Room-temperature NO2 Gas Sensor Research Articles

The kinetics of a light irradiation enhanced room temperature NO2 gas sensor using hybrid ZnO/ZnTe nanorod structures.

This study focuses on fabricating a hybrid structure consisting of ZnO nanorods and ZnTe nanoparticles for NO2 gas detection, particularly exploring the impact of light irradiation at room temperature (RT). The morphology, physical characteristics, and chemical properties of the ZnO/ZnTe hybrid structure are carefully studied under diverse analytical methods such as X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and other measurements. The ZnO/ZnTe composite displayed an improved response toward 500 ppb NO2 under the blue light radiation effect. It demonstrated higher response (more than 2500%), response time (faster than 3000%), and recovery time (faster than 1000%) at RT compared with pure ZnO. Hence, blue light irradiation revealed a more promising sensing performance than UV irradiation's case (200% at sensitivity). The depletion theory, the oxygen vacancy, the catalytic effect of zinc telluride, and the absorption coefficient modulation of the gas sensor based on different materials explained the overall performance of the nanohybrid structured sensor.

Engineering an Ultrafast Ambient NO2 Gas Sensor Using Cotton-Modified LaFeO3/MXene Composites.

This work presents a room-temperature (RT) NO2 gas sensor based on cotton-modified LaFeO3 (CLFO) combined with MXene. LaFeO3 (LFO), CLFO, and CLFO/MXene composites were synthesized via a hydrothermal method. The fabricated sensor, utilizing MXene/CLFO, exhibits a p-type behavior and fully recoverable sensing capabilities for low concentrations of NO2, achieving a higher response of 14.2 times at 5 ppm. The sensor demonstrates excellent performance with a response time of 2.7 s and a recovery time of 6.2 s, along with notable stability. The sensor's sensitivity is attributed to gas interactions on the material's surface, adsorption energy, and charge-transfer mechanisms. Techniques such as in situ FTIR (Fourier transform infrared) spectroscopy, GC-MS (gas chromatography-mass spectroscopy), and near-ambient pressure X-ray photoelectron spectroscopy were employed to verify gas interactions and their byproducts. Additionally, finite-difference time-domain simulations were used to model the electromagnetic field distribution and provide insight into the interaction between NO2 molecules and the sensor surface at the nanoscale. A prototype wireless IoT (Internet of Things)-based NO2 gas leakage detection system was also developed, showcasing the sensor's practical application. This study offers valuable insight into the development of room-temperature NO2 sensors with a low detection limit.

Highly Sensitive and Selective Room Temperature NO2 Gas Sensor Based on 3D BiFeO3 − x Microflowers

Highly Sensitive and Selective Room Temperature NO2 Gas Sensor Based on 3D BiFeO3 − x Microflowers

A room-temperature NO2 gas sensor based on Zn2+ doped Cu2O/CuO composites with ultra-high response

Metal oxide semiconductors (MOS) have attracted increasing interest in gas sensors recently due to their exceptional design flexibility and superior gas sensing capabilities. However, the high operating temperatures and reliance on light activation in MOS-based gas sensors limit their potential applications. In this work, the Zn2+ doped Cu2O/CuO composites were successfully fabricated by one-step hydrothermal method for the detection of NO2 gas at room temperature. The experimental results show that the optimal Zn-Cu2O/CuO composite presents responses that are 2.9, 3.4, 3.1 times higher than those of the pure Cu2O/CuO composite to 10, 5 and 1 ppm NO2. Additionally, the response and recovery times are shortened by factors of 3.1 and 1.4, respectively. Notably, the detection limit of the Zn-Cu2O/CuO composite is 2 ppb at room temperature, significantly below China's annual average NO2 concentration limit of ∼18 ppm. Furthermore, the Zn-Cu2O/CuO based sensor demonstrates the great selectivity, repeatability and long-term stability for NO2 detection. The gas sensitivity enhancement mechanism is thoroughly discussed. This result provides a new approach for the effective detection of ppb-level NO2 by CuO-based gas sensing materials at room temperature.

Flexible and highly selective NO2 gas sensor based on direct-ink-writing of eco-friendly graphene oxide for smart wearable application

Nitrogen dioxide (NO2) is a major cause of respiratory disorders in outdoor and indoor environments. Real-time NO2 monitoring using nonintrusive wearable devices can save lives and provide valuable health data. This study reports a room-temperature, wearable, and flexible smart NO2 gas sensor fabricated via cost-effective printing technology on a polyimide substrate. The sensor uses alkali lignin with edge-oxidised graphene oxide (EGO-AL) ink, demonstrating a sensitivity of 1.70% ppm⁻1 and a detection limit of 12.70 ppb, with excellent selectivity towards NO2. The high sensing properties are attributed to labile oxygen functional groups from GO and alkali lignin, offering abundant interacting sites for NO2 adsorption and electron transfer. The sensor fully recovers to the baseline after heat treatment at 150 °C, indicating its reusability. Integration into lab coats showcased its wearable application, utilising a flexible printed circuit board to wirelessly alert the wearer via cell phone to harmful NO2 levels (>3 ppm) in the environment. This smart sensing application underscores the potential for practical, real-time air quality monitoring, personal safety enhancement, and health management.

Room temperature NO2 gas sensor based mesoporous Zn/Al-layered double hydroxide: The effect of molar ratio

This study elucidates the fabrication and performance evaluation of mesoporous Zn/Al-layered double hydroxide (LDH) for nitrogen dioxide (NO2) efficient room temperature (RT) gas sensor through two-steps solution processed. The correlation between the microstructural analysis and gas sensing performance evaluation was clearly investigated. In detail, average porosity and surface area enhancement from 19.4 to 56.6 nm and 27.50 to 47.85 (m2/g) were perceived for molar ratios of 3:1 and 7:1 of Zn2+ to Al3+, respectively. This in turn resulted in gas sensor response enhancement from 10.21 to 16.41 % for the optimum device (molar ratio of 7:1) under gas concentration of 100 ppm. Continuously, the fabricated devices responded linearly to the applied gas concentration alteration wherein R2 average value of 0.995 was attained. In conjunction, the time-resolved characteristics revealed considerably fast response time along comparatively longer recovery window wherein the average rise/fall periods were estimated to be 2.98 and 19.3 sec., respectively.

A room temperature NO2 gas sensor based on Rb-doped ZnO/In2O3 nano-heterojunction with high performance

In this study, we prepared Rb-doped ZnO/In2O3 n-n nano-heterojunction, which functioned as highly responsive gas sensors for NO2 at room temperature. The experiments demonstrated a significant enhancement in the gas-sensing capabilities for low concentrations of NO2 at room temperature. ZnO/In2O3 NO2 gas sensors were synthesized with varying concentrations of Rb-doped using a two-step method. Gas-sensing experiments showed that the sensor with 6 mol% Rb-doped exhibited excellent selectivity and remarkable response values to NO2. At a NO2 concentration of 1 ppm, the response value was ten times greater than that of the undoped ZnO/In2O3 sensor, reaching a value as high as 119.5. This exceptional NO2 detection performance can be attributed to several factors. The presence of Rb-doped increased the concentration of oxygen vacancies on the material's surface, leading to a 14 % increase in adsorbed oxygen content compared to the undoped material. Additionally, Rb-doped resulted in a thicker depletion layer on the material's surface, which enhanced charge-transfer density. The band gap of Rb-doped ZnO/In2O3 decreased by 0.21 eV compared to the undoped ZnO/In2O3, enhancing the electron-leaping capability. The combined effects of these sensitization phenomena resulted in a significant improvement in the NO2 detection performance of the Rb-doped ZnO/In2O3 gas sensor.

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.

A room-temperature ppb-level detection limit of NO2 sensor based on Cellulose/SnO2 heterojunction under UV illumination

In light of growing concerns over air pollution, particularly NO2 emissions from vehicular and industrial sources, there is a critical demand for advanced gas sensors. Traditional metal oxide semiconductors, while widely used, face challenges such as poor selectivity and high operating temperatures. In this work, we have achieved a high selectivity and room temperature NO2 gas sensor by composite of sponge-like porous cellulose with SnO2 nanoparticle. As a result, the gas sensor exhibits excellent performance in terms of high response (260.4 at 20 ppm), excellent selectivity and low detection limit (100 ppb) for NO2 gas, due to the unique sponge-like porous structure of cellulose with its high specific surface area facilitating the uniform distribution of SnO2 particles. This study not only highlights the superior sensing capabilities of cellulose-based sensors but also lays the foundation for further advancements in environmentally-friendly gas sensing applications.

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.