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      WSe2 nanoparticles with enhanced hydrogen evolution reaction prepared by bipolar electrochemistry: application in competitive magneto-immunoassay

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          Abstract

          We have exfoliated WSe 2 particles by the bipolar electrochemistry (BE). Thus obtained nanoparticles were tested towards hydrogen evolution reaction and then used as the electrochemical label in the immunoassay.

          Abstract

          Among groups of layered nanomaterials, transition metal dichalcogenides (TMDs) are the most studied group, especially for their hydrogen evolution reaction (HER) electrocatalytic activity and good stability in a highly corrosive environment. However, TMDs possess only low catalytic activity in the bulk form consisting of 2H phase, therefore, exfoliation must take place to enlarge the surface area and create new catalytically active sites (edges and defects). The most common exfoliation routes use organometallic reagents, such as tert-butyllithium ( t-BuLi). Recently, bipolar electrochemistry (BE) was reported as a new efficient exfoliation and down-sizing technique applied on several layered materials. In this work, we used BE for further down-sizing of WSe 2 micro-sheets, which were pre-exfoliated using tert-bulyllithium intercalator, down to nanoparticles (NPs). These WSe 2 NPs outperformed t-BuLi exfoliated particles in terms of the overpotential needed for HER electrocatalysis. Moreover, WSe 2 NPs were used effectively as a label for a competitive magneto-inmunoassay. This competitive magneto-immunoassay offers high selectivity with a wide linearity range, high sensitivity and a low limit of detection. We believe that such labels possess a great potential for bioassays.

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          Most cited references38

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          Core–Shell ZIF-8@ZIF-67-Derived CoP Nanoparticle-Embedded N-Doped Carbon Nanotube Hollow Polyhedron for Efficient Overall Water Splitting

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            Preparation and applications of mechanically exfoliated single-layer and multilayer MoS₂ and WSe₂ nanosheets.

            Although great progress has been achieved in the study of graphene, the small current ON/OFF ratio in graphene-based field-effect transistors (FETs) limits its application in the fields of conventional transistors or logic circuits for low-power electronic switching. Recently, layered transition metal dichalcogenide (TMD) materials, especially MoS2, have attracted increasing attention. In contrast to its bulk material with an indirect band gap, a single-layer (1L) MoS2 nanosheet is a semiconductor with a direct band gap of ~1.8 eV, which makes it a promising candidate for optoelectronic applications due to the enhancement of photoluminescence and high current ON/OFF ratio. Compared with TMD nanosheets prepared by chemical vapor deposition and liquid exfoliation, mechanically exfoliated ones possess pristine, clean, and high-quality structures, which are suitable for the fundamental study and potential applications based on their intrinsic thickness-dependent properties. In this Account, we summarize our recent research on the preparation, characterization, and applications of 1L and multilayer MoS2 and WSe2 nanosheets produced by mechanical exfoliation. During the preparation of nanosheets, we proposed a simple optical identification method to distinguish 1L and multilayer MoS2 and WSe2 nanosheets on a Si substrate coated with 90 and 300 nm SiO2. In addition, we used Raman spectroscopy to characterize mechanically exfoliated 1L and multilayer WSe2 nanosheets. For the first time, a new Raman peak at 308 cm(-1) was observed in the spectra of WSe2 nanosheets except for the 1L WSe2 nanosheet. Importantly, we found that the 1L WSe2 nanosheet is very sensitive to the laser power during characterization. The high power laser-induced local oxidation of WSe2 nanosheets and single crystals was monitored by Raman spectroscopy and atomic force microscopy (AFM). Hexagonal and monoclinic structured WO3 thin films were obtained from the local oxidization of single- to triple-layer (1L-3L) and quadruple- to quintuple-layer (4L-5L) WSe2 nanosheets, respectively. Then, we present Raman characterization of shear and breathing modes of 1L and multilayer MoS2 and WSe2 nanosheets in the low frequency range (<50 cm(-1)), which can be used to accurately identify the layer number of nanosheets. Magnetic force microscopy was used to characterize 1L and multilayer MoS2 nanosheets, and thickness-dependent magnetic response was found. In the last part, we briefly introduce the applications of 1L and multilayer MoS2 nanosheets in the fields of gas sensors and phototransistors.
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              Transition metal dichalcogenides and beyond: synthesis, properties, and applications of single- and few-layer nanosheets.

              CONSPECTUS: In the wake of the discovery of the remarkable electronic and physical properties of graphene, a vibrant research area on two-dimensional (2D) layered materials has emerged during the past decade. Transition metal dichalcogenides (TMDs) represent an alternative group of 2D layered materials that differ from the semimetallic character of graphene. They exhibit diverse properties that depend on their composition and can be semiconductors (e.g., MoS2, WS2), semimetals (e.g., WTe2, TiSe2), true metals (e.g., NbS2, VSe2), and superconductors (e.g., NbSe2, TaS2). The properties of TMDs can also be tailored according to the crystalline structure and the number and stacking sequence of layers in their crystals and thin films. For example, 2H-MoS2 is semiconducting, whereas 1T-MoS2 is metallic. Bulk 2H-MoS2 possesses an indirect band gap, but when 2H-MoS2 is exfoliated into monolayers, it exhibits direct electronic and optical band gaps, which leads to enhanced photoluminescence. Therefore, it is important to learn to control the growth of 2D TMD structures in order to exploit their properties in energy conversion and storage, catalysis, sensing, memory devices, and other applications. In this Account, we first introduce the history and structural basics of TMDs. We then briefly introduce the Raman fingerprints of TMDs of different layer numbers. Then, we summarize our progress on the controlled synthesis of 2D layered materials using wet chemical approaches, chemical exfoliation, and chemical vapor deposition (CVD). It is now possible to control the number of layers when synthesizing these materials, and novel van der Waals heterostructures (e.g., MoS2/graphene, WSe2/graphene, hBN/graphene) have recently been successfully assembled. Finally, the unique optical, electrical, photovoltaic, and catalytic properties of few-layered TMDs are summarized and discussed. In particular, their enhanced photoluminescence (PL), photosensing, photovoltaic conversion, and hydrogen evolution reaction (HER) catalysis are discussed in detail. Finally, challenges along each direction are described. For instance, how to grow perfect single crystalline monolayer TMDs without the presence of grain boundaries and dislocations is still an open question. Moreover, the morphology and crystal structure control of few-layered TMDs still requires further research. For wet chemical approaches and chemical exfoliation methods, it is still a significant challenge to control the lateral growth of TMDs without expansion in the c-axis direction. In fact, there is plenty of room in the 2D world beyond graphene. We envisage that with increasing progress in the controlled synthesis of these systems the unusual properties of mono- and few-layered TMDs and TMD heterostructures will be unveiled.
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                Author and article information

                Journal
                NANOHL
                Nanoscale
                Nanoscale
                Royal Society of Chemistry (RSC)
                2040-3364
                2040-3372
                December 13 2018
                2018
                : 10
                : 48
                : 23149-23156
                Affiliations
                [1 ]Center for Advanced Functional Nanorobots
                [2 ]Department of Inorganic Chemistry
                [3 ]Faculty of Chemical Technology
                [4 ]University of Chemistry and Technology Prague
                [5 ]166 28 Prague 6
                Article
                10.1039/C8NR04670K
                30921357-9d8b-4e09-b2d2-9fdaab712b27
                © 2018

                http://rsc.li/journals-terms-of-use

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