Metal Oxide-based Gas Sensors Research Articles

Recent advances in different materials for moisture resistance of metal oxide-based gas sensors: A review

Recent advances in different materials for moisture resistance of metal oxide-based gas sensors: A review

Ultrasensitive Chemiresistive Gas Sensors Based on Dual-Mesoporous Zinc Stannate Composites for Room Temperature Rice Quality Monitoring

The integration of dual-mesoporous structures, the construction of heterojunctions, and the incorporation of highly concentrated oxygen vacancies are pivotal for advancing metal oxide-based gas sensors. Nonetheless, achieving an optimal design that simultaneously combines mesoporous structures, precise heterojunction modulation, and controlled oxygen vacancies through a one-step process remains challenging. This study proposes an innovative method for fabricating zinc stannate semiconductors featuring dual-mesoporous structures and tunable oxygen vacancies via a direct solution precursor plasma spray technique. As a proof of concept, the resulting zinc stannate-based coatings are applied to detect 2-undecanone, a key biomarker for rice aging. Remarkably, the zinc oxide/zinc stannate heterojunctions with a well-defined secondary pore structure exhibit exceptional gas-sensing performance for 2-undecanone at room temperature. Furthermore, practical experiments indicate that the developed sensor effectively identifies adulteration in various rice varieties. These results underscore the potential of this method for designing metal oxides with tailored properties for high-performance gas sensors. The enhanced adsorption capacity and dual-mesoporous features of this semiconductor make it a promising candidate for sensing applications in agricultural food safety inspections.

Oxygen Vacancy Mediated-Bismuth Molybdate/Graphitic Carbon Nitride Type II Heterojunction Chemiresistor for Efficient NH3 Detection at Room Temperature.

Metal oxide-based chemiresistive gas sensors are expected to play a significant role in assessing human health and evaluating food spoilage. However, the high operating temperature, insufficient limit of detection (LOD), and long response/recovery time restrict their broad application. Herein, 3D Bi2MoO6/2D Eg-C3N4 heterocomposites are developed for advanced NH3 gas sensors with RT operational mode. Utilizing the synergetic engineering of micro-nanostructure, surface oxygen vacancies, and well-defined Type II n-n heterojunctions, BMOCN3 demonstrated superior NH3 sensing properties at 23 °C, including the high response (S = 13.6 at 10 ppm), fast response/recovery speed (8/30 s), excellent selectivity, and low LOD (166 ppb). Based on the experimental, DFT, and MD studies, the improved sensing performance can be ascribed to accelerated charge transfer, superior redox capacity, and improved adsorption/desorption kinetics. Moreover, the practical application in rapid exhaled NH3 biomarker detection of the as-fabricated gas sensor was preliminarily verified. This work highlights that the novel synergetic engineering can effectively modulate the electronic structure and charge transfer, offering a rational solution for room temperature chemiresistive gas sensors.

Metal-Organic Framework-Derived Ni-Doped Indium Oxide Nanorods for Parts per Billion-Level Nitrogen Dioxide Gas Sensing at High Humidity.

Detecting parts per billion (ppb)-level nitrogen dioxide in high-moisture environments at room temperature without reducing sensing performance is a well-recognized significant challenge for metal oxide-based gas sensors. In this study, metal-organic framework-derived nickel-doped indium oxide (Ni-doped In2O3) mesoporous nanorods were prepared by a solvothermal method combined with the calcination process. The sensors prepared using the obtained Ni-doped In2O3 nanorods showcase an ultrahigh response, low detection limit, and excellent selectivity. Moreover, the abundant active sites triggered by nickel doping and the capillary enhancement effect caused by mesopores endow the sensor with ppb-level (20 ppb) NO2 detection capability in high-moisture environments (95% RH) at room temperature. With the increase in humidity, the carrier concentration of the sensor increases, and the nitric acid generated by nitrogen dioxide dissolved in water can be completely ionized in water and has high conductivity. Therefore, the gas response of the sensors increases with the increase in humidity. This study establishes a promising approach for the development of trace nitrogen dioxide-sensing devices that are resilient in high-humidity environments.

Facile synthesis of silver and copper modified graphitic carbon nitride for volatile organic compounds sensing

Facile synthesis of silver and copper modified graphitic carbon nitride for volatile organic compounds sensing

Intelligent Evaluation and Dynamic Prediction of Oysters Freshness with Electronic Nose Non-Destructive Monitoring and Machine Learning.

Physiological and environmental fluctuations in the oyster cold chain can lead to quality deterioration, highlighting the importance of monitoring and evaluating oyster freshness. In this study, an electronic nose was developed using ten partially selective metal oxide-based gas sensors for rapid freshness assessment. Simultaneous analyses, including GC-MS, TVBN, microorganism, texture, and sensory evaluations, were conducted to assess the quality status of oysters. Real-time electronic nose measurements were taken at various storage temperatures (4 °C, 12 °C, 20 °C, 28 °C) to thoroughly investigate quality changes under different storage conditions. Principal component analysis was utilized to reduce the 10-dimensional vectors to 3-dimensional vectors, enabling the clustering of samples into fresh, sub-fresh, and decayed categories. A GA-BP neural network model based on these three classes achieved a test data accuracy rate exceeding 93%. Expert input was solicited for performance analysis and optimization suggestions enhanced the efficiency and applicability of the established prediction system. The results demonstrate that combining an electronic nose with quality indices is an effective approach for diagnosing oyster spoilage and mitigating quality and safety risks in the oyster industry.

Ir doping improved oxygen activation of WO3 for boosting acetone sensing performance at low working temperature

Ir doping improved oxygen activation of WO3 for boosting acetone sensing performance at low working temperature

Defect-enabled room-temperature acetone gas sensors based on Zn-doped cauliflower-like bismuth oxide

Defect-enabled room-temperature acetone gas sensors based on Zn-doped cauliflower-like bismuth oxide

Advances in Synthesis and Applications of Single-Atom Catalysts for Metal Oxide-Based Gas Sensors.

As a stable, low-cost, environment-friendly, and gas-sensitive material, semiconductor metal oxides have been widely used for gas sensing. In the past few years, single-atom catalysts (SACs) have gained increasing attention in the field of gas sensing with the advantages of maximized atomic utilization and unique electronic and chemical properties and have successfully been applied to enhance the detection sensitivity and selectivity of metal oxide gas sensors. However, the application of SACs in gas sensors is still in its infancy. Herein, we critically review the recent advances and current status of single-atom catalysts in metal oxide gas sensors, providing some suggestions for the development of this field. The synthesis methods and characterization techniques of SAC-modified metal oxides are summarized. The interactions between SACs and metal oxides are crucial for the stable loading of single-atom catalysts and for improving gas-sensitive performance. Then, the current application progress of various SACs (Au, Pt, Cu, Ni, etc.) in metal oxide gas sensors is introduced. Finally, the challenges and perspectives of SACs in metal oxide gas sensors are presented.

Metal oxide-based gas sensor array for VOCs determination in complex mixtures using machine learning

Detection of volatile organic compounds (VOCs) from the breath is becoming a viable route for the early detection of diseases non-invasively. This paper presents a sensor array of 3 component metal oxides that give maximal cross-sensitivity and can successfully use machine learning methods to identify four distinct VOCs in a mixture. The metal oxide sensor array comprises NiO-Au (ohmic), CuO-Au (Schottky), and ZnO–Au (Schottky) sensors made by the DC reactive sputtering method and having a film thickness of 80–100 nm. The NiO and CuO films have ultrafine particle sizes of < 50 nm and rough surface texture, while ZnO films consist of nanoscale platelets. This array was subjected to various VOC concentrations, including ethanol, acetone, toluene, and chloroform, one by one and in a pair/mix of gases. Thus, the response values show severe interference and departure from commonly observed power law behavior. The dataset obtained from individual gases and their mixtures were analyzed using multiple machine learning algorithms, such as Random Forest (RF), K-Nearest Neighbor (KNN), Decision Tree, Linear Regression, Logistic Regression, Naive Bayes, Linear Discriminant Analysis, Artificial Neural Network, and Support Vector Machine. KNN and RF have shown more than 99% accuracy in classifying different varying chemicals in the gas mixtures. In regression analysis, KNN has delivered the best results with an R2 value of more than 0.99 and LOD of 0.012 ppm, 0.015 ppm, 0.014 ppm, and 0.025 ppm for predicting the concentrations of acetone, toluene, ethanol, and chloroform, respectively, in complex mixtures. Therefore, it is demonstrated that the array utilizing the provided algorithms can classify and predict the concentrations of the four gases simultaneously for disease diagnosis and treatment monitoring.Graphical

Enhanced hydrogen gas sensing characteristics of CuO/ZnO heterojunction for thickness-dependence and its application

Enhanced hydrogen gas sensing characteristics of CuO/ZnO heterojunction for thickness-dependence and its application

Lacunary polyoxometalates-induced controllable synthesis of Fe2O3/Si-FeWO4 heterostructure nanotubes for selective sensing of m-xylene

Lacunary polyoxometalates-induced controllable synthesis of Fe2O3/Si-FeWO4 heterostructure nanotubes for selective sensing of m-xylene

Facile preparation of Au-loaded mesoporous In2O3 nanoparticles with improved ethanol sensing performance.

The in situ monitoring of toxic volatile organic compound gases using metal oxide-based gas sensors is still challenging. Herein, mesoporous In2O3 nanoparticles, assembled using smaller nanoparticles, were synthesized via a facile solvothermal method and used to load Au nanoparticles to prepare mesoporous Au/In2O3 for ethanol detection. The obtained In2O3 and Au/In2O3 were meticulously analysed by XRD, SEM, BET, TEM and XPS techniques. It was revealed that Au nanoparticles were uniformly distributed on mesoporous In2O3 nanoparticles. Notably, the obtained mesoporous 1% Au/In2O3 is highly sensitive to ethanol gas at an optimal working temperature of 180 °C, showing a response of 55 to 50 ppm of ethanol, which is considerably higher compared to that of In2O3 nanoparticles. The significantly enhanced sensitivity results from the electronic and chemical sensitization effects of Au nanoparticles. Moreover, the mesoporous Au/In2O3 nanoparticles also showed eminent selectivity, short response/recovery time, low detection limit, good linear relationship, superb repeatability, and wonderful long-term stability, suggesting that Au/In2O3 nanoparticles have great potential application for in situ monitoring of ethanol gas.

Study of the response behavior of a CdS-SnO2 thick film for high selectivity towards propanol gas.

Gas monitoring devices are in demand for a rapidly growing range of applications. Metal oxide-based gas sensors have been extensively used for the detection of toxic pollutant gases, combustible gases, and hydrocarbon vapors. The sensitivity for a low concentration and observed response and the recovery times of the reported gas sensors are not satisfactory, and it needs further detailed studies. In the present work, undoped SnO2 and cadmium sulfide (CdS)-doped SnO2 thick films were fabricated using the screen-printing method to study their sensing behavior towards tested organic vapors such as acetone, propanol, and ethanol. The sensing properties of fabricated sensors were investigated for the test gases, i.e. acetone, propanol, and ethanol, at an elevated temperature of 473 K. It was observed that the 2 wt% CdS-doped SnO2 sensor showed a maximum response (78%) and was highly selective (44.6%) to propanol over acetone and ethanol. The results showed that the diminution of the SnO2 crystallite size with the CdS content leads to an improvement in the response of the SnO2 sensor for the tested gases. The microstructural properties are also correlated to the sensing behavior. The measurement showed that the CdS-SnO2 thick film sensor is highly sensitive. At the same time, it is more selective to propanol than the other test gases, ethanol and acetone.

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.

Low-Power Consumption IGZO Memristor-Based Gas Sensor Embedded in an Internet of Things Monitoring System for Isopropanol Alcohol Gas.

Low-power-consumption gas sensors are crucial for diverse applications, including environmental monitoring and portable Internet of Things (IoT) systems. However, the desorption and adsorption characteristics of conventional metal oxide-based gas sensors require supplementary equipment, such as heaters, which is not optimal for low-power IoT monitoring systems. Memristor-based sensors (gasistors) have been investigated as innovative gas sensors owing to their advantages, including high response, low power consumption, and room-temperature (RT) operation. Based on IGZO, the proposed isopropanol alcohol (IPA) gas sensor demonstrates a detection speed of 105 s and a high response of 55.15 for 50 ppm of IPA gas at RT. Moreover, rapid recovery to the initial state was achievable in 50 μs using pulsed voltage and without gas purging. Finally, a low-power circuit module was integrated for wireless signal transmission and processing to ensure IoT compatibility. The stability of sensing results from gasistors based on IGZO has been demonstrated, even when integrated into IoT systems. This enables energy-efficient gas analysis and real-time monitoring at ~0.34 mW, supporting recovery via pulse bias. This research offers practical insights into IoT gas detection, presenting a wireless sensing system for sensitive, low-powered sensors.

High-Sensitivity Hydrogen Sulfide Electrochemical Gas Sensor Based on CNT/Pt Cluster Electrode

Recently, due to the development of industrial technology, harmful gases discharged from industrial sites are gradually increasing, and as a result, inconvenience and civil complaints due to odor in the community are rapidly increasing. Among several types of harmful gases, hydrogen sulfide (H2S) is a colorless representative harmful gas that can cause pain through irritation of the mucous membranes of the eyes and respiratory tract, and can cause central nerve paralysis and suffocation at the same time when exposed to high concentrations. In addition, H2S is not only harmful to the human body, but also can create an unpleasant feeling by causing an odor even in a very small amount. Therefore, in order to manage H2S, research on a gas sensor capable of quickly and stably detecting H2S has been actively conducted. Most of the sensors that have been studied in the past are metal oxide-based semiconductor H2S gas sensors, which have high sensitivity, but have disadvantages in that low selectivity and high-temperature operating conditions are required. On the other hand, the electrochemical gas sensor can measure H2S gas with high selectivity because a chemical reaction occurs with respect to a specific gas depending on the type of electrolyte and electrode, and a potential difference due to electrons generated thereby is measured. Therefore, in this study, a CNT/Pt-based electrochemical H2S gas sensor capable of detecting at room temperature with high selectivity for H2S was developed. After forming a CNT thin film on a PTFE membrane, Pt was deposited through an E-beam to fabricate a working electrode capable of selectively detecting only H2S, and applied to an electrochemical H2S gas sensor using sulfuric acid (H2SO4) electrolyte. H2S was measured at a concentration of 100 to 10 ppm in units of 10 ppm using the manufactured CNT/Pt-based electrochemical H2S gas sensor. As a result, the amount of current change was confirmed to be 100uA at a concentration of 100 ppm, and the response time and recovery time were confirmed to be about 10 seconds.This work was supported by the Korea Innovation Foundation(INNOPOLIS) grant funded by the Korea government(MSIT) (2020-DD-UP-0348). This study has been conducted with the support of the Korea Institute of Industrial Technology as "Development of a thermal convection-type flow sensor with high-sensitivity for emergency patients breathing monitoring in real-time" (Kitech UI-23-0012).

MOF-derived flower-like Fe-doped Co3O4 porous hollow structures with enhanced n-butanol sensing properties at low temperature

MOF-derived flower-like Fe-doped Co3O4 porous hollow structures with enhanced n-butanol sensing properties at low temperature

Nano Hotplate Fabrication for Metal Oxide-Based Gas Sensors by Combining Electron Beam and Focused Ion Beam Lithography.

Metal oxide semiconductor (MOS) gas sensors are widely used for gas detection. Typically, the hotplate element is the key component in MOS gas sensors which provide a proper and tunable operation temperature. However, the low power efficiency of the standard hotplates greatly limits the portable application of MOS gas sensors. The miniaturization of the hotplate geometry is one of the most effective methods used to reduce its power consumption. In this work, a new method is presented, combining electron beam lithography (EBL) and focused ion beam (FIB) technologies to obtain low power consumption. EBL is used to define the low-resolution section of the electrode, and FIB technology is utilized to pattern the high-resolution part. Different Au++ ion fluences in FIBs are tested in different milling strategies. The resulting devices are characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), and secondary ion mass spectrometry (SIMS). Furthermore, the electrical resistance of the hotplate is measured at different voltages, and the operational temperature is calculated based on the Pt temperature coefficient of resistance value. In addition, the thermal heater and electrical stability is studied at different temperatures for 110 h. Finally, the implementation of the fabricated hotplate in ZnO gas sensors is investigated using ethanol at 250 °C.

Epitaxial growth of Co3O4/In2O3 p-n heterostructure with rich oxygen vacancies for ultrahigh triethylamine sensing

Epitaxial growth of Co3O4/In2O3 p-n heterostructure with rich oxygen vacancies for ultrahigh triethylamine sensing