Structural Properties and Phase Transition of Exfoliated-Restacked Molybdenum Disulfide

The product of exfoliation and restacking of MoS₂ in acidic conditions is studied in detail using X-ray powder diffraction, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The temperature dependence of powder patterns reveals that the heating of exfoliated-restacked MoS₂ is a way to a new nanostructured MoS₂-based layered material that remains nanosized even upon heating to 850 °C. Previously this material has been described as 2H-MoS₂, but according to the X-ray diffraction (XRD) data, its structure cannot be correctly described by any of the “usual” MoS₂ polytypes. A model of the structure of the material describing its XRD patterns and thermal behavior is discussed in detail

Highly Flexible Molecule “Chameleon”: Reversible Thermochromism and Phase Transitions in Solid Copper(II) Diiminate Cu[CF₃C(NH)CFC(NH)CF₃]₂

Three thermochromic phases (α, green; β, red; γ, yellow) and six polymorphic modifications (α₁, monoclinic, <i>P</i>2₁/<i>n</i>, <i>Z</i> = 2; β₁, monoclinic, <i>P</i>2₁/<i>c</i>, <i>Z</i> = 4; β₂, triclinic, <i>P</i>1̅, <i>Z</i> = 4; β₃, monoclinic, <i>P</i>2₁/<i>n</i>, <i>Z</i> = 4; γ₁ and γ₂, tetragonal, <i>P</i>4₂/<i>n</i>, <i>Z</i> = 4) have been found and structurally characterized for copper­(II) diiminate Cu­[CF₃C­(NH)CFC­(NH)CF₃]₂ (<b>1</b>). The α phase is stable under normal conditions, whereas the high-temperature β and γ phases are metastable at room temperature and transform slowly into the more stable α phase over several days or even weeks. X-ray diffraction study revealed that the title molecules adopt different conformations in the α, β, and γ phases, namely, staircase-like, twisted, and planar, respectively. The investigation of the α, β, and γ phases by differential scanning calorimetry showed that the three endothermic peaks in the range 283, 360, and 438 K are present on their thermograms upon heating/cooling. The two peaks at 283 and 360 K correspond to the solid–solid phase transitions, and the high-temperature peak at 438 K belongs to the melting process of <b>1</b>. The temperature and thermal effect of all the observed transitions depend on the prehistory of the crystalline sample obtained. A reversible thermochromic single-crystal-to-single-crystal α₁⇌β₁ phase transition occurring within a temperature interval of 353–358 K can be directly observed using a CCD video camera of the X-ray diffractometer. A series of other solid–solid α₁→γ₁, β₂→γ₁, β₃→γ₁, and γ₁⇌γ₂ phase transitions can be triggered in <b>1</b> by temperature. It has been suggested that, under equilibrium conditions, the α₁→γ₁ and β₂→γ₁ phase transitions should proceed stepwise through the α₁→β₁→β₂→β₃→γ₁ and β₂→β₃→γ₁ stages, respectively. The mechanism of the phase transitions is discussed on the basis of experimental and theoretical data

Multifunctional Nanohybrids by Self-Assembly of Monodisperse Iron Oxide Nanoparticles and Nanolamellar MoS₂ Plates

Here, we report the synthesis, characterization, and properties of novel nanohybrids formed by self-assembly of negatively charged MoS₂ nanoplates and positively charged iron oxide nanoparticles (NPs) of two different sizes, 5.1 and 11.6 nm. Iron oxide NPs were functionalized with an amphiphilic random copolymer, quaternized poly­(2-(di­methyl­amino)­ethyl metacrylate-<i>co</i>-stearyl meta­crylate), synthesized for the first time using atom transfer radical polymerization. The influence of the MoS₂ fraction and the iron oxide NP size on the structure of the nanohybrids has been studied. Surprisingly, larger NPs retained a larger fraction of the copolymer, thus requiring more MoS₂ nanoplates for charge compensation. The nanohybrid based on 11.6 nm NPs was studied in oxidation of sulfide ions. This reaction could be used for removing the dangerous pollutant from wastewater and in the production of hydrogen from water using solar energy. We demonstrated a higher catalytic activity of the NP/MoS₂ nanohybrid than that of merely dispersed MoS₂ in catalytic oxidation of sulfide ions and facile magnetic recovery of the catalyst after the reaction