Reducing the size of a material, from a bulk solid to a nanomaterial, may lead to drastic changes of various properties including reactivity and optical properties. Chemical reactivity is often increased due to the nanomaterial’s higher effective surface area, while confinement and geometric effects lead to systematic changes in optical properties. Here, we investigate the size-dependent properties of Ni2P2S6 nanosheets that were obtained from liquid phase exfoliation in N-cyclohexyl-2-pyrrolidone. The as-obtained stock dispersion was size-selected by liquid cascade centrifugation resulting in fractions with distinct size and thickness distributions, as quantified by statistical atomic force microscopy. Raman, TEM, XRD, and XPS characterization revealed that the exfoliated flakes have good crystallinity and high structural integrity across all sizes. The optical extinction and absorbance spectra systematically change with the lateral dimensions and layer number, respectively. Linking these changes to nanosheet dimensions allows us to establish quantitative metrics for size and thickness from optical properties. To gain insights into the environmental stability, extinction/absorbance behavior was followed as a function of time at different storage temperatures. Degradation is observed following first-order kinetics, and activation energies were extracted from the temperature dependent data. The decomposition is due to oxidation which appears to occur both at edges and on the basal plane.

In this work, we apply an amine-assisted silica pillaring method to create the first example of a porous Mo2TiC2 MXene with nanoengineered interlayer distances. The pillared Mo2TiC2 has a surface...

MXenes are a recently discovered class of two-dimensional materials that have shown great potential as electrodes in electrochemical energy storage devices. Despite their promise in this area, MXenes can still suffer limitations in the form of restricted ion accessibility between the closely spaced multistacked MXene layers causing low capacities and poor cycle life. Pillaring, where a secondary species is inserted between layers, has been used to increase interlayer spacings in clays with great success but has had limited application in MXenes. We report a new amine-assisted pillaring methodology that successfully intercalates silica-based pillars between Ti 3 C 2 layers. Using this technique, the interlayer spacing can be controlled with the choice of amine and calcination temperature, up to a maximum of 3.2 nm, the largest interlayer spacing reported for an MXene. Another effect of the pillaring is a dramatic increase in surface area, achieving BET surface areas of 235 m 2 g –1 , a sixty-fold increase over the unpillared material and the highest reported for MXenes using an intercalation-based method. The intercalation mechanism was revealed by different characterization techniques, allowing the surface chemistry to be optimized for the pillaring process. The porous MXene was tested for Na-ion battery applications and showed superior capacity, rate capability and remarkable stability compared with those of the nonpillared materials, retaining 98.5% capacity between the 50th and 100th cycles. These results demonstrate the applicability and promise of pillaring techniques applied to MXenes providing a new approach to optimizing their properties for a range of applications, including energy storage, conversion, catalysis, and gas separations.

Accurately determining the morphology and hence the true surface areas of catalytic nanoparticles remains challenging.

The family of antiferromagnetic layered metal hexathiohypo diphosphates, M2P2S6 represents a versatile class of materials, particularly interesting for fundamental studies on magnetic properties in low dimensional structures, and yet exhibiting great potential for a broad variety of applications including catalysis, energy storage and conversion, and spintronics. In this work, three representatives of this family of 2D materials (M = Fe, Ni, and Mn) are exfoliated in the liquid phase under inert conditions and the nanosheet’s properties are studied in detail for different sizes of all three compounds. Centrifugation-based size selection is performed for this purpose. The exfoliability and structural integrity of the nanosheets is studied by statistical AFM and TEM measurements. Further, we report size and thickness dependent optical properties and spectroscopic metrics for the average material dimensions in dispersion, as well as the nanomaterials’ magnetic response using a combination of cryo-Raman and SQUID measurements. Finally, the material stability is studied semi-quantitatively, using time and temperature dependent extinction and absorbance spectroscopy, enabling the determination of the materials’ half-life, portion of reacted substance and the macroscopic activation energy for the degradation.

<p>In this work, we apply an amine-assisted silica pillaring method to create the first example of a porous Mo₂TiC₂MXene with nanoengineered interlayer distances. The pillared Mo₂TiC₂ has a surface area of 202 m² g^-1, which is among the highest reported for any MXene, and has a variable gallery height between 0.7 and 3 nm. The expanded interlayer distance leads to significantly enhanced cycling performance for Li-ion storage, with superior capacities, rate capabilities and cycling stabilities in comparison to the non-pillared version. The pillared Mo₂TiC₂ achieved capacities over 1.7 times greater than multilayered MXene at 20 mA g^-1 (≈ 320 mAh g^-1) and 2.5 times higher at 1 A g^-1 (≈ 150 mAh g^-1). The fast-charging properties of pillared Mo₂TiC₂ are further demonstrated by outstanding stability even at 1 A g^-1 (under 8 min charge time), retaining 80% of the initial capacity after 500 cycles. Furthermore, we use a combination of spectroscopic techniques (i.e. XPS, NMR and Raman) to show unambiguously that the charge storage mechanism of this MXene occurs by a conversion reaction through the formation of Li₂O. This reaction increases by 2-fold the capacity beyond intercalation, and therefore, its understanding is crucial for further development of this family of compounds. In addition, we also investigate for the first time the sodium storage properties of the pillared and non-pillared Mo₂TiC₂.</p>

Copper sulphide (covellite) nanoplatelets have recently emerged as a plasmonic platform in the near- infrared with ultrafast nonlinear optical properties. Here we demonstrate that the free-carrier density in CuS, which...

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