Gas Sensors For NO2 Detection Research Articles

Exploring Pore Formation and Gas Sensing Kinetics Using Conjugated Polymer-Small Molecule Blends.

Controlling miscibility between mixture components helps induce spontaneous phase separation into distinct domain sizes, thereby resulting in porous conjugated polymer (CP) films with different pore sizes after selective removal of auxiliary components. The miscibility of the CP mixture can be tailored by blending auxiliary model components designed by reflecting the difference in solubility parameters with the CP. The pore size increases as the difference in solubility parameters between the matrix CP and auxiliary component increases. Electrical properties are not critically damaged even after forming pores in the CP; however, excessive pore formation enables pores to spread to the vicinity of the dielectric layer of CP-based field-effect transistors (FETs), leading to partial loss of the carrier-transporting active channel in the FET. The porous structure is advantageous for not only increasing detection sensitivity but also improving the detection speed when porous CP films are applied to FET-based gas sensors for NO2 detection. The quantitative analysis of the response-recovery trend of the FET sensor using the Langmuir isotherm suggests that the response speed can be improved by more than 2.5 times with a 50-fold increase in NO2 sensitivity compared with pristine CP, which has no pores.

First-principles exploration of N- and Pd-doped graphene as CO and NO2 gas sensor for operation status evaluation in AIS

To evaluate the operation status of air insulated switchgears (AIS), this work purposes N- and Pd- embedded graphene (N- and Pd-graphene) as potential gas sensors upon two typical faults gases (CO and NO2) from the first-principles simulations. It is found that the N and Pd atoms can be stably trapped on the C-vacancy of the C-defected graphene with the formation energy of −12.17 and −5.12 eV, respectively. N-graphene behaves physisorption towards CO and NO2 molecules while Pd-graphene behaves chemisorption instead. The resistance-type and work function (WF)-based sensing mechanisms of N- and Pd-graphene upon such two gas species are illustrated and uncovered by analyzing their deformations of electronic property and WF in the gas adsorption systems, which reveals the potential of Pd-graphene as a resistive CO and NO2 sensor, N-graphene as a resistive NO2 sensor, as well as the N- and Pd-graphene as WF-based gas sensor for NO2 detection. This work highlights the comparison of adsorption and sensing performances between N- and Pd-graphene upon two typical gas sensors in AIS, which would be meaningful to explore novel graphene-based sensing materials facilitating their investigations and applications in the power system.

Template-assisted mesoporous SnO2 based gas sensor for NO2 detection at low temperature

Template-assisted mesoporous SnO2 based gas sensor for NO2 detection at low temperature

Temperature-driven n- to p-type transition of a chemiresistive NiO/CdS-CdO NO2 gas sensor

A new NiO/CdS-CdO composite-based chemiresistive gas sensor for NO2 detection exhibits temperature-driven adsorption switching. In-situ CdS nanoparticle growth on Ni-based metal-organic framework (MOF) spheres produced Ni-MOF/CdS, and then calcinating the Ni-MOF/CdS in air yielded NiO/CdS-CdO composite. The composite's NO2 sensing characteristics were examined at 25–350 °C, demonstrating that the NiO/CdS-CdO composite switches from n- to p-type above 200 °C with strong NO2 sensitivity and selectivity. Adsorption switching allows the NiO/CdS-CdO composite to serve as a dual-mode sensor, where NiO and CdS-CdO dominate at higher temperatures (>200 °C) and lower temperatures (≤200 °C) with realistic detection ability, respectively. This switching is mainly caused by variations in charge carrier concentration and NO2 adsorption/desorption behavior on the composite surface. At 150 °C, NiO/CdS-CdO sensors have a low detection limit of 100 ppb, high response (Rg/Ra, ∼215), quick response time (∼47 s), and recovery time (∼66 s) at 100 ppm. FTIR analysis, estimation of activation energies, and a qualitative comparison of n- to p-type transition with a typical full-wave rectification process explain the adsorption switching phenomenon. Adsorption switching in NiO/CdS-CdO-based gas sensors with great repeatability, stability, and fast response may be a promising route for high-performance gas sensing applications.

Interfacial oxygen vacancies and energy-level engineering on CeO2-PPy-rGO nanocomposites towards boosted NO2 sensor performance

Monitoring of harmful nitrogen dioxide (NO2) gases is imperative for our health and environmental protection. The room-temperature operating NO2 gas sensors still suffer a limited sensitivity and slow response/recovery rate. In this work, novel CeO2-PPy-rGO nanocomposites were synthesized for improved NO2 sensing performance. The decoration of rGO introduced additional oxygen vacancies on CeO2 for enhancing the sensor response. PPy acted as a buffer layer of energy level connecting CeO2 and rGO components and promoted the response and recovery rate. The designed sensor demonstrated ppb-level NO2 detection in p-type sensing behaviors with rapid response/recovery characteristics as expected at room temperature (RT). The hybrid sensor also showed excellent selectivity, long-term stability and extremely low detection limit toward NO2. The significantly enhanced sensing properties to NO2 could be attributed to activity enhancement, a gently gradient energy level and π-π stacking between rGO and PPy. This study offers a perspective on the design of CeO2-based gas sensors for NO2 detection at RT.

V2O5-rGO based chemiresistive gas sensor for NO2 detection

Current study displays an actual hydrothermal synthesis of V2O5-rGO composite and further investigates how changes in rGO composition in V2O5-rGO composites affected their NO2 sensing property. The orthorhombic crystal structure is confirmed by XRD and Raman techniques, and the optimum proportion of disorders in the composite as a result of rGO is also confirmed. Porous nanostructure is observed in SEM images. The C, V, and O present in the composite are confirmed by the XPS results, along with a fluctuation in V4+/V5+. The BET technique was used to measure specific surface area (25.91 m2g−1) and pore radius (6.4140 nm). A prominent PL peak confirm presence of oxygen vacancies. At 150 °C, gas sensing for 100 ppm concentration of NO2 gas revealed improved response about 121.85%. The calculated response/ recovery time for sample consisting 10 mg rGO are 39 and 262 s, respectively. Along with response, sample C shows excellent reproducibility and good stability.

Carbon Nanofibers Synthesized at Different Pressures for Detection of NO2 at Room Temperature

In this paper, room-temperature chemiresistive gas sensors for NO2 detection based on CVD-grown carbon nanofibers (CNFs) were investigated. Transmission electron microscopy, low-temperature nitrogen adsorption, and X-ray diffraction were used to investigate the carbon nanomaterials. CNFs were synthesized in a wide range of pressure (1–5 bar) by COx-free decomposition of methane over the Ni/Al2O3 catalyst. It was found that the increase in pressure during the synthesis of CNFs induced the later deactivation of the catalyst, and the yield of CNFs decreased when increasing pressure. Sensing properties were determined in a dynamic flow-through installation at NO2 concentrations ranging from 1 to 400 ppm. Ammonia detection was tested for comparison in a range of 100–500 ppm. The obtained sensors based on CNFs synthesized at 1 bar showed high responses of 1.7%, 5.0%, and 10.0% to 1 ppm, 5 ppm, and 10 ppm NO2 at 25 ± 2 °C, respectively. It was shown that the obtained non-modified carbon nanomaterials can be used successfully used for room temperature detection of nitrogen dioxide. It was found that the increase in relative humidity (RH) of air induced growth of response, and this effect was facilitated after reaching RH ~35% for CNFs synthesized at elevated pressures.

Heterojunction and exposed facet engineering of ZnO/ WO3 flower structure for fast and sensitive low-concentration NO2 sensing

A novel silybum flower-like ZnO/ hexagonal WO3 heterostructure is synthesized via hydrothermal method and applied in gas sensors for NO2 detection. The morphology, composition, and possible growth mechanism are systematically investigated by a series of characterizations. In comparison with the pure WO3 and other ZnO/WO3 samples, the silybum flower-like ZnO/ hexagonal WO3 sensor presents superior NO2 sensing performance at 190 °C, particularly at low concentrations, consisting of high response (5.9), quick response (7–12 s)/recovery time (9–13 s), strong selectivity and stability toward 100 ppb NO2. The excellent sensing characteristics are attributed to the synergy of heterojunction and exposed (001) facet with more oxygen vacancies. Furthermore, the well-defined open flower structure provides unique opportunities to form n-n heterostructures, inducing the adequate sensing reactions and ultrafast the response/recovery kinetics. The findings in this study open a new route for WO3-based hierarchical materials to detect NO2 efficiently and accurately.

Highly sensitive In2O3/PANI nanosheets gas sensor for NO2 detection

Indium oxide (In2O3) gas sensors are regarded as one of the potential materials for detecting and quantifying hazardous gases for monitoring systems and public safety assurance to address the severe environmental problems plaguing our civilization. In this work, In2O3/PANI composites were synthesized using the hydrothermal technique to explore nitrogen dioxide (NO2) sensing capabilities. The scanning electron micrographs (SEM), crystal structures (XRD), energy dispersive X-ray analysis (EDS), and the gas sensing properties were investigated to ascertain the morphology, purity, response/recovery time, optimal temperature, and recyclability. The samples displayed a gas-accessible structure with stacks of several porous nanosheets. The as-synthesized In2O3/PANI-1 sensors have extremely high responses (341.5 @ 30 ppm, 12.8 @ 3 ppm) to NO2 gas at a working temperature (250 °C), quick response times (24 s @ 30 ppm, 47 s @ 3 ppm) and recovery times (53 s @ 30 ppm, 74 s @ 3 ppm), and a low detection limit (300 ppb). Following a series of testing, high repeatability and selectivity were obtained. Furthermore, the In2O3/PANI sensor's fundamental detecting mechanism for NO2 gas was completely discussed. In addition, a developed mechanism defining the performance of the nanosheet-based sensors in NO2 gas is shown, which is backed by density functional theory (DFT) calculations to investigate the electrical characteristics of In2O3/PANI composites. This work offers an intriguing perspective as well as a useful strategy for fabricating long-lifetime In2O3-based nanosheets using the hydrothermal process.

High Sensitive, Selective and Low Cost Meso-Porous-Based Gas Sensor for No2 Detection at Room Temperature

High Sensitive, Selective and Low Cost Meso-Porous-Based Gas Sensor for No2 Detection at Room Temperature

Design and Fabrication of Nanostructure TiO2 Doped NiO as A Gas Sensor for NO2 Detection

In this paper, thin films of undoped and nickel oxide (NiO) doped titanium dioxide (TiO2) were prepared using the chemical spray pyrolysis deposition (CSP) technique, with different concentrations of nickel oxide (NiO) in the range (3-9) wt%. The morphological, structural, electrical, and sensing properties of a gas of the prepared thin films were examined. XRD measurements showed that TiO2 films have a polycrystalline structure. AFM analysis showed that these films have a regular structure both before and after doping . The roughness of these films decreased after adding impurities but then the opposite of that took place. The electrical and gas sensing properties of titanium dioxide was also affected after doping. The highest sensitivity value was obtained at doping concentration of 5wt% and working temperature 473ºK.

Optoelectronic Gas Sensor Based on Few-Layered InSe Nanosheets for NO2 Detection with Ultrahigh Antihumidity Ability.

Two-dimensional (2D) transition-metal/metal chalcogenides including MoS2, MoSe2, WS2, SnS2, etc. have shown considerable potential for the fabrication of gas sensors for NO2 detection. However, these sensors usually suffer from sluggish and incomplete recovery at room temperature, and their sensitivities are limited by presorbed O2. In this work, a novel optoelectronic gas sensor based on direct-bandgap InSe nanosheets was demonstrated. Because of the excellent photoelectric and sensing properties in few-layer InSe, detection of NO2 at room temperature was realized. Ultrahigh and reversible responses were obtained under ultraviolet (UV) light illumination, and the limit of detection (0.98 ppb) was ∼40 times lower than that observed without UV light. Furthermore, the effects of O2 and H2O molecules on sensor performance were fully studied through experiments and density functional theory. Some new mechanisms of NO2 detection in high relative humidity conditions under UV illumination were proposed, including regulation of proton transfer and induction of H2O2 reduction. In all, this work not only broadens the application field of 2D InSe, but also demonstrates the potential prospect of detecting ppb-level NO2 in complex circumstances such as human breath by using 2D material-based sensors with light activation.

Development of LED Gas Sensor for NO2 Detection for Indoor Spaces

Development of LED Gas Sensor for NO2 Detection for Indoor Spaces

Adsorption of gas molecules on a C3N monolayer and the implications for NO2 sensors

Recent reports have raised exciting prospects for the use of C3N monolayers exhibiting excellent adsorptive properties in nanodevice applications. In this study, we carried out first-principle calculations to investigate the adsorption of NO2, NO, CO, HCN, NH3, CO2, H2, N2, CH4, H2O, O2, and N2O gas molecules on a C3N monolayer as well as its potential applications in gas sensor devices. Our results reveal that the chemisorption of NO2 can significantly influence the electronic properties of the C3N monolayer (e.g., changing semiconducting behavior to conducting behavior). In contrast, physisorption of the other gas molecules had little effect on the electronic properties of the C3N monolayer. These results suggest that the C3N monolayer is much more sensitive and selective to NO2 than to the other gases. The recovery time of NO2 at T = 300 K is only 0.62 s. Moreover, the optical properties of the C3N monolayer can be modified as a result of the adsorption of different molecules, especially the NO2 molecule. Thus, the C3N monolayer is a promising and desirable candidate for use as a suitable material in gas sensors for NO2 detection.

Ultrasensitive and Fully Reversible NO2 Gas Sensing Based on p-Type MoTe2 under Ultraviolet Illumination.

The unique properties of two-dimensional (2D) materials make them promising candidates for chemical and biological sensing applications. However, most 2D material sensors suffer from extremely long recovery time due to the slow molecular desorption at room temperature. Here, we report an ultrasensitive p-type molybdenum ditelluride (MoTe2) gas sensor for NO2 detection with greatly enhanced sensitivity and recovery rate under ultraviolet (UV) illumination. Specifically, the sensitivity of the sensor to NO2 is dramatically enhanced by 1 order of magnitude under 254 nm UV illumination as compared to that in the dark condition, leading to a remarkable low detection limit of 252 ppt. More importantly, the p-type MoTe2 sensor can achieve full recovery after each sensing cycle well within 160 s at room temperature. Finally, the p-type MoTe2 sensor also exhibits excellent sensing performance to NO2 in ambient air and negligible response to H2O, indicating its great potential in practical applications, such as breath analysis and ambient NO2 detection. Such impressive features originate from the activated interface interaction between the gas molecules and p-type MoTe2 surface under UV illumination. This work provides a promising and easily applicable strategy to improve the performance of the gas sensors based on 2D materials.

Cu-modified carbon spheres/reduced graphene oxide as a high sensitivity of gas sensor for NO2 detection at room temperature

Nitrogen dioxide (NO2) as one of the most serious air pollution is harmful to people’s health, therefore high-performance gas sensors is critically needed. Here, Cu-modified carbon spheres/reduced graphene oxide (Cu@CS/RGO) composite have been prepared as NO2 gas sensor material. Carbon sphere in the interlayer of RGO can increase the specific surface area of RGO. Copper nanoparticles decorated on the surface of CS can effectively enhance the adsorption activity of RGO as supplier of free electrons. The experimental results showed that its particular structure improved the gas sensitivity of RGO at different NO2 concentrations at room temperature.

High selectivity of sulfur-doped SnO2 in NO2 detection at lower operating temperatures.

Resistive gas sensors based on metal oxides have aroused great interest in the sensing of NO2 gas due to their low cost, good stability, and easy fabrication. However, drawbacks such as low sensitivity and a lack of selectivity, which originate from the limited kinds of intrinsic active centers on the surface of the metal oxides that could be involved in the gas-sensing reaction, remain great challenges to overcome. To solve these problems, surface modification of SnO2 by S-doping was carried out by the sintering of flower-like SnS2. Gas-sensing tests revealed that the S-doped SnO2 showed ultra-high sensitivity to NO2 (Rg/Ra = 600 toward 5 ppm) with low optimal operating temperature (50 °C). The detection limit of the sensor was as low as 50 ppb (Rg/Ra = 11). Notably, the S-doped SnO2 showed negligible cross-responses to alcohol, acetone, HCHO, SO2, H2S, and xylene. The ultra-high sensitivity and selectivity toward NO2 were closely related to the content of the S-dopant. This phenomenon is attributed to the active role of S-dopant during the surface reactions with NO2, which was substantiated by in situ Raman characterization and DFT-based calculations. This study offers an important guide for surface modification by doping to improve the sensitivity and selectivity of metal oxides and sheds new light on material design to develop resistive gas sensors for NO2 detection.

Ultrasensitive WO3 gas sensors for NO2 detection in air and low oxygen environment

We report here on the results of a study into the response of a tungsten oxide based low power MEMS gas sensor to ppb of nitrogen dioxide at low levels of ambient oxygen. It was found that the resistive gas sensors not only had a high sensitivity to NO2 (3.4%/ppb vs. 0.2%/ppb obtained for commercial MOX) but can still operate reliably at lower oxygen levels (down to 0.5%) - albeit with slightly longer response and recovery times. The optimal operating temperature was determined to be ca. 350°C and so easily within the range of a MEMS based SOI CMOS substrate. The response was sensitive to significant changes in ambient humidity, but was found to have low cross-sensitivity to CO, hydrogen, methane, and acetone even at much higher ppm levels. We believe that these tungsten oxide gas sensors could be exploited in harsh applications, i.e. with a low oxygen (lean) environment often associated in the exhaust gases from combustion systems.

Hybrid Zinc Oxide Nanorods/Carbon Nanotubes Composite for Nitrogen Dioxide Gas Sensing

This study reports on the synthesis and fabrication of hybrid nanocomposite based on single-walled carbon nanotubes–ZnO nanorods (SWCNT-ZnONR) as resistive gas sensors for NO2 detection. The sensor was prepared using the standard simple and cost-effective hydrothermal process. The sensor was characterized by x-ray diffraction (XRD) and scanning electron microscopy. The findings revealed enhanced porous SWCNT-ZnONR nanocomposites due to the high porosity of the SWCNT. It was also found that the sensor exhibited average response and recovery times of about 70 s and 100 s, respectively. The XRD peak at 26° indicated that the SWCNT pattern was not disturbed, while sensitivity increased with temperature up to 150°C, at which the sensitivity was maximum. Similarly, the sensor sensitivity increased with NO2 concentration at all levels examined. Moreover, the results indicate that the sensor shows significant promise for NO2 gas sensing applications.

UV light activated gas sensor for NO2 detection

In the present study, UV light activated gas sensor was investigated for Al/Al2O3/p-Si and Al/TiO2/Al2O3/p-Si samplesby atomic layer deposition method (ALD). Generally, in order to obtain the sensing performance, traditional metal oxide semiconductor gas sensors are operated at 100–400°C. However, this temperature range limits their applications to flammable gases, and causes high power consumption. It is important to note that sensing performance experiments should have been performed at room temperature. With the support of UV light, gas sensors do not need to be heated and they can work at room temperature easily. For this purpose, electrical measurements have been performed on sensing performance with and without UV irradiation for dedection of NO2 gas. With the help of UV irradition, we obtained good sensitivity at the room temperature for Al/TiO2/Al2O3/p-Sistructure but under the same conditions no result was obtained for Al/Al2O3/p-Si structure. Without UV irradiation, there was no sensitivity for both.We observed that increasing of sensitivities at the room temperature show a direct effect of the light on the adsorbed oxygen ions. According to the relation of photocatalytic reaction and photoactivated gas sensing process, we concluded that TiO2 might be an acceptable sensor for detection of nitrogen dioxide (NO2) at room temperature under UV illumination.