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Topical Collection "Gas Sensors"

Editor

Collection Editor
Prof. Dr. Giovanni Neri

Department of Engineering, University of Messina, 98166 Messina, Italy
Website | E-Mail
Fax: +39 090 397 7464
Interests: chemical synthesis of sensing materials; oxide semiconductor-based gas sensors; nanostructures for chemical and electrochemical sensing; automotive gas sensors; biomedical sensors

Topical Collection Information

Dear Colleagues,

Gas sensors play an important role in many aspects of technology, in fields such as industrial processes, automotive technologies, environmental monitoring, or air quality assurance, to name just a few, and are increasingly becoming part of our day-to-day lives at work and home. Today’s devices exploit numerous solid-state, electrochemical, optical and other phenomena related to gas sensing. Research and development of gas sensor devices continue to be faced with numerous challenges in terms of sensitivity, selectivity, stability, and many other aspects. Thus, while the fundamental understanding of underlying sensing processes continues to improve, the discovery of novel functional sensing materials open up new opportunities, the format/architecture of gas sensors is rapidly changing. In recent decades, the evolution of sensors has been strongly influenced by ICT technologies, with integration of microcontrollers, wireless communications modules, and permanent data storage. New sensing technology platforms provide the ability to monitor, control, optimize, and provide autonomy to smart, connected devices, enabled by advances in component miniaturization, microelectromechanical systems (MEMS), low-power devices, onboard processing, and Internet-connected “cloud” computing.  

This Topical Collection on 'Gas Sensors' aims to cover the above-mentioned aspects regarding gas sensors. Key issues, such as the developments of novel gas sensing materials, new insights in gas sensing mechanisms, new devices and fabrication technologies, testing and characterization of micro- and nano-fabricated systems for gas sensing, are, therefore, collected together to give an overview of the recent fundamental and applied research carried out in this field. Topics covered are:

  • Gas sensing materials
  • Principles and phenomena of gas sensing
  • Gas-sensing mechanisms
  • Gas sensor technologies
  • Micro- and nanofabrication
  • Applications

Prof. Dr. Giovanni Neri
Collection Editor

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Published Papers (17 papers)

2018

Jump to: 2017

Open AccessArticle A Micro-Resonant Gas Sensor with Nanometer Clearance between the Pole Plates
Sensors 2018, 18(2), 362; doi:10.3390/s18020362
Received: 26 December 2017 / Revised: 20 January 2018 / Accepted: 25 January 2018 / Published: 26 January 2018
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Abstract
In micro-resonant gas sensors, the capacitive detection is widely used because of its simple structure. However, its shortcoming is a weak signal output caused by a small capacitance change. Here, we reduced the initial clearance between the pole plates to the nanometer level,
[...] Read more.
In micro-resonant gas sensors, the capacitive detection is widely used because of its simple structure. However, its shortcoming is a weak signal output caused by a small capacitance change. Here, we reduced the initial clearance between the pole plates to the nanometer level, and increased the capacitance between the pole plates and its change during resonator vibration. We propose a fabricating process of the micro-resonant gas sensor by which the initial clearance between the pole plates is reduced to the nanometer level and a micro-resonant gas sensor with 200 nm initial clearance is fabricated. With this sensor, the resonant frequency shifts were measured when they were exposed to several different vapors, and high detection accuracies were obtained. The detection accuracy with respect to ethanol vapor was 0.4 ppm per Hz shift, and the detection accuracy with respect to hydrogen and ammonias vapors was 3 ppm and 0.5 ppm per Hz shift, respectively. Full article
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Open AccessArticle A Prototype Sensor for In Situ Sensing of Fine Particulate Matter and Volatile Organic Compounds
Sensors 2018, 18(1), 265; doi:10.3390/s18010265
Received: 16 December 2017 / Revised: 12 January 2018 / Accepted: 16 January 2018 / Published: 18 January 2018
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Abstract
Air pollution exposure causes seven million deaths per year, according to the World Health Organization. Possessing knowledge of air quality and sources of air pollution is crucial for managing air pollution and providing early warning so that a swift counteractive response can be
[...] Read more.
Air pollution exposure causes seven million deaths per year, according to the World Health Organization. Possessing knowledge of air quality and sources of air pollution is crucial for managing air pollution and providing early warning so that a swift counteractive response can be carried out. An optical prototype sensor (AtmOptic) capable of scattering and absorbance measurements has been developed to target in situ sensing of fine particulate matter (PM2.5) and volatile organic compounds (VOCs). For particulate matter testing, a test chamber was constructed and the emission of PM2.5 from incense burning inside the chamber was measured using the AtmOptic. The weight of PM2.5 particles was collected and measured with a filter to determine their concentration and the sensor signal-to-concentration correlation. The results of the AtmOptic were also compared and found to trend well with the Dylos DC 1100 Pro air quality monitor. The absorbance spectrum of VOCs emitted from various laboratory chemicals and household products as well as a two chemical mixtures were recorded. The quantification was demonstrated, using toluene as an example, by calibrating the AtmOptic with compressed gas standards containing VOCs at different concentrations. The results demonstrated the sensor capabilities in measuring PM2.5 and volatile organic compounds. Full article
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2017

Jump to: 2018

Open AccessReview Porous TiO2-Based Gas Sensors for Cyber Chemical Systems to Provide Security and Medical Diagnosis
Sensors 2017, 17(12), 2947; doi:10.3390/s17122947
Received: 8 November 2017 / Revised: 13 December 2017 / Accepted: 17 December 2017 / Published: 19 December 2017
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Abstract
Gas sensors play an important role in our life, providing control and security of technical processes, environment, transportation and healthcare. Consequently, the development of high performance gas sensor devices is the subject of intense research. TiO2, with its excellent physical and
[...] Read more.
Gas sensors play an important role in our life, providing control and security of technical processes, environment, transportation and healthcare. Consequently, the development of high performance gas sensor devices is the subject of intense research. TiO2, with its excellent physical and chemical properties, is a very attractive material for the fabrication of chemical sensors. Meanwhile, the emerging technologies are focused on the fabrication of more flexible and smart systems for precise monitoring and diagnosis in real-time. The proposed cyber chemical systems in this paper are based on the integration of cyber elements with the chemical sensor devices. These systems may have a crucial effect on the environmental and industrial safety, control of carriage of dangerous goods and medicine. This review highlights the recent developments on fabrication of porous TiO2-based chemical gas sensors for their application in cyber chemical system showing the convenience and feasibility of such a model to provide the security and to perform the diagnostics. The most of reports have demonstrated that the fabrication of doped, mixed and composite structures based on porous TiO2 may drastically improve its sensing performance. In addition, each component has its unique effect on the sensing properties of material. Full article
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Open AccessArticle Gas Leak Detection by Dilution of Atmospheric Oxygen
Sensors 2017, 17(12), 2804; doi:10.3390/s17122804
Received: 31 August 2017 / Revised: 18 November 2017 / Accepted: 30 November 2017 / Published: 5 December 2017
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Abstract
Gas leak detection is an important issue in infrastructure monitoring and industrial production. In this context, infrared (IR) absorption spectroscopy is a major measurement method. It can be applied in an extractive or remote detection scheme. Tunable laser spectroscopy (TLS) instruments are able
[...] Read more.
Gas leak detection is an important issue in infrastructure monitoring and industrial production. In this context, infrared (IR) absorption spectroscopy is a major measurement method. It can be applied in an extractive or remote detection scheme. Tunable laser spectroscopy (TLS) instruments are able to detect CH4 leaks with column densities below 10 ppm·m from a distance of 30 m in less than a second. However, leak detection of non-IR absorbing gases such as N2 is not possible in this manner. Due to the fact that any leaking gas displaces or dilutes the surrounding background gas, an indirect detection is still possible. It is shown by sensitive TLS measurements of the ambient background concentration of O2 that N2 leaks can be localized with extractive and standoff methods for distances below 1 m. Minimum leak rates of 0.1 mbar·L/s were determined. Flow simulations confirm that the leakage gas typically effuses in a narrow jet. The sensitivity is mainly determined by ambient flow conditions. Compared to TLS detection of CH4 at 1651 nm, the indirect method using O2 at 761 nm is experimentally found to be less sensitive by a factor of 100. However, the well-established TLS of O2 may become a universal tool for rapid leakage screening of vessels that contain unknown or inexpensive gases, such as N2. Full article
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Open AccessFeature PaperArticle Screen-Printed Graphite Electrodes as Low-Cost Devices for Oxygen Gas Detection in Room-Temperature Ionic Liquids
Sensors 2017, 17(12), 2734; doi:10.3390/s17122734
Received: 10 October 2017 / Revised: 20 November 2017 / Accepted: 21 November 2017 / Published: 26 November 2017
PDF Full-text (2710 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Screen-printed graphite electrodes (SPGEs) have been used for the first time as platforms to detect oxygen gas in room-temperature ionic liquids (RTILs). Up until now, carbon-based SPEs have shown inferior behaviour compared to platinum and gold SPEs for gas sensing with RTIL solvents.
[...] Read more.
Screen-printed graphite electrodes (SPGEs) have been used for the first time as platforms to detect oxygen gas in room-temperature ionic liquids (RTILs). Up until now, carbon-based SPEs have shown inferior behaviour compared to platinum and gold SPEs for gas sensing with RTIL solvents. The electrochemical reduction of oxygen (O2) in a range of RTILs has therefore been explored on home-made SPGEs, and is compared to the behaviour on commercially-available carbon SPEs (C-SPEs). Six common RTILs are initially employed for O2 detection using cyclic voltammetry (CV), and two RTILs ([C2mim][NTf2] and [C4mim][PF6]) chosen for further detailed analytical studies. Long-term chronoamperometry (LTCA) was also performed to test the ability of the sensor surface for real-time gas monitoring. Both CV and LTCA gave linear calibration graphs—for CV in the 10–100% vol. range, and for LTCA in the 0.1–20% vol. range—on the SPGE. The responses on the SPGE were far superior to the commercial C-SPEs; more instability in the electrochemical responses were observed on the C-SPEs, together with some breaking-up or dissolution of the electrode surface materials. This study highlights that not all screen-printed ink formulations are compatible with RTIL solvents for longer-term electrochemical experiments, and that the choice of RTIL is also important. Overall, the low-cost SPGEs appear to be promising platforms for the detection of O2, particularly in [C4mim][PF6]. Full article
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Open AccessFeature PaperArticle Planar Microstrip Ring Resonators for Microwave-Based Gas Sensing: Design Aspects and Initial Transducers for Humidity and Ammonia Sensing
Sensors 2017, 17(10), 2422; doi:10.3390/s17102422
Received: 21 September 2017 / Revised: 16 October 2017 / Accepted: 17 October 2017 / Published: 24 October 2017
Cited by 1 | PDF Full-text (4071 KB) | HTML Full-text | XML Full-text
Abstract
A planar microstrip ring resonator structure on alumina was developed using the commercial FEM software COMSOL. Design parameters were evaluated, eventually leading to an optimized design of a miniaturized microwave gas sensor. The sensor was covered with a zeolite film. The device was
[...] Read more.
A planar microstrip ring resonator structure on alumina was developed using the commercial FEM software COMSOL. Design parameters were evaluated, eventually leading to an optimized design of a miniaturized microwave gas sensor. The sensor was covered with a zeolite film. The device was successfully operated at around 8.5 GHz at room temperature as a humidity sensor. In the next step, an additional planar heater will be included on the reverse side of the resonator structure to allow for testing of gas-sensitive materials under sensor conditions. Full article
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Open AccessReview TiO2-Based Nanoheterostructures for Promoting Gas Sensitivity Performance: Designs, Developments, and Prospects
Sensors 2017, 17(9), 1971; doi:10.3390/s17091971
Received: 2 July 2017 / Revised: 19 August 2017 / Accepted: 25 August 2017 / Published: 27 August 2017
Cited by 1 | PDF Full-text (10673 KB) | HTML Full-text | XML Full-text
Abstract
Gas sensors based on titanium dioxide (TiO2) have attracted much public attention during the past decades due to their excellent potential for applications in environmental pollution remediation, transportation industries, personal safety, biology, and medicine. Numerous efforts have therefore been devoted to
[...] Read more.
Gas sensors based on titanium dioxide (TiO2) have attracted much public attention during the past decades due to their excellent potential for applications in environmental pollution remediation, transportation industries, personal safety, biology, and medicine. Numerous efforts have therefore been devoted to improving the sensing performance of TiO2. In those effects, the construct of nanoheterostructures is a promising tactic in gas sensing modification, which shows superior sensing performance to that of the single component-based sensors. In this review, we briefly summarize and highlight the development of TiO2-based heterostructure gas sensing materials with diverse models, including semiconductor/semiconductor nanoheterostructures, noble metal/semiconductor nanoheterostructures, carbon-group-materials/semiconductor nano- heterostructures, and organic/inorganic nanoheterostructures, which have been investigated for effective enhancement of gas sensing properties through the increase of sensitivity, selectivity, and stability, decrease of optimal work temperature and response/recovery time, and minimization of detectable levels. Full article
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Open AccessArticle A Fast Room Temperature NH3 Sensor Based on an Al/p-Si/Al Structure with Schottky Electrodes
Sensors 2017, 17(8), 1929; doi:10.3390/s17081929
Received: 12 July 2017 / Revised: 18 August 2017 / Accepted: 19 August 2017 / Published: 22 August 2017
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Abstract
In this paper, an electrical-based NH3 sensor with an Al/p-Si/Al structure is reported. The p-Si substrate is microstructured by fs-laser irradiation and then etched by 30% alkaline solution. This sensor works well at room temperature with fast response/recovery for NH3 gas
[...] Read more.
In this paper, an electrical-based NH3 sensor with an Al/p-Si/Al structure is reported. The p-Si substrate is microstructured by fs-laser irradiation and then etched by 30% alkaline solution. This sensor works well at room temperature with fast response/recovery for NH3 gas at 5–100 ppm concentration. However, when the sensor is annealed in N2/H2 forming gas or short-circuited for Al/Si electrodes, its sensitivity decreases drastically and almost vanishes. Further I-V and FT-IR results show that the two back-to-back Schottky diodes on the device play a key role in its sensing performance. Full article
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Open AccessArticle CeO2 Enhanced Ethanol Sensing Performance in a CdS Gas Sensor
Sensors 2017, 17(7), 1577; doi:10.3390/s17071577
Received: 5 June 2017 / Revised: 29 June 2017 / Accepted: 3 July 2017 / Published: 5 July 2017
Cited by 2 | PDF Full-text (1377 KB) | HTML Full-text | XML Full-text
Abstract
CdS nanowires (NWs) were fabricated through a facile low-temperature solvothermal method, following which CeO2 nanoparticles were modified on the NWs. The ethanol sensing characteristics of pure CdS and decorated ones with different CeO2 content were studied. It was found that the
[...] Read more.
CdS nanowires (NWs) were fabricated through a facile low-temperature solvothermal method, following which CeO2 nanoparticles were modified on the NWs. The ethanol sensing characteristics of pure CdS and decorated ones with different CeO2 content were studied. It was found that the sensing performance of CdS was significantly improved after CeO2 decoration. In particular, the 5 at% CeO2/CdS composite exhibited a much higher response to 100 ppm ethanol (about 52), which was 2.6 times larger than that of pure CdS. A fast response and recovery time (less than 12 s and 3 s, respectively) were obtained as well as an excellent selectivity. These results make the CeO2-decorated CdS NWs good candidates for ethanol sensing applications. Full article
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Open AccessArticle Optimization of Perovskite Gas Sensor Performance: Characterization, Measurement and Experimental Design
Sensors 2017, 17(6), 1352; doi:10.3390/s17061352
Received: 8 April 2017 / Revised: 1 June 2017 / Accepted: 4 June 2017 / Published: 10 June 2017
Cited by 1 | PDF Full-text (783 KB) | HTML Full-text | XML Full-text
Abstract
Eight different types of nanostructured perovskites based on YCoO3 with different chemical compositions are prepared as gas sensor materials, and they are studied with two target gases NO2 and CO. Moreover, a statistical approach is adopted to optimize their performance. The
[...] Read more.
Eight different types of nanostructured perovskites based on YCoO 3 with different chemical compositions are prepared as gas sensor materials, and they are studied with two target gases NO 2 and CO. Moreover, a statistical approach is adopted to optimize their performance. The innovative contribution is carried out through a split-plot design planning and modeling, also involving random effects, for studying Metal Oxide Semiconductors (MOX) sensors in a robust design context. The statistical results prove the validity of the proposed approach; in fact, for each material type, the variation of the electrical resistance achieves a satisfactory optimized value conditional to the working temperature and by controlling for the gas concentration variability. Just to mention some results, the sensing material YCo 0 . 9 Pd 0 . 1 O 3 (Mt1) achieved excellent solutions during the optimization procedure. In particular, Mt1 resulted in being useful and feasible for the detection of both gases, with optimal response equal to +10.23% and working temperature at 312 C for CO (284 ppm, from design) and response equal to −14.17% at 185 C for NO 2 (16 ppm, from design). Analogously, for NO 2 (16 ppm, from design), the material type YCo 0 . 9 O 2 . 85 + 1 % Pd (Mt8) allows for optimizing the response value at 15 . 39 % with a working temperature at 181 . 0 C, whereas for YCo 0 . 95 Pd 0 . 05 O 3 (Mt3), the best response value is achieved at 15 . 40 % with the temperature equal to 204 C. Full article
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Open AccessArticle A Study of the CO Sensing Responses of Cu-, Pt- and Pd-Activated SnO2 Sensors: Effect of Precipitation Agents, Dopants and Doping Methods
Sensors 2017, 17(5), 1011; doi:10.3390/s17051011
Received: 27 February 2017 / Revised: 25 April 2017 / Accepted: 27 April 2017 / Published: 3 May 2017
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Abstract
In this work, we report the synthesis of Cu, Pt and Pd doped SnO2 powders and a comparative study of their CO gas sensing performance. Dopants were incorporated into SnO2 nanostructures using chemical and impregnation methods by using urea and ammonia
[...] Read more.
In this work, we report the synthesis of Cu, Pt and Pd doped SnO2 powders and a comparative study of their CO gas sensing performance. Dopants were incorporated into SnO2 nanostructures using chemical and impregnation methods by using urea and ammonia as precipitation agents. The synthesized samples were characterized using X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HR-TEM). The presence of dopants within the SnO2 nanostructures was evidenced from the HR-TEM results. Powders doped utilizing chemical methods with urea as precipitation agent presented higher sensing responses compared to the other forms, which is due to the formation of uniform and homogeneous particles resulting from the temperature-assisted synthesis. The particle sizes of doped SnO2 nanostructures were in the range of 40–100 nm. An enhanced sensing response around 1783 was achieved with Cu-doped SnO2 when compared with two other dopants i.e., Pt (1200) and Pd:SnO2 (502). The high sensing response of Cu:SnO2 is due to formation of CuO and its excellent association and dissociation with adsorbed atmospheric oxygen in the presence of CO at the sensor operation temperature, which results in high conductance. Cu:SnO2 may thus be an alternative and cost effective sensor for industrial applications. Full article
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Open AccessFeature PaperArticle Non-Gaussian Resistance Fluctuations in Gold-Nanoparticle-Based Gas Sensors: An Appraisal of Different Evaluation Techniques
Sensors 2017, 17(4), 757; doi:10.3390/s17040757
Received: 18 February 2017 / Revised: 30 March 2017 / Accepted: 31 March 2017 / Published: 3 April 2017
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Abstract
Volatile organic compounds, such as formaldehyde, can be used as biomarkers in human exhaled breath in order to non-invasively detect various diseases, and the same compounds are of much interest also in the context of environmental monitoring and protection. Here, we report on
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Volatile organic compounds, such as formaldehyde, can be used as biomarkers in human exhaled breath in order to non-invasively detect various diseases, and the same compounds are of much interest also in the context of environmental monitoring and protection. Here, we report on a recently-developed gas sensor, based on surface-functionalized gold nanoparticles, which is able to generate voltage noise with a distinctly non-Gaussian component upon exposure to formaldehyde with concentrations on the ppm level, whereas this component is absent, or at least much weaker, when the sensor is exposed to ethanol or to pure air. We survey four different statistical methods to elucidate a non-Gaussian component and assess their pros and cons with regard to efficient gas detection. Specifically, the non-Gaussian component was clearly exposed in analysis using level-crossing parameters, which require nothing but a modest computational effort and simple electronic circuitry, and analogous results could be reached through the bispectrum function, albeit with more intense computation. Useful information could be obtained also via the Lévy-stable distribution and, possibly, the second spectrum. Full article
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Open AccessArticle Gas Sensor Based on 3-D WO3 Inverse Opal: Design and Applications
Sensors 2017, 17(4), 710; doi:10.3390/s17040710
Received: 12 February 2017 / Revised: 21 March 2017 / Accepted: 21 March 2017 / Published: 29 March 2017
Cited by 2 | PDF Full-text (3047 KB) | HTML Full-text | XML Full-text
Abstract
A three-dimensional inverse opal (3DIO) WO3 architecture has been synthesized via a simple sacrificial template method. Morphology features of the 3DIO were characterized by scanning electron microscope (SEM) and its structure was characterized by X-ray diffraction (XRD). The shrinking ratio of the
[...] Read more.
A three-dimensional inverse opal (3DIO) WO3 architecture has been synthesized via a simple sacrificial template method. Morphology features of the 3DIO were characterized by scanning electron microscope (SEM) and its structure was characterized by X-ray diffraction (XRD). The shrinking ratio of the PMMA spheres was ~28.2% through measuring the distribution of the PMMA spheres and 3DIO WO3 center-to-center distance between the spheres and macropores, respectively. Beyond that, the 3DIO gas sensing properties were investigated systematically and the sensing mechanism of 3DIO WO3 was proposed. The results indicated that the response of the 3DIO sensor possessed excellent sensitivity to acetone gas, especially at trace levels. The 3DIO gas sensor response was ~7 to 5 ppm of acetone and could detect acetone low to 0.2 ppm effectively, which was in close proximity to the theoretical low detection limit of 0.14 ppm when Ra/Rg ≥ 1.2 was used as the criterion for reliable gas sensing. All in all, the obvious satisfaction of the gas-sensing properties was ascribed to the structure of the 3DIO, and the sensor could be a promising novel device in the future. Full article
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Open AccessReview Electrodes for Semiconductor Gas Sensors
Sensors 2017, 17(4), 683; doi:10.3390/s17040683
Received: 7 February 2017 / Revised: 11 March 2017 / Accepted: 22 March 2017 / Published: 25 March 2017
Cited by 2 | PDF Full-text (2663 KB) | HTML Full-text | XML Full-text
Abstract
The electrodes of semiconductor gas sensors are important in characterizing sensors based on their sensitivity, selectivity, reversibility, response time, and long-term stability. The types and materials of electrodes used for semiconductor gas sensors are analyzed. In addition, the effect of interfacial zones and
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The electrodes of semiconductor gas sensors are important in characterizing sensors based on their sensitivity, selectivity, reversibility, response time, and long-term stability. The types and materials of electrodes used for semiconductor gas sensors are analyzed. In addition, the effect of interfacial zones and surface states of electrode–semiconductor interfaces on their characteristics is studied. This study describes that the gas interaction mechanism of the electrode–semiconductor interfaces should take into account the interfacial zone, surface states, image force, and tunneling effect. Full article
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Open AccessArticle Ratiometric Dissolved Oxygen Sensors Based on Ruthenium Complex Doped with Silver Nanoparticles
Sensors 2017, 17(3), 548; doi:10.3390/s17030548
Received: 28 December 2016 / Revised: 19 February 2017 / Accepted: 6 March 2017 / Published: 9 March 2017
Cited by 2 | PDF Full-text (5055 KB) | HTML Full-text | XML Full-text
Abstract
A ratiometric optical sensor has been developed with electrospinning processing method for dissolved oxygen measurement. The sensing film is fabricated by using silver nano-particles (Ag NPs) doped with tris(4,7-diphenyl-1,10-phenanthroline) ruthenium(II) dichloride complex (Ru(DPP)3Cl2) encapsulated in plasticized polymethyl methacrylate (PMMA).
[...] Read more.
A ratiometric optical sensor has been developed with electrospinning processing method for dissolved oxygen measurement. The sensing film is fabricated by using silver nano-particles (Ag NPs) doped with tris(4,7-diphenyl-1,10-phenanthroline) ruthenium(II) dichloride complex (Ru(DPP)3Cl2) encapsulated in plasticized polymethyl methacrylate (PMMA). An insensitive 3-(2-benzothiazolyl)-7-(diethy lamino)-(6CI,7CI) (Coumarin6) is adopted as reference. The ratio of oxygenation is calculated at each image pixel of a 3CCD camera to quantify the oxygen concentration in aqueous environment. Compared to Ag-free film, the response time of Ag-containing films were improved from 1.5 s to 1.0 s upon switching from deoxygenated to air saturation and from 65 s to 45 s from air saturation to fully deoxygenated. The response times of the Ag-free film obtained by knifing was 2.0 s upon switching from deoxygenated to air saturation and 104 s from air saturation to fully deoxygenated. Results of the evaluation of accuracy, limit of detection, stability, and photostability are presented. An experiment measuring the spatiotemporal variation of oxygen distribution within the photosynthesis and respiration of Chlorella vulgaris is demonstrated. It is shown that the nanofiber-based optical sensor film could serve as a promising method for rapid oxygen monitoring in aqueous applications. Full article
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Open AccessArticle Comparative Study of Different Methods for Soot Sensing and Filter Monitoring in Diesel Exhausts
Sensors 2017, 17(2), 400; doi:10.3390/s17020400
Received: 20 November 2016 / Revised: 29 January 2017 / Accepted: 11 February 2017 / Published: 18 February 2017
Cited by 2 | PDF Full-text (3483 KB) | HTML Full-text | XML Full-text
Abstract
Due to increasingly tighter emission limits for diesel and gasoline engines, especially concerning particulate matter emissions, particulate filters are becoming indispensable devices for exhaust gas after treatment. Thereby, for an efficient engine and filter control strategy and a cost-efficient filter design, reliable technologies
[...] Read more.
Due to increasingly tighter emission limits for diesel and gasoline engines, especially concerning particulate matter emissions, particulate filters are becoming indispensable devices for exhaust gas after treatment. Thereby, for an efficient engine and filter control strategy and a cost-efficient filter design, reliable technologies to determine the soot load of the filters and to measure particulate matter concentrations in the exhaust gas during vehicle operation are highly needed. In this study, different approaches for soot sensing are compared. Measurements were conducted on a dynamometer diesel engine test bench with a diesel particulate filter (DPF). The DPF was monitored by a relatively new microwave-based approach. Simultaneously, a resistive type soot sensor and a Pegasor soot sensing device as a reference system measured the soot concentration exhaust upstream of the DPF. By changing engine parameters, different engine out soot emission rates were set. It was found that the microwave-based signal may not only indicate directly the filter loading, but by a time derivative, the engine out soot emission rate can be deduced. Furthermore, by integrating the measured particulate mass in the exhaust, the soot load of the filter can be determined. In summary, all systems coincide well within certain boundaries and the filter itself can act as a soot sensor. Full article
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Open AccessArticle Highly Sensitive Sensors Based on Metal-Oxide Nanocolumns for Fire Detection
Sensors 2017, 17(2), 303; doi:10.3390/s17020303
Received: 21 November 2016 / Revised: 18 January 2017 / Accepted: 3 February 2017 / Published: 7 February 2017
Cited by 4 | PDF Full-text (3809 KB) | HTML Full-text | XML Full-text
Abstract
A fire detector is the most important component in a fire alarm system. Herein, we present the feasibility of a highly sensitive and rapid response gas sensor based on metal oxides as a high performance fire detector. The glancing angle deposition (GLAD) technique
[...] Read more.
A fire detector is the most important component in a fire alarm system. Herein, we present the feasibility of a highly sensitive and rapid response gas sensor based on metal oxides as a high performance fire detector. The glancing angle deposition (GLAD) technique is used to make the highly porous structure such as nanocolumns (NCs) of various metal oxides for enhancing the gas-sensing performance. To measure the fire detection, the interface circuitry for our sensors (NiO, SnO2, WO3 and In2O3 NCs) is designed. When all the sensors with various metal-oxide NCs are exposed to fire environment, they entirely react with the target gases emitted from Poly(vinyl chlorides) (PVC) decomposed at high temperature. Before the emission of smoke from the PVC (a hot-plate temperature of 200 °C), the resistances of the metal-oxide NCs are abruptly changed and SnO2 NCs show the highest response of 2.1. However, a commercial smoke detector did not inform any warning. Interestingly, although the NiO NCs are a p-type semiconductor, they show the highest response of 577.1 after the emission of smoke from the PVC (a hot-plate temperature of 350 °C). The response time of SnO2 NCs is much faster than that of a commercial smoke detector at the hot-plate temperature of 350 °C. In addition, we investigated the selectivity of our sensors by analyzing the responses of all sensors. Our results show the high potential of a gas sensor based on metal-oxide NCs for early fire detection. Full article
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