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Here we demonstrate that liquid phase exfoliation can be used to convert layered crystals of nickel hydroxide into Ni(OH)2 nanosheets in relatively large quantities and without the need for ion intercalation. While other procedures require harsh synthesis conditions and multiple reaction steps, this method involves ultrasonication of commercially available powders in aqueous surfactant solutions and so is relatively mild and potentially scalable. Such mild exfoliation is possible because the surface energy of Ni(OH)2, as measured by inverse gas chromatography, is relatively low at ∼70 mJ m−2, similar to other layered materials. TEM, AFM, XPS and Raman spectroscopy show the exfoliated nanosheets to be relatively thin (mean ∼10 monolayers thick) and of good quality. Size selection by liquid cascade centrifugation allowed the production of samples with mean nanosheet lengths ranging from 55 to 195 nm. Optical measurements on dispersions showed the optical absorption coefficient spectra to be relatively invariant with nanosheet size while the scattering coefficient spectra varied strongly with size. The resultant size-dependence allows the extinction spectra to be used to estimate nanosheet size as well as concentration. We used the exfoliated nanosheets to prepare thin film electrodes for use in supercapacitors and as oxygen evolution catalysts. While the resultant capacitance was reasonably high at ∼1200 F cm−3 (20 mV s−1), the catalytic performance was exceptional with currents of 10 mA cm−2 observed at overpotentials as low as 297 mV, close to the state of the art. [ABSTRACT FROM AUTHOR]

Two-dimensional layered transition metal dichalcogenides (TMDs) have attracted great interest owing to their unique properties and a wide array of potential applications. However, due to their inert nature, pristine TMDs are very challenging to functionalize. We demonstrate a general route to functionalize exfoliated 2H-MoS2 with cysteine. Critically, MoS2 was found to be facilitating the oxidation of the thiol cysteine to the disulfide cystine during functionalization. The resulting cystine was physisorbed on MoS2 rather than coordinated as a thiol (cysteine) filling S-vacancies in the 2H-MoS2 surface, as originally conceived. These observations were found to be true for other organic thiols and indeed other TMDs. Our findings suggest that functionalization of two-dimensional MoS2 using organic thiols may not yield covalently or datively tethered functionalities, rather, in this instance, they yield physisorbed disulfides that are easily removed. [ABSTRACT FROM AUTHOR]

While liquid phase exfoliation can be used to produce nanosheets stabilized in polymer solutions, very little is known about the resultant nanosheet size, thickness, or monolayer content. The present study uses semiquantitative spectroscopic metrics based on extinction, Raman, and photoluminescence (PL) spectroscopy to investigate these parameters for WS2 nanosheets exfoliated in aqueous poly(vinyl alcohol) (PVA) solutions. By measuring Raman and PL simultaneously, the monolayer content can be tracked via the PL/Raman intensity ratio while varying processing conditions. The PL is found to be maximized for a stabilizing polymer concentration of 2 g L−1. In addition, the monolayer content can be controlled via the centrifugation conditions, exceeding 5% by mass in some cases. These techniques have allowed tracking the ratio of PL/Raman in a droplet of polymer-stabilized WS2 nanosheets as the water evaporates during composite formation. No evidence of nanosheet aggregation is found under these conditions although the PL becomes dominated by trion emission as drying proceeds and the balance of doping from PVA/water changes. Finally, bulk PVA/WS2 composites are produced by freeze drying where >50% of the monolayers remain unaggregated, even at WS2 volume fractions as high as 10%. [ABSTRACT FROM AUTHOR]

Layered two-dimensional (2D) inorganic transition-metal dichalchogenides (TMDs) have attracted great interest as a result of their potential application in optoelectronics, catalysis, and medicine. However, methods to functionalize and process such 2D TMDs remain scarce. We have established a facile route towards functionalized layered MoS2. We found that the reaction of liquid-exfoliated 2D MoS2, with M(OAc)2 salts (M=Ni, Cu, Zn; OAc=acetate) yielded functionalized MoS2-M(OAc)2 materials. Importantly, this method furnished the 2H-polytype of MoS2 which is a semiconductor. X-ray photoelectron spectroscopy (XPS), diffuse reflectance infrared Fourier transform spectroscopy (DRIFT-IR), and thermogravimetric analysis (TGA) provide strong evidence for the coordination of MoS2 surface sulfur atoms to the M(OAc)2 salt. Interestingly, functionalization of 2H-MoS2 allows for its dispersion/processing in more conventional laboratory solvents. [ABSTRACT FROM AUTHOR]

Layered two-dimensional (2D) inorganic transition-metal dichalchogenides (TMDs) have attracted great interest as a result of their potential application in optoelectronics, catalysis, and medicine. However, methods to functionalize and process such 2D TMDs remain scarce. We have established a facile route towards functionalized layered MoS2. We found that the reaction of liquid-exfoliated 2D MoS2, with M(OAc)2 salts (M=Ni, Cu, Zn; OAc=acetate) yielded functionalized MoS2–M(OAc)2 materials. Importantly, this method furnished the 2H-polytype of MoS2 which is a semiconductor. X-ray photoelectron spectroscopy (XPS), diffuse reflectance infrared Fourier transform spectroscopy (DRIFT–IR), and thermogravimetric analysis (TGA) provide strong evidence for the coordination of MoS2 surface sulfur atoms to the M(OAc)2 salt. Interestingly, functionalization of 2H-MoS2 allows for its dispersion/processing in more conventional laboratory solvents. [ABSTRACT FROM AUTHOR]

Layered two-dimensional (2D) inorganic transition-metal dichalchogenides (TMDs) have attracted great interest as a result of their potential application in optoelectronics, catalysis, and medicine. However, methods to functionalize and process such 2D TMDs remain scarce. We have established a facile route towards functionalized layered MoS2. We found that the reaction of liquid-exfoliated 2D MoS2, with M(OAc)2 salts (M=Ni, Cu, Zn; OAc=acetate) yielded functionalized MoS2-M(OAc)2 materials. Importantly, this method furnished the 2H-polytype of MoS2 which is a semiconductor. X-ray photoelectron spectroscopy (XPS), diffuse reflectance infrared Fourier transform spectroscopy (DRIFT-IR), and thermogravimetric analysis (TGA) provide strong evidence for the coordination of MoS2 surface sulfur atoms to the M(OAc)2 salt. Interestingly, functionalization of 2H-MoS2 allows for its dispersion/processing in more conventional laboratory solvents. [ABSTRACT FROM AUTHOR]

Layered two-dimensional (2D) inorganic transition-metal dichalchogenides (TMDs) have attracted great interest as a result of their potential application in optoelectronics, catalysis, and medicine. However, methods to functionalize and process such 2D TMDs remain scarce. We have established a facile route towards functionalized layered MoS2. We found that the reaction of liquid-exfoliated 2D MoS2, with M(OAc)2 salts (M=Ni, Cu, Zn; OAc=acetate) yielded functionalized MoS2–M(OAc)2 materials. Importantly, this method furnished the 2H-polytype of MoS2 which is a semiconductor. X-ray photoelectron spectroscopy (XPS), diffuse reflectance infrared Fourier transform spectroscopy (DRIFT–IR), and thermogravimetric analysis (TGA) provide strong evidence for the coordination of MoS2 surface sulfur atoms to the M(OAc)2 salt. Interestingly, functionalization of 2H-MoS2 allows for its dispersion/processing in more conventional laboratory solvents. [ABSTRACT FROM AUTHOR]

In order to fulfill their potentialfor applications, it will benecessary to develop large-scale production methods for two-dimensional(2D) inorganic nanosheets. Here we demonstrate the large-scale shear-exfoliationof molybdenum disulfide nanosheets in aqueous surfactant solutionusing a kitchen blender. Using standard procedures, we measure howthe MoS2concentration and production rate scale with processingparameters. However, we also use recently developed methods basedon optical spectroscopy to simultaneously measure both nanosheet lateralsize and thickness, allowing us to also study the dependence of nanosheetdimensions on processing parameters. We found the nanosheet concentrationand production rates to depend sensitively on the mixing parameters(the MoS2concentration, Ci; the mixing time, t; the liquid volume, V; and the rotor speed, N). By optimizingmixing parameters, we achieved concentrations and production ratesas high as 0.4 mg/mL and 1.3 mg/min, respectively. Conversely, thenanosheet size and thickness were largely invariant with these parameters.The nanosheet concentration is also extremely sensitive to the surfactantconcentration. However, more interestingly the nanosheet lateral sizeand thickness also varied strongly with the surfactant concentration.This allows the mean nanosheet dimensions to be controlled duringshear exfoliation at least in the range ∼40–220 nm forlength and ∼2–12 layers for thickness. We demonstratethe importance of this by showing that the MoS2nanosheetsprepared using different surfactant concentrations, and so displayingdifferent nanosheets sizes, perform differently when used as hydrogenevolution catalysts. We find the nanosheets produced using high surfactantconcentrations, which gives smaller flake sizes, perform significantlybetter, consistent with catalysis occurring at nanosheet edges. Finally,we also demonstrate that shear exfoliation using a kitchen blenderis not limited to MoS2but can also be achieved for boronnitride and tungsten disulfide. [ABSTRACT FROM AUTHOR]

Here,we demonstrate a simple method to exfoliate layered molybdenumtrioxide (MoO3) crystallites to give multilayer MoO3nanosheets dispersed in solvents. Exfoliation is achievedby sonicating MoO3powder in the presence of suitable solventsfollowed by centrifugation to remove undispersed material. This procedureworks well in a range of solvents with Hildebrand solubility parametersclose to 21 MPa1/2and is consistent with the predictionsof classical solubility theory. We have fully optimized this processand demonstrated methods to separate the resultant nanosheets by size.Raman spectroscopy suggests the exfoliation process does not damagethe MoO3. This is supported by measurements showing thatthe reaggregated nanosheets display very similar photoluminescenceto bulk MoO3. However, the dispersed nanosheets had distinctlydifferent photoluminescence, indicating a decoupling of the monolayerson exfoliation. We have used liquid-exfoliated MoO3toprepare supercapacitor electrodes that have relatively low capacitance(∼2 F/g at 10 mV/s) because of the low electrical conductivityof the MoO3. However, addition of carbon nanotubes beyondthe percolation threshold yielded a 100-fold increase in capacitance.Some MoO3/nanotube composites displayed a capacitance ashigh as 540 F/g at 0.1 mV/s. This is the first example of solventexfoliation of a layered metal oxide. We believe this work opens theway to liquid exfoliation of a wide range of layered compounds, leadingto an array of new solution-processed 2D materials. [ABSTRACT FROM AUTHOR]

Solution-exfoliated MoS2 nano-platelets were formed into thin films by deposition onto a water surface followed by transfer to indium tin oxide coated glass. After drying, a gold electrode was evaporated on top to give a sandwich structure with quasi-Ohmic contacts. Illumination of this device with broadband light of ∼1 kW m−2 intensity gave a fourfold increase in conductivity. The photocurrent increased sub-linearly with intensity and exponentially with time indicating the presence of traps. The photo-responsively at low intensity was ∼10−4 A per W at 15 V. This work demonstrates the potential for liquid-exfoliated, inorganic nanosheets to be fabricated into low-cost optoelectronic devices. [ABSTRACT FROM AUTHOR]

Single-wall carbon nanotubes (SWNTs) are emerging as materials with much potential in several disciplines, in particular in electronics and photovoltaics. The combination of SWNTs with electron donors or acceptors generates active materials, which can produce electrical energy when irradiated. However, SWNTs are very elusive species when characterization of their metastable states is required. This problem mainly arises because of the polydispersive nature of SWNT samples and the inevitable presence of SWNTs in bundles of different sizes. Here, we report the complete and thorough characterization of an SWNT radical ion-pair state induced by complexation with a perylene dye, which combines excellent electron-accepting and -conducting features with a five-fused ring π-system. At the same time, the perylene dye enables the dispersion of SWNTs by means of π-π interactions, which gives individual SWNTs in solution. This work clears a path towards electronic and optoelectronic devices in which regulated electrical transport properties are important. [ABSTRACT FROM AUTHOR]

Liquid phase exfoliation (LPE) is widely used to produce colloidal dispersions of nanomaterials, in particular two-dimensional nanosheets. The degree of exfoliation, i.e., the length to thickness aspect ratio was shown to be intrinsically limited by the ratio of in-plane to out-of-plane binding strength. In this work, we investigate whether simple pretreatment of the starting material can be used to change the in-plane to out-of-plane binding strength through mild intercalation to improve the sample quality in sonication-assisted LPE. Five different pretreatment conditions of WS2 were tested and the dispersions size-selected through centrifugation. From optical spectroscopy (extinction, Raman, photoluminescence), information on nanosheet dimension (average lateral size, layer number, monolayer size) and optical quality (relative photoluminescence quantum yield) was extracted. We find that the pretreatment has a minor impact on the length/thickness aspect ratio, but that photoluminescence quantum yield can be increased in particular using mild sonication conditions. We attribute this to the successful exfoliation of nanosheets with a lower degree of basal plane defectiveness. This work emphasizes the complexity of the exfoliation process and suggests that the role of defects has to be considered for a comprehensive picture. [ABSTRACT FROM AUTHOR]

HiPco and CoMoCAT single-walled carbon nanotubes (SWCNT) were fractionated with the aid of a novel perylene bisimide surfactant by combined co-surfactant and replacement density gradient ultracentrifugation (DGU). [ABSTRACT FROM AUTHOR]

Cover Feature: Defect Engineering of Two-Dimensional Molybdenum Disulfide (Chem. Eur. J. 29/2020) Keywords: 2D materials; defect engineering; functionalization; MoS2; thiophenol EN 2D materials defect engineering functionalization MoS2 thiophenol 6290 6290 1 05/23/20 20200520 NES 200520 B An approach to controllably engineer the sulfur vacancies b of chemically-exfoliated MoS SB 2 sb nanosheets using a series of substituted thiophenols in solution was demonstrated in this work. 2D materials, defect engineering, functionalization, MoS2, thiophenol. [Extracted from the article]