Development Of Gas Sensors Research Articles

Humidity activated ultra-selective room temperature gas sensor based on W doped MoS2/RGO composites for trace level ammonia detection

The lack of highly efficient, cost effective and stable ammonia gas sensors functionable at room temperature even in extreme humid environments poses significant challenge for the future generation gas sensors. The prime factors that impede the development of such next generation gas sensors are the strong interference of humidity and sluggish selectivity. Herein, we fabricated tungsten doped molybdenum disulphide/reduced graphene oxide composite by an in-situ hydrothermal method to exploit the adsorption, dissolution (solubility), ionization and transmission process of ammonia and thereby to effectuate its trace level detection even in indispensable humid environments. The protype based on 5 at.% Tungsten doped MoS2/RGO (W5) gas sensor exhibited 3.8-fold increment in its response to 50 ppm of ammonia when the relative humidity varied from 20 % to 70 % with ultra-high selectivity at room temperature. The as prepared gas sensor revealed a practical detection limit down to 1 ppm with a substantial response and rapid recovery time. Furthermore, W5 gas sensor exhibited a 42-fold increment in response to 50 ppm of ammonia relative to its pristine (MoS2/RGO) MG composite with a RH of 70 %. The proton hopping mechanism accountable for such an enormous enhancement in ammonia sensing and its potential for breath sensor are briefly annotated.

Blue phosphorus phase GeSe monolayer for nitrogenous toxic gas sensing: A DFT study

Continuing industrialization, a variety of toxic gases are emitted into the air, yet gas concentrations at low levels are extremely hard to detect. So the development of high-performance toxic gas sensors is imminent. Two-dimensional materials with advantages such as large specific surface area and unique electronic properties open new paths for gas sensors. In this study, a monolayer of blue phosphorus phase germanium selenide (GeSe) was used as the substrate material. The absorption performance of ambient nitrogenous toxic gases (NO, NO2, NH3, N2O) on the surface of GeSe monolayers was explored by the density-functional theory (DFT) calculations. The results show that the interaction between GeSe and the four gases exhibits physisorption. Based on four optimal adsorption structures, Bader charge, work function, band structure, density of states, and recovery time were calculated. Charge transfer is promoted due to the presence of GeSe intrinsic dipoles and only NH3 was found to be the charge donor. The significant changes in work function and electronic properties of GeSe monolayer adsorption of NO indicate significant changes in electrical signals during gas detection. This work reveals that GeSe monolayer has higher sensitivity and selectivity for NO hazardous gas.

Microwave-assisted efficient synthesis of ZnO nanospheres for low temperature NO2 gas sensor

The development of high-performance nitrogen dioxide gas sensors is indispensable and critical for environmental monitoring and medical fields. Different nanostructural ZnO were efficiently synthesized via a microwave-assisted gas-liquid interface method and the gas sensing performance of ZnO-based gas sensors with different morphologies was comparatively investigated. The results show that the ZnO-3 sensor (microwave reaction temperature is 180 ℃) has the best sensing performance to NO2 at lower operating temperature (120 ℃). It exhibits a high response (Rg/Ra = 397), short response/recovery time (21 s/30 s), and good selectivity to 100 ppm NO2. Moreover, the ZnO-3 sensor exhibits remarkably high response (185 to 100 ppm NO2) even at 25 ℃. In addition, the ZnO sensor can maintain good stability and repeatability in long-term cycling tests to 5 ppm NO2. Evidently, this research offers a reference value for the efficient synthesis of ZnO nanomaterials and real-time detection of nitrogen dioxide emissions.

Preparation and Gas-Sensing Properties of Two-Dimensional Molybdenum Disulfide/One-Dimensional Copper Phthalocyanine Heterojunction

Although 2D MoS2 alone shows excellent gas-sensing performance, it is prone to stacking when used as the sensitive layer, resulting in insufficient contact with the target gas and lower sensitivity. To solve this, a 2D-MoS2/1D-CuPc heterojunction was prepared with different weight ratios of MoS2 nanosheets to CuPc micro-nanowires, and its room-temperature gas-sensing properties were studied. The response of the 2D-MoS2/1D-CuPc heterojunction to a target gas was related to the weight ratio of MoS2 to CuPc. When the weight ratio of MoS2 to CuPc was 20:7 (7-CM), the gas sensitivity of MoS2/CuPc composites was the best. Compared with the pure MoS2 sensor, the responses of 7-CM to 1000 ppm formaldehyde (CH2O), acetone (C3H6O), ethanol (C2H6O), and 98% RH increased by 122.7, 734.6, 1639.8, and 440.5, respectively. The response of the heterojunction toward C2H6O was twice that of C3H6O and 13 times that of CH2O. In addition, the response time of all sensors was less than 60 s, and the recovery time was less than 10 s. These results provide an experimental reference for the development of high-performance MoS2-based gas sensors.

A new approach for ammonia gas sensing using a source pocket dopingless tunnel FET with PANI catalyst

This article presents a new ammonia (NH3) gas sensor designed using a dopingless tunnel field effect transistor with a SiGe source pocket (SP-DLT) and investigates its sensitivity using a polyaniline (PANI) conducting polymer as the gate catalyst. PANI nanofiber has a greater specific surface area and a linked network structure, which increases its sensing performance as a catalyst. Combining an HfO2 gate dielectric and SiGe source pocket improves the drain current. The sensing film is deprotonated when the PANI conducting polymer is exposed to the gas, reducing the film’s resistance. As a result, more electron or proton transfer is possible, ensuring a more substantial interaction between the sensor and the analyte gas. This modulates the electrical characteristics and work function of the TFET. The sensor’s electrical performance is examined in terms of drain current, average subthreshold swing (SS), electric field, band-to-band tunneling rate (BTBT), and energy band diagram for an ammonia gas pressure (AGP) range of 10−12 torr to 10−9 torr. The sensitivity and selectivity of the proposed PANI-SP-DLT sensor in terms of different metrics, including drain current, average SS, current ratio, transconductance, and gain factor, are further investigated. The study is expanded to consider the impact of temperature affectability and the germanium mole fraction on current sensitivity performance. The Silvaco ATLAS device simulator is used for the brief simulation work for the developed gas sensor.

Adsorption and gas sensing properties of Cun and Pdn (n = 1–3) clusters modified MoSe2 for lithium battery thermal runaway gases

The manuscript mainly explores the adsorption behavior and related parameters of Cun and Pdn (n = 1–3) clusters modified MoSe2 substrates for thermal runaway gases (CO, CO2, H2) in lithium batteries by DFT. The modified structures are analyzed through Eb, band structure, Qt, and DCD. Compared with the MoSe2 bandgap (1.710 eV), Cun and Pdn (n = 1–3) clusters modifications reduce the bandgap and become more compact. During the modification process, the metal clusters acquire electrons from the substrate and change the DOS of the substrate. The metal clusters improve the conductivity of the substrate. The adsorption and sensing properties between target gases and the substrates through the analysis of the Ed, Qt, DCD, and DOS. The adsorption capacity of target gases on Cu-MoSe2, Pd-MoSe2, Cu2-MoSe2, Pd2-MoSe2, and Pd3-MoSe2 substrates is ranked as follows: CO > H2 > CO2. The adsorption effect of Cu3-MoS2 substrate on target gases is ranked as follows: CO > CO2 > H2. Analysis of molecular orbitals, work functions, and sensitivity can describe the adsorption effect of the substrates on the target gases. The results provide a theoretical basis for the development of gas sensors for detecting the operating status of lithium batteries.

Transition metal (Au, Ag, Pt, Pd, Ni) doped MoS2 as gas sensing materials for C4F7N leakage detection: A comparative study

Fluorinated nitrile (C4F7N) has been considered a novel eco-friendly gas insulating medium, while the low toxicity and leakage risk urgently urge the development of C4F7N gas sensor. Herein, we analyzed the sensing performance of transition metal doped MoS2 to C4F7N based on the density functional theory (DFT). Au, Ag, Pt, Pd and Ni can be strongly chemically doped on the surface of MoS2. The adsorption energy, charge transfer, deformation charge density and density of states were explored. The adsorption energies of Au, Ag, Pt, Pd and Ni-doped MoS2 for C4F7N are -0.55 eV, -0.59 eV, -1.43 eV, -0.95 eV and -1.59 eV, respectively, which belong to chemical adsorption. Furthermore, the sensitivity and recovery performance were analyzed based on frontier orbital and transition state theories. The results show that all five atom-MoS2 exhibit good sensitivity with conductance changes of more than 80 %, but only Pd-MoS2 can achieve a recovery time in the order of seconds at lower temperatures (1.01 s at 125 °C). The subsequent analysis shows that O2 and H2O in the air do not attach to the surface of Pd-MoS2, confirming its good stability. With its high sensitivity, satisfactory recovery time and strong stability, Pd-MoS2 shows promising potential for C4F7N leak detection engineering applications.

Impedance spectroscopy analysis on reduced graphene oxide and CeO2 nanocomposites coated on screen-printed alumina substrate for highly selective H2S gas detection at room temperature

Impedance spectroscopic-based gas sensing analysis is a highly sensitive technique. Impedance and its fitted RC circuits provide us with fundamental information about grain boundary, grain bulk, and the interface between sensing film and electrode contact. In this work, an n-CeO2/rGO composite-based gas sensing film with high selectivity, sensitivity, stability and moisture resistance potency for the detection of H2S was developed on screen-printed alumina substrate using a drop casting process, and the H2S gas sensing performance was evaluated using electrochemical impedance spectroscopy (EIS) at various temperatures. The n-CeO2/rGO-3 composite produced stable and rapid responses towards H2S with a response of 97.41 % for 50 ppm of H2S gas at the optimum temperature of room temperature (27 °C). The LOD and LOQ were calculated and found to be ∼0.9 and ∼2.9 ppm for n-CeO2 and n-CeO2/rGO-3 composites, respectively. The superior selectivity with interfering gases such as NH3, H2, SO2 and CO, response and recovery time (∼9s and ∼12s), long-time stability and gas sensing mechanism were investigated. This impedance-based gas sensor development opens up the path for the fabrication of n-CeO2/rGO composite-based H2S gas sensors for future applications.

Vertically aligned mesoporous Ce doped NiO nanowalls with multilevel gas channels for high-performance acetone gas sensors

In recent years, the potential use and development of acetone gas sensors in health monitoring and self-diagnostic applications has attracted increasing attention. Thus, accurate sensing of acetone is of crucial importance in the non-invasive diagnosis of diabetes. However, challenges remain in the detection of acetone, such as high concentrations detection limit, high operating temperature and slow response dynamics. Herein, vertically aligned Ce-doped mesoporous NiO nanowalls are prepared on Ag-Pd interdigitated electrode substrate using an in-situ growth method. The gas sensing performances show that the as-made 4 mol% Ce-doped NiO nanowalls has excellent gas response value (3.2) to 10 ppm acetone at a lower operating temperature (175 ℃) with fast adsorption and desorption equilibrium (13 s/7 s). Vertically aligned mesoporous NiO nanowalls doped by Ce element could pave the way for ultra-sensitive and low power consumption acetone gas sensors for breath gas detection.

ZnO quantum dots sensitized ZnSnO3 for highly formaldehyde sensing at a low temperature

Developing gas sensors for formaldehyde vapor detection is necessary. Metal oxide semiconductor (MOS) exhibited good formaldehyde sensing properties but with high working temperature and unsatisfactory selectivity. Herein, ZnSnO3 was sensitized by ZnO QDs modification for high-performance formaldehyde sensing at low working temperatures via simple immersion method. Meanwhile, SnO2 QDs instead of ZnO QDs was also modified on ZnSnO3 nanocubes. The result indicated both ZnO QDs and SnO2 QDs modification greatly improved gas sensing response and lower the working temperature of ZnSnO3 to formaldehyde. Whereas, the obtained ZnSnO3/ZnO QDs composite (ZSO/ZQD) containing 5 wt% ZnO QDs (ZSO/ZQD-0.05) showed a highest response value of 613.3–100 ppm formaldehyde at 70℃ with good reversibility and stability, which was nearly 20 times of bare ZnSnO3 and 6 times of SnO2 QDs modified ZnSnO3. The detection limit reached 100 ppb formaldehyde. The formaldehyde sensing performance of ZSO/ZQD-0.05 composite was checked in presence of simulated indoor pollutants. Its improved sensor performance was mainly attributed to ZnO QDs, which played roles in forming rich heterojunctions with ZnSnO3, increasing the surface area, and providing oxygen deficiency for formaldehyde sensing reaction. This provided an alternative way to improving the sensing properties of MOS by QDs modification.

Fabrication of ZnO-SnO2 heterojunction inverse opal photonic balls for chemiresistive acetone sensing

The development of metal oxide semiconductor-based chemiresistive gas sensors with ultra-fast response/recovery for toxic and flammable gases is of great importance, but still challenging. Here, ZnO-SnO2 heterojunction three-dimensional (3D) inverse opal photonic crystal balls (IOPBs) were fabricated based on rapid and liquid waste-free spray drying. The spherical three-dimensional (3D) ordered macroporous skeleton can provide more active sites and faster gas diffusion channels. Furthermore, the n-n heterojunction established by ZnO and SnO2 is favorable for electron transport. The response (Ra/Rg) of IOPBs to 50 ppm acetone reaches 40.3 at an optimal operating temperature of 260 °C when the Zn/Sn atomic ratio is 1:4, which is 5 times higher than that of the pure SnO2 sensor. Response/recovery time also reduces from 23/47 s for pure SnO2 to 6/10 s. In addition, the IOPBs gas sensors also exhibit good selectivity and excellent long-term stability. This work provides a straightforward and versatile synthetic route for the preparation of 3D IOPBs to explore novel gas sensors with ultra-fast response speed.

Advances of Nano-Enabled ZnFe2O4 Based-Gas Sensors for VOC Detection and Their Potential Applications: A Review

The demand for reliable gas sensing technologies in chemical, manufacturing, environmental, and occupational sites has increased in the last few decades following the global volatile gas sensor market, which is expected to grow further beyond 2025. Currently, several types of sensors have been employed for applications in different fields. Optical sensors are widely implemented in mining and environmental monitoring. Conventional food testing methods are utilized for the detection of any chemical or microbial agent in the food industry. Although robust and sensitive, most sensing technologies are expensive, labor-intensive, and necessitate the use of time-consuming gas sampling pretreatment steps, and these issues impede the achievement of quick, simple detection, portable, and cost-effective gas monitoring. For this reason, researchers around the world are investigating the possibility of using gas sensors as a promising technology that has the potential to alleviate industrial safety concerns. As a highly sensitive semiconducting metal oxide, gas sensors based on ZnFe2O4 have the potential to ensure environmental and occupational safety in real time. This review introduces and highlights recent developments in ZnFe2O4 gas sensors for application in different fields. The challenges limiting the wide application of the ZnFe2O4 sensor are outlined. Furthermore, this review discusses the common strategies adopted to improve the sensing properties of ZnFe2O4 for gas detection. Finally, future perspectives on further improvements of ZnFe2O4 sensing properties are discussed, and integration of ZnFe2O4 sensors into electronic noses to tackle the selectivity issue and how they can feature on the Internet of Things is outlined.

Highly efficient and stable NiSe2-rGO composite-based room temperature hydrogen gas sensor

The widespread consumption of hydrogen in commercial and industrial applications has resulted in the development of different hydrogen gas sensors. However, their practical application is restricted due to their non-cost efficiency, low sensitivity, poor selectivity and high temperature sensing properties. Thus, the development of a sensor capable of overcoming the aforementioned limitations is critical for commercial deployment. As a result, a NiSe2-rGO composite-based H2 gas sensor has been prepared for the first time using a simple hydrothermal technique. The developed material has been systematically characterized for its morphological properties and thoroughly investigated for H2 gas sensing applications. The findings show that the developed NiSe2-rGO composite exhibited enhanced H2 gas sensing properties, besides possessing appreciable selectivity, repeatability as well as long-term stability. Furthermore, the results demonstrate a stable sensor response of 254% within 43 s and 13 s of response and recovery time respectively at a hydrogen concentration of 500 ppm which is 8 and 500 times higher than that of its individual counterparts (NiSe2 and rGO) over a wide relative humidity range, indicating the material's potential for application in industrial environments. Thus, this work paves the way for the development of stable, effective, fast-responding, and selective hydrogen gas sensors that are functional at room temperature.

Design of high-sensitivity La-doped ZnO sensors for CO2 gas detection at room temperature

For the sake of people's health and the safety of the environment, more efforts should be directed towards the fabrication of gas sensors that can operate effectively at room temperature (RT). In this context, increased attention has been paid to developing gas sensors based on rare-earth (RE)-doped transparent conducting oxides (TCO). In this report, lanthanum-doped zinc oxide (La-doped ZnO) films were fabricated by sol–gel and spin-coating techniques. XRD analysis revealed the hexagonal structure of the ZnO films, with preferred growth along the (002) direction. The crystallite size was decreased from 33.21 to 26.41 nm with increasing La content to 4.0 at.%. The UV–vis–NIR indicating that the films are highly transparent (˃ 80%), La-doping increased the UV blocking ability of the films and narrowed the optical band gap (Eg) from 3.275 to 3.125 eV. Additionally, La-doping has influenced the refractive index of the samples. Gas sensing measurements were performed at ambient temperature (30 °C) and a relative humidity (RH) of 30%, employing different flow rates of carbon dioxide (CO2) gas used synthetically with air. Among the evaluated sensors, the ZnO: 4.0 at.% La sensor exhibited the most significant gas response, with a value of 114.22%. This response was observed when the sensor was subjected to a flow rate of 200 SCCM of CO2 gas. Additionally, the sensor revealed a response time of 24.4 s and a recovery time of 44 s. The exceptional performance exhibited by the sensor makes it very appropriate for a wide range of industrial applications. Additionally, we assessed the effect of humidity, selectivity, reusability, repeatability, detection limit, and limit of quantification.

Gas-Sensing Mechanisms and Performances of MXenes and MXene-Based Heterostructures

MXenes are a class of 2D transition-metal carbides, nitrides, and carbonitrides with exceptional properties, including substantial electrical and thermal conductivities, outstanding mechanical strength, and a considerable surface area, rendering them an appealing choice for gas sensors. This manuscript provides a comprehensive analysis of heterostructures based on MXenes employed in gas-sensing applications and focuses on addressing the limited understanding of the sensor mechanisms of MXene-based heterostructures while highlighting their potential to enhance gas-sensing performance. The manuscript begins with a broad overview of gas-sensing mechanisms in both pristine materials and MXene-based heterostructures. Subsequently, it explores various features of MXene-based heterostructures, including their composites with other materials and their prospects for gas-sensing applications. Additionally, the manuscript evaluates different engineering strategies for MXenes and compares their advantages to other materials while discussing the limitations of current state-of-the-art sensors. Ultimately, this review seeks to foster collaboration and knowledge exchange within the field, facilitating the development of high-performance gas sensors based on MXenes.

Ultrafast response of Pt functionalized Fe2(MoO4)3 nanoflower gas sensors for ultra-low ppm level H2 gas detection

The high and ultrafast response of hydrogen gas sensors is very critical during H2 transportation and storage. For detecting the ultra-low ppm level H2, a new Pt functionalized Fe2(MoO4)3 (FMO) nanoflower gas sensor (Pt/Fe2(MoO4)3 briefed as Pt/FMO) was fabricated in this work by a simple solvothermal method and calcination process. The Pt/FMO gas sensor shows excellent H2 sensing performances, which can be attributed to the high catalytic activity of Pt and the large surface area of 3D FMO. The optimal operating temperature of Pt/FMO was investigated and determined at 300 °C. The response/recovery time of Pt/FMO was only 16/38 s, which displayed excellent stability and ultrafast response/recovery time toward ultra-low ppm level H2 (10 ppm) at 300 °C, respectively. The enhancement mechanism was also studied and discussed. This newly developed gas sensor may have great application potential in the rapid detection of low-concentration hydrogen gas.

Highly Breathable, Stretchable, and Tailorable TPU Foam for Flexible Gas Sensors.

Continuous real-time monitoring of air quality is of great significance in the realms of environmental monitoring, personal safety, and healthcare. Recently, flexible gas sensors have gained great popularity for their potential to be integrated into various smart wearable electronics and display devices. However, the development of gas sensors with superior sensitivity, breathability, and stretchability remains a challenge. Here, a new high porosity thermoplastic polyurethane (HP-TPU) foam was reported for gas sensors, which exhibited large three-dimensional network structures and excellent mechanical properties. The HP-TPU foam was achieved by using a simple steam-induced method, which was suitable for mass production. The unique structure endowed this foam with 77.5% porosity, 260% strain ability, and 0.45 MPa Young's modulus, which improved 35, 31, and 80%, respectively, compared to previously reported traditional TPU foam (T-TPU) prepared by the drying method. In addition, the foam presented high gas permeability (312 g/m-2, 24 h) and excellent stability, and it remained undamaged even after 2000 cycles at 70% strain. The sensing material was coated on a PET flexible interdigital electrode and sandwiched between two HP-TPU foam layers for a gas sensitivity test. Due to the easy diffusion of gas between the pores and contact with the sensing materials, the HP-TPU foam exhibited a significant reduction of 85% in average response time and 46% in average recovery time, compared to the T-TPU foam. A wearable sensing device, comprising sensing, data processing, and wireless transmission modules, was successfully developed to enable outdoor testing and achieved a detection range at the ppb level. Finally, the cytotoxicity test results confirmed that this flexible gas sensor did not harm human health. These results proved that this HP-TPU foam was an ideal matrix for the flexible gas sensor, exhibiting great application potential in the fields of seamless human-machine integration.

Passivation of MXene via atomic layer deposition of SnO2 to achieve improved NO2 sensing

MXene is a promising candidate for low power electronic devices, such as gas sensor at room temperature. However, achieving rapid response and complete recovery and simultaneously addressing the issue of baseline drift due to the oxidation of MXene are challenging for MXene sensors. Herein, we demonstrate a general strategy by using atomic layer deposition (ALD) to passivate Ti3C2Tx MXene. The abundant hydroxyl groups on MXene, which could lead to the oxidation of MXene, facilitate efficient deposition of SnO2. Gas sensor tests reveal that the passivated MXene@SnO2 exhibits a response of 35.2% to 20 ppm NO2, which is approximately three times higher than that of pure MXene. Importantly, the response time to NO2 was as fast as 18 s, with full and complete recovery to baseline within 27 s. Our strategy highlights the prospects of utilizing ALD technique for the development of MXene-based gas sensors.

UV-triggered carrier transport regulation of fibrous NiO/SnO2 heterostructures for triethylamine detection

Constructing heterojunctions by using the synergistic and complementary effects of different metal oxide semiconductors (MOSs) properties can effectively increase catalytic activity, enhance adsorption capacity and improve carrier transport characteristics. Therefore, a series of NiO/SnO2 nanofibers with p-n heterojunction were prepared by coaxial electrospinning method, and triethylamine (TEA) detection was realized at low temperature or even room temperature by UV light (375 nm) photoactivation. Gas sensing measurements revealed that NiO/2SnO2 showed highresponse of 262 at 75 ℃ towards 50 ppm TEA, which is 6 times higher than that of pure SnO2. And NiO/2SnO2 based gas sensor has excellent repeatability and stability. The enhanced gas sensing mechanism was also discussed in detail, which is attributedto the synergistic effects aroused by p-n heterojunction and photoactivation. The present work provides a promising strategy for improving the gas sensitive characteristics of MOSs as well as a new idea for the development and application of room temperature TEA gas sensor.

Extrinsic oxygen defects in SnO/SnO2 heterostructure for efficient NO2 gas detection

High selectivity and fast response in the detection of NO2 are key factors in protecting human health in life-threatening environments. The p-n SnO/SnO2 heterostructure is a promising material as a metal oxide for effective chemical reactions with a target gas. It has a synergistic effect on the intrinsic semiconducting properties and the formation of an interfacial electric field in the heterojunction. The extrinsic oxygen vacancies in the SnO/SnO2 structure enhance the chemical reaction in the sensing property. In this study, we developed a defect-SnO/SnO2 heterostructure-based NO2 gas sensor. It shows excellent sensing performances with a high response of 100.86, fast response time of 5.83 s, and superior selectivity (approximately 23 times higher than those of other target gases) in the detection of 50 ppm NO2 at 150 °C. Raman and electron paramagnetic resonance (EPR) results supported the presence of oxygen vacancies in the defect-rich SnO/SnO2 crystal and X-ray photoelectron spectroscopy (XPS) and time-of flight secondary ion mass spectrometry (ToF-SIMS) analyses described the role of SnO/SnO2 heterostructure with oxygen defects as an effective electron donor for the adsorbed oxygen molecules and NO2 target gas. We believe that the direct formation of oxygen vacancies in the SnO/SnO2 heterostructures is a significant reference for the development of high-performance NO2 gas sensors.