Enhanced Gas-sensing Performance Research Articles

Advanced triethylamine sensor utilizing 3D microspheres of La-doped MoO3: Performance enhancement and mechanism insights

Triethylamine (TEA) as an excellent solvent, polymer inhibitor and preservative often appears in various places in industrial production, but its harm can not be underestimated. For the detection of TEA, molybdenum trioxide (MoO3) is a great gas-sensitive material, but its response and recovery time are long. In addressing improvements to MoO3, the paper introduced a method involving the introduction of the rare earth metal La and further pinpointed an optimal doping concentration strategy. In this paper, three-dimensional (3D) microspheres of La-doped MoO3 with different doping concentrations were synthesized using a facile hydrothermal method. Among these, the sensor based on 1 wt% La-doped MoO3 exhibits the highest gas-sensing response to TEA, with a response value of approximately 30–20 ppm TEA when the temperature is 240 ℃, accompanied by shortened response and recovery times of 10 and 29 s, respectively. Moreover, this doping level demonstrates excellent selectivity, reproducibility and long-term stability. The enhancement of gas-sensing performance is elucidated through the electron depletion layer theory and the increase in oxygen vacancies. Additionally, first-principles density functional theory (DFT) calculation was employed to deeply analyze the adsorption behavior of the MoO3 towards TEA before and after doping. This study provides valuable insights into the development of high-performance TEA sensors.

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.

MoS2/MoO3 heterojunctions enabled by surface oxidization of MoS2 nanosheets for high-performance room-temperature NO2 gas sensing

Transition-metal dichalcogenides (TMDs) have emerged as ideal candidates for room-temperature gas sensing due to their remarkable semiconductor properties. However, bare TMDs typically exhibit drawbacks such as low sensitivity, slow response, and low recovery speeds, which limit their applicability. In comparison to single materials, enhancing the sensing performance of the material can be achieved through the realization of heterostructures. Therefore, the key to improving the performance of metal-sulfide gas sensors lies in the controlled construction of unique heterostructures. In this work, surface heterostructures composed of molybdenum disulfide (MoS2) nanoflowers loaded with molybdenum trioxide (MoO3) enabled are realized through the surface oxidization of MoS2 nanosheets for high-performance room-temperature detection of NO2 gas. The heterostructures were easily constructed by oxidizing flower-like MoS2 using a hydrogen peroxide aqueous solution. The gas sensor based on the MoS2/MoO3 heterojunction exhibits a response of 18.9 % to 1 ppm NO2, which is nine times higher than that of the MoS2 sensor (2.1 %). Furthermore, even at a NO2 concentration as low as 50 ppb, the sensor response can reach 6.9 %. The sensor displays good repeatability and excellent selectivity. The enhanced gas-sensing performance of the MoS2/MoO3 heterostructure may result from the unique structure of MoS2 and the p-n heterojunction formed at the interfaces. The proposed design strategy and the surface heterostructure constructed in this work can provide guidance for the development of high-performance gas-sensitive materials and devices.

Flower-like SnS2/In2S3 heterostructures with available state density resonance effect for low-temperature gas-sensing performance to triethylamine

Currently, the construction of three-dimensional (3D) flower-like SnS2/In2S3 heterostructures has been primarily developed for low-temperature gas-sensing detection of triethylamine (TEA) by a facile hydrothermal treatment. The thickness of nanosheets and the number of folds of self-assembled products can be well regulated as the introduction of In component increasing, as well as the distribution of effective SnS2–In2S3 heterojunctions. All the as-prepared SnS2-based sensors can exhibit good gas sensitive response behavior to TEA at various low operating temperatures, even for the first time at room temperature. For example, the optimal SnS2-1% In have the highest response (21.01), the relatively fast response/recovery times, and superior gas selectivity and stability to 100 ppm TEA at 40 °C, compared with other samples. Besides the combination of the formation of SnS2–In2S3 heterojunctions, abundant active sites of the self-assembled structures, and unique surface/interface transmission mechanism is beneficial to the enhanced gas-sensing performance, significantly, the generation of state density resonance effect can be employed for improving the electron transport efficiency due to the adjustment of state density near the Femi level. The available long-term, cycling, and humidity stabilities and the linear response relationship of the sensors greatly contribute for the potential application of seafood storage evaluation.

Constructing bilayer sensors with Co-MOF-derived Co3O4 porous sensing films and SnO2 catalytic overlayers to enhance room-temperature triethylamine sensing performance

Gas sensors with good repeatability and controllable fabrication method are extremely desired for practical applications. Co-MOF-derived Co3O4 is a promising gas-sensing material candidate because of its large surface area, ultrahigh porosities, and abundant oxygen defects. However, the advantages of Co-MOF precursor were limited by the traditional sensor fabrication methods. Moreover, the high resistance and poor surface activity of Co3O4 resulted in low gas-sensing performance at room temperature (RT). To overcome these challenges, in-situ sensors based on Co3O4 porous films with controlled nanoscale thickness were directly prepared on ceramic substrates by using Co-MOF films as precursors. To further improve the conductivity, SnO2 catalytic overlayers were introduced on top of Co3O4 sensors to construct SnO2/Co3O4 bilayer sensors, which were promising for triethylamine (TEA) detection at RT. As a result, the optimized SnO2/Co3O4 sensor exhibited a fast response/recovery rate (11 s/16 s), high selectivity, and a satisfactory sensitivity (150%) to TEA at RT. The enhanced gas-sensing performance could be attributed to the unique bilayer structures, improved conductivity, and synergistic effects of the SnO2 catalytic overlayers and Co3O4 sensing layers.

Controlled Synthesis and Enhanced Gas Sensing Performance of Zinc-Doped Indium Oxide Nanowires.

Indium oxide (In2O3) is a widely used n-type semiconductor for detection of pollutant gases; however, its gas selectivity and sensitivity have been suboptimal in previous studies. In this work, zinc-doped indium oxide nanowires with appropriate morphologies and high crystallinity were synthesized using chemical vapor deposition (CVD). An accurate method for electrical measurement was attained using a single nanowire microdevice, showing that electrical resistivity increased after doping with zinc. This is attributed to the lower valence of the dopant, which acts as an acceptor, leading to the decrease in electrical conductivity. X-ray photoelectron spectroscopy (XPS) analysis confirms the increased oxygen vacancies due to doping a suitable number of atoms, which altered oxygen adsorption on the nanowires and contributed to improved gas sensing performance. The sensing performance was evaluated using reducing gases, including carbon monoxide, acetone, and ethanol. Overall, the response of the doped nanowires was found to be higher than that of undoped nanowires at a low concentration (5 ppm) and low operating temperatures. At 300 °C, the gas sensing response of zinc-doped In2O3 nanowires was 13 times higher than that of undoped In2O3 nanowires. The study concludes that higher zinc doping concentration in In2O3 nanowires improves gas sensing properties by increasing oxygen vacancies after doping and enhancing gas molecule adsorption. With better response to reducing gases, zinc-doped In2O3 nanowires will be applicable in environmental detection and life science.

On-chip CuFe2O4 nanofiber for conductometric NO2 and H2S gas-sensors

xCuO-(1-x)Fe2O3 composite nanofibers (NFs) for gas-sensing applications were thoroughly investigated in this work employing on-chip electrospinning. The fabricated NFs had a characteristic spider-net-like morphology and had diameters of 50–100 nm. The NFs composed of nanograins with diameters ranging from 16 to 35 nm have multi-porous structures. The composite NFs enhanced sensor response compared to that of single metal oxides. At the optimal composition of 0.5CuO-0.5Fe2O3 NFs, which formed a complex oxide of copper ferrite (CuFe2O4), the sensor showed the highest response (15.3 and 10) to 1 ppm H2S gas at 350 °C and 10 ppm NO2 gas at 300 °C, respectively. Additionally, the detection of on-chip NF sensors to target gases was considerably impacted by the electrospinning time. The maximum response to H2S gas was achieved after 30 min of the electrospinning process, while that to NO2 gas is 10 min. The enhanced gas-sensing performance was attributed to nanograin-based NF structure, the formation of binary complex CuFe2O4 oxide, and the heterojunctions between CuFe2O4 and single oxide (CuO or α-Fe2O3) in composite NFs. Furthermore, the high sensitivity and selectivity of the CuFe2O4 NF sensor toward target gases are also discussed by using density functional theory (DFT) calculation.

ZnO nanorods assembled microflower-based gas sensor for detecting formaldehyde

Herein, we report the facile hydrothermal synthesis and characterizations of ZnO nanorods assembled microflowers and their efficient sensing application for the detection of formalydehyde gas. The synthesized ZnO microflowers were examined by several techniques. The scanning electron microscopy (SEM) was employed to evaluate the surface morphology, X-ray diffraction (XRD) analysis for the crystal structure while the Fourier transformation infrared (FTIR), and Raman-scattering spectroscopy were employed to understand the functional groups in the synthesized material. The optical properties were evaluated by UV-visible spectroscopy Furthermore, the synthesized ZnO microflowers were used as a functional material to fabricate formaldehyde gas sensor which exhibited a high gas response of 113.36 (Rg/Ra) towards 50 ppm formaldehyde gas at 200 °C. The observed response and recovery times for the fabricated sensor were ∼65 s and ∼117 s, respectively. Finally, the enhancement of gas-sensing performance and mechanism were thoroughly discussed. This work revealed that simply prepared ZnO nanostructures can be used to fabricate high-performance gas sensors.

Hollow porous GaN nanofibers gas sensor for superior stability and sub-ppb-level NO2 gas detection

Accurate detection of NO2 gas with low concentration and high stability is of great significance to ecological protection and human health. In this work, hollow porous GaN nanofibers were fabricated by a low-cost solvothermal method and controlled nitridation process. Systematic characterizations results demonstrate large specific surface and abundant adsorpation sites of the GaN nanofibers. Excellent NO2 sensing performances were tested at 200 °C, including the high sensitivity of 22.9 (200 ppm), rapid response time within 11 s, high selectivity, and low detection limit (0.5 ppb). Furthermore, the anti-interference ability, cross-sensitivity characteristics, and long-term stability of the sensor in the actual working environment were also systematically investigated. The surface depletion layer model and the change of the potential barrier were used to explain the enhanced gas-sensing performance. The fabricated GaN sensor offered a promising candidate for real-time monitoring of sub-ppb-level NO2 gas in actual environments.

Synthesis of ZIF-8 Coating on ZnO Nanorods for Enhanced Gas-Sensing Performance

Firstly, ZnO nanorods were prepared by a relatively simple method, and then self-sacrificed by a water bath heating method to generate a commonly used porous ZIF-8 and firmly attached to the ZnO surface. The successful synthesis of synthetic composites was demonstrated with various detection methods. The gas-sensing results show that the ZIF-8-coated ZnO with a core-shell structure exhibits better response than the raw ZnO because of the increased specific surface area and active sites.

SnO2 Quantum Dots-Functionalized MoO3 Nanobelts for High-Selectivity Ethylene Sensing

Highly selective and sensitive detection of the phytohormone ethylene, especially at low concentrations, is essential for control of plant growth, development, senescence, and fruit ripening. Metal oxide semiconductors exhibit excellent sensing properties due to their excellent physicochemical properties and unique structures. This study developed SnO2 quantum dots (QDs)-functionalized MoO3 nanobelts (NBs) for highly selective and sensitive ethylene detection. The prepared nanocomposite is composed of MoO3 NBs surface loaded with fine SnO2 QDs, and the n-n heterojunction is formed at the interface. Sensing properties of the SnO2 QDs/MoO3 NBs to ethylene are measured, and results reveal that 2.5%-SnO2 QDs/MoO3 NBs exhibited excellent response (100 ppm 40%), low detection limit (500 ppb), and selectivity to ethylene at a low operating temperature (150 °C) compared with pure MoO3 NBs and SnO2 QDs. The enhanced gas-sensing performance is explained based on the modulation of the interface barrier caused by the formation of n-n heterojunctions at the SnO2/MoO3 interface and the synergetic effect of these two materials. This heterojunction indicates that SnO2 QDs/MoO3 NBs are promising sensing materials for the ethylene gas sensor.

Fabrication of sheet-like ZnO/ZnS heterostructures with enhanced H2S sensing performance at low operation temperatures

A sheet-like ZnO/ZnS-based sensor with a sensitive response and excellent selectivity to H2S at low operation temperatures was prepared using a hydrothermal method combined with a sulfuration process. Meanwhile, x-ray diffraction, x-ray spectroscopy, scanning electron microscopy, and transmission electron microscopy measures were carried out to characterize the crystallographic information, elemental distribution, and microstructure of the sheet-like ZnO/ZnS. Results of the gas-sensing tests show that the response value of ZnO/ZnS-6 to 10 ppm of H2S reaches 90 at 100 °C, and the effective detection limit is as low as 1 ppm. The enhanced gas-sensing performance is attributed to the sheet-like microstructure and the formation of ZnO/ZnS heterojunctions. To H2S, the prepared ZnO/ZnS sensor shows satisfactory sensitivity, selectivity, and stability, and the lower heating temperature augurs wider potential applications.

Ag-Modified Porous Perovskite-Type LaFeO3 for Efficient Ethanol Detection.

Perovskite (ABO3) nanosheets with a high carrier mobility have been regarded as the best candidates for gas-sensitive materials arising from their exceptional crystal structure and physical–chemical properties that often exhibit good gas reactivity and stability. Herein, Ag in situ modified porous LaFeO3 nanosheets were synthesized by the simple and efficient graphene oxide (GO)-assisted co-precipitation method which was used for sensitive and selective ethanol detection. The Ag modification ratio was studied, and the best performance was obtained with 5% Ag modification. The Ag/LaFeO3 nanomaterials with high surface areas achieved a sensing response value (Rg/Ra) of 20.9 to 20 ppm ethanol at 180 °C with relatively fast response/recovery times (26/27 s). In addition, they showed significantly high selectivity for ethanol but only a slight response to other interfering gases. The enhanced gas-sensing performance was attributed to the combination of well-designed porous nanomaterials with noble metal sensitization. The new approach is provided for this strategy for the potential application of more P-type ABO3 perovskite-based gas-sensitive devices.

Single-Atom Tailoring of Two-Dimensional Atomic Crystals Enables Highly Efficient Detection and Pattern Recognition of Chemical Vapors

Low-dimensional semiconductor materials, such as single-walled carbon nanotubes, two-dimensional (2D) atomic crystals, and organic frameworks, have been widely adapted as ideal platforms to construct various chemo/biosensors with satisfying sensitivity. However, the general drawbacks in chemiresistive devices, including high operation temperatures, low response to low-polarity molecules, and poor selectivity, have limited their real-world applications. In this study, 2D materials (graphene, MoS2, and WSe2) were systematically functionalized with series of monodispersed single atomic sites (Pt, Co, and Ru) through a facile approach to construct single-atom sensors (SASs) for the detection of VOCs at room temperature. The structural and catalytic characteristics of SAs successfully translated into enhanced gas-sensing performance, with a 1-2 orders of magnitude increase in relative response to ethanol (@5 ppm) and acetone (@20 ppm) vapors (in all M-2D SASs as compared to pristine substrates), high selectivity to VOCs against relative humidity (M-WSe2 SASs), and fast response/recovery time (11/58 s for Pt-Graphene and 22/48 s for Pt-MoS2 to 50 ppm ethanol, 9/57 s for Pt-Graphene and 15/75 s for Pt-MoS2 to 200 ppm acetone) that are several times faster than the pristine 2D materials. Density functional theory (DFT) calculations revealed the signaling mechanism in SASs, and the data were further trained to build machine learning (ML) models for predicting the adsorption energies and sensing performance using the features of adsorption heights, metal charge, and charge transfer between the adsorbed VOCs and SASs sites. Finally, the rich combination of the metal single atoms and 2D atomic crystal supports were converted to cross-sensitive SA sensor array that allows for detection and identification of different VOCs.

Nanometer-Thick ZnO/SnO2 Heterostructures Grown on Alumina for H2S Sensing.

Designing heterostructure materials at the nanoscale is a well-known method to enhance gas sensing performance. In this study, a mixed solution of zinc chloride and tin (II) chloride dihydrate, dissolved in ethanol solvent, was used as the initial precursor for depositing the sensing layer on alumina substrates using the ultrasonic spray pyrolysis (USP) method. Several ZnO/SnO2 heterostructures were grown by applying different ratios in the initial precursors. These heterostructures were used as active materials for the sensing of H2S gas molecules. The results revealed that an increase in the zinc chloride in the USP precursor alters the H2S sensitivity of the sensor. The optimal working temperature was found to be 450 °C. The sensor, containing 5:1 (ZnCl2: SnCl2·2H2O) ratio in the USP precursor, demonstrates a higher response than the pure SnO2 (∼95 times) sample and other heterostructures. Later, the selectivity of the ZnO/SnO2 heterostructures toward 5 ppm NO2, 200 ppm methanol, and 100 ppm of CH4, acetone, and ethanol was also examined. The gas sensing mechanism of the ZnO/SnO2 was analyzed and the remarkably enhanced gas-sensing performance was mainly attributed to the heterostructure formation between ZnO and SnO2. The synthesized materials were also analyzed by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray, transmission electron microscopy, and X-ray photoelectron spectra to investigate the material distribution, grain size, and material quality of ZnO/SnO2 heterostructures.

Enhanced ethanol sensing performance of N-doped ZnO derived from ZIF-8

Metal oxides derived from metal-organic framework (MOF) have attracted considerable attention due to its excellent performance and unique structure. Doping is considered as an effective method to improve gas-sensing performance. However, nonmetal doped metal oxides derived from MOF as gas-sensing materials have not been reported. Within this work, N atoms were successfully doped into the lattice of ZnO nanoparticles using ZIF-8 as a self-sacrificial template through a thermal treatment process with the assistant of urea. The obtained N-ZnO exhibited competitive ethanol-sensing performance, in which the response value of N-ZnO-5 to 100 ppm ethanol reached 115 at 190 °C with a satisfactory selectivity. It was found that the N-doping in ZnO facilitated the formation of oxygen vacancy that promoted the generation of adsorbed oxygen species to achieve the enhanced gas-sensing performance. Besides, the larger specific surface area resulting from the size reduction during the urea-assisted pyrolysis process can also be responsible for the improving of the ethanol-sensing performance.

Formation of Cu/Cuo Nanostructure with Enhanced Gas Sensing Performance

Formation of Cu/Cuo Nanostructure with Enhanced Gas Sensing Performance

Enhanced hydrogen sensing performances of PdO nanoparticles-decorated ZnO flower-like nanostructures

In this work, PdO nanoparticles-decorated ZnO flower-like nanostructures (PdO/ZnO) were synthesized by a one-step facile hydrothermal route and investigated their performance for hydrogen sensing applications. The structural and morphological characterizations were examined by XRD, FESEM, EDS, TEM, and XPS techniques and confirmed the homogenous decoration of PdO nanoparticles on the surface of ZnO flowers. UV-Vis spectroscopy and photoluminescence (PL) spectroscopy were used to investigate the optical characteristics. The ZnO and PdO/ZnO sensors were explored towards different target gases such as hydrogen (H2), carbon monoxide (CO), nitrogen dioxide (NO2), and ethanol. The concentration range of target gases was 2–100 ppm at an operating temperature range of 200–400 °C. It was concluded that PdO/ZnO flowers sensor showed high sensitivity, a speedy response time (20 s), and recovery time (960 s) towards H2 at 350 °C in comparison to the ZnO sensor. In addition, the PdO decorated ZnO flowers-based sensor showed high selectivity towards H2 against CO, NO2, and ethanol. This enhanced gas-sensing performance of the PdO/ZnO sensor has been attributed to the catalytic effect of PdO nanoparticles, and the formation of the PdO-ZnO p-n heterojunction, and their unique flower-like nanostructures. As a result, our research shows that coating PdO on ZnO flowers is an effective technique to improve hydrogen gas sensing performance and can be employed in various applications. The synergist impact of PdO nanoparticles, the arrangement of the PdO-ZnO p-n heterojunction, and their remarkable blossom-like nanostructures were the significant elements for improved gas-detecting execution of PdO/ZnO sensor.

Low-Operating-Temperature NO2 Sensor Based on a CeO2/ZnO Heterojunction.

CeO2/ZnO-heterojunction-nanorod-array-based chemiresistive sensors were studied for their low-operating-temperature and gas-detecting characteristics. Arrays of CeO2/ZnO heterojunction nanorods were synthesized using anodic electrodeposition coating followed by hydrothermal treatment. The sensor based on this CeO2/ZnO heterojunction demonstrated a much higher sensitivity to NO2 at a low operating temperature (120 °C) than the pure-ZnO-based sensor. Moreover, even at room temperature (RT, 25 °C) the CeO2/ZnO-heterojunction-based sensor responds linearly and rapidly to NO2. This sensor’s reaction to interfering gases was substantially less than that of NO2, suggesting exceptional selectivity. Experimental results revealed that the enhanced gas-sensing performance at the low operating temperature of the CeO2/ZnO heterojunction due to the built-in field formed after the construction of heterojunctions provides additional carriers for ZnO. Thanks to more carriers in the ZnO conduction band, more oxygen and target gases can be adsorbed. This explains the enhanced gas sensitivity of the CeO2/ZnO heterojunction at low operating temperatures.

Visible-light-activated TiO2–NiFe2O4 heterojunction for detecting sub-ppm trimethylamine

Trimethylamine (TMA), which mainly emanates from decaying fish, is an important freshness indicator of seafood. In this work, a TiO2–NiFe2O4 heterojunction was successfully synthesized for TMA detection using a simple and efficient hydrothermal method. The materials were characterized using X-ray diffraction, scanning electron microscopy, photoluminescence spectroscopy, and ultraviolet–visible diffuse reflectance spectroscopy. The TiO2–NiFe2O4-based sensor exhibited the largest response (12) to 10 ppm of TMA at 307 ℃. The response was further improved under white-light irradiation, increasing from 2.5 to 4.5 as the TMA concentration approached 3 ppm. The enhanced gas-sensing performance of the TiO2–NiFe2O4 sensor under light irradiation was then explored by density functional theory (DFT) with an optical carrier. We believe that the developed strategy improves the gas-sensing ability for TMA detection and can potentially be used in gas sensors.