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Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to readers, or important in the respective research area. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.

14 pages, 4648 KiB

Open AccessEditor’s ChoiceArticle

Synthesis of Cu₂O/CuO Nanocrystals and Their Application to H₂S Sensing

by Kazuki Mikami, Yuta Kido, Yuji Akaishi, Armando Quitain and Tetsuya Kida

Sensors 2019, 19(1), 211; https://doi.org/10.3390/s19010211 - 8 Jan 2019

Cited by 75 | Viewed by 10935

Abstract

Semiconducting metal oxide nanocrystals are an important class of materials that have versatile applications because of their useful properties and high stability. Here, we developed a simple route to synthesize nanocrystals (NCs) of copper oxides such as Cu₂O and CuO using a hot-soap method, and applied them to H₂S sensing. Cu₂O NCs were synthesized by simply heating a copper precursor in oleylamine in the presence of diol at 160 °C under an Ar flow. X-ray diffractometry (XRD), dynamic light scattering (DLS), and transmission electron microscopy (TEM) results indicated the formation of monodispersed Cu₂O NCs having approximately 5 nm in crystallite size and 12 nm in colloidal size. The conversion of the Cu₂O NCs to CuO NCs was undertaken by straightforward air oxidation at room temperature, as confirmed by XRD and UV-vis analyses. A thin film Cu₂O NC sensor fabricated by spin coating showed responses to H₂S in dilute concentrations (1–8 ppm) at 50–150 °C, but the stability was poor because of the formation of metallic Cu₂S in a H₂S atmosphere. We found that Pd loading improved the stability of the sensor response. The Pd-loaded Cu₂O NC sensor exhibited reproducible responses to H₂S at 200 °C. Based on the gas sensing mechanism, it is suggested that Pd loading facilitates the reaction of adsorbed oxygen with H₂S and suppresses the irreversible formation of Cu₂S. Full article

(This article belongs to the Special Issue Functional Materials for the Applications of Advanced Gas Sensors)

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32 pages, 2379 KiB

Open AccessEditor’s ChoiceReview

A Comprehensive Survey on Spectrum Sensing in Cognitive Radio Networks: Recent Advances, New Challenges, and Future Research Directions

by Youness Arjoune and Naima Kaabouch

Sensors 2019, 19(1), 126; https://doi.org/10.3390/s19010126 - 2 Jan 2019

Cited by 357 | Viewed by 18769

Abstract

Cognitive radio technology has the potential to address the shortage of available radio spectrum by enabling dynamic spectrum access. Since its introduction, researchers have been working on enabling this innovative technology in managing the radio spectrum. As a result, this research field has been progressing at a rapid pace and significant advances have been made. To help researchers stay abreast of these advances, surveys and tutorial papers are strongly needed. Therefore, in this paper, we aimed to provide an in-depth survey on the most recent advances in spectrum sensing, covering its development from its inception to its current state and beyond. In addition, we highlight the efficiency and limitations of both narrowband and wideband spectrum sensing techniques as well as the challenges involved in their implementation. TV white spaces are also discussed in this paper as the first real application of cognitive radio. Last but by no means least, we discuss future research directions. This survey paper was designed in a way to help new researchers in the field to become familiar with the concepts of spectrum sensing, compressive sensing, and machine learning, all of which are the enabling technologies of the future networks, yet to help researchers further improve the efficiently of spectrum sensing. Full article

(This article belongs to the Section Sensor Networks)

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