NO2 Gas Concentration Research Articles

Poly (3, 3‴-dialkylquaterthiophene) Based Flexible Nitrogen Dioxide Gas Sensor

A poly (3, 3 -dialkylquaterthiophene) (PQT-12) based flexible metal-semiconductor-metal nitrogen dioxide (NO2) gas sensor fabricated on a flexible polyamide substrate has been reported in this article for the first time. The thin PQT-12 film deposited on the polyamide substrate is investigated by X-ray diffraction, atomic force microscopy, and scanning electron microscopy. The sensor shows a gas response of 24 with a response time of 41s at a very low concentration of 100-ppb NO2 gas under ambient air atmosphere. The gas response of 48 is measured at higher concentration of 500-ppb NO2 gas. The NO2 gas detection has been illustrated using a prototype circuit for the proposed sensor.

Comparative NO2 Sensing Characteristics of SnO2:WO3 Thin Film Against Bulk and Investigation of Optical Properties of the Thin Film

A comparative investigation of gas sensing properties of SnO2 doped with WO3 based on thin film and bulk forms was achieved. Thin films were deposited by thermal evaporation technique on glass substrates. Bulk sensors in the shape of pellets were prepared by pressing SnO2:WO3 powder. The polycrystalline nature of the obtained films with tetragonal structure was confirmed by X-ray diffraction. The calculated crystalline size was 52.43 nm. Thickness of the prepared films was found 134 nm. The optical characteristics of the thin films were studied by using UV-VIS Spectrophotometer in the wavelength range 200 nm to 1100 nm, the energy band gap, extinction coefficient and refractive index of the thin film were 2.5 eV , 0.024 and 2.51, respectively. Hall measurements confirmed that the films are n-type. The NO2 sensing characteristics of the SnO2:WO3 sensors were studied with various temperatures and NO2 gas concentrations. Both thin film and bulk sensors showed maximum sensitivity at temperature of 250 oC. Thin film sensors showed enhanced response in comparison to that of pellets.

Evaluating the efficiency of red mud material in removing NO2 gas

The way of using red mud - a hazardous substance created from the producing of aluminum hydroxide in removing NO2 gas is perfectly suitable with sustainable development of society in the future. This study focuses on estimating the efficacy of two different materials on treating NO2 gas: pure red mud material (non-neutralised by seawater - RM1) and hydrotalcite material created from red mud with the participant of the seawater (Seawaterneutralised red mud - RM2). Experiments were made to survey the treating ability through various factors: concentrations of input NO2 gas, flow speed of NO2 gas pass through materials, mass of materials, temperature of material used in experiments and saturated time of materials have also been tested. The results showed that seawater-neutralised red mud and red mud material were potent in the NO2 adsorption. However, RM2 material had the higher treating ability of NO2 gas than RM1 about 5 %. The result showed that optimal conditions were determined at concentrations of input NO2 were 303–397 ppm, flow speed of NO2 gas pass through materials was 0.4L/min, 10 g mass of materials, temperature of material was 30 oC. The efficiency of treating NO2 gas of RM1 and RM2 are 89.50 % and 84.43 %, respectively. The results of this study showed that both seawater-neutralised red mud and red mud have the potential to remove NO2 gas.

Fabrication of surface acoustic wave based wireless NO2 gas sensor

Surface acoustic wave (SAW) devices provide a convenient platform for the realization of sensors in the present decade. 99.4MHz SAW resonator has been fabricated over the ST cut quartz. Subsequently PZT thin film has been deposited by pulsed laser deposition technique as a sensing layer over the fabricated SAW resonator. Shift in resonance frequency was measured precisely for varying concentration of NO2 gas. The calibration curve was found to be linear having a sensitivity of 9.6Hz/ppm. The fabricated sensor is advantageous for its room temperature, handheld and wireless sensing.

Evaluation of low-cost electro-chemical sensors for environmental monitoring of ozone, nitrogen dioxide, and carbon monoxide

ABSTRACTDevelopment of an air quality monitoring network with high spatio-temporal resolution requires installation of a large number of air pollutant monitors. However, state-of-the-art monitors are costly and may not be compatible with wireless data logging systems. In this study, low-cost electro-chemical sensors manufactured by Alphasense Ltd. for detection of CO and oxidative gases (predominantly O3 and NO2) were evaluated. The voltages from three oxidative gas sensors and three CO sensors were recorded every 2.5 sec when exposed to controlled gas concentrations in a 0.125-m3 acrylic glass chamber. Electro-chemical sensors for detection of oxidative gases demonstrated sensitivity to both NO2 and O3 with similar voltages recorded when exposed to equivalent environmental concentrations of NO2 or O3 gases, when evaluated separately. There was a strong linear relationship between the recorded voltages and target concentrations of oxidative gases (R2 > 0.98) over a wide range of concentrations. Although a strong linear relationship was also observed for CO concentrations below 12 ppm, a saturation effect was observed wherein the voltage only changes minimally for higher CO concentrations (12–50 ppm). The nonlinear behavior of the CO sensors implied their unsuitability for environments where high CO concentrations are expected. Using a manufacturer-supplied shroud, sensors were tested at 2 different flow rates (0.25 and 0.5 Lpm) to mimic field calibration of the sensors with zero air and a span gas concentration (2 ppm NO2 or 15 ppm CO). As with all electrochemical sensors, the tested devices were subject to drift with a bias up to 20% after 9 months of continuous operation. Alphasense CO sensors were found to be a proper choice for occupational and environmental CO monitoring with maximum concentration of 12 ppm, especially due to the field-ready calibration capability. Alphasense oxidative gas sensors are usable only if it is valuable to know the sum of the NO2 and O3 concentrations.

The gas sensing properties of hafnium oxide thin films depending on the annealing environment

The main focus of this study is to investigate the NO2 gas-sensing properties of HfO2 thin films, taking into the account the importance of the annealing environment and temperature. HfO2 films were produced with 10 nm and 20 nm thicknesses by atomic layer deposition (ALD). They were annealed under N2 and O2 environment with rapid thermal annealing system at two different temperatures. It was found that the NO2 responses of annealed in N2 environment were higher than annealed in O2 environment. The response of 10 nm thickness HfO2 thin film was calculated 22% for N2 environment whereas, it was calculated 18% for O2 environment. The highest gas response is obtained for 10 nm thickness of HfO2 thin film annealed in N2 environment. The performance of the HfO2 thin films reveals that the gas responses rely on annealing temperature as well as annealing atmosphere. The linear dependences of the sensitivity were also observed as the NO2 gas concentrations varied from 10 ppm to 30 ppm in logarithmic forms, indicating that HfO2 thin films offer promising potential for future practical applications in monitoring the NO2 gas.

ZnO thin film prepared by a sol-gel spin coating technique for NO2 detection

The ZnO thin film sensor is developed by a low-cost sol–gel spin coating technique on a glass substrate. The structural, morphological, surface compositional, optical and electrical properties of the ZnO thin film were studied using XRD, FESEM, XPS, HRTEM, FTIR and UV–VIS techniques. The gas sensing performance of ZnO thin film is studied at different operating temperature for various gases like NO2, NH3, CH3OH, Cl2 and H2S. The ZnO thin film sensor was highly selective towards NO2 gas with a maximum response of 12.3 at 100ppm concentration at 200°C operating temperature. ZnO film sensor can also detect low concentration of NO2 gas up to 5ppm with the response of 4.1. The ZnO thin film sensor shows excellent repeatability, high stability and moderate response and recovery time, for NO2 gas in the 5–100ppm concentration range.

Palladium (Pd) sensitized molybdenum trioxide (MoO3) nanobelts for nitrogen dioxide (NO2) gas detection

The MoO3 nanobelts have been grown onto the glass substrates using chemical spray pyrolysis (CSP) deposition technique at optimized substrate temperature of 400°C. XRD study shows that the film is polycrystalline in nature and possesses an orthorhombic crystal structure. The FE-SEM micrographs show the formation of nanobelts-like morphology of MoO3. The presence of Pd and its oxidation states in Pd-sensitized MoO3 film is confirmed using EDAX and XPS study, respectively. The percentage gas response is defined as |Rg-Ra|Ra×100% where, Ra and Rg are the film resistances in presence of air and analyte gas, respectively. Before Pd sensitization, MoO3 nanobelts show NO2 gas response of 68% for 100ppm concentration at operating temperature of 200°C with response and recovery times of 15s and 150s, respectively. Selectivity coefficient study shows that the Pd-sensitized MoO3 nanobelts are more sensitive and selective towards NO2 gas among various gases such as NH3, H2S, CO, CO2 and SO2. The Pd-sensitized MoO3 nanobelts shows the enhanced response of 95.3% towards 100ppm NO2 gas concentration with response and recovery times of 74s and 297s, respectively. The lower detection limit is found to be 5ppm which is four times less than immediately dangerous to life or health (IDLH) value of 20ppm. Finally, the proposed NO2 gas sensing mechanism based on chemisorption model is discussed.

Gas sensing properties of (MoO3)0.4(V2O5)0.6 microsheets: Effect of Pd sensitization

The (MoO3)0.4(V2O5)0.6 microsheets have been successfully prepared onto the glass substrates using chemical spray pyrolysis (CSP) deposition method at optimized substrate temperature of 400 °C. The structural characterization using XRD confirm that both MoO3 and V2O5 exhibit an orthorhombic crystal structure. The two-dimensional FE-SEM micrograph shows the more porous distribution due to the random orientation of microsheets on the film surface. The EDAX analysis of Pd-sensitized (MoO3)0.4(V2O5)0.6 microsheets confirm the presence of Pd, Mo, V and O on the surface of microsheets. Selectivity study show the sensitive and selective response to NO2 gas than NH3, H2S, CO, CO2, SO2 gases at operating temperature of 200 °C. Before Pd-sensitization (MoO3)0.4(V2O5)0.6 microsheets show the NO2 gas response of 80% whereas Pd-sensitized (MoO3)0.4(V2O5)0.6 microsheets exhibit an enhanced response of 115% at 200 °C for 100 ppm NO2 gas concentration. The spill-over gas sensing mechanism reactions based on the chemisorption process at different operating temperatures is discussed to explain how Pd affect on the NO2 gas sensing properties of (MoO3)0.4(V2O5)0.6 microsheets.

ZnO/ST-Quartz SAW resonator: An efficient NO2 gas sensor

A Surface Acoustic Wave (SAW) resonator operating at a frequency of 99.50MHz using piezoelectric ST-cut quartz has been fabricated. The resonator device has been successfully integrated with ZnO sensing layer for detection of NO2 gas. The fabricated sensor device is found to be detecting trace level concentration of NO2 gas (400ppb to 16ppm) efficiently and selectively. The ZnO/Quartz SAW sensor is useful for wireless detection of NO2 gas.

Implementasi Metode Fuzzy Time Series Cheng untuk prediksi Kosentrasi Gas NO2 Di Udara

The forecasting process is essential for determining air quality to monitor NO2 gas in the air. The research aims to develop prediction information system of NO2 gas in air. The method used is Fuzzy Time Series Cheng method. The process of acquiring NO2 gas data is integrated with Multichannel-Multistasion. The data acquisition process uses Wireless Sensor Network technology via broadband internet that is sent and stored in an online database form on the web server. Recorded data is used as material for prediction. Acquisition result of NO2 gas data is obtained from the sensor which is sent to the web server in the data base in the network by on line, then for futher it is predicted using fuzzy time series Cheng applying re-divide to the results of intervals the first partition of the value of the universe of discourse by historical data fuzzification to determine Fuzzy Logical Relationship dan Fuzzy Logical Relationship Group, so that is obtained result value prediction of NO2 gas concentration. By using 36 sample data of NO2 gas, it is obtained that the value of root of mean squared error of 2.08%. This result indicates that the method of Fuzzy Time Series Cheng is good enough to be used in predicting the NO2 gas.

Effect of film thickness on NO2 gas sensing properties of sprayed orthorhombic nanocrystalline V2O5 thin films

The nanocrystalline V2O5 thin films with different thicknesses have been grown onto the glass substrates using chemical spray pyrolysis (CSP) deposition method. The XRD study shows that the films exhibit an orthorhombic crystal structure. The narrow scan X-ray photoelectron spectrum of V-2p core level doublet gives the binding energy difference of 7.3eV, indicating that the V5+ oxidation state of vanadium. The FE-SEM micrographs show the formation of nanorods-like morphology. The AFM micrographs show the high surface area to volume ratio of nanocrystalline V2O5 thin films. The optical study gives the band gap energy values of 2.41eV, 2.44eV, 2.47eV and 2.38eV for V2O5 thin films deposited with the thicknesses of 423nm, 559nm, 694nm and 730nm, respectively. The V2O5 film of thickness 559nm shows the NO2 gas response of 41% for 100ppm concentration at operating temperature of 200°C with response and recovery times of 20s and 150s, respectively. Further, it shows the rapid response and reproducibility towards 10ppm NO2 gas concentration at 200°C. Finally, NO2 gas sensing mechanism based on chemisorption process is discussed.

Improving the sensitive property of graphene-based gas sensor by illumination and heating

PurposeGraphene is a two-dimensional material. Its use has many advantages in gas sensing, but its long desorption process is problematic. The aim of this paper is to design a graphene-based gas sensor, study the response to NO2 gas concentrations and find ways to accelerate the desorption process.Design/methodology/approachIn one group, the sensor was placed in air to measure its initial resistance. Then, it was exposed to the NO2 gas at a certain concentration. Finally, the sensor was exposed to light immediately after NO2 gas exposure was ended. In another group, the sensor was heated using a heating plate at a stable temperature, before taking the measurements. Then the adsorption and desorption experiments were carried on.FindingsIllumination and heating at a suitable temperature can expedite desorption of NO2 molecules on graphene.Originality/valueIn the paper, two main methods are introduced to accelerate the desorption process when the NO2 gas is absorbed on graphene. Through a series of experiments and analysis, the authors found that the recovery time could be reduced observably and the recovery performance of the graphene-based NO2 sensor could be improved effectively.

Thermally evaporated copper oxide films: A view of annealing effect on physical and gas sensing properties

The present paper reports a facile approach to prepare copper oxide (CuO) films directly onto a glass substrate by thermal evaporation method and their chemiresistive properties towards hazardous nitrogen dioxide (NO2). The influence of annealing temperature on structural, morphological, and gas sensing properties of the CuO films has been thoroughly investigated and reported. Structural and morphological analyses has confirmed the formation of polycrystalline monoclinic CuO with uniformly distributed nanoparticles over the substrate surface. Gas sensing measurements on CuO films reveal the high response, excellent selectivity, fast response-recovery time signatures, good repeatability, and stability towards lower concentration of NO2 gas @150°C. A maximum response of 48% towards 100ppm NO2 has been achieved. Gas sensing results demonstrate an influence of morphology on the NO2 sensing performance of CuO films. In addition, the interactions between CuO sensor film and NO2 gas molecules are studied through an impendence spectroscopy analysis.

Superior selectivity and enhanced response characteristics of palladium sensitized vanadium pentoxide nanorods for detection of nitrogen dioxide gas

Vanadium pentoxide (V2O5) nanorods have been deposited onto the glass substrates by spraying 75ml of 30mM vanadium trichloride (VCl3) solution at optimized substrate temperature of 400°C. The XRD study confirms the formation of orthorhombic crystal structure of V2O5 nanorods. The FE-SEM micrograph shows the nanorods-like morphology of V2O5. The presence of palladium (Pd) in the Pd-sensitized V2O5 nanorods is confirmed using EDAX study. The gas sensing measurements show that the Pd-sensitized V2O5 sensing material is an outstanding candidate for nitrogen dioxide (NO2) gas detection. Obtained results demonstrate that the Pd-sensitized V2O5 nanorods show the superior selectivity for NO2 gas in comparison with other gases such as NH3, H2S, CO, CO2 and SO2 at an operating temperature of 200°C. It shows the 75% response for 100ppm NO2 gas concentration with response and recovery times of 22s and 126s, respectively. Finally, the gas sensing mechanism based on chemisorption process is proposed to illustrate how Pd nanoparticles affect the gas sensing characteristics (response and response-recovery times).

Fast response of sprayed vanadium pentoxide (V2O5) nanorods towards nitrogen dioxide (NO2) gas detection

The V2O5 nanorods have been successfully spray deposited at optimized substrate temperature of 400°C onto the glass substrates using vanadium trichloride (VCl3) solution of different concentrations. The effect of solution concentration on the physicochemical and NO2 gas sensing properties of sprayed V2O5 nanorods is studied at different operating temperatures and gas concentrations. The XRD study reveals the formation of V2O5 having an orthorhombic symmetry. The FE-SEM micrographs show the nanorods-like morphology of V2O5. The AFM micrographs exhibit a well covered granular surface topography. For direct allowed transition, the band gap energy values are found to be decreased from 2.45eV to 2.42eV. The nanorods deposited with 30mM solution concentration shows the maximum response of 24.2% for 100ppm NO2 gas concentration at an operating temperature of 200°C with response and recovery times of 13s and 140s, respectively. Finally, the chemisorption mechanism of NO2 gas on the V2O5 nanorods is discussed.

Nanostructured tin oxide films: Physical synthesis, characterization, and gas sensing properties

Nanostructured tin oxide (SnO2) films are synthesized using physical method i.e. thermal evaporation and are further characterized with X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy measurement techniques for confirming its structure and morphology. The chemiresistive properties of SnO2 films are studied towards different oxidizing and reducing gases where these films have demonstrated considerable selectivity towards oxidizing nitrogen dioxide (NO2) gas with a maximum response of 403% to 100ppm @200°C, and fast response and recovery times of 4s and 210s, respectively, than other test gases. In addition, SnO2 films are enabling to detect as low as 1ppm NO2 gas concentration @200°C with 23% response enhancement. Chemiresistive performances of SnO2 films are carried out in the range of 1–100ppm and reported. Finally, plausible adsorption and desorption reaction mechanism of NO2 gas molecules with SnO2 film surface has been thoroughly discussed by means of an impedance spectroscopy analysis.

Concentration dependent dielectric, AC conductivity and sensing study of ZnO-polyvinyl alcohol nanocomposite films

The dielectric properties of polyvinyl alcohol (PVA) - zinc oxide (ZnO) hybrid nanocomposite films for different concentrations of nano ZnO (5 mol%-20 mol%) have been studied at ambient temperature in the frequency range 10 Hz-10 MHz. These studies indicate that the dielectric constant is maximum for 10 mol% ZnO-PVA hybrid film. An unusual low intensity loss peak is observed around 2.5-5 MHz in all the samples and this peak is more pronounced in the 10 mol% ZnO film. Impedance and modulus spectroscopy have been used to understand the dielectric and conductivity behaviour of these samples. These samples exhibit high bulk resistance and the Cole-Cole plot shows only the onset of the semicircles at room temperature. AC conductivity is found to obey Jonscher's power law and the enhancement in the conductivity is found to be highest for 10 mol% ZnO doped PVA nanocomposite film suggesting its suitability for use in sensing applications. The gas sensing performance of the hybrid films for detection of various gases such as NO2, H2S, NH3, LPG, and C2H5OH was studied and compared with that of pure PVA film. It was found that the hybrid sensor can complement the drawbacks of pure PVA as porous surface morphology and surface area of interface of nano-ZnO plays a vital role in sensing applications. At ambient temperature, 100 ppm concentration of both NO2 gas and H2S gas exhibit maximum response of 7.1% and 4.1% respectively for the 10 mol% hybrid sensor, whereas at 50 ppm concentration of H2S gas the 20 mol% ZnO-PVA sensor was found to be more sensitive with a reasonable response of 7%.

Visible photoassisted room-temperature oxidizing gas-sensing behavior of Sn2S3 semiconductor sheets through facile thermal annealing.

Well-crystallized Sn2S3 semiconductor thin films with a highly (111)-crystallographic orientation were grown using RF sputtering. The surface morphology of the Sn2S3 thin films exhibited a sheet-like feature. The Sn2S3 crystallites with a sheet-like surface had a sharp periphery with a thickness in a nanoscale size, and the crystallite size ranged from approximately 150 to 300 nm. Postannealing the as-synthesized Sn2S3 thin films further in ambient air at 400 °C engendered roughened and oxidized surfaces on the Sn2S3 thin films. Transmission electron microscopy analysis revealed that the surfaces of the Sn2S3 thin films transformed into a SnO2 phase, and well-layered Sn2S3–SnO2 heterostructure thin films were thus formed. The Sn2S3–SnO2 heterostructure thin film exhibited a visible photoassisted room-temperature gas-sensing behavior toward low concentrations of NO2 gases (0.2–2.5 ppm). By contrast, the pure Sn2S3 thin film exhibited an unapparent room-temperature NO2 gas-sensing behavior under illumination. The suitable band alignment at the interface of the Sn2S3–SnO2 heterostructure thin film and rough surface features might explain the visible photoassisted room-temperature NO2 gas-sensing responses of the heterostructure thin film on exposure to NO2 gas at low concentrations in this work.

Development of highly sensitive ZnO/In2O3 composite gas sensor activated by UV-LED

The photo-responsive behavior of ZnO/In2O3 composite sensors was investigated for detecting low concentrations of NO2 gas under 365nm UV-LED irradiation at room temperature. The composite samples were prepared by the co-precipitation method with the appropriate components ratio to obtain superior sensing performance. The composition, structure, and optical properties of the synthesized sensing materials were characterized by EDS, XRD, SEM, XPS and UV–vis analyses. In terms of gas sensing performance, the synergistic effects of combined materials led to an enhanced response of the composite sensors, compared to those of pristine ZnO and In2O3 sensors under UV illumination. The considerable improvement in sensor response was attributed to the ZnO role in charge carrier mobility enhancement and low recombination rate of active charge carriers, as well as In2O3 contributions as radiation absorption centers and chemisorption promoters in the composite structure. It was found that the response of the composite gas sensor is largely dependent on the UV irradiance in which increasing the UV flux reduced the response, but shortened the response time.