Gas-sensing Performance Research Articles

Bimetallic Co-Mn catalysts for synergistic enhancement of VOC gas-sensing performance of ZnO hierarchical nanostructures.

The synergistic effect between bonding dissimilar metals is a very effective way to improve the performance of metal catalysts. In this work, we prepared a series of bimetallic co-doped ZnO hierarchical nanostructures by controlling Mn and Co contents. The gas-sensing properties of the sensors based on the bimetallic co-doped ZnO hierarchical nanostructures were studied systematically through different volatile organic compound (VOC) vapors for the temperature range from 160 to 400 °C. In the testing of normal butanol gas by the bimetallic co-doped ZnO sensor, its performance was tens of times higher than that of pure zinc oxide, and the response values to other VOCs tested were very low, which also indicates that the sensor has good selectivity. The promoted performance is attributed to the increase of adsorbed oxygen content on the surface of the sensor material due to the bimetallic synergistic enhancement effect. XPS spectra of O 1s region of the sensor show that the adsorbed oxygen content is 22.4%, which is higher than that of the pure ZnO (8.5%). The synergistic effect between bimetallic Mn and Co leads to electron enrichment on the surface of ZnO. Electron enrichment can not only promote the activation of ZnO, but also can help to improve the gas-sensing performance.

Porous double-channel α-Fe2O3/SnO2 heterostructures with multiple electronic transmission routes for the enhanced N,N-dimethylformamide gas-sensing performance

Porous double-channel α-Fe2O3/SnO2 heterostructures with multiple electronic transmission routes for the enhanced N,N-dimethylformamide gas-sensing performance

Transformation of zinc acetate into ZnO nanofibers for enhanced NOx gas sensing: Cost-effective strategies and additive-free optimization

Gas sensors based on ZnO nanocomposites have been widely investigated for the detection of various gases. However, few studies have reported electrospun ZnO for NOx gases, especially NO (nitrogen monoxide), due to its high tendency for oxidation upon contact with air. The development of gas sensors that operate at temperatures below 300°C is challenging for metal oxide gas sensors, as decreasing the temperature can lead to lack of sensitivity and very long recovery times. In this study, the operating temperature was improved to 200°C while achieving a high response to a low concentration of 0.5 ppm gas, with recovery times of 572s and 105s for NO and NO2 (nitrogen dioxide), respectively. Detecting NO and NO2 at low ppm and ppb levels is a major demand and challenge for the development of metal oxide-based gas sensors, especially for health monitoring portable sensors. This study focuses on the design and performance of a NOx gas sensor based on ZnO nanofibrous material with precise structural optimization. The study optimizes the precursor for electrospinning without using any additives. The sensing materials proportion were optimized by changing the ratio of ZnAc:PVA in the precursor of electrospinning solution. Choosing ZnAc:PVA = 1.5 as the optimum precursor for synthesizing ZnO nanofibers resulted in the highest response of 27 and 16 (Ohm/Ohm) for 0.5 ppm NO and NO2, respectively, at 200°C and relative humidity of 50%. Additionally, reproducible sensors were developed, which is crucial for mass production. This remarkable sensitivity in low concentration indicates that the design of material structure and the control of zinc acetate amount in the electrospun solution has great practical applications to detect both gases.

Enhanced Gas Sensing Performance of Heterostructure Sensors Based on H-NCD, MoS₂, and Functionalized Graphene Oxide for Ethanol, NH₃, and NO₂ Detection

This study investigates the gas-sensing capabilities of heterostructure sensors based on hydrogen-terminated nanocrystalline diamond (H-NCD), molybdenum disulfide (MoS₂), and functionalized graphene oxide (SH-GO, GO) for detecting ethanol, ammonia (NH₃), and nitrogen dioxide (NO₂) gases at 100 ppm concentrations. Sensors were tested at two distinct temperatures: 125°C and room temperature (22°C). Among the tested sensors, the SH-GO/H-NCD exhibited the highest sensitivity to ethanol, with a response of 634% at 22°C and 554% at 125°C. The Au NPs/H-NCD sensor showed the second-best ethanol response of 587% at 125°C. For NH₃, SH-GO/H-NCD demonstrated the best response at 125°C with a value of 76%, while at room temperature, it showed 41%. NO₂ sensing showed negative responses, with the SH-GO/H-NCD sensor exhibiting the least degradation at -47% at 125°C and -19% at 22°C. The results highlight those combining materials into heterostructures significantly enhances gas detection performance, even at room temperature, showing comparable responses to commercial sensors.

Enhanced gas sensing performance of Ag-Doped BiFeO3 microspheres synthesized via flash auto combustion technology

This investigation demonstrates the successful synthesis of well-crystallized pristine and Ag-doped BiFeO3 microspheres using flash auto combustion technology. The effects of Ag doping on the morphology and microstructural characteristics were thoroughly examined through SEM, EDS, and powder X-ray diffraction (XRD) studies. Gas sensing experiments were performed to evaluate the response of the synthesized materials to NO gas. The results revealed a remarkable enhancement in the gas sensing capabilities of 5% wt Ag-doped BiFeO3 compared to pure BiFeO3. Specifically, the gas response towards NO was found to be 2.4 times higher for Ag-doped BiFeO3. This significant improvement can be attributed to the presence of Ag atoms within the lattice structure, which not only increased the density of holes in the material but also created additional gas molecule adsorption sites. Furthermore, the Ag dopant exhibited a catalytic effect, contributing to the excellent gas sensor performance of the material. These findings hold great promise for the development of highly sensitive and efficient gas sensors, particularly in applications where the detection of low concentrations of NO is crucial. The utilization of flash auto combustion technology in the synthesis process offers a viable route for scalable production of advanced gas sensing materials with enhanced performance.

Development of Pd/In2O3 hybrid nanoclusters to optimize ethanol vapor sensing.

In this study, we successfully synthesize palladium-decorated indium trioxide (Pd/In2O3) hybrid nanoclusters (NCs) using an advanced dual-target cluster beam deposition (CBD) method, a significant stride in developing high-performance ethanol sensors. The prepared Pd/In2O3 hybrid NCs exhibit exceptional sensitivity, stability, and selectivity to low concentrations of ethanol vapor, with a maximum response value of 101.2 at an optimal operating temperature of 260 °C for 6 at% Pd loading. The dynamic response of the Pd/In2O3-based sensor shows an increase in response with increasing ethanol vapor concentrations within the range of 50 to 1000 ppm. The limit of detection is as low as 24 ppb. The sensor exhibits a high sensitivity of 28.24 ppm-1/2, with response and recovery times of 2.7 and 4.4 seconds, respectively, for 100 ppm ethanol vapor. Additionally, the sensor demonstrates excellent repeatability and stability, with only a minor decrease in response observed over 30 days and notable selectivity for ethanol compared to other common volatile organic compounds. The study highlights the potential of Pd/In2O3 NCs as promising materials for ethanol gas sensors, leveraging the unique capabilities of CBD for controlled synthesis and the catalytic properties of Pd for enhanced gas-sensing performance.

First-principles study on adsorption of gas molecules by metal Sc modified Ti<sub>2</sub>CO<sub>2</sub>

MXene materials have received increasing attention due to their unique properties and potential applications. Ti<sub>2</sub>CO<sub>2</sub>, as a typical MXene material that has been prepared, has been widely studied. The adsorption characteristics of two-dimensional materials for gas molecules can be significantly improved through transition metal modification. However, there are few studies on the use of transition metals to modify Ti<sub>2</sub>CO<sub>2</sub>. In this work, the adsorption processes of different harmful gases (CO, NH<sub>3</sub>, NO, SO<sub>2</sub>, CH<sub>4</sub>, H<sub>2</sub>S) on the surfaces of these two materials, i.e. Ti<sub>2</sub>CO<sub>2</sub> and metal Sc modified Ti<sub>2</sub>CO<sub>2,</sub> are studied and analyzed based on first-principles density functional theory and generalized gradient method. The geometric optimization calculation of the metal-modified adsorption harmful gas structure is carried out, and the kinetic energy cutoff energy of the plane wave basis set is taken as 450 eV. The calculation results show that the structure in which Sc atoms are located above the C atoms in the hollow position has a large binding energy, but it is smaller than the experimental value of the cohesive energy of solid Sc (3.90 eV). Sc atoms can effectively avoid clustering. Surface Sc metal provides active sites for gas adsorption. By analyzing the optimal adsorption points, adsorption energy and other parameters of different gases, the adsorption effects of metal Sc-modified Ti<sub>2</sub>CO<sub>2</sub> on these gases are analyzed. Among them, the adsorption effect of SO<sub>2</sub> is better, the adsorption energy is increased from –0.314 eV to –2.043 eV, and the adsorption effects of other gases are improved. Due to the introduction of new atoms on the surface of Ti<sub>2</sub>CO<sub>2</sub>, the carrier density and carrier mobility of the material are increased, thereby improving the charge transfer on the surface of the material, which is beneficial to its sensitivity to gas molecules. The results of density of states and work function further verify that the carrier density and carrier mobility of Sc-Ti<sub>2</sub>CO<sub>2</sub> are increased, which is beneficial to gas adsorption. It is expected that the metal Sc-modified Ti<sub>2</sub>CO<sub>2</sub> becomes an excellent gas-sensing material for the detection of CO, NH<sub>3</sub>, NO, SO<sub>2</sub>, CH<sub>4</sub> and H<sub>2</sub>S, and the present work can provide a reference for theoretically studying the gas-sensing performance of metal Sc-modified Ti<sub>2</sub>CO<sub>2</sub> materials.

Sensitive detection of H2S based on Ce doped ZnCo2O4 hollow microspheres at low working temperature.

In order to develop a highly efficient H2S gas sensor at low working temperature, in this work, a kind of novel Ce-doped ZnCo2O4 hollow microspheres (Ce/ZnCo2O4 HMSs) were successfully synthesized using a template-free one-pot method, showing a sensitive response toward H2S. The microstructure and morphology of the material were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The gas-sensing performance of the composite was investigated, showing that the ZnCo2O4 doped with 6 mol% Ce had the highest response to 20 ppm H2S at a low operating temperature of 160 °C with a response value of 67.42, which was about 2 times higher than that of original ZnCo2O4. The prepared Ce/ZnCo2O4 HMS sensor in response to H2S exhibited a linear range of 0.1-200 ppm with a low detection limit of 0.1 ppm under the conditions of ambient humidity of 45% and ambient temperature of 20 °C. Meanwhile, it also possessed good selectivity, repeatability and reproducibility. The response value of the sensor decreased by 5.32% after 7 months of continuous monitoring of H2S in an atmospheric environment of a pig farm, indicating that the sensor had a long-term stability and continuous service life with important application prospects.

Pt and black phosphorus co-modified flower-like WS2 composites for fast NO2 gas detection at low temperature.

Incomplete recovery, baseline drift, and a long response time have been impeding the practical applications of transition metal dichalcogenide (TMD)-based gas sensors. Here, we report WS2 sensors with significantly improved gas recovery, rapid response, and negligible baseline drift by the incorporation of black phosphorus (BP) as well as the decoration of Pt to detect NO2 for the first time. Compared to bare WS2, the BP-WS2 sensors show higher sensitivity, better repeatability, and more excellent selectivity towards NO2 at the optimal operating temperature of 50 °C. Furthermore, the optimized 30%BP-WS2/Pt sensors exhibit a continuous enhancement in the recovery level and sensitivity with negligible baseline drift. The 30%BP-WS2/Pt sensor also exhibits a shorter response time of 28 s than 49.5 s for its counterpart WS2 sensor towards 32 ppm NO2. The enhanced sensing properties are primarily due to the combined effects of more adsorption sites provided by BP, the spill-over effect of Pt catalysis, and the WS2/BP heterostructure. Therefore, the Pt-decorated 30%BP-WS2 sensor exhibits prominent gas-sensing properties of high gas sensitivity, a low detection limit of 100 ppb, good selectivity, and fast response. Our strategy provides a new route for designing and optimizing TMD-based gas sensors with excellent gas-sensing performance.

Effect of SnO2 particle size on gas-sensing performance for ppb-level NO2 at room temperature under UV light

Effect of SnO2 particle size on gas-sensing performance for ppb-level NO2 at room temperature under UV light

Effect of Manganese Doping in SnO2 Thin Films and its NO2 Gas Sensing Performance

By using an automated nebulizer spray pyrolysis technique with varied concentrations of manganese chloride (0 - 3%) in the spray solution of tin chloride, thin films of pure and manganese-doped tin oxides (Mn-SnO2) were deposited. X-ray diffraction investigations indicated that 2% Manganese chloride concentration in the spray solution promoted development along (200) and (220) directions. The preferred growth direction in the (200) and (220) planes decreased with increasing manganese chloride doping concentration (2-3%) in the solution. The surface morphology of the films had changed as a result of adding Manganese as a dopant. Compositional analysis was carried out using EDAX. From UV-Vis spectroscopy, the optical properties of the SnO2 and Mn-SnO2 thin film were observed; the maximum optical absorbance was in the wavelength range of 300 - 400 nm. The concentration of Mn in the films affected the intensity of the photoluminescence emission peak detected at 347 and 392 nm for pure SnO2 and Mn-SnO2 films, respectively. The gas sensing performance of the films was examined by dynamic method against NO2 gas, at an operating temperature of 250 °C and 400 ppm gas concentration. Mn-SnO2 films achieved quick response and recovery times of 17 s and 34 s.

Effect of Voltage on Gas Sensor Performance of Anodization Synthesized TiO2 Nanotubes Arrays

Serious gases have been highly related to being prejudiced against human life within the environment. The evolution of a trustworthy gas sensor with an elevated response is of major importance for detecting various hazardous gases. Titanium dioxide (TiO2) nanotubes (TNTs) are favorable candidates with considerable potential and stellar performance in gas sensor applications. In this work, we have studied the effect of voltage on preparing TiO2 nanotubular arrays via the anodization technique for gas sensor applications. A simple electrochemical anodization approach was used to synthesize titanium dioxide nanotubes. Diverse techniques of characterization were used to evaluate TNTs. The results gained from field emission scanning electron microscopy (FESEM), energy dispersion spectroscopy (EDS), and X-ray diffraction (XRD) indicate that TiO2 was formed. Gas sensors were created, and the gas detection characteristics were directed towards hydrogen sulfide (H2S), which is not a healthy gas. The sensor made from these nanotubes responds well to this gas at different temperatures and has high sensitivity. The H2S-detecting characteristics were evaluated at values ranging from room temperature up to 300 oC. Results show that the gas sensor TNTs that was prepared at 30 volt for H2S gas sensing has the highest sensitivity and shortest response time at room temperature.

MOF-derived Al3+-doped Co3O4 nanocomposites for highly n-butanol gas sensing performance at low operating temperature

High-performance gas sensors based on metal oxides for detecting Volatile Organic Compounds (VOCs) at low operating temperatures have garnered considerable attention due to their practical utility and energy efficiency. In this study, we synthesized the Al/Co metal-organic framework (MOF) by using a hydrothermal method. Subsequently, Al3+-doped Co3O4 (Al3+-Co3O4) nanocomposites with varying Al3+ concentrations were obtained through calcination. When applied to gas sensors, the Al3+-Co3O4 nanocomposites-based gas sensors exhibited excellent sensing properties toward n-butanol at a low operating temperature (100 ℃). Specifically, the response of the 10% Al3+-Co3O4 nanocomposite to 20 ppm n-butanol reached 116.7, representing an approximately 5.5-fold improvement compared to pristine Co3O4. The gas sensor based on the 10% Al3+-Co3O4 nanocomposite also demonstrated commendable repeatability, selectivity, and stability. This suggests that Al3+ doping results in Al3+-Co3O4 possessing a more intact spherical morphology. Doping significantly enhances the gas-sensing performance of Al3+-Co3O4 due to increased oxygen vacancies and a narrower band gap energy. These findings inspire the development of new p-type metal oxide semiconductor gas sensors operating at low temperatures.

Bismuth tungstate nanosheets sensors based on Temkin adsorption model for triethylamine detection

Nanostructured Bi2WO6 and Bi2W2O9 were synthesized using a hydrothermal method. The crystal structure, morphology, and specific surface area were analyzed via X-ray diffraction, scanning electron microscopy, Brunauer–Emmett–Teller and X-ray photoelectron spectroscopy (XPS) analysis, respectively. The characterization results show that Bi2WO6 has a higher specific surface area and a larger pore size than Bi2W2O9, which promote oxygen adsorption and surface reactions. Gas-sensitive tests show that both sensors have a lower detection limit of 2.5 ppm as well as short response and recovery times for detecting triethylamine (TEA). They also have excellent cycling and long-term stability at 180 °C and exhibit excellent gas-sensing performance. The Bi2WO6 sensor has a higher response and sensitivity, as well as better selectivity, than the Bi2W2O9 sensor, which is related to the uniformly layered structure of the former material. We have analyzed the mechanism that enables these sensors to detect TEA and have used the Temkin adsorption model to explain the linear relationship. We find that this model provides an excellent theoretical foundation for fitting the working curve of these semiconductor sensors.

Two-dimension Cd-N co-doped α-AsP as high sensitivity and selectivity NO and NO2 sensor: A first-principles study

This study aims to develop a newfangled toxic gas (NO and NO2) sensor. The adsorption and gas-sensing performance of toxic gas absorbed on the two-dimension arsenic-phosphorus (α-AsP) monolayer was theoretically researched using the DFT calculations. It is found that α-AsP monolayer has weak adsorption performance, and the single non-metal/metal atom doped AsP systems have weak-physical/strong-chemical adsorption behaviors. However, metallic (Cd, Ag, Au, Pt and Fe) and N co-doped AsP systems exhibit excellent gas sensing performance to NO and NO2 gases. These adsorption systems exhibit enhanced gas-sensing performance by regulating the adsorption energy between weak physical adsorption and strong chemical adsorption. It is worth mentioning that the sensitivity of NO and NO2 adsorption on Cd-N co-doped AsP reaches a surprising 94.908% and 78.291%, respectively. Moreover, we predicted that the CdN-AsP system is suitable for NO and NO2 gas-sensing under multiple gas environment by comparing the selectivity, electronic and adsorption properties. Our work has provided a critical reference to develop the potential gas sensor for NO and NO2 detections.

Amorphous Pt-decorated α-Fe2O3 sensor with superior triethylamine sensing performance prepared by a one-step impregnation method

Noble metals are widely used additives to improve the sensing performance of conductometric metal oxide gas sensors. Although amorphous noble metal particles are expected to further improve the gas sensor response, common techniques often result in crystalline nanoparticles. Herein, an amorphous Pt nanoparticle-decorated α-Fe2O3 sensor was prepared via a temperature-controlled facile one-step impregnation method without the use of a reductant, surfactant, or subsequent thermal reduction. The amorphous Pt-functionalized α-Fe2O3 exhibited superior sensing performance to triethylamine, achieving 100 °C and 140 °C decreases in the optimal working temperature, and had better selectivity, with 22-fold and 14-fold improvements in gas response when compared to those of crystallized Pt-functionalized α-Fe2O3 and pristine α-Fe2O3, respectively. The as-prepared amorphous Pt-decorated α-Fe2O3 sensor showed great promise as a promising triethylamine sensor, and the newly developed facile impregnation method was shown to be an effective strategy to synthesize amorphous noble metal-decorated metal oxide gas sensors.

The Role of Zn Ions in the Structural, Surface, and Gas-Sensing Properties of SnO2:Zn Nanocrystals Synthesized via a Microwave-Assisted Route.

Although semiconducting metal oxide (SMOx) nanoparticles (NPs) have attracted attention as sensing materials, the methodologies available to synthesize them with desirable properties are quite limited and/or often require relatively high energy consumption. Thus, we report herein the processing of Zn-doped SnO2 NPs via a microwave-assisted nonaqueous route at a relatively low temperature (160 °C) and with a short treatment time (20 min). In addition, the effects of adding Zn in the structural, electronic, and gas-sensing properties of SnO2 NPs were investigated. X-ray diffraction and high-resolution transmission electron microscopy analyses revealed the single-phase of rutile SnO2, with an average crystal size of 7 nm. X-ray absorption near edge spectroscopy measurements revealed the homogenous incorporation of Zn ions into the SnO2 network. Gas sensing tests showed that Zn-doped SnO2 NPs were highly sensitive to sub-ppm levels of NO2 gas at 150 °C, with good recovery and stability even under ambient moisture. We observed an increase in the response of the Zn-doped sample of up to 100 times compared to the pristine one. This enhancement in the gas-sensing performance was linked to the Zn ions that provided more surface oxygen defects acting as active sites for the NO2 adsorption on the sensing material.

Polypyrrole-Tungsten Oxide Nanocomposite Fabrication through Laser-Based Techniques for an Ammonia Sensor: Achieving Room Temperature Operation.

A highly sensitive ammonia-gas sensor based on a tungsten trioxide and polypyrrole (WO3/PPy) nanocomposite synthesized using pulsed-laser deposition (PLD) and matrix-assisted pulsed-laser evaporation (MAPLE) is presented in this study. The WO3/PPy nanocomposite is prepared through a layer-by-layer alternate deposition of the PPy thin layer on the WO3 mesoporous layer. Extensive characterization using X-ray diffraction, FTIR and Raman spectroscopy, scanning electron microscopy, atomic force microscopy, and water contact angle are carried out on the as-prepared layers. The gas-sensing properties of the WO3/PPy nanocomposite layers are systematically investigated upon exposure to ammonia gas. The results demonstrate that the WO3/PPy nanocomposite sensor exhibits a lower detection limit, higher response, faster response/recovery time, and exceptional repeatability compared to the pure PPy and WO3 counterparts. The significant improvement in gas-sensing properties observed in the WO3/PPy nanocomposite layer can be attributed to the distinctive interactions occurring at the p-n heterojunction established between the n-type WO3 and p-type PPy. Additionally, the enhanced surface area of the WO3/PPy nanocomposite, achieved through the PLD and MAPLE synthesis techniques, contributes to its exceptional gas-sensing performance.

Influence of Different Pt Functionalization Modes on the Properties of CuO Gas-Sensing Materials.

The functionalization of noble metals is an effective approach to lowering the sensing temperature and improving the sensitivity of metal oxide semiconductor (MOS)-based gas sensors. However, there is a dearth of comparative analyses regarding the differences in sensitization mechanisms between the two functionalization modes of noble metal loading and doping. In this investigation, we synthesized Pt-doped CuO gas-sensing materials using a one-pot hydrothermal method. And for Pt-loaded CuO, Pt was deposited on the synthesized pristine CuO surface by using a dipping method. We found that both functionalization methods can considerably enhance the response and selectivity of CuO toward NO2 at low temperatures. However, we observed that CuO with Pt loading had superior sensing performance at 25 °C, while CuO with Pt doping showed more substantial response changes with an increase in the operating temperature. This is mainly due to the different dominant roles of electron sensitization and chemical sensitization resulting from the different forms of Pt present in different functionalization modes. For Pt doping, electron sensitization is stronger, and for Pt loading, chemical sensitization is stronger. The results of this study present innovative ideas for understanding the optimization of noble metal functionalization for the gas-sensing performance of metal oxide semiconductors.

GaN/rGO nanocomposite gas sensor for enhanced NH3 sensing performances at room temperature

In this work, we developed a high-performance NH3 sensor based on GaN/rGO nanocomposites via a low-cost solvothermal method and subsequent nitridation process. The morphological, structural, and chemical compositions were investigated to demonstrate that GaN and rGO were coupled together by interfacial modulation, and the GaN/rGO heterostructure chemical bonds are successfully formed. Gas-sensing performance test results show that the fabricated GaN/rGO (2.2 wt%) NH3 sensor exhibited a high response value (92%), fast response time (11 s), and low limit of detection (500 ppb) at room temperature. In addition, reproducibility, humidity, and long-term stability tests of the GaN/rGO sensor were also conducted in this work. The enhancement sensing mechanisms are attributed to the large specific surface area, the excellent conductivity of rGO, and resistance modulation effect of the heterojunction potential. Hence, the GaN/rGO gas sensor can be regarded as a promising sensing solution for atmospheric and exhaled NH3 detection at room temperature.