Future Gas Sensors Research Articles

Highly selective ethanol vapour sensing materials for a new generation of gas sensors based on molecularly imprinted polymers

A simple gas sensor consisting of a molecularly imprinted polymer-carbon nanotube composite cast onto a screen-printed electrode has been developed with extremely high selectivity for ethanol vapour over methanol vapour. Ethanol gas sensors typically display selectivity for ethanol over methanol in the range 2–4 times, while the mean ratio of ethanol to methanol response observed with the described device was 672. This selectivity was achieved under ambient conditions. Additionally, the molecularly imprinted polymer was produced using reagents previously applied in the development of a device selective for methanol, with only the template being changed. This demonstrates the versatility of molecular imprinting and provides a foundation for their greater integration into future gas sensors.

Gas Sensing Performance of Zinc Oxide Nanoparticles Fabricated via Ochradenus baccatus Leaf

ZnO nanoparticles (NPs) were prepared by green synthesis using plant leaf extraction of Ochradenus baccatus and characterized by XRD, FESEM, HRTEM, and Raman spectroscopy techniques. Since elevated CO levels have been associated with inflammatory conditions, cardiovascular diseases, and respiratory disorders and the methane gas primarily produced by gut microbiota and linked to gastrointestinal disorders and other abnormal methane levels in breath samples, the nanoparticles were applied for gas sensor fabrication. Thus, the gas sensors fabricated using ZnO nanoparticles were investigated for CH4, H2, CO, and NO2 gases. The gas sensing was performed for the fabricated sensors at various operating temperatures and gas concentrations. Interestingly, leaf-extracted green synthesized ZnO NPs were more sensitive to CH4, CO, and NO2 gases than to H2. The results of sensing studies revealed that the nanoparticles exhibit a selectivity toward gas depending on the gas type. The sensor response was also studied against the humidity. These findings bridge between the laboratory and industry sectors for future gas sensors development, which can be used for exhaled breath analysis and serve as potential diagnostic tools for highly sensitive contagious diseases.

Theoretical study of adsorption properties and electrical transport performance of toxic gas molecules on novel orthorhombic BN monolayer semiconductor

The adsorption properties of toxic gases on the surface of low-dimensional nanomaterials are a research hot topic and key issue for developing semiconductor sensors to detect toxic gas molecules. Recently, a novel orthorhombic BN monolayer has attracted extensive attention from researchers. Using first principles calculations, we investigate the adsorption properties of typical toxic gas molecules, such as CO, H<sub>2</sub>S, NH<sub>3</sub>, NO, NO<sub>2</sub>, and SO<sub>2</sub> molecules, on the surface of two-dimensional (2D) orthorhombic BN monolayer adsorption. The calculated adsorption energy show that the adsorptions of the above six molecules on the surface of BN monolayer are energy-favorable exothermic processes. It is found that NO<sub>2</sub> and NH<sub>3</sub> molecules are of chemical adsorption, while other systems are of physical adsorption, and NO adsorbing system exhibits a spin-polarized electronic band structure. The calculated density of states reveals that the adsorption of NO molecule and SO<sub>2</sub> molecule have significant influences on the electronic structure near the Fermi level. Moreover, the adsorption of the NO<sub>2</sub> molecule on the substrate exhibits remarkable variation of the work function, suggesting that the o-BN monolayer possesses excellent selectivity and sensitivity to NO<sub>2</sub> molecule. In addition, we use first principles combined with non-equilibrium Green’s function to simulate the electrical transport properties of monolayered o-BN semiconductor based nanodevice with adsorption of typical toxic gas molecules. The <i>I-V</i><sub>b</sub> curve shows that the current through the nanodevice is 6500 nA for the NO<sub>2</sub> molecule adsorbing system under 1 V bias voltage. The calculation results reveal that the adsorption of NO<sub>2</sub> molecule on the o-BN monolayer can significantly enhance its electrical transport performance, and the o-BN monolayer possesses excellent sensitivity and selectivity to the NO<sub>2</sub> gas molecule. The work function and the charge transfer can be effectively manipulated by tensile strain, indicating its potential application in anisotropic electronics. Our results indicate that the o-BN monolayer has excellent adsorption performance to toxic gases, showing its practical application in capturing toxic gas molecules as a gas sensor in future.

Enhanced hydrogen gas sensing through the utilization of a hybrid nanostructure combining ZnO nanotubes and HiPIMS Cu3N thin film

Hydrogen (H2), a renewable energy source, has emerged as a promising and clean fuel alternative to conventional fossil fuels. It has garnered significant attention from researchers due to its wide-ranging applications in promoting sustainable growth. However, accurately detecting atmospheric H2 levels becomes crucial due to its flammability. This study introduces a room temperature-based hydrogen gas sensor composed of vertically hydrothermally grown ZnO nanotubes (ZNTs) with or without the incorporation of a Cu3N thin film, creating a hybrid nanostructure. The ZNTs and ZNTs/Cu3N nanohybrid samples were fabricated with multi-finger configurations of Palladium (Pd) interdigitated electrodes. The ZNTs/Cu3N nanohybrid exhibited exceptional sensing capabilities compared to those of the as-prepared ZNTs. It was tested with varying concentrations of H2, ranging from 10 to 500 ppm, at room temperature. The ZNTs/Cu3N nanohybrid's superior performance is due to its larger surface area, enabling improved gas ion adsorption, increased oxygen vacancies, and more surface-active sites compared to ZNTs alone. The Cu3N layer beneath the ZNTs greatly impacts the gas sensor's performance by lowering the ZNTs/Cu3N nanohybrid's band gap (1.85 eV), enhancing its H2 detection capabilities. The ZNTs/Cu3N nanohybrid demonstrates great potential for future gas sensor applications, offering valuable insights for advanced sensing technology development.

Experimental Investigation of Pure Spinel Mn3O4 Properties Synthesized through Chemical Spray Pyrolysis for Future Gas Sensor Application

AbstractThe semiconductor realization is a very significant stage in gas sensor application. Herein, the Mn3O4 semiconductor was deposited using chemical spray pyrolysis. The effect of deposition temperature on structural, vibrational optical and electrical Mn3O4 thin layers properties were investigated through: X‐ray diffraction, Raman spectroscopy, UV‐visible spectrophotometer, and two points electrometers respectively. The X‐ray diffraction showed the appearance of spinel phase of tetragonal Mn3O4 with strong formation direction along (101) plan and without any secondary phase indicating the formation of pure Mn3O4. The Raman spectroscopy confirmed the results obtained in XRD and certified the high‐quality formation of Mn3O4. In addition, the crystallinity improvement (the increase of crystallite size and the decrease of dislocation density) was caused by the increasing of deposition temperature from 350 °C to 450 °C. Optical properties such as transmittance, absorbance and band gap energy were extracted by UV‐Visible spectrophotometer. Thus, low transmittance, high absorbance and small band gap energy were observed at the highest substrate temperature (450 °C). The electrical conductivity showed good values between 4.83 and 13.89 mS.cm−1. These properties make Mn3O4 an appropriate material to be used as a sensitive layer in gas sensors applications.

The High Efficient Investigations of Properties of Co3O4 Nanostructured by Facile Spray Pyrolysis Technique for Future Gas Sensors Application

Herein, the cobalt oxide thin films are elaborated by spray pyrolysis technique. The effect of temperature of substrates on several properties of cobalt oxide is studied. The thin layers are characterized by using X‐ray diffraction (XRD), Raman spectrometry (RS), and UV–vis spectrophotometer. The XRD analysis shows that Co3O4 thin layers have been formed along <111> preferential orientation. The RS displays the characteristic vibration modes of cobalt oxide phase, which confirms the formation of a single phase of spinel Co3O4 thin layers. The UV–vis spectrophotometer allows us to investigate the optical properties such as the absorbance, the transmittance, and the optical bandgap. The variation of electrical properties with the variation of temperature deposition confirms the high impact of the effect that study to make the cobalt oxide an important candidate for gas sensor devices.

Study on graphene grown on SiC substrate by heat-sublimation method applied for NO2 gas sensor fabrication

This article aimed to build a low-cost system and synthesized graphene on 4H-silicon carbide (4H-SiC) wafer by the thermal sublimation method toward the gas-sensing applications. The advantage of this epitaxy growth obtained the large-area graphene sheet on 4H-SiC substrate. The graphene layers were grown directly on a semiconductor material without the complicated transfer process as previous methods, making this method suitable to fabricate the electronic devices, MEMS, and sensors. The characterization of graphene on 4H-SiC (Graphene@SiC) was analyzed by various methods of surface morphology, structure, and spectroscopy. The low sheet resistance ([Formula: see text]) with large area of Graphene@SiC had the attention for application in gas sensor. While exposed to the nitrogen dioxide gas, the resistivity of Graphene@SiC sample also was changed. It is the hope of a designed gas sensor in future.

Oxygen vacancy‐rich ZnO nanorods‐based MEMS sensors for swift trace ethanol recognition

AbstractEthanol vapor plays a significant role in the aspects of human health and industrial production, thus necessitating a swift, sensitive, and low‐power ethanol detection in the field of future gas sensors. In this work, we prepared micro–electro–mechanical system ethanol sensors based on ZnO nanorods (NRs) and nanoparticles (NPs) for trace ethanol detection. Both ZnO samples were synthesized by a facile hydrothermal method. The comparison results exhibited that ZnO NRs based sensors prevailed over NPs‐based counterparts in terms of sensitivity, optimal operation temperature, and reaction speeds. Briefly, that ZnO NRs‐based sensors presented a large response (11.5 toward 5 ppm), fast response/recovery times (5 s/5 s), ultralow detection limit (400 ppb), and tiny power consumption (30 mW) at 245°C, surpassing most of recently reported ethanol sensors and commercial products based metal oxides. The abundant oxygen vacancies, large specific surface area, and porous structure were primarily responsible for the excellent sensor performance. This work also offers a facile and competitive approach to realize a sensitive and swift trace ethanol recognition with minimal power consumption, catering for the demanding requirements of future gas sensors in the fields of wearable devices and Internet of Things.

Toward a Gas Sensor Interface Circuit—A Review

With the development of science and technology, gas sensors have gradually expanded to many vertical fields. However, each application requires different technical requirements for gas sensors, such as low cost, small size, high sensitivity, high precision, and low power consumption. To create gas sensors that meet the performance requirements, researchers worldwide are working on solutions in fields such as sensitive materials, sensor arrays, and interface circuits. However, there are bottlenecks in the research of interface circuits, which limits the volume, power consumption, and intelligent design development of gas sensors. Therefore, this article reviews various types of gas sensors and interface circuits implemented with different technologies, analyzes their research significance in various areas, and provides ideas for future gas sensor research directions.

Mesoporous WS2/MoO3 Hybrids for High-Performance Trace Ammonia Detection.

Mesoporous WS2/MoO3 hybrids were synthesized by a facile two-step and additive-free hydrothermal approach and employed for high-performance trace ammonia gas (NH3) detection. Compared with single WS2 and MoO3 counterparts, WS2/MoO3 sensors exhibited an improvement in NH3-sensing performance at room temperature (22 ± 3 °C). Typically, the optimal WS2/MoO3 sensor showed a higher and quicker response of 31.58% within 57 s toward 3 ppm of NH3, which was 17.7- and 57.4-fold larger than that of pure MoO3 (1.78% within 251 s) and WS2 (0.55% within 153 s) ones. Meanwhile, good reversibility, sensitivity, and selectivity, reliable long-term stability, and the lowest detection limit of 9.0 ppb were achieved. These superior properties were probably ascribed to numerous heterojunctions favorable for additional carrier-concentration modulation via the synergetic effect between WS2 and MoO3 components and the large specific surface area beneficial for richer sorption sites and faster molecular transfer at room temperature. Such achievements also imply that the designed WS2/MoO3 heterostructure nanomaterials have the potential in achieving trace NH3 recognition catering for the requirements of high sensitivity and low power consumption in future gas sensors.

Self-powered and flexible gas sensor using defect-engineered WS2/G heterostructure

Two-dimensional (2D) Transition Metal Dichalcogenides (TMDCs) are considered leading candidates for ultrathin and wearable gas sensors, owing to their unique properties, including high sensitivity to gas adsorption and flexibility. However, the ongoing Internet of Things (IoT) revolution further puts forward requirements of self-contained power for future gas sensors, and the study of the self-power performance of 2D TMDCs gas sensors to date has lagged behind other characteristics. Here, we demonstrate a photovoltaic self-powered gas sensor based on the defect-engineered WS2/G heterostructure, exhibiting excellent sensing performances, including ultra-sensitivity, and fast response. Defects induced by the ion irradiation engineer the homogeneous WS2/G into a heterogeneous WS2–0.2/G-WS2/G forming a Schottky diode with photovoltaic functions. Driven by the indoor light (500 Lx, 0.9 mW/cm2), this WS2–0.2/G-WS2/G heterostructure identifies NO2 gas by the positive change of the photocurrent and the limit of detection (LOD) toward NO2 is 50 ppb with a response time of 110 s. The sensing performance of the defect-engineered heterostructure remains stable even after 1000 cycles of bending, confirming the application potential as a flexible device. This work presents an efficient strategy for preparing the self-powered gas sensor based on two-dimensional materials, meeting the emerging Internet of Things requirements.

Optimization with Taguchi Approach to Prepare Pure TiO2 Thin Films for Future Gas Sensor Application

Optimization with Taguchi Approach to Prepare Pure TiO2 Thin Films for Future Gas Sensor Application

Effects of electric field and biaxial strain on the (NO2, NO, O2, and SO2) gas adsorption properties of Sc2CO2 monolayer

Herein, we present a first-principles study of the effects of electric field and biaxial strain on the adsorption properties of Sc2CO2 monolayer in respect of O2, SO2, NO, and NO2 gases. We calculated the optimized configuration, adsorption energy, charge transfer, band structure, and densities of states of the adsorption systems under various electric fields and biaxial strains. We found that the adsorption intensities of NO2, NO, O2, and SO2 on the Sc2CO2 monolayer decrease with increasing the positive electric field. However, the electric field of 0.408 ​V/Å is not large enough to cause the desorption of O2, SO2, NO, and NO2 molecules, and it does not change their chemisorption nature on the Sc2CO2 monolayer. On the other hand, the gas adsorption intensity increases with increasing the biaxial strain from −10% to 10%. The Sc2CO2 monolayer with the −10% compressive strain physisorbs NO2, NO, O2, and SO2 molecules as compared to the chemisorption on the pristine one. The biaxial strains ϵ≥2% change the selectivity in gas adsorption of Sc2CO2 monolayer to NO2 molecule, compared with the O2 molecule on the pristine Sc2CO2 monolayer. The present work suggests an effective way to obtain attractive gas adsorption properties of two-dimensional materials using strain engineering for future gas sensors, gas capture or toxic gas filtration applications.

Copper Oxide/Functionalized Graphene Hybrid Nanostructures for Room Temperature Gas Sensing Applications

Oxide semiconductors are conventionally used as sensing materials in gas sensors, however, there are limitations on the detection of gases at room temperature (RT). In this work, a hybrid of copper oxide (CuO) with functionalized graphene (rGO) is proposed to achieve gas sensing at RT. The combination of a high surface area and the presence of many functional groups in the CuO/rGO hybrid material makes it highly sensitive for gas absorption and desorption. To prepare the hybrid material, a copper oxide suspension synthesized using a copper acetate precursor is added to a graphene oxide solution during its reduction using ascorbic acid. Material properties of the CuO/rGO hybrid and its drop-casted thin-films are investigated using Raman, FTIR, SEM, TEM, and four-point probe measurement systems. We found that the hybrid material was enriched with oxygen functional groups (OFGs) and defective sites, along with good electrical conductivity (Sheet resistance~1.5 kΩ/□). The fabricated QCM (quartz crystal microbalance) sensor with a thin layer of the CuO/rGO hybrid demonstrated a high sensing response which was twice the response of the rGO-based sensor for CO2 gas at RT. We believe that the CuO/rGO hybrid is highly suitable for existing and future gas sensors used for domestic and industrial safety.

Hierarchical CuO nanostructured materials for acetaldehyde sensor application

A nanocrystalline CuO with mixed morphologies (nanorods, nanoplates and nanoparticles) were prepared using simple room temperature wet chemical synthesis route. The nanostructured CuO material was characterized using FESEM, TEM, EDS, elemental mapping, UV–visible spectroscopy, and BET surface area techniques for various physicochemical characteristics. The gas sensor device was fabricated using CuO nano-powder and its acetaldehyde gas sensing properties was investigated. The CuO sensor showed excellent sensing response towards 20–100 ppm acetaldehyde. The acetaldehyde response of the CuO sensor was recorded at various operating temperatures as well as concentrations. The responses of 418% and 115% were noted for 100 ppm and 20 ppm acetaldehyde concentration at 180 °C respectively. The higher selectivity of the CuO sensor was observed towards acetaldehyde among various gases. The transient response of the sensor was observed to be consistent with concentrations. The dynamic repetitive response of the sensor was tested at 100 ppm acetaldehyde that revealed to be same. The sensor's stability was tested and observed to be quite stable. A brief acetaldehyde sensing mechanism for CuO sensor was elucidated. The easy and large-scale formation of CuO nanostructures without growth controlling surfactants, and the good selectivity of the high response acetaldehyde sensor at relatively low operating temperatures may pave pathway for future gas sensor technology.

Controlled preparation and gas sensitive properties of two-dimensional and cubic structure ZnSnO3

Two-dimensional (2D) ZnSnO3 is a promising candidate for future gas sensors due to its high chemical response and excellent electronic properties. However, the preparation of 2D ZnSnO3 nanosheets by utilizing soluble inorganic salts and nonorganic solvents remains a challenge. In this work, 2D ZnSnO3 was synthesized via a facile graphene oxide (GO)-assisted co-precipitation method, in which inorganic salts in the aqueous phase replaced metal organic salts in a non-aqueous system. Meanwhile, a “dissolution and recrystallization” mechanism was proposed to explain the transformation from 3D nanocubes to 2D nanosheets. In comparison, the 2D ZnSnO3 nanosheets showed a higher response to formaldehyde (HCHO) at low operating temperature (100 °C). The response (Ra/Rg) of the 2D ZnSnO3 sensor to 10 ppm HCHO was as high as 57, which was approximately 5 times the response of the ZnSnO3 nanocubes sensor. However, the ZnSnO3 nanocubes sensor showed better gas sensing performance to ethanol at high temperature (200 °C). Different gas-sensitive properties were attributed to the different gas diffusion and adsorption processes caused by the morphology and nanostructure. Moreover, both sensors could detect either 0.1 ppm HCHO or ethanol at their optimum operating temperature. This work presents a relatively economical method to prepare 2D compound metal oxides, provides a novel “dissolution and recrystallization” mechanism for 2D multi-metal oxide preparation, and sheds light on the great potential of high-efficiency HCHO and/or ethanol gas sensors.

Effect of MoS2 solution on reducing the wall thickness of ZnO nanotubes to enhance their hydrogen gas sensing properties

Herein, we report on the facile soft chemical synthesis of hybrid interlinked ZnO nanotubes (HIZNTs) with dispersed molybdenum disulfide (MoS2). Nanostructures were grown under two different conditions, with and without the addition of MoS2 during the hydrothermal process. Systematic structural and material analysis of the MoS2-HIZNTs was conducted. Then, both the MoS2-HIZNTs and as-prepared ZnO nanotubes were fabricated with an interdigitated Pt electrode to produce materials for subsequent gas sensing studies. Remarkably, the MoS2-HIZNT hybrid materials exhibited an excellent sensing capability of 51.1%, significantly higher than that of the as-prepared ZNTs. The MoS2-HIZNT samples were tested using various concentrations of H2 from 10 to 500 ppm at room temperature. It is presumed that the larger surface area exhibited by the MoS2-HIZNTs allowed the adsorption of more gas ions leading to was a linear increase in oxygen vacancies and surface-active sites compared to the ZNTs. Also, the addition of MoS2 had a significant influence on the morphology, with a reduction in the wall thickness of the etched tubes. This reduced wall thickness of the MoS2-HIZNTs produced a striking improvement in the mobility of the electrons leading to no trapping of electrons at numerous sites and improved gas sensing performance. The results demonstrate the excellent MoS2-HIZNT hybrid materials for future gas sensor applications.

Tuning the structural, electronic and adsorption properties of Au-embedded 2D WSe2 and Arsenene nanosheets: A DFT study

In this paper, we examined the adsorption of NO2, NO, and CO molecules on the Au-adsorbed WSe2 and arsenene nanosheets using the density functional theory calculations. The adsorption of Au on the hollow sites of the nanosheets was considered. Au-embedded WSe2 and arsenene nanosheets have higher sensitivity than the perfect ones for application as gas sensor for the detection of NO2, NO, and CO molecules. Based on our calculations, we found that Au-adsorbed arsenene and WSe2 systems can be effectively applied for practical sensing purposes. We also found that Au-WSe2 nanosheets strongly satisfy the requirements for toxic gas sensing due to their higher binding energies and consequently improved electronic structure and adsorption performance as compared to the Au-arsenene nanosheets. Our calculated results suggested that Au-arsenene and Au-WSe2 systems are promising nanomaterials for future gas sensor systems.

Effect of annealing time on structural and optical proprieties of TiO2 thin films elaborated by spray pyrolysis technique for future gas sensor application

In this study we tested the effect of annealing time on some properties of titanium dioxide thin films, elaborated by the chemical technique spray pyrolysis deposited on the glass with a fixed temperature. An annealing was carried out at a temperature of 500 °C for three times 1 h, 2 h and 3 h. The structural characterization with X-ray diffraction (XRD) shows a significant increase in the crystallite size and also the preferential peak intensity of TiO2 of the anatase phase if the annealing time is decreased, the typical Scanning Electron Microscopy (SEM) image shows the morphological properties of TiO2 thin film and the optical measurement with UV–Visible spectrophotometer represent the semiconductor properties of TiO2 with an optical band gap that varies with the variation of the annealing time from 3.30 to 3.26 eV for 3 h to 2 h and from 3.26 to 3.19 eV for 2 h to 1 h.

Selective H2S sensing without external heat by a synergy effect in self-heated CuO-functionalized SnO2-ZnO core-shell nanowires

Future gas sensors require minimal power consumption to enable their integration into portable electronics such as smart mobile phones. We developed H2S gas sensors based on a self-heating effect using metal oxide nanowires (NWs). We fabricated bare SnO2 NWs, CuO functionalized SnO2 NWs, and a CuO functionalized SnO2-ZnO core-shell (C–S) NW sensor, and tested their sensor response towards H2S gas by applying different external voltages at room temperature. It was found that the CuO functionalized SnO2-ZnO C-S NW gas sensor had higher response to H2S gas relative to other tested sensors due to higher self-heating effect, formation of heterojunctions, phase transformation, and spillover effects of CuO nanoparticles. Without external heat, the selective H2S detection obtained in this work demonstrates the possibility of embedding low power consumption gas sensors in portable devices for detection of H2S as a biomarker for early diagnosis of diseases.