflection is effectively isolated, an inexpensive broadband diode laser (LD) can excite multiple cavity modes and stabilize the cavity output signal with an optical feedback (OF) method. To improve the measuring accuracy for low concentrations of NO2 gases, we also design and machine a cavity with several mixing rooms. Several standard concentrations NO2 gases are used to test the apparatus. The results prove a great agreement between measured and theoretical values over the full range.

MoO3/Ti3C2Tx MXene nanocomposites with rapid response for enhanced ethanol-sensing at a low temperature

Ethanol, as one of the most widely used volatile organic compounds (VOCs), can cause serious harm to the human respiratory system when exposed to low concentrations of ethanol gas for a long time. Here, we successfully prepared MoO3/Ti3C2Tx MXene nanocomposites by a simple hydrothermal synthesis method, realizing the effective monitoring of low-concentration ethanol gas (1.61@1 ppm). The specific surface area of MoO3/Ti3C2Tx MXene nanocomposites (61.044 m2/g) is doubled compared with Ti3C2Tx MXene (33.385 m2/g), which provides more reaction centers and active sites for ethanol molecules. Meanwhile, the gas-sensing results revealed that MoO3/Ti3C2Tx MXene nanocomposites show outstanding selectivity and reproducibility, as well as fast response-recovery (10/49 s). Subsequently, the possible sensing mechanism of the composite was further discussed in detail in combination with density functional theory (DFT). This work provides a new sensing design strategy for detecting VOCs at low-temperature.

Enhanced Gas Sensitivity of Au-Decorated Flowery WSe2 Nanostructures.

With the continuous improvement in material life, people are paying more and more attention to air quality; therefore, it is critical to design efficient and stable gas sensor devices. In this work, a flowery WSe2 nanostructure and its nanocomposite (Au@WSe2) decorated with Au nanoparticles were fabricated by the hydrothermal method. The performance of a resistive sensor with flowery WSe2 and Au@WSe2 sensors was evaluated by detecting volatile organic compounds such as ethanol, isoamylol, n-butyl alcohol, isopropanol, isobutanol and n-propanol. The results show that Au-nanoparticle-decorated flowery WSe2 can decrease the optimal working temperature from 215 °C to 205 °C and significantly enhance the response of flowery WSe2. The response values to isoamylol are the highest (as high as 44.5) at a low gas concentration (100 ppm), while the response values to ethanol are the highest (as high as 178.5) at a high gas concentration (1000 ppm) among the six different alcohols. Moreover, the response is steady and repeatable. The results demonstrate that the Au@WSe2 substrate has good responsiveness and selectivity, which makes it a promising candidate for gas detection.

A Multi-Model Prediction Method for Coal Mine Gas Concentration with Hierarchical Structure

ABSTRACT The low concentration of gas in the gas blending process is influenced by a number of factors and is characterized by some time variation and non-linearity. Therefore, the gas concentration needs to be predicted. This paper proposes a multi-model forecasting method with a hierarchical structure. First, because the measured gas concentration time-series data contain a lot of noise, the time-series data are decomposed into several independent eigenmode functions by using empirical mode decomposition, adaptively denoising by low-pass filtering, and then using phase space reconstruction technology to obtain a new time-series sample. Then, the training samples are grouped by conditional fuzzy clustering to determine the number of sub-modules. Finally, the maximum membership method is used to select sub-models and sub-sub-models, and then a multi-model time-series prediction model is established. The model can not only select different sub-models to process data in different regions but also can process each data jointly by multiple sub-models in different sub-models. Experiments were carried out on low-concentration measured data extracted from mines. The experimental results show that the proposed prediction model can capture the nonlinear characteristics of gas concentration time series and is superior to other existing prediction models in accuracy.

Nanostructured Diamond Composites for Multifunctional Sensing Applications

We report studies of multifunctional, nanostructured diamond composites that were fabricated using chemical vapor deposition (CVD) techniques. Grain sizes from micrometer, to submicron, nano, and ultrananocrystalline diamond (UNCD) were controlled by varying CH4, hydrogen, and argon gas concentrations during the syntheses. Scanning electron microscopy (SEM) and Raman scattering spectroscopy were used to investigate the morphologies, composites, and crystallinities of the films. Four multifunctional sensor prototypes were designed, fabricated, and tested, based on the four diamond materials of different grain sizes. The responses of the four prototypes to either pollution gas or UV light illumination were systematically investigated at different operating temperatures. Experimental data indicated the obtained UNCD composite from the low-cost simple CVD fabrication technique appeared to have very good sensitivities when exposed to low concentrations of H2 or NH3 gas with a decent response and fast recovery time. Furthermore, highly induced photocurrents from both microdiamond- and UNCD-based prototypes to deep UV illumination were also demonstrated, with responsivities up to 2750 mA/W and 550 mA/W at 250 nm wavelength, respectively. Overall, the fabricated UNCD prototypes displayed a good balance in performance for multifunctional sensor applications in terms of responsivity, stability, and repeatability.

Highly vertical 3D bio-inspired hierarchical and multiscale superstructures on microcantilever for gas sensing of organophosphorous agents

Microgravimetric sensors offer promising solution to detect volatile compounds. However, they suffer from a low surface-to-volume ratio limiting the maximum amount of adsorbate that can be fixed on their 2D surface. In this study, we report a bio-inspired method to elaborate highly vertical 3D hierarchical and multiscale superstructures in order to greatly increase the surface area of the microcantilever and to capture more molecules in vapor phase. However, building such superstructures on the microcantilever surface remains challenging in terms of structural design and synthesis while preserving a sufficient response of the sensor at low gas concentration. These particular superstructures are inspired from the antenna of the silkmoth Bombyx mori which is composed of a stem with branches on either side, themselves covered with sensilla. A patterned-microcantilever with high-aspect-ratio silicon micropillars is therefore used as support to generate a dense array of titanium dioxide nanorods decorated by goethite nanobranches. 3D hierarchical superstructures show a high enhancement in the response of the sensor to vapor of dimethyl methylphosphonate, a common simulant of sarin considered as one of the most toxic molecules. This design generates mass and surface stress effects under exposure to low vapor concentrations allowing to reach a limit of detection of 3 ppb. The sensor shows also a fast response to a wide range of concentrations. These results provide promising prospects to improve the detection potential of microcantilever-based sensors by using complex superstructures and dedicated materials to generate stress effect on the microcantilever surface and overcome the conventional microcantilever sensors based only on mass variation.

Star-forming and gas-rich brightest cluster galaxies at z ∼ 0.4 in the Kilo-Degree Survey

Brightest cluster galaxies (BCGs) are typically massive ellipticals at the centers of clusters. They are believed to experience strong environmental processing, and their mass assembly and star formation history are still debated. We have selected three star-forming BCGs in the equatorial field of the Kilo-Degree Survey (KiDS). They are KiDS 0920 (z = 0.3216), KiDS 1220 (z = 0.3886), and KiDS 1444 (z = 0.4417). We have observed them with the IRAM 30 m telescope in the first three CO transitions. We remarkably detected all BCGs at high signal-to-noise ratio, S/N ≃ (3.8 − 10.2), for a total of seven detected lines out of eight, corresponding to a success rate of 88%. This allows us to double the number of distant BCGs with clear detections in at least two CO lines. We then combined our observations with available stellar, star formation, and dust properties of the BCGs and compared them with a sample of ∼100 distant cluster galaxies with observations in CO. Our analysis yields large molecular gas reservoirs MH2 ≃ (0.5 − 1.4)×1011 M⊙, high excitation ratios r31 = LCO(3→2)′/LCO(1→0)′ ≃ (0.1 − 0.3), long depletion times τdep ≃ (2 − 4) Gyr, and high MH2/Mdust ≃ (170 − 300) for the three targeted BCGs. The excitation ratio r31 of intermediate-z BCGs, including RX1532 and M1932 from previous studies, appears to be well correlated with the star formation rate and efficiency, which suggests that excited gas is found only in highly star-forming and cool-core BCGs. By performing color-magnitude plots and a red-sequence modeling, we find that recent bursts of star formation are needed to explain the fact that the BCGs are measurably bluer than photometrically selected cluster members. To explain the global observed phenomenology, we suggest that a substantial amount of the molecular gas has been accreted by the KiDS BCGs but still not efficiently converted into stars. KiDS 1220 also shows a double-horn emission in CO(3→2), which implies a low gas concentration. The modeling of the spectrum yields an extended molecular gas reservoir of ∼9 kpc, which is reminiscent of the mature extended-disk phase observed in some local BCGs.

ZnO/Ti3C2 composite with oxygen vacancies and Schottky barrier for effective detection of ppb-level NO2 at room temperature

Room-temperature detection of low concentrations of toxic and harmful gases is of great significance for the health and life of human being and contributes to long-term stability and low power consumption of gas sensors. In this work, we firstly prepared a ZnO1-x/Ti3C2 composite with rich oxygen vacancies by a hydrothermal process and subsequent annealing in hydrogen atmosphere. The experimental results reveal that the ZnO1-x/Ti3C2 composite exhibits very high responses (ΔR/Ra) of 0.03, 0.21 and 2.28 to 0.01, 1 and 10 ppm NO2 at room temperature, among which the response to 10 ppm NO2 is 2.3 and 14.2 times higher than those of ZnO/Ti3C2 composite and pristine Ti3C2, respectively. Moreover, the ZnO1-x/Ti3C2 composite presents good linear response (R2 = 0.99509), reproducibility and long-term stability to NO2. The outstanding NO2 sensing properties of ZnO1-x/Ti3C2 composite are mainly attributed to the presence of abundant oxygen vacancies and the formation of ZnO1-x/Ti3C2 Schottky barrier. Both the gas responses and calculated adsorption energies of ZnO1-x/Ti3C2 and ZnO/Ti3C2 composites to NO2, NH3, CO, HCHO and acetone demonstrate the high selectivity of the ZnO1-x/Ti3C2 composite to NO2. This work provides a new perspective on enhancing the room-temperature gas sensitivity of MOS-containing composites by constructing oxygen vacancies and heterojunction.

The Effect of Rare Earths on the Response of Photo UV-Activate ZnO Gas Sensors.

In this work, ZnO nanoparticle resistive sensors decorated with rare earths (REs; including Er, Tb, Eu and Dy) were used at room temperature to detect atmospheric pollutant gases (NO2, CO and CH4). Sensitive films were prepared by drop casting from aqueous solutions of ZnO nanoparticles (NPs) and trivalent RE ions. The sensors were continuously illuminated by ultraviolet light during the detection processes. The effect of photoactivation of the sensitive films was studied, as well as the influence of humidity on the response of the sensors to polluting gases. Comparative studies on the detection properties of the sensors showed how the presence of REs increased the response to the gases detected. Low concentrations of pollutant gases (50 ppb NO2, 1 ppm CO and 3 ppm CH4) were detected at room temperature. The detection mechanisms were then discussed in terms of the possible oxidation-reduction (redox) reaction in both dry and humid air atmospheres.

Fabrication of Na0.4MnO2 Microrods for Room-Temperature Oxidation of Sulfurous Gases.

Phase pure Na0.4MnO2 microrods crystallized in the orthorhombic symmetry were fabricated for the wet oxidation of H2S and SO2 gases at room temperature. The material was found highly effective for the mineralization of low concentrations of acidic gases. The material was fully regenerable after soaking in a basic H2O2 solution.

Impact of PM10 Particles on the Measurement Error of SO2 Electrochemical Gas Sensor

To address the problems of poor measurement accuracy and long service life of SO2 electrochemical gas sensors when used in thermal power plant areas, fly ash emitted from a thermal power plant in China was used as the research object. Based on the analysis of the morphological characteristics of fly ash particles, theoretical calculations were used to obtain the settling speed of fly ash particles and the amount of fly ash deposited at different times, and then the impact of fly ash on the measurement error of a SO2 electrochemical gas sensor was investigated by experimental tests. The research results show that the particle size distribution of fly ash is 2–11 μm, the average settling speed of fly ash particles is 1.34 × 10−3 m/s, and the deposition amount of fly ash on the surface of the sensor inlet film is 0.95 mg per day. The deposition time of fly ash affects the sensor measurement error, and the longer the deposition time, the larger the sensor measurement error, which is due to the reduction of gas diffusion area S and diffusion coefficient K in the sensor caused by fly ash deposition. Fly ash deposition has a greater impact on the sensor when measuring low concentration gases. The higher the gas concentration, the lower the measurement error, because the higher the gas concentration, the faster the gas reaches the working electrode area and the higher the effective SO2 concentration detected in the limited response time. When using SO2 electrochemical sensors in environments with high concentrations of fly ash or dust, it is recommended to install dust-proof devices (such as air-permeable filter membranes with a pore size of less than 4 μm) and regularly clean the deposited fly ash, which can improve the accuracy of the sensor measurement and extend the service life.

Hydrogen Sulfide Gas Detection in ppb Levels at Room Temperature with a Printed, Flexible, Disposable In2O3 NPs‐Based Sensor for IoT Food Packaging Applications

AbstractFlexible printed sensors are essential components for modern Internet of Things applications. They may twist and bend to fit any shape or surface. New potential applications emerge as these sensors’ sophistication and sensing efficiency improve. In this study, a printed sensor is prepared from indium oxide nanoparticles (In2O3 NPs)‐based nanocomposite for hydrogen sulfide (H2S) gas detection at ambient conditions. The as‐fabricated sensor has excellent capabilities, including sensitivity and selectivity to low gas concentrations than 100 ppb (<100 ppb), anti‐humid property up to relative humidity (RH) ≈ 100%, high chemical stability in severe environments, good mechanical flexibility up to 50 bending cycles at 30° bending angle, and good thermomechanical stability between ‐40 °C ‐ 40 °C. Moreover, the sensor detects the low concentrations of H2S gas produced during the spoilage of organosulfur‐rich food (beef and fish) while remaining insensitive to humidity changes up to RH ≈ 100%, resulting in the fist‐of‐its‐type chemiresistive sensor for food packaging application. The sensors’ response to H2S gas is based on the contribution of the physical and chemical sensing mechanisms, which rely on the H2S molecules’ reactions on the sensor's surface with the adsorbed oxygen molecules and the sensing materials (copper acetate (CuAc) and In2O3 NPs), respectively.

Overlaying Monolayer Metal–Organic Framework on PtSe2‐Based Gas Sensor for Tuning Selectivity

AbstractTransition metal dichalcogenides (TMDs) have attracted significant interest as gas‐sensing materials due to their unique crystal structure and surface. However, there are still issues when it comes to expanding the types of sensing gases for the TMD gas sensors. To extend gas‐sensing selectivity for the TMD gas sensors in this study, a monolayer (ML) 2D metal–organic framework (MOF) is introduced on top of the PtSe2 gas sensor, thereby tuning the major sensing analyte of PtSe2 from NO2 to H2S. Density functional theory calculations elucidate that the metal species of ML MOFs are attributed to the tuned selectivity of the analytes, based on the difference in binding energies. It is also demonstrated that ML MOF maintained the high responsivity of the pristine PtSe2 even at a low concentration of gas (200 ppb). This is further confirmed through the molecular dynamics simulations, which reveal that the ML feature of the ML MOF is highly essential to preserve the intrinsic ultra‐low limit detection properties of pristine PtSe2.

Effects of Low-Concentration Carbon Dioxide Exposure at Bedtime on Sleep in Adults With Insomnia Symptoms

Objectives: Carbon dioxide (CO2) accumulation in an enclosed space might cause drowsiness. This study aimed to assess the effect of bedtime exposure to low concentrations of CO2 gas on the sleep quality of adults with insomnia.Methods: In this double-blind, randomized, sham-controlled cross-over study, we consecutively recruited 24 adults (9 men; age, 55.4±6.3 y) complaining of sleep disturbances (Pittsburgh Sleep Quality Index ≥5). The following two interventions were used in the study: exposure to 2% low-concentration edible CO2 gas (experimental intervention) and exposure to room air (sham-controlled intervention). A sleep air device (Gosleep®, NYX), which atomizes CO2 gas, was used in both experimental and sham-controlled interventions. For the sham session, room air was generated for 18 min, and then, gradually reduced by degrees in the next 5 min with the device finally being turned off.Results: The group exposed to CO2 gas had longer time in bed (361.3±55.2 min vs. 347.2±35.7 min, p=0.034) and total sleep time (311.0±74.3 min vs. 287.2±69.4 min, p=0.010) than the group exposed to room air. Meanwhile, the total arousal (19.7±9.5/h vs. 24.0±13.7/h, p=0.011) and non-REM arousal (20.9±11.3/h vs. 25.1±14.9/h, p=0.008) indices were lower in the group exposed to CO2 gas than in the group exposed to room air. However, perceived total sleep time or sleep latency and Karolinska Sleepiness Scale scores were not significantly different between the two groups.Conclusion: Exposure to low concentrations of CO2 improved the total sleep time and arousal index in adults with insomnia. Unexpectedly, CO2 administration was found to be effective for sleep maintenance.

Improved NO2 gas sensing performance of 2D MoS2/Ti3C2Tx MXene nanocomposite

In this study, novel MoS2/Ti3C2Tx heterostructures were prepared from Ti3C2Tx MXene via a hydrothermal strategy. The well-bonded interface developed between the MoS2 nanostructure and the conductive Ti3C2Tx MXene played a crucial role in improving the sensing abilities of the prepared heterostructures compared to their pristine counterparts. Owing to the synergistic interplay effect, the optimal MoS2/Ti3C2Tx heterostructure exhibited room-temperature NO2 sensing activity with a rapid response and full recovery at low gas concentrations. To understand the high sensitivity, density functional theory calculations were used to observe stable configurations and adsorption behaviors. The proposed concept may provide an archetype for understanding the sensing characteristics of materials for NO2 detection at room temperatures.

Thermal conductivity detector (TCD)-type gas sensor based on a batch-fabricated 1D nanoheater for ultra-low power consumption

Thermal conductivity detectors (TCDs) are widely used to detect high-concentration gases or identify low-concentration gases in chromatography, owing to their fast response and recovery time for a wide range of gases. However, conventional TCD devices require large power consumption because of their relatively large sizes, which limits their applicability, specifically in IoT. In this study, an ultralow-power TCD was implemented for use as a gas sensor by manufacturing a suspended nanoheater via cost-effective wafer-level microfabrication technology (i.e., carbon-microelectromechanical systems). The aspect ratio of the nanoheater was optimized for a fixed minimum section area (width = 200–300 nm, thickness = 300–400 nm) using simulations and experiments. The small size, high aspect ratio (~ 270, corresponding to a nanoheater length of 80 µm), and suspended architecture allowed the nanoheater-based gas sensor to operate with high sensitivity and ultrafast response/recovery (time constant of less than 1 μs). This fast response enabled the sensor to operate with pulse-width modulation, reducing the power by 1/1000 (240 nW). The nanoheater-based gas sensor exhibited a linear gas response for various high-concentration gases (H2: 1–20 %, Ar: 1–100 %, He: 1–5 %). Moreover, the nanoheater was fabricated using only wafer-level microfabrication processes, ensuring cost-effective sensor manufacturing. Thus, nanoheater-based gas sensors are expected to be used in various portable IoT devices.

Arc-discharge deposition of SWCNTs over SnO2 nanowires for highly sensitive NO2 gas sensor

The air pollution caused by the emission of NO2 from vehicles in large cities is threatening human health. Thus, a highly sensitive gas sensor is required to monitor this gas. Here, we introduced the arc-discharge deposition of single-walled carbon nanotubes (SWCNTs) over SnO2 nanowires for highly sensitive NO2 gas sensors. The high-quality SnO2 nanowires were grown on-chip on interdigital Pt electrodes, whereas the SWCNTs were deposited by in situ arc-discharge method. To form the heterojunction between SnO2 nanowires and SWCNTs film, we controlled the length of the SnO2 nanowires to avoid bridging of the two electrode fingers while covering the entire surface of Pt electrodes. The SWCNTs were deposited through a shadow mask to ensure the contact between the SWCNTs and SnO2 nanowires but not the Pt electrodes. Electrical measurements confirmed the formation of non-linear contact between SnO2 nanowires and SWCNTs because of the n-p heterojunction. An increment in resistance (decrease in resistance) of the sensor was observed when measured in NO2 gas, indicating the good response characteristics of the device based on heterojunction between SnO2 nanowires and SWCNTs. In addition, gas-sensing measurement at different temperatures indicated that the fabricated sensor could detect low concentrations of NO2 gas in the range of 1–10 ppm, with response values of 20–80. The results demonstrated that the arc-discharge deposition of SWCNTs over SnO2 nanowires is effective for the fabrication of highly sensitive NO2 gas sensors.

Poly(ionic liquid) boosts overall performance of electrocatalytic reduction of low concentration of CO gas

Electrocatalytic reduction of CO (CORR) provides a feasible way for not only CO2 conversion via tandem CO2-to-CO-to-C2+ process but also CO utilization from industrial exhaust gases. In this work, poly(ionic liquid) modified Cu catalyst (Cu@PIL) was employed as the electrocatalyst to convert low concentration CO gas to high-value C2+ products. An over 90 % faradaic efficiency of C2+ products (FEC2+) was obtained at a constant current density of 125.0 mA cm−2 within a broad range of feedstock concentrations from 100.0 to 40.0 vol%. Remarkably, excellent comprehensive performance was achieved with feeding CO gas as less as 5.0 vol%, delivering a high FEC2+ of 71.1 % with high CO conversion (67.4 %) and high energetic efficiency (29.1 %). Mechanistic studies suggest the local enrichment of CO via adsorption and accelerated mass transfer by porous PIL layer as well as the suppression of hydrogen evolution reaction enables the CO-to-C2+ transformation with diluted CO gas.