Sergii Nedilko

Thermal analysis of polyethylene + X% carbon nanotubes

The aim of this research is to study the influence of the multi-walled carbon nanotubes (MWCNTs) on the thermomechanical and structural properties of high-density polyethylene. Several, complementary experimental techniques were used, namely, dilatometry, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Raman spectroscopy, and infrared (IR) spectroscopy. Dilatometry data showed that nanocomposites exhibit anisotropic behavior, and intensity of the anisotropy depends on the MWCNT concentration. The shapes of the dilatometric curves of the nanocomposites under study differ significantly for the radial and longitudinal directions of the samples. DSC results show that MWCNTs weekly influence calorimetry data, while Raman spectra show that the ID/IG ratio decreases when MWCNT concentration increases. The IR spectra demonstrate improvement of the crystallinity of the samples as the content in MWCNTs rises.

Ab Initio Computational Study of Chromate Molecular Anion Adsorption on the Surfaces of Pristine and B- or N-Doped Carbon Nanotubes and Graphene

Density functional theory (DFT) computations of the electronic structures of undoped, B- and N-doped CNT(3,3), CNT(5,5) carbon nanotubes, and graphene with adsorbed chromate anions CrO42− were performed within molecular cluster approach. Relaxed geometries, binding energies, charge differences of the adsorbed CrO42− anions, and electronic wave function contour plots were calculated using B3LYP hybrid exchange-correlation functional. Oscillator strengths of electronic transitions of CrO42− anions adsorbed on the surfaces of studied carbon nanostructures were calculated by the TD-DFT method. Calculations reveal covalent bonding between the anion and the adsorbents in all studied adsorption configurations. For all studied types of adsorbent structures, doping with N strengthens chemical bonding with CrO42− anions, providing a ~2-eV increase in binding energies comparatively to adsorption of the anion on undoped adsorbents. Additional electronic transitions of CrO42− anions appear in the orange-green spectral region when the anions are adsorbed on the N-doped low-diameter carbon nanotubes CNT(3,3) and CNT(5,5).

Structural Modification of Single-Layer Graphene Under Laser Irradiation Featured by Micro-Raman Spectroscopy

Confocal micro-Raman spectroscopy is used as a sensitive tool to study the nature of laser-induced defects in single-layer graphene. Appearance and drastic intensity increase of D- and D′ modes in the Raman spectra at high power of laser irradiation is related to generation of structural defects. Time- and power-dependent evolution of Raman spectra is studied. The dependence of relative intensity of defective D- and D′ bands is analyzed to relate the certain types of structural defects. The surface density of structural defects is estimated from the intensity ratio of D- and G bands using the D-band activation model. Unusual broadening of the D band and splitting of the G band into G− and G+ components with redistribution of their intensities is observed at high laser power and exposition. Position of the G+ band is discussed in relation with nonuniform doping of graphene with charge impurities. Simultaneous presence in the Raman spectra of heavily irradiated graphene of rather narrow G band and broaden D band is explained by coexistence within the Raman probe of more and less damaged graphene areas. This assumption is additionally confirmed by confocal Raman mapping of the heavily irradiated area.

Synthesis and Luminescence Properties of KBi(MoO4)2:Eu3+

Polycrystalline KBi(MoO4)2 has been grown from molten system K-Bi-Mo-O. Solid solutions KBi1-xEux(MoO4)2 (x = 0.001 - 0.100) have been prepared by solid state synthesis and characterized by powder IR spectroscopy, DTA analysis, X-Ray powder diffraction and luminescence spectroscopy. It was found that all investigated Eu3+-containing molybdates reveal intensive photoluminescence lines related to f-f electronic transitions in Eu3+ ions. The KBi1-XEuX(MoO4)2 crystals with low Eu3+ concentration reveal also intrinsic host luminescence under excitation in the ultraviolet (UV) spectral region at T = 4.2 K.