Titanium (IV) sulphide (TiS 2 ) is a layered transition metal dichalcogenide, which we exfoliate using liquid phase exfoliation. TiS 2 is a candidate for being part of a range of future technologies. These applications are varied, and include supercapacitor and battery energy storage devices, catalytic substrates and the splitting of water. The driving force behind our interest was as a material for energy storage devices. Here we investigate a potential failure mechanism for such devices, namely oxidation and subsequent loss of sulphur. This degradation is important to understand, since these applications are highly property-dependent, and changes to the chemistry will result in changes in desired properties. Two approaches to study oxidisation were taken: ex situ oxidation by water and oxygen at room temperature and in situ oxidation by a 5% O 2 /Ar gas at elevated temperatures. Both sources of oxygen resulted in oxidation of the starting TiS 2 flakes, with differing morphologies. Water produced amorphous oxide slowly growing in from the edge of the flakes. Oxygen gas at ≥375°C produced crystalline oxide, with a range of structures due to oxidation initiating from various regions of the observed flakes. npj 2D Materials and Applications (2017) 1:22 ; doi:10.1038/s41699-017-0024-4 INTRODUCTION Titanium (IV) sulphide, TiS 2 , is a candidate for applications in a range of future technologies, including catalytic substrates and the splitting of water, supercapacitors and energy storage devices. TiS 2 is a layered transition metal dichalcogenide (TMD) with hexagonal crystal symmetry and takes the 1T phase and is relatively under explored in two-dimensional form. Each layer consists of three sheets of atoms: the two outer planes are sulphur, coordinated to three titanium atoms with a trigonal pyramidal geometry; the middle plane is titanium and each atom takes octahedral coordination to six sulphur atoms. These atomic sheets are stacked ABC (Supplemental Information Fig. 1), while the layers themselves stack AA in the 1T phase.The excellent capacitive properties of bulk TiS 2 (high energydensity and power-density 1, 2 and excellent electronic conductivity 3 ) have attracted interest since the 1970s, with bulk TiS 2 used as a cathode material in lithium-metal/alloy anode batteries, where lithium metal ions were intercalated, transferring charge to reduce titanium 3d orbitals and causing reduction from Ti 4+ to Ti 3+ (refs. 4, 5). High rates of charging and discharging were demonstrated with near-perfect reversibility. In addition, the material forms a single phase with lithium (Li x TiS 2 ) over the entirety of the range 0 ≤ x ≤ 1, avoiding the need for phase changes upon (de-) lithiation which removes much of the strain induced in cycling, prolonging battery life. However, TMD/Lithium-metal batteries were withdrawn from consumers due to accidents in 1989 where the metallic lithium caught fire as a consequence of shortcircuiting due to lithium-dendrite growth.

Liquid phase exfoliation allows large scale production of 2D materials in solution. The particles are highly anisotropic and strongly scatter light. While spherical particles can be accurately and precisely described by a single parameter-the radius, 2D nanoflakes, however, cannot be so easily described. We investigate light scattering in aqueous solutions of 2D hexagonal boron nitride nanoflakes in the single and multiple scattering regimes. In the single scattering regime, the anisotropic 2D materials show a much stronger depolarization of light when compared to spherical particles of similar size. In the multiple scattering regime, the scattering as a function of optical path for hexagonal boron nitride nanoflakes of a given lateral length was found to be qualitatively equivalent to scattering from spheres with the same diameter. We also report the presence of random lasing in high concentration suspensions of aqueous h-BN mixed with Rhodamine B dye. The h-BN works as a scattering agent and Rhodamine B as a gain medium for the process. We observed random lasing at 587 nm with a threshold energy of 0.8 mJ.

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