Gas-sensing Technology Research Articles

Gas-sensitive synergistic effect of Au-decorated ZnO nano-structured materials for rapid ethanol detection based on simulated sunlight activation

Local surface plasmon resonance (LSPR) and noble metal modification/doping are classical methods for improving the performance of metal-oxide-semiconductor (MOS)-based gas sensors. However, relatively less attention is paid to their synergies. In particular, research on synergistic gas-sensing technology that combines sunlight activation with other methods is significant for using friendly energy. In this study, Au-decorated ZnO (Au/ZnO) nano-structured materials (NMs) are successfully synthesised using a cost-effective nano-seed-assisted chemical bath and UV irradiation growth methods. The sensor based on this material exhibits superior performance in ethanol vapour under simulated sunlight, maintaining high sensitivity and repeatability at a low optimal working temperature. In particular, the sensitivity to 100 ppm of ethanol is 7.5 times better and the response time is 20 times shorter (tres < 1 s) in simulated sunlight than in the dark environment. The limit of detection (LOD) of ethanol is as low as 97 ppb, which is much lower than the concentration in exhaled breath of driving under the influence of alcohol according to Chinese law (20–80 ppm). This study provides a reliable and ultra-fast ethanol detection method, with potential applications in environmental monitoring and traffic safety. A possible gas-sensitive mechanism of the Au/ZnO ethanol vapour sensor is proposed based on the synergistic effect between simulated sunlight activation (LSPR, humidity resistance and thermal activation) and noble metal modification (electron sensitisation and chemical sensitisation). It provides a promising method for exploring the utilisation of sunlight for rapid gas detection.

Characterization and Ambient Temperature Hydrogen Sulfide Sensing of Annealed NiO-MnO₂ Thin Films Prepared via Jet Nebulizer Spray Pyrolysis

A jet nebulizer spray pyrolysis technique to synthesize NiO-MnO2 thin films was demonstrated. These nanosheets were annealed at 350, 450 and 550 °C for 2 hours. The thin films surface morphology and structure were characterized using scanning electron microscopy, XRD, and UV spectroscopy. Subsequently, utilized as gas sensors for the detection of hydrogen sulphide gas. The introduction of NiO into MnO2 nanosheets significantly improved the gas-sensing performance. Notably, the gas-sensing response of the NiO-MnO2 nanosheet sensor surpassed that of both NiO and MnO2 alone, reaching a notable value of 165 when detecting 100 ppm hydrogen sulfide gas with the NiO-MnO2 thin film sensor. A remarkable feature of the NiO-MnO2 thin film sensor is its accelerated response time, registering at 10 seconds when exposed to 100 ppm of hydrogen sulfide gas. The mechanism underlying gas sensing and the factors contributing to the enhanced gas response of NiO-MnO2 thin film is thoroughly discussed. From a broader perspective, these developed sensors present a novel platform for the identification and monitoring of hydrogen sulfide gas, showcasing significant advancements in gas-sensing technology.

Emerging Low Detection Limit of Optically Activated Gas Sensors Based on 2D and Hybrid Nanostructures.

Gas sensing is essential for detecting and measuring gas concentrations across various environments, with applications in environmental monitoring, industrial safety, and healthcare. The integration of two-dimensional (2D) materials, organic materials, and metal oxides has significantly advanced gas sensor technology, enhancing its sensitivity, selectivity, and response times at room temperature. This review examines the progress in optically activated gas sensors, with emphasis on 2D materials, metal oxides, and organic materials, due to limited studies on their use in optically activated gas sensors, in contrast to other traditional gas-sensing technologies. We detail the unique properties of these materials and their impact on improving the figures of merit (FoMs) of gas sensors. Transition metal dichalcogenides (TMDCs), with their high surface-to-volume ratio and tunable band gap, show exceptional performance in gas detection, especially when activated by UV light. Graphene-based sensors also demonstrate high sensitivity and low detection limits, making them suitable for various applications. Although organic materials and hybrid structures, such as metal-organic frameworks (MoFs) and conducting polymers, face challenges related to stability and sensitivity at room temperature, they hold potential for future advancements. Optically activated gas sensors incorporating metal oxides benefit from photoactive nanomaterials and UV irradiation, further enhancing their performance. This review highlights the potential of the advanced materials in developing the next generation of gas sensors, addressing current research gaps and paving the way for future innovations.

Advances in analytical techniques for assessing volatile organic compounds in pulse crops: a comprehensive review

Pulse crops, including beans, peas, chickpeas, and lentils, are vital sources of protein, fiber, and essential nutrients worldwide. They serve not only as staple foods but also as key components of sustainable agricultural practices, contributing to soil fertility through nitrogen fixation and enhancing overall productivity. However, pulse crops face numerous abiotic and biotic stresses mainly insect pest attack and pathogen invasion, which pose significant threats to pulse crops, impacting both production and food security. To overcome these challenges, plants have evolved diverse defense mechanisms, including the emission of specific volatile organic compounds (VOCs). These volatiles play crucial roles in plant communication, protection, and real-time health status indication. Monitoring VOCs offers a promising approach for early detection of pest infestations or pathogen infections, enabling the grower to take early action and decide on the proper control measure to minimize losses. The identification of plant-emitted VOCs requires robust and sensitive analytical techniques such as gas chromatography and mass spectrometry, which are the mainly used techniques for in pulse crops studies. However, traditional methods have limitations, prompting the need for advanced, portable, and real-time detection alternatives, such as gas-sensing technologies. This paper provides a comprehensive review of VOC measuring methods, including extraction, separation, and analytical techniques, focusing on their application in pulse crops. Recent advancements in gas-sensing technologies are also discussed, highlighting their potential in enhancing crop protection and agricultural sustainability.

Amorphous RhOx decorated black indium oxide for rapid and flexible NO2 detection at room temperature

This paper focuses on the preparation and characterization of a composite material made from rhodium oxide amorphous-decorated black indium oxide (RhOx/B-In2O3) for use in MEMS gas sensors. The sensors were utilized for the detection of NO2 gas at room temperature, and the results demonstrate that the RhOx/B-In2O3 sensor exhibits excellent gas selectivity, high response, and extremely short response/recovery times (8 s/17 s) to 5 ppm NO2 gas at room temperature. Additionally, a flexible NO2 gas sensor based on the optimized RhOx/B-In2O3 composite was fabricated to expand its application. One of the unique aspects of the RhOx/B-In2O3 material is the existence of defects, which allows for greater adsorption of NO2 gas. This feature contributes to the increased gas selectivity seen in the B-In2O3 material as compared with common In2O3. The chemical sensitization and electron-rich properties of amorphous RhOx further enhance the gas-sensing performance of the material by reducing the reaction activation energy and increasing surface-adsorbed oxygen. Overall, the results demonstrate the potential of the RhOx/B-In2O3 composite material for use in advanced gas-sensing technologies.

Live-tracking of beef freshness by sub-ppb level ammonia detection using WS2/rGO nanoflakes incorporating edge site-enriched acidic sulfur

Highly accurate, easily accessible room temperature wireless gas-sensing technology can be utilized to monitor food freshness in real time to prevent food fraud and spoiled food consumption, thus safeguarding humans from diseases.

Recent Progress on Functionalized Graphene Quantum Dots and Their Nanocomposites for Enhanced Gas Sensing Applications.

Gas-sensing technology has witnessed significant advancements that have been driven by the emergence of graphene quantum dots (GQDs) and their tailored nanocomposites. This comprehensive review surveys the recent progress made in the construction methods and applications of functionalized GQDs and GQD-based nanocomposites for gas sensing. The gas-sensing mechanisms, based on the Fermi-level control and charge carrier depletion layer theory, are briefly explained through the formation of heterojunctions and the adsorption/desorption principle. Furthermore, this review explores the enhancements achieved through the incorporation of GQDs into nanocomposites with diverse matrices, including polymers, metal oxides, and 2D materials. We also provide an overview of the key progress in various hazardous gas sensing applications using functionalized GQDs and GQD-based nanocomposites, focusing on key detection parameters such as sensitivity, selectivity, stability, response and recovery time, repeatability, and limit of detection (LOD). According to the most recent data, the normally reported values for the LOD of various toxic gases using GQD-based sensors are in the range of 1-10 ppm. Remarkably, some GQD-based sensors exhibit extremely low detection limits, such as N-GQDs/SnO2 (0.01 ppb for formaldehyde) and GQD@SnO2 (0.10 ppb for NO2). This review provides an up-to-date perspective on the evolving landscape of functionalized GQDs and their nanocomposites as pivotal components in the development of advanced gas sensors.

Highly responsive hydrogen sensor based on Pd nanoparticle-decorated transfer-free 3D graphene

H2 sensors play a crucial role in the development of hydrogen (H2) energy and safety monitoring. Therefore, efficiently and rapidly detecting low concentrations of H2 is a fundamental challenge that needs to be addressed in the field of H2 sensors. In this study, we present a highly sensitive H2 gas sensor based on Pd-nanoparticles (NPs)-decorated transfer-free three-dimensional (3D) graphene. 3D graphene provides an increased surface area for enhanced gas adsorption and reaction kinetics. The integration of PdNPs improved the electron transport properties, resulting in a higher sensitivity. The PdNP-decorated 3D graphene sensor exhibited a remarkable gas response of 41.9% under 3% H2 exposure. The transfer-free synthesis process ensures the excellent conductivity of 3D graphene to further enhance its overall sensing performance. These discoveries propel current gas-sensing technologies forward and introduce fresh opportunities for the development of dependable sensors that can effectively enhance industrial safety and public security.

Recent Progress in Spinel Ferrite (MFe2O4) Chemiresistive Based Gas Sensors.

Gas-sensing technology has gained significant attention in recent years due to the increasing concern for environmental safety and human health caused by reactive gases. In particular, spinel ferrite (MFe2O4), a metal oxide semiconductor with a spinel structure, has emerged as a promising material for gas-sensing applications. This review article aims to provide an overview of the latest developments in spinel-ferrite-based gas sensors. It begins by discussing the gas-sensing mechanism of spinel ferrite sensors, which involves the interaction between the target gas molecules and the surface of the sensor material. The unique properties of spinel ferrite, such as its high surface area, tunable bandgap, and excellent stability, contribute to its gas-sensing capabilities. The article then delves into recent advancements in gas sensors based on spinel ferrite, focusing on various aspects such as microstructures, element doping, and heterostructure materials. The microstructure of spinel ferrite can be tailored to enhance the gas-sensing performance by controlling factors such as the grain size, porosity, and surface area. Element doping, such as incorporating transition metal ions, can further enhance the gas-sensing properties by modifying the electronic structure and surface chemistry of the sensor material. Additionally, the integration of spinel ferrite with other semiconductors in heterostructure configurations has shown potential for improving the selectivity and overall sensing performance. Furthermore, the article suggests that the combination of spinel ferrite and semiconductors can enhance the selectivity, stability, and sensing performance of gas sensors at room or low temperatures. This is particularly important for practical applications where real-time and accurate gas detection is crucial. In conclusion, this review highlights the potential of spinel-ferrite-based gas sensors and provides insights into the latest advancements in this field. The combination of spinel ferrite with other materials and the optimization of sensor parameters offer opportunities for the development of highly efficient and reliable gas-sensing devices for early detection and warning systems.

Response Characteristics Study of Ethylene Sensor for Fruit Ripening under Temperature Control.

Post-ripening fruits need to be ripened to reach edible conditions, as they are not yet mature enough when picked. Ripening technology is based mainly on temperature control and gas regulation, with the proportion of ethylene being one of the key gas regulation parameters. A sensor's time domain response characteristic curve was obtained through the ethylene monitoring system. The first experiment showed that the sensor has good response speed (maximum of first derivative: 2.01714; minimum of first derivative: -2.01714), stability (xg: 2.42%; trec: 2.05%; Dres: 3.28%), and repeatability (xg: 20.6; trec: 52.4; Dres: 2.31). The second experiment showed that optimal ripening parameters include color, hardness (Change Ⅰ: 88.53%, Change Ⅱ: 75.28%), adhesiveness (Change Ⅰ: 95.29%, Change Ⅱ: 74.72%), and chewiness (Change Ⅰ: 95.18%, Change Ⅱ: 74.25%), verifying the response characteristics of the sensor. This paper proves that the sensor was able to accurately monitor changes in concentration which reflect changes in fruit ripeness, and that the optimal parameters were the ethylene response parameter (Change Ⅰ: 27.78%, Change Ⅱ: 32.53%) and the first derivative parameter (Change Ⅰ: 202.38%, Change Ⅱ: -293.28%). Developing a gas-sensing technology suitable for fruit ripening is of great significance.

Fe-based metal-organic framework as a chemiresistive sensor for low-temperature monitoring of acetone gas

This work demonstrates the potential of a novel iron-based metal-organic framework (Fe-MOF or VNU-15) to effectively detect low-concentration volatile organic compounds (VOCs), particularly acetone (CH3COCH3). A facile solvothermal strategy was used to synthesize Fe-MOFs, comprising Fe(II)/Fe(III) and two distinct linkers—BDC (benzene-1,4-dicarboxylate) and NDC (naphthalene-2,6-dicarboxylic acid). As a first step, Fe-MOFs were characterized to determine their pure phase formation and identify their structural and morphological characteristics. Fe-MOFs processed via the solvothermal method demonstrated high crystallinity, high thermal stability, polyhedral crystal-shaped surface morphology, and a surface area of 735 m2g−1, making them suitable for gas-sensing applications. Laboratory-scale gas-sensing devices were fabricated by printing Fe-MOF powder onto patterned interdigitated electrodes, with performance measurements conducted on these devices in response to exposure to various target gases at temperatures between 25 and 200 °C and gas concentrations between 1 and 10 ppm. Gas-sensing tests confirmed that the VNU-15 sensor selectivity detects CH3COCH3 with a gas response of 1.68–10 ppm and a response time of 64 s, followed by a recovery time of 166 s at 50 °C. This study demonstrates the feasibility of using novel MOF-based sensing channels as low-temperature gas sensors, providing new insights into gas-sensing technology.

Nanocomposites of Quasicrystal Nanosheets and MoS2 Nanoflakes for NO2 Gas Sensors

Nitrogen dioxide (NO2) is one of the air pollutant gases that harms the environment, human health, and the world ecosystem. The main source of NO2 emission is the combustion engine, and therefore, it requires a gas-sensing device to monitor the emission. Herein, we report a highly sensitive and selective NO2 sensor by low-cost and scalable fabrication methods using a hybrid nanocomposite of two-dimensional (2D) Al70Co10Fe5Ni10Cu5 quasicrystal (QC) nanosheets and MoS2 nanoflakes. The 2D-QC nanosheets combined with MoS2 nanoflakes form a heterostructure, which improves the gas sensor’s performance. The Al70Co10Fe5Ni10Cu5/MoS2 heterostructure showed an excellent gas-sensing response (ΔR/Ra %) of ∼66%, which is about 2.27 times higher than that of the pristine MoS2 nanoflakes-based sensor for 100 ppm NO2 at 100 °C. In addition, the hybrid nanocomposite gas sensor device also exhibited high selectivity and good sensitivity. The improvement in the gas sensor performance is explained using the density functional theory analysis, which illustrates that the 2D-QC provides a lot of active sites for the adsorption of NO2 molecules, explained using the adsorption energy, charge difference density, and Bader charges analysis. These gas-sensing results emphasize the significance of the integration of the 2D Al70Co10Fe5Ni10Cu5 QC with MoS2 nanoflakes, being useful to the design and development of NO2-based gas-sensing technology and holding great promise in environmental protection.

Review on Algorithm Design in Electronic Noses: Challenges, Status, and Trends

Electronic noses, or e-noses, refer to systems powered by chemical gas sensors, signal processing, and machine learning algorithms for realizing artificial olfaction. They play a crucial role in various applications for decoding chemical environmental information. Despite decades of advances in gas-sensing technology and artificial intelligence, the reliability and stability of e-nose systems remain challenging, which is also one of the major obstacles that prevent e-noses from large-scale deployment. This paper presents a wide-ranging and structured review of the methods and algorithms developed in the e-nose literature over the past few decades. The review adopts a problem-oriented taxonomy aimed at clarifying the motivations and challenges of different methods and algorithms and their pros and cons. Moreover, several promising research directions in this field have been presented.

Room-temperature chemiresistive ammonia sensors based on 2D MXenes and their hybrids: recent developments and future prospects.

Detection of ammonia (NH3) gas at room temperature is essential in a variety of sectors, including pollution monitoring, commercial safety and medical services, etc. Two-dimensional (2D) materials have emerged as fascinating candidates for gas-sensing applications due to their distinct properties. MXenes, a type of 2D transition metal carbides/nitrides/carbonotrides, have drawn the interest of researchers due to their high conductivity, large surface area, and changing surface chemistry. The review begins by describing the NH3 gas-detecting methods of 2D materials and then concentrates on MXene-based sensors, emphasising the benefits that MXenes provide in this context. The study also explains the prime factors involved in evaluating sensor performance, which include sensor response, sensitivity, selectivity, stability, charge transfer values, adsorption energy and response/recovery times. Subsequently, the review covers two main categories: pristine/intercalated MXenes and MXene-based hybrid materials. The review investigates the approaches for improving the sensing characteristics of pristine and intercalated MXenes by introducing MXene hybrids like MXene-metal oxide hybrids, MXene-transition metal dichalcogenides hybrid, MXene-other 2D materials hybrid, MXene-polymers and other hybrids and other MXene-derived materials. In summary, this review offers a thorough overview of current advancements and potential applications for room-temperature ammonia sensors based on 2D MXenes and their hybrids. In order to pave the way for future improvements in MXene-based gas-sensing technology for room temperature ammonia detection, the study concludes by outlining potential future scope and conclusions.

Nitrous Oxide Is No Laughing Matter: A Historical Review of Nitrous Oxide Gas-Sensing Capabilities Highlighting the Need for Further Exploration.

Nitrous oxide (N2O), also known as laughing gas, is arguably one of the most detrimental greenhouse gases while concurrently being overlooked by the public. Specifically, N2O is ∼300 times more damaging than its better-known counterpart carbon dioxide (CO2) and has a longer-lived lifetime in the atmosphere than CO2. There exist both natural and anthropogenic sources of N2O, and thus, for a better understanding of sources, capture, and decomposition, it is pivotal to identify N2O within the nitrogen biosphere. This review covers the past and current low-cost N2O gas-sensing technologies, focusing specifically on low-cost metal oxide semiconductors (MOSs), chemiresistive and electrochemical sensors that can provide spatial and temporal monitoring of N2O emissions from various sources. Additionally, compositional modifications to MOsS using metal-organic frameworks (MOFs) are discussed, potentially facilitating new awareness and efforts for increased sensing performance and functionality in N2O detection.

MOF-derived nest-like hierarchical In2O3 structures with enhanced gas sensing performance for formaldehyde detection at low temperature

• The nest-like hierarchical In 2 O 3 structures derived from metal-organic framework were prepared. • The nest-like hierarchical In 2 O 3 structures present enhanced gas sensing performance to formaldehyde at low temperature. • The synergetic strategy of ultra-thin sheet and hierarchical structure was used for enhancing gas sensing performance. Formaldehyde (HCHO), as one kind of human carcinogen, exists in indoor home decoration materials, which is a potential threat to human health. Therefore, the development of a portable gas-sensing technology for high efficiency detection of HCHO is of great worth for human health and environmental monitoring. Herein, the nest-like hierarchical In 2 O 3 structures derived from metal-organic framework (MOF) were prepared and the efficient detection of HCHO gas was realized. The sensor generates high response values of 9.47 to 20 ppm HCHO at low temperature of 140°C. Besides, the sensor shows good response and recovery characteristics, and the response and recovery time 20 s and 40 s, respectively. Moreover, the sensor possesses good reproducibility and selectivity. This work provides a new gas-sensing technology for HCHO detection, which holds important application value for the sensitive detection of formaldehyde in the environment.

Porous Oxide-Functionalized Seaweed Fabric as a Flexible Breath Sensor for Noninvasive Nephropathy Diagnosis.

Ever-increasing quality of life demands low-power and reliable gas-sensing technology for point-of-care monitoring of human health by relevant breath biomarkers. However, precise identification is rather challenging due to the relatively small concentration and an abundance of interferents. Herein, a breath sensor that can detect ppb-level ammonia is constructed based on a soft-hard interface design of biocompatible seaweed fabric and nanosheet-assembled bismuth oxide architectures after undergoing heat treatment. Benefiting from abundant defective sites and surface chemical state changes, the flexible sensor can work at room temperature and exhibits superior characteristics for ammonia detection, including ultrahigh response (1296), short response/recovery time (12/6 s), small detection limit (117 ppb), and remarkable anti-interference, even after repetitive mechanical bending and long-term fatigue. Furthermore, the flexible sensor demonstrates a noticeable response to the exhaled breath of a patient with Helicobacter pylori infection. After connecting the sensor with a green-light-emitting diode (LED) in the circuit, an alarm system successfully warns about ammonia levels based on the brightness of the LED. This work provides a potential strategy for wide-range ammonia detection and opens new applications in predictive and personalized healthcare platforms for noninvasive medical diagnosis.

Mixed potential type sensor based on Gd2Zr2O7 solid electrolyte and BiVO4 sensing electrode for effective detection of triethylamine

Triethylamine (TEA), as a common and widely used industrial raw material, is extremely hazardous to the environment and human health. Therefore, the development of a portable gas-sensing technology for high-efficiency detection of TEA is of great worth for human health and environmental monitoring. In this work, a mixed potential type TEA sensor was initially developed based on pyrochlore Gd2Zr2O7 solid state electrolyte and BiVO4 sensing electrode. The sensor generates high response values of − 62.2 mV and − 134.4 mV to 5 ppm and 100 ppm TEA at 500 °C, respectively. The response value of the sensor displays a logarithmic linear relationship with the concentration of TEA in the range of 1–100 ppm with the sensitivity of − 50.8 mV/decade. Besides, the sensor shows good response and recovery characteristics, and the response and recovery time to 10 ppm TEA is 10 s and 89 s, respectively. Moreover, the sensor possesses good humidity resistance, reproducibility and stability. The sensing behavior of the sensor is explained by the mixed potential sensing mechanism, which is confirmed by the measurement of the polarization curves. This work provides a good supplement for TEA gas sensor, which holds important application value for the sensitive detection of TEA in the environment.

Gas Sensing Technology for the Detection and Early Warning of Battery Thermal Runaway: A Review

Gas Sensing Technology for the Detection and Early Warning of Battery Thermal Runaway: A Review

Emerging Methods of Monitoring Volatile Organic Compounds for Detection of Plant Pests and Disease.

Each year, unwanted plant pests and diseases, such as Hendel or potato soft rot, cause damage to crops and ecosystems all over the world. To continue to feed the growing population and protect the global ecosystems, the surveillance and management of the spread of these pests and diseases are crucial. Traditional methods of detection are often expensive, bulky and require expertise and training. Therefore, inexpensive, portable, and user-friendly methods are required. These include the use of different gas-sensing technologies to exploit volatile organic compounds released by plants under stress. These methods often meet these requirements, although they come with their own set of advantages and disadvantages, including the sheer number of variables that affect the profile of volatile organic compounds released, such as sensitivity to environmental factors and availability of soil nutrients or water, and sensor drift. Furthermore, most of these methods lack research on their use under field conditions. More research is needed to overcome these disadvantages and further understand the feasibility of the use of these methods under field conditions. This paper focuses on applications of different gas-sensing technologies from over the past decade to detect plant pests and diseases more efficiently.