Liquid phase methods for design and engineering of two-dimensional nanocrystals

Triazine 2D Nanosheets as a New Class of Nanomaterials: Crystallinity, Properties and Applications

Based on the recent (2015–2021) literature data, the authors analyze the mutual dependence of crystallinity/amorphism and specific surface area and porosity in covalent triazine frameworks (CTFs), taking into account thermodynamic and kinetic control in the synthesis of these 2D nanosheets. CTFs have now become a promising new class of high-performance porous organic materials. They can be recycled and reused easily, and thus have great potential as sustainable materials. For 2D CTFs, numerous examples are given to support the known rule that the structure and properties of any material with a given composition depend on the conditions of its synthesis. The review may be useful for elder students, postgraduate students, engineers and research fellows dealing with chemical synthesis and modern nanotechnologies based on 2D covalent triazine frameworks.

2D Monomolecular Nanosheets Based on Thiacalixarene Derivatives: Synthesis, Solid State Self-Assembly and Crystal Polymorphism

Synthetic organic 2D materials are attracting careful attention of researchers due to their excellent functionality in various applications, including storage batteries, catalysis, thermoelectricity, advanced electronics, superconductors, optoelectronics, etc. In this work, thiacalix[4]arene derivatives functionalized by geranyl fragments at the lower rim in cone and 1,3-alternate conformations, that are capable of controlled self-assembly in a 2D nanostructures were synthesized. X-ray diffraction analysis showed the formation of 2D monomolecular-layer nanosheets from synthesized thiacalix[4]arenes, the distance between which depends on the stereoisomer used. It was established by DSC, FSC, and PXRD methods that the obtained macrocycles are capable of forming different crystalline polymorphs, moreover dimethyl sulphoxide (DMSO) is contributing to the formation of a more stable polymorph for cone stereoisomer. The obtained crystalline 2D materials based on synthesized thiacalix[4]arenes can find application in material science and medicine for the development of modern pharmaceuticals and new generation materials.

Mechanistic insight into the formation of colloidal WS2 nanoflakes in hot alkylamine media

Developing convenient and reliable synthetic methodologies for solution processable 2D layered ultrathin nanostructures with lateral size control is one of the major challenges for practical applications. In this study, a rational understanding a long-chain amphiphilic surfactant assisted non-hydrolytic synthesis that is able to generate dimension-controllable 2D-WS₂ nanocrystal flakes in a single-step protocol is proposed. The evolution of the starting soft organic-inorganic lamellar template into ultrathin few-layer 2D-WS₂ nanostructures with lateral size modulation over a range between 3 and 30 nm is monitored. The initial formation of WS₂ nanoseeds occurs in a self-assembled sacrificial precursor source, acting as a template, where larger two-dimensional nanostructures can grow without undergoing significant thickness variation. Overall, the chemical nature and steric hindrance of the alkylamines are essential to modulate the reactivity of such WS₂ nanoclusters, which correlate with the lateral size of the resulting nanoflakes.

Exfoliation of crystals

The review is concerned with progress in methods for exfoliation of crystals, from mechanical exfoliation using sticky tape to modern techniques involving sonication-assisted exfoliation, shear exfoliation in liquids using intercalating agents and stabilizers, direct liquid exfoliation and cosolvent exfoliation. The potential of methods of osmotic swelling in water and in organic dispersion media with constant and variable chemical composition of nanosheets, chemical and electrochemical intercalation, exfoliation by hydrazine (including versions resulting in changes in the chemical composition of nanosheets), ionic liquids and supercritical fluids is discussed. Methods for size sorting of nanosheets by density-gradient and cascade centrifugation and the possibility of nanosheet size control are analyzed.

The bibliography includes 136 references.

Design of 2D-nanocrystals in water: preparation, structure and functionalization

A new method for synthesis of 2D nanocrystals in water was proposed. The use of perfluorothiophenolate ions as surfactant allowed us to produce 2D single-crystal nanosheets of CaS at pH=9 and flat nanocrystals of PbS at pH=9 at room temperature. Mesocrystalline nanobelts of CdS and mesocrystals of PbS were obtained at pH=3–5 and pH=10–12, respectively. Morphology, structure and chemical composition of nanoparticles were characterized by high-resolution transmission electron microscopy, electron diffraction and energy dispersive X-ray spectroscopy. A mechanism of nanoparticles formation was discussed.