Sensitive NO2 Gas Sensor Research Articles

MoS2-xSex lamellae assembled with lotus-leaf-like structures for sensitive NO2 gas sensors at room temperature

MoS2-xSex lamellae assembled with lotus-leaf-like structures for sensitive NO2 gas sensors at room temperature

Highly Sensitive and Selective Room Temperature NO2 Gas Sensor Based on 3D BiFeO3 − x Microflowers

Highly Sensitive and Selective Room Temperature NO2 Gas Sensor Based on 3D BiFeO3 − x Microflowers

Development and Performance of ZnO/MoS2 Gas Sensors for NO2 Monitoring and Protection in Library Environments

The presence of harmful oxidizing gases accelerates the oxidation of cellulose fibers in paper, resulting in reduced strength and fading ink. Therefore, the development of highly sensitive NO2 gas sensors for monitoring and protecting books holds significant practical value. In this manuscript, ZnO/MoS2 composites were synthesized using sodium molybdate and thiourea as raw materials through a hydrothermal method. The morphology and microstructure were characterized by X-ray diffraction analysis (XRD), energy dispersive spectroscopy (EDS), field emission scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The ZnO/MoS2 composite exhibited a flower-like structure, with ZnO nanoparticles uniformly attached to the surface of MoS2, demonstrating advantages such as high specific surface area and good uniformity. The gas sensitivity of the ZnO/MoS2 nanocomposites reached its peak at 260 °C, with a sensitivity value around 3.5, which represents an improvement compared to pure ZnO, while also enhancing sensitivity. The resistance of the ZnO/MoS2 gas sensor remained relatively stable in air, exhibiting short response times during transitions between air and NO2 environments while consistently returning to a stable state. In addition to increasing adsorption capacity and improving light utilization efficiency, the formation of hetero-junctions at the ZnO-MoS2 interface creates an internal electric field that effectively promotes the rapid separation of photo-generated charge carriers within ZnO, thereby extending carrier lifetime.

TiO2@ZrO2 p-n heterostructured nanocomposites for enhanced NO2 gas sensing

Hydrothermal approach was used to synthesize pure TiO2, ZrO2 and 2.5–10 % TiO2-ZrO2 p-n type nanocomposite heterojunctions. Morphological and structural features of heterostructures were established by XRD, TEM/HRTEM and SEM investigations. Band gap energy calculations revealed a reduction in band structure from 4.96 eV of pure ZrO2 to 3.50 eV of 7.5 % TiO2-ZrO2 heterostructures. BET surface area characterization displayed large surface area of the nanocomposites which performed an essential part in the enhanced sensing activity of the nanocomposite heterostructures. 7.5 % TiO2-ZrO2 sensor exhibited enhanced response to NO2 gas possessing excellent response and recovery times. The maximum sensitivity of 991 was shown by 7.5 % TiO2-ZrO2 sensor to 100 ppm NO2 gas that was nearly four folds compared to pristine ZrO2 nanospheres (263). The improved NO2 gas sensing of the nanocomposites was stemmed to the construction of p-n heterostructures that resulted in the emancipation of more reactive sites and thus led to the better sensing result of the nanocomposites. The gas sensing mechanism and improved sensing characteristics have been also elaborated. The strategy thus suggested in this report may offer considerably to the understanding of more sensitive NO2 gas sensors.

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.

Influence of ZnO hexagonal pyramid nanostructures for highly sensitive and selective NO2 gas sensor

In this work, we have synthesized the ZnO Hexagonal pyramid structures (ZnO HPs) for low detection limit of NO2 gas sensors by a facile hydrothermal method. The structural, morphological analysis has been evinced by X-ray diffraction (XRD), Field Emission Scanning electron microscope (FESEM), and high-resolution transmission electron microscope (HRTEM) analysis, which witness as formed HPs are hexagonal crystal structure and it seems homogenous morphological features. The gas sensing performance of ZnO HPs towards NO2 gas at different temperature was investigated. The findings of the gas sensing showed that the ZnO HPs has a better response and recovery time towards 3 ppm concentration of NO2 gas at 270 °C. This outstanding gas sensing response of 4.31 of ZnO HPs sensor leads exceptionally strong surface contact between the NO2 gas molecules and the surface-active sites of ZnO HPs gas sensor.

Improving the Performance of Titanium Oxide Nanocomposites as NO2 Gas Sensors for Optimum Sensitivity

In this study, we investigate the performance improvement of titanium oxide (TiO2) nanocomposites as NO2 gas sensors for optimum sensitivity. The TiO2 nanocomposites were synthesized using a solvothermal method and were modified with different dopants and additives to enhance their sensing properties. The sensing performance of the TiO2 nanocomposites was evaluated in terms of sensitivity, selectivity, response time, and recovery time. The synthesized nanocomposites were successfully characterized using AFM, FTIR, SEM-EDX and XRD techniques. The results showed that the addition of additives such as TiO2/GO, TiO2-Ag/GO and TiO2- Al2O3/GO: TiO2/GO significantly improved the sensing properties of the TiO2 nanocomposites. The Ag-doped TiO2 nanocomposites exhibited the highest sensitivity towards NO2 gas with a very low detection limit. The Al2O3-doped TiO2 nanocomposites showed good selectivity towards NO2 gas compared to other interfering gases and has led to increase in the surface area. In conclusion, the addition of additives and the optimization of the annealing temperature can significantly improve the sensing properties of TiO2 nanocomposites towards NO2 gas. The findings of this study can contribute to the development of highly sensitive and selective NO2 gas sensors for various applications such as environmental monitoring and industrial safety.

Ultra Responsive NO2 silicon nanowires gas sensor

Nitrogen dioxide (NO2) is a hazardous gas emitted primarily from burning fossil fuels. When inhaled, it can have severe health implications, particularly for individuals with respiratory conditions such as asthma. It contributes to ground-level ozone formation, which can cause reduced lung function and increased susceptibility to respiratory infections. When in contact with water moisture in the air, NO2 is easily oxidized into nitric acid (HNO3), causing acid rain. Detection of NO2 levels is therefore important for monitoring air quality and protecting public health. Among the possible technical solutions for gas sensing, silicon nanowires (SiNWs) have proven to be a promising candidate, partly due to their high sensitivity, low manufacturing cost, and ability to perform in various air qualities. This paper presents using SiNWs, fabricated by metal-assisted chemical etching, as a fast, accurate, sensitive, robust, and cost-effective NO2 gas sensor. Our SiNWs gas sensor can experimentally detect 20 parts per billion (ppb) of NO2 under a wide range of relative humidity. Our sensor shows ultra-high sensitivity with fast response and recovery time.

Highly sensitive room-temperture NO2 gas sensor based on Bi2S3 nanorods

Highly sensitive room-temperture NO2 gas sensor based on Bi2S3 nanorods

Cation substitution effects (Mn, Ni, and Zn) on ZIF-67 derived spinel modified with 3DGO for the detection of NO2 gas with high sensitivity and selectivity

Detailed cation substitution studies of MCo2O4 (M = Mn, Ni, Zn) spinel structures supported on 3D graphene oxide via solvothermal method have been carried out and used as a highly sensitive and selective NO2 gas sensor at room temperature.

Facile engineering of TiO2@Pd based hybrid heterogeneous nanostructures for enhanced NO2 gas sensing at room temperature under UV activation.

Highly sensitive sub-ppb level NO2 gas sensors based on hybrid heterostructures made out of metal nanoparticles (NPs) and porous metal oxide semiconductors are of great significance in environmental monitoring and medical diagnosis. Herein, we report the successful synthesis of a Pd nanoparticle decorated porous TiO2 nanostructure-based hybrid Schottky heterostructure and its application in room temperature (RT ∼ 30 °C) low-ppb level NO2 detection under UV activation. The optimized TiO2@Pd 50 hybrid heterogeneous nanostructures (HNs) showed an excellent NO2 (100 ppm) gas sensing response of 175.42%, excellent cycling stability, outstanding selectivity, low detection limit (∼82 ppb) and fast response/recovery speed (48/72 s) under UV illumination. Moreover, the as-prepared hybrid sensor demonstrates reliable reproducibility and robust sensing responses under various elevated temperatures (30-200 °C) and relative humidity conditions (0-80% RH) towards NO2. The excellent RT NO2 gas sensing properties of TiO2@Pd 50 HNs are primarily attributed to the improved surface area, enhanced oxygen vacancies, low charge carrier recombination, and catalytic effect triggered by the hot electrons induced, from the localized plasmonic resonance effect of Pd NPs, resulting in effective NO2 adsorption/desorption dynamics. The Schottky junction formation at the hybrid TiO2@Pd 50 HNs interface effectively aids in the separation of charge carriers via band bending, leading to excellent charge transfer between the NO2 molecules and the heterointerface under UV light, yielding substantial sensitivity and selectivity to NO2. The present work is expected to provide a strategic route for designing and fabricating sub-ppb level high-performance NO2 sensors based on hybrid heterostructures.

Ultrathin layered MoS2/N-doped graphene quantum dots (NGQDs) heterostructures for highly sensitive room temperature NO2 gas sensor

Due to high surface-to-volume ratio, stability, and more active sites, molybdenum disulfide (MoS2) has been attracted as a promising gas-sensing material. However, the room temperature (RT- 30 ℃) MoS2-based gas sensors still suffer slow response, recovery rates, and less sensitivity, notably for NO2. Herewith, we synthesized a novel molybdenum disulfide/nitrogen-doped graphene quantum dot (MoS2/NGQD) heterostructure via hydrothermal method for NO2 detection. The MNG-3 heterostructure is endowed with enhanced response of 82.4% towards 50 ppm of NO2 at 30 ℃, which is 6.5 folds greater than that of pristine MoS2 nanosheets (NSs). MNG-3 samples outperform with a quick recovery (30 s), excellent repeatability (5 cycles), long-term stability (5 weeks), and good selectivity towards 30 ℃ NO2 detection concentration of 50 ppm. The unique 2D/0D heterostructures and synergistic effect of NGQD and MoS2 NSs are responsible for the improved sensing performance. It undoubtedly suggests the feasible nature of prepared MoS2/NGQD heterostructures for 30 ℃ NO2 detection.

Expanding the range of trackable environmental pollutants for Nafion based fuel cell type gas sensor

Expanding the application field of fuel cell type gas sensors is of great significance for achieving high sensitivity, real-time gas detection at room temperature. Here, we developed a fuel cell type NO2 gas sensor based on MoS2 nanosheet/Carbon fiber (CF) sensing electrode and Nafion proton conductor, enabling the fuel cell type sensor to detect NO2 for the first time. The effect of MoS2 loadings(10, 20, 40, 60 and 80 mg) on the sensors’ performance and the sensitizing mechanism are investigated, the sensor containing 40 mg MoS2 exhibits the best performance, which can be attributed to the large number of active sites and efficient carrier transport properties of the corresponding electrode materials. At room temperature, the optimal sensor demonstrates a sensitivity of 45.6 nA/ppm to 1–50 ppm NO2 and an ultra-low detection limit of 28.8 ppb, both the response and recovery time are less than 60 s. This work not only develops a highly sensitive, reversible and fast response NO2 gas sensor, but also provides insights into sensing electrochemistry, material selection and catalyst/support materials, offering guidelines for future fuel cell type gas sensors to monitor a wider range of environmental pollutants.

Polymer-Based Thermally Stable Chemiresistive Sensor for Real-Time Monitoring of NO2 Gas Emission.

We present a thermally stable, mechanically compliant, and sensitive polymer-based NO2 gas sensor design. Interconnected nanoscale morphology driven from spinodal decomposition between conjugated polymers tethered with polar side chains and thermally stable matrix polymers offers judicious design of NO2-sensitive and thermally tolerant thin films. The resulting chemiresitive sensors exhibit stable NO2 sensing even at 170 °C over 6 h. Controlling the density of polar side chains along conjugated polymer backbone enables optimal design for coupling high NO2 sensitivity, selectivity, and thermal stability of polymer sensors. Lastly, thermally stable films are used to implement chemiresistive sensors onto flexible and heat-resistant substrates and demonstrate a reliable gas sensing response even after 500 bending cycles at 170 °C. Such unprecedented sensor performance as well as environmental stability are promising for real-time monitoring of gas emission from vehicles and industrial chemical processes.

Chemiresistive room temperature NO2 sensor based on nitrogen doped zinc oxide nanowires

The prevalence of nitrogen dioxide (NO2) in the atmosphere is causing a steady increase in air pollution. As such, there is an urgent need to create a sensitive and energy-efficient NO2 gas sensor to ensure environmental and health safety. In this study, we explore the effectiveness of nitrogen-doped zinc oxide nanowires in detecting harmful NO2 gas. Through the hydrothermal method, we synthesized zinc oxide (NW-0) and nitrogen-doped zinc oxide nanowire sensors (NW-1, NW-2 & NW-4). The introduction of nitrogen induced changes in both the crystallite size and nanowire density in ZnO. Additionally, an increase in oxygen vacancy concentration was observed with nitrogen doping. At room temperature, the NW-2 sensor exhibited exceptional NO2 sensing performance (response of 110) compared to NW-0 sensor (response of 1.9) for 10 ppm of gas. The NW-2 sensor also demonstrated a rapid response/recovery time of 50 s/5 s for a 10 ppm NO2 concentration. Moreover, the sensor showed stability over an extended period, minimal response variation with changes in relative humidity, and selectivity towards NO2 over other gases. Complementing the experimental findings, density functional theory (DFT) calculations were employed to estimate the adsorption energies of NO2 on the sensor surface.

Ocimum sanctum Leaf Extract-Assisted Green Synthesis of Pd-Doped CuO Nanoparticles for Highly Sensitive and Selective NO2 Gas Sensors.

In view of facile, cost-effective, and environmentally friendly synthetic methods, palladium-doped copper oxide (Pd-CuO) nanoparticles have been synthesized from Ocimum sanctum (commonly known as "Tulsi") phytoextract for gas-sensing applications. The structural, morphological, and compositional properties of Pd-doped CuO nanoparticles were studied using various techniques such as XRD, FESEM, XPS, and EDX. The characterization results confirmed the doping of Pd on CuO nanoparticles, and Pd-CuO nanostructures appear as nanoflakes in FESEM analysis. The gas-sensing response of Pd (1.12 wt %)-CuO nanoflake-based sensor was measured at 5-100 ppm concentration of different gases, NO2, H2S, NH3, and H2, at 125 °C. Gas-sensing tests reveal that the sensitivity of the sensor were 81.7 and 38.9% for 100 and 5 ppm concentrations of NO2, respectively, which was significantly greater than that of pure CuO. The response and recovery times of the sensor were 72 and 98 s for 100 ppm of NO2 gas, while they were 90 and 50 s for 5 ppm NO2. The calculated limit of detection (LOD) value of the sensor is 0.8235. This appealing LOD is suitable for real-time gas detection. The gas sensor was found to exhibit excellent selectivity toward NO2 gas and repeatability and stability in humid (80%) conditions. The Pd doping in CuO nanostructures plays a significant role in escalating the sensitivity and selectivity of CuO-based NO2 gas sensor suitable to work at low operating temperatures.

A Highly Sensitive Room-Temperature NO2 Gas Sensor based on Porous MnO2/rGO Hybrid Composites

Background: The NOX (e.g. NO2) is harmful to human health and environmental quality. It is of great interest to monitor the hazardous NOx with a simple, reliable, and sensitive sensor. Currently, the commonly used detection methods have disadvantages of complex operation, unstable cycling performance and low sensitivity. Objective: In this paper, rGO coated Ni foam supported MnO2 is synthesized to develop a more advanced detection method for the rapid analysis of NO2. Methods: A three-dimensional nickel foam supported MnO2 and rGO (MnO2/rGO@NF) was prepared by a hydrothermal method for application in binder-free electrode of NO2 sensor. Results: The MnO2/rGO@NF composite displayed significantly better NO2 sensing performance compared to single MnO2@NF or rGO@NF. The excellent sensing response (5.9%) as well as high cycling stability were observed in the presence of 50.0 ppm NO2 at room temperature. Furthermore, the mechanism of the great gas-sensing performance was also investigated by the density functional theory (DFT). Conclusion: These results were very important to further design and prepare new sensitive materials applied in binder-free electrode of gas NO2 sensors.

Fabrication and Computational Study of a Chemiresistive NO2 Gas Sensor Based on the Carbon Dots-WO3 Heterostructure for Operating below Room Temperature.

For a long time, chemiresistive gas sensors based on metal oxide semiconductors (MOSs) suffer from higher operating temperatures, resulting in higher energy consumption and instability of the sensors. Generally, a MOS-based chemiresistive gas sensor being able to work at room temperature is considered to be outstanding already. Here, a highly sensitive NO2 gas sensor based on the carbon dots-WO3 heterostructure, which can work below room temperature at -6 °C, is fabricated. At 18, -1, and -6 °C, its detection limits are 200 ppb, 5 ppm, and 20 ppm, respectively, and the corresponding response values (Ra/Rg) are 1.11, 1.04, and 1.13, respectively. The sensor exhibits good selectivity, stability, and linearity between relative humidity and response values too. A peculiar response behavior was observed. Toward oxidizing gas NO2, the resistance of the sensor based mainly on n-type WO3 shows decrease behavior. Its peculiar response behavior and strong gas sensing ability at lower temperatures were elucidated theoretically using the results of first-principles calculations. The reduction of NO2 into NO by surface oxygen vacancies of WO3 and the following adsorption of NO on the surface of WO3 lead to electron transfer from NO to WO3, and the Fermi level shifts toward the conduction band, making the sensor exhibit the peculiar response behavior. The stronger adsorption capability of carbon dots toward NO2 and a synergistic effect of carbon dots and WO3 together make the sensor capable of working at lower temperatures and own higher sensitivity.

Highly sensitive and low detection limit NO2 gas sensor based on In2O3 nanoparticles modified peach kernel-like GaN composites

The effective detection of ppb-level NO2 is of great significance to the natural environment and human health. In this work, a series of In2O3 nanoparticles modified peach kernel-like GaN for NO2 detection was synthesized by a concise two-step method. The gas-sensing results showed that 10 mol% In2O3-decorated GaN (In: Ga) exhibited a response as high as 1070.9–1 ppm NO2 at the working temperature of 100 ℃, as well as a low limit of detection (1 ppb). Furthermore, the sensor also possessed excellent selectivity, repeatability and fast response-recovery speed. The outstanding sensing performance was contributed to the rough and porous microstructure of GaN, abundant negative oxygen ion species originating from In2O3, and the heterojunction effect between GaN and In2O3. The sensor proposed herein provide a useful reference for reliable detection of ppb-level NO2 gas.

Highly sensitive NO2 gas sensor based on ZnO nanoarray modulated by oxygen vacancy with Ce doping

Developments of advanced sensors for NO2 gas with high sensitivity and selectivity are essential but challenging. In this work, a Ce-doped ZnO nanoarray (termed as CZO) was successfully constructed via a one-pot hydrothermal method, and further demonstrated as a promising NO2 chemiresistive sensing material. It proves that Ce doping not only changes the morphology of the initial ZnO nanoarray, but brings abundant oxygen vacancy in particular, as comprehensively proofed by scanning electron microscopy, transmission electron microscopy, and electron spin resonance spectroscopy. Gas sensing tests at 250 °C reveal that CZO-2 (Ce wt% = 2 %) offers a 10-fold higher sensing response to NO2 and much lower limit of detection (LOD = 1.4 ppb), compared to those of the initial ZnO nanoarray. Additionally, high selectivity for NO2 and excellent long-term stability are also obtained in such a Ce-doped sensor. Density function theory calculation results show that ZnO modulated by oxygen vacancy has a much stronger affinity toward NO2 than pure ZnO, thus resulting in the improved sensing performance observed in CZO-2.