Room-temperature NO2 Gas Sensor Research Articles

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.

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.

Light-activated ultrasensitive NO2 gas sensor based on heterojunctions of CuO nanospheres/MoS2 nanosheets at room temperature

MoS2-based gas sensor has become an effective platform to detect NO2 gas. However, room-temperature NO2 gas sensor based on MoS2 are facing low sensitivity and poor response/recovery behaviors because of low-reacting activity between gas-sensing materials and NO2 gas at room temperature. Purposefully, a room-temperature NO2 gas sensor based on CuO/MoS2 heterojunctions with excellent sensitivity and fast response/recovery speeds is successfully realized. More attractively, the CuO/MoS2-3 sensor exhibits remarkable response (8.98) and short response/recovery time of 18.5/53.5 s to 10 ppm NO2 at room temperature under red light illumination, which is obviously better than that under dark. The improved sensitivity and fast response/recovery behaviors are attributed not only to the charge separation efficiency derived from the effect of heterojunctions, but also to the charge flow on the sensing layer in the context of NO2/MoS2/CuO interaction under red light illumination. In addition, the fabricated sensor has low detection limit (50 ppb), excellent reversibility and high selectivity to NO2 against other gases. After 40 days, the CuO/MoS2-3 sensor still maintains a relatively stable response with the fast response time (<18.5 s) under red light illumination, ensuring a long-term and fast detection to NO2 in practical applications.

MoS2 functionalized AlGaN/GaN transistor based room temperature NO2 gas sensor

The ability to monitor toxic gases under room-temperature conditions, with enhanced response and selectivity present in the atmosphere, is still considered as a technical challenge. In this context, we have fabricated AlGaN/GaN high electron mobility transistors (HEMTs) based sensors incorporating molybdenum disulphide (MoS2) functionalization for very sensitive, selective, and quick measurement of even trace amounts of hazardous NO2 gas in the ambient under room-temperature conditions. MoS2 structures with vertically aligned flower-like structure were synthesised using a simple hydrothermal technique and applied to the gate region of AlGaN/GaN HEMTs. The electrical characterisations of MoS2 functionalized AlGaN/GaN HEMTs are then used to detect the presence of NO2 gas. The fabricated sensor showed an enhanced relative sensing response in the range of 40.5–56.7% for 1–100 ppm NO2 gas with complete recovery to 1 ppm NO2 concentration under room-temperature conditions (25ᵒC) without applying any external thermal or optical stimuli. Furthermore, the cyclic and selectivity tests were performed and we found our sensor to be highly selective towards NO2 gas among various other gases. The experimental results showed that MoS2 had excellent properties for NO2 gas detection when used on such GaN-based sensing platform. These findings may be attributed to the exposed edge sites of MoS2 which compliment with configurations with sulphur and the chemisorption phenomenon on its surface that results in altering the drain to source current (IDS) of the HEMT at a constant drain to source voltage (VDS) of 0.5 V. These findings suggest that gas sensors based on the AlGaN/GaN HEMT structure appear to be a promising candidate for the advancement of application potentials of nitride-based integrated electronics.

Three-Dimensional MoS2/Reduced Graphene Oxide Nanosheets/Graphene Quantum Dots Hybrids for High-Performance Room-Temperature NO2 Gas Sensors.

This study presents three-dimensional (3D) MoS2/reduced graphene oxide (rGO)/graphene quantum dots (GQDs) hybrids with improved gas sensing performance for NO2 sensors. GQDs were introduced to prevent the agglomeration of nanosheets during mixing of rGO and MoS2. The resultant MoS2/rGO/GQDs hybrids exhibit a well-defined 3D nanostructure, with a firm connection among components. The prepared MoS2/rGO/GQDs-based sensor exhibits a response of 23.2% toward 50 ppm NO2 at room temperature. Furthermore, when exposed to NO2 gas with a concentration as low as 5 ppm, the prepared sensor retains a response of 15.2%. Compared with the MoS2/rGO nanocomposites, the addition of GQDs improves the sensitivity to 21.1% and 23.2% when the sensor is exposed to 30 and 50 ppm NO2 gas, respectively. Additionally, the MoS2/rGO/GQDs-based sensor exhibits outstanding repeatability and gas selectivity. When exposed to certain typical interference gases, the MoS2/rGO/GQDs-based sensor has over 10 times higher sensitivity toward NO2 than the other gases. This study indicates that MoS2/rGO/GQDs hybrids are potential candidates for the development of NO2 sensors with excellent gas sensitivity.

Room temperature NO2 gas sensor based on stain-etched porous silicon: Towards a low-cost gas sensor integrated on silicon

In this work, we investigate the use of a new low-cost gas sensor based on porous silicon to detect low concentration of NO2 at room temperature. In this work, we focused on the gas sensing properties of two different types of porous silicon (PS) prepared by a simple chemical method namely nano-porous silicon (nano-PS) and macro-porous silicon (macro-PS). The prepared sensors are characterized by different pores size, thicknesses and porosity. Electronic properties of the synthesized structures were studied by measuring the effective minority carrier lifetime using a µPCD lifetime tester. Structural properties and morphology of PS samples were also presented using Fourier transforms infrared (FTIR) spectroscopy and scanning electron microscope (SEM). The gas sensing properties of nano-PS and macro-PS were performed at room temperature for NO2 gas. Macro-PS and nano-PS sensors exhibit different behaviors attributed to the difference in their morphologies. The tested sensors exhibit considerable sensitivity at room temperature to low concentration of NO2 (4 ppm) during response time up to 45 s.

Supramolecularly assembled isonicotinamide/reduced graphene oxide nanocomposite for room-temperature NO2 gas sensor

Herein, room-temperature NO 2 gas sensor based on supramolecularly assembled isonicotinamide–graphene oxide nanocomposite (Iso-rGO) and Iso-rGO/Carbon felt (CF) electrode was prepared and studied. The morphology of the synthesized Iso-rGO nanocomposite was studied by field emission scanning electron microscopy (SEM), which revealed the uniform coating of isonicotinamide over the surface of the composite. Further studies confirmed the supramolecular functionalization assembly of isonicotinamide onto the surface of GO. The prepared nanocomposite was used as functional electrode material to fabricate room-temperature NO 2 gas sensor. The fabricated electrode (Iso-rGO/CF) exhibited excellent reductive behavior of NO 2 gas at room-temperature. The fabricated sensor exhibited a linear range from 1–30 ppm and a low detection limit (LOD) of 1 ppm towards NO 2 gas. The NO 2 sensitivity of the Iso-rGO/CF electrode is well correlated with online gas chromatography which demonstrate high sensitivity and good stability for more than 30 days. The observed results revealed that the proposed Iso-rGO/CF electrode could be a suitable sensor electrode for the sensitive detection of gaseous NO 2 in the real samples. • Synthesis of supramolecularly assembled isonicotinamide/ reduced graphene oxide (Iso-rGO) nanocomposite. • Fabrication of room-temperature NO 2 gas sensor based on Iso-rGO nanocomposite. • The fabricated Iso-rGO/CF electrode based NO 2 sensor exhibited a linear dynamic range of 1–30 ppm and low limit of detection (LOD) of 1 ppm. • The developed sensor demonstrates good selectivity towards NO 2 gas in presence of other interfering gases such as CO 2 , acetone, N 2 O, SOx, Phenol and dichloromethane.

Visible-Light-Driven Room Temperature NO2 Gas Sensor Based on Localized Surface Plasmon Resonance: The Case of Gold Nanoparticle Decorated Zinc Oxide Nanorods (ZnO NRs)

In this work, nitrogen dioxide (NO2) gas sensors based on zinc oxide nanorods (ZnO NRs) decorated with gold nanoparticles (Au NPs) working under visible-light illumination with different wavelengths at room temperature are presented. The contribution of localized surface plasmon resonant (LSPR) by Au NPs attached to the ZnO NRs is demonstrated. According to our results, the presence of LSPR not only extends the functionality of ZnO NRs towards longer wavelengths (green light) but also increases the response at shorter wavelengths (blue light) by providing new inter-band gap energetic states. Finally, the sensing mechanism based on LSPR Au NPs is proposed.

Rapidly responding room temperature NO2 gas sensor based on SnSe nanostructured film

Excess of NO2 in the environment has become a big problem for the lives of humans and animals. It is necessary to know its concentration in the atmosphere. SnSe is made from earth-abundant, non-toxic materials. SnSe nanostructured film was fabricated using an industrially viable thermal evaporation method. In-house grown SnSe powder was used for this purpose. For characterizing SnSe nanostructured film, X-ray diffraction (XRD), scanning electron microscope (SEM), and UV–visible spectroscopy was used. The SnSe nanostructured film-based gas sensor response was around 174% for 5 ppm NO2 at room temperature, and it showed a low limit of detection (LOD) of 345 ppb with 106% response. It showed a fast response time of 5 s, and the recovery time was around 232 s. The sensor showed good selectivity towards NO2 compared to NO, NH3, H2, and SO2 gases. Although the theoretical report on SnSe for NO2 detection is in the literature, this is the first experimental report on SnSe based NO2 gas sensors. Thus, the work opens up a new dimension for the SnSe material-based selective gas sensor.

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

High performance langasite based SAW NO2 gas sensor using 2D g-C3N4@TiO2 hybrid nanocomposite

Nitrogen dioxide (NO2) gas has emerged as a severe air pollutant that causes damages to the environment, human life and global ecosystems etc. However, the currently available NO2 gas sensors suffers from insufficient selectivity, sensitivity and long response times that impeding their practical applicability for room temperature (RT) gas sensing. Herein, we report a high performance langasite (LGS) based surface acoustic wave (SAW) RT NO2 gas sensor using 2-dimensional (2D) g-C3N4@TiO2 nanoplates (NP) with {001} facets hybrid nanocomposite as a chemical interface. The g-C3N4@TiO2 NP/LGS SAW device showed a significant negative frequency shift (∆f) of ~19.8 kHz which is 2.4 fold higher than that of the pristine TiO2 NP/LGS SAW sensor toward 100 ppm of NO2 at RT. In addition, the hybrid SAW device fascinatingly exhibited a fast response/recovery time with a low detection limit, high selectivity, and an effective long term stability toward NO2 gas. It also exhibited an enhanced and robust negative frequency shifts under various relative humidity conditions ranging from 20% to 80% for 100 ppm of NO2 gas. The high performance of the g-C3N4 @TiO2 NP/LGS SAW gas sensor can be attributed to the enhanced mass loading effect which was assisted by the large surface area, oxygen vacancies, OH and amine functional groups of the n-n hybrid heterojunction of g-C3N4@TiO2 NP that provide abundant active sites for the adsorption and diffusion of NO2 gas molecules. These results emphasize the significance of the integration of 2D materials with metal oxides for SAW based RT gas sensing technology holds great promise in environmental protection.

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.

N-doped three-dimensional needle-like CoS2 bridge connection Co3O4 core–shell structure as high-efficiency room temperature NO2 gas sensor

The N-doped three-dimensional (3D) needle bridge connection core-shell structure N-CoS2@Co3O4 synthesized in this work was prepared by simple hydrothermal and high-temperature vulcanization methods. The optimized N-CoS2@Co3O4-2 composite response to NO2 is 62.3–100 ppm, a response time of 1.3 s, the recovery time of 17.98 s, the detection limit of 5 ppb and stability of as long as 10 weeks at room temperature (RT). Its excellent NO2 sensing performance is attributed to the unique porous and bridge connection core-shell structure of the N-CoS2@Co3O4-2 with high specific surface area, interconnected internal channels, abundant exposed S edge active sites, and high catalytic performance promoted by N-doping. This simple manufacturing method of high-performance sensing materials paves the way for the design of N-doped bridge connection core–shell structures.

Polyoxometalate electron acceptor incorporated improved properties of Cu2ZnSnS4-based room temperature NO2 gas sensor

In this work, a Cu2ZnSnS4(CZTS)-based gas sensor incorporated by polyoxometalate(POMs) electron acceptor were synthesized by hydrothermal method. For the first time we investigated on the application of CZTS in NO2 sensor and the influence of POMs incorporating on gas sensing performances of CZTS sensor. As a result, the gas sensing response could be remarkably improved to 6.12 times by incorporating POMs compared with pure CZTS. This is mainly attributed to introducing POMs into CZTS could reduce electron-hole recombination and facilitate electrons transfer. The research results exhibit the highest gas sensing response of CZTS-based gas sensor up to now. This research reveals a new idea for developing high-performance gas sensors based on CZTS by introducing POMs.

Suppression of Sn2+ and Lewis acidity in SnS2/black phosphorus heterostructure for ppb-level room temperature NO2 gas sensor

The selective detection of harmful gases is of great significance to human health and air quality, triggering the need for special customizations of sensing material structure. In this study, we prepared a novel SnS2/black phosphorus (BP) two-dimensional (2D)-2D heterostructure via the in situ hydrothermal growth of SnS2 nanosheets on exfoliated BP lamellae for NO2 sensing applications. In the SnS2/BP composite, the holes with high oxidizability in p-type BP could oxidize Sn2+ into Sn4+, thus inhibiting the formation of Lewis acidic S vacancies. This Sn2+/Lewis acidity suppression of the composite was further confirmed by X-ray photoelectron spectroscopy and acidic double-layer capacitance analyses, and promoted the adsorption and detection of acidic NO2. Owing to its valence and Lewis acidity engineering, the SnS2/BP heterostructure sensor could detect trace levels of NO2 as low as 100 ppb (parts per billion) with high response, fast response/recovery, good stability, and selectivity at room temperature. The high absorption energy of NO2 (−0.74 eV), as indicated by the density functional theory calculations, suggests that NO2 was chemically adsorbed on the SnS2/BP surface, which was also evidenced by the in situ Raman spectroscopy results. This work opens up interesting opportunities for the rational design of highly efficient NO2 gas sensors through Lewis acidity modification and interface engineering.

Highly sensitive and selective room-temperature NO2 gas sensor based on novel Fe2O3 nanorings/reduced graphene oxide heterojunction nanocomposites

Novel Fe2O3 nanorings/reduced graphene oxide (Fe2O3 NRs/rGO) heterojunction nanocomposites were synthesized by a simple hydrothermal method. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier Transform infrared spectrometer and transmission electron microscope (TEM) were used to analysis the microstructure and morphology of Fe2O3 NRs/rGO nanocomposites. Gas sensing results indicated that the optimal NO2 gas sensor based on Fe2O3 NRs/rGO nanocomposites exhibited a room temperature response of 23.8 toward NO2 concentration of 5 ppm, which was 12 times higher than that of α-Fe2O3 nanorings. The HR-TEM results showed that there was a close interface between α-Fe2O3 and rGO, which proved the formation of heterojunction nanocomposite structure. In addition, the sensor based on Fe2O3 NRs/rGO nanocomposites has a short response time of 15 s and excellent NO2 selectivity. The detection limit of NO2 is as low as 1 ppm at room temperature. The enhancement of NO2 sensing performances can be attributed to the improved electronic conductivity, much higher specific surface area, more adsorption sites and the formation of the heterojunction between Fe2O3 nanorings and reduced graphene oxide.

VS2 nanosheet as a promising candidate of recycle and reuse NO2 gas sensor and capturer: a DFT study

We describe the utilization of VS2 nanosheet as high sensing response, reuse, and thermodynamic stability at room temperature NO2 and NO gas sensors by using the density functional theory method. We focus on the electronic structures and adsorption energy toward a variety of gaseous molecules (such as O2, CO, H2O, NH3, NO, and NO2) adsorbed on the VS2 nanosheet. The results show that chemical interactions existed between NO/NO2 molecules and VS2 nanosheet due to sizable adsorption energy and strong covalent (S–N) bonds. In particular, the adsorption energies, charge transfer and electronic properties between NO2 adsorbed system is significantly changed compared with the other gas molecules (CO, NO, H2O, NH3, and O2) adsorbed systems under biaxial strains, which is effective to achieve the capture or reversible release of NO2 for cycling capability. Our analysis indicates that VS2 nanosheet is promising as electrical devices candidate for NO2 high-performance gas sensor or capturer.

Thin-layered MoS2 nanoflakes vertically grown on SnO2 nanotubes as highly effective room-temperature NO2 gas sensor

The unique properties of heterostructure materials make them become a promising candidate for high-performance room-temperature (RT) NO2 sensing. Herein, a p-n heterojunction consisting of two-dimensional (2D) MoS2 nanoflakes vertically grown on one-dimensional (1D) SnO2 nanotubes (NTs) was fabricated via electrospinning and subsequent hydrothermal route. The sulfur edge active sites are fully exposed in the MoS2@SnO2 heterostructure due to the vertically oriented thin-layered morphology features. Moreover, the interface of p-n heterojunction provides an electronic transfer channel from SnO2 to MoS2, which enables MoS2 act as the generous electron donor involved in NO2 gas senor detection. As a result, the optimized MoS2@SnO2-2 heterostructure presents an impressive sensitivity and selectivity for NO2 gas detection at RT. The response value is 34.67 (Ra/Rg) to 100 ppm, which is 26.5 times to that of pure SnO2. It also exhibits a fast response and recovery time (2.2 s, 10.54 s), as well as a low detection limit (10 ppb) and as long as 20 weeks of stability. This simple fabrication of high-performance sensing materials may facilitate the large-scale production of RT NO2 gas sensors.

A room-temperature NO2 gas sensor based on CuO nanoflakes modified with rGO nanosheets

Abstract Conventional gas-sensing materials for detecting trace NO2 gas are suffering from limitations such as low selectivity, high operation temperature and an agglomerated tendency during synthesis. In this work, uniform CuO nanoflakes modified with rGO nanosheets (CuO/rGO) were synthesized via an ultra-low-cost hydrothermal process with a thermal treatment. The gas sensor based on the as-synthesized CuO/rGO was fabricated by spin-coated method and applied to detect ppb-level NO2 gas at room temperature (23℃). Remarkably, the CuO/rGO-based sensor maintained an ultrahigh response behavior of approximately 400.8 % towards 5 ppm NO2 gas with ultrafast response time of 6.8 s at 23℃, and the limit of detection was down to 50 ppb (S = 20.6 %). In addition, the gas sensor had outstanding consistency, reliable repeatability, and long-term stability (30 days). The improved gas-sensing response was attributed to the synergetic effects of CuO and rGO. Specifically, the porous flake-like nanostructures of CuO and high surface areas of CuO/rGO may provide additional active adsorption sites for NO2 gas and accelerate the redox reaction on the surface of CuO/rGO, leading to the ultrahigh response. On the other hand, the rGO nanosheets with excellent transport capability may serve as highly conductive channels to accelerate carrier transfer, which dramatically reduced the response and recovery time. Furthermore, abundant surface defects of CuO/rGO were also conducive to surface reactions in the gas-sensing process. Undoubtedly, the scientific study of the present work will promote potential applications of ppb-level NO2 detection at room temperature.