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3 pages, 194 KiB

Open AccessEditorial

Chemical Sensors for Volatile Organic Compound Detection

by Fanli Meng, Zhenyu Yuan and Dan Meng

Chemosensors 2023, 11(11), 553; https://doi.org/10.3390/chemosensors11110553 - 03 Nov 2023

Cited by 1 | Viewed by 1212

Abstract

The detection of volatile organic compounds (VOCs) is in high demand in various fields, such as environmental pollution monitoring, early disease screening, and food freshness assessment [...] Full article

(This article belongs to the Special Issue Chemical Sensors for Volatile Organic Compound Detection)

Research

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12 pages, 6074 KiB

Open AccessArticle

Engineering Band Structure of SnO₂ Nanoparticles via Coupling with g-C₃N₄ Nanosheet for the Detection of Ethanolamine

by Jiuyu Li, Kerui Xie, Yating Wang, Ruihua Zhao, Yangyang Shang and Jianping Du

Chemosensors 2023, 11(5), 296; https://doi.org/10.3390/chemosensors11050296 - 16 May 2023

Cited by 3 | Viewed by 1062

Abstract

Volatile organoamines are important industrial raw materials and chemicals. Long-term exposure to amines could be harmful to human health and even cause serious pollution. In this study, SnO₂ decorated g-C₃N₄ material was fabricated and used as a sensor material [...] Read more.

Volatile organoamines are important industrial raw materials and chemicals. Long-term exposure to amines could be harmful to human health and even cause serious pollution. In this study, SnO₂ decorated g-C₃N₄ material was fabricated and used as a sensor material for the detection of ethanolamine (EA). The structures, morphology, surface chemical states, and band structure were characterized, and gas sensing was studied. The results showed that SnO₂ nanoparticles were dispersed on g-C₃N₄, and band structure was dependent on g-C₃N₄ doping. Notably, the interface heterojunction was conducive to electron transferring and O₂ molecule adsorption; the formed reactive oxygen species enhanced the reaction between oxygen and EA, thus leading to high sensitivity to EA. This composite exhibited a high response that was 2.6 times higher than that of pure SnO₂, and the detection limit reached 294 ppb. A g-C₃N₄/SnO₂-based sensor displayed a high selectivity to EA with a fast response time (1 s) and recovery time (20 s) at low operating temperatures. In particular, this sensor exhibited a linear relationship between the response and concentration, which is required for quantitative analysis. Full article

(This article belongs to the Special Issue Chemical Sensors for Volatile Organic Compound Detection)

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12 pages, 3442 KiB

Open AccessArticle

Ppb-Level NO₂ Sensor with High Selectivity Fabricated by Flower-like Au-Loaded In₂O₃

by Ji Zhang, Fangfang Zhang, Xu Li and Qingji Wang

Chemosensors 2023, 11(5), 289; https://doi.org/10.3390/chemosensors11050289 - 12 May 2023

Cited by 1 | Viewed by 1439

Abstract

With increasingly serious environmental problems caused by the improvement in people’s living standards, the number of cars has increased sharply in recent years, which directly leads to the continuous increase in the concentration of NO₂ in the air. NO₂ is a [...] Read more.

With increasingly serious environmental problems caused by the improvement in people’s living standards, the number of cars has increased sharply in recent years, which directly leads to the continuous increase in the concentration of NO₂ in the air. NO₂ is a common toxic and irritant gas, which is harmful to both the human body and the environment. Therefore, this research focuses on NO₂ detection and is committed to developing high-performance, low detection limit NO₂ sensors. In this study, flower-like Au-loaded In₂O₃ was successfully fabricated using the hydrothermal method and the wet impregnation method. The morphological features and chemical compositions of the as-prepared samples were characterized using SEM, TEM, XRD and XPS. A variety of sensors were fabricated and the gas-sensing properties of sensors were investigated. The results indicate that the sensor based on 0.5 mol% Au/In₂O₃ shows a response value of 1624 to 1 ppm NO₂ at 100 °C, which is 14 times that based on pure In₂O₃. Meanwhile, the detection limit of the sensor based on 0.5 mol% Au/In₂O₃ for NO₂ is 10 ppb, and the response value is 10.4. In addition, the sensor based on 0.5 mol% Au/In₂O₃ also has high selectivity to NO₂ among CO, CO₂, H₂, CH₄, NH₃, SO₂ and H₂S. Finally, the sensitization mechanism of Au/In₂O₃ was discussed, and the reasons for improving the performance of the sensor were analyzed. The above results and analysis demonstrate that the gas-sensing attributes of the sensor based on 0.5 mol% Au/In₂O₃ to NO₂ improved remarkably; at the same time, it has been proved that the composite material has extensive potential in practical applications. Full article

(This article belongs to the Special Issue Chemical Sensors for Volatile Organic Compound Detection)

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15 pages, 8075 KiB

Open AccessArticle

Nickel-Doped ZnO Porous Sea Urchin Nanostructures with Various Amounts of Oxygen Defects for Volatile Organic Compound Detection

by Haibo Ren, Huaipeng Weng, Xumeng Dong, Jiarui Huang and Sang Woo Joo

Chemosensors 2023, 11(4), 223; https://doi.org/10.3390/chemosensors11040223 - 04 Apr 2023

Cited by 1 | Viewed by 1084

Abstract

Porous sea urchin-like nickel-doped ZnO with various nickel contents and high specific surface area were synthesized using a solution method followed by calcination. The nickel-doped ZnO products consisted of numerous porous nanoleaves. The Ni content in these products ranged from 5% to 20%. [...] Read more.

Porous sea urchin-like nickel-doped ZnO with various nickel contents and high specific surface area were synthesized using a solution method followed by calcination. The nickel-doped ZnO products consisted of numerous porous nanoleaves. The Ni content in these products ranged from 5% to 20%. The Ni dopants in the ZnO lattice were verified by X-ray diffraction and X-ray photoelectron spectroscopy. The sensors based on nickel-doped ZnO sea urchins showed superior sensing performance for some volatile organic compounds (VOCs). ZnO sea urchins with 10% nickel doping exhibited the best gas-sensing performance, including a low working temperature, short response/recovery time, and high sensor response. In particular, the 10% Ni-doped ZnO sea urchin sensor exhibited a response of 84.4 with response/recovery times of 17/20 s towards 100 ppm formaldehyde vapor. These superior sensing behaviors were attributed mainly to a suitable Ni content with high content of oxygen defects, small nanocrystals, and a porous hierarchical structure with a high specific surface area. Full article

(This article belongs to the Special Issue Chemical Sensors for Volatile Organic Compound Detection)

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14 pages, 32178 KiB

Open AccessArticle

Study on Denoising Method of Photoionization Detector Based on Wavelet Packet Transform

by Zengyuan Liu, Xiujuan Feng, Chengliang Dong and Mingzhi Jiao

Chemosensors 2023, 11(2), 146; https://doi.org/10.3390/chemosensors11020146 - 16 Feb 2023

Cited by 1 | Viewed by 1302

Abstract

Aiming at the task of noise suppression caused by the photoionization detector (PID) monitoring signal of volatile organic compounds (VOCs) due to local non-uniformity of the photocathode surface of PID in the ionization chamber, this paper proposes an analytical method of a PID [...] Read more.

Aiming at the task of noise suppression caused by the photoionization detector (PID) monitoring signal of volatile organic compounds (VOCs) due to local non-uniformity of the photocathode surface of PID in the ionization chamber, this paper proposes an analytical method of a PID signal with the adaptive weight of the small wave package decomposition node. The PID signal is transmitted to the upper machine software through the single-chip microcontroller. The appropriate wavelet packet decomposition level is determined according to the time frequency characteristics of the original signal of the PID, and the optimal wavelet packet base is selected through the polynomial fitting of the signal quality evaluation index. By comparing the quality of signals processed by the traditional wavelet packet denoising method and the denoising method presented in this paper, the superiority of the proposed method in the denoising signals of PID was verified. This method can eliminate the noise generated by local non-uniformity on the photocathode surface of the PID ionization chamber in a high humidity environment, which lays a foundation for the accurate monitoring of VOCs in a high humidity environment. Full article

(This article belongs to the Special Issue Chemical Sensors for Volatile Organic Compound Detection)

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14 pages, 10637 KiB

Open AccessArticle

Cross-Linked SnO₂ Nanosheets Modified by Ag Nanoparticles for Formaldehyde Vapor Detection

by Huaipeng Weng, Xumeng Dong, Yufeng Sun, Haibo Ren, Jiarui Huang and Sang Woo Joo

Chemosensors 2023, 11(2), 116; https://doi.org/10.3390/chemosensors11020116 - 04 Feb 2023

Viewed by 1306

Abstract

Ag@SnO₂ nanosheets were prepared through a hydrothermal method followed by heat treatment and a liquid reduction process. Many Ag nanoparticles (Ag NPs) were dispersed uniformly over the surface of the SnO₂ nanosheets. The thickness of the SnO₂ nanosheets was approximately [...] Read more.

Ag@SnO₂ nanosheets were prepared through a hydrothermal method followed by heat treatment and a liquid reduction process. Many Ag nanoparticles (Ag NPs) were dispersed uniformly over the surface of the SnO₂ nanosheets. The thickness of the SnO₂ nanosheets was approximately 10 nm. After decoration with Ag NPs, the Ag@SnO₂ nanosheet sensors exhibited improved gas-sensing behaviors compared to the pure SnO₂ nanosheet sensor. The response of cross-linked SnO₂ nanosheets decorated by Ag NP sensors for 100 ppm formaldehyde vapor was up to 101.4, which was double that (45.5) of the pure SnO₂ nanosheet sensor. The response and recovery times of the Ag@SnO₂ sensor were 21 s and 23 s, respectively. The Ag@SnO₂ nanosheet sensors showed reasonable cycling stability, as demonstrated by testing with 100 ppm formaldehyde 10 times. The superior gas-sensing behaviors of the Ag@SnO₂ sensor were due to the large specific surface area, cross-linked nanostructure, and synergistic effect of the Ag NPs with huge sensitizing active sites and numerous SnO₂ nanosheets. Full article

(This article belongs to the Special Issue Chemical Sensors for Volatile Organic Compound Detection)

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22 pages, 5562 KiB

Open AccessArticle

A Novel Gas Recognition Algorithm for Gas Sensor Array Combining Savitzky–Golay Smooth and Image Conversion Route

by Xi Wang, Chen Qian, Zhikai Zhao, Jiaming Li and Mingzhi Jiao

Chemosensors 2023, 11(2), 96; https://doi.org/10.3390/chemosensors11020096 - 29 Jan 2023

Cited by 2 | Viewed by 1822

Abstract

In recent years, the application of Deep Neural Networks to gas recognition has been developing. The classification performance of the Deep Neural Network depends on the efficient representation of the input data samples. Therefore, a variety of filtering methods are firstly adopted to [...] Read more.

In recent years, the application of Deep Neural Networks to gas recognition has been developing. The classification performance of the Deep Neural Network depends on the efficient representation of the input data samples. Therefore, a variety of filtering methods are firstly adopted to smooth filter the gas sensing response data, which can remove redundant information and greatly improve the performance of the classifier. Additionally, the optimization experiment of the Savitzky–Golay filtering algorithm is carried out. After that, we used the Gramian Angular Summation Field (GASF) method to encode the gas sensing response data into two-dimensional sensing images. In addition, data augmentation technology is used to reduce the impact of small sample numbers on the classifier and improve the robustness and generalization ability of the model. Then, combined with fine-tuning of the GoogLeNet neural network, which owns the ability to automatically learn the characteristics of deep samples, the classification of four gases has finally been realized: methane, ethanol, ethylene, and carbon monoxide. Through setting a variety of different comparison experiments, it is known that the Savitzky–Golay smooth filtering pretreatment method effectively improves the recognition accuracy of the classifier, and the gas recognition network adopted is superior to the fine-tuned ResNet50, Alex-Net, and ResNet34 networks in both accuracy and sample processing times. Finally, the highest recognition accuracy of the classification results of our proposed route is 99.9%, which is better than other similar work. Full article

(This article belongs to the Special Issue Chemical Sensors for Volatile Organic Compound Detection)

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13 pages, 7320 KiB

Open AccessArticle

Synthesis of Graphene-Oxide-Decorated Porous ZnO Nanosheet Composites and Their Gas Sensing Properties

by Jie Li, Zhen Jin, Yang Chao, Aijing Wang, Decai Wang, Shaohua Chen and Quan Qian

Chemosensors 2023, 11(1), 65; https://doi.org/10.3390/chemosensors11010065 - 13 Jan 2023

Cited by 5 | Viewed by 2046

Abstract

In this work, graphene-oxide-decorated porous ZnO nanosheets were prepared using a hydrothermal method. The graphene oxide/porous ZnO nanosheet (GO/ZnO nanosheet) composites were characterized with SEM, HRTEM, XRD, Raman spectroscopy, XPS and BET. The results indicate that the ZnO nanosheets have a porous, single-crystal [...] Read more.

In this work, graphene-oxide-decorated porous ZnO nanosheets were prepared using a hydrothermal method. The graphene oxide/porous ZnO nanosheet (GO/ZnO nanosheet) composites were characterized with SEM, HRTEM, XRD, Raman spectroscopy, XPS and BET. The results indicate that the ZnO nanosheets have a porous, single-crystal structure. Thin GO nanosheets closely cover the surface of porous ZnO nanosheets. The sensing performance of GO/ZnO nanosheet composites is investigated. At the optimized temperature of 300 °C, the GO/ZnO nanosheet composites exhibit a superior sensing performance in n-propanol detection. In a wide range of 5–200 ppm, the composites exhibit a linear response to n-propanol. Moreover, the sensing performance of the GO/ZnO nanosheet composites to n-propanol is largely higher than that to other VOC gases, indicating a high selectivity in n-propanol detection. This can be ascribed to the higher electron-separation efficiency and larger depletion layer brought by the modification of the GO on ZnO nanosheets. It is considered that the GO/ZnO nanosheet composites have a great application potential in n-propanol detection. Full article

(This article belongs to the Special Issue Chemical Sensors for Volatile Organic Compound Detection)

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15 pages, 2156 KiB

Open AccessArticle

Nanostructuring of SnO₂ Thin Films by Associating Glancing Angle Deposition and Sputtering Pressure for Gas Sensing Applications

by Achraf El Mohajir, Mohammad Arab Pour Yazdi, Anna Krystianiak, Olivier Heintz, Nicolas Martin, Franck Berger and Jean-Baptiste Sanchez

Chemosensors 2022, 10(10), 426; https://doi.org/10.3390/chemosensors10100426 - 17 Oct 2022

Cited by 4 | Viewed by 1703

Abstract

SnO₂ thin films were prepared by conventional and Glancing Angle Deposition reactive sputtering, and their gas sensing properties were investigated. The porosity of the as-prepared films was widely assessed using optical methods, and the sensing performances of these active layers were correlated [...] Read more.

SnO₂ thin films were prepared by conventional and Glancing Angle Deposition reactive sputtering, and their gas sensing properties were investigated. The porosity of the as-prepared films was widely assessed using optical methods, and the sensing performances of these active layers were correlated with the evolution of surface and film porosity as a function of deposition conditions and annealing treatment. The sensor made of inclined columns grown at high sputtering pressure (6 × 10⁻³ mbar) and annealed at 500 °C in air exhibited the best response to benzene, with a limit of detection of 30 ppb. In addition, successful BTEX (i.e., benzene, toluene, ethylbenzene, and xylenes) discrimination was achieved by combining the sensing signals of four nanostructured tin-oxide-based gas sensors. Full article

(This article belongs to the Special Issue Chemical Sensors for Volatile Organic Compound Detection)

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13 pages, 4256 KiB

Open AccessArticle

High-Performance Sulfur Dioxide Gas Sensor Based on Graphite-Phase Carbon-Nitride-Functionalized Tin Diselenide Nanorods Composite

by Hao Zhang, Qiannan Pan, Yating Zhang, Yanting Zhang and Dongzhi Zhang

Chemosensors 2022, 10(10), 401; https://doi.org/10.3390/chemosensors10100401 - 08 Oct 2022

Cited by 2 | Viewed by 1765

Abstract

In this paper, a composite of tin diselenide (SnSe₂) functionalized by graphite-phase carbon nitride (g-C₃N₄) was successfully prepared by a hydrothermal method, and was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and X-ray photoelectron spectroscopy [...] Read more.

In this paper, a composite of tin diselenide (SnSe₂) functionalized by graphite-phase carbon nitride (g-C₃N₄) was successfully prepared by a hydrothermal method, and was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). These microstructure characterization results verified the successful synthesis of a multilayer g-C₃N₄/rod-shaped SnSe₂ composite. The gas sensitivity results showed that when the g-C₃N₄ ratio was 30%, the g-C₃N₄/SnSe₂ composite sensor had the highest response (28.9%) at 200 °C to 20 ppm sulfur dioxide (SO₂) gas, which was much higher than those of pristine g-C₃N₄ and SnSe₂ sensors at the optimum temperature. A series of comparative experiments proved that the g-C₃N₄/SnSe₂ composite sensor demonstrated an excellent response, strong reversibility and good selectivity for ppm-level SO₂ gas detection. The possible SO₂ sensing mechanism was ascribed to the heterostructure between the n-type SnSe₂ and n-type g-C₃N₄ nanomaterials. Furthermore, we also proposed the influence of the special structure of the g-C₃N₄ functionalized SnSe₂ composite on the gas-sensing characteristics. Full article

(This article belongs to the Special Issue Chemical Sensors for Volatile Organic Compound Detection)

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12 pages, 2553 KiB

Open AccessArticle

Non-Invasive Rapid Detection of Lung Cancer Biomarker Toluene with a Cataluminescence Sensor Based on the Two-Dimensional Nanocomposite Pt/Ti₃C₂T_x-CNT

by Hongyan Wang, Xiaoqi Shi, Fei Liu, Tingmei Duan and Bai Sun

Chemosensors 2022, 10(8), 333; https://doi.org/10.3390/chemosensors10080333 - 14 Aug 2022

Cited by 9 | Viewed by 2219

Abstract

A novel two-dimensional nanocomposite Pt/Ti₃C₂T_x-CNT was synthesized for the non-invasive rapid detection of toluene, a lung cancer biomarker, via cataluminescence (CTL). Pt/Ti₃C₂T_x-CNT exhibited a good catalytic performance toward toluene. The CTL [...] Read more.

A novel two-dimensional nanocomposite Pt/Ti₃C₂T_x-CNT was synthesized for the non-invasive rapid detection of toluene, a lung cancer biomarker, via cataluminescence (CTL). Pt/Ti₃C₂T_x-CNT exhibited a good catalytic performance toward toluene. The CTL sensor based on Pt/Ti₃C₂T_x-CNT has the advantage of rapid response: The average response time was about 1 s, and the average recovery time was about 30 s. Moreover, the material has a wide scope of detection for toluene, and the limit of detection defined as 3 S/N was about 2 ppm. The optimal working temperature (150 °C) is lower than common sensors, so it has a broad prospect in the actual detection process. Aside from its weak response to formaldehyde, the sensor only exerted a strong response signal to toluene, and no response was observed to other VOCs, indicating that this CTL sensor has good selectivity for toluene. The possible sensing mechanism of CTL showed that toluene was oxidized to generate excited-state CO₂*, which emitted a luminescent signal when it returned to the ground state. Full article

(This article belongs to the Special Issue Chemical Sensors for Volatile Organic Compound Detection)

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15 pages, 6930 KiB

Open AccessArticle

Influence of Nickel Doping on Ultrahigh Toluene Sensing Performance of Core-Shell ZnO Microsphere Gas Sensor

by Zhenhua Li, Sijia Li, Zijian Song, Xueli Yang, Ziyan Wang, Hao Zhang, Lanlan Guo, Caixuan Sun, Hongyan Liu, Junkai Shao, Yehong Cheng and Guofeng Pan

Chemosensors 2022, 10(8), 327; https://doi.org/10.3390/chemosensors10080327 - 12 Aug 2022

Cited by 7 | Viewed by 1817

Abstract

As a volatile organic compound, toluene is extremely harmful to the environment and human health. In this work, through a simple one-step solvothermal method, Ni-doped ZnO sensitive materials (0.5, 1, and 2 at% Ni-doped ZnO) with a core-shell morphology were synthesized for the [...] Read more.

As a volatile organic compound, toluene is extremely harmful to the environment and human health. In this work, through a simple one-step solvothermal method, Ni-doped ZnO sensitive materials (0.5, 1, and 2 at% Ni-doped ZnO) with a core-shell morphology were synthesized for the first time for toluene gas detection. The sensing test results showed that the sensor based on 1 at% Ni-doped ZnO exhibited the best toluene sensing performance. The response was up to 210 to 100 ppm toluene at 325 °C. The sensor exhibited high selectivity, fast response/recovery characteristics (2/77 s), and low detection limit (500 ppb, 3.5). Furthermore, we carried out molecular-level research on the sensitive material prepared in this experiment by various characterization methods. The SEM characterization results showed that ZnO and Ni-doped ZnO possessed the core-shell morphology, and the average grain size decreased with the increase in the Ni doping content. The UV–Vis test showed that the band gap of ZnO became smaller with the increase in the Ni doping amount. The enhanced toluene sensing performance of 1 at% Ni-doped ZnO could be ascribed to the structural sensitization and Ni doping sensitization, which are discussed in detail in the sensing mechanism section. Full article

(This article belongs to the Special Issue Chemical Sensors for Volatile Organic Compound Detection)

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14 pages, 10551 KiB

Open AccessArticle

One-Step Hydrothermal Synthesis of 3D Interconnected rGO/In₂O₃ Heterojunction Structures for Enhanced Acetone Detection

by Xiaoguang San, Yue Zhang, Lei Zhang, Guosheng Wang, Dan Meng, Jia Cui and Quan Jin

Chemosensors 2022, 10(7), 270; https://doi.org/10.3390/chemosensors10070270 - 11 Jul 2022

Cited by 4 | Viewed by 1651

Abstract

Acetone detection is of great significance for environmental monitoring or diagnosis of diabetes. Nevertheless, fast and sensitive detection of acetone at low temperatures remains challenging. Herein, a series of rGO-functionalized three-dimensional (3D) In₂O₃ flower-like structures were designed and synthesized via [...] Read more.

Acetone detection is of great significance for environmental monitoring or diagnosis of diabetes. Nevertheless, fast and sensitive detection of acetone at low temperatures remains challenging. Herein, a series of rGO-functionalized three-dimensional (3D) In₂O₃ flower-like structures were designed and synthesized via a facile hydrothermal method, and their acetone-sensing properties were systematically investigated. Compared to the pure 3D In₂O₃ flower-like structures, the rGO-functionalized 3D In₂O₃ flower-like structures demonstrated greatly improved acetone-sensing performance at relatively low temperatures. In particular, the 5-rGO/In₂O₃ sensor with an optimized decoration exhibited the highest response value (5.6) to 10 ppm acetone at 150 °C, which was about 2.3 times higher than that of the In₂O₃ sensor (2.4 at 200 °C). Furthermore, the 5-rGO/In₂O₃ sensor also showed good reproducibility, a sub-ppm-level detection limit (1.3 to 0.5 ppm), fast response and recovery rates (3 s and 18 s, respectively), and good long-term stability. The extraordinary acetone-sensing performance of rGO/In₂O₃ composites can be attributed to the synergistic effect of the formation of p-n heterojunctions between rGO and In₂O₃, the large specific surface area, the unique flower-like structures, and the high conductivity of rGO. This work provides a novel sensing material design strategy for effective detection of acetone. Full article

(This article belongs to the Special Issue Chemical Sensors for Volatile Organic Compound Detection)

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13 pages, 3950 KiB

Open AccessArticle

Dynamic Measurement of VOCs with Multiple Characteristic Peaks Based on Temperature Modulation of ZnO Gas Sensor

by Xue Shi, Hua Zhang, Hanyang Ji and Fanli Meng

Chemosensors 2022, 10(6), 226; https://doi.org/10.3390/chemosensors10060226 - 15 Jun 2022

Cited by 2 | Viewed by 1710

Abstract

Volatile organic compounds (VOC) harm human health seriously in the air. Therefore, it is essential to recognize VOC gases qualitatively and quantitatively. The dynamic measurement method can improve the selectivity of metal oxide semiconductor (MOS) gas sensors to VOC, but there is a [...] Read more.

Volatile organic compounds (VOC) harm human health seriously in the air. Therefore, it is essential to recognize VOC gases qualitatively and quantitatively. The dynamic measurement method can improve the selectivity of metal oxide semiconductor (MOS) gas sensors to VOC, but there is a problem of the insufficient number of characteristic peaks. From the experimental point of view, the primary judgment basis for the correct qualitative and quantitative recognition of VOC gases by the dynamic measurement method is the characteristic peak of the dynamic response signal. However, the traditional dynamic measurement method generally only has two characteristic peaks. In this experiment, the voltage was changed at the time of the second characteristic peak by controlling the constant dynamic response period. Taking ethyl alcohol as an example, the experimental results show that the characteristic peak of the dynamic response signal does not increase when the voltage is constant. However, a new characteristic peak will appear based on a continuously rising heating voltage. The characteristic peaks of the dynamic response of n-propyl alcohol, isopropyl alcohol, and n-butyl alcohol were also increased based on the rising heating voltage waveform. Based on the K-Nearest-Neighbors algorithm, the qualitative and quantitative recognition rate of the four alcohol homologue gases reached 100%. Full article

(This article belongs to the Special Issue Chemical Sensors for Volatile Organic Compound Detection)

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10 pages, 2043 KiB

Open AccessArticle

A New Kind of Chemical Nanosensors for Discrimination of Espresso Coffee

by Giuseppe Greco, Estefanía Núñez Carmona, Giorgio Sberveglieri, Dario Genzardi and Veronica Sberveglieri

Chemosensors 2022, 10(5), 186; https://doi.org/10.3390/chemosensors10050186 - 16 May 2022

Cited by 6 | Viewed by 2030

Abstract

There are different methods to extract and brew coffee, therefore, coffee processing is an important factor and should be studied in detail. Herein, coffee was brewed by means of a new espresso professional coffee machine, using coffee powder or portioned coffee (capsule). Four [...] Read more.

There are different methods to extract and brew coffee, therefore, coffee processing is an important factor and should be studied in detail. Herein, coffee was brewed by means of a new espresso professional coffee machine, using coffee powder or portioned coffee (capsule). Four different kinds of coffees (Biologico, Dolce, Deciso, Guatemala) were investigated with and without capsules and the goal was to classify the volatiloma of each one by Small Sensor System (S3). The response of the semiconductor metal oxide sensors (MOX) of S3 where recorded, for all 288 replicates and after normalization ∆R/R0 was extracted as a feature. PCA analysis was used to compare and differentiate the same kind of coffee sample with and without a capsule. It could be concluded that the coffee capsules affect the quality, changing on the flavor profile of espresso coffee when extracted different methods confirming the use of s3 device as a rapid and user-friendly tool in the food quality control chain. Full article

(This article belongs to the Special Issue Chemical Sensors for Volatile Organic Compound Detection)

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14 pages, 4286 KiB

Open AccessArticle

Wireless Volatile Organic Compound Detection for Restricted Internet of Things Environments Based on Cataluminescence Sensors

by Xinyi Shen, Guolong Shi, Yongxing Zhang and Shizhuang Weng

Chemosensors 2022, 10(5), 179; https://doi.org/10.3390/chemosensors10050179 - 09 May 2022

Cited by 12 | Viewed by 2176

Abstract

Cataluminescence-based sensors do not require external light sources and complex circuitry, which enables them to avoid light scattering with high sensitivity, selectivity, and widely linear range. In this study, a wireless sensor system based on hierarchical CuO microspheres assembled from nano-sheets was constructed [...] Read more.

Cataluminescence-based sensors do not require external light sources and complex circuitry, which enables them to avoid light scattering with high sensitivity, selectivity, and widely linear range. In this study, a wireless sensor system based on hierarchical CuO microspheres assembled from nano-sheets was constructed for Volatile Organic Compound (VOC) online detection. Through sensor characteristics and data process analysis, the results showed that the luminous sensor system has good luminous characteristics, including the intensity of visible light, high signal/noise (S/N) values, and very short response and recovery times. Different VOC concentration values can be detected on multiple wavelength channels and different Cataluminescence signal spectra separations can process multiple sets of Cataluminescence data combinations concurrently. This study also briefly studied the mechanism action of the Cataluminescence sensor, which can specifically be used for VOC detecting. Full article

(This article belongs to the Special Issue Chemical Sensors for Volatile Organic Compound Detection)

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14 pages, 5702 KiB

Open AccessArticle

Porous Pb-Doped ZnO Nanobelts with Enriched Oxygen Vacancies: Preparation and Their Chemiresistive Sensing Performance

by Kai-Ge Zheng, Tian-Yu Yang and Zheng Guo

Chemosensors 2022, 10(3), 96; https://doi.org/10.3390/chemosensors10030096 - 01 Mar 2022

Cited by 9 | Viewed by 2229

Abstract

Among various approaches to improve the sensing performance of metal oxide, the metal-doped method is perceived as effective, and has received great attention and is widely investigated. However, it is still a challenge to construct heterogeneous metal-doped metal oxide with an excellent sensing [...] Read more.

Among various approaches to improve the sensing performance of metal oxide, the metal-doped method is perceived as effective, and has received great attention and is widely investigated. However, it is still a challenge to construct heterogeneous metal-doped metal oxide with an excellent sensing performance. In the present study, porous Pb-doped ZnO nanobelts were prepared by a simply partial cation exchange method, followed by in situ thermal oxidation. Detailed characterization confirmed that Pb was uniformly distributed on porous nanobelts. Additionally, it occupied the Zn situation, not forming its oxides. The gas-sensing measurements revealed that 0.61 at% Pb-doped ZnO porous nanobelts exhibited a selectively enhanced response with long-term stability toward n-butanol among the investigated VOCs. The relative response to 50 ppm of n-butanol was up to 47.7 at the working temperature of 300 °C. Additionally, the response time was short (about 5 s). These results were mainly ascribed to the porous nanostructure, two-dimensional belt-like morphology, enriched oxygen vacancies and the specific synergistic effect from the Pb dopant. Finally, a possible sensing mechanism of porous Pb-doped ZnO nanobelts is proposed and discussed. Full article

(This article belongs to the Special Issue Chemical Sensors for Volatile Organic Compound Detection)

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Review

Jump to: Editorial, Research

31 pages, 10422 KiB

Open AccessReview

Metal Oxide Semiconductor Sensors for Triethylamine Detection: Sensing Performance and Improvements

by Hua Zhang, Yinghao Guo and Fanli Meng

Chemosensors 2022, 10(6), 231; https://doi.org/10.3390/chemosensors10060231 - 17 Jun 2022

Cited by 26 | Viewed by 3773

Abstract

Triethylamine (TEA) is an organic compound that is commonly used in industries, but its volatile, inflammable, corrosive, and toxic nature leads to explosions and tissue damage. A sensitive, accurate, and in situ monitoring of TEA is of great significance to production safety and [...] Read more.

Triethylamine (TEA) is an organic compound that is commonly used in industries, but its volatile, inflammable, corrosive, and toxic nature leads to explosions and tissue damage. A sensitive, accurate, and in situ monitoring of TEA is of great significance to production safety and human health. Metal oxide semiconductors (MOSs) are widely used as gas sensors for volatile organic compounds due to their high bandgap and unique microstructure. This review aims to provide insights into the further development of MOSs by generalizing existing MOSs for TEA detection and measures to improve their sensing performance. This review starts by proposing the basic gas-sensing characteristics of the sensor and two typical TEA sensing mechanisms. Then, recent developments to improve the sensing performance of TEA sensors are summarized from different aspects, such as the optimization of material morphology, the incorporation of other materials (metal elements, conducting polymers, etc.), the development of new materials (graphene, TMDs, etc.), the application of advanced fabrication devices, and the introduction of external stimulation. Finally, this review concludes with prospects for using the aforementioned methods in the fabrication of high-performance TEA gas sensors, as well as highlighting the significance and research challenges in this emerging field. Full article

(This article belongs to the Special Issue Chemical Sensors for Volatile Organic Compound Detection)

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