Gas-sensing Properties Research Articles

Significant improvement of dielectric, magnetic, and gas-sensing properties of the (La0.8Ca0.2)0.6Bi0.4FeO3 nanomaterial: particles size effects

Significant improvement of dielectric, magnetic, and gas-sensing properties of the (La0.8Ca0.2)0.6Bi0.4FeO3 nanomaterial: particles size effects

Gas sensors based on the oxide skin of liquid indium.

Various non-stratified two-dimensional (2D) materials can be obtained from liquid metal surfaces that are not naturally accessible. Homogenous nucleation on atomically flat interfaces of liquid metals with air produces unprecedented high-quality oxide layers that can be transferred onto desired substrates. The atomically flat and large areas provide large surface-to-volume ratios ideal for sensing applications. Versatile crucial applications of the liquid metal-derived 2D oxides have been realized; however, their gas-sensing properties remain largely underexplored. The cubic In2O3 structure, which is nonlayered, can be formed as an ultrathin layer on the surface of liquid indium during the self-limiting Cabrera-Mott oxidation process in the air. The morphology, crystal structure, and band structure of the harvested 2D In2O3 nanosheets from liquid indium are characterized. Sensing capability toward several gases, both inorganic and organic, entailing NO2, O2, NH3, H2, H2S, CO, and Methyl ethyl ketone (MEK) are explored. A high ohmic resistance change of 1974% at 10 ppm, fast response, and recovery times are observed for NO2 at an optimum temperature of 200 °C. The sensing fundamentals are investigated for NO2, and its performances and cross-selectivity to different gases are analyzed. The NO2 sensing response from room temperature to 300 °C has been measured and discussed, and stability after 24 hours of continuous operation is presented. The results demonstrate liquid metal-derived 2D oxides as promising materials for gas sensing applications.

Pt nanoparticle decoration on femtosecond laser-irradiated SnO2 nanowires for enhancing C7H8 gas sensing

In this study, we have fabricated a sensitive and selective toluene gas sensor based on SnO2 nanowires (NWs) using the femtosecond (FS) laser irradiation and Pt nanoparticle (NPs) decoration. The effects of different laser parameters, including wavelength, laser pulse energy, hatch distance, and scan speed, are investigated on the gas-sensing properties. The FS laser irradiation-induced embossing surface is found to be a dominant factor in determining the gas-sensing behavior, which provides more oxygen absorption sites, resulting in an increase in the width of the electron depletion layer (EDL) and the sensor response. The Pt decoration on the FS laser-irradiated SnO2 NWs developed additional EDL, which further enhances the sensor response. The Pt-decorated and FS laser-irradiated SnO2 NWs gas sensor shows a high selectivity toward C7H8 owing to the catalytic effect of Pt toward toluene, where the sensor response to 50 ppm C7H8 is as high as 53 at 300 °C. Based on X-ray photoelectron spectroscopy and transmission electron microscopy analyses, a gas-sensing mechanism of the Pt-decorated and FS laser-irradiated SnO2 NWs gas sensor is proposed. This study highlights a promising combination of Pt decoration and FS laser irradiation for the realization of reliable toluene gas sensors.

Ultra-sensitive triethylamine gas sensor based on ZnO/MoO3 heterostructures with ppb level detection

Selective detection of Triethylamine (TEA) is of great significance for environmental monitoring and daily life. In this work, ZnO/MoO3 heterostructures with ultra-sensitive and rapid response-recovery for TEA gas were prepared by a facile hydrothermal method. The ZnO/MoO3 sensor exhibits remarkable reproducibility and long-term stability. Notably, the ZnO/MoO3 sensor achieves a response of 519 for 100 ppm TEA gas at 180 ºC with a detection limit as low as 10 ppb. The superb sensing performance of the ZnO/MoO3 sensor is mainly attributed to the synergistic effect of ZnO and MoO3, and the enhanced electron transfer rate of the heterostructures. In addition, the density functional theory (DFT) calculations were used to explore the sensing mechanism in detail, further confirming the experimental conclusion. Therefore, ZnO/MoO3 sensor has potential application in practical TEA-detection, thus establishing a feasible strategy for promoting gas-sensing properties of metal oxide sensors.

Highly Selective Gas Sensor Based on Litchi-like g-C3N4/In2O3 for Rapid Detection of H2.

Hydrogen (H2) has gradually become a substitute for traditional energy, but its potential danger cannot be ignored. In this study, litchi-like g-C3N4/In2O3 composites were synthesized by a hydrothermal method and used to develop H2 sensors. The morphology characteristics and chemical composition of the samples were characterized to analyze the gas-sensing properties. Meanwhile, a series of sensors were tested to evaluate the gas-sensing performance. Among these sensors, the sensor based on the 3 wt% g-C3N4/In2O3 (the mass ratio of g-C3N4 to In2O3 is 3:100) showeds good response properties to H2, exhibiting fast response/recovery time and excellent selectivity to H2. The improvement in the gas-sensing performance may be related to the special morphology, the oxygen state and the g-C3N4/In2O3 heterojunction. To sum up, a sensor based on 3 wt% g-C3N4/In2O3 exhibits preeminent performance for H2 with high sensitivity, fast response, and excellent selectivity.

Preparation and characterization of the phthalocyanine–zinc(II) complex-based nanothin films: optical and gas-sensing properties

Preparation and characterization of the phthalocyanine–zinc(II) complex-based nanothin films: optical and gas-sensing properties

Polyethyleneimine-Starch Functionalization of Single-Walled Carbon Nanotubes for Carbon Dioxide Sensing at Room Temperature.

There is an ever-growing interest in the detection of carbon dioxide (CO2) due to health risks associated with CO2 emissions. Hence, there is a need for low-power and low-cost CO2 sensors for efficient monitoring and sensing of CO2 analyte molecules in the environment. This study reports on the synthesis of single-walled carbon nanotubes (SWCNTs) that are functionalized using polyethyleneimine and starch (PEI-starch) in order to fabricate a PEI-starch functionalized SWCNT sensor for reversible CO2 detection under ambient room conditions (T = 25 °C; RH = 53%). Field-emission scanning electron microscopy, high-resolution transmission electron microscopy, Raman spectroscopy, and Fourier transform infrared spectroscopy are used to analyze the physiochemical properties of the as-synthesized gas sensor. Due to the large specific surface area of SWCNTs and the efficient CO2 capturing capabilities of the amine-rich PEI layer, the sensor possesses a high CO2 adsorption capacity. When exposed to varying CO2 concentrations between 50 and 500 ppm, the sensor response exhibits a linear relationship with an increase in analyte concentration, allowing it to operate reliably throughout a broad range of CO2 concentrations. The sensing mechanism of the PEI-starch-functionalized SWCNT sensor is based on the reversible acid-base equilibrium chemical reactions between amino groups of PEI and adsorbed CO2 molecules, which produce carbamates and bicarbonates. Due to the presence of hygroscopic starch that attracts more water molecules to the surface of SWCNTs, the adsorption capacity of CO2 gas molecules is enhanced. After multiple cycles of analyte exposure, the sensor recovers to its initial resistance level via a UV-assisted recovery approach. In addition, the sensor exhibits great stability and reliability in multiple analyte gas exposures as well as excellent selectivity to carbon dioxide over other interfering gases such as carbon monoxide, oxygen, and ammonia, thereby showing the potential to monitor CO2 levels in various infrastructure.

Molecular Engineering of Silicon Phthalocyanine to Improve the Charge Transport and Ammonia Sensing Properties of Organic Heterojunction Gas Sensors

AbstractNovel organic heterostructures fabricated with a bilayer consisting of an axially substituted silicon phthalocyanine (R2‐SiPc) derivative and lutetium bis‐phthalocyanine (LuPc2) are investigated for their ammonia sensing properties. Surface and microstructure characterization of the heterostructure films reveal either compact or highly porous surface topography in (345F)2‐SiPc and Cl2‐SiPc‐based heterostructures, while electrical characterization reveals a strong influence of the axial substituent in R2‐SiPc on NH3 sensing capabilities. Electrical characterization further demonstrates an apparent energy barrier for interfacial charge transport, which is higher in the (345F)2‐SiPc/LuPc2 heterojunction device. In‐depth charge transport studies by impedance spectroscopy further reveal a resistive interface in (345F)2‐SiPc/LuPc2 and faster bulk and interfacial charge transport in Cl2‐SiPc/LuPc2 heterojunction devices. Different interfacial charge transport capabilities and surface topographies affect NH3 sensing properties of the two heterojunction devices, in which (345F)2‐SiPc/LuPc2 reveals a fast and non‐linear response with a limit of detection (LOD) of 310 ppb, while Cl2‐SiPc/LuPc2 exhibits a slow, and linear response to NH3 with LOD of 100 ppb. Finally, different metrological parameters of the two sensors are correlated to the respective gas‐material interactions, in which adsorption and diffusion regimes are modulated by the surface topography and hydrophobicity of the sensing layer.

Electrical and Gas Sensor Properties of Nb(V) Doped Nanocrystalline β-Ga2O3.

A flame spray pyrolysis (FSP) technique was applied to obtain pure and Nb(V)-doped nanocrystalline β-Ga2O3, which were further studied as gas sensor materials. The obtained samples were characterized with XRD, XPS, TEM, Raman spectroscopy and BET method. Formation of GaNbO4 phase is observed at high annealing temperatures. Transition of Ga(III) into Ga(I) state during Nb(V) doping prevents donor charge carriers generation and hinders considerable improvement of electrical and gas sensor properties of β-Ga2O3. Superior gas sensor performance of obtained ultrafine materials at lower operating temperatures compared to previously reported thin film Ga2O3 materials is shown.

Comparative Study on Gas-Sensing Properties of 2D (MoS2, WS2)/PANI Nanocomposites-Based Sensor.

NH3 is a highly harmful gas; when inhaled at levels that are too high for comfort, it is very dangerous to human health. One of the challenging tasks in research is developing ammonia sensors that operate at room temperature. In this study, we proposed a new design of an NH3 gas sensor that was comprised of two-dimensional (TMDs, mainly WS2 and MoS2) and PANI. The 2D-TMDs metal was successfully incorporated into the PANI lattice based on the results of XRD and SEM. The elemental EDX analysis results indicated that C, N, O, W, S and Mo were found in the composite samples. The bandgap of the materials decreased due to the addition of MoS2 and WS2. We also analyzed its structural, optical and morphological properties. When compared to MoS2 and PANI, the proposed NH3 sensor with the WS2 composite was found to have high sensitivity. The composite films also exhibited response and recovery times of 10/16 and 14/16 s. Therefore, the composite PANI/2D-TMDs is a suitable material for NH3 gas detection applications.

First-Principles Investigation of Adsorption Behaviors and Electronic, Optical, and Gas-Sensing Properties of Pure and Pd-Decorated GeS2 Monolayers.

The extensive applications of two-dimensional (2D) transition metal disulfides in gas sensing prompt us to explore the adsorption, electronic, optical, and gas-sensing properties of the pure and Pd-decorated GeS2 monolayers interacting with NO2, NO, CO2, CO, SO2, NH3, H2S, HCN, HF, CH4, N2, and H2 gases by using first-principles methods. Our results showed that the pure GeS2 monolayer is not appropriate to develop gas sensors. The stability of the Pd-decorated GeS2 (Pd-GeS2) monolayer was determined by binding energy, transition state theory, and molecular dynamics simulations, and the Pd decoration has a significant effect on adsorption strength and the change in electronic properties (especially electrical conductivity). The Pd-GeS2 monolayer-based sensor has relatively high sensitivity toward NO and NO2 gases with moderate recovery time. In addition, the adsorption of NO and NO2 can conspicuously change the optical properties of the Pd-GeS2 monolayer. Therefore, the Pd-GeS2 monolayer is predicted to be reusable and a highly sensitive (optical) gas sensing material for the detection of NO and NO2.

Study of Electrical and Gas Sensing Properties of as Deposited Niobium Pentoxide (Nb2O5) Thick Films Fabricated by Screen Printing Method

Study of Electrical and Gas Sensing Properties of as Deposited Niobium Pentoxide (Nb2O5) Thick Films Fabricated by Screen Printing Method

Hydrogen-Sensing Properties of Ultrathin Pt-Co Alloy Films

The present work aims to investigate the feasibility of utilizing Pt and PtCo alloy ultrathin films as hydrogen gas sensors in order to reduce the cost of the hydrogen gas sensors by using low-cost metallic materials. In this study, ultrathin Pt and PtCo alloy thin films are evaluated for hydrogen sensors. The stoichiometry and structural characterization of the thin films are observed from XPS, SEM, and EDX measurements. The 2-nm-thick Pt and PtCo films deposited by sputtering onto Si/SiO2 covers homogeneously the surface in an fcc crystalline plane (111). The hydrogen gas-sensing properties of the films are assessed from the resistance measurement between 25 °C and 150 °C temperature range, under atmospheres with hydrogen concentration ranging from 10 ppm to 5%. The hydrogen-sensing mechanism of ultrathin PtxCo1-x alloy films can be elucidated with the surface scattering phenomenon. PtCo thin alloy films show better response time than pure Pt thin films, but the alloy films show lower sensor response than pure Pt film’s sensor response. Aside from these experimental investigations, first-principles calculations have also been carried out for bare Pt and Co, and also PtCo alloys. Compared to the theoretical calculations, the sensor response to change decreases with increasing Co content, a result that is compatible with the experimental results. In an attempt to explain the decrease in the sensor response of PtCo alloy films compared to bare Pt film, a variety of different phenomena are discussed, including the shrinking lattice of the structure or dendritic surface structure of PtCo alloy films by the increasing cobalt ratio.

Hollow Mesoporous SnO2/Zn2SnO4 Heterojunction and RGO Decoration for High-Performance Detection of Acetone.

In this article, the synthesis procedure and sensing properties toward acetone of rGO-HM-SnO2/Zn2SnO4 composites with a hollow mesoporous structure are presented comprehensively. The rGO-HM-SnO2/Zn2SnO4 heterojunction structure is prepared through a self-sacrificial template strategy with a concise acid-assisted etching method. The as-prepared hollow mesoporous architectures are investigated by SEM, TEM, and HRTEM. The phase structure and valence state are also characterized by XRD and XPS, respectively. It is obvious that the hollow mesoporous architecture affords a large specific surface area, which can provide more reaction active sites of sensing materials significantly. Compared to the initial SnO2/Zn2SnO4 composites, the gas sensor fabricated by rGO-HM-SnO2/Zn2SnO4 shows the best gas-sensing properties, and the response value toward 100 ppm acetone is as high as 107 at 200 °C. Moreover, the rGO-HM-SnO2/Zn2SnO4 sensing material reveals excellent properties of shorter response-recovery times and higher long-term stability. This excellent performance can be ascribed to the synergistic effect of the hollow mesoporous n-n heterojunction and abundant-defect rGO. The relevant sensing mechanism of rGO-HM-SnO2/Zn2SnO4 sensing materials is investigated in detail.

Adsorption and Gas-Sensing Properties of Agn (n = 1-4) Cluster Doped GeSe for CH4 and CO Gases in Oil-Immersed Transformer.

The adsorption mechanism of CO and CH4 on GeSe, modified with the most stable 1-4 Ag-atom clusters, is studied with the help of density functional theory. Adsorption distance, adsorption energy, total density of states (TDOS), projected density of states (PDOS), and molecular orbital theory were all used to analyze the results. CO was found to chemisorb exothermically on GeSe, independent of Ag cluster size, with Ag4-GeSe representing the optimum choice for CO gas sensors. CH4, in contrast, was found to chemisorb on Ag-GeSe and Ag2-GeSe and to physisorb on Ag3-GeSe and Ag4-GeSe. Here, Ag GeSe was found to be the optimum choice for CH4 gas sensors. Overall, our calculations suggest that GeSe modified by Ag clusters of different sizes could be used to advantage to detect CO and CH4 gas in ambient air.

Ultra-low voltage adenine based gas sensor to detect H2 and NH3 at room temperature: First-principles paradigm

The molecular system-level detection of H2 and NH3 gas using an electrically doped Adenine bio-molecular gas sensor has been proposed and investigated using Density Functional Theory (DFT) combined with Non-Equilibrium Green's Function (NEGF) formalisms. First-principles calculations were applied and the structures and electronic properties of the Adenine gas sensor have calculated. This sensor reveals that the current-voltage response and conductivity of the bio-molecules increased evidently after the adsorption of these gas molecules. The Adenine sensor offers approximately 1800 times and 3300 times better current response during H2 and NH3 adsorption respectively. The significant gap between Highest Occupied Molecular Orbital (HOMO) and Lowest Un-occupied Molecular Orbital (LUMO) indicates the system's thermodynamic stability. Therefore, we hope that the Adenine monolayer could be a room temperature H2 and NH3 sensor with high selectivity and sensitivity and fast response and recovery time. Therefore, we hope that the Adenine monolayer will be a good candidate forH2 and NH3 work-function-type gas sensors.

Detection of ammonia gas at room temperature through Sb doped SnO2 thin films: Improvement in sensing performance of SnO2

This paper presents the effects of Sb doping on the gas-sensing properties of SnO2 thin films prepared through a nebulizer-assisted spray pyrolysis technique. An improvement in the inherent characteristics of the transparent conducting oxide after 0 to 5 wt% Sb doping is reported. The deposited films were used to sense the presence of 50 to 250 ppm of ammonia at room temperature. Various analytical techniques were used to analyze the properties of the Sb-doped SnO2 films. X-ray diffraction spectra revealed the tetragonal structure of crystallites, and the maximum crystallite size was observed in the 2-wt%-Sb-doped SnO2 film. The morphological images showed spherical grains in pristine SnO2 films and their transformation to a trigonal shape after Sb doping; particularly, a large grain size was observed at 2 wt% doping. PL studies of the materials revealed that a large number of oxygen vacancies exist in the 2-wt%-Sb-doped SnO2 thin film. The transmittance of the films remained at approximately 75%, and the band gap varied from 3.94 to 4.01 eV as the doping concentration varied from 1 to 5%. A high response of 138% was observed for 250 ppm of ammonia in the case of the 2-wt%-Sb-doped SnO2 film, with a 42 s response time and a 11 s recovery time. Thus, the 2-wt%-Sb-doped SnO2 thin film has suitable characteristics for application as an efficient gas sensor to detect ammonia.

Enhanced Sensing Performance of Electrospun Tin Dioxide Nanofibers Decorated with Cerium Dioxide Nanoparticles for the Detection of Liquefied Petroleum Gas

Tin dioxide (SnO2) nanofibers and cerium dioxide (CeO2) nanoparticles were prepared by electrospinning and hydrothermal methods, respectively. The morphology and structure of the synthesized SnO2/CeO2 samples were characterized by a variety of methods. The gas-sensing properties of the SnO2/CeO2 sensor were investigated for liquefied petroleum gas (LPG) detection at room temperature. Compared with pure SnO2 nanofibers, the SnO2/CeO2 composite sensor showed a much higher response and shorter response time for LPG sensing after doping with CeO2 nanoparticles. Furthermore, the SnO2/CeO2 composite sensor had better resistance to interference from humidity than the pure SnO2 sensor. The significantly enhanced sensing performance of the SnO2/CeO2 composite sensor for LPG can be attributed to the modification with CeO2 to increase oxygen vacancies and form a heterostructure with SnO2 nanofibers. Meanwhile, the LPG detection circuit was built to realize real-time concentration display and alarm for practical applications.

Excellent sensitivity of SnO2 nanoparticles to formaldehyde

The room temperature gas sensors have always been an important research direction of the gas sensor, and the room temperature gas sensors without the assistance of the light is more valuable. The SnO2 nanoparticles were synthesized by hydrothermal method, which showed good formaldehyde sensitivity, had the advantages of low test temperature, only [Formula: see text]C, good formaldehyde selectivity, and especially the good response to formaldehyde at room temperature. The nanostructure and gas-sensing properties were characterized by scanning electron microscopy, EDS mapping, nitrogen physical adsorption, and X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and WS-60B gas-sensing measurement system. Compared with the reported research results, we carefully discuss the physical mechanism of the SnO2 formaldehyde sensor with low operating temperature and good formaldehyde selectivity in this paper.

Room-temperature highly sensitive and selective NH3 gas sensor using vertically aligned WS2 nanosheets

Here, we report the room temperature (35 °C) NH3 gas sensor device made from WS2 nanosheets obtained via a facile and low-cost probe sonication method. The gas-sensing properties of devices made from these nanosheets were examined for various analytes such as ammonia, ethanol, methanol, formaldehyde, acetone, chloroform, and benzene. The fabricated gas sensor is selective towards NH3 and exhibits excellent sensitivity, faster response, and recovery time in comparison to previously reported values. The device can detect NH3 down to 5 ppm, much below the maximum allowed workspace NH3 level (20 ppm), and have a sensing response of the order of 112% with a response and recovery time of 54 s and 66 s, respectively. On the other hand, a sensor made from nanostructures has a bit longer recovery time than a device made from nanosheets. This was attributed to the fact that NH3 molecules adsorbed on the surface site and those trapped in between WS2 layers may have different adsorption energies . In the latter case, desorption becomes difficult and may give rise to slower recovery as noticed. Further, stiffened Raman modes upon exposure to NH3 reveal strong electron-phonon interaction between NH3 and the WS2 channel. The present work highlights the potential use of scaled two-dimensional nanosheets in sensing devices and particularly when used with inter-digitized electrodes, may offer enhanced performance.