Transformative Two-Dimensional Layered Nanocrystals

Abstract

Regioselective chemical reactions and structural transformations of two-dimensional (2D) layered transition-metal chalcogenide (TMC) nanocrystals are described. Upon exposure of 2D TiS(2) nanodiscs to a chemical stimulus, such as Cu ion, selective chemical reaction begins to occur at the peripheral edges. This edge reaction is followed by ion diffusion, which is facilitated by interlayer nanochannels and leads to the formation of a heteroepitaxial TiS(2)-Cu(2)S intermediate. These processes eventually result in the generation of a single-crystalline, double-convex toroidal Cu(2)S nanostructure. Such 2D regioselective chemical reactions also take place when other ionic reactants are used. The observations made and chemical principles uncovered in this effort indicate that a general approach exists for building various toroidal nanocrystals of substances such as Ag(2)S, MnS, and CdS.

Two-Dimensional Colloidal Nanocrystals

“…Syntheses carried out using the same precursors (sulfur and titanium tetrachloride) but using 1-octadecene as the solvent 243 followed by the introduction of TiCl4 at room temperature and heating up the mixture at 300°C for 3 h. By changing the sulfur precursor to carbon disulfide (CS2) and using a hot-injection protocol at 300°C (directly injecting CS2 into a mixture of titanium(IV) chloride and oleylamine), Cheon group reported the formation of well-defined TiS2 colloidal nanodiscs 242 .…”

“…In a first paper, 242 they reported the reaction of TiS2 nanosheets with copper (II) cations. The cations react preferentially at the edges of the nanodisks, leading to the formation of TiS2_Cu2S heterostructures and then to pure Cu2S toroidal nanocrystals if the reaction is complete (Figure 34 a-f).…”

Gold nanorings synthesized via a stress-driven collapse and etching mechanism

“…[17][18][19][20] In addition, a structural transformation via an edge-selective reaction of two-dimensional (2D) layered nanocrystals or via a Kirkendall effect has been used to prepare TiO 2 toroids, Cu 2 S nanorings and Cu-NaInS 2 nanorings. [21][22][23] Recently, the self-assembly mechanism of NPs with intrinsic polygons led to the growth of ring-like CdS, Ni-Co and PbSe nanorings. [24][25][26] However, until now, it seems that these growth mechanisms have not been observed in the synthesis of ring-like Au or Ag nanostructures, particularly in direct solution-based growth.…”

Hexagonal Transition‐Metal Chalcogenide Nanoflakes with Pronounced Lateral Quantum Confinement

“…[15][16][17][18] In this respect, the recent advances in the growth of TMC nanocrystals with a bottom-up synthetic approach have provided a route towards true control on the nanoscale that has led to highly pure nanoflakes, produced at low-cost in a wide variety of chemical compositions, thicknesses, and sizes. [19][20][21] The synthesized nanocrystals are usually present in well-defined equilateral hexagonal shape. As an example, a synthesized 60 nm TiS 2 nanoflake is shown in Figure 1.…”