Gas-sensitive Characteristics Research Articles

ZnO nanowire/NiO foam 3D nanostructures for high-performance ethylene glycol sensing

Ethylene glycol is widely used in industrial production but poses potential safety hazards to human life and health. Unfortunately, conventional glycol gas sensors have limitations that impede their effectiveness, such as sluggish response rates, high operational temperatures, and complex preparation procedures. A new approach has been explored to address these challenges. A ZnO nanowire/NiO foam nanostructured sensor was developed specifically for rapid ethylene glycol detection. The NiO/ZnO heterojunction-based gas sensor (NZO-6) has inherent p-type gas-sensitive characteristics. Notably, it delivers a response of 58.98–100 ppm of ethylene glycol at a relatively low operating temperature of 175 ℃. At a relatively low operating temperature of 175 ℃, it exhibits a response of 58.98–100 ppm ethylene glycol, 2.28 times higher than NiO foam, and a fast response/recovery time (4 s/26 s). This improvement is attributed to the porous structure of NiO foam/ZnO nanowires, with a large specific surface area and numerous oxygen vacancies generated during synthesis. Additionally, the catalysis of Ni metal and the formation of p/n heterojunctions further contribute to the improved sensing performance. This research offers a promising solution for developing high-performance ethylene glycol gas sensors with potential environmental monitoring, industrial safety, and public health applications. Further, this synthesis method provides an effective strategy for constructing other NiO-based heterostructure-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.

Comparison of Gas-sensitive properties of Au, Ag and Cu Metal-doped GaNNT for SF6 decomposition gases

SF6 gas will produce various decomposition products When the partial discharge fault occurs in SF6 gas-insulated equipment, resulting in significantly reduced insulation performance of the insulated equipment. Early latent insulation faults in gas-insulated equipment can be diagnosed by monitoring the concentration of SF6 typical decomposition products (H2S, SO2, SO2F2 and SOF2) inside the insulated equipment. Gallium nitride nanotubes (GaNNT) have shown promising applications as gas-sensitive materials for sensors, and the gas-sensitive properties of the materials can be better improved by doped-metal. Therefore, the Density functional theory (DFT) calculation approach is proposed to compare with the gas-sensitive response characteristics of Au, Ag and Cu metal-doped GaNNT (M−GaNNT) to SF6 typical decomposition gases in the paper. The adsorption mechanism is analyzed by band structure, density of states, frontier molecular orbital theory and differential charge density, and the results are in high consistency. The metal-doped GaNNT introduces a large number of impurity bands which makes the probability of electrons crossing the forbidden band to reach the conduction band larger, and thus the gas-sensitive characteristics are improved. The adsorption of gases by M−GaNNT causes the resistivity of the system to vary, and sensing response (SR) and response time (RT) of M−GaNNT adsorbs gases are also analyzed. The results show that the ability of metal-doped GaNNT is Ag-GaNNT>Cu-GaNNT>Au-GaNNT, and the average values of SR are 516.9, 29.3 and 8.7, respectively. Ag-GaNNT has higher selectivity for SO2F2 gas. In summary, it shows that Ag-GaNNT is a potential gas-sensitive material that can be a new material for the online monitoring of fault gas content in gas-insulated equipment.

Высокая чувствительность пленок оксида индия, полученных методом хлоридной газофазной эпитаксии, к аммиаку

The effect of H2, NH3, CO and O2 on the electrically conductive properties of In2O3 films grown by halide vapor phase epitaxy has been studied. In the temperature range of 200−550°C, In2O3 films demonstrate gas sensitivity to all considered gases, a relatively high operation speed and repeatability of cycles. The greatest response to NH3 was obtained, which exceeded 33 arb.units at a temperature of 400°C and a gas concentration of 1000 ppm. A qualitative mechanism of gas sensitivity of In2O3 films is proposed. The obtained gas-sensitive characteristics are compared with known NH3 sensors based on various materials. It is shown that the method of halide vapor phase epitaxy makes it possible to obtain indium oxide films with high gas sensitivity

High sensitivity of halide vapor phase epitaxy grown indium oxide films to ammonia

The effect of H2, NH3, CO and O2 on the electrically conductive properties of In2O3 films grown by halide vapor phase epitaxy has been studied. In the temperature range of 200-550oC, In2O3 films demonstrate gas sensitivity to all considered gases, a relatively high operation speed and repeatability of cycles. The greatest response to NH3 was obtained, which exceeded 33 arb. units at a temperature of 400oC and a gas concentration of 1000 ppm-1. A qualitative mechanism of gas sensitivity of In2O3 films is proposed. The obtained gas-sensitive characteristics are compared with known In2O3 sensors based on various materials. It is shown that the method of halide vapor phase epitaxy makes it possible to obtain indium oxide films with high gas sensitivity. Keywords: In2O3 films, halide vapor phase epitaxy, gas-sensitive properties, response.

ITO Thin Films for Low-Resistance Gas Sensors.

Indium tin oxide thin films were deposited by magnetron sputtering on ceramic aluminum nitride substrates and were annealed at temperatures of 500 °C and 600 °C. The structural, optical, electrically conductive and gas-sensitive properties of indium tin oxide thin films were studied. The possibility of developing sensors with low nominal resistance and relatively high sensitivity to gases was shown. The resistance of indium tin oxide thin films annealed at 500 °C in pure dry air did not exceed 350 Ohms and dropped by about 2 times when increasing the annealing temperature to 100 °C. Indium tin oxide thin films annealed at 500 °C were characterized by high sensitivity to gases. The maximum responses to 2000 ppm hydrogen, 1000 ppm ammonia and 100 ppm nitrogen dioxide for these films were 2.21 arbitrary units, 2.39 arbitrary units and 2.14 arbitrary units at operating temperatures of 400 °C, 350 °C and 350 °C, respectively. These films were characterized by short response and recovery times. The drift of indium tin oxide thin-film gas-sensitive characteristics during cyclic exposure to reducing gases did not exceed 1%. A qualitative model of the sensory effect is proposed.

Study on the Detection Characteristics and Response Mechanism of SnS2-Based Sensors for SO2 and SOF2

Based on the wide application of sulfur hexafluoride (SF6) gas in the power industry, the analysis and detection of its decomposition components have become important technical means for state detection and fault evaluation of gas-insulated equipment. The gas-sensitive characteristics and adsorption mechanism of the SnS2 sensor for SO2 and SOF2 gases were investigated using SO2 and SOF2, the main SF6 decomposition components, as the target detection gases. SnS2 gas-sensitive materials and components were prepared, and the temperature response, concentration response, response recovery and stability of the SnS2 sensor for the two SF6 decomposition components were tested based on the gas-sensitive test platform. The results demonstrate that the sensor had the best working performance at 200 °C, with obvious response and ideal recovery for both target gases and good stability in a certain time. Based on the first principle, the SnS2 surface structure model and the target gas adsorption model were established, and the adsorption mechanism was analyzed in terms of frontier molecular orbital theory to verify the correctness of the gas-sensitive test results. The gas-sensitive test analysis and simulation calculation can provide data basis and theoretical support for the study of SF6 decomposition components detected by gas sensors.

Adsorption and gas sensing properties of Co modified InN to SF6-N2 mixture decomposition components

• It is the first time that Co-InN is used as the adsorbent to remove the decomposition components of SF 6 -N 2. • Co-InN shows good adsorption properties to NO 2 , SOF 4 , SOF 2 , SO 2 F 2 by chemisorption. • The theoretical calculation results are important to guide the development of resistive gas sensor based on the Co-InN. This paper presents a detection method of partial discharge decomposition components of SF 6 -N 2 mixture by Co-doped InN. The severity of partial discharge in gas insulated switchgear (GIS) can be judged by the gas components when SF 6 -N 2 decomposes. Exploring sensors with excellent gas-sensing detection capabilities can provide method to partial discharge decomposition component detection and fault diagnosis of GIS. Undoped InN is a wide bandgap semiconductor with good sensing properties. In this paper, the adsorption of SF 6 -N 2 decomposition components on Co-doped InN monolayer, as well as the adsorption mechanism and gas sensitivity characteristics were investigated by density functional theory (DFT), including adsorption energy, charge transfer, the density of state theory and molecular orbital theory. Our calculations found that Co-doped InN has the optimal structure at the T N site and has good adsorption performance for NO 2 , SOF 4 , SOF 2 , and SO 2 F 2 gas molecule. All adsorption reactions belong to chemisorption. These results could direct the development of gas sensor based on the Co-doped InN monolayer, and provides methods to online monitoring of GIS discharge failures.

Gas-Sensitive Characteristics of Graphene Composite Tungsten Disulfide to Ammonia.

Two-dimensional materials have outstanding application prospects in gas sensing. By constructing composite structures of various gas-sensitive materials, more-efficient and sensitive gas sensors can be further developed. After graphene is compounded with WS2, the composite material can improve the gas detection performance. In this work, the adsorption energy and the electronic properties of a graphene/WS2 structure were calculated by first-principles before and after adsorption of NH3. The calculation results indicate that the bandgap of the material was appreciably reduced after NH3 was adsorbed. In addition, a graphene/WS2 gas sensor was prepared. The response of the sensor to NH3 at a concentration of 100 ppm was 2.42% and 1.73% at 30 °C and 60 °C, respectively. Combining simulation with experiment, it is feasible to use graphene composite WS2 to detect NH3, which provides a new idea for applications of graphene and other composite materials in gas sensing.

Novel insights into the unique intrinsic sensing essences of 2D tin chalcogenides for ethanol: From hexagonal SnS2 to orthorhombic SnS

Introducing orthorhombic SnS phase into two-dimensional (2D) hexagonal SnS2 crystal to form in-plane heterojunctions has become a promising approach to facilitate the sensitivity of SnS2 towards trace gases. However, its surface sensitization mechanism remains to be exploited in addition to the heterointerface effect. Hence, to dig into it, we explored the surface adsorption of SnS and SnS2 from unique surface electron configurations by combing experimental, computational and bionic approaches. Taking ethanol vapor as the target gas, orthorhombic SnS shows rapid detection of trace ethanol with a sub-ppm level at room temperature (RT). In contrast, hexagonal SnS2 is more suitable for detecting ethanol vapor with much higher concentrations (above 50 ppm). First-principles calculations and porcupine quill models further reveal that unlike the inactive symmetry of electrons on SnS2 surface, the rotational symmetry breaking of the stereochemically-active SnS surface leads to the oriented rearrangement of its surface electrons, which greatly facilitates the adsorption of trace ethanol molecules on SnS. On these basis, we renew the design concept of SnS–SnS2 in-plane heterostructures. This work reveals the structure-property relationship between the crystalline structures and gas-sensitive characteristics of 2D tin chalcogenides from a brand-new perspective, and helps the design and research of novel lateral heterostructures.

Strain-engineered S-HfSe2 monolayer as a promising gas sensor for detecting NH3: A first-principles study

The development of high-performance gas sensing materials is one of the development trends of new gas sensor technology. In this work, in order to predict the gas-sensitive characteristics of HfSe2 and its potential as a gas-sensitive material, the interactions of nonmetallic element (O, S, Te) doped HfSe2 monolayer and small molecules (NH3 and O3) have been studied by first-principles based on density functional theory. The results show that the adsorption of NH3 and O3 on pristine HfSe2 monolayer is weak, and the adsorption strength can be significantly improved by doping O. And O-HfSe2 is chemical adsorption to O3 with large adsorption energy and transfer charge, and the band gap of OHfSe2 disappears after adsorbing O3, indicating that the adsorption of O3 has a significant effect on the electrical properties of the substrate. These mean that O3 is difficult to recover from the substrate surface, thus preventing O-HfSe2 from developing into a sensitive material for O3 detection. After doping S, the charge transfers and adsorption strength to NH3 are the largest, but it is still small. So, the strain effect on the S-HfSe2/NH3 adsorption system is also studied. The results indicate that the adsorption strength of S-HfSe2 to NH3 can be enhanced by stretching S-HfSe2 along x-axis. After absorbing NH3, the conductivity of x-axis strained S-HfSe2 changes, which suggest its sensitivity. And the predicted recovery times of S-HfSe2 surfaces with εx=4%, 6% and 8% are 0.027 s, 1.153 s and 102.467 s, respectively, which suggests that the S-HfSe2 monolayer has the potential to be developed as a sensitive material for NH3 detection. These adsorption mechanism studies can also serve as a theoretical foundation for the experimental design of gas-sensing materials.

Gas Sensitive Characteristics of Polyaniline Decorated with Molybdenum Ditelluride Nanosheets

In this work, hydrochloric acid (HCl)-doped molybdenum ditelluride (MoTe2) nanosheets/polyaniline (PANI) nanofiber composites are prepared by in situ chemical oxidation polymerization, and then the composites are deposited on interdigital electrodes (IDEs) to fabricate a NH3 gas sensor. Morphological analysis of the composites reveals that the PANI fibers are deposited on 2D MoTe2 sheets, showing a porous mesh microstructure structure with a more continuous distribution of PANI layer. FTIR spectrum analysis indicates the interaction between the MoTe2 nanosheets and the PANI in the MoTe2/PANI composites. The results demonstrate that the as-prepared MoTe2/PANI composites exhibit higher response than the pure PANI, in particular, the 8 wt.% MoTe2/PANI composites display about 4.23 times enhancement in response value toward 1000 ppm NH3 gas compared with the pure PANI. The enhanced NH3 gas-sensitive properties may be due to the increasing surface area of MoTe2/PANI composite films and the possible interaction of the P-N heterojunctions formed between PANI and the 2H-MoTe2 nanosheets.

A fiber-optic formic acid gas sensor based on molybdenum disulfide nanosheets and chitosan works at room temperature

In this paper, two optical fiber gas sensors were successfully developed, and the detection of formic acid gas was realized at room temperature. The limit of detection for the chitosan material modified probe for formic acid can reach 1 ppm. The combination of molybdenum disulfide (MoS2) nanosheets and chitosan effectively improves sensor response and recovery time. The gas-sensitivity characteristics of the two sensors have been studied, compared and discussed respectively, and the good selectivity and repeatability have been verified by experiments. By combining the gas-sensitive material with the optical fiber structure, this paper verifies and broadens the method for enhancing the sensitivity of the formic acid gas sensor and the realization of concentration detection at room temperature. Because it breaks through the limitation of high-temperature catalytic conditions, the probe is expected to be used for formic acid gas detection, and can be extended to the room temperature detection of other gases under harsh environmental conditions such as strong electromagnetic interference.

The Oxygen Vacancy Defect of ZnO/NiO Nanomaterials Improves Photocatalytic Performance and Ammonia Sensing Performance.

In this paper, ZnO/NiO composites rich in oxygen vacancies are prepared by the solvothermal method and reduction method. In the test, through the use of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscope (TEM), diffuse reflectance spectroscopy (DRS), photoluminescence spectroscopy (PL), and electron paramagnetic resonance (EPR), we effectively prove the existence of phase, morphology and oxygen vacancies in the material. Through the photocatalysis test and gas sensitivity test, it is found that 10% Ni doped OZN-10 has the best photocatalytic activity and gas sensitivity characteristics. The degradation rate of methylene blue (MB) was 98%. The gas sensitivity test shows that OZN-10 has good selectivity, good response performance (3000 ppm, 27,887%) and excellent response recovery time (response time: 50 s, recovery time: 5–7 s) for saturated NH3 gas at standard atmospheric pressure (101.325 KPa) and room temperature (25 °C). The synergistic effect of oxygen vacancy as the center of a trap and p–n heterojunction forming an electric potential field at the interface is explained, and the mechanism of improving photocatalysis and gas sensitivity is analyzed. This work will provide an innovative vision for dual-performance oxygen vacancy modification of heterojunctions through photocatalysis.

CuPc nanowires PVD preparation and its extra high gas sensitivity to chlorine

Efficient copper phthalocyanine gas sensors capable of sensitive and selective analysis of toxic gases at room temperature have shown their great potential for gas sensing in recent years. In this work, a gas sensor based on phthalocyanine copper (II) (CuPc) was prepared by a one-step low-temperature physical vapor deposition (PVD) method. The uniform cotton-wool nanowires film has high yield, and can also be easily peeled off. PVD preparation temperature had a significant influence on both the recovery and cyclic properties of the gas sensor to chlorine. High-performance CuPc nanowires prepared at 230 °C had the lowest detection limit of 1.5 ppm with a recovery time of 2.74 s (this time is over 100 times faster than previous results 260–600 s). In addition, it showed excellent light-induced gas-sensitive characteristics to Cl2 and at room temperature. This sensor can be potentially useful in photo-gas sensors, photocatalytic devices, or photoelectric devices.

Structural and gas-sensitive characteristics of thin semiconductor PdO films of various thicknesses during ozone detection

PdO films were obtained by thermal deposition of palladium metal with a thickness of 30 and 90 nm, followed by its oxidation in air at different temperatures. PdO oxide films are characterized by transmission electron microscopy (TEM) and reflection high-energy electron diffraction (RHEED). Data on the semiconductor properties and gas sensitivity to different concentrations of ozone in the air are obtained. The optimal temperature conditions for the oxidation of the films are established, which ensure their uniform phase composition and the absence of electrical noise during the detection of gases. The mechanism of the electrical noise appearance in ultrathin films associated with their fragmentation during oxidative annealing is proposed and justified. The possibility of detecting ozone impurities in the air below the maximum permissible concentration (MPC) by PdO semiconductor films is shown. Keywords: palladium oxide thin films, phase composition, electrical noise, gas sensor properties.

Promotion on Formaldehyde Sensing of 3D Porous SnO2 by Eu Doping

The formaldehyde sensor with excellent performance has a wide range of applications in industrial production and the monitoring of many household products. Eu-doped 3D porous SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> with a pore size of 120 nm were synthesized as a base material for high-performance formaldehyde sensors. The gas sensitivity test results show that the sensitivity of 3.6% Eu-doped 3D porous SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> with a pore size of 120 nm to 20 ppm formaldehyde is 24 at an operating temperature of 230 °C, which is 1.8 times that of pure 3D porous SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> with the same aperture. Moreover, the formaldehyde sensor made of 3.6% Eu-doped 3D porous SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> with a pore size of 120 nm has good selectivity, with a selectivity coefficient of 5.5 for formaldehyde, good repeatability, and low detection limit (0.5 ppm/1.7). These excellent gas sensitivity characteristics are mainly attributed to the 3D porous SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> with a loose and nano-scale porous morphology, more oxygen vacancies and Eu doping. Therefore, the gas-sensing of the metal oxide semiconductor material can be further improved by doping.

Mo-doped SnO2 nanotubes sensor with abundant oxygen vacancies for ethanol detection

This work describes a synthesizing method for Mo-doped SnO2 nanotubes (NTs) with uniform morphology by combining electrostatic spinning and air sintering. The method uses Mo ions to do substitutional doping of Sn ions in SnO2 to construct new lattice defects (such as oxygen vacancies), which provides more active sites for gas adsorption. Ethanol was taken as an example to study gas sensitivity characteristics of synthesized products. The analysis showed that 5 mol% of Mo-doped SnO2 nanotubes sensor exhibited the highest response (46.8) to 100 ppm ethanol at a lower optimum temperature (220 °C) and reduced the response/recovery time to 7/103 s. Also, it manifested excellent selectivity and long-term stability. The functionalized nanotubes structure and optimized parameters (oxygen vacancies concentration, metal vacancies defects, carrier concentration, catalytic sites, and base resistance increased) are the reasons for enhancing gas-sensing performance. This work provides direction that the optimal doping concentration of transition metal elements for metal-oxide NTs gas sensors can achieve the best sensing response.

Sensors based on tin dioxide thin films for the detection of pre-explosive hydrogen concentrations

In this work, novel semiconductor sensors were developed for detecting high pre-explosive concentrations of H2 (0.1–2.5 vol%) with high selectivity and stability. The sensors were based on thin (∼100 nm) nanocrystalline SnO2 films produced by magnetron sputtering of dispersed Pt and Pd layers deposited on the surface and addition of 13–14 at% Pt in the bulk. Studies on their nanostructure, composition, electrical properties, and gas-sensitive characteristics were carried out. X-ray photoelectron and Raman spectroscopies revealed that in the process of stabilizing annealing in Pt/Pd/SnO2:Sb,Pt film platinum introduced into the bulk segregates on the surface of the SnO2 microcrystals in the form of Pt° metal clusters and dispersed Pt2+ ions. The dispersed Pt2+ ions form bonds with lattice oxygen and contribute to the overlap of conduction channels. In the sensor subjected to annealing at Tan1 =723 K and Tan2=873 K, the optimal situation is realized when under the action of low (n < 0.1 vol%) H2 concentrations, the condition 2d0 = dM is satisfied and G1/G0 = 9–12. In the range of 0.1–2.5 vol% H2, narrowing of the space-charge region favors the formation of a conducting layer, and at 2d0 ≤ dM there is a sharp increase in the values of the responses to G1/G0 = 220–250 at 2.5 vol%.

Стабильность сенсоров паров жидких углеводородов на основе тонких пленок SnO-=SUB=-2-=/SUB=-, модифицированных различными катализаторами

The electrical and gas-sensitive characteristics of sensors based on thin nanocrystalline SnO2 films with various catalysts deposited on the surface (Pt/Pd, Au) and introduced into the bulk (Au, Ni, Co) are studied in the modes of constant and pulsed heating. Atomic force microscopy and laser Raman spectroscopy were used to study the micromorphology and structural defects depending on the composition of nanoscale films. it is shown that sensors with au and co additives introduced into the volume can detect liquid hydrocarbon vapors (for example, aviation kerosene) at a concentration level of 5 ppm (0.1 permissible exposure limit) and are characterized by increased stability of parameters during testing under prolonged exposure to vapors, as well as in conditions of changing humidity. Sensors with Au and Co additives in bulk and ultrathin Pt/Pd catalysts applied to the surface of the films are characterized by the highest performance after testing.