NO2 Gas Research Articles

Highly efficient NO2 gas sensor based on sputter-grown nanocrystalline MoO3 thin films

This work explores an easy and efficient approach for developing NO2 gas sensors based on one-step sputtered nanocrystalline molybdenum trioxide (nc-MoO3). The sample’s morphology, crystallinity, and purity were analyzed using FESEM, XRD, and XPS, respectively. The MoO3 thin film sensor displayed its highest sensor response (SR = Rg/Ra) of ∼ 9.15 when exposed to 200 ppm of NO2 gas at the optimal operating temperature of 300℃, with response and recovery times of about 114 and 106 s, respectively. The sensor also displayed high selectivity and stability. With the expeditious approach and outstanding performance, the sputtered bare MoO3 thin films can be used for sparing NO2 gas detection.

A room-temperature ppb-level detection limit of NO2 sensor based on Cellulose/SnO2 heterojunction under UV illumination

In light of growing concerns over air pollution, particularly NO2 emissions from vehicular and industrial sources, there is a critical demand for advanced gas sensors. Traditional metal oxide semiconductors, while widely used, face challenges such as poor selectivity and high operating temperatures. In this work, we have achieved a high selectivity and room temperature NO2 gas sensor by composite of sponge-like porous cellulose with SnO2 nanoparticle. As a result, the gas sensor exhibits excellent performance in terms of high response (260.4 at 20 ppm), excellent selectivity and low detection limit (100 ppb) for NO2 gas, due to the unique sponge-like porous structure of cellulose with its high specific surface area facilitating the uniform distribution of SnO2 particles. This study not only highlights the superior sensing capabilities of cellulose-based sensors but also lays the foundation for further advancements in environmentally-friendly gas sensing applications.

Self-heated WO3 nanowires for selective and sensitive detection of NO2 gas at room temperature

Self-heated WO3 nanowires for selective and sensitive detection of NO2 gas at room temperature

Fabrication of Carbon Quantum Dots/Alq3 Layer for NO2 Gas Sensor

The gas sensors were prepared using carbon quantum dots (CQDs) using an electrochemical method after mixing the CQDs with Tris (8-hydroxyquinoline) aluminum (III) (Alq3) polymer. A spin coating technique was used to deposit CQDs/Alq3 composite film on glass substrates with a ratio of 1:1. The CQDs/Alq3 gas sensor showed a sensitivity of about 24٪ at a temperature of 300 ℃, and this was calculated after measuring the change in the resistance of the samples with a response time of 2 and 8sec recovery time. The sensor showed a good response for nitrogen dioxide (NO2) gas. However, the sensitivity, response time, and recovery time for the CQDs gas sensor when exposed to NO2 gas at 300 °C were 78%, 4s, and 129s, respectively. The results showed that the best sensor CQDs/Alq3 led to a reduction in the recovery time, which shows the importance of the Alq3 polymer in improving the properties of the gas sensor.

Adsorption and sensing behavior of Cr-doped WS2 monolayer for hazardous gases in agricultural greenhouses: A DFT study

This study used Density functional theory (DFT) to analyze the adsorption behavior of the Cr-doped WS2 monolayer on five hazardous gases (NH3, SO2, NO, NO2, and CO) in agricultural greenhouses. The optimal stable doped site for the Cr atom was identified, and various adsorption parameters such as adsorption energy, adsorption distance, charge transfer and desorption time were calculated. Results indicated that intrinsic WS2 had limited adsorption capacity for five target gases. Moreover, Cr doped significantly enhanced WS2 monolayer conductivity, shifting NH3, SO2, NO and NO2 adsorption from physisorption to chemisorption with Eads <0.6 eV, while CO remained physisorbed. The conductivity of the five gases underwent significant changes after adsorption on Cr-WS2. Desorption times at four temperatures (298 K, 398 K, 498 K and 598 K) indicate that Cr-WS2 demonstrates ideal gas sensor behavior for NH3 gas. However, the physisorbed and short desorption at room temperature suggested unsuitability for CO detection in practical applications. Conversely, the extended desorption time at 598 K made Cr-WS2 more appropriate as a gas scavenger for SO2, NO and NO2 gases. These findings underscore the potential of Cr-WS2 monolayers as novel gas warning or adsorbent materials, offering crucial applications in detecting and removing hazardous gases in agricultural greenhouses.

A dual-mode fluorometric and colorimetric sensor based on N-doped carbon dots for selective and sensitive detection of nitrite in food samples

A highly sensitive and selective nitrite sensing platform based on nitrogen-doped carbon quantum dots (N-CDs), by means of a headspace single drop microextraction process, was constructed for dual-mode fluorometric and visual colorimetric determination of nitrite. In this system, the two-channel selective sensing of nitrite was achieved at the same time, with color ranging from colorless to red and N-CDs fluorescence quenching gradually. Meanwhile, gaseous NO was generated from the redox chemical vapor generation process and further extracted into a single drop, which effectively improving the analytical sensitivity and alleviating the matrix interference. By fluorescence and colorimetry, the limits of detection were calculated to be 0.03 and 0.08 μg mL−1, respectively, while 0.8 μg mL−1 nitrite was discernable by the naked eye. This method was utilized to analysis of diversified real food samples (vegetables, milk and ham), and the results were proved to be nearly consistent with a standard method. Furthermore, the storage conditions of vegetable juice have also been explored.

Preparation of SnS2/MoS2 with p–n heterojunction for NO2 sensing

Conventional metal sulfide (SnS2) gas-sensitive sensing materials still have insufficient surface area and slow response/recovery times. To increase its gas-sensing performance, MoS2 nanoflower was produced hydrothermally and mechanically combined with SnS2 nanoplate. Extensive characterization results show that MoS2 was effectively integrated into SnS2. Four different concentrations of SnS2–MoS2 composites were evaluated for their NO2 gas sensitization capabilities. Among them, SnS2–15% MoS2 at 170 °C demonstrated the greatest response values to NO2, 7.3 for 1 ppm NO2, which is about three times greater than the SnS2 sensor at 170 °C (2.58). The creation of pn junctions following compositing with SnS2 was determined to be the primary reason for the composite’s faster recovery time, while the heterojunction allowed for the rapid separation of hole–electron pairs. Because the MoS2 surface has multiple vacancy defects, the adsorption energy of these vacancies is significantly higher than that of other places, resulting in increased NO2 adsorption. Furthermore, MoS2 can serve as active adsorption sites for SnS2 micrometer sheets during gas sensing. This study may help to build new NO2 gas sensors.

Characteristics of Aqueous Chemical Species Generation in Plasma-Facing Liquid Systems Using Helium Jet Plasma.

Plasma-facing liquids (PFLs) facilitate the storage of reactive O and N species (RONS), including H2O2 and NO2 -, which remain in the PFL after plasma treatment, and they can continuously influence the target immersed in the liquid. However, their behaviors and levels of generation and extinction depend strongly on the plasma characteristics and liquid condition. Therefore, understanding the effects of the liquid type on the plasma discharge characteristics and the RONS generated via plasma discharge is necessary. We compared the RONS generation and storage trends of deionized H2O and a high-conductivity PFL, RPMI 1640, which is a well-known cell culture medium commonly used to culture mammalian cells. RPMI 1640 acted as an electrode and enhanced the plasma discharge power by supplying abundant radicals and RONS. The production of gaseous hydroxyl radicals and NO markedly increased, which facilitated H2O2 and NO2 - production in the PFL for the first 200 s, and then the increase in the RONS concentration stagnated. With respect to storage, as the components within RMPI 1640 exhibited high reaction constants for their reactions with H2O2, H2O2 elimination was completed in <30 min. Unlike H2O2, the concentration of NO2 - in the PFL was unchanged.

In-situ growth of vertically stacked 2D SnS2/SnS heterostructure for highly sensitive and rapid room temperature NO2 gas sensor

Construction of 2D heterostructure is a potential strategy to improve the sensing performance of 2D layered materials owing to the high-quality of heterointerfaces. This attributed to the remarkable electronic band alignment between the constituent materials and their distinctive characteristics. Woefully, very limited attempts have been taken to investigate the effect of 2D heterointerface for gas sensing applications. Here, the SnS2/SnS heterostructure is fabricated on a SiO2/Si substrate using a single-step atmospheric chemical vapor deposition technique for room temperature NO2 sensing. The heterostructure has imparted a 1.3 times enhancement in response (S(%)), with ultra-fast response (τres) and recovery time (τrec) of 32 s and 382 s, towards 40 ppm of NO2 at 30 °C. Moreover, the impact of humidity on the sensing performance of SnS2/SnS has also been studied, confirming its negligible effect on relative humidity. Additionally, it also demonstrates a remarkable stability of 93% over a period of 40 days. Besides, due to strong adsorption energy of SnS2 (1914 meV) and SnS (600 meV) towards NO2 endorses the reaction kinetic parameters validated by the gas adsorption/desorption isotherm analysis of heterostructure. The substantial interface contacts between the SnS2/SnS heterostructure facilities the fermi-level mediated charge transfer, contributing significantly towards the improvement in sensing performance. Therefore, the formation of hierarchical 2D heterostructure with electron depletion layer can be considered as a conducive way for the future development low-powered gas sensor.

Nutrient release pattern and mitigation of N2O emissions under the application of activated poultry manure compost biochar with organic resources

Biochar was generally used to reduce the macronutrient releases and to mitigate N2O gas emissions in cropland. This experiment evaluated the trend of major plant nutrient releases using the modified Hyperbola model and the greenhouse gas emissions by incorporating different poultry manure compost biochar with organic resources. The treatments consisted of the control as the organic fertilizer materials, the incorporated poultry manure compost biochar with organic fertilizer materials (PMCBF), and the incorporated plasma-activated poultry manure compost biochar with organic fertilizer materials (PAMBF) under redox conditions. The results showed that the cumulated highest concentrations of NH4–N and NO3–N were 2168.6 mg L−1 and 21.7 mg L−1 in the control, respectively. Compared with the control, the predicted reduction rates of NH4–N release from the PMCBF and PAMBF were 26.2% and 15.4%, respectively. In the control, the cumulated highest concentrations of PO4–P and K in leachate were 681.04 mg L−1 and 120.5 mg L−1, respectively. The predicted reduction rates of PO4–P and K were 55.1% and 15.5%, respectively, under the PAMBF compared to the control. The modified Hyperbola model with cumulated NH4–N, PO4–P, and K-releases under the treatments was a good fit (p < 0.0001). For greenhouse gas (GHG) emissions, the lowest cumulative N2O was 59.59 mg m−2 in the soil incorporated with PMCBF, and its reduction rate was 23.5% compared with the control. The findings of this study will contribute to more profound insights into the potential application of PAMBF and PMCBF as bio-fertilizers adapted to mitigate NH4–N, PO4–P, and K releases and N2O emissions, offering scientific evidence for organic farming strategies.

High-performance NO2 gas sensor enabled by Fe, N co-doped GQDs modification and pulse-driven temperature modulation

Nitrogen dioxide (NO2) is a typical reactive nitrogen species harmful to health and the environment. However, NO2 sensors still suffer from low sensitivity and poor response/recovery rates. Herein, 3D In2O3 assembled by stacked nanosheets were prepared and modified with N element-doped GQDs (N-GQDs) and Fe, N co-doped GQDs (Fe,N-GQDs), respectively. The results of NO2-sensing performance indicated that the optimal sample (0.3 wt% Fe,N-GQDs/In2O3) showed a high response of 414.5 to 1 ppm NO2 and could detect as low as 10 ppb at 50℃, which was 1.3 and 4.0 times higher than that of 0.3 wt% N-GQDs/In2O3 and In2O3, respectively. The gas-sensing kinetics were analyzed by establishing gas adsorption/desorption isotherms. The enhanced NO2 sensing properties of 0.3 wt% Fe,N-GQDs/In2O3 were mainly due to the enhanced active site accessibility of stacked nanosheets with open layer spaces, the heterointerface between Fe,N-GQDs and In2O3, and electrical modulation of Fe,N-GQDs. Additionally, A pulse-driving circuit was designed for a pulse temperature modulation (PTM) strategy to further boost NO2 detection. The sensor response is further enhanced by 1.7 times, and the response/recovery time is reduced by 42.5 %/60.1 %. The NO2 concentration in vehicle exhaust was determined using PTM mode with good spike recoveries. It validated the reliability of the sensor for the quantitative detection of NO2 in the real environment. This work provides insights into sensor design and has the potential to contribute to the development of novel sensing platforms for other gas pollutants.

Low-temperature NO2 sensor based on γ-In2Se3/In2O3 nanoflower heterojunction

The γ-In2Se3/In2O3 nanoflower-like heterojunctions were synthesized by solvothermal treatment followed by thermal oxidation in Air. The nanoflower-like γ-In2Se3/In2O3-based chemiresistive-type sensor showed a significantly enhanced response to NO2 at an operating temperature of 170°C. The sensor achieves a response of 2.69–0.2 ppm NO2 at 170°C. The sensor exhibits remarkable selectivity to several possible interferents such as carbon monoxide, ammonia, formaldehyde, acetone, methanol, and toluene, and good stability at 170°C. The nanoflower structure increases the specific surface area and introduces more active sites, which improves the sensitivity of the sensor to NO2. The heterojunction formed between γ-In2Se3 and In2O3 improves the charge carrier transfer between NO2 gas molecules and sensing materials, thereby increasing the response of the sensor to NO2. Density functional theory was used to elucidate this sensing mechanism, and it was found that improved sensing performance is mainly due to heterojunction formation, which increases the adsorption energy of nitrogen dioxide molecules on a sensing material surface and facilitates charge transfer between molecules.

Defect Engineering for SnO2 Improves NO2 Gas Sensitivity by Plasma Spraying.

Large emissions of nitrogen dioxide (NO2) pose a significant threat to human health, Monitoring its content and implementing timely measures are crucial. Utilizing oxide semiconductors, such as tin dioxide (SnO2), has proven to be an effective way to detect and analyze NO2. The design and preparation of sensing materials with high sensitivity and excellent selectivity is the key to improve the detection efficiency. SnO2 nanopowders with small and uniform particle size, large specific surface area, adjustable defect content, and no impurities were prepared by a new plasma spraying method. The SnO2 nanopowders exhibit outstanding performance in detecting NO2 at a low temperature of 100 °C, the response to 5 ppm of NO2 reaches 48, and the material demonstrates rapid response and recovery times, coupled with excellent selectivity. The exceptional gas-sensitive properties can be attributed to the superior morphology and structure of SnO2. It provides more reaction sites for gas sensitive reactions, fast electron transport, a large number of charge carriers, and improved adsorption of the material to the target gas. This study provides valuable insights into nanomaterial preparation and the enhancement of gas-sensitive properties for SnO2.

Nanotransfer Printing for Synthesis of Vertically Aligned Carbon Nanotubes with Enhanced Atomic Penetration

AbstractVertically aligned carbon nanotubes (VACNTs) exhibit outstanding mechanical strength, chemical stability, and electrical characteristics; however, their constrained mechanical elasticity and chemical responsiveness spurred research on atomic decoration techniques for enhancing their mechanochemical attributes. Nevertheless, achieving uniform atomic decoration on the VACNT surface is difficult because of the high density and large aspect ratio of VACNT. Herein, a strategy to design and apply nanopatterned VACNTs (nVACNTs) based on a nanotransfer printing process is proposed to improve atomic penetrability. Nanopatterns inherent to nVACNTs facilitate atomic penetration, allowing for the more consistent and higher quality deposition of functional materials such as zinc oxide and alumina by atomic layer deposition. Furthermore, physical vapor deposition provides an improved coating of metal catalysts such as gold. The uniform deposition of ceramic layers on the entire surface of nVACNTs strengthens its mechanical resilience, owing to the diminished van der Waals forces of CNTs. Surface‐decorated nVACNTs display an increased sensitivity to NO2 gas, which is attributed to the enhanced quality of the reactive catalyst deposition and augmented permeability. This strategy achieves a larger decorated area while increasing a catalytically active reaction area. The obtained results promise that the enhanced nVACNTs will expand the industrial applications of carbon nanotubes.

Synergistic tailoring of adsorption and vacancy enrichment in lamellar stacked layers of α-MoO3 nanorods by Mg2+ for NO2 gas sensor

Extremely toxic nitrogen dioxide (NO2) was detected using lamellar layered α-MoO3. The stable orthorhombic phase of MoO3 (α-MoO3) with preferential growth along (02k0) and the nano-rectangular rods (NRs) like morphology were observed. The incorporation of Mg2+ in α-MoO3 influenced the morphology and the oxygen vacancies (VO), which were analyzed through Raman, photoluminescence, and X-ray photoelectron spectroscopy. The core level spectra provided direct evidence for VO enrichment in 3 %Mg-α-MoO3 via emergence of peak at 531.02 eV with an area of 45.15 %. NO2 response was analyzed at 150–200 °C with various NO2 concentrations. 3 %Mg-α-MoO3 NRs provided maximum response of 133.9 % for 50 ppm with low limit of detection (LOD) of 250 ppb with good response (193 s) and recovery (260 s) transient behaviors. The fabricated sensor shows high selectivity to NO2 among H2S, SO2, N2O, and NH3, also good repeatability suggesting potential suitability for NO2 detection.

Nitrous oxide respiration in acidophilic methanotrophs

Aerobic methanotrophic bacteria are considered strict aerobes but are often highly abundant in hypoxic and even anoxic environments. Despite possessing denitrification genes, it remains to be verified whether denitrification contributes to their growth. Here, we show that acidophilic methanotrophs can respire nitrous oxide (N2O) and grow anaerobically on diverse non-methane substrates, including methanol, C-C substrates, and hydrogen. We study two strains that possess N2O reductase genes: Methylocella tundrae T4 and Methylacidiphilum caldifontis IT6. We show that N2O respiration supports growth of Methylacidiphilum caldifontis at an extremely acidic pH of 2.0, exceeding the known physiological pH limits for microbial N2O consumption. Methylocella tundrae simultaneously consumes N2O and CH4 in suboxic conditions, indicating robustness of its N2O reductase activity in the presence of O2. Furthermore, in O2-limiting conditions, the amount of CH4 oxidized per O2 reduced increases when N2O is added, indicating that Methylocella tundrae can direct more O2 towards methane monooxygenase. Thus, our results demonstrate that some methanotrophs can respire N2O independently or simultaneously with O2, which may facilitate their growth and survival in dynamic environments. Such metabolic capability enables these bacteria to simultaneously reduce the release of the key greenhouse gases CO2, CH4, and N2O.

Development of an NO2 Gas Sensor Based on Laser-Induced Graphene Operating at Room Temperature.

A novel, in situ, low-cost and facile method has been developed to fabricate flexible NO2 sensors capable of operating at ambient temperature, addressing the urgent need for monitoring this toxic gas. This technique involves the synthesis of highly porous structures, as well as the specific development of laser-induced graphene (LIG) and its heterostructures with SnO2, all through laser scribing. The morphology, phases, and compositions of the sensors were analyzed using scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy. The effects of SnO2 addition on structural and sensor properties were investigated. Gas-sensing measurements were conducted at room temperature with NO2 concentrations ranging from 50 to 10 ppm. LIG and LIG/SnO2 sensors exhibited distinct trends in response to NO2, and the gas-sensing mechanism was elucidated. Overall, this study demonstrates the feasibility of utilizing LIG and LIG/SnO2 heterostructures in gas-sensing applications at ambient temperatures, underscoring their broad potential across diverse fields.

Improvement of gas-sensing performance of TO8C monolayers as high-efficient room-temperature NO and NO2 gas sensors induced by electric field

The gas-sensing application potential of the TO8C monolayer for the target gases (NO, NO2, CO, CO2, NH3, CH4, H2O, and H2) was systematically investigated via DFT calculations. Only NO and NO2 adsorption can tune the electronic properties of the TO8C monolayer. Since the weak adsorption strength of NO and NO2 is unfavorable for the sensor device, E-field modulation was applied. Except as the enhancement of adsorption strength into desired ranges for NO and NO2, E-field modulation of −0.14 ∼ −0.21 V/Å for NO (0.08 ∼ 0.12 V/Å and −0.26 ∼ −0.29 V/Å for NO2) makes semiconducting transfer into conducting properties, indicating the sensitivity of the monolayer towards NO and NO2 gases was also effectively improved. However, the electronic properties of TO8C monolayer adsorbed with the other gases were hardly changed by the above-mentioned E-fields. When the applied E-fields were in −0.12 ∼ −0.17 V/Å (or −0.26 ∼ −0.29 V/Å), the conducting properties for NO (or NO2) adsorption were maintained in the existence of humidity, indicating that the determinate E-field is much favorable for the TO8C-based sensor to detect NO and NO2 gases without considering whether the humidity exists. Our findings reveal that the TO8C monolayers are compelling and feasible candidates for NO and NO2 resistance-type sensors at room temperature under the E-field modulation.

Investigation on thermal annealing effect on the physical properties of CuO-SnO2:F sprayed thin films for NO2 gas sensor and solar cell simulation

Thin films, owing to their versatility, are extensively employed in various applications, including solar cells and gas detection. In this study, CuO-SnO2:F thin films were fabricated using spray method. The influence of annealing temperature on their properties was examined. X-ray diffraction analysis of post-annealing at 300 °C revealed the emergence of the Cu2O phase, which disappeared at higher annealing temperatures of 500 °C. Substantial improvements in structural, optical, and electrical characteristics were observed, with the optimized films exhibiting heightened responsiveness at low NO2 gas concentration (4 ppm). The optimum operating temperature was determined at 150 °C, demonstrating small response and recovery times, and good reproducibility. Furthermore, Silvaco TCAD simulation was employed to model CIGS (Copper Indium Gallium Selenide) solar cells incorporating CuO-SnO2:F thin films as a buffer layer, yielding an impressive efficiency of 15.31 %.

Impact of oxygen vacancies on enhanced NO2 gas sensing performance of lithium doped Co:ZnO thin films

This article explored the influence of lithium on cobalt-doped ZnO thin films fabricated via the sol–gel spin coating technique for NO2 gas sensing applications. The abundance of oxygen vacancies in ZnO can be proven by scanning electron microscopy, four-probe Hall measurements, photoluminescence spectroscopy, UV-visible spectroscopy, and x-ray photoelectron spectroscopy. The presence of lithium plays a crucial role in generating more oxygen vacancies in Co-doped ZnO was discussed. Among the fabricated samples, (Li-Co) co-doped ZnO exhibits better sensitivity (2940.17%), selectivity, repeatability, and stability (after 90 days) toward 75 ppm NO2 gas.