Research

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15 pages, 6867 KiB

Open AccessArticle

Pd-Functionalized SnO₂ Nanofibers Prepared by Shaddock Peels as Bio-Templates for High Gas Sensing Performance toward Butane

by Rongjun Zhao, Zhezhe Wang, Yue Yang, Xinxin Xing, Tong Zou, Zidong Wang, Ping Hong, Sijia Peng and Yude Wang

Nanomaterials 2019, 9(1), 13; https://doi.org/10.3390/nano9010013 - 23 Dec 2018

Cited by 18 | Viewed by 3464

Abstract

Pd-functionalized one-dimensional (1D) SnO₂ nanostructures were synthesized via a facile hydrothermal method and shaddock peels were used as bio-templates to induce a 1D-fiber-like morphology into the gas sensing materials. The gas-sensing performances of sensors based on different ratios of Pd-functionalized SnO₂ [...] Read more.

Pd-functionalized one-dimensional (1D) SnO₂ nanostructures were synthesized via a facile hydrothermal method and shaddock peels were used as bio-templates to induce a 1D-fiber-like morphology into the gas sensing materials. The gas-sensing performances of sensors based on different ratios of Pd-functionalized SnO₂ composites were measured. All results indicate that the sensor based on 5 mol % Pd-functionalized SnO₂ composites exhibited significantly enhanced gas-sensing performances toward butane. With regard to pure SnO₂, enhanced levels of gas response and selectivity were observed. With 5 mol % Pd-functionalized SnO₂ composites, detection limits as low as 10 ppm with responses of 1.38 ± 0.26 were attained. Additionally, the sensor exhibited rapid response/recovery times (3.20/6.28 s) at 3000 ppm butane, good repeatability and long-term stability, demonstrating their potential in practical applications. The excellent gas-sensing performances are attributed to the unique one-dimensional morphology and the large internal surface area of sensing materials afforded using bio-templates, which provide more active sites for the reaction between butane molecules and adsorbed oxygen ions. The catalysis and “spillover effect” of Pd nanoparticles also play an important role in the sensing of butane gas as further discussed in the paper. Full article

(This article belongs to the Special Issue Development of Semiconductor Nanomaterials for Gas Sensors)

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16 pages, 5559 KiB

Open AccessArticle

Influence of Mono- and Bimetallic PtO_x, PdO_x, PtPdO_x Clusters on CO Sensing by SnO₂ Based Gas Sensors

by Pavel Kutukov, Marina Rumyantseva, Valeriy Krivetskiy, Darya Filatova, Maria Batuk, Joke Hadermann, Nikolay Khmelevsky, Anatoly Aksenenko and Alexander Gaskov

Nanomaterials 2018, 8(11), 917; https://doi.org/10.3390/nano8110917 - 07 Nov 2018

Cited by 22 | Viewed by 3534

Abstract

To obtain a nanocrystalline SnO₂ matrix and mono- and bimetallic nanocomposites SnO₂/Pd, SnO₂/Pt, and SnO₂/PtPd, a flame spray pyrolysis with subsequent impregnation was used. The materials were characterized using X-ray diffraction (XRD), a single-point BET method, [...] Read more.

To obtain a nanocrystalline SnO₂ matrix and mono- and bimetallic nanocomposites SnO₂/Pd, SnO₂/Pt, and SnO₂/PtPd, a flame spray pyrolysis with subsequent impregnation was used. The materials were characterized using X-ray diffraction (XRD), a single-point BET method, transmission electron microscopy (TEM), and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) with energy dispersive X-ray (EDX) mapping. The electronic state of the metals in mono- and bimetallic clusters was determined using X-ray photoelectron spectroscopy (XPS). The active surface sites were investigated using the Fourier Transform infrared spectroscopy (FTIR) and thermo-programmed reduction with hydrogen (TPR-H₂) methods. The sensor response of blank SnO₂ and nanocomposites had a carbon monoxide (CO) level of 6.7 ppm and was determined in the temperature range 60–300 °C in dry (Relative Humidity (RH) = 0%) and humid (RH = 20%) air. The sensor properties of the mono- and bimetallic nanocomposites were analyzed on the basis of information on the electronic state, the distribution of modifiers in SnO₂ matrix, and active surface centers. For SnO₂/PtPd, the combined effect of the modifiers on the electrophysical properties of SnO₂ explained the inversion of sensor response from n- to p-types observed in dry conditions. Full article

(This article belongs to the Special Issue Development of Semiconductor Nanomaterials for Gas Sensors)

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17 pages, 4370 KiB

Open AccessArticle

Significant Enhancement of Hydrogen-Sensing Properties of ZnO Nanofibers through NiO Loading

by Jae-Hyoung Lee, Jin-Young Kim, Ali Mirzaei, Hyoun Woo Kim and Sang Sub Kim

Nanomaterials 2018, 8(11), 902; https://doi.org/10.3390/nano8110902 - 03 Nov 2018

Cited by 43 | Viewed by 3864

Abstract

Metal oxide p-n heterojunction nanofibers (NFs) are among the most promising approaches to enhancing the efficiency of gas sensors. In this paper, we report the preparation of a series of p-NiO-loaded n-ZnO NFs, namely (1−x)ZnO-xNiO (x = 0.03, 0.05, [...] Read more.

Metal oxide p-n heterojunction nanofibers (NFs) are among the most promising approaches to enhancing the efficiency of gas sensors. In this paper, we report the preparation of a series of p-NiO-loaded n-ZnO NFs, namely (1−x)ZnO-xNiO (x = 0.03, 0.05, 0.7, 0.1, and 0.15 wt%), for hydrogen gas sensing experiments. Samples were prepared through the electrospinning technique followed by a calcination process. The sensing experiments showed that the sample with 0.05 wt% NiO loading resulted in the highest sensing performance at an optimal sensing temperature of 200 °C. The sensing mechanism is discussed in detail and contributions of the p-n heterojunctions, metallization of ZnO and catalytic effect of NiO on the sensing enhancements of an optimized gas sensor are analyzed. This study demonstrates the possibility of fabricating high-performance H₂ sensors through the optimization of p-type metal oxide loading on the surfaces of n-type metal oxides. Full article

(This article belongs to the Special Issue Development of Semiconductor Nanomaterials for Gas Sensors)

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17 pages, 4399 KiB

Open AccessArticle

Rhodium Oxide Surface-Loaded Gas Sensors

by Anna Staerz, Inci Boehme, David Degler, Mounib Bahri, Dmitry E. Doronkin, Anna Zimina, Helena Brinkmann, Sina Herrmann, Benjamin Junker, Ovidiu Ersen, Jan-Dierk Grunwaldt, Udo Weimar and Nicolae Barsan

Nanomaterials 2018, 8(11), 892; https://doi.org/10.3390/nano8110892 - 01 Nov 2018

Cited by 25 | Viewed by 4529

Abstract

In order to increase their stability and tune-sensing characteristics, metal oxides are often surface-loaded with noble metals. Although a great deal of empirical work shows that surface-loading with noble metals drastically changes sensing characteristics, little information exists on the mechanism. Here, a systematic [...] Read more.

In order to increase their stability and tune-sensing characteristics, metal oxides are often surface-loaded with noble metals. Although a great deal of empirical work shows that surface-loading with noble metals drastically changes sensing characteristics, little information exists on the mechanism. Here, a systematic study of sensors based on rhodium-loaded WO₃, SnO₂, and In₂O₃—examined using X-ray diffraction, high-resolution scanning transmission electron microscopy, direct current (DC) resistance measurements, operando diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, and operando X-ray absorption spectroscopy—is presented. Under normal sensing conditions, the rhodium clusters were oxidized. Significant evidence is provided that, in this case, the sensing is dominated by a Fermi-level pinning mechanism, i.e., the reaction with the target gas takes place on the noble-metal cluster, changing its oxidation state. As a result, the heterojunction between the oxidized rhodium clusters and the base metal oxide was altered and a change in the resistance was detected. Through measurements done in low-oxygen background, it was possible to induce a mechanism switch by reducing the clusters to their metallic state. At this point, there was a significant drop in the overall resistance, and the reaction between the target gas and the base material was again visible. For decades, noble metal loading was used to change the characteristics of metal-oxide-based sensors. The study presented here is an attempt to clarify the mechanism responsible for the change. Generalities are shown between the sensing mechanisms of different supporting materials loaded with rhodium, and sample-specific aspects that must be considered are identified. Full article

(This article belongs to the Special Issue Development of Semiconductor Nanomaterials for Gas Sensors)

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15 pages, 7257 KiB

Open AccessArticle

Effects of Ag Additive in Low Temperature CO Detection with In₂O₃ Based Gas Sensors

by Daniil Naberezhnyi, Marina Rumyantseva, Darya Filatova, Maria Batuk, Joke Hadermann, Alexander Baranchikov, Nikolay Khmelevsky, Anatoly Aksenenko, Elizaveta Konstantinova and Alexander Gaskov

Nanomaterials 2018, 8(10), 801; https://doi.org/10.3390/nano8100801 - 08 Oct 2018

Cited by 17 | Viewed by 4351

Abstract

Nanocomposites In₂O₃/Ag obtained by ultraviolet (UV) photoreduction and impregnation methods were studied as materials for CO sensors operating in the temperature range 25–250 °C. Nanocrystalline In₂O₃ and In₂O₃/Ag nanocomposites were characterized by [...] Read more.

Nanocomposites In₂O₃/Ag obtained by ultraviolet (UV) photoreduction and impregnation methods were studied as materials for CO sensors operating in the temperature range 25–250 °C. Nanocrystalline In₂O₃ and In₂O₃/Ag nanocomposites were characterized by X-ray diffraction (XRD), single-point Brunauer-Emmet-Teller (BET) method, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) with energy dispersive X-ray (EDX) mapping. The active surface sites were investigated using Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR) spectroscopy and thermo-programmed reduction with hydrogen (TPR-H₂) method. Sensor measurements in the presence of 15 ppm CO demonstrated that UV treatment leads to a complete loss of In₂O₃ sensor sensitivity, while In₂O₃/Ag-UV nanocomposite synthesized by UV photoreduction demonstrates an increased sensor signal to CO at T < 200 °C. The observed high sensor response of the In₂O₃/Ag-UV nanocomposite at room temperature may be due to the realization of an additional mechanism of CO oxidation with participation of surface hydroxyl groups associated via hydrogen bonds. Full article

(This article belongs to the Special Issue Development of Semiconductor Nanomaterials for Gas Sensors)

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10 pages, 1683 KiB

Open AccessArticle

Surface Properties of SnO₂ Nanowires Deposited on Si Substrate Covered by Au Catalyst Studies by XPS, TDS and SEM

by Monika Kwoka, Barbara Lyson-Sypien, Anna Kulis, Dario Zappa and Elisabetta Comini

Nanomaterials 2018, 8(9), 738; https://doi.org/10.3390/nano8090738 - 18 Sep 2018

Cited by 23 | Viewed by 7839

Abstract

The surface chemistry and the morphology of SnO₂ nanowires of average length and diameter of several µm and around 100 nm, respectively, deposited by vapor phase deposition (VPD) method on Au-covered Si substrate, were studied before and after subsequent air exposure. For [...] Read more.

The surface chemistry and the morphology of SnO₂ nanowires of average length and diameter of several µm and around 100 nm, respectively, deposited by vapor phase deposition (VPD) method on Au-covered Si substrate, were studied before and after subsequent air exposure. For this purpose, surface-sensitive methods, including X-ray photoelectron spectroscopy (XPS), thermal desorption spectroscopy (TDS) and the scanning electron microscopy (SEM), were applied. The studies presented within this paper allowed to determine their surface non-stoichiometry combined with the presence of carbon contaminations, in a good correlation with their surface morphology. The relative concentrations of the main components [O]/[Sn]; [C]/[Sn]; [Au]/[Sn], together with the O–Sn; O–Si bonds, were analyzed. The results of TDS remained in a good agreement with the observations from XPS. Moreover, conclusions obtained for SnO₂ nanowires deposited with the use of Au catalyst were compared to the previous obtained for Ag-assisted tin dioxide nanowires. The information obtained within these studies is of a great importance for the potential application of SnO₂ nanowires in the field of novel chemical nanosensor devices, since the results can provide an interpretation of how aging effects influence gas sensor dynamic characteristics. Full article

(This article belongs to the Special Issue Development of Semiconductor Nanomaterials for Gas Sensors)

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16 pages, 3916 KiB

Open AccessArticle

Zinc Oxide Coated Tin Oxide Nanofibers for Improved Selective Acetone Sensing

by Haiying Du, Xiaogan Li, Pengjun Yao, Jing Wang, Yanhui Sun and Liang Dong

Nanomaterials 2018, 8(7), 509; https://doi.org/10.3390/nano8070509 - 09 Jul 2018

Cited by 30 | Viewed by 4588

Abstract

Three-dimensional hierarchical SnO₂/ZnO hetero-nanofibers were fabricated by the electrospinning method followed with a low-temperature water bath treatment. These hierarchical hollow SnO₂ nanofibers were assembled by the SnO₂ nanoparticles through the electrospinning process and then the ZnO nanorods were grown [...] Read more.

Three-dimensional hierarchical SnO₂/ZnO hetero-nanofibers were fabricated by the electrospinning method followed with a low-temperature water bath treatment. These hierarchical hollow SnO₂ nanofibers were assembled by the SnO₂ nanoparticles through the electrospinning process and then the ZnO nanorods were grown vertically on the surface of SnO₂ nanoparticles, forming the 3D nanostructure. The synthesized hollow SnO₂/ZnO heterojunctions nanofibers were further employed to be a gas-sensing material for detection of volatile organic compound (VOC) species such as acetone vapor, which is proposed as a gas biomarker for diabetes. It shows that the heterojunction nanofibers-based sensor exhibited excellent sensing properties to acetone vapor. The sensor shows a good selectivity to acetone in the interfering gases of ethanol, ammonia, formaldehyde, toluene, and methanol. The enhanced sensing performance may be due to the fact that n-n 3D heterojunctions, existing at the interface between ZnO nanorods and SnO₂ particles in the SnO₂/ZnO nanocomposites, could prompt significant changes in potential barrier height when exposed to acetone vapor, and gas-sensing mechanisms were analyzed and explained by Schottky barrier changes in SnO₂/ZnO 3D hetero-nanofibers. Full article

(This article belongs to the Special Issue Development of Semiconductor Nanomaterials for Gas Sensors)

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Review

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22 pages, 6187 KiB

Open AccessReview

Sensitivity-Selectivity Trade-Offs in Surface Ionization Gas Detection

by Gerhard Müller, J. Daniel Prades, Angelika Hackner, Andrea Ponzoni, Elisabetta Comini and Giorgio Sberveglieri

Nanomaterials 2018, 8(12), 1017; https://doi.org/10.3390/nano8121017 - 06 Dec 2018

Cited by 5 | Viewed by 5736

Abstract

Surface ionization (SI) provides a simple, sensitive, and selective method for the detection of high-proton affinity substances, such as organic decay products, medical and illicit drugs as well as a range of other hazardous materials. Tests on different kinds of SI sensors showed [...] Read more.

Surface ionization (SI) provides a simple, sensitive, and selective method for the detection of high-proton affinity substances, such as organic decay products, medical and illicit drugs as well as a range of other hazardous materials. Tests on different kinds of SI sensors showed that the sensitivity and selectivity of such devices is not only dependent on the stoichiometry and nanomorphology of the emitter materials, but also on the shape of the electrode configurations that are used to read out the SI signals. Whereas, in parallel-plate capacitor devices, different kinds of emitter materials exhibit a high level of amine-selectivity, MEMS (micro-electro-mechanical-systems) and NEMS (nanowire) versions of SI sensors employing the same kinds of emitter materials provide significantly higher sensitivity, however, at the expense of a reduced chemical selectivity. In this paper, it is argued that such sensitivity-selectivity trade-offs arise from unselective physical ionization phenomena that occur in the high-field regions immediately adjacent to the surfaces of sharply curved MEMS (NEMS) emitter and collector electrodes. Full article

(This article belongs to the Special Issue Development of Semiconductor Nanomaterials for Gas Sensors)

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16 pages, 1592 KiB

Open AccessReview

Two-Dimensional Nanomaterials for Gas Sensing Applications: The Role of Theoretical Calculations

by Yamei Zeng, Shiwei Lin, Ding Gu and Xiaogan Li

Nanomaterials 2018, 8(10), 851; https://doi.org/10.3390/nano8100851 - 19 Oct 2018

Cited by 87 | Viewed by 5951

Abstract

Two-dimensional (2D) nanomaterials have attracted a large amount of attention regarding gas sensing applications, because of their high surface-to-volume ratio and unique chemical or physical gas adsorption capabilities. As an important research method, theoretical calculations have been massively applied in predicting the potentially [...] Read more.

Two-dimensional (2D) nanomaterials have attracted a large amount of attention regarding gas sensing applications, because of their high surface-to-volume ratio and unique chemical or physical gas adsorption capabilities. As an important research method, theoretical calculations have been massively applied in predicting the potentially excellent gas sensing properties of these 2D nanomaterials. In this review, we discuss the contributions of theoretical calculations in the study of the gas sensing properties of 2D nanomaterials. Firstly, we elaborate on the gas sensing mechanisms of 2D layered nanomaterials, such as the traditional charge transfer mechanism, and a standard for distinguishing between physical and chemical adsorption, from the perspective of theoretical calculations. Then, we describe how to conduct a theoretical analysis to explain or predict the gas sensing properties of 2D nanomaterials. Thirdly, we discuss three important methods that have been applied in order to improve the gas sensing properties, that is, defect functionalization (vacancy, edge, grain boundary, and doping), heterojunctions, and electric fields. Among these strategies, theoretical calculations play a very important role in explaining the mechanisms underlying the enhanced gas sensing properties. Finally, we summarize both the advantages and limitations of the theoretical calculations, and present perspectives for further research on the 2D nanomaterials-based gas sensors. Full article

(This article belongs to the Special Issue Development of Semiconductor Nanomaterials for Gas Sensors)

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