Sensitive NO2 Gas Sensor Research Articles

Highly Sensitive, Selective and Stable NO2 Gas Sensor Based on Porous Influenced SnO2 Bilayer Thin Films

In this work, an attempt has been made to fabricate SnO2 porous films using automated nebulizer spray pyrolysis technique with the influence of a porogen. Pure tin dioxide and porous tin dioxide (SnO2/SnO2) thin films were prepared from a precursor solution composed of SnCl2·2H2O and polyethylene glycol as a porogen. The structural, morphological, optical and gas sensing performance of the prepared thin films were characterized. The inclusion of porogen significantly improved the sensing property of porous SnO2 bilayer thin films and it was confirmed by structural, morphological and gas sensing performance studies. The optimized spray process parameter was determined finally in this work as SnO2 precursor strength of 0.2 M for porous SnO2 layer. Under this condition, the increased lattice constant, lattice defect and increased pores diameter were achieved, which exhibited good gas sensitivity and selectivity towards NO2 gas at 250 ºC. The response and recovery time is decreased as 50%, the deduction limit is 0.9 ppm. In addition, during the five weeks test, the response level was observed nearly constant, which indicated that the SnO2 bilayer sensor has long-term stability.

Highly sensitive and lower detection-limit NO[formula omitted] gas sensor based on Rh-doped ZnO nanofibers prepared by electrospinning

As a kind of toxic gas, NO2 can cause damages to the environment and threaten the health of human beings. To develop highly sensitive NO2 gas sensor is necessary. Here, the Rh-doped ZnO nanofibers were prepared by electrospinning. The Rietveld refinements results of XRD patterns have proved the successful doping of Rh into the crystal lattice of ZnO. The XPS spectra reveals the existence of large amounts of surface oxygen vacancy defects, which are beneficial to the enhancement of the sensitivity. The morphology and crystal lattice of the nanofibers were investigated by SEM and HRTEM, respectively. The highly sensitive NO2 gas sensor based on 1% Rh-doped ZnO nanofibers, with the experimental detection limit of 50 ppb (or 18.6 ppb, theoretical signal-to-noise ratio ¿ 3) was fabricated. At the optimal operating temperature of 150 °C, its response values (Rg/Ra) are 1.04 and 36.17, with the corresponding response time of 45 s and 32 s, towards 50 ppb and 10 ppm NO2, respectively. The sensor also exhibits good selectivity, repeatability and linearity between the relative humidity and the response values. The doping of Rh introduces large amounts of surface oxygen vacancy defects. The defects are more favored adsorption sites for NO2. The reasons for the ultrasensitivity of the sensor are as followings: (1) The binding energy between NO2 and ZnO with surface oxygen vacancy defects is about 1.5 times stronger than that for adsorption on the stoichiometric surface; (2) The surface oxygen vacancies of ZnO can have a reaction with NO2 to produce NO inducing the charge transfer; (3) The catalytic activities of Rh towards NO2 and H2O.

Highly sensitive NO2 gas sensor with a low detection limit based on Pt-modified MoS2 flakes

Slow response/recovery speed and high detection limit have always been bottlenecks for MoS2-based gas sensors to solve. Herein, MoS2 flakes are prepared via a hydrothermal route. The autoclave temperature is adjusted to acquire the best crystallinity of MoS2. Pt doping is utilized to improve the gas sensing properties of MoS2 flakes to NO2. The results show that the optimized autoclave temperature and Pt modification greatly enhance the gas response of the MoS2-based sensors. The sensors exhibit high sensitivity, good repeatability, excellent selectivity, a low detection limit of 0.1 ppm, and a fast response/recovery time of 35 s/210 s to 32 ppm NO2 at 157 °C. Our work provides a helpful design thought for optimizing the gas sensing properties of MoS2-based sensors.

RF Sputtered ZnO Nanoballs on Porous Substrate for Highly Sensitive NO2 Gas Sensing Applications

In this work, zinc oxide (ZnO) nanoballs were directly deposited on porous silicon (PS) substrates using RF magnetron sputtering method. The PS substrates were synthesised at room temperature via metal assisted chemical etching technique. The structural, surface morphological and cross-sectional properties of as prepared ZnO nanoballs were investigated by x-ray diffraction, Raman spectroscopy and field emission scanning electron microscopy techniques, respectively. The interaction of nitrogen dioxide (NO2 ) gas molecules with sensing layer and all sensing properties under lower detection limit (2 ppm–100 ppm) were studied in detail. The proposed ZnO nanoballs sensor chip exhibits high sensing response (29.2%) with fast response/recovery times (70 sec/96 sec) to 20 ppm NO2 in dry air at 250°C. Thus, the findings recommend the viability of ZnO nanoballs sensor as highly sensitive and selective NO2 gas sensor at moderate operating temperature regime.

Arc-discharge deposition of SWCNTs over SnO2 nanowires for highly sensitive NO2 gas sensor

The air pollution caused by the emission of NO2 from vehicles in large cities is threatening human health. Thus, a highly sensitive gas sensor is required to monitor this gas. Here, we introduced the arc-discharge deposition of single-walled carbon nanotubes (SWCNTs) over SnO2 nanowires for highly sensitive NO2 gas sensors. The high-quality SnO2 nanowires were grown on-chip on interdigital Pt electrodes, whereas the SWCNTs were deposited by in situ arc-discharge method. To form the heterojunction between SnO2 nanowires and SWCNTs film, we controlled the length of the SnO2 nanowires to avoid bridging of the two electrode fingers while covering the entire surface of Pt electrodes. The SWCNTs were deposited through a shadow mask to ensure the contact between the SWCNTs and SnO2 nanowires but not the Pt electrodes. Electrical measurements confirmed the formation of non-linear contact between SnO2 nanowires and SWCNTs because of the n-p heterojunction. An increment in resistance (decrease in resistance) of the sensor was observed when measured in NO2 gas, indicating the good response characteristics of the device based on heterojunction between SnO2 nanowires and SWCNTs. In addition, gas-sensing measurement at different temperatures indicated that the fabricated sensor could detect low concentrations of NO2 gas in the range of 1–10 ppm, with response values of 20–80. The results demonstrated that the arc-discharge deposition of SWCNTs over SnO2 nanowires is effective for the fabrication of highly sensitive NO2 gas sensors.

High sensitive room temperature NO2 gas sensor based on the avalanche breakdown induced by Schottky junction in TiO2-Sn3O4 nanoheterojunctions

A novel sensor based on Schottky junction inducing avalanche breakdown effect in TiO 2 -Sn 3 O 4 nanoheterojunctions is assembled. High sensitivity for NO 2 gas sensing is demonstrated at room temperature. TiO 2 -Sn 3 O 4 nanocompositewas synthesized as the gas sensing layer and Schottky contact was formed by Au electrodes. The Schottky contact functions as a “gate” which can trigger the avalanche breakdown effect in the TiO 2 -Sn 3 O 4 heterojunctions. By tuning the Schottky barrier height through the responsive variation of the surface chemisorbed gas and the bias on the device, NO 2 at a concentration from 5 to 50 ppm can be detected with an average response time of 8 s at room temperature. This nanostructured device is a promising candidate for application in high-sensitivity and high-speed NO 2 gas sensor. The methodology and working principle illustrated in this paper present a new sensing mechanism that can be readily and extensively applied to other gas sensing systems. • TiO 2 -Sn 3 O 4 heterostructure was designed and synthesized in order to detect NO 2 gas in room temperature. • Avalanche breakdown effect was used to obtain 900% responsivity when exposed to 50 ppm NO 2 at room temperature. • High sensitivity and excellent selectivity to NO 2 is obtained at room temperature.

Enhanced charge transfer in 2D carbon- rich g-C3N4 nanosheets for highly sensitive NO2 gas sensor applications

Two-dimensional (2D) materials have fascinated tremendous attention in many areas of the research field. Especially, the gas sensor is considered as a promising application in utilizing 2D materials. Recently, Graphitic carbon nitrides (g-C3N4) have sparked wide attention in the research due to their performance in chemiresistive gas sensing properties. Herein, pristine g-C3N4 and C/g-C3N4 (carbon enrich-graphitic carbon nitride) were prepared via a polycondensation process. Structural and elemental analysis confirms the formation of C/g-C3N4. High-Resolution Scanning Electron Microscopy and High-Resolution Transmission Electron Microscopy revealed the sheet-like morphology with more number of active sites. The NO2 gas sensing performance of the sensor based on C/g-C3N4 were systematically studied. The response of the C/g-C3N4 sensing films has significantly enhanced compared to the pristine g-C3N4. The maximum sensor response is attained for 10 wt% of C/g-C3N4 with 71.36 % towards 50 ppm of NO2 at 200 °C. The gas sensing response of 10 wt% C/g-C3N4 showed 3 times more enhancement than the pristine g-C3N4. This study revealed the development of a highly sensitive gas sensor for next-generation toxic gases detection.

Solution processed edge activated Ni-MoS2 nanosheets for highly sensitive room temperature NO2 gas sensor applications

In this work, we report the effect of nickel incorporation into MoS2 nanosheets for room temperature sensing of NO2 gas. Interestingly, the concentration of Ni (3, 5, 7 at.%) ions plays a vital role in enhancing the morphological and optical properties. The increased edge active sites in nickel incorporated samples play a vital role in high-performance gas sensing. 7 at.% of Ni incorporated MoS2 showed 115% enhancement for 200 ppm of NO2 gas molecules at room temperature, compared to pristine and other concentrations of Ni-incorporated sensors. The enhancement in the gas sensing performance was explained by the possible mechanism. In addition to this, the first principle calculations were performed to identify the influence of Ni-atom into the MoS2 matrix. The electronic structure of the material was tuned by the incorporation of Ni-atom into the MoS2. This was confirmed from electronic band structure, PDOS, electron density difference and Bader charge transfer analyses.

Highly sensitive NO2 gas sensor based on Ag decorated ZnO nanorods

Highly sensitive NO2 gas sensor based on Ag decorated ZnO nanorods

Highly Sensitive NO2 Gas Sensors Based on MoS2@MoO3 Magnetic Heterostructure.

Recently, two-dimensional (2D) materials and their heterostructures have attracted considerable attention in gas sensing applications. In this work, we synthesized 2D MoS2@MoO3 heterostructures through post-sulfurization of α-MoO3 nanoribbons grown via vapor phase transport (VPT) and demonstrated highly sensitive NO2 gas sensors based on the hybrid heterostructures. The morphological, structural, and compositional properties of the MoS2@MoO3 hybrids were studied by a combination of advanced characterization techniques revealing a core-shell structure with the coexistence of 2H-MoS2 multilayers and intermediate molybdenum oxysulfides on the surface of α-MoO3. The MoS2@MoO3 hybrids also exhibit room-temperature ferromagnetism, revealed by vibrating sample magnetometry (VSM), as a result of the sulfurization process. The MoS2@MoO3 gas sensors display a p-type-like response towards NO2 with a detection limit of 0.15 ppm at a working temperature of 125 °C, as well as superb selectivity and reversibility. This p-type-like sensing behavior is attributed to the heterointerface of MoS2-MoO3 where interfacial charge transfer leads to a p-type inversion layer in MoS2, and is enhanced by magnetic dipole interactions between the paramagnetic NO2 and the ferromagnetic sensing layer. Our study demonstrates the promising application of 2D molybdenum hybrid compounds in gas sensing applications with a unique combination of electronic and magnetic properties.

Intrinsically Breathable and Flexible NO2 Gas Sensors Produced by Laser Direct Writing of Self-Assembled Block Copolymers.

The surge in air pollution and respiratory diseases across the globe has spurred significant interest in the development of flexible gas sensors prepared by low-cost and scalable fabrication methods. However, the limited breathability in the commonly used substrate materials reduces the exchange of air and moisture to result in irritation and a low level of comfort. This study presents the design and demonstration of a breathable, flexible, and highly sensitive NO2 gas sensor based on the silver (Ag)-decorated laser-induced graphene (LIG) foam. The scalable laser direct writing transforms the self-assembled block copolymer and resin mixture with different mass ratios into highly porous LIG with varying pore sizes. Decoration of Ag nanoparticles on the porous LIG further increases the specific surface area and conductivity to result in a highly sensitive and selective composite to detect nitrogen oxides. The as-fabricated Ag/LIG gas sensor on a flexible polyethylene substrate exhibits a large response of -12‰, a fast response/recovery of 40/291 s, and a low detection limit of a few parts per billion at room temperature. Integrating the Ag/LIG composite on diverse fabric substrates further results in breathable gas sensors and intelligent clothing, which allows permeation of air and moisture to provide long-term practical use with an improved level of comfort.

Low temperature operated highly sensitive, selective and stable NO2 gas sensors using N-doped SnO2-rGO nanohybrids

In this study, we report synthesis of SnO2-rGO and N-doped SnO2-rGO nanohybrids by facile hydrothermal method. The XRD analysis of the synthesized nanohybrids revealed a tetragonal rutile structure of SnO2 lattice.Further structural, chemical, morphological and optical properties of SnO2-rGO and SnO2-NrGO nanohybrids were investigated by Raman, X-Ray Photoelectron spectroscopy, Transmission Electron Microscopy, UV–Vis spectroscopy and Photoluminescence spectroscopy. Furthermore, the gas sensing properties of the synthesized nanohybrids were studied in detail. It was observed that SR2 and SRN2 nanohybrids exhibited superior NO2 sensing response (55.2 and 84.5% respectively) at low operating temperature (120 °C) and low gas concentration (0.5 ppm). Moreover, SR2 and SRN2 also exhibited excellent selectively towards NO2 along with remarkable stability upto 90% over 30 days. This improved performance can be attributed to the synergetic effect of small particle size, high defect concentration and high surface area due to incorporation of SnO2 along with N doping in rGO. Therefore, SR2 and SRN2 can be utilized as effective NO2 gas sensors.

Highly sensitive and selective NO2 gas sensor fabricated from Cu2O-CuO microflowers

Three-dimensional (3D) hierarchical Cu2O-CuO microflowers assembled by nanorods were successfully obtained through an environmentally friendly hydrothermal route. Compared with other gases, the Cu2O-CuO microflowers-2 sensor had excellent selectivity, repeatability and long-term stability to NO2 at 187 °C. Moreover, during dynamic gas sensing measurement, the Cu2O-CuO microflowers-2 sensor showed the highest gas sensitivity (5–100 ppb), fast response time (35 s) and recovery time (47 s) to NO2, even under relatively high humidity. Significantly, at the optimal working temperature, the detection limit of the sensor was 5 ppb. The excellent sensing properties can be attributed to its unique structural advantages, more surface adsorbed oxygen, and the synergistic influence between the two-phase coexistence.

Conductometric NO2 gas sensors based on MOF-derived porous ZnO nanoparticles

As a typical metal oxide semiconductor, ZnO has been investigated deeply for the application of gas sensing materials. In this study, an ultrahigh sensitive and selective NO2 gas sensor based on porous ZnO nanocubes derived from metal organic frameworks (MOFs) was reported. The MOF-derivatives were obtained by precisely control of the subsequent pyrolysis process. The sensitivity of MOF-derivatives toward 1 ppm NO2 at 200 ºC was 51.41 under 500 ºC pyrolysis treatment. Compared with similar work, the sensitivity has been greatly improved. Furthermore, the fabricated gas sensor demonstrated excellent selectivity to NO2 over other gases (CO, C2H5OH, H2, H2S, NO, NH3). The ultrahigh sensitivity and selectivity were attributed to the unique structure after pyrolysis, which provides more exposed active sites and connected pore channels.

High Sensitive Room Temperature No2 Gas Sensor Based on the Avalanche Breakdown Induced by Schottky Junction in Tio2-Sn3o4 Nanoheterojunctions

High Sensitive Room Temperature No2 Gas Sensor Based on the Avalanche Breakdown Induced by Schottky Junction in Tio2-Sn3o4 Nanoheterojunctions

High Sensitive Room Temperature No2 Gas Sensor Based on the Avalanche Breakdown Induced by Schottky Junction in Tio2-Sn3o4 Nanoheterojunctions

High Sensitive Room Temperature No2 Gas Sensor Based on the Avalanche Breakdown Induced by Schottky Junction in Tio2-Sn3o4 Nanoheterojunctions

Cross-linked structure of self-aligned p-type SnS nanoplates for highly sensitive NO2 detection at room temperature

A highly sensitive NO2 gas sensor of p-type SnS operating at room temperature is developed using crosslinked SnS nanoplates self-formed only on SiO2 nanorods, without an additional patterning process.

Growth and NO2 gas sensing mechanisms of vertically aligned 2D SnS2 flakes by CVD: Experimental and DFT studies

Two dimensional chalcogenides and metal sulfide materials with their sensitive surfaces are promising and potential postulant for the purpose of chemical gas sensing as a consequence of extraordinary vast surface area to volume ratio and significant band gap. We demonstrate a highly selective and sensitive NO2 gas sensor using vertically aligned 2D SnS2 flakes, grown by a chemical vapor deposition method in controlled gas flow. The vertically aligned SnS2 flakes were confirmed by scanning electron microscopy, Raman spectroscopy, and X-ray diffraction. The sensing behaviour of the vertical aligned structures was analyzed for various concentrations of NO2 at different temperatures. The sensor exhibits high gas sensing response (ΔR/R%) of ~164 at 120 °C with 50 ppm of NO2 gas, which is the highest response among the SnS2 based reports. The device shows excellent sensing response at room temperature but poor recovery. The selectivity of the sensor was performed under different gas environments and found highly selective towards NO2 gas, and the results are supported by electronic structure calculations. Based on experimental results and electronic structure calculations, a gas sensing mechanism is proposed. The result indicates that fabricated sensor can be used in air purification industries and in air monitoring.

Highly Sensitive, Selective, Flexible and Scalable Room-Temperature NO2 Gas Sensor Based on Hollow SnO2/ZnO Nanofibers.

Semiconducting metal oxides can detect low concentrations of NO2 and other toxic gases, which have been widely investigated in the field of gas sensors. However, most studies on the gas sensing properties of these materials are carried out at high temperatures. In this work, Hollow SnO2 nanofibers were successfully synthesized by electrospinning and calcination, followed by surface modification using ZnO to improve the sensitivity of the SnO2 nanofibers sensor to NO2 gas. The gas sensing behavior of SnO2/ZnO sensors was then investigated at room temperature (~20 °C). The results showed that SnO2/ZnO nanocomposites exhibited high sensitivity and selectivity to 0.5 ppm of NO2 gas with a response value of 336%, which was much higher than that of pure SnO2 (13%). In addition to the increase in the specific surface area of SnO2/ZnO-3 compared with pure SnO2, it also had a positive impact on the detection sensitivity. This increase was attributed to the heterojunction effect and the selective NO2 physisorption sensing mechanism of SnO2/ZnO nanocomposites. In addition, patterned electrodes of silver paste were printed on different flexible substrates, such as paper, polyethylene terephthalate and polydimethylsiloxane using a facile screen-printing process. Silver electrodes were integrated with SnO2/ZnO into a flexible wearable sensor array, which could detect 0.1 ppm NO2 gas after 10,000 bending cycles. The findings of this study therefore open a general approach for the fabrication of flexible devices for gas detection applications.

Highly sensitive and wearable NO2 gas sensor based on PVDF nanofabric containing embedded polyaniline/g-C3N4 nanosheet composites

In this study, a highly flexible and wearable nitrogen dioxide (NO2) gas sensor was fabricated based on electrospun poly(vinylidene fluoride) (PVDF)/polyaniline (PANi)/graphitic-carbon nitride (g-C3N4) blend nanocomposite (EBNC). g-C3N4/PANi nanocomposite (GPC) was synthesized by in situ polymerization technique prior to its incorporation into PVDF nanofibers, which ensured uniformity of dispersion. For the comparison study, PVDF/GPC nanocomposite film was fabricated using doctor blade technique. EBNC sensor exhibited high sensitivity, selectivity, reproducibility along with quick response and complete recovery. Electrospinning and GPC synergistically improved the performance of the EBNC based gas sensor. The superior gas sensing ability along with its low cost and the use of scalable electrospinning technique could make this system a promising one for the detection of gaseous NO2.