Room-temperature Gas Sensor Research Articles

Highly sensitive and stable room-temperature gas sensors based on the photochemically activated p-type CuAlO2 thin films

Activating metal oxide-based gas sensors using UV-LED is a promising approach to operating them at low temperatures. This method preserves the film characteristics, thereby ensuring the stability of the devices. In this report, we present a remarkably sensitive and stable gas sensor based on solution-processed p-type copper aluminum oxide (CuAlO2), which can sense O3 gas at room temperature. Moreover, the sensitivity is further improved through exposure to ultraviolet (UV) radiation. The optimal gas response of 12.32 can be achieved under UV illumination of 20 mW/cm2 at room temperature. More importantly, the CuAlO2 sensor exhibits outstanding stability, with a deterioration of only ∼10% over a period of 3 months. These findings suggest that CuAlO2 is a promising material for gas sensing at room temperature.

Ultrasensitive room-temperature flexible ammonia gas sensor based on Au-functionalized polypyrrole wrapped enriched edge sulfur vacancies MoS2 nanosheets

Au/MoS2/polypyrrole (Au/MoS2/PPy) nanocomposite is successfully synthesized by the liquid-phase ultrasonic exfoliation process combined with in-situ polymerization method and then Au particles are decorated on its surface. Abundant sulfur (S) vacancies in the exfoliated layered MoS2 nanosheets act as active adsorption sites, and Au particles also play an efficient catalyst to enhance the NH3 gas sensing properties of Au/MoS2/PPy flexible sensor at room temperature. It results in higher NH3 gas sensing response, faster recovery rate, and more stable sensing performance even under complex environment conditions such as high relative humidity and high bending angle/numbers compared with that of pristine PPy sensor. The enhancement sensing mechanisms of Au/MoS2/PPy sensor are attributed to the p-n heterojunction between layered MoS2 and PPy, the active sites of S vacancies, the catalysis and dehydrogenation effect of Au particles, which have been verified by XPS, current-voltage (I-V), and in-situ FITR, etc. Moreover, the density-functional theory (DFT) calculations are employed to further illustrate the selectivity sensing mechanism, and reveal the S vacancies, the nanocomposite of MoS2/PPy possess high superiority for improving NH3 sensing properties at room temperature.

Effect of Ultraviolet Light on Mn3O4 Thin Films that are Grown Using SILAR for Room-Temperature Ozone Gas Sensors

Successive ionic layer adsorption and reaction (SILAR) is a promising technique to fabricate gas sensors at room temperature. However, the quality of the films is poor, leading to reduced surface area and increased defects within the film structure, thus decreasing the overall gas response. Inferior film quality also negatively affects the stability and reproducibility of the gas sensors over time. This study determines the effect of UV treatment on the structural, morphological, and ozone (O3) gas-sensing properties of p-type Mn3O4 thin films. As UV treatment time increases, the O3 gas-sensing characteristics increase because a porous structure with a higher surface area is formed and electrical conductivity is increased. Under a UV intensity of 20 mW cm−2, the Mn3O4 sensor exhibits gas response, response time, and recovery time of 1.62, 58, and 39 s, respectively, against 5 ppm concentration of O3 gas. Moreover, the Mn3O4 gas sensor exhibits excellent long-term stability showing around 3% variation in gas response over 60 d. This strategy allows the deposition of high-quality p-type Mn3O4 thin films using SILAR for applications in flexible gas sensors.

Room-temperature ammonia gas sensor based on Ni-doped MoO3 thin film prepared by spray pyrolysis method

Room-temperature ammonia gas sensor based on Ni-doped MoO3 thin film prepared by spray pyrolysis method

Polyethylene glycol embedded reduced graphene oxide supramolecular assemblies for enhanced room-temperature gas sensors

Herein, we present the gas-dependent electrical properties of a reduced graphene oxide nanocomposite. The reduced graphene oxide (rGO) was synthesized by reducing GO with sodium borohydride (NaBH4). As-synthesized rGO was dispersed in DI water containing 1, 2, 3, 4, and 5 wt% polyethylene glycol (PEG) to prepare PEG-rGO supramolecular assemblies. The successful preparation of supramolecular assemblies was verified by their characterization using XRD, FESEM, EDS, TEM, FTIR, and Raman spectroscopy. At room temperature, the gas-dependent electrical properties of these supramolecular assemblies were investigated. The results showed that sensors composed of PEG-rGO supramolecular assemblies performed better against benzene and methanol at 3% and 4% PEG, respectively. However, high selectivity and a wide range of activation energies (∼1.64–1.91 eV) were observed for H2 gas for 4% PEG-modified supramolecular assemblies. The PEG-rGO supramolecular assemblies may be an excellent candidate for constructing ultrahigh-performance gas sensors for a variety of applications due to their high sensitivity and selectivity.

Laser-Ablated Transmutation of Bulk TiO2 into Nanospheres onto a Clad-Polished Optical Fiber for Room-Temperature Gas Sensing

Laser-Ablated Transmutation of Bulk TiO₂ into Nanospheres onto a Clad-Polished Optical Fiber for Room-Temperature Gas Sensing

Insecticide Monitoring in Cattle Dip with an E-Nose System and Room Temperature Screen-Printed ZnO Gas Sensors

Taktic, an Amitraz-based insecticide, is commonly used in sub-Saharan Africa to treat cattle for ticks. Due to misuse in rural dipping pools, some ticks are showing resistance to Taktic. This work presents a low-cost e-nose with commercial sensors to monitor Taktic levels in dipping pool water. The device shows distinctly different measurements for the odours of air, distilled water, farm water, and four levels of Taktic insecticide in farm water. A naive Bayes algorithm with a Gaussian distribution is trained on the data and a validation set achieves a 96.5% accuracy. This work also compares two sol-gel ZnO nanoparticle solutions with an off-the-shelf ZnO nanoparticle ink for use as active material in chemiresistive gas sensors to be employed in an e-nose array. The ZnO solutions are screen-printed onto gold electrodes, auto-sintered with a built in heater, and used with UV illumination to operate as low-power, room temperature gas sensors. All of the screen-printed ZnO sensors show distinct changes in resistance when exposed to Taktic vapours under room temperature and humidity conditions. The custom room temperature ZnO gas sensors fabricated via facile and low-cost processes are suitable for future integration in a point-of-need microsystem for the detection of Taktic in water.

A highly selective room-temperature formaldehyde gas sensor based on vertically aligned 1D NiCo2O4 nanoneedles

The challenge to detect formaldehyde gas at room-temperature (RT) using metal oxide semiconductors is still unaddressed. High temperature requirement of metal oxide gas sensors restricts their usage in various hand-held devices. To address this unattended regime of metal oxide gas sensors,a novel RT-based formaldehyde sensor using the 1D nickel cobalt oxide (NiCo2O4) has been reported. It is synthesized via a single-step hydrothermal route. FESEM and TEM micrographs reveal micro-flower like morphology, consisting of huge numbers of interwoven, vertically aligned 1D nanoneedles while chemical characterization data confirm successful growth of this binary metal oxide. This sensor exhibits quick response/recovery time (22 s /57 s) at RT over the linear region of 10–100 ppm formaldehyde with excellent selectivity and stability. Thus, it paves an avenue for development of affordable, RT gas sensing devices for air quality monitoring applications.

Single-atom Ce targeted regulation SnS/SnS2 heterojunction for sensitive and stable room-temperature ppb-level gas sensor

Metal sulfide-based gas sensors have the advantage of high sensitivity at room temperature, enabling high integration and low power consumption. However, a trade-off between low baseline resistance and good long-term stability at room temperature still needs to be addressed. Therefore, a single-atom Ce-targeted regulation strategy for p-SnS/n-SnS2 was proposed. By doping different amounts of Ce, the amount and size of SnS quantum dots on the surface of SnS2 can be regulated. Furthermore, Sn-S-Ce bonds are formed by combining single-atom Ce with SnS, which effectively hinders the growth and oxidation of SnS quantum dots, as evidenced by STEM, XPS, DFT, FTIR and EAXFS methods. Due to the unique energy band structure of p-SnS and n-SnS2, Ce-doped SnS quantum dots serve as electronic sensitizers, effectively increasing the carrier concentration in SnS2. The optimal gas sensor based on the 1% Ce-doped SnS/SnS2 composites enables high sensitivity (with a response of 22.1 to 1 ppm NO2), ultralow detection limit (1 ppb), excellent long-term stability at room temperature, and a lower baseline resistance. This engineering strategy of metal sulfide semiconductor heterostructures through single-atom targeted regulation provides new insights for further optimizing the composite system.

Carbon Nanofibers Synthesized at Different Pressures for Detection of NO2 at Room Temperature

In this paper, room-temperature chemiresistive gas sensors for NO2 detection based on CVD-grown carbon nanofibers (CNFs) were investigated. Transmission electron microscopy, low-temperature nitrogen adsorption, and X-ray diffraction were used to investigate the carbon nanomaterials. CNFs were synthesized in a wide range of pressure (1–5 bar) by COx-free decomposition of methane over the Ni/Al2O3 catalyst. It was found that the increase in pressure during the synthesis of CNFs induced the later deactivation of the catalyst, and the yield of CNFs decreased when increasing pressure. Sensing properties were determined in a dynamic flow-through installation at NO2 concentrations ranging from 1 to 400 ppm. Ammonia detection was tested for comparison in a range of 100–500 ppm. The obtained sensors based on CNFs synthesized at 1 bar showed high responses of 1.7%, 5.0%, and 10.0% to 1 ppm, 5 ppm, and 10 ppm NO2 at 25 ± 2 °C, respectively. It was shown that the obtained non-modified carbon nanomaterials can be used successfully used for room temperature detection of nitrogen dioxide. It was found that the increase in relative humidity (RH) of air induced growth of response, and this effect was facilitated after reaching RH ~35% for CNFs synthesized at elevated pressures.

A multisite strategy to improve room-temperature DMMP sensing performances on reduced graphene oxide modulated by N-doped carbon nanoparticles and copper ions

Development of room-temperature gas sensors with excellent sensing performances for detection of dimethyl methylphosphonate (DMMP, a simulant of organophosphate) has aroused considerable attention. However, the weak adsorption ability of sensing materials toward DMMP molecules causes poor sensing performances. In this work, a multisite strategy for enhancing sensitivity was proposed by introduction of both N-doped carbon nanoparticles (N-CNPs) and copper ions onto the surface of rGO (designated as GNC). Impressively, optimal GNC-3 exhibits the response value of 10.2% toward 100 ppm DMMP, which is 5.3 times higher than that of pristine rGO. This mechanism for multisite-assisted enhanced DMMP sensing performances was investigated by combined characterizations of Fourier-transform infrared spectra, UV-Vis spectra, photoluminescence spectra and Mott-Schottky curves. Besides the construction of multisite, improvement of hydrogen bonding interactions between DMMP molecules and N-CNPs in hybrids assisted by copper ions, and decrease of conduction band potential by formation of ternary hybrids also contribute to enhance the sensitivity of DMMP sensors. These findings not only provided new insights into designing high-performance room-temperature gas sensors, but also promoted the fundamental research on sensing mechanism for room-temperature gas sensors.

Room Temperature Wearable Gas Sensors for Fabrication and Applications

AbstractThe recent surge in demand for human–machine interaction (HMI), Internet of Things (IoTs), and artificial intelligence (AI) has created both opportunities and challenges for room‐temperature wearable gas sensors. These sensors serve as a source of perceptual information and can be easily integrated into wearable electronic devices due to their portability and miniaturization. In recent years, various types of wearable room temperature gas sensors have been developed for fields like environmental monitoring, healthcare, smart home, industrial security, food safety monitoring, and public security. These sensors not only adjust to the movements of human effortlessly but also have reduced power consumption. Therefore, room temperature wearable gas sensors hold great promise for the development of integrated intelligent gas sensing system worn on the human body. These sensors can be fabricated using various sensing materials to detect diverse target gases. This review provides a comprehensive summary of the preparation of sensing materials with extraordinary sensing capabilities at room temperature. Additionally, the article includes a brief discussion of the sensing mechanism, employing four models to explain it: oxygen adsorption, direct electron transfer, proton transfer, and ions conduction. Finally, this article discusses the various applications and future perspectives of room‐temperature wearable gas sensors.

Room-temperature sensing of NH3 gas using CsPbBr3 thin films grown via dual-source evaporation

An effective ammonia sensor was developed using a CsPbBr3 thin film prepared directly by dual-source thermal evaporation. The CsPbBr3-based sensor exhibited good selectivity toward ammonia gas at room temperature, showing a high responsivity (958% at 10 ppm) and low detection limit (250 ppb). The sensor also demonstrated good reversibility, repeatability and fast rise/recovery times (12/16 s). Additionally, the effect of humidity on ammonia responsivity was investigated for the application of CsPbBr3 films in practical room-temperature ammonia gas sensors. The ammonia-sensing mechanism of the CsPbBr3 film was proposed and discussed.

Layer-Dependent NO2-Sensing Performance in MoS2 for Room-Temperature Monitoring

Few-layer MoS2 with exceptional physical and chemical properties has attracted notable attention for next-generation gas sensors. The layer-dependent sensing performance for detecting NO2 based on MoS2 is not fully understood. Here, we report the direct synthesis of high-crystallinity uniform few-layer MoS2 via chemical vapor deposition. The influence of layer thickness on the NO2-sensing performance is evaluated. We show that, as compared to the monolayer and trilayer counterparts, the bilayer MoS2 presents the best sensitivity at room temperature. Further density functional theory calculations reveal that the bilayer MoS2 with an AA stacking sequence is more favorable for the physisorption of NO2 molecules due to the more negative adsorption energy, facilitating charge transfer during the NO2 adsorption and thus increasing the electrical response of the gas sensors. This work provides a basic understanding of layer-dependent gas-sensing performance and serves as a reference for designing room-temperature gas sensors for low power consumption and reliable responsivity.

Room-Temperature Ammonia Gas Sensor Based on Ti3C2Tx MXene/Graphene Oxide/CuO/ZnO Nanocomposite

Two-dimensional (2D) Ti3C2Tx Mxene has currently demonstrated significant potential for gas sensing application with a high signal-to-noise ratio at room temperature. Herein, we present the mixture of popular NH3 sensing materials such as graphene oxide (GO), copper oxide (CuO), and zinc oxide (ZnO) into Ti3C2Tx Mxene to be a high-performance NH3 gas sensor at room temperature. Various nanocomposites such as Mxene/GO, Mxene/ZnO, Mxene/CuO, Mxene/GO/ZnO, Mxene/GO/CuO, Mxene/ZnO/CuO, and Mxene/GO/ZnO/CuO were synthesized via the hydrothermal method and used as NH3 sensing materials in room-temperature gas sensors. The Ti3C2Tx MXene/GO/CuO/ZnO nanocomposite gas sensor exhibited the best NH3 gas sensor. The effects on the weight ratios of Ti3C2Tx MXene/GO/CuO/ZnO were also investigated, and the optimal Ti3C2Tx MXene/GO/CuO/ZnO weight ratio was determined to be 9:1:5:5. The optimal Ti3C2Tx MXene/GO/CuO/ZnO based gas sensor showed a high response of 96% at 200 ppm of NH3, humidity independence in the range of 30–70%RH, good linear relationship (R2 = 0.998), low limit of detection of 4.1 ppm, and high selectivity to NH3 over several gases/VOCs including formaldehyde, ethanol, methanol, isopropanol, toluene, and acetone. The NH3-sensing mechanism was proposed based on the modulation of complex p–n heterojunctions via the electron accumulation layer in the n-type of GO/CuO/ZnO and the electron depletion layer in the p-type Ti3C2Tx Mxene.

SnO2 submicron porous cube derived from metal-organic framework for n-butanol sensing at room temperature

SnO2 is a typical metal oxide semiconductor gas sensitive material, which has been studied deeply. However, pure SnO2 sensing materials usually have good performance at high operating temperatures. In this study, we reported an n-butanol sensor with high selectivity and fast response based on SnO2 submicron porous cube prepared by heating and decomposing the Sn-based metal-organic framework material (Sn-MOF) in air at a certain temperature. SnO2 submicron porous cube prepared at 450 °C shows good response and selectivity for n-butanol. And it has a response (%) of 175% to 100 ppm n-butanol and a relatively fast response/recovery time of 184 s/183 s at room temperature. The (110) crystal plane with sufficient oxygen-rich vacancy can adsorb O2 and n-butanol molecules more effectively. Therefore, its sensitivity to n-butanol gas can be significantly improved. This work provides a good idea for further research on pure metal oxide semiconductor room temperature gas sensors.

Au-functionalized MoO3 nanoribbons towards rapid and selective formaldehyde gas sensing at room temperature

The detection of indoor formaldehyde concentration attracted great attention owing to its serious harm to human bodies. Traditional semiconductor formaldehyde sensors are still suffering from high working temperature and slow response and recovery performance. In this work, a room-temperature semiconductor formaldehyde gas sensor with fast response and high selectivity were developed by exploiting the synergistic effect of Au decoration on MoO3 nanoribbons. The metallic Au nanocrystals with size lower than 10 nm were prepared by a chemical reduction method and uniformly distributed on the surface of the [1 0 0] -oriented orthorhombic MoO3 nanoribbons after the surface decoration. The results show that the surface decoration by Au nanoparticles could greatly fasten the response and recovery speed of the sensors at room temperature. Under an optimal composition with Au/Mo atomic ratio of 0.10%, the response and recovery time towards 100 ppm HCHO could be decreased to 4.5 and 3 s. The sample also exhibited high sensitivity and low limit of detection of 1 ppm. Meanwhile, the sensor exhibited highly selective HCHO response with 1–2 magnitude higher sensor response against toluene, ethanal, methanol and acetone. The performance enhancement should be attributed to synergistic effect induced by the surface Au decoration, which not only serves as the catalysts improving the gas adsorption and desorption efficiency, but also introduced additional contribution to the formaldehyde response by forming the metal–semiconductor interface states.

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.

Zinc oxide incorporated molybdenum diselenide nanosheets for chemiresistive detection of ethanol gas

Herein, a room-temperature chemiresistive ethanol gas sensor based on hydrothermally synthesized zinc oxide (ZnO) incorporated-molybdenum diselenide (MoSe2) nanosheets was demonstrated. The sensing properties of the MoSe2/ZnO nanocomposite sensor were investigated systematically by exposing the sensor to various ethanol gas concentrations (10–500 ppm) in dry N2 and dry air. The synergistic effect due to the incorporation of ZnO nanorods in MoSe2 nanosheets was found to enhance the sensor response to ethanol gas (when operated in dry N2) with improved response and recovery time of 8.4 and 14.7 s respectively, high selectivity, stability, and reproducibility. The nanocomposite-based sensor showed high gas sensing response (Rg/Ra) of 37.8 to 500 ppm of ethanol gas. While the response of the nanocomposite-based sensor decreased to 15.3, to 500 ppm of ethanol gas in dry air which suggests that the sensor performs better when operated in dry N2 than in dry air. On the basis of experimental results, a plausible mechanism has been proposed based on the formation of p-n heterojunction and potential barrier modulation at the interface of the MoSe2/ZnO nanocomposite sensor. The results demonstrated that MoSe2/ZnO-based nanocomposite may pave the way for the fabrication of ethanol gas sensors for real-time electronics applications.