Exfoliation Of Layered Materials Research Articles

Structural Features Dictate the Photoelectrochemical Activities of Two-Dimensional MoSe2 and WSe2 Nanostructures.

The exfoliation of layered materials into two-dimensional (2D) semiconductors creates new structural domains, for example, basal planes, defect-rich in-planes, and edge sites. These surface species affect the photoelectrochemical (PEC) performance, which in turn determines their applicability in solar energy conversion technologies. In this study, a custom-designed microdroplet cell-based spatially resolved PEC approach was employed to identify the structural parts and to measure the PEC activity of the mechanically exfoliated MoSe2 and WSe2 nanosheets for bulk, few-layer, and monolayer specimens. The PEC performance decreased with the decreasing thickness of nanoflakes, and the relative PEC activity (photo/total current) reduced by introducing more defects to the 2D flakes: 1–3% loss was found for in-plane defects and 30–40% for edge defects. While edge sites act as charge carrier recombination centers, their electrocatalytic activity is higher than that of the basal planes. The comparison of PEC activity of micromechanically and liquid phase exfoliated bulk and few-layer MoSe2 and WSe2 flakes further confirmed that the PEC performance of 2D flakes decreases with an increasing number of edge sites.

Exfoliation Chemistry of Soft Layered Materials toward Tailored 2D Materials

Abstract Exfoliation of layered materials provides nanosheets, such as monolayers and few-layers. In recent years, nanosheets have attracted much interest as two-dimensional (2D) materials for their diverse properties and applications originating from the anisotropic characteristic structures. Exfoliation methods have been developed depending on the types of interactions between the layers, such as van der Waals and electrostatic interactions. The present review focuses on exfoliation chemistry based on rigid and soft natures of the layered materials. The rigid inorganic layered compounds are converted to the soft layered materials with interaction of organic guests. The surface-functionalized nanosheets are obtained by exfoliation of the soft layered composites with dispersion in organic media. The exfoliation behavior is governed by the flexibility of the precursor layered materials, i.e. interaction between the interlayer guest and dispersion medium. Although exfoliation is generally an uncontrollable top-down process, materials informatics on our own experimental small data assists elucidation of the control factors toward tailored 2D materials. The exfoliation schemes are applied to a variety of layered materials. The present review shows potential new insights for exfoliation chemistry of soft layered materials.

In Situ Dynamics during Heating of Copper-Intercalated Bismuth Telluride

Summary The presence of a van der Waals gap within layered materials enables the intercalation of guest species, which can be used for tuning properties. The introduction of intercalant species may also lead to structural transformations across a range of temperatures and use conditions, but we have a limited understanding of the high-temperature evolution of intercalated layered materials. Here, we use in situ transmission electron microscopy to investigate temperature-dependent structural evolution of Bi2Te3, a layered material with well-known application as a thermoelectric, which contains intercalated Cu. As temperature is increased, the initially disordered Cu undergoes local ordering within the van der Waals gap, along with anisotropic sublimation behavior of the crystals. As the temperature is raised further, layered Cu2Te crystals nucleate and grow with a crystallographic relationship to the Bi2Te3 lattice. Notably, the presence of Cu decreases the thermal stability of the Bi2Te3 and substantially alters the transformation pathways during heating.

Exfoliation of layered materials using electrochemistry.

After the isolation and discovery of the extraordinary properties of graphene, tremendous interest has been directed towards other layered materials. Known also as van der Waals solids, these materials can offer a much wider range of properties than graphene when exfoliated to single or few-layer sheets with benefits for several different applications. Similar to graphene, a key aspect for the actual application of these materials is certainly represented by the development of efficient fabrication methods able to produce a large quantity of individual sheets of good quality. Electrochemically-assisted exfoliation of bulk crystals represents one of the most promising methods for mass-production of graphene and also other 2D material sheets due to the mild operational conditions, short time, simple instrumentation and high yield of individual layers obtained. We review here the latest and most representative electrochemically-assisted methods of exfoliation of layered materials categorized by the intercalation ion employed. A separate section is also included and dedicated to the recent bipolar electrochemical procedures which through different mechanistic avenues recently demonstrated efficient reduction of both lateral size and thickness of bulk particles of layered materials dispersed in solution. A summary discussion along with future perspectives is also provided in the last section.

Exfoliation of zinc-layered hydroxide by luminescent conjugate polyelectrolyte: synthesis and photophysical aspects

Exfoliation of layered materials is of significant interest for both the fundamental scientific studies and technological applications. In this work, the π-conjugated polymer, poly[5-methoxy-2-(3-sulfopropoxy)-1,4-phenylenevinylene] potassium (MSP-PPV), was intercalated/exfoliated between the lamellae of the zinc-layered hydroxide (ZHL) to produce luminescent hybrid materials. This process is highly attractive because the intercalation/exfoliation of the MSP-PPV polymer in the sheets of zinc-layered hydroxide was realized by anionic exchange at room temperature. Depending on the amount of polyelectrolyte used in the preparation of the hybrid compounds (MPS-PPV/ZHL), the intercalation reaction was followed by exfoliation of the zinc-layered hydroxide layers. At higher MSP-PPV concentration used in the experiment, the resulting material presented a high degree of exfoliation of the zinc-layered hydroxide sheets, as suggested by both the X-ray diffraction and scanning electron microscopic images. Elemental analysis, nuclear magnetic resonance and Fourier transform infrared spectroscopy also confirmed the interaction between MSP-PPV anionic polyelectrolyte and the sheets of zinc-layered hydroxide matrix. In addition, in order to better understand the photoluminescent behavior, a complete characterization of optical properties of the MSP-PPV/ZHL hybrids was also performed. Due to the MPS-PPV presence, all hybrid materials showed absorption bands in the visible region (≈450 m) with emission band in the green region (≈560 m). Moreover, the photophysical properties of the MSP-PPV intercalated/exfoliated can be easily tuned by changing their concentration demonstrating that the zinc-layered hydroxide material plays an important role in preventing the aggregation and photostability of the anionic polyelectrolyte.

Liquid Exfoliation of Layered Materials in Water for Inkjet Printing

Liquid Exfoliation of Layered Materials in Water for Inkjet Printing

Green synthesis route for WS2 nanosheets using water intercalation

The exfoliation of layered materials has attracted a lot of attention in recent times. In this report, we have exfoliated WS2 in deionized water (without using any chemical solvents, surfactants, etc) using the thermal coefficient mismatch between WS2 and H2O along with other anomalous properties of water, such as the formation of five-, six- and seven-ring structures while freezing. Two different green synthesis routes have been proposed for WS2 exfoliation. We call them the ‘hard’ and ‘soft’ quenching methods. The nanosheets were investigated using different characterization tools and we found the exfoliation of the bulk into <4 layers with an average lateral dimension of 200 nm. The exfoliation method is unique in the sense of producing pristine nanosheets due to the absence of any organic solvents, which are difficult to remove.

Nd3+-doped perovskite nanosheets with NIR luminescence

Exfoliation of layered materials into ultrathin nanosheets introduces a new cost-effective and environmentally safe fabrication method for novel nanostructured devices. In the present study, we have developed for the first time inorganic oxide nanosheets with near-infrared (NIR) luminescence properties. KLa1−xNdxNb2O7 (x=0.025, 0.05, 0.1, 0.2, or 0.3) powders obtained by a solid state reaction were exfoliated into single-layer metal oxide nanosheets with approximately 1.7nm thickness by osmotic swelling with tetrabutylammonium cations, followed by the protonation of KLa1−xNdxNb2O7. We observed strong coupling of high-energy OH vibration with the Nd3+ energy levels upon protonation and exfoliation steps because of the extremely thin nature of oxide nanosheet-layers. Colloidal oxide nanosheets with an optimized Nd-doping concentration yielded detectable NIR luminescence due to 4F3/2–4I11/2 (Nd3+) radiative transitions, which opens possible application of these oxide nanosheets as bioimaging probes and bioanalytical sensors.