Nitrogen Dioxide Sensor Research Articles

Oxygen Plasma-Assisted Defect Engineering of Graphene Nanocomposites with Ultrasmall Co3O4 Nanocrystals for Monitoring Toxic Nitrogen Dioxide at Room Temperature.

Functional adjustment of graphene with metal oxide can in fact progress the affectability of graphene-based gas sensors. However, it could be a huge challenge to upgrade the detecting execution of nitrogen dioxide (NO2) sensors at room temperature. The ultrasmall size of nanocrystals (NCs) and copious defects are two key variables for moving forward gas detecting execution. Herein, we provide an effective strategy that the hydrothermal reaction is combined with room-temperature oxygen plasma treatment to prepare Co3O4 NCs and reduced graphene oxide (RGO) nanohybrids (Co3O4-RGO). Among all of Co3O4-RGO nanohybrids, Co3O4-RGO-60 W exhibits the most superior NO2 sensing properties and achieves the low-concentration detection of NO2. The sensitivity of Co3O4-RGO-60 W to 20 ppm NO2 at room temperature is the highest (72.36%). The excellent sensing properties can mainly depend on the change in the microstructure of Co3O4-RGO. Compared with Co3O4-RGO, Co3O4-RGO-60 W with oxygen plasma treatment shows more favorable properties for NO2 adsorption, including the smaller size of Co3O4 NCs, larger specific surface area, pore size, and more oxygen vacancies (OVs). Especially, OVs make the surface of NCs have a unique chemical state, which can increase active sites and improve the adsorption property of NO2. Besides, the agreeable impact of the p-p heterojunction (Co3O4 and RGO) and the doping of N molecule contribute to the improved NO2 detecting properties. It is demonstrated that the Co3O4-RGO-60 W sensor is expected to monitor NO2 at room temperature sensitively.

Facile solvothermal synthesis of ZnO/Ti3C2Tx MXene nanocomposites for NO2 detection at low working temperature

Nitrogen dioxide sensors with high performance have been expected for practical applications in environmental monitoring. Herein, we demonstrate a NO2 gas sensor with enhanced performance based on ZnO/Ti3C2Tx nanocomposites. The hawthorn shaped ZnO spheres/Ti3C2Tx nanocomposites with regular morphology are successfully synthesized via a facile solvothermal method. The NO2 sensing properties are greatly improved by introducing the Ti3C2Tx sheets which significantly reduce the operating temperature and improve the gas sensitivity. The response to 8 ppm NO2 improves to 3.4, and the response and recovery characteristic substantially speeds up to 191 s and 254 s at lower working temperature. The excellent NO2 sensing properties of ZnO/Ti3C2Tx nanocomposites are attributed to the high surface area, the modulation of carrier density, the formation of ZnO/Ti3C2Tx heterojunction. Such excellent performance showed the promising application of hawthorn shaped ZnO spheres/Ti3C2Tx nanocomposites for NO2 gas sensing.

High sensitivity organic transistor nitrogen dioxide sensor based on three component conjugated polymer

High sensitivity organic transistor nitrogen dioxide sensor based on three component conjugated polymer

Seasonal Influence on the Performance of Low-Cost NO2 Sensor Calibrations.

Low-cost sensor technology has been available for several years and has the potential to complement official monitoring networks. The current generation of nitrogen dioxide (NO2) sensors suffers from various technical problems. This study explores the added value of calibration models based on (multiple) linear regression including cross terms on the performance of an electrochemical NO2 sensor, the B43F manufactured by Alphasense. Sensor data were collected in duplicate at four reference sites in the Netherlands over a period of one year. It is shown that a calibration, using O3 and temperature in addition to a reference NO2 measurement, improves the prediction in terms of R2 from less than 0.5 to 0.69–0.84. The uncertainty of the calibrated sensors meets the Data Quality Objective for indicative methods specified by the EU directive in some cases and it was verified that the sensor signal itself remains an important predictor in the multilinear regressions. In practice, these sensors are likely to be calibrated over a period (much) shorter than one year. This study shows the dependence of the quality of the calibrated signal on the choice of these short (monthly) calibration and validation periods. This information will be valuable for determining short-period calibration strategies.

High Performance Acoustic Wave Nitrogen Dioxide Sensor with Ultraviolet Activated 3D Porous Architecture of Ag-Decorated Reduced Graphene Oxide and Polypyrrole Aerogel.

Surface acoustic wave (SAW) devices have been widely explored for real-time monitoring of toxic and irritant chemical gases such as nitrogen oxide (NO2), but they often have issues such as a complicated process of the sensing layer, low sensitivity, long response time, irreversibility, and/or requirement of high temperatures to enhance sensitivity. Herein, we report a sensing material design for room-temperature NO2 detection based on a 3D porous architecture of Ag-decorated reduced graphene oxide-polypyrrole hybrid aerogels (rGO-PPy/Ag) and apply UV activation as an effective strategy to further enhance the NO2 sensing performance. The rGO-PPy/Ag-based SAW sensor with the UV activation exhibits high sensitivity (127.68 Hz/ppm), fast response/recovery time (36.7 s/58.5 s), excellent reproducibility and selectivity, and fast recoverability. Its enhancement mechanisms for highly sensitive and selective detection of NO2 are based on a 3D porous architecture, Ag-decorated rGO-PPy, p-p heterojunction in rGO-PPy/Ag, and UV photogenerated carriers generated in the sensing layer. The scientific findings of this work will provide the guidance for future exploration of next-generation acoustic-wave-based gas sensors.

Highly Sensitive Nitrogen Dioxide Sensor Based on Enhancement of Surface Plasmon Resonance Response in Glass Waveguides by C–Ag Nanodots

Highly Sensitive Nitrogen Dioxide Sensor Based on Enhancement of Surface Plasmon Resonance Response in Glass Waveguides by C–Ag Nanodots

Wearable NO2 sensing and wireless application based on ZnS nanoparticles/nitrogen-doped reduced graphene oxide

Wearable electronics consists of mechanically flexible sensor networks and the corresponding circuit system can provide real-time monitoring and recording of toxic gases. In this work, we present a convenient watch-type wearable nitrogen dioxide (NO2) sensor based on ZnS nanoparticles/nitrogen-doped reduced graphene oxide (ZnS NPs/N-rGO) as a flexible device. The power consumption of the flexible sensor is as low as 0.52 μW. The response value of the device for 10 ppm NO2 is 2.2; while the recovery time is 724 s, with a low theoretical limit of detection at 69 ppb, with the device maintaining stable mechanical durability. By reading and analyzing the signal data through wireless bluetooth transmission, the device can provide timely monitoring and early warning for NO2 leakage. Furthermore, the impressive room-temperature sensing performance of ZnS NPs/N-rGO is attributed to factors of geometrical and electronic effects. More specifically, ZnS NP uniformly dispersed on rGO greatly expands the effective contact area with the target gas molecules, and the built-in electric field formed by the strong charge interaction between them also effectively improves the detection sensitivity. The successful development of this type of wireless wearable sensor provides an effective reference for the future application and development of high-performance, low-power, and lightweight sensing equipment.

Progressive NO2 Sensors with Rapid Alarm and Persistent Memory‐Type Responses for Wide‐Range Sensing Using Antimony Triselenide Nanoflakes

AbstractAntimony triselenide (Sb2Se3) nanoflake‐based nitrogen dioxide (NO2) sensors exhibit a progressive bifunctional gas‐sensing performance, with a rapid alarm for hazardous highly concentrated gases, and an advanced memory‐type function for low‐concentration (<1 ppm) monitoring repeated under potentially fatal exposure. Rectangular and cuboid shaped Sb2Se3 nanoflakes, comprising van der Waals planes with large surface areas and covalent bond planes with small areas, can rapidly detect a wide range of NO2 gas concentrations from 0.1 to 100 ppm. These Sb2Se3 nanoflakes are found to be suitable for physisorption‐based gas sensing owing to their anisotropic quasi‐2D crystal structure with extremely enlarged van der Waals planes, where they are humidity‐insensitive and consequently exhibit an extremely stable baseline current. The Sb2Se3 nanoflake sensor exhibits a room‐temperature/low‐voltage operation, which is noticeable owing to its low energy consumption and rapid response even under a NO2 gas flow of only 1 ppm. As a result, the Sb2Se3 nanoflake sensor is suitable for the development of a rapid alarm system. Furthermore, the persistent gas‐sensing conductivity of the sensor with a slow decaying current can enable the development of a progressive memory‐type sensor that retains the previous signal under irregular gas injection at low concentrations.

Metal-Organic Framework as a Functional Analyte Channel of Organic-Transistor-Based Air Pollution Sensors.

Air pollution sensors based on organic transistors have attracted much interest recently; however, the devices suffer from low responsivity and slow response and recovery rates for gas analytes. These shortcomings are attributed to the low charge-carrier mobility of organic semiconductors and to a structural limitation resulting from the use of a thick and continuous active layer. In the present work, we investigated the material properties of a multiscale porous zeolitic imidazolate framework, [Zn(2-methylimidazole)2]n (ZIF-8), and examined its potential as an analyte channel material inserted at an organic-transistor active layer. A series of carbonized zeolitic imidazolate frameworks (ZIFs) were prepared by thermal conversion of ZIF-8 and also studied for comparison. The microstructures, morphologies, and optical/electrical characteristics of polythiophene/ZIF-8 hybrid films were systematically investigated. Organic-transistor-type nitrogen dioxide sensors based on the polythiophene/ZIF-8 hybrid films showed substantially improved sensing properties, including responsivity, response rate, and recovery rate. The electrical conductivity of the carbonized ZIF-8s enhanced the field-effect mobility of the organic transistors; however, the sensing performance was not improved, because of the closed pore structures resulting from the carbonization. These results provide invaluable information and useful insights into the design of transistor-type gas sensors based on organic semiconductor/metal-organic framework hybrid films.

Amperometric gas sensors based on screen printed electrodes with porous ceramic substrates

In the present study, an amperometric gas sensor based on room temperature ionic liquid (RTIL) electrolyte and screen-printed electrodes (SPE) was fabricated. In order to compose the sensor device, a porous alumina ceramic was used as gas diffusion barrier and substrate of SPE, simultaneously. While RTIL electrolytes were also solidified with casting method to form a solid film and attached onto porous ceramics equipped with printed electrodes. It was found that with this design, the amperometric sensor could become smaller and easier to intergrade. Additionally, the porous ceramics as the diffusion barrier as substrate enable gas molecules diffuse into the three-phase (gas/electrode/electrolyte) interface directly without passing through RTIL membranes. For demonstration, an amperometric nitrogen dioxide (NO2) sensor was composed with our proposed structure and the sensing performance were characterized in terms of sensitivity, selectivity and stability. It was indicated that indeed our NO2 sensor show a very rapid response speed, only 20 s and 10 s for responding and recovering, respectively. This is 4 times shorter than the traditional sensor structure based on RTIL. In addition, the sensor has a good sensitivity (33 nA / ppm) and limit of detection (LOD) around 0.02 ppm with a signal noise ratio (SNR) around 3. It was also detected that the sensor has a wide operating temperature range (-20 to 40 °C), suggesting our sensor devices could work in extreme environments.

Sub‐ppb nitrogen dioxide detection based on resonant photoacoustic spectroscopy

AbstractA photoacoustic spectroscopy sensor for nitrogen dioxide (NO2) detection was presented based on a high‐power broadband blue diode laser emitting at 446 nm. An optical chopper was replaced by a transistor transistor logic modulation signal generated by the signal generator to reduce mechanical noise. The detection limit of NO2 sensor system reached to 46 ppt by the Allan variance analysis on the benefit of reflection‐enhanced. A continuous detection of NO2 in the atmosphere for 48 h was implemented in collaboration with an adaptive Kalman filter for lessening the noise in the measurement. The experimental results were highly consistent with the data of the China National Environmental Monitoring Center, demonstrating the accuracy and reliability of our NO2 sensor system. This work provides a promising method for NO2 and other atmospheric pollution gasses.

Microstructure control of organic semiconductors via UV-ozone for high-sensitivity NO2 detection

Developing high sensitive organic semiconductors (OSCs) in organic thin-film transistors (OTFTs) is the key for OTFT based gas sensors. Herein, we report a simple processing route of highly sensitive OSCs for high performance OTFT based nitrogen dioxide (NO2) sensors, where the active OSC layer is based on ultraviolet-ozone (UVO) treated poly(3-hexylthiophene-2,5-diyl) (P3HT). Compared to conventional P3HT based OTFT sensors, the reported device exhibits a remarkable improvement of the gas response from 350% to 30000%. The studies in morphologies, chemical compositions and microstructures of the UVO-treated films reveal that a large number of carrier traps generated in the P3HT films is the decisive reason for the enhancement of sensing performance. Moreover, the optimized device shows great potential of practical applications on the stand points of sensitivity, selectivity, reusability and the ability of recovery, as well as limit of detection of ~7.3 ppb. This simple method provides an innovative understanding for the role of the carrier traps in sensing performance and demonstrates a bright future for developing high performance OTFT gas sensors.

Design of a Dual-Mode Graphene-on-Microring Resonator for Optical Gas Sensing

On-chip optical gas sensors, which use resonant shifts of cavities to detect molecular concentrations, have the advantages of high sensitivity, real-time detection, and compact footprint. However, such sensors are usually limited by a serious cross-sensitivity issue induced by environmental temperature variations. To overcome this limitation, we study a dual-mode graphene-on-microring resonator to accurately measure gas concentrations without suffering from temperature variations. To be specific, the influences of gas-induced graphene’s optical conductivity changes and environmental temperature variations on effective refractive indices of TE0 and TE1 modes in the resonator can be decoupled based on the modal linear independent responses. With this method, we designed a nitrogen dioxide sensor with a sensitivity of 0.02 nm/ppm and a limit of detection of 0.5 ppm. Our study paves the way for developing on-chip optical gas sensors with excellent sensitivity and temperature stability.

Porous Co3O4 nanocrystals derived by metal-organic frameworks on reduced graphene oxide for efficient room-temperature NO2 sensing properties

The combination of metal oxide and reduced graphene oxide (RGO) is a promising route but remains challenges to develop high-performance room-temperature nitrogen dioxide (NO2) sensors. The low gas sensitive properties of metal oxides-based sensors are mainly related to the poor surface activity of metal oxides at room temperature. Herein, a novel strategy for detecting ppm-level NO2 at room temperature is proposed. Highly porous Co3O4 nanoframeworks coated with polypyrrole (PPy) on RGO (Co3O4/PPy/RGO) are prepared by using metal-organic frameworks (MOFs) as precursors. Co3O4/PPy/RGO with Co3O4 nanocrystals (~5 nm) exhibit highly gas-accessible structure (pore size: 12.8 nm and surface area: 108.4 m2 g−1), which can serve as promising sensing materials for sensitive room-temperature NO2 gas sensors. As a result, the sensor based on Co3O4/PPy/RGO exhibits improved NO2 sensing properties with the sensitivity of 37.6% towards 3 ppm NO2, as compared with that of Co3O4/RGO (28.5%) and PPy/RGO (18.7%) at room temperature. In order to further investigate the mechanism of NO2 sensing, Brunauer-Emmett-Teller (BET), Current vs voltage (I-V) curves, In-situ X-ray photoelectron spectroscopy (XPS) and other characterizations are used to analyze the surface microstructure, surface chemistry and electrical properties of Co3O4/PPy/RGO, when the sensor is exposed to NO2.

High performance nitrogen dioxide sensor based on organic thin-film transistor utilizing P3HT/OH-MWCNTs blend film

Organic thin-film transistor (OTFT) based nitrogen dioxide (NO2) gas sensors were fabricated by utilizing blend film as active layer, which was composed by poly (3-hexylthiophene-2,5-diyl) (P3HT) and hydroxylated multi-walled carbon nanotubes (OH-MWCNTs). By optimizing the blend ratios (P3HT/OH-MWCNTs), the sensitivity of OTFTs to 30 ppm NO2 is up to 1320 %, while the pristine P3HT device is only 96 %, realizing a ca. 10 times enhancement. The OTFTs with P3HT/OH-MWCNTs blend active layer also exhibit excellent selectivity for NO2 against CO, NH3 and. H2S. By investigating the morphologies and microstructures of blend films via atomic force microscope, optical microscopy and UV–vis spectrophotometer, the improvement of sensing performance was mainly attributed to more gaps between the P3HT aggregations with the introduction of OH-MWCNTs, which was beneficial to the diffusion and adsorption of NO2. This work demonstrates that OH-MWCNTs can be applied in the field of OTFT by simple solution method for realizing high sensing performance gas sensor.

NO2 gas sensors based on CVD tungsten diselenide monolayer

Two-dimensional (2D) transition metal dichalcogenides (TMDs) are promising for gas sensors owing to their large surface-to-volume ratios, but the long recovery times stemming from the slow molecular desorption have been an important limitation. In this work, we report on a sensor for nitrogen dioxide (NO2) made with a diselenide (WSe2) monolayer synthesized via chemical vapor deposition, which functions within a range of concentrations from 100 ppb to 5 ppm and at various temperatures, including room temperature. When operated at an optimized temperature of 250 °C, the WSe2 sensor exhibited the fast recovery, with the response (τres) and recovery (τrec) times of 18 s and 38 s, respectively, when exposed to 100 ppb NO2. The sensor also features high selectivity toward NO2 in the presence of other target gases, in addition to reversibility and long-term stability within 60 days. The overall characteristics of the WSe2 sensor make it suitable to monitor indoor/outdoor environments, mainly if further optimization is made with sensor design based on a model for the sensing mechanism we present in this paper.

Fully Integrated Photoacoustic NO2 Sensor for Sub-ppb Level Measurement.

A fully integrated photoacoustic nitrogen dioxide (NO2) sensor is developed and demonstrated. In this sensor, an embedded photoacoustic cell was manufactured by using an up-to-date 3D printing technique. A blue laser diode was used as a light source for excitation of photoacoustic wave in the photoacoustic cell. The photoacoustic wave is detected by a sensitive microelectromechanical system (MEMS) microphone. Homemade circuits are integrated into the sensor for laser diode driving and signal processing. The sensor was calibrated by using a chemiluminescence NO–NO2–NOX gas analyzer. And the performance of this sensor was evaluated. The linear relationship between photoacoustic signals and NO2 concentrations was verified in a range of below 202 ppb. The limit of detection was determined to 0.86 ppb with an integration time of 1 s. The corresponding normalized noise equivalent absorption was 2.0 × 10−8 cm−1∙W∙Hz−1/2. The stability and the optimal integration time were evaluated with an Allan deviation analysis, from which a detection limit of 0.25 ppb at the optimal integration time of 240 s was obtained. The sensor was used to measure outdoor air and the results agree with that obtained from the NO–NO2–NOX gas analyzer. The low-cost and portable photoacoustic NO2 sensor has a potential application for atmospheric NO2 monitoring.

Ionization-based nitrogen dioxide sensor with incorporated carbon nanotubes and temperature compensation

The accurate and rapid determination of NO2 is a requirement for industrial monitoring and environmental protection. The ionization-based nitrogen dioxide sensor has the advantages of rapid detection, high sensitivity and wide measurement range but is affected by temperature. In this paper, an ionization-based nitrogen dioxide sensor with incorporated carbon nanotubes and temperature compensation is reported. Measurements were conducted as the NO2 concentration was varied from 0 to 3000 ppm at a 150 V operating voltage and different temperatures. The output current of the ionized NO2 sensor decreases with the NO2 concentration, but increases with the temperature. The results showed that the first ionization coefficient, emitted electrons, and secondary emitted electrons are the temperature factors affecting the ionized gas sensor. Bivariate regression analysis and regression model of least-square support vector machine were used to treat the experimental measurements. The results showed that least-square support vector machine provided a better analysis by significantly reducing the maximum fiducial error to less than 1% and greatly improved the ability of ionized NO2 sensor using carbon nanotube to correct for temperature interferences.

Structure and gas sensitive properties of oxide compositions WO3—In2O3 and WO3—CO3O4

Nanocrystalline tungsten oxide (WO3), indium oxide (In2O3), cobalt oxide (Co3O4) and mixed composites with different WO3—In2O3 and WO3—Co3O4 ratios were obtained by the sol-gel method after calcination of xerogels at 400—600 °C. The morphology, phase composition, and structural features of the materials obtained were studied by X-ray diffraction, infrared spectroscopy, and scanning electron microscopy. The increase in the gas sensitivity of the joint composition compared to the initial oxides can be explained by a decrease in the crystallite size and an increase in the specific surface, as well as by the dependence of the surface state of the grains on the composition. The highest sensory response to nitrogen dioxide in both compositions lies in the range of 130—150 °C, and to carbon monoxide, above 230 °C. Low-power planar nitrogen dioxide sensors with a sensitivity of << 1 ppm and power consumption ≤ 85 mW were produced.

Phase Separation of P3HT/PMMA Blend Film for Forming Semiconducting and Dielectric Layers in Organic Thin-Film Transistors for High-Sensitivity NO2 Detection.

Formation of the semiconductor/dielectric double-layered films via vertical phase separations from polymer blends is an effective method to fabricate organic thin-film transistors (OTFTs). Here, we introduce a simple one-step processing method for the vertical phase separation of poly(3-hexylthiophene-2,5-diyl) (P3HT) and poly(methyl methacrylate) (PMMA) blends in OTFTs and their applications for high-performance nitrogen dioxide (NO2) sensors. Compared to the conventional two-step coated OTFT sensors, one-step processed devices exhibit a great enhancement of the responsivity from 116 to 1481% for 30 ppm NO2 concentration and a limit of detection of ∼0.7 ppb. Studies of the microstructures of the blend films and the electrical properties of the sensors reveal that the devices formed by the one-step vertical phase separation have better capability for the adsorption of NO2 molecules. Moreover, a careful adjustment of the blend ratio between P3HT and PMMA can further improve the performance of the NO2 sensors, ranging from sensitivity to selectivity and to the ability of recovery. This simple one-step processing method demonstrates a potential possibility for developing high-performance, low-cost, and large-area OTFT gas sensors.