Gas Sensitivity Research Articles

Porous and Homogeneous Nanoheterojunction-Accumulating PdO@ZnO Structure for Exhaled Breath Ammonia Sensing.

The functional gas sensor device plays a pivotal role in intelligent medical treatment, among which metal oxide semiconductors are widely studied because of their inexpensiveness and ease of fabrication. However, the metal oxide sensors present a significant challenge in detecting NH3 at ppm levels within complex exhaled gases. Herein, the ZnO/PdO-x series were prepared by in situ loading palladium particles and calcining using nano-ZIF-8 as a precursor, which not only provided more transport path for ammonia adsorption but also achieved homogeneous nanoheterojunction accumulation structure. The tailor-made ZnO/PdO-2 sensor exhibits the optimum gas sensitivity, with a response value of 5.56 for 100 ppm of NH3 at 160 °C and a lower detection limit of 0.75 ppm. Particularly, it has a clear quantitative response to the actual exhaled gas of liver and kidney patients. By elucidating the intrinsic link between the in situ loading of MOF templates and the sensing mechanism, it is expected to broaden the rational design of metal-oxide sensors and thus provide an effective method for clinical detection.

Development and Performance of ZnO/MoS2 Gas Sensors for NO2 Monitoring and Protection in Library Environments

The presence of harmful oxidizing gases accelerates the oxidation of cellulose fibers in paper, resulting in reduced strength and fading ink. Therefore, the development of highly sensitive NO2 gas sensors for monitoring and protecting books holds significant practical value. In this manuscript, ZnO/MoS2 composites were synthesized using sodium molybdate and thiourea as raw materials through a hydrothermal method. The morphology and microstructure were characterized by X-ray diffraction analysis (XRD), energy dispersive spectroscopy (EDS), field emission scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The ZnO/MoS2 composite exhibited a flower-like structure, with ZnO nanoparticles uniformly attached to the surface of MoS2, demonstrating advantages such as high specific surface area and good uniformity. The gas sensitivity of the ZnO/MoS2 nanocomposites reached its peak at 260 °C, with a sensitivity value around 3.5, which represents an improvement compared to pure ZnO, while also enhancing sensitivity. The resistance of the ZnO/MoS2 gas sensor remained relatively stable in air, exhibiting short response times during transitions between air and NO2 environments while consistently returning to a stable state. In addition to increasing adsorption capacity and improving light utilization efficiency, the formation of hetero-junctions at the ZnO-MoS2 interface creates an internal electric field that effectively promotes the rapid separation of photo-generated charge carriers within ZnO, thereby extending carrier lifetime.

Ultrasensitive Room Temperature Formaldehyde Sensors Based on F Doped ZnO Nanostructures Activated by UV Light.

It is urgent to develop an ultrasensitive formaldehyde (HCHO) sensor that can operate at room temperature and has a low detection limit. Metal oxide semiconductors are excellent gas sensitive materials. Therefore, in this paper, we present the synthesis of fluorine (F) doped zinc oxide (ZnO) porous nanomaterials through a straightforward one-pot method with the optimization of F doping levels to achieve the detection of low concentrations of HCHO under UV light at room temperature. Under 375 nm UV light, the sensor exhibits a response value of 386% to 10 ppm of HCHO, which is 2.6 times higher than that of pure ZnO, and its detection limit is as low as 75 ppb. It has excellent selectivity, stability, and moisture resistance, which can meet the requirements of HCHO detection in daily life. Analysis reveals that doping ZnO with F not only increases the material's specific surface area but also introduces active sites. Furthermore, it alters the state of HCHO on the material's surface from physical adsorption to chemical adsorption. The above reasons together enhance the adsorption of HCHO on the gas sensitive material, thereby improving its gas sensitivity performance. Overall, this work demonstrates that F-doped ZnO is a potential material for ultrasensitive HCHO sensors and provides insights into the interpretation of the effect of doping on the gas sensitivity properties of materials.

A Sensitive Frequency Band Study for Distributed Acoustical Sensing Monitoring Based on the Coupled Simulation of Gas–Liquid Two-Phase Flow and Acoustic Processes

The sensitivity of gas and water phases to DAS acoustic frequency bands can be used to interpret the production profile of horizontal wells. DAS typically collects acoustic signals in the kilohertz range, presenting a key challenge in identifying the sensitive frequency bands of the gas and water phases in the production well for accurate interpretation. In this study, a gas–water two-phase flow–acoustic coupling model for a horizontal well is developed by integrating a gas–water separation flow model with a pipeline acoustic model. The model simulates the sound pressure level (SPL) and amplitude variations of acoustic waves under different flow patterns, spatial locations, and gas–water ratio schemes. The results demonstrate that within the same flow pattern, an increase in the gas–water ratio significantly elevates acoustic amplitude and SPL peaks within the 5–50 Hz frequency band. Analysis of oil field DAS data reveals that the amplitude response range for stages with a lower gas–water ratio falls within 5–10 Hz, whereas stages with a higher gas–water ratio exhibit an amplitude response range of 10–50 Hz.

MXene/WO3 Sensor Array with Improved SNN Algorithm for Accurate Identification of Toxic Gases.

Gas sensing is pivotal in critical areas such as industrial production and food safety. This study explores the gas classification capabilities of MXene-based gas sensors. Pure V2CTx MXene and an MXene/WO3 nanocomposite were synthesized, and MXene-based gas sensors were integrated into a 2 × 2 rudimentary electronic nose array. The tests on gas sensitivity revealed that the inclusion of WO3 nanoparticles (NPs) boosted the sensor's response to 10 ppm of NO2 from 2.82 to 3.45 at room temperature. Moreover, the sensor showcased a rapid response/recovery duration of 74.5/149.0 s, excellent environmental stability, and long-term reliable sensing performance. Furthermore, we have improved the method of accurately identifying four toxic gases detected by an MXene-based sensor array using a spiking neural network (SNN) based on the memristive system. Also, the performance of this identification method revealed that the method achieved 95.83% accuracy in the identification of the four gases. Notably, the improved SNN demonstrated approximately 5% higher accuracy than the other gas recognition algorithm. These results highlight the potential of SNN as a powerful tool to accurately and reliably identify toxic gases based on the gas sensor array.

Co ions doping enhances n-butanol sensing performance of In2O3 nanospheres

In this work, In2O3 nanospheres were synthesized using urea as a carbon template and modified with Co ions. The synthesized materials were characterized using various instruments to obtain information about the elemental composition and morphology of the materials. The results showed that Co ions replaced the lattice position of In ions and synthesized nanospheres aggregated from 20 nm particles. The results of gas sensitivity tests on all the samples showed that the response to 50 ppm n-butanol at 250 °C reached 540 when Co was doped up to 5 at%. In comparison, the sensor showed very low response to benzene gas with good selectivity. The high response of the sensor to n-butanol is due to the increase in vacancy oxygen content and redox reactions due to the multivalent nature of Co ions. The article concludes with a detailed analysis of the sensing mechanism.

Improved gas sensing properties of copper-doped MoSe2 monolayers: a first-principles study on CO2 and NO2 adsorption

Abstract This paper investigates the impact of copper (Cu)-doped MoSe2 monolayer (ML) on gas sensing properties. The adsorption behaviour of CO2 and NO2 gas molecules on Cu-doped MoSe2 ML is reported and various sensing and electronic parameters such as adsorption energy, charge transfer and recovery time, are computed to delineate the adsorption characteristics and gas sensitivity. In our study, the doped Cu-atom in Se vacant MoSe2 ML shows the adsorption energies to be −1.32 eV (O-orient) and −1.72 eV (C-orient), for CO2, while for NO2, they are −0.879 eV (O-orient) and −1.06 eV (N-orient), respectively. The negative formation energy of −6.62 eV shows the electronic stability of Cu-doped MoSe2 ML and thermal stability, demonstrated by the molecular dynamics study through the Nose-Vervlet Thermostat (NVT) algorithm. Also, significant changes are observed in electronic conductivity and work function upon adsorbed Cu-MoSe2 ML. Lastly, these outcomes illustrate that Cu doping amplifies the capture ability of MoSe2 ML towards gas molecules, fostering improved electron interaction between the substrate surface and gas molecules, consequently enhancing its gas sensing ability.

Theoretically design of 2D penta-BN2/penta-Graphene wdW heterostructure for NO gas sensing implications: a first-principles study

As air pollution becomes more and more serious, the detection of harmful gas of NO has become an urgent need in daily life. In this paper, the electronic and gas-sensing properties of penta-BN2/penta-Graphene heterojunction (P-BN2/P-G) are studied by density functional theory and non-equilibrium Green's function method. The analysis results indicate that the P-BN2/P-G heterojunction has metallic properties. The electronic structures in combination with the adsorption behavior shows that the P-BN2/P-G heterojunction can chemically adsorb NO gas molecules, and there is obvious charge transfer, indicating that it has high gas sensitivity to NO gas. In addition, the sensing performance of the gas sensor constructed by NO adsorption on upper, middle and lower layers of the P-BN2/P-G heterojunction is deeply studied. Transport calculations show that when NO is adsorbed on the upper and middle layers of the P-BN2/P-G heterojunction-based gas sensor, the current of the device decreases significantly. When adsorbed on the lower layer, the current shows a trend of first decreasing and then increasing. Under a bias of 0.1 V, the gas sensitivity can reach up to 49% when NO is adsorbed in the middle layer, which is substantially higher than that of the P-BN2 monolayer device. It can be seen that the gas sensitivity is significantly improved after forming the heterojunction. In addition, the bias transport spectrum and scattering state can reveal the change in device current caused by the adsorption of NO gas molecules, thereby clarifying its microscopic mechanism. Finally, all the findings indicate that penta-based materials can be used as a very promising gas-sensitive material for detecting NO.

Room temperature n-butanol detection by Ag-modified In2O3 gas sensor with UV excitation

The aim of this study is to develop a sensor for the detection of n-butanol gas at room temperature, which in turn facilitates sensor integration. To this end, porous In2O3 nanosheets were prepared in this experiment, along with noble metal Ag modification and UV excitation, to achieve effective monitoring of low concentrations of n-butanol at room temperature. The material composition and structure were analyzed by various analysis techniques. The addition of precious metals promotes the absorption of UV light by the material. The n-butanol gas sensitivity test was completed on individual samples under 365 nm UV. The response of 5wt% Ag/In2O3 to 10 ppm n-butanol under UV irradiation reaches 127.5% at room temperature, which is twice as much as pure In2O3. The sensor showed a well regular answer at different concentrations of n-butanol. This paper also discusses the sensing mechanism for the improved gas-sensitive behavior of Ag/In2O3, which mainly benefits from the chemical and electron sensitizing of Ag. The results show that the Ag/In2O3 material excited by ultraviolet light in this paper lays a certain foundation for the preparation of room temperature n-butanol gas sensor.

Perovskite-structured LaFeO3 gas sensor modified by polyoxometalate electron acceptor with high sensitivity and low detection limit for acetone gas☆

Lanthanum ferrite is a representative perovskite-structured rare earth-based bimetallic oxide, which has been widely studied in magnetic materials, sensors, catalysts and batteries. Herein, we designed and prepared polyoxometalate electron acceptor decorated LaFeO3 gas-sensitive composite materials with one-dimensional nanoribbons morphology by electrospinning. The effects of different mass fraction of Keggin type phosphotungstic acid (PW12) on the gas-sensitive properties of LaFeO3 nanoribbons were investigated. The results show that the response value of LaFeO3/PW12 sensor to acetone gas first increases and then decreases with the increase of PW12 content. The LaFeO3/3%PW12 sensor exhibits a maximum response of 3.35 to 5 ppm acetone at 250 °C, a 2.6 times increase in response value and a 90 °C reduction in operating temperature compared to pure LaFeO3 nanoribbons. The LaFeO3/3%PW12 sensor exhibits good linear relation in ppb-level concentrations and the lowest detection concentration is 100 ppb. The sensors also show good repeatability in 6 tests and excellent long-term stability in 30 d. The improvement of the gas sensitive properties of the composite can be attributed to the synergistic effect between the two components. As an electron acceptor, PW12 promotes carrier migration between PW12 and LaFeO3, thereby improving the gas sensing performance of LaFeO3. This work promotes the practical application of polyoxometalate to promote rare earth-based gas sensitive materials in sensing field.

A novel peony shaped ZnO and its excellent ethanol gas-sensing performance

In order to improve the gas-sensing performance of ZnO, a novel peony shaped ZnO stacked with nanosheets were prepared using hydrothermal method, and the obtained ZnO was characterized and tested for gas sensitivity. The results showed that the particle distribution of the peony shaped ZnO was uniform, with a particle size of about 0.8μm. The gas-sensing response test results show that the peony shaped ZnO has excellent selectivity to ethanol gas. When the concentration of ethanol gas is 100ppm, the gas-sensing response of the peony shaped ZnO to ethanol gas reaches 17.4, and the response time and recovery time are 8 seconds and 12 seconds, respectively. Even at an ethanol gas concentration of 2ppm, the gas-sensing response of the peony shaped ZnO to ethanol gas can reach 2.1. Compared to existing literature reports, the peony shaped ZnO prepared in this paper has better gas-sensing performance. This study will provide data support and theoretical reference for the development of high-performance gas sensors.

Mining PANI/Ti3AlC2/CeO2 ternary composite CO sensor: Material synthesis, gas sensing performance and mechanism research

To address the issue of poor gas sensitivity in existing mining semiconductor CO sensor materials like PANI at room temperature, this study employed an ice-water bath in conjunction with an in-situ polymerization method to incorporate 2D sheet-like Ti3AlC2 and nano-CeO2 materials with oxygen vacancies into PANI. As a result, nanometer-sized PANI/Ti3AlC2/CeO2 ternary composite nanomaterial was synthesized. The morphology, synthesis mechanism, and thermal stability of the ternary composite material were investigated using scanning electron microscopy-energy dispersive analysis (SEM-EDS), transmission electron microscopy analysis (TEM), spectral analysis, and thermogravimetric methods. Furthermore, the CO gas sensing mechanism of the ternary composite material was also examined. The study discovered that the nano-PANI/Ti3AlC2/CeO2 ternary composite nanomaterial, when deposited on the Au interdigital electrode of the IDE substrate, exhibits superior gas transmission of 400 ppm CO compared to gas sensors based on nano-PANI, nano-PANI/Ti3AlC2, and nano-PANI/CeO2. The sensing response was enhanced by 1.75 times, 1.4 times, and 1.2 times, respectively. This improvement in sensing mechanism can be attributed to the pn heterojunction and interfacial interaction forces between the components. Hence, the nano-PANI/Ti3AlC2/CeO2 ternary composite nanomaterial holds potential as a high-performance CO detection sensing material at room temperature. Additionally, it can serve as a theoretical basis for further research on low-power, integrable sensor materials in coal mines.

Sub-Ppb H2S Sensing with Screen-Printed Porous ZnO/SnO2 Nanocomposite.

Hydrogen sulfide (H2S) is a highly toxic and corrosive gas commonly found in industrial emissions and natural gas processing, posing serious risks to human health and environmental safety even at low concentrations. The early detection of H2S is therefore critical for preventing accidents and ensuring compliance with safety regulations. This study presents the development of porous ZnO/SnO2-nanocomposite gas sensors tailored for the ultrasensitive detection of H2S at sub-ppb levels. Utilizing a screen-printing method, we fabricated five different sensor compositions-ranging from pure SnO2 to pure ZnO-and characterized their structural and morphological properties through X-ray diffraction (XRD) and scanning electron microscopy (SEM). Among these, the SnO2/ZnO sensor with a composition-weight ratio of 3:4 demonstrated the highest response at 325 °C, achieving a low detection limit of 0.14 ppb. The sensor was evaluated for detecting H2S concentrations ranging from 5 ppb to 500 ppb under dry, humid air and N2 conditions. The relative concentration error was carefully calculated based on analytical sensitivity, confirming the sensor's precision in measuring gas concentrations. Our findings underscore the significant advantages of mixture nanocomposites in enhancing gas sensitivity, offering promising applications in environmental monitoring and industrial safety. This research paves the way for the advancement of highly effective gas sensors capable of operating under diverse conditions with high accuracy.

The influence of Rh-doped SnO2 microspheres on the sensitivity of benzene detection

In this article, Rh-doped SnO2 microspheres were prepared by a convenient hydrothermal treatment. Compared with the non-doped SnO2 microspheres, the Rh-doped SnO2 microspheres had larger specific surface area, faster electron transfer rate and increased oxygen vacancies, which is beneficial to improve the gas sensitivity of the material. The optimal sensitivity was observed of Rh-0.1 at 250 °C, and the response-recovery time of Rh-0.1 were 46 and 25 s, respectively. Besides, the Rh-doped SnO2 microspheres exhibited excellent gas selectivity and stability to benzene vapor. The novel Rh-doped SnO2 microspheres are potential gas detection materials for accessing benzene vapor.

Promoted room temperature NH3 gas sensitivity using interstitial Na dopant and structure distortion in Fe0.2Ni0.8WO4.

The demand for gas-sensing operations with lower electrical power and guaranteed sensitivity has increased over the decades due to worsening indoor air pollution. In this report, we develop room-temperature operational NH3 gas-sensing materials, which are activated through electron doping and crystal structure distortion effect in Fe0.2Ni0.8WO4. The base material, synthesized through solid-state synthesis, involves Fe cations substitutionally located at the Ni sites of the NiWO4 crystal structure and shows no gas-sensing response at room temperature. However, doping Na into the interstitial sites of Fe0.2Ni0.8WO4 activates gas adsorption on the surface via electron donation to the cations. Additionally, the hydrothermal method used to achieve a more than 70-fold increase in the surface area of structure-distorted Na-doped Fe0.2Ni0.8WO4 powder significantly enhances gas sensitivity, resulting in a 4-times increase in NH3 gas response (Rg/Ra). Photoluminescence and XPS results indicate negligible oxygen vacancies, demonstrating that cation contributions are crucial for gas-sensing activities in Na-doped Fe0.2Ni0.8WO4. This suggests the potential for modulating gas sensitivity through carrier concentration and crystal structure distortion. These findings can be applied to the development of room-temperature operational gas-sensing materials based on the cations.

High Performance H2S Sensor Based on Ordered Fe2O3/Ti3C2 Nanostructure at Room Temperature.

The utilization of a heterogeneous nanojunction design has shown significant enhancements in the gas sensing capabilities of traditional metal oxide gas sensors. In this study, a novel room temperature H2S gas sensor employing Fe2O3 functionalized Ti3C2 MXene as the sensing material has been developed. This sensor exhibits a broad detection range (0.01-500 ppm), low detection limit (10 ppb), and rapid response/recovery times (10 s/15 s), making it ideal for ppb-level H2S detection. The exceptional gas sensitivity of Fe2O3/Ti3C2 composite to H2S can be attributed to several key factors. First, the unique layered frame structure of Fe2O3/Ti3C2 significantly amplifies the surface area of the hybrid material, enhancing the absorption and diffusion capabilities of H2S molecules. Second, the abundance of functional groups (-O, -OH, and -F) on the surface of Ti3C2 MXene nanosheets provides additional active sites for H2S adsorption, The density functional theory calculation confirms that the adsorption energy of the Fe2O3/Ti3C2 composite for H2S (-2.93 eV) is significantly lower than that of pure Fe2O3 (-2.37 eV) and Ti3C2 (-0.2 eV). Lastly, the remarkable metal conductivity of Ti3C2 MXene ensures efficient electron transfer, thereby enhancing overall sensing performance.

A Novel Mechanism Based on Oxygen Vacancies to Describe Isobutylene and Ammonia Sensing of p-Type Cr2O3 and Ti-Doped Cr2O3 Thin Films

Gas sensors based on metal oxide semiconductors (MOS) have been widely used for the detection and monitoring of flammable and toxic gases. In this paper, p-type Cr2O3 and Ti-doped Cr2O3 (CTO) thin films were synthesized using an aerosol-assisted chemical vapor deposition (AACVD) method. Detailed analysis of the thin films deposited, including structural information, their elemental composition, oxidation state, and morphology, was investigated using XRD, Raman analysis, SEM, and XPS. All the gas sensors based on pristine Cr2O3 and CTO exhibited a reversible response and good sensitivity to isobutylene (C4H8) and ammonia (NH3) gases. Doping Ti into the Cr2O3 lattice improves the response of the CTO-based sensors to C4H8 and NH3. We describe a novel mechanism for the gas sensitivity of p-type metal oxides based on variations in the oxygen vacancy concentration.

New Parameter for Benchmarking Plasmonic Gas Sensors Demonstrated with Densely Packed Au Nanoparticle Layers.

Localized surface plasmon resonance (LSPR) gas sensitivity is introduced as a new parameter to evaluate the performance of plasmonic gas sensors. A model is proposed to consider the plasmonic sensors' surface sensitivity and plasmon decay length and correlate the LSPR response, measured upon gas exchange, with an equivalent refractive index change consistent with adsorbed gas layers. To demonstrate the applicability of this new parameter, ellipsoidal gold nanoparticles (NPs) arranged in densely packed hexagonal lattices were fabricated. The main advantages of these sensors are the small and tunable interparticle gaps (18-29 nm) between nanoparticles (diameters: 72-88 nm), with their robust and scalable fabrication technology that allows the well-ordered arrangement to be maintained on a large (cm2 range) area. The LSPR response of the sensors was tested using an LSPR sensing system by switching the gas atmosphere between inorganic gases, namely He/Ar and Ar/CO2, at constant pressure and room temperature. It was shown that this newly proposed parameter can be generally used for benchmarking plasmonic gas sensors and is independent of the type and pressure of the tested gases for a sensor structure. Furthermore, it resolves the apparent disagreement when comparing the response of plasmonic sensors tested in liquids and gases.

Acetone Sensors Based on Al-Coated and Ni-Doped Copper Oxide Nanocrystalline Thin Films.

Acetone detection is of significant importance in various industries, from cosmetics to pharmaceuticals, bioengineering, and paints. Sensor manufacturing involves the use of different semiconductor materials as well as different metals for doping and functionalization, allowing them to achieve advanced or unique properties in different sensor applications. In the healthcare field, these sensors play a crucial role in the non-invasive diagnosis of various diseases, offering a potential way to monitor metabolic conditions by analyzing respiration. This article presents the synthesis method, using chemical solutions and rapid thermal annealing technology, to obtain Al-functionalized and Ni-doped copper oxide (Al/CuO:Ni) nanostructured thin films for biosensors. The nanocrystalline thin films are subjected to a thorough characterization, with examination of the morphological properties by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) analysis. The results reveal notable changes in the surface morphology and structure following different treatments, providing insight into the mechanism of function and selectivity of these nanostructures for gases and volatile compounds. The study highlights the high selectivity of developed Al/CuO:Ni nanostructures towards acetone vapors at different concentrations from 1 ppm to 1000 ppm. Gas sensitivity is evaluated over a range of operating temperatures, indicating optimum performance at 300 °C and 350 °C with the maximum sensor signal (S) response obtained being 45% and 50%, respectively, to 50 ppm gas concentration. This work shows the high potential of developed technology for obtaining Al/CuO:Ni nanostructured thin films as next-generation materials for improving the sensitivity and selectivity of acetone sensors for practical applications as breath detectors in biomedical diagnostics, in particular for diabetes monitoring. It also emphasizes the importance of these sensors in ensuring industrial safety by preventing adverse health and environmental effects of exposure to acetone.

High Sensitivity Bi2O3/Ti3C2Tx Ammonia Sensor Based on Improved Synthetic MXene Method at Room Temperature.

The MXene Ti3C2Tx was synthesized using hydrofluoric acid and an improved multilayer method in this study. Subsequently, a Bi2O3/Ti3C2Tx composite material was produced through hydrothermal synthesis. This composite boasts a unique layered structure, offering a large surface area that provides numerous contact and reaction sites, facilitating the adsorption of ammonia on its surface. The prepared Bi2O3/Ti3C2Tx-based sensor exhibits excellent sensing performance for ammonia gas, including high responsiveness, good repeatability, and rapid response-recovery time. The sensor's response to 100 ppm ammonia gas is 61%, which is 11.3 times and 1.6 times the response values of the Ti3C2Tx gas sensor and Bi2O3 gas sensor, with response/recovery times of 61 s/164 s at room temperature, respectively. Additionally, the gas sensitivity mechanism of the Bi2O3/Ti3C2Tx-based sensor was analyzed, and the gas sensing response mechanism was proposed. This study shows that the sensor can effectively enhance the accuracy and precision of ammonia detection at room temperature and has a wide range of application scenarios.