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5689 KiB

Open AccessArticle

Metal Sulfides as Sensing Materials for Chemoresistive Gas Sensors

by Andrea Gaiardo, Barbara Fabbri, Vincenzo Guidi, Pierluigi Bellutti, Alessio Giberti, Sandro Gherardi, Lia Vanzetti, Cesare Malagù and Giulia Zonta

Sensors 2016, 16(3), 296; https://doi.org/10.3390/s16030296 - 26 Feb 2016

Cited by 85 | Viewed by 11737

Abstract

This work aims at a broad overview of the results obtained with metal-sulfide materials in the field of chemoresistive gas sensing. Indeed, despite the well-known electrical, optical, structural and morphological features previously described in the literature, metal sulfides present lack of investigation for [...] Read more.

This work aims at a broad overview of the results obtained with metal-sulfide materials in the field of chemoresistive gas sensing. Indeed, despite the well-known electrical, optical, structural and morphological features previously described in the literature, metal sulfides present lack of investigation for gas sensing applications, a field in which the metal oxides still maintain a leading role owing to their high sensitivity, low cost, small dimensions and simple integration, in spite of the wide assortment of sensing materials. However, despite their great advantages, metal oxides have shown significant drawbacks, which have led to the search for new materials for gas sensing devices. In this work, Cadmium Sulfide and Tin (IV) Sulfide were investigated as functional materials for thick-film chemoresistive gas-sensors fabrication and they were tested both in thermo- and in photo-activation modes. Furthermore, electrical characterization was carried out in order to verify their gas sensing properties and material stability, by comparing the results obtained with metal sulfides to those obtained by using their metal-oxides counterparts. The results highlighted the possibility to use metal sulfides as a novel class of sensing materials, owing to their selectivity to specific compounds, stability, and the possibility to operate at room temperature. Full article

(This article belongs to the Special Issue Gas Sensors—Designs and Applications)

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2304 KiB

Open AccessArticle

Study on the Sensing Coating of the Optical Fibre CO₂ Sensor

by Karol Wysokiński, Marek Napierała, Tomasz Stańczyk, Stanisław Lipiński and Tomasz Nasiłowski

Sensors 2015, 15(12), 31888-31903; https://doi.org/10.3390/s151229890 - 17 Dec 2015

Cited by 30 | Viewed by 8497

Abstract

Optical fibre carbon dioxide (CO₂) sensors are reported in this article. The principle of operation of the sensors relies on the absorption of light transmitted through the fibre by a silica gel coating containing active dyes, including methyl red, thymol blue [...] Read more.

Optical fibre carbon dioxide (CO₂) sensors are reported in this article. The principle of operation of the sensors relies on the absorption of light transmitted through the fibre by a silica gel coating containing active dyes, including methyl red, thymol blue and phenol red. Stability of the sensor has been investigated for the first time for an absorption based CO₂ optical fiber sensor. Influence of the silica gel coating thickness on the sensitivity and response time has also been studied. The impact of temperature and humidity on the sensor performance has been examined too. Response times of reported sensors are very short and reach 2–3 s, whereas the sensitivity of the sensor ranges from 3 to 10 for different coating thicknesses. Reported parameters make the sensor suitable for indoor and industrial use. Full article

(This article belongs to the Special Issue Gas Sensors—Designs and Applications)

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676 KiB

Open AccessArticle

Single ZnO Nanowire-Based Gas Sensors to Detect Low Concentrations of Hydrogen

by Marlene N. Cardoza-Contreras, José M. Romo-Herrera, Luis A. Ríos, R. García-Gutiérrez, T. A. Zepeda and Oscar E. Contreras

Sensors 2015, 15(12), 30539-30544; https://doi.org/10.3390/s151229816 - 4 Dec 2015

Cited by 30 | Viewed by 7280

Abstract

Low concentrations of hazardous gases are difficult to detect with common gas sensors. Using semiconductor nanostructures as a sensor element is an alternative. Single ZnO nanowire gas sensor devices were fabricated by manipulation and connection of a single nanowire into a four-electrode aluminum [...] Read more.

Low concentrations of hazardous gases are difficult to detect with common gas sensors. Using semiconductor nanostructures as a sensor element is an alternative. Single ZnO nanowire gas sensor devices were fabricated by manipulation and connection of a single nanowire into a four-electrode aluminum probe in situ in a dual-beam scanning electron microscope-focused ion beam with a manipulator and a gas injection system in/column. The electrical response of the manufactured devices shows response times up to 29 s for a 121 ppm of H₂ pulse, with a variation in the nanowire resistance appreciable at room temperature and at 373.15 K of approximately 8% and 14% respectively, showing that ZnO nanowires are good candidates to detect low concentrations of H₂. Full article

(This article belongs to the Special Issue Gas Sensors—Designs and Applications)

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2972 KiB

Open AccessArticle

A Single Eu-Doped In₂O₃ Nanobelt Device for Selective H₂S Detection

by Weiwu Chen, Yingkai Liu, Zhaojun Qin, Yuemei Wu, Shuanghui Li and Peng Ai

Sensors 2015, 15(12), 29950-29957; https://doi.org/10.3390/s151229775 - 30 Nov 2015

Cited by 29 | Viewed by 6523

Abstract

Eu-doped In₂O₃ nanobelts (Eu-In₂O₃ NBs) and pure In₂O₃ nanobelts (In₂O₃ NBs) are synthesized by the carbon thermal reduction method. Single nanobelt sensors are fabricated via an ion beam deposition system with [...] Read more.

Eu-doped In₂O₃ nanobelts (Eu-In₂O₃ NBs) and pure In₂O₃ nanobelts (In₂O₃ NBs) are synthesized by the carbon thermal reduction method. Single nanobelt sensors are fabricated via an ion beam deposition system with a mesh-grid mask. The gas-sensing response properties of the Eu-In₂O₃ NB device and its undoped counterpart are investigated with several kinds of gases (including H₂S, CO, NO₂, HCHO, and C₂H₅OH) at different concentrations and different temperatures. It is found that the response of the Eu-In₂O₃ NB device to 100 ppm of H₂S is the best among these gases and the sensitivity reaches 5.74, which is five times that of pure In₂O₃ NB at 260 °C. We also found that the former has an excellent sensitive response and great selectivity to H₂S compared to the latter. Besides, there is a linear relationship between the response and H₂S concentration when its concentration changes from 5 to 100 ppm and from 100 to 1000 ppm. The response/recovery time is quite short and remains stable with an increase of H₂S concentration. These results mean that the doping of Eu can improve the gas-sensing performance of In₂O₃ NB effectually. Full article

(This article belongs to the Special Issue Gas Sensors—Designs and Applications)

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1198 KiB

Open AccessArticle

Quantitative Ethylene Measurements with MOx Chemiresistive Sensors at Different Relative Air Humidities

by Matic Krivec, Gerald Mc Gunnigle, Anže Abram, Dieter Maier, Roland Waldner, Johanna M. Gostner, Florian Überall and Raimund Leitner

Sensors 2015, 15(11), 28088-28098; https://doi.org/10.3390/s151128088 - 6 Nov 2015

Cited by 29 | Viewed by 11636

Abstract

The sensitivity of two commercial metal oxide (MOx) sensors to ethylene is tested at different relative humidities. One sensor (MiCS-5914) is based on tungsten oxide, the other (MQ-3) on tin oxide. Both sensors were found to be sensitive to ethylene concentrations down to [...] Read more.

The sensitivity of two commercial metal oxide (MOx) sensors to ethylene is tested at different relative humidities. One sensor (MiCS-5914) is based on tungsten oxide, the other (MQ-3) on tin oxide. Both sensors were found to be sensitive to ethylene concentrations down to 10 ppm. Both sensors have significant response times; however, the tungsten sensor is the faster one. Sensor models are developed that predict the concentration of ethylene given the sensor output and the relative humidity. The MQ-3 sensor model achieves an accuracy of ±9.2 ppm and the MiCS-5914 sensor model predicts concentration to ±7.0 ppm. Both sensors are more accurate for concentrations below 50 ppm, achieving ±6.7 ppm (MQ-3) and 5.7 ppm (MiCS-5914). Full article

(This article belongs to the Special Issue Gas Sensors—Designs and Applications)

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4871 KiB

Open AccessArticle

Quantification Method for Electrolytic Sensors in Long-Term Monitoring of Ambient Air Quality

by Nicholas Masson, Ricardo Piedrahita and Michael Hannigan

Sensors 2015, 15(10), 27283-27302; https://doi.org/10.3390/s151027283 - 27 Oct 2015

Cited by 68 | Viewed by 8514

Abstract

Traditional air quality monitoring relies on point measurements from a small number of high-end devices. The recent growth in low-cost air sensing technology stands to revolutionize the way in which air quality data are collected and utilized. While several technologies have emerged in [...] Read more.

Traditional air quality monitoring relies on point measurements from a small number of high-end devices. The recent growth in low-cost air sensing technology stands to revolutionize the way in which air quality data are collected and utilized. While several technologies have emerged in the field of low-cost monitoring, all suffer from similar challenges in data quality. One technology that shows particular promise is that of electrolytic (also known as amperometric) sensors. These sensors produce an electric current in response to target pollutants. This work addresses the development of practical models for understanding and quantifying the signal response of electrolytic sensors. Such models compensate for confounding effects on the sensor response, such as ambient temperature and humidity, and address other issues that affect the usability of low-cost sensors, such as sensor drift and inter-sensor variability Full article

(This article belongs to the Special Issue Gas Sensors—Designs and Applications)

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2198 KiB

Open AccessArticle

Fabrication and Characterization of a Micro Methanol Sensor Using the CMOS-MEMS Technique

by Chien-Fu Fong, Ching-Liang Dai and Chyan-Chyi Wu

Sensors 2015, 15(10), 27047-27059; https://doi.org/10.3390/s151027047 - 23 Oct 2015

Cited by 19 | Viewed by 7262

Abstract

A methanol microsensor integrated with a micro heater manufactured using the complementary metal oxide semiconductor (CMOS)-microelectromechanical system (MEMS) technique was presented. The sensor has a capability of detecting low concentration methanol gas. Structure of the sensor is composed of interdigitated electrodes, a sensitive [...] Read more.

A methanol microsensor integrated with a micro heater manufactured using the complementary metal oxide semiconductor (CMOS)-microelectromechanical system (MEMS) technique was presented. The sensor has a capability of detecting low concentration methanol gas. Structure of the sensor is composed of interdigitated electrodes, a sensitive film and a heater. The heater located under the interdigitated electrodes is utilized to provide a working temperature to the sensitive film. The sensitive film prepared by the sol-gel method is tin dioxide doped cadmium sulfide, which is deposited on the interdigitated electrodes. To obtain the suspended structure and deposit the sensitive film, the sensor needs a post-CMOS process to etch the sacrificial silicon dioxide layer and silicon substrate. The methanol senor is a resistive type. A readout circuit converts the resistance variation of the sensor into the output voltage. The experimental results show that the methanol sensor has a sensitivity of 0.18 V/ppm. Full article

(This article belongs to the Special Issue Gas Sensors—Designs and Applications)

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1266 KiB

Open AccessArticle

Nanostructured Tungsten Oxide Composite for High-Performance Gas Sensors

by Siyuan Feng Chen, Ali Aldalbahi and Peter Xianping Feng

Sensors 2015, 15(10), 27035-27046; https://doi.org/10.3390/s151027035 - 23 Oct 2015

Cited by 11 | Viewed by 6793

Abstract

We report the results of composite tungsten oxide nanowires-based gas sensors. The morphologic surface, crystallographic structures, and chemical compositions of the obtained nanowires have been investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman scattering, respectively. The experimental measurements reveal that [...] Read more.

We report the results of composite tungsten oxide nanowires-based gas sensors. The morphologic surface, crystallographic structures, and chemical compositions of the obtained nanowires have been investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman scattering, respectively. The experimental measurements reveal that each wire consists of crystalline nanoparticles with an average diameter of less than 250 nm. By using the synthesized nanowires, highly sensitive prototypic gas sensors have been designed and fabricated. The dependence of the sensitivity of tungsten oxide nanowires to the methane and hydrogen gases as a function of time has been obtained. Various sensing parameters such as sensitivity, response time, stability, and repeatability were investigated in order to reveal the sensing ability. Full article

(This article belongs to the Special Issue Gas Sensors—Designs and Applications)

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2300 KiB

Open AccessArticle

Why does the Conductivity of a Nickel Catalyst Increase during Sulfidation? An Exemplary Study Using an In Operando Sensor Device

by Peter Fremerey, Andreas Jess and Ralf Moos

Sensors 2015, 15(10), 27021-27034; https://doi.org/10.3390/s151027021 - 23 Oct 2015

Cited by 2 | Viewed by 6647

Abstract

In order to study the sulfidation of a catalyst fixed bed, an in operando single pellet sensor was designed. A catalyst pellet from the fixed bed was electrically contacted and its electrical response was correlated with the catalyst behavior. For the sulfidation tests, [...] Read more.

In order to study the sulfidation of a catalyst fixed bed, an in operando single pellet sensor was designed. A catalyst pellet from the fixed bed was electrically contacted and its electrical response was correlated with the catalyst behavior. For the sulfidation tests, a nickel catalyst was used and was sulfidized with H₂S. This catalyst had a very low conductivity in the reduced state. During sulfidation, the conductivity of the catalyst increased by decades. A reaction from nickel to nickel sulfide occurred. This conductivity increase by decades during sulfidation had not been expected since both nickel and nickel sulfides behave metallic. Only by assuming a percolation phenomenon that originates from a volume increase of the nickel contacts when reacting to nickel sulfides, this effect can be explained. This assumption was supported by sulfidation tests with differently nickel loaded catalysts and it was quantitatively estimated by a general effective media theory. The single pellet sensor device for in operando investigation of sulfidation can be considered as a valuable tool to get further insights into catalysts under reaction conditions. Full article

(This article belongs to the Special Issue Gas Sensors—Designs and Applications)

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1999 KiB

Open AccessArticle

Fiber-Amplifier-Enhanced QEPAS Sensor for Simultaneous Trace Gas Detection of NH₃ and H₂S

by Hongpeng Wu, Lei Dong, Xiaoli Liu, Huadan Zheng, Xukun Yin, Weiguang Ma, Lei Zhang, Wangbao Yin and Suotang Jia

Sensors 2015, 15(10), 26743-26755; https://doi.org/10.3390/s151026743 - 21 Oct 2015

Cited by 45 | Viewed by 7789

Abstract

A selective and sensitive quartz enhanced photoacoustic spectroscopy (QEPAS) sensor, employing an erbium-doped fiber amplifier (EDFA), and a distributed feedback (DFB) laser operating at 1582 nm was demonstrated for simultaneous detection of ammonia (NH₃) and hydrogen sulfide (H₂S). Two [...] Read more.

A selective and sensitive quartz enhanced photoacoustic spectroscopy (QEPAS) sensor, employing an erbium-doped fiber amplifier (EDFA), and a distributed feedback (DFB) laser operating at 1582 nm was demonstrated for simultaneous detection of ammonia (NH₃) and hydrogen sulfide (H₂S). Two interference-free absorption lines located at 6322.45 cm⁻¹ and 6328.88 cm⁻¹ for NH₃ and H₂S detection, respectively, were identified. The sensor was optimized in terms of current modulation depth for both of the two target gases. An electrical modulation cancellation unit was equipped to suppress the background noise caused by the stray light. An Allan-Werle variance analysis was performed to investigate the long-term performance of the fiber-amplifier-enhanced QEPAS sensor. Benefitting from the high power boosted by the EDFA, a detection sensitivity (1σ) of 52 parts per billion by volume (ppbv) and 17 ppbv for NH₃ and H₂S, respectively, were achieved with a 132 s data acquisition time at atmospheric pressure and room temperature. Full article

(This article belongs to the Special Issue Gas Sensors—Designs and Applications)

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3850 KiB

Open AccessArticle

Ammonia Gas Sensing Behavior of Tanninsulfonic Acid Doped Polyaniline-TiO₂ Composite

by Venu Gopal Bairi, Shawn E. Bourdo, Nicolas Sacre, Dev Nair, Brian C. Berry, Alexandru S. Biris and Tito Viswanathan

Sensors 2015, 15(10), 26415-26429; https://doi.org/10.3390/s151026415 - 16 Oct 2015

Cited by 43 | Viewed by 7979

Abstract

A highly active tannin doped polyaniline-TiO₂ composite ammonia gas sensor was developed and the mechanism behind the gas sensing activity was reported for the first time. A tanninsulfonic acid doped polyaniline (TANIPANI)-titanium dioxide nanocomposite was synthesized by an in situ polymerization of [...] Read more.

A highly active tannin doped polyaniline-TiO₂ composite ammonia gas sensor was developed and the mechanism behind the gas sensing activity was reported for the first time. A tanninsulfonic acid doped polyaniline (TANIPANI)-titanium dioxide nanocomposite was synthesized by an in situ polymerization of aniline in the presence of tanninsulfonic acid and titanium dioxide nanoparticles. X-ray diffraction and thermogravimetric analysis were utilized to determine the incorporation of TiO₂ in TANIPANI matrix. UV-Visible and infrared spectroscopy studies provided information about the electronic interactions among tannin, polyaniline, and TiO₂. Scanning electron microscopy (SEM) along with energy dispersive X-ray spectroscopy (EDS) and atomic force microscopy (AFM) surface analysis techniques were used to investigate the metal oxide dispersions inside polyaniline matrix. Gas sensors were prepared by spin coating solutions of TANIPANI-TiO₂ and TANIPANI composites onto glass slides. Sensors were tested at three different concentrations (20 ppm, 40 ppm, and 60 ppm) of ammonia gas at ambient temperature conditions by measuring the changes in surface resistivity of the films with respect to time. Ammonia gas sensing plots are presented showing the response values, response times and recovery times. The TANIPANI-TiO₂ composite exhibited better response and shorter recovery times when compared to TANIPANI control and other polyaniline composites that have been reported in the literature. For the first time a proposed mechanism of gas sensing basing on the polaron band localization and its effects on the gas sensing behavior of polyaniline are reported. Full article

(This article belongs to the Special Issue Gas Sensors—Designs and Applications)

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3662 KiB

Open AccessArticle

Study of Interdigitated Electrode Arrays Using Experiments and Finite Element Models for the Evaluation of Sterilization Processes

by Jan Oberländer, Zaid B. Jildeh, Patrick Kirchner, Luisa Wendeler, Alexander Bromm, Heiko Iken, Patrick Wagner, Michael Keusgen and Michael J. Schöning

Sensors 2015, 15(10), 26115-26127; https://doi.org/10.3390/s151026115 - 14 Oct 2015

Cited by 32 | Viewed by 9846

Abstract

In this work, a sensor to evaluate sterilization processes with hydrogen peroxide vapor has been characterized. Experimental, analytical and numerical methods were applied to evaluate and study the sensor behavior. The sensor set-up is based on planar interdigitated electrodes. The interdigitated electrode structure [...] Read more.

In this work, a sensor to evaluate sterilization processes with hydrogen peroxide vapor has been characterized. Experimental, analytical and numerical methods were applied to evaluate and study the sensor behavior. The sensor set-up is based on planar interdigitated electrodes. The interdigitated electrode structure consists of 614 electrode fingers spanning over a total sensing area of 20 mm². Sensor measurements were conducted with and without microbiological spores as well as after an industrial sterilization protocol. The measurements were verified using an analytical expression based on a first-order elliptical integral. A model based on the finite element method with periodic boundary conditions in two dimensions was developed and utilized to validate the experimental findings. Full article

(This article belongs to the Special Issue Gas Sensors—Designs and Applications)

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1731 KiB

Open AccessArticle

Metal Decoration Effects on the Gas-Sensing Properties of 2D Hybrid-Structures on Flexible Substrates

by Byungjin Cho, Jongwon Yoon, Sung Kwan Lim, Ah Ra Kim, Sun-Young Choi, Dong-Ho Kim, Kyu Hwan Lee, Byoung Hun Lee, Heung Cho Ko and Myung Gwan Hahm

Sensors 2015, 15(10), 24903-24913; https://doi.org/10.3390/s151024903 - 25 Sep 2015

Cited by 43 | Viewed by 10302

Abstract

We have investigated the effects of metal decoration on the gas-sensing properties of a device with two-dimensional (2D) molybdenum disulfide (MoS₂) flake channels and graphene electrodes. The 2D hybrid-structure device sensitively detected NO₂ gas molecules (>1.2 ppm) as well as [...] Read more.

We have investigated the effects of metal decoration on the gas-sensing properties of a device with two-dimensional (2D) molybdenum disulfide (MoS₂) flake channels and graphene electrodes. The 2D hybrid-structure device sensitively detected NO₂ gas molecules (>1.2 ppm) as well as NH₃ (>10 ppm). Metal nanoparticles (NPs) could tune the electronic properties of the 2D graphene/MoS₂ device, increasing sensitivity to a specific gas molecule. For instance, palladium NPs accumulate hole carriers of graphene/MoS₂, electronically sensitizing NH₃ gas molecules. Contrarily, aluminum NPs deplete hole carriers, enhancing NO₂ sensitivity. The synergistic combination of metal NPs and 2D hybrid layers could be also applied to a flexible gas sensor. There was no serious degradation in the sensing performance of metal-decorated MoS₂ flexible devices before/after 5000 bending cycles. Thus, highly sensitive and endurable gas sensor could be achieved through the metal-decorated 2D hybrid-structure, offering a useful route to wearable electronic sensing platforms. Full article

(This article belongs to the Special Issue Gas Sensors—Designs and Applications)

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705 KiB

Open AccessArticle

Effect of Electrode Configuration on Nitric Oxide Gas Sensor Behavior

by Ling Cui and Erica P. Murray

Sensors 2015, 15(9), 24573-24584; https://doi.org/10.3390/s150924573 - 23 Sep 2015

Cited by 7 | Viewed by 6635

Abstract

The influence of electrode configuration on the impedancemetric response of nitric oxide (NO) gas sensors was investigated for solid electrochemical cells [Au/yttria-stabilized zirconia (YSZ)/Au)]. Fabrication of the sensors was carried out at 1050 °C in order to establish a porous YSZ electrolyte that [...] Read more.

The influence of electrode configuration on the impedancemetric response of nitric oxide (NO) gas sensors was investigated for solid electrochemical cells [Au/yttria-stabilized zirconia (YSZ)/Au)]. Fabrication of the sensors was carried out at 1050 °C in order to establish a porous YSZ electrolyte that enabled gas diffusion. Two electrode configurations were studied where Au wire electrodes were either embedded within or wrapped around the YSZ electrolyte. The electrical response of the sensors was collected via impedance spectroscopy under various operating conditions where gas concentrations ranged from 0 to 100 ppm NO and 1%–18% O₂ at temperatures varying from 600 to 700 °C. Gas diffusion appeared to be a rate-limiting mechanism in sensors where the electrode configuration resulted in longer diffusion pathways. The temperature dependence of the NO sensors studied was independent of the electrode configuration. Analysis of the impedance data, along with equivalent circuit modeling indicated the electrode configuration of the sensor effected gas and ionic transport pathways, capacitance behavior, and NO sensitivity. Full article

(This article belongs to the Special Issue Gas Sensors—Designs and Applications)

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3392 KiB

Open AccessArticle

Numerical Modeling and Experimental Validation by Calorimetric Detection of Energetic Materials Using Thermal Bimorph Microcantilever Array: A Case Study on Sensing Vapors of Volatile Organic Compounds (VOCs)

by Seok-Won Kang, Joe Fragala and Debjyoti Banerjee

Sensors 2015, 15(9), 21785-21806; https://doi.org/10.3390/s150921785 - 31 Aug 2015

Cited by 4 | Viewed by 7440

Abstract

Bi-layer (Au-Si₃N₄) microcantilevers fabricated in an array were used to detect vapors of energetic materials such as explosives under ambient conditions. The changes in the bending response of each thermal bimorph (i.e., microcantilever) with changes in actuation [...] Read more.

Bi-layer (Au-Si₃N₄) microcantilevers fabricated in an array were used to detect vapors of energetic materials such as explosives under ambient conditions. The changes in the bending response of each thermal bimorph (i.e., microcantilever) with changes in actuation currents were experimentally monitored by measuring the angle of the reflected ray from a laser source used to illuminate the gold nanocoating on the surface of silicon nitride microcantilevers in the absence and presence of a designated combustible species. Experiments were performed to determine the signature response of this nano-calorimeter platform for each explosive material considered for this study. Numerical modeling was performed to predict the bending response of the microcantilevers for various explosive materials, species concentrations, and actuation currents. The experimental validation of the numerical predictions demonstrated that in the presence of different explosive or combustible materials, the microcantilevers exhibited unique trends in their bending responses with increasing values of the actuation current. Full article

(This article belongs to the Special Issue Gas Sensors—Designs and Applications)

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1715 KiB

Open AccessArticle

Enhanced Dibutyl Phthalate Sensing Performance of a Quartz Crystal Microbalance Coated with Au-Decorated ZnO Porous Microspheres

by Kaihuan Zhang, Guokang Fan, Ruifen Hu and Guang Li

Sensors 2015, 15(9), 21153-21168; https://doi.org/10.3390/s150921153 - 27 Aug 2015

Cited by 18 | Viewed by 6366

Abstract

Noble metals addition on nanostructured metal oxides is an attractive way to enhance gas sensing properties. Herein, hierarchical zinc oxide (ZnO) porous microspheres decorated with cubic gold particles (Au particles) were synthesized using a facile hydrothermal method. The as-prepared Au-decorated ZnO was then [...] Read more.

Noble metals addition on nanostructured metal oxides is an attractive way to enhance gas sensing properties. Herein, hierarchical zinc oxide (ZnO) porous microspheres decorated with cubic gold particles (Au particles) were synthesized using a facile hydrothermal method. The as-prepared Au-decorated ZnO was then utilized as the sensing film of a gas sensor based on a quartz crystal microbalance (QCM). This fabricated sensor was applied to detect dibutyl phthalate (DBP), which is a widely used plasticizer, and its coating load was optimized. When tested at room temperature, the sensor exhibited a high sensitivity of 38.10 Hz/ppb to DBP in a low concentration range from 2 ppb to 30 ppb and the calculated theoretical detection limit is below 1 ppb. It maintains good repeatability as well as long-term stability. Compared with the undecorated ZnO based QCM, the Au-decorated one achieved a 1.62-time enhancement in sensitivity to DBP, and the selectivity was also improved. According to the experimental results, Au-functionalized ZnO porous microspheres displayed superior sensing performance towards DBP, indicating its potential use in monitoring plasticizers in the gaseous state. Moreover, Au decoration of porous metal oxide nanostructures is proved to be an effective approach for enhancing the gas sensing properties and the corresponding mechanism was investigated. Full article

(This article belongs to the Special Issue Gas Sensors—Designs and Applications)

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4519 KiB

Open AccessArticle

Gas-Sensing Performance of M-Doped CuO-Based Thin Films Working at Different Temperatures upon Exposure to Propane

by Artur Rydosz and Aleksandra Szkudlarek

Sensors 2015, 15(8), 20069-20085; https://doi.org/10.3390/s150820069 - 14 Aug 2015

Cited by 52 | Viewed by 7128

Abstract

Cupric oxide (CuO) thin films are promising materials in gas sensor applications. The CuO-based gas sensors behaved as p-type semiconductors and can be used as part of an e-nose or smart sensor array for breath analysis. The authors present the investigation results on [...] Read more.

Cupric oxide (CuO) thin films are promising materials in gas sensor applications. The CuO-based gas sensors behaved as p-type semiconductors and can be used as part of an e-nose or smart sensor array for breath analysis. The authors present the investigation results on M-doped CuO-based (M = Ag, Au, Cr, Pd, Pt, Sb, Si) sensors working at various temperatures upon exposure to a low concentration of C3H8, which can be found in exhaled human breath, and it can be considered as a one of the biomarkers of several diseases. The films have been deposited in magnetron sputtering technology on low temperature cofired ceramics substrates. The results of the gas sensors’ response are also presented and discussed. The Cr:CuO-based structure, annealed at 400 °C for 4 h in air, showed the highest sensor response, of the order of 2.7 at an operation temperature of 250 °C. The response and recovery time(s) were 10 s and 24 s, respectively. The results show that the addition of M-dopants in the cupric oxide films effectively act as catalysts in propane sensors and improve the gas sensing properties. The films’ phase composition, microstructure and surface topography have been assessed by the X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) methods. Full article

(This article belongs to the Special Issue Gas Sensors—Designs and Applications)

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2827 KiB

Open AccessArticle

A Micro-Preconcentrator Combined Olfactory Sensing System with a Micromechanical Cantilever Sensor for Detecting 2,4-Dinitrotoluene Gas Vapor

by Myung-Sic Chae, Jinsik Kim, Yong Kyoung Yoo, Ji Yoon Kang, Jeong Hoon Lee and Kyo Seon Hwang

Sensors 2015, 15(8), 18167-18177; https://doi.org/10.3390/s150818167 - 24 Jul 2015

Cited by 19 | Viewed by 7951

Abstract

Preventing unexpected explosive attacks and tracing explosion-related molecules require the development of highly sensitive gas-vapor detection systems. For that purpose, a micromechanical cantilever-based olfactory sensing system including a sample preconcentrator was developed to detect 2,4-dinitrotoluene (2,4-DNT), which is a well-known by-product of the [...] Read more.

Preventing unexpected explosive attacks and tracing explosion-related molecules require the development of highly sensitive gas-vapor detection systems. For that purpose, a micromechanical cantilever-based olfactory sensing system including a sample preconcentrator was developed to detect 2,4-dinitrotoluene (2,4-DNT), which is a well-known by-product of the explosive molecule trinitrotoluene (TNT) and exists in concentrations on the order of parts per billion in the atmosphere at room temperature. A peptide receptor (His-Pro-Asn-Phe-Ser-Lys-Tyr-Ile-Leu-His-Gln-Arg) that has high binding affinity for 2,4-DNT was immobilized on the surface of the cantilever sensors to detect 2,4-DNT vapor for highly selective detection. A micro-preconcentrator (µPC) was developed using Tenax-TA adsorbent to produce higher concentrations of 2,4-DNT molecules. The preconcentration was achieved via adsorption and thermal desorption phenomena occurring between target molecules and the adsorbent. The µPC directly integrated with a cantilever sensor and enhanced the sensitivity of the cantilever sensor as a pretreatment tool for the target vapor. The response was rapidly saturated within 5 min and sustained for more than 10 min when the concentrated vapor was introduced. By calculating preconcentration factor values, we verified that the cantilever sensor provides up to an eightfold improvement in sensing performance. Full article

(This article belongs to the Special Issue Gas Sensors—Designs and Applications)

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2041 KiB

Open AccessArticle

Insights on Capacitive Interdigitated Electrodes Coated with MOF Thin Films: Humidity and VOCs Sensing as a Case Study

by Christos Sapsanis, Hesham Omran, Valeriya Chernikova, Osama Shekhah, Youssef Belmabkhout, Ulrich Buttner, Mohamed Eddaoudi and Khaled N. Salama

Sensors 2015, 15(8), 18153-18166; https://doi.org/10.3390/s150818153 - 24 Jul 2015

Cited by 123 | Viewed by 15599

Abstract

A prototypical metal-organic framework (MOF), a 2D periodic porous structure based on the assembly of copper ions and benzene dicarboxylate (bdc) ligands (Cu(bdc)·xH₂O), was grown successfully as a thin film on interdigitated electrodes (IDEs). IDEs have been used for achieving planar [...] Read more.

A prototypical metal-organic framework (MOF), a 2D periodic porous structure based on the assembly of copper ions and benzene dicarboxylate (bdc) ligands (Cu(bdc)·xH₂O), was grown successfully as a thin film on interdigitated electrodes (IDEs). IDEs have been used for achieving planar CMOS-compatible low-cost capacitive sensing structures for the detection of humidity and volatile organic compounds (VOCs). Accordingly, the resultant IDEs coated with the Cu(bdc)·xH₂O thin film was evaluated, for the first time, as a capacitive sensor for gas sensing applications. A fully automated setup, using LabVIEW interfaces to experiment conduction and data acquisition, was developed in order to measure the associated gas sensing performance. Full article

(This article belongs to the Special Issue Gas Sensors—Designs and Applications)

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3464 KiB

Open AccessArticle

Potentiometric NO₂ Sensors Based on Thin Stabilized Zirconia Electrolytes and Asymmetric (La_0.8Sr_0.2)_0.95MnO₃ Electrodes

by Jie Zou, Yangong Zheng, Junliang Li, Zhongliang Zhan and Jiawen Jian

Sensors 2015, 15(7), 17558-17571; https://doi.org/10.3390/s150717558 - 20 Jul 2015

Cited by 10 | Viewed by 7718

Abstract

Here we report on a new architecture for potentiometric NO₂ sensors that features thin 8YSZ electrolytes sandwiched between two porous (La_0.8Sr_0.2)_0.95MnO₃ (LSM95) layers—one thick and the other thin—fabricated by the tape casting and co-firing techniques. [...] Read more.

Here we report on a new architecture for potentiometric NO₂ sensors that features thin 8YSZ electrolytes sandwiched between two porous (La_0.8Sr_0.2)_0.95MnO₃ (LSM95) layers—one thick and the other thin—fabricated by the tape casting and co-firing techniques. Measurements of their sensing characteristics show that reducing the porosity of the supporting LSM95 reference electrodes can increase the response voltages. In the meanwhile, thin LSM95 layers perform better than Pt as the sensing electrode since the former can provide higher response voltages and better linear relationship between the sensitivities and the NO₂ concentrations over 40–1000 ppm. The best linear coefficient can be as high as 0.99 with a sensitivity value of 52 mV/decade as obtained at 500 °C. Analysis of the sensing mechanism suggests that the gas phase reactions within the porous LSM95 layers are critically important in determining the response voltages. Full article

(This article belongs to the Special Issue Gas Sensors—Designs and Applications)

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602 KiB

Open AccessArticle

Fabrication and Characterization of a CMOS-MEMS Humidity Sensor

by John-Ojur Dennis, Abdelaziz-Yousif Ahmed and Mohd-Haris Khir

Sensors 2015, 15(7), 16674-16687; https://doi.org/10.3390/s150716674 - 10 Jul 2015

Cited by 40 | Viewed by 9288

Abstract

This paper reports on the fabrication and characterization of a Complementary Metal Oxide Semiconductor-Microelectromechanical System (CMOS-MEMS) device with embedded microheater operated at relatively elevated temperatures (40 °C to 80 °C) for the purpose of relative humidity measurement. The sensing principle is based on [...] Read more.

This paper reports on the fabrication and characterization of a Complementary Metal Oxide Semiconductor-Microelectromechanical System (CMOS-MEMS) device with embedded microheater operated at relatively elevated temperatures (40 °C to 80 °C) for the purpose of relative humidity measurement. The sensing principle is based on the change in amplitude of the device due to adsorption or desorption of humidity on the active material layer of titanium dioxide (TiO₂) nanoparticles deposited on the moving plate, which results in changes in the mass of the device. The sensor has been designed and fabricated through a standard 0.35 µm CMOS process technology and post-CMOS micromachining technique has been successfully implemented to release the MEMS structures. The sensor is operated in the dynamic mode using electrothermal actuation and the output signal measured using a piezoresistive (PZR) sensor connected in a Wheatstone bridge circuit. The output voltage of the humidity sensor increases from 0.585 mV to 30.580 mV as the humidity increases from 35% RH to 95% RH. The output voltage is found to be linear from 0.585 mV to 3.250 mV as the humidity increased from 35% RH to 60% RH, with sensitivity of 0.107 mV/% RH; and again linear from 3.250 mV to 30.580 mV as the humidity level increases from 60% RH to 95% RH, with higher sensitivity of 0.781 mV/% RH. On the other hand, the sensitivity of the humidity sensor increases linearly from 0.102 mV/% RH to 0.501 mV/% RH with increase in the temperature from 40 °C to 80 °C and a maximum hysteresis of 0.87% RH is found at a relative humidity of 80%. The sensitivity is also frequency dependent, increasing from 0.500 mV/% RH at 2 Hz to reach a maximum value of 1.634 mV/% RH at a frequency of 12 Hz, then decreasing to 1.110 mV/% RH at a frequency of 20 Hz. Finally, the CMOS-MEMS humidity sensor showed comparable response, recovery, and repeatability of measurements in three cycles as compared to a standard sensor that directly measures humidity in % RH. Full article

(This article belongs to the Special Issue Gas Sensors—Designs and Applications)

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3155 KiB

Open AccessArticle

Highly Sensitive H₂S Sensor Based on the Metal-Catalyzed SnO₂ Nanocolumns Fabricated by Glancing Angle Deposition

by Kwang Soo Yoo, Soo Deok Han, Hi Gyu Moon, Seok-Jin Yoon and Chong-Yun Kang

Sensors 2015, 15(7), 15468-15477; https://doi.org/10.3390/s150715468 - 30 Jun 2015

Cited by 47 | Viewed by 6782

Abstract

As highly sensitive H₂S gas sensors, Au- and Ag-catalyzed SnO₂ thin films with morphology-controlled nanostructures were fabricated by using e-beam evaporation in combination with the glancing angle deposition (GAD) technique. After annealing at 500 °C for 40 h, the sensors [...] Read more.

As highly sensitive H₂S gas sensors, Au- and Ag-catalyzed SnO₂ thin films with morphology-controlled nanostructures were fabricated by using e-beam evaporation in combination with the glancing angle deposition (GAD) technique. After annealing at 500 °C for 40 h, the sensors showed a polycrystalline phase with a porous, tilted columnar nanostructure. The gas sensitivities (S = R_gas/R_air) of Au and Ag-catalyzed SnO₂ sensors fabricated by the GAD process were 0.009 and 0.015, respectively, under 5 ppm H₂S at 300 °C, and the 90% response time was approximately 5 s. These sensors showed excellent sensitivities compared with the SnO₂ thin film sensors that were deposited normally (glancing angle = 0°, S = 0.48). Full article

(This article belongs to the Special Issue Gas Sensors—Designs and Applications)

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2760 KiB

Open AccessArticle

A Room Temperature H₂ Sensor Fabricated Using High Performance Pt-Loaded SnO₂ Nanoparticles

by Sheng-Chang Wang and Muhammad Omar Shaikh

Sensors 2015, 15(6), 14286-14297; https://doi.org/10.3390/s150614286 - 17 Jun 2015

Cited by 44 | Viewed by 8050

Abstract

Highly sensitive H₂ gas sensors were prepared using pure and Pt-loaded SnO₂ nanoparticles. Thick film sensors (~35 μm) were fabricated that showed a highly porous interconnected structure made of high density small grained nanoparticles. Using Pt as catalyst improved sensor response [...] Read more.

Highly sensitive H₂ gas sensors were prepared using pure and Pt-loaded SnO₂ nanoparticles. Thick film sensors (~35 μm) were fabricated that showed a highly porous interconnected structure made of high density small grained nanoparticles. Using Pt as catalyst improved sensor response and reduced the operating temperature for achieving high sensitivity because of the negative temperature coefficient observed in Pt-loaded SnO₂. The highest sensor response to 1000 ppm H₂ was 10,500 at room temperature with a response time of 20 s. The morphology of the SnO₂ nanoparticles, the surface loading concentration and dispersion of the Pt catalyst and the microstructure of the sensing layer all play a key role in the development of an effective gas sensing device. Full article

(This article belongs to the Special Issue Gas Sensors—Designs and Applications)

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1178 KiB

Open AccessArticle

A Ni-Doped Carbon Nanotube Sensor for Detecting Oil-Dissolved Gases in Transformers

by Jia Lu, Xiaoxing Zhang, Xiaoqing Wu, Ziqiang Dai and Jinbin Zhang

Sensors 2015, 15(6), 13522-13532; https://doi.org/10.3390/s150613522 - 9 Jun 2015

Cited by 45 | Viewed by 7261

Abstract

C₂H₂, C₂H₄, and C₂H₆ are important oil-dissolved gases in power transformers. Detection of the composition and content of oil-dissolved gases in transformers is very significant in the diagnosis and assessment of the [...] Read more.

C₂H₂, C₂H₄, and C₂H₆ are important oil-dissolved gases in power transformers. Detection of the composition and content of oil-dissolved gases in transformers is very significant in the diagnosis and assessment of the state of transformer operations. The commonly used oil-gas analysis methods have many disadvantages, so this paper proposes a Ni-doped carbon nanotube (Ni-CNT) gas sensor to effectively detect oil-dissolved gases in a transformer. The gas-sensing properties of the sensor to C₂H₂, C₂H₄, and C₂H₆ were studied using the test device. Based on the density functional theory (DFT) the adsorption behaviors of the three gases on intrinsic carbon nanotubes (CNTs) and Ni-CNTs were calculated. The adsorption energy, charge transfer, and molecular frontier orbital of the adsorption system were also analyzed. Results showed that the sensitivity of the CNT sensor to the three kinds of gases was in the following order: C₂H₂ > C₂H₄ > C₂H₆. Moreover, the doped Ni improved the sensor response, and the sensor response and gas concentration have a good linear relationship. Full article

(This article belongs to the Special Issue Gas Sensors—Designs and Applications)

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1840 KiB

Open AccessArticle

Signal-to-Noise Enhancement of a Nanospring Redox-Based Sensor by Lock-in Amplification

by Pavel V. Bakharev and David N. McIlroy

Sensors 2015, 15(6), 13110-13120; https://doi.org/10.3390/s150613110 - 4 Jun 2015

Cited by 9 | Viewed by 5967

Abstract

A significant improvement of the response characteristics of a redox chemical gas sensor (chemiresistor) constructed with a single ZnO coated silica nanospring has been achieved with the technique of lock-in signal amplification. The comparison of DC and analog lock-in amplifier (LIA) AC measurements [...] Read more.

A significant improvement of the response characteristics of a redox chemical gas sensor (chemiresistor) constructed with a single ZnO coated silica nanospring has been achieved with the technique of lock-in signal amplification. The comparison of DC and analog lock-in amplifier (LIA) AC measurements of the electrical sensor response to toluene vapor, at the ppm level, has been conducted. When operated in the DC detection mode, the sensor exhibits a relatively high sensitivity to the analyte vapor, as well as a low detection limit at the 10 ppm level. However, at 10 ppm the signal-to-noise ratio is 5 dB, which is less than desirable. When operated in the analog LIA mode, the signal-to-noise ratio at 10 ppm increases by 30 dB and extends the detection limit to the ppb range. Full article

(This article belongs to the Special Issue Gas Sensors—Designs and Applications)

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1043 KiB

Open AccessArticle

Free-Base Carboxyphenyl Porphyrin Films Using a TiO₂ Columnar Matrix: Characterization and Application as NO₂ Sensors

by Javier Roales, José M. Pedrosa, María G. Guillén, Tânia Lopes-Costa, Pedro Castillero, Angel Barranco and Agustín R. González-Elipe

Sensors 2015, 15(5), 11118-11132; https://doi.org/10.3390/s150511118 - 12 May 2015

Cited by 31 | Viewed by 7043

Abstract

The anchoring effect on free-base carboxyphenyl porphyrin films using TiO₂ microstructured columns as a host matrix and its influence on NO₂ sensing have been studied in this work. Three porphyrins have been used: 5-(4-carboxyphenyl)10,15,20-triphenyl-21H,23H-porphyrin (MCTPP); 5,10,15,20-tetrakis(4-carboxyphenyl)-21H [...] Read more.

The anchoring effect on free-base carboxyphenyl porphyrin films using TiO₂ microstructured columns as a host matrix and its influence on NO₂ sensing have been studied in this work. Three porphyrins have been used: 5-(4-carboxyphenyl)10,15,20-triphenyl-21H,23H-porphyrin (MCTPP); 5,10,15,20-tetrakis(4-carboxyphenyl)-21H,23H-porphyrin (p-TCPP); and 5,10,15,20-tetrakis(3-carboxyphenyl)-21H,23H-porphyrin (m-TCPP). The analysis of UV-Vis spectra of MCTPP/TiO₂, p-TCPP/TiO₂ and m-TCPP/TiO₂ composite films has revealed that m-TCPP/TiO₂films are the most stable, showing less aggregation than the other porphyrins. IR spectroscopy has shown that m-TCPP is bound to TiO₂ through its four carboxylic acid groups, while p-TCPP is anchored by only one or two of these groups. MCTPP can only be bound by one carboxylic acid. Consequently, the binding of p-TCPP and MCTPP to the substrate allows them to form aggregates, whereas the more fixed anchoring of m-TCPP reduces this effect. The exposure of MCTPP/TiO₂, p-TCPP/TiO₂ and m-TCPP/TiO₂ films to NO₂ has resulted in important changes in their UV-Vis spectra, revealing good sensing capabilities in all cases. The improved stability of films made with m-TCPP suggests this molecule as the best candidate among our set of porphyrins for the fabrication of NO₂ sensors. Moreover, their concentration-dependent responses upon exposure to low concentrations of NO₂ confirm the potential of m-TCPP as a NO₂ sensor. Full article

(This article belongs to the Special Issue Gas Sensors—Designs and Applications)

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286 KiB

Open AccessArticle

Metal Oxide Gas Sensor Drift Compensation Using a Two-Dimensional Classifier Ensemble

by Hang Liu, Renzhi Chu and Zhenan Tang

Sensors 2015, 15(5), 10180-10193; https://doi.org/10.3390/s150510180 - 30 Apr 2015

Cited by 34 | Viewed by 6449

Abstract

Sensor drift is the most challenging problem in gas sensing at present. We propose a novel two-dimensional classifier ensemble strategy to solve the gas discrimination problem, regardless of the gas concentration, with high accuracy over extended periods of time. This strategy is appropriate [...] Read more.

Sensor drift is the most challenging problem in gas sensing at present. We propose a novel two-dimensional classifier ensemble strategy to solve the gas discrimination problem, regardless of the gas concentration, with high accuracy over extended periods of time. This strategy is appropriate for multi-class classifiers that consist of combinations of pairwise classifiers, such as support vector machines. We compare the performance of the strategy with those of competing methods in an experiment based on a public dataset that was compiled over a period of three years. The experimental results demonstrate that the two-dimensional ensemble outperforms the other methods considered. Furthermore, we propose a pre-aging process inspired by that applied to the sensors to improve the stability of the classifier ensemble. The experimental results demonstrate that the weight of each multi-class classifier model in the ensemble remains fairly static before and after the addition of new classifier models to the ensemble, when a pre-aging procedure is applied. Full article

(This article belongs to the Special Issue Gas Sensors—Designs and Applications)

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1158 KiB

Open AccessArticle

Enhanced Sensitivity of Gas Sensor Based on Poly(3-hexylthiophene) Thin-Film Transistors for Disease Diagnosis and Environment Monitoring

by Marco R. Cavallari, José E. E. Izquierdo, Guilherme S. Braga, Ely A. T. Dirani, Marcelo A. Pereira-da-Silva, Estrella F. G. Rodríguez and Fernando J. Fonseca

Sensors 2015, 15(4), 9592-9609; https://doi.org/10.3390/s150409592 - 22 Apr 2015

Cited by 55 | Viewed by 8718

Abstract

Electronic devices based on organic thin-film transistors (OTFT) have the potential to supply the demand for portable and low-cost gadgets, mainly as sensors for in situ disease diagnosis and environment monitoring. For that reason, poly(3-hexylthiophene) (P3HT) as the active layer in the widely-used [...] Read more.

Electronic devices based on organic thin-film transistors (OTFT) have the potential to supply the demand for portable and low-cost gadgets, mainly as sensors for in situ disease diagnosis and environment monitoring. For that reason, poly(3-hexylthiophene) (P3HT) as the active layer in the widely-used bottom-gate/bottom-contact OTFT structure was deposited over highly-doped silicon substrates covered with thermally-grown oxide to detect vapor-phase compounds. A ten-fold organochloride and ammonia sensitivity compared to bare sensors corroborated the application of this semiconducting polymer in sensors. Furthermore, P3HT TFTs presented approximately three-order higher normalized sensitivity than any chemical sensor addressed herein. The results demonstrate that while TFTs respond linearly at the lowest concentration values herein, chemical sensors present such an operating regime mostly above 2000 ppm. Simultaneous alteration of charge carrier mobility and threshold voltage is responsible for pushing the detection limit down to units of ppm of ammonia, as well as tens of ppm of alcohol or ketones. Nevertheless, P3HT transistors and chemical sensors could compose an electronic nose operated at room temperature for a wide range concentration evaluation (1–10,000 ppm) of gaseous analytes. Targeted analytes include not only biomarkers for diseases, such as uremia, cirrhosis, lung cancer and diabetes, but also gases for environment monitoring in food, cosmetic and microelectronics industries. Full article

(This article belongs to the Special Issue Gas Sensors—Designs and Applications)

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3186 KiB

Open AccessArticle

A Study of a QCM Sensor Based on TiO₂ Nanostructures for the Detection of NO₂ and Explosives Vapours in Air

by Marcin Procek, Agnieszka Stolarczyk, Tadeusz Pustelny and Erwin Maciak

Sensors 2015, 15(4), 9563-9581; https://doi.org/10.3390/s150409563 - 22 Apr 2015

Cited by 67 | Viewed by 10429

Abstract

The paper deals with investigations concerning the construction of sensors based on a quartz crystal microbalance (QCM) containing a TiO₂ nanostructures sensor layer. A chemical method of synthesizing these nanostructures is presented. The prepared prototype of the QCM sensing system, as well [...] Read more.

The paper deals with investigations concerning the construction of sensors based on a quartz crystal microbalance (QCM) containing a TiO₂ nanostructures sensor layer. A chemical method of synthesizing these nanostructures is presented. The prepared prototype of the QCM sensing system, as well as the results of tests for detecting low NO₂ concentrations in an atmosphere of synthetic air have been described. The constructed NO₂ sensors operate at room temperature, which is a great advantage, because resistance sensors based on wide gap semiconductors often require much higher operation temperatures, sometimes as high as 500 °C. The sensors constructed by the authors can be used, among other applications, in medical and chemical diagnostics, and also for the purpose of detecting explosive vapours. Reactions of the sensor to nitroglycerine vapours are presented as an example of its application. The influence of humidity on the operation of the sensor was studied. Full article

(This article belongs to the Special Issue Gas Sensors—Designs and Applications)

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1416 KiB

Open AccessArticle

Elimination of Flammable Gas Effects in Cerium Oxide Semiconductor-Type Resistive Oxygen Sensors for Monitoring Low Oxygen Concentrations

by Toshio Itoh, Noriya Izu, Takafumi Akamatsu, Woosuck Shin, Yusuke Miki and Yasuo Hirose

Sensors 2015, 15(4), 9427-9437; https://doi.org/10.3390/s150409427 - 21 Apr 2015

Cited by 10 | Viewed by 6327

Abstract

We have investigated the catalytic layer in zirconium-doped cerium oxide, Ce_0.9Zr_0.1O₂ (CeZr10) resistive oxygen sensors for reducing the effects of flammable gases, namely hydrogen and carbon monoxide. When the concentration of flammable gases is comparable to that of [...] Read more.

We have investigated the catalytic layer in zirconium-doped cerium oxide, Ce_0.9Zr_0.1O₂ (CeZr10) resistive oxygen sensors for reducing the effects of flammable gases, namely hydrogen and carbon monoxide. When the concentration of flammable gases is comparable to that of oxygen, the resistance of CeZr10 is affected by the presence of these gases. We have developed layered thick films, which consist of an oxygen sensor layer (CeZr10), an insulation layer (Al₂O₃), and a catalytic layer consisting of CeZr10 with 3 wt% added platinum, which was prepared via the screen printing method. The Pt-CeZr10 catalytic layer was found to prevent the detrimental effects of the flammable gases on the resistance of the sensor layer. This effect is due to the catalytic layer promoting the oxidation of hydrogen and carbon monoxide through the consumption of ambient O₂ and/or the lattice oxygen atoms of the Pt-CeZr10 catalytic layer. Full article

(This article belongs to the Special Issue Gas Sensors—Designs and Applications)

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785 KiB

Open AccessArticle

The Development of Love Wave-Based Humidity Sensors Incorporating Multiple Layers

by Lijun Wang, Jiansheng Liu and Shitang He

Sensors 2015, 15(4), 8615-8623; https://doi.org/10.3390/s150408615 - 14 Apr 2015

Cited by 12 | Viewed by 5350

Abstract

A Love wave humidity sensor is developed by using a multilayer structure consisting of PVA/SiO₂ layers on an ST-90°X quartz substrate. The theoretical result shows that the sensor with such a two-layer structure can achieve a higher sensitivity and a smaller loss [...] Read more.

A Love wave humidity sensor is developed by using a multilayer structure consisting of PVA/SiO₂ layers on an ST-90°X quartz substrate. The theoretical result shows that the sensor with such a two-layer structure can achieve a higher sensitivity and a smaller loss than the structures with a single polymer layer. Comparative experiments are performed for the sensor incorporating PVA/SiO₂ layers and the sensor incorporating a PVA layer. The experimental results agree well with the theoretical predication. Full article

(This article belongs to the Special Issue Gas Sensors—Designs and Applications)

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3100 KiB

Open AccessArticle

Sensing Properties of Pd-Loaded Co₃O₄ Film for a ppb-Level NO Gas Sensor

by Takafumi Akamatsu, Toshio Itoh, Noriya Izu, Woosuck Shin and Kazuo Sato

Sensors 2015, 15(4), 8109-8120; https://doi.org/10.3390/s150408109 - 7 Apr 2015

Cited by 26 | Viewed by 7143

Abstract

We prepared 0.1 wt%–30 wt% Pd-loaded Co₃O₄ by a colloidal mixing method and investigated the sensing properties of a Pd-loaded Co₃O₄ sensor element, such as the sensor response, 90% response time, 90% recovery time, and signal-to-noise ( [...] Read more.

We prepared 0.1 wt%–30 wt% Pd-loaded Co₃O₄ by a colloidal mixing method and investigated the sensing properties of a Pd-loaded Co₃O₄ sensor element, such as the sensor response, 90% response time, 90% recovery time, and signal-to-noise (S/N) ratio, toward low nitric oxide (NO) gas levels in the range from 50 to 200 parts per billion. The structural properties of the Pd-loaded Co₃O₄ powder were investigated using X-ray diffraction analysis and transmission electron microscopy. Pd in the powder existed as PdO. The sensor elements with 0.1 wt%–10 wt% Pd content have higher sensor properties than those without any Pd content. The response of the sensor element with a 30 wt% Pd content decreased markedly because of the aggregation and poor dispersibility of the PdO particles. High sensor response and S/N ratio toward the NO gas were achieved when a sensor element with 10 wt% Pd content was used. Full article

(This article belongs to the Special Issue Gas Sensors—Designs and Applications)

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Open AccessReview

Graphene Hybrid Materials in Gas Sensing Applications

by Usman Latif and Franz L. Dickert

Sensors 2015, 15(12), 30504-30524; https://doi.org/10.3390/s151229814 - 4 Dec 2015

Cited by 110 | Viewed by 11986

Abstract

Graphene, a two dimensional structure of carbon atoms, has been widely used as a material for gas sensing applications because of its large surface area, excellent conductivity, and ease of functionalization. This article reviews the most recent advances in graphene hybrid materials developed [...] Read more.

Graphene, a two dimensional structure of carbon atoms, has been widely used as a material for gas sensing applications because of its large surface area, excellent conductivity, and ease of functionalization. This article reviews the most recent advances in graphene hybrid materials developed for gas sensing applications. In this review, synthetic approaches to fabricate graphene sensors, the nano structures of hybrid materials, and their sensing mechanism are presented. Future perspectives of this rapidly growing field are also discussed. Full article

(This article belongs to the Special Issue Gas Sensors—Designs and Applications)

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3276 KiB

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Correlating the Integral Sensing Properties of Zeolites with Molecular Processes by Combining Broadband Impedance and DRIFT Spectroscopy—A New Approach for Bridging the Scales

by Peirong Chen, Simon Schönebaum, Thomas Simons, Dieter Rauch, Markus Dietrich, Ralf Moos and Ulrich Simon

Sensors 2015, 15(11), 28915-28941; https://doi.org/10.3390/s151128915 - 13 Nov 2015

Cited by 27 | Viewed by 10002

Abstract

Zeolites have been found to be promising sensor materials for a variety of gas molecules such as NH₃, NO_x, hydrocarbons, etc. The sensing effect results from the interaction of the adsorbed gas molecules with mobile cations, which are non-covalently [...] Read more.

Zeolites have been found to be promising sensor materials for a variety of gas molecules such as NH₃, NO_x, hydrocarbons, etc. The sensing effect results from the interaction of the adsorbed gas molecules with mobile cations, which are non-covalently bound to the zeolite lattice. The mobility of the cations can be accessed by electrical low-frequency (LF; mHz to MHz) and high-frequency (HF; GHz) impedance measurements. Recent developments allow in situ monitoring of catalytic reactions on proton-conducting zeolites used as catalysts. The combination of such in situ impedance measurements with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), which was applied to monitor the selective catalytic reduction of nitrogen oxides (DeNO_x-SCR), not only improves our understanding of the sensing properties of zeolite catalysts from integral electric signal to molecular processes, but also bridges the length scales being studied, from centimeters to nanometers. In this work, recent developments of zeolite-based, impedimetric sensors for automotive exhaust gases, in particular NH₃, are summarized. The electrical response to NH₃ obtained from LF impedance measurements will be compared with that from HF impedance measurements, and correlated with the infrared spectroscopic characteristics obtained from the DRIFTS studies of molecules involved in the catalytic conversion. The future perspectives, which arise from the combination of these methods, will be discussed. Full article

(This article belongs to the Special Issue Gas Sensors—Designs and Applications)

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1157 KiB

Open AccessReview

Electronic Nose Feature Extraction Methods: A Review

by Jia Yan, Xiuzhen Guo, Shukai Duan, Pengfei Jia, Lidan Wang, Chao Peng and Songlin Zhang

Sensors 2015, 15(11), 27804-27831; https://doi.org/10.3390/s151127804 - 2 Nov 2015

Cited by 247 | Viewed by 14980

Abstract

Many research groups in academia and industry are focusing on the performance improvement of electronic nose (E-nose) systems mainly involving three optimizations, which are sensitive material selection and sensor array optimization, enhanced feature extraction methods and pattern recognition method selection. For a specific [...] Read more.

Many research groups in academia and industry are focusing on the performance improvement of electronic nose (E-nose) systems mainly involving three optimizations, which are sensitive material selection and sensor array optimization, enhanced feature extraction methods and pattern recognition method selection. For a specific application, the feature extraction method is a basic part of these three optimizations and a key point in E-nose system performance improvement. The aim of a feature extraction method is to extract robust information from the sensor response with less redundancy to ensure the effectiveness of the subsequent pattern recognition algorithm. Many kinds of feature extraction methods have been used in E-nose applications, such as extraction from the original response curves, curve fitting parameters, transform domains, phase space (PS) and dynamic moments (DM), parallel factor analysis (PARAFAC), energy vector (EV), power density spectrum (PSD), window time slicing (WTS) and moving window time slicing (MWTS), moving window function capture (MWFC), etc. The object of this review is to provide a summary of the various feature extraction methods used in E-noses in recent years, as well as to give some suggestions and new inspiration to propose more effective feature extraction methods for the development of E-nose technology. Full article

(This article belongs to the Special Issue Gas Sensors—Designs and Applications)

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