Selective Detection Of NO2 Research Articles

Highly sensitive and selective NO2 detection using face-centered cubic Zn2SnO4 nanostructures

This study reports the synthesis and modification of hexagonal ZnO to face-centered cubic (Fcc) Zn2SnO4 via a single hydrothermal method. We systematically investigated the synthesized materials' structural, morphological, surface area, and sensing properties. X-ray diffraction (XRD) analysis confirmed the Fcc structure of the Sn-modified ZnO samples. X-ray photoelectron spectroscopy (XPS) was employed to elucidate the influence of Sn modified on defect levels in these chemical sensors. Remarkably, Zn2SnO4 exhibited outstanding NO2 sensing properties, including high response, selectivity, and recovery characteristics. The sensor demonstrated a rapid response time of less than 18s and an optimal operating temperature of 260 °C. Furthermore, the cubic face-centered Zn2SnO4 displayed a wide detection range of 1–100 ppm for NO2. The synergistic effects of chemical sensitization and catalytic activity are responsible for the enhanced sensing mechanism in Zn2SnO4.

Nitrogen-Doped Indium Oxide Electrochemical Sensor for Stable and Selective NO2 Detection.

Efficient gas sensors are critical for environmental monitoring and industrial safety. While metal oxide semiconductor (MOS) sensors are cost-effective, they struggle with poor selectivity, high operating temperatures, and limited stability. Electrochemical sensors, though selective and energy-efficient, face high costs, and stability issues due to precious metal catalysts like platinum on carbon (Pt/C). Herein, a novel, cost-effective electrochemical sensor using nitrogen-doped indium oxide In2O3- xN2 x /3Vx /3 (0.01≤x≤0.14), synthesized with varying nitriding times is presented. The optimized In2O3 N-40min sensor demonstrates a remarkable response current of 771 nA to 10ppm nitrogen dioxide (NO2) at ambient temperature, with outstanding long-term stability (over 30 days) and rapid response/recovery times (5/16 s). Compared to Pt/C sensors, it shows 84% and 67% reductions in response and recovery times, respectively, and maintains 98% performance after a month, versus 68% for Pt/C. This cost-effective sensor presents a promising alternative for electrochemical gas sensing, eliminating the need for precious metal catalysts.

Advancing room temperature NO2 gas sensing performance through high-energy mechanical milling of Tin-dichalcogenides

Eco-friendly gas sensing devices with simple architecture, reduced cost, and high performance at room temperature are being sought to replace the traditional metallic oxide materials, aiming to address environmental concerns. Lamellae semiconducting materials have shown promising detection properties for this purpose. Here, we investigated the sensing response of SnS2, Sn(S0.5Se0.5)2, and SnSe2 tin-dichalcogenides prepared by high-energy mechanical milling. High RNO2/Rair response signals, from 102 to 106, for 2–100 ppm of NO2 were observed for temperatures between 30 °C and 300 °C. The materials were not sensitive to CO, while H2 detection could only be observed above 200 °C, implying high NO2 selectivity. Additionally, we investigated the influence of samples suspension in water and isopropanol on grain size and morphology. We found that isopropanol crystallizes amorphous selenium phase dispersed in the Sn-Se system and increase the agglomeration in the Sn(S0.5Se0.5)2 system. Deformed and defective particles were observed regardless the preparation methodology. This unique defect-rich morphology might increase surface reactivity for selective NO2 detection by physisorption, owing a high adsorption/desorption rate at room temperature.

Enhanced Gas Sensing Performance of CuO-ZnO Composite Nanostructures for Low-Concentration NO2 Detection

The detection of nitrogen dioxide (NO2) is essential for safeguarding human health and addressing environmental sustainability. That is why, in the last decades, gas sensors have been developed to detect NO2 to overcome these hazards. This study explores the use of a novel CuO-ZnO composite synthesized through a polyol and sol–gel technique to enhance gas sensing performance. The CuO-ZnO composite offers the advantage of a synergic combination of its properties, leading to improved sensitivity, selectivity, and low detection limit. The innovative polyol technique employed in this research enables the controlled synthesis of hierarchical CuO and porous ZnO structures. The composite formation is achieved using the sol–gel method, resulting in CuO-ZnO composites with different ratios. The structural, morphological, and optical properties of the materials have been characterized using FESEM, X-ray diffraction, and UV-vis spectroscopy. Gas sensing experiments demonstrate enhanced performance, particularly in sensitivity and selectivity for NO2, even at low concentrations. The composites also exhibit improved baseline stability compared to pristine CuO and ZnO. This study explains the influence of humidity on gas sensing properties by examining interactions between water molecules and sensor surfaces. Notably, the developed CuO-ZnO composite displays excellent selectivity towards NO2, attributed to favorable bonding characteristics and acid-base properties. Overall, this research contributes to advancing gas sensor technology, providing a promising potential for sensitive and selective NO2 detection, thereby addressing critical needs for human health and environmental protection.

Black Phosphorus-Tungsten Oxide Sandwich-like Nanostructures for Highly Selective NO2 Detection.

Modern chemical production processes often emit complex mixtures of gases, including hazardous pollutants such as NO2. Although widely used, gas sensors based on metal oxide semiconductors such as WO3 respond to a wide range of interfering gases other than NO2. Consequently, developing WO3 gas sensors with high NO2 selectivity is challenging. In this study, a simple one-step hydrothermal method was used to prepare WO3 nanorods modified with black phosphorus (BP) flakes as sensitive materials for NO2 sensing, and BP-WO3-based micro-electromechanical system gas sensors were fabricated. The characterization of the as-prepared BP-WO3 composite through X-ray diffraction scanning electron microscopy and X-ray photoelectron spectroscopy confirmed the successful formation of the sandwich-like nanostructures. The result of gas-sensing tests with 2-14 ppm NO2 indicated that the sensor response was 1.25-2.21 with response-recovery times of 36 and 36 s, respectively, at 190 °C. In contrast to pure WO3, which exhibited a response of 1.07-2.2 to 0.3-5 ppm H2S at 160 °C, BP-WO3 showed almost no response to H2S. Thus, compared with pure WO3, BP-WO3 exhibited significantly improved NO2 selectivity. Overall, the BP-WO3 composite with sandwich-like nanostructures is a promising material for developing highly selective NO2 sensors for practical applications.

Influence of Pt-loading on the energy band gap and gas sensing of titanium perovskite

Nickel titanate (NiTiO3) and zinc titanate (ZnTiO3) perovskite nanostructures were fabricated via a facile microwave-assisted hydrothermal method, followed by loading 1 wt% of Pt using a precipitation method to obtain Pt–NiTiO3 and Pt–ZnTiO3. Scanning electron microscope revealed a tube-like arrangement of the NiTiO3 nanoparticles and a porous network of ZnTiO3 nanoparticles. X-ray powder diffraction confirmed the single-phase ilmenite structure of both NiTiO3 and ZnTiO3 nanoparticles, which was further preserved after Pt-loading. UV–Vis diffused reflectance, photoelectron yield, and photoluminescence as well as the x-ray photoelectron spectroscopy analyses provided insight into the energy band gap, ionization energy, and the type of defects present in the synthesized titania perovskites. The gas sensing results revealed that Pt-loading enhanced the sensitivity and induced Pt–NiTiO3 selective detection of NO2 among the other tested corrosive gases, such as CO2, and SO2. This improvement was justified by the synergetic contribution of the catalytic ability of both Pt and NiTiO3 as well as the metal/semiconductor heterojunction leading to improved NO2 adsorption.

Selective detection of NO using the perovskite-type oxide LaMO3 (M = Cr, Mn, Fe, Co, and Ni) as the electrode material for yttrium-stabilized zirconia-based electrochemical sensors

An yttrium-stabilized zirconia-based electrochemical sensor with LaCrO3 as the electrode material was used to selectively detect NO.

Ag-Doped MoSe2/ZnO Heterojunctions: A Highly Responsive Gas-Sensitive Material for Selective Detection of NO Based on DFT Study.

In this work, the adsorption and sensing behavior of Ag-doped MoSe2/ZnO heterojunctions for H2, CH4, CO2, NO, CO, and C2H4 have been studied based on density functional theory (DFT). In gas adsorption analysis, the adsorption energy, adsorption distance, transfer charge, total electron density, density of states (DOS), energy band structure, frontier molecular orbital, and work function (WF) of each gas has been calculated. Furthermore, the reusability and stability of the Ag-doped MoSe2/ZnO heterojunctions have also been studied. The results showed that Ag-doped MoSe2/ZnO heterojunctions have great potential to be a candidate of highly selective and responsive gas sensors for NO detection with excellent reusability and stability.

Thickness dependent p-n switching in SnSe2/SnOx/SnSe heterojunction-based NO2 gas sensor as well as photodetector

SnSe2/SnOx/SnSe heterojunction thin films with different thicknesses 137, 241 and 297 nm were fabricated via the thermal evaporation technique. XRD, FESEM, Raman spectroscopy, XPS, and U–V visible spectroscopy were used to study the structural, morphological, chemical, and optical properties of the deposited thin films, which revealed that the heterojunction thin films had a microcrystalline structure and a mixed SnSe2, SnSe, SnO, and SnO2 phases. Only the sample with the lower thickness (137 nm) exhibited the p-n type behaviour when concentration (1–5 ppm) and temperature (RT-75 °C) increased. Furthermore, the SnSe2/SnOx/SnSe heterojunction thin-film gas sensor demonstrated good NO2 detecting selectivity. The development of SnSe2/SnOx/SnSe p–n junctions at the thin-film surface may be responsible for the improved NO2-sensing capability of the constructed gas sensor at low operating temperatures. For five ppm NO2, the device response was 151% at RT. Response/recovery times were 134/494 s, respectively. The estimated detection limit (LOD) was 515 ppb. NO2 gas had a higher response than SO2, NO, H2S, CO, H2, C2H5OH, and NH3. The mechanism of concentration, temperature-dependent p–n switching, selective detection of NO2 at RT, and complete response and recovery have been deliberated based on physisorption and charge transfer. The lower thickness (137 nm) sample exhibits good photo response in visible light with power (32 mW). It has good responsivity, detectivity and external quantum efficiency. This research will give 2D materials a new dimension of selective gas sensors and photodetection at room temperature.

Room temperature selective detection of NO2 using Au-decorated In2O3 nanoparticles embedded in porous ZnO nanofibers

A series of porous Au nanoparticles (NPs) decorated with In2O3 nanoparticles (NPs) was embedded in ZnO nanofibers (NFs) using a facile electrospinning method, followed by calcination treatment at 400 °C. The crystal phase structure, morphology, elemental composition, and specific surface area were characterized using FESEM, XRD, FETEM, XPS, and BET analysis. The gas-sensing properties of the resulting Au-In2O3-ZnO NFs-based gas sensors were systematically assessed. The results showed that a small amount of In2O3 dopant improved the gas-sensing response properties. In particular, the sensor fabricated with a mixture containing 0.03 g In(NO3)3 (S2) exhibited excellent stability, selectivity, and a response of 95.15 towards 5 ppm of NO2 gas at room temperature (RT, 25 ℃) under ultraviolet (UV) irradiation. The S2 sensor also showed a high response of 90–5 ppm of NO2 at 80% relative humidity (RH). The high response sensing performance at low operating temperature (RT) of the fabricated Au-In2O3-ZnO sensors may be due to a synergistic effect between ZnO and In2O3, as well as the excellent catalytic effect of Au.

A stable and highly-sensitive flexible gas sensor based on Ceria (CeO2) nano-cube decorated rGO nanosheets for selective detection of NO2 at room temperature

Sensing and monitoring nitrogen dioxide (NO2) gas is essential, due to its adverse effect on humans and the environment. However, conventional NO2 gas-sensing materials have limitations like elevated temperature operations, lower response, and low selectivity. Herewith, ceria nano-cube decorated reduced graphene oxide nanosheets (CeO2@rGO) were synthesized by a hydrothermal process, and as-synthesized products were characterized by various methods, viz. XRD, FE-SEM, FTIR, Raman spectrometer, BET, and IV characteristics. Afterwards, CeO2@rGO flexible gas sensor was fabricated by drop-cast technique, which is utilized for real-time monitoring of NO2 at room temperature (RT) (24ºC). Notably, the CeO2@rGO-based sensor upholds a significantly high response of 52.84 % towards 70 ppm of NO2, with an ultrafast response and recovery time of 7 s and 58 s respectively, with the LOD of 1 ppm. In addition, the CeO2@rGO flexible gas sensor exhibited long-term stability up to 30 days, solid repeatability, and stability in high relative humidity (RH) conditions. The marvelous sensing characteristics of the CeO2@rGO were attributed to the synergetic effect between CeO2 and rGO. The mechanism of sensing response was exhaustively interpreted by the “surface electron depletion layer mechanism”. Certainly, the scientific investigation conducted in the present study will undeniably advance the possible uses of detecting NO2 at RT.

One-step controlled synthesis of ZnO-ZnSe hollow nanospheres with surface defects for selective detection of NO2

The introduction of surface defects in sensing materials is an important means to improve sensor performance. In this work, we design a simple one-step route to synthesize ZnO-ZnSe without any template or surfactant, and obtain ZnO-ZnSe hollow spherical composite with a diameter of ∼ 200 nm. The shell of the hollow spheres is assembled by nanoparticles with a lot of surface defects after sintering at 800 °C in N2 atmosphere. The surface defects can promote the sensing materials release more electrons and facilitate the reaction of oxygen ions on the material surface. It is beneficial to the adsorption of NO2 on sensing materials for enhancing the sensing performance. The composite shows excellent sensitivity for 10 ppm NO2 at 170 °C, which is 5.32 times that of pure ZnO. And the sensor can recover quickly within 28 s after responding to NO2. It is also satisfactory for the sensor to detect the lowest concentration of 100 ppb. The chemical characterizations such as DRS, PL, XPS, GC–MS, and Kelvin probe are used, combined with the calculation of DFT theory to further explore the synergy effect of the formation of ZnO and ZnSe heterojunction and the surface defects caused by high-temperature sintering on the improvement of sensor performance.

Selective NO2 Detection of CaCu3Ti4O12 Ceramic Prepared by the Sol-Gel Technique and DRIFT Measurements to Elucidate the Gas Sensing Mechanism.

NO2 is one of the main greenhouse gases, which is mainly generated by the combustion of fossil fuels. In addition to its contribution to global warming, this gas is also directly dangerous to humans. The present work reports the structural and gas sensing properties of the CaCu3Ti4O12 compound prepared by the sol-gel technique. Rietveld refinement confirmed the formation of the pseudo-cubic CaCu3Ti4O12 compound, with less than 4 wt% of the secondary phases. The microstructural and elemental composition analysis were carried out using scanning electron microscopy and X-ray energy dispersive spectroscopy, respectively, while the elemental oxidation states of the samples were determined by X-ray photoelectron spectroscopy. The gas sensing response of the samples was performed for different concentrations of NO2, H2, CO, C2H2 and C2H4 at temperatures between 100 and 300 °C. The materials exhibited selectivity for NO2, showing a greater sensor signal at 250 °C, which was correlated with the highest concentration of nitrite and nitrate species on the CCTO surface using DRIFT spectroscopy.

An enhanced-stability metal–organic framework of NH2-MIL-101 as an improved fluorescent and colorimetric sensor for nitrite detection based on diazotization reaction

Nitrite ion (NO2-) is a typical contaminant that can cause severe damage to the human body. Diazotization-based fluorimetric methods used for the efficient and selective detection of NO2- under a strong acidic condition remain a huge challenge. In this study, a specific nanoprobe was developed through the functionalization of the luminescent MOF of NH2-MIL-101 with Polyvinylidene fluoride/polyvinylpyrrolidone (PVDF/PVP) for detecting NO2- based on diazotization reaction. After functionalization, the resultant NH2-MIL-101 @PVDF/PVP exhibited enhanced stability even under a strong acidic condition and featured higher fluorescence intensity. Because NO2- reacted with the -NH2 group of the probe to form diazonium salt, a significant fluorescence signal was obtained. With the addition of N-(1-Naphthyl) ethylenediamine, the diazonium salt significantly changed from colorless to a purple-red color under direct sunlight. The developed dual-signal readout sensor exhibited high sensitivity, high selectivity, and good linearity in the range of 0.67–20 μM with a limit of detection of 0.67 μM. Owing to the unique properties of MOFs, the proposed sensor was characterized by simple preparation, high sensitivity, and fast response kinetics compared with the traditional sensing reagents. This study provides a potential strategy for fabricating smart fluorimetric probes used for nitrite detection.

The Application of Combined Visible and Ultraviolet Irradiation to Improve the Functional Characteristics of Gas Sensors Based on ZnO/SnO2 and ZnO/Au Nanorods

Arrays of zinc oxide (ZnO) nanorods were synthesized over quartz substrates by the hydrothermal method. These nanorods were grown in a predominantly vertical orientation with lengths of 500–800 nm and an average cross-sectional size of 40–80 nm. Gold, with average sizes of 9 ± 1 nm and 4 ± 0.5 nm, and tin nanoclusters, with average sizes of 30 ± 5 nm and 15 ± 3 nm, were formed on top of the ZnO nanorods. Annealing was carried out at 300 °C for 2 h to form ZnO/SnO2 and ZnO/Au nanorods. The resulting nanorod-arrayed films were comprehensively studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDS) and X-ray photoelectron spectroscopy (XPS). To fabricate resistive sensor elements, the films were supplied with V/Ni contact metallization on top of the nanorods. The gas sensor performance of the prepared films was evaluated at various temperatures in order to select 200 °C as the optimum one which enabled a selective detection of NO2. Adding UV-viz irradiation via a light-emitting diode, λ = 400 nm, allowed us to reduce the working temperature to 50 °C and to advance the detection limit of NO2 to 0.5 ppm. The minimum response time of the samples was 92 s, which is 9 times faster than in studies without exposure to UV-viz radiation.

Investigations of Vacancy-Assisted Selective Detection of NO2 Molecules in Vertically Aligned SnS2.

Two important methods for enhancing gas sensing performance are vacancy/defect and interlayer engineering. Tin sulfide (SnS2) has recently attracted much attention for sensing of the NO2 gas due to its active surface sites and tunable electronic structure. Herein, SnS2 has been synthesized by the chemical vapor deposition (CVD) method followed by nitrogen plasma treatment with different exposure times for fast detection of NO2 molecules. Plasma treatment created a substantial number of surface vacancies on SnS2 flakes, which were controlled by the exposure period to modify the surface of flakes. After 12 min of nitrogen plasma treatment, SnS2 nanoflakes show considerable improvement in NO2 sensing characteristics, including a high sensing response of ∼264% toward 100 ppm NO2 at 120°C. The enhancement in the relative response of the sensor is due to the electronic interaction between NO2 molecules and the S vacancies on the surface of SnS2. Density functional theory (DFT) computations indicate that the S-vacancy defects on the surface dominate the effective NO2 detection and the NO2 adsorption mechanism transition from physisorption to chemisorption. Adsorption kinetics of the NO2 gas over SnS2 nanoflake-based chemiresistor sensors were studied using the Lee and Strano model [ Langmuir 2005, 21(11), 5192-5196]. The irreversible rate of the reaction for various NO2 concentrations exposed to the gas sensor is extracted using this model, which also appropriately describes the response curves. The forward rate constant of the irreversible gas sensor increased with the increase of the N2 plasma treatment time and reached the maximum in the 12 min plasma-treated sample. Through defect engineering, this research may open up new vistas for the design and synthesis of 2D materials with enhanced sensing properties.

Au-doped ZnO@ZIF-7 core-shell nanorod arrays for highly sensitive and selective NO2 detection

The exploration of novel NO2 sensors with high performance is of great importance for air quality monitoring and human health. In this work, Au-doped ZnO@ZIF-7 core-shell nanorod arrays were fabricated for high-performance NO2 detection. Due to the spill-over effects of Au nanoparticles, gas enriching and molecular sieving effects provided by ZIF-7 membranes, the ZnO-Au@ZIF-7 sensor affords highly sensitive and selective detection of NO2. The heterostructured ZnO-Au@ZIF-7 allows for ppb-level detection of NO2 (Response = 1.7–5 ppb) with excellent repeatability and provides improved selectivity, anti-humidity capacity, and long-term stability compared with bare ZnO, Au-doped ZnO or ZnO@ZIF-7 core-shell nanorod arrays. According to the calculation of density functional theory (DFT), the ZnO-Au@ZIF-7 sensor renders higher adsorption energy towards NO2 molecules compared with the aforementioned other materials, which also explains its outstanding sensing performances. We believe our approach that combines noble metals doped semiconductor metal oxides (SMOs) and MOF filtration membranes can be further extended to numerous new heterostructured SMO@MOF materials, which opens venues to the development of advanced chemiresistive gas sensors.

The Influence of Surfactants on the Deposition and Performance of Single-Walled Carbon Nanotube-Based Gas Sensors for NO2 and NH3 Detection

Solid-state chemiresistive gas sensors have attracted a lot of researchers’ attention during the last half-century thanks to their ability to detect different gases with high sensitivity, low power consumption, low cost, and high portability. Among the most promising sensitive materials, carbon nanotubes (CNTs) have attracted a lot of interest due to their large active surface area (in the range of 50–1400 m2/g, depending on their composition) and the fact that they can operate at room temperature. In this study, single-walled carbon nanotube (SWCNT)-based sensing films were prepared and deposited by spray deposition for the fabrication of gas sensors. For the deposition, various SWCNTs were prepared in deionized water with the addition of specific surfactants, i.e., carboxymethyl cellulose (CMC) and sodium dodecyl sulfate (SDS), which act as dispersing agents to create a suitable ink for deposition. This study aims to elucidate the possible differences in the sensing performance of the fabricated devices due to the use of the two different surfactants. To achieve this goal, all the devices were tested versus ethanol (C2H5OH), carbon monoxide (CO), nitrogen dioxide (NO2), and ammonia (NH3). The produced devices demonstrated high selectivity towards NH3 and NO2. The different sensors, prepared with different deposition thicknesses (from 0.51 nm to 18.41 nm), were tested in dry and wet conditions (40% humidity), highlighting an enhanced response as a function of relative humidity. In addition, sensor performance was evaluated at different working temperatures, showing the best performance when heated up to 150 °C. The best sensing conditions we found were against NO2, sensors with 10 layers of deposition and an operating temperature of 150 °C; in this condition, sensors showed high responses compared those found in the literature (62.5%—SDS-based and 78.6%—CMC-based). Finally, cross-sensitivity measurements showed how the produced sensors are good candidates for the practical and selective detection of NO2, even in the presence of the most important interfering gases identified, i.e., NH3.

Synergistic effects of Pd decoration and substrates on the NO2 sensing performance of sprayed WO3 thin films

The selective detection of NO2 is achieved using Pd decorated WO3 thin films deposited on glass (WO3G) and alumina (WO3A) substrates. WO3A film shows superior performance over WO3G film in terms of sensitivity, response magnitude and response and recovery time. Lower detection limit of 2 ppm is achieved using WO3A film for which gas response was 20 % whereas for WO3G film response was 9 %. In particular, higher gas response towards NO2 is observed for WO3A film, which is attributed to the high surface roughness and high catalytic activity of Pd causing enhanced spillover and effective diffusion of NO2.

Synthesis of porous spherical ZnO nanomaterials and the selective detection of NO at room temperature

The microstructure of ZnO nanomaterials determines their sensing performance. Here, porous spherical ZnO nanomaterials were synthesized by hydrothermal combined with high temperature calcination using zinc acetate, urea, sodium citrate, and oxalic acid as raw materials. The ZnO nanomaterials exhibit excellent response and fast response/recovery behavior towards NO at room temperature. The response to 0.5 ppm NO reached 3.08, and the response and recovery times were less than 35 s in the concentration range of 0.5 ∼ 8.0 ppm. The introduction of oxalic acid improved crystallinity, increased the oxygen vacancy content and selective response to NO at room temperature. The results show that ZnO can be used as an ideal candidate material for detecting NO at room temperature.