Room-temperature NO2 Gas Sensor Research Articles

Upcycled Graphene Oxide Nanosheets for Reversible Room Temperature NO2 Gas Sensor

Graphene oxide (GO) nanosheets, as one of the most studied graphene derivatives, have demonstrated an intrinsically strong physisorption-based gas–matter behavior, owing to its enhanced volume–surface ratio and abundant surface functional groups. The exploration of efficient and cost-effective synthesis methods for GO is an ongoing task. In this work, we explored a novel approach to upcycle inexpensive polyethylene terephthalate (PET) plastic waste into high-quality GO using a combination of chemical and thermal treatments based on a montmorillonite template. The obtained material had a nanosheet morphology with a lateral dimension of around ~2 µm and a thickness of ~3 nm. In addition, the GO nanosheets were found to be a p-type semiconductor with a bandgap of 2.41 eV and was subsequently realized as a gas sensor. As a result, the GO sensor exhibited a fully reversible sensing response towards ultra-low-concentration NO2 gas with a limit of detection of ~1.43 ppb, without the implementation of an external excitation stimulus including elevating the operating temperature or bias voltages. When given a thorough test, the sensor maintained an impressive long-term stability and repeatability with little performance degradation after 5 days of experiments. The response factor was estimated to be ~11% when exposed to 1026 ppb NO2, which is at least one order of magnitude higher than that of other commonly seen gas species including CH4, H2, and CO2.

In-situ growth of vertically stacked 2D SnS2/SnS heterostructure for highly sensitive and rapid room temperature NO2 gas sensor

Construction of 2D heterostructure is a potential strategy to improve the sensing performance of 2D layered materials owing to the high-quality of heterointerfaces. This attributed to the remarkable electronic band alignment between the constituent materials and their distinctive characteristics. Woefully, very limited attempts have been taken to investigate the effect of 2D heterointerface for gas sensing applications. Here, the SnS2/SnS heterostructure is fabricated on a SiO2/Si substrate using a single-step atmospheric chemical vapor deposition technique for room temperature NO2 sensing. The heterostructure has imparted a 1.3 times enhancement in response (S(%)), with ultra-fast response (τres) and recovery time (τrec) of 32 s and 382 s, towards 40 ppm of NO2 at 30 °C. Moreover, the impact of humidity on the sensing performance of SnS2/SnS has also been studied, confirming its negligible effect on relative humidity. Additionally, it also demonstrates a remarkable stability of 93% over a period of 40 days. Besides, due to strong adsorption energy of SnS2 (1914 meV) and SnS (600 meV) towards NO2 endorses the reaction kinetic parameters validated by the gas adsorption/desorption isotherm analysis of heterostructure. The substantial interface contacts between the SnS2/SnS heterostructure facilities the fermi-level mediated charge transfer, contributing significantly towards the improvement in sensing performance. Therefore, the formation of hierarchical 2D heterostructure with electron depletion layer can be considered as a conducive way for the future development low-powered gas sensor.

Improvement of gas-sensing performance of TO8C monolayers as high-efficient room-temperature NO and NO2 gas sensors induced by electric field

The gas-sensing application potential of the TO8C monolayer for the target gases (NO, NO2, CO, CO2, NH3, CH4, H2O, and H2) was systematically investigated via DFT calculations. Only NO and NO2 adsorption can tune the electronic properties of the TO8C monolayer. Since the weak adsorption strength of NO and NO2 is unfavorable for the sensor device, E-field modulation was applied. Except as the enhancement of adsorption strength into desired ranges for NO and NO2, E-field modulation of −0.14 ∼ −0.21 V/Å for NO (0.08 ∼ 0.12 V/Å and −0.26 ∼ −0.29 V/Å for NO2) makes semiconducting transfer into conducting properties, indicating the sensitivity of the monolayer towards NO and NO2 gases was also effectively improved. However, the electronic properties of TO8C monolayer adsorbed with the other gases were hardly changed by the above-mentioned E-fields. When the applied E-fields were in −0.12 ∼ −0.17 V/Å (or −0.26 ∼ −0.29 V/Å), the conducting properties for NO (or NO2) adsorption were maintained in the existence of humidity, indicating that the determinate E-field is much favorable for the TO8C-based sensor to detect NO and NO2 gases without considering whether the humidity exists. Our findings reveal that the TO8C monolayers are compelling and feasible candidates for NO and NO2 resistance-type sensors at room temperature under the E-field modulation.

Highly Efficient Room Temperature NO2 Sensor Using Two-Phase TiOx Heterogeneous Nanoparticles.

In this study, we successfully synthesized two-phase titanium oxide (TiOx) heterogeneous nanoparticles (NPs) using an advanced sol-gel method, a significant stride in developing efficient, room temperature (RT) NO2 gas sensors. The prepared two-phase TiOx heterogeneous NPs exhibited exceptional sensitivity to low concentrations of NO2 gas at RT. The heightened gas response was attributed to a significant presence of oxygen vacancies, creating intermediate states within the two-phase heterostructures and thus narrowing the band gap. This facilitated electron transport from the valence band (VB) to the conduction band (CB), resulting in increased current at RT. The XPS analysis confirmed a substantial amount of chemisorbed oxygen O2(ads)- within the two-phase heterostructures, providing more chemisorption sites for nitrogen dioxide gas. This increase in chemisorption sites significantly improved the gas response. Furthermore, the introduction of zinc into the TiOx NPs reduced their band gap, enhancing the background resistance signal-to-noise ratio and increasing the response while maintaining remarkable stability. In summary, our work introduces a promising RT NO2 sensor based on two-phase TiOx heterogeneous NPs, holding great potential for applications in environmental monitoring and gas sensing technology. In future work, we aim to delve deeper into the capabilities of the sensor, exploring broader applications and refining its design for enhanced practicality in environmental monitoring.

Vertically aligned MoSe2-WS2 nanoworms heterojunction towards room temperature NO2 gas sensors

Gas sensing devices have gained substantial attention by using semiconducting heterojunctions composed of two-dimensional (2D) transition metal dichalcogenide (TMDs) materials, offering increased sensitivity, stability, selectivity, and full recoverability. However, a deeper understanding of the sensing behavior of these heterojunctions is necessary. In this investigation, the focus centers on the fabrication of p-n heterojunction consisting of hexagonal molybdenum diselenide-tungsten disulfide (MoSe2-WS2) for room-temperature (RT, 27 °C) NO2 (Nitrogen dioxide) gas detection. A catalyst-free magnetron sputtering technique has been employed to fabricate the composite thin film of vertically aligned hydrophobic MoSe2-WS2 nanoworms on the n-type silicon substrate. The resulting sensor exhibited exceptional sensitivity (59.63%), quick response (68.90 s), and full recovery (65.68 s) towards 50 ppb NO2 even at RT, highlighting its strong affinity for NO2 molecules. The reliability of the as-fabricated MoSe2-WS2 composite thin film sensor has been confirmed by its high selectivity (59.63%) and long-term stability (> 60 days) towards 50 ppb NO2 at RT. The remarkable sensing capabilities of this innovative TMDs composite hold promising potential for future low-power and room-temperature NO2 gas sensors.

Interface engineering of a highly sensitive porous CuO modified rGO layers for room temperature NO2 gas sensor

The process of combusting non-renewable energy sources results in the emission of a variety of harmful gases into the environment. As a result, there is a continuing need for a high-sensitivity gas sensor capable of promptly identifying these gases at room temperature (RT). Herein, we developed a high-sensitive CuO/rGO heterostructures sensor for NO2 gas detection at RT (30 °C) with enhanced sensitivity and short response rate. Interestingly, the developed CuO/rGO (CR10) sample illustrated an incredibly high sensitivity of 1004% against 5 ppm NO2 gas with an extremely rapid response rate of 9 s at RT. The developed CR10 sensor exhibits a 5.17 times ameliorated sensing response against 5 ppm of NO2 gas in contrast to the pristine CuO (CR0) sensor. The developed NO2 sensor also exhibits high selectivity, long-term stability (30 days), good linearity, and impressive repeatability. The synergistic interaction between CuO and reduced graphene oxide (rGO) are primary reason for the enrichment of the sensing performance. In particular, a thin layer of rGO arranged over CuO porous nanosheets and the enormous surface area of CuO/rGO could serve as additional available adsorption centres for NO2 gas and increase the speed of redox reaction on the CuO/rGO sensor surface, resulting in an extremely high sensing response. Furthermore, the rGO thin layer exhibits exceptional carrier transfer capabilities that can be utilized as ultra-responsive conductive channels, thereby enhancing the sensing response significantly. Besides, a significant amount of chemisorbed oxygen species are also relatively favourable for the sensing performance. This study opens up a novel avenue to develop a high-performance NO2 sensors at RT.

High-response room-temperature NO2 gas sensor fabricated with thermally reduced graphene oxide-coated commercial cotton fabric

Electronic textile-based gas sensors with a high response for NO2 gas were fabricated using reduced graphene oxide (rGO)-coated commercial cotton fabric (rGOC). Graphene oxide (GO) was coated on cotton fabric by simply dipping the cotton into a GO solution. To investigate the relationship between the degree of reduction and the sensing response, the GO-coated fabrics were thermally reduced at various temperatures (190, 200, 300, and 400 °C). The change in the amount of oxygen functional groups on the rGOCs was observed by x-ray photoelectron spectroscopy, Raman spectroscopy, and x-ray diffraction patterns. The maximum sensing response of 45.90 % at 10 ppm of NO2 gas at room temperature was exhibited by the rGOC treated at 190 °C, which was the lowest heat-treatment temperature. The high response comes from the greater amount of oxygen functional groups compared to other rGOC samples, and the tubular structure of the cotton.

Cu-MOF-74-derived Cu2O/CuO-C nanocomposite as an effective chemiresistive sensor for detection of NO2 at room temperature

We report a Cu2O/CuO-C nanocomposite which fabricated by thermal decomposition of Cu-based metal-organic framework (Cu-MOF-74) precursor. The attractive advantages of MOF-74 incorporating the abundant unsaturated (open) metal sites and excellent stability provide a guarantee for developing of efficient gas-sensing materials. After annealing, the material retains its skeleton structure and the surface area is greatly increased. The high porosity feature of the as-prepared Cu2O/CuO-C offers plentiful active sites for adsorption of gas molecules, thus ensuring high sensing performance. The results indicate that the Cu2O/CuO-C-based sensor exhibits high sensitivity (1.03–30 ppb NO2), good linear relationship and excellent selectivity to NO2 at room temperature (RT, 25 ℃). Notably, the theoretical detection limit of the as-prepared sensor is ∼7 ppb, which is significantly below the annual average NO2 concentration limit (40 ppm) imposed by China. The synergistic effect between CuO/Cu2O heterostructure and carbon, and the derived solid structure are considered as the main reason for high sensitivity and selectivity. In addition, the high oxygen vacancy concentration is also the key to ensure excellent gas sensitivity. This work provides a new choice for developing high performance room temperature NO2 gas sensor.

Ultrathin layered MoS2/N-doped graphene quantum dots (NGQDs) heterostructures for highly sensitive room temperature NO2 gas sensor

Due to high surface-to-volume ratio, stability, and more active sites, molybdenum disulfide (MoS2) has been attracted as a promising gas-sensing material. However, the room temperature (RT- 30 ℃) MoS2-based gas sensors still suffer slow response, recovery rates, and less sensitivity, notably for NO2. Herewith, we synthesized a novel molybdenum disulfide/nitrogen-doped graphene quantum dot (MoS2/NGQD) heterostructure via hydrothermal method for NO2 detection. The MNG-3 heterostructure is endowed with enhanced response of 82.4% towards 50 ppm of NO2 at 30 ℃, which is 6.5 folds greater than that of pristine MoS2 nanosheets (NSs). MNG-3 samples outperform with a quick recovery (30 s), excellent repeatability (5 cycles), long-term stability (5 weeks), and good selectivity towards 30 ℃ NO2 detection concentration of 50 ppm. The unique 2D/0D heterostructures and synergistic effect of NGQD and MoS2 NSs are responsible for the improved sensing performance. It undoubtedly suggests the feasible nature of prepared MoS2/NGQD heterostructures for 30 ℃ NO2 detection.

Interfacial oxygen vacancies and energy-level engineering on CeO2-PPy-rGO nanocomposites towards boosted NO2 sensor performance

Monitoring of harmful nitrogen dioxide (NO2) gases is imperative for our health and environmental protection. The room-temperature operating NO2 gas sensors still suffer a limited sensitivity and slow response/recovery rate. In this work, novel CeO2-PPy-rGO nanocomposites were synthesized for improved NO2 sensing performance. The decoration of rGO introduced additional oxygen vacancies on CeO2 for enhancing the sensor response. PPy acted as a buffer layer of energy level connecting CeO2 and rGO components and promoted the response and recovery rate. The designed sensor demonstrated ppb-level NO2 detection in p-type sensing behaviors with rapid response/recovery characteristics as expected at room temperature (RT). The hybrid sensor also showed excellent selectivity, long-term stability and extremely low detection limit toward NO2. The significantly enhanced sensing properties to NO2 could be attributed to activity enhancement, a gently gradient energy level and π-π stacking between rGO and PPy. This study offers a perspective on the design of CeO2-based gas sensors for NO2 detection at RT.

2D/2D SnS2/SnSe2 van der Waals heterostructure for highly sensitive room-temperature NO2 sensor: Key role of interface contact

2D/2D van der Waals (vdW) heterostructure is an effective strategy for improving the functions of 2D layered nanomaterials due to the high-quality heterointerfaces with the lacked dangling bonds at the interfaces. However, little attention was paid to investigating the effect of heterointerface amount and quality on gas-sensing performance. Here, two sets of 2D/2D SnS2/SnSe2 vdW heterostructures with tunable SnSe2 content are fabricated by physical mixing and solvothermal growth methods for room-temperature NO2 gas sensors. Compared to pure SnS2 and SnSe2 layers, the creation of 2D/2D vdW heterostructure shows a great improvement in sensing performance at room temperature. Moreover, the response and sensitivity are further enhanced by increasing the amount of heterointerface. More importantly, the SSSe-1.0 vdW heterostructures with improved interface contact by solvothermal growth exhibit a much higher response and sensitivity than that of MSSe-1.4 prepared by physical mixing, showing the highest response (1274.1% for 2 ppm) with the sensitivity of 598.2 % ppm−1 to NO2 gas. The mechanism of enhanced response and sensitivity for the SSSe-1.0 sensor is investigated by DFT calculation and XPS analysis, revealing that the strengthening of the interface contact improves the charge transfer and NO2 adsorption in 2D/2D SnS2/SnSe2 vdW heterostructure. Such effect of heterojunction number and interface contact on sensing performance paves a solid step toward the development of 2D layered crystals-based NO2 sensors and extends to applications in other fields.

A Highly Sensitive Room-Temperature NO2 Gas Sensor based on Porous MnO2/rGO Hybrid Composites

Background: The NOX (e.g. NO2) is harmful to human health and environmental quality. It is of great interest to monitor the hazardous NOx with a simple, reliable, and sensitive sensor. Currently, the commonly used detection methods have disadvantages of complex operation, unstable cycling performance and low sensitivity. Objective: In this paper, rGO coated Ni foam supported MnO2 is synthesized to develop a more advanced detection method for the rapid analysis of NO2. Methods: A three-dimensional nickel foam supported MnO2 and rGO (MnO2/rGO@NF) was prepared by a hydrothermal method for application in binder-free electrode of NO2 sensor. Results: The MnO2/rGO@NF composite displayed significantly better NO2 sensing performance compared to single MnO2@NF or rGO@NF. The excellent sensing response (5.9%) as well as high cycling stability were observed in the presence of 50.0 ppm NO2 at room temperature. Furthermore, the mechanism of the great gas-sensing performance was also investigated by the density functional theory (DFT). Conclusion: These results were very important to further design and prepare new sensitive materials applied in binder-free electrode of gas NO2 sensors.

S-doped SnO2 derived from SnS nanoparticles for highly sensitive NO2 detection at room temperature

As the main pollutant in the air, NO2 is hugely harmful to the environment and health. It is crucial to develop a room temperature NO2 gas sensor with high response and good selectivity. In this work, S-doped SnO2 was successfully prepared by annealing with SnS nanoparticles as the precursor. S-doped SnO2 showed excellent response to 5 ppm NO2 (10.7), with a fast response (27 s) and recovery times (32 s), and good selectivity at room temperature (RT). The excellent NO2 sensitivity of S-doped SnO2 is attributed to its large specific surface area and large charge transfer between the substrate and NO2. This work can be extended to prepare high-performance NO2 gas sensors by annealing other transition metal dichalcogenides.

Recent developments in 2D MXene-based materials for next generation room temperature NO2 gas sensors.

MXenes with distinctive structures, good electrical conductivity and abundant functional groups have shown great potential in the fabrication of high performance gas sensors. Since the sensing mechanism of MXene-based gas sensors often involves a surface-dominant process, they can work at room temperature. In this regard, a significant amount of research has been carried out on MXene-based room temperature gas sensors and they can be viewed as one of the possible materials for NO2 sensing applications in the future. In this review, we focus on the most recent research and improvements in pure MXenes and their nanocomposites for NO2 gas sensing applications. First, we have explored the mechanisms involved in MXenes for NO2 gas sensing. Following that, other ways to tune the MXene sensing performance are investigated, including nanocomposite formation with metal oxides, polymers, and other 2D materials. A comparative analysis of the RT NO2 sensor performance based on MXenes and their hybrids is provided. We also discuss the major challenges of using MXene-related materials and the areas that can further advance in the future for the development of high-performance room temperature NO2 gas sensors.

Controlled growth and fabrication of edge enriched SnS2 nanostructures for room temperature NO2 gas sensor applications

Nanostructured SnS2 with enhanced edge sites was prepared and investigated the impact on NO2 gas molecules detection at room temperature (RT). SnS2 flower-like structure with exposed active sites provides more interaction channels for the NO2 gas molecules. The crystal orientation along with the (011) plane exhibits more active edge sites, thus enhancing the sensing performance of the flower-like structure. The fabricated SnS2 gas sensor showed more selective towards NO2 gas molecules. SnS2 flower-like structure provides more stability of 81.22% and 32.63% increased sensing response compared to the platelet-like structure. This result provides a pathway for the development of a practical room temperature NO2 gas sensor.

High-Performance Room-Temperature NO2 Gas Sensor Based on Au-Loaded SnO2 Nanowires under UV Light Activation.

Optical excitation is widely acknowledged as one of the most effective means of balancing sensor responses and response/recovery properties at room temperature (RT, 25 °C). Moreover, noble metals have been proven to be suitable as photosensitizers for optical excitation. Localized surface plasmon resonance (LSPR) determines the liberalization of quasi-free electrons in noble metals under light irradiation, and numerous injected electrons in semiconductors will greatly promote the generation of chemisorbed oxygen, thus elevating the sensor response. In this study, pure SnO2 and Au/SnO2 nanowires (NWs) were successfully synthesized through the electrospinning method and validated using XRD, EDS, HRTEM, and XPS. Although a Schottky barrier led to a much higher initial resistance of the Au/SnO2 composite compared with pure SnO2 at RT in the dark, the photoinduced resistance of the Au/SnO2 composite became lower than that of pure SnO2 under UV irradiation with the same intensity, which confirmed the effect of LSPR. Furthermore, when used as sensing materials, a detailed comparison between the sensing properties of pure SnO2 and Au/SnO2 composite toward NO2 in the dark and under UV irradiation highlighted the crucial role of the LSPR effects. In particular, the response of Au/SnO2 NWs toward 5 ppm NO2 could reach 65 at RT under UV irradiation, and the response/recovery time was only 82/42 s, which far exceeded those under Au modification-only or optical excitation-only. Finally, the gas-sensing mechanism corresponding to the change in sensor performance in each case was systematically proposed.

In-situ sulfidation-derived three-dimensional cobalt sulfide nanoflower/graphene nanosheet hybrid for ultrasensitive room-temperature NO2 gas sensor

Two-dimensional (2D) nanosheets show great potential for gas sensing, but they can hinder the penetration of gas molecules and lead to deteriorated sensing performances. Hence, construction of 2D nanosheet-based gas sensing materials with unique structures is desirable for high-performance gas sensing. Herein, a three-dimensional (3D) binary nanosheet heterostructure based on 3D cobalt sulfide (CoS) nanoflower/graphene nanosheet hybrid was constructed for room-temperature NO2 gas sensing. The 3D CoS/reduced graphene oxide (rGO) hybrid derived from a mixture of Co3O4 nanoflowers and graphene oxide nanosheets was facilely formed via in-situ sulfidation and reduction processes. The resistance response of as-assembled gas sensor based on 3D CoS nanoflower/graphene nanosheet hybrid to 1 ppm NO2 was 39.7%, which was 4.2 and 3.1 times higher than that of CoS and rGO sensors, respectively. A response as high as 10.5% was achieved even when the device was exposed to NO2 gas with a low concentration of 50 ppb. Furthermore, the hybrid device exhibited linear response characteristic, high selectivity, good repeatability, as well as long-term stability. Overall, the proposed design strategy together with the as-constructed structures can pave the way for the development of high-performance gas sensors based on graphene hybrids.

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.