Irina B. Dorosheva

Titanium dioxide nanoparticles were synthesized by the sol-gel method. The phase composition (amorphous), particle size (from 20 to 80 nm), pycnometric density (3.50 g/cm³), specific surface area (300 m²/g) and band gap width (3.4 eV) were determined. As(III) sorption experiments were carried out in the dark and under 440 nm LED irradiation, varying the pH of the aqueous medium from 1 to 12 and the sorption time from 15 to 180 min. Sorption kinetic curves were obtained and the maximum allowable concentration of arsenic in water was achieved.

Studying the electrophysical properties and conduction mechanisms of Au/TiO₂/Ti memristive structures based on nanoporous and nanotubular layers made of anodized titanium dioxide contributes to the improvement of quality indicators of prospective elements and nano-electronic devices derived from them. The paper measures the current–voltage characteristics and temperature dependencies of conductance in high-(HRS) and low-resistance states (LRS) for Au/TiO₂/Ti memristors with different thickness of nanoporous/nanotubular active layer. The importance of forming a nanotubular structure of the oxide layer with a thickness of 155–200 nm and an internal diameter of nanotubes of 21 ± 4 nm for improving the main characteristics of Au/TiO₂/Ti memristors when realizing the filamentary mechanism of resistive switching with the participation of oxygen vacancies is shown. The main parameters of electron transport, such as activation energy of electron conduction, electron mobility, dielectric relaxation time, and concentration of allowed states in the conduction band, are calculated for nanoporous and nanotubular TiO₂ layers in HRS using the framework of charge limited conduction mechanism. The parameters of the electron trap distribution are determined, such as concentration, capture cross-section, energy depth, distribution type, and characteristic temperature. It is shown that electron transport in LRS occurs by the Poole–Frenkel emission through filaments with metallic conduction type. Band diagrams are proposed to describe the conduction mechanisms involving oxygen vacancies for Au/TiO₂/Ti memristors in high- and low-resistance states.

Composites based on melamine and titanium dioxide at different initial ratios 4 : 1, 6 : 1, 8 : 1, and 10 : 1 were obtained by polymerization in air at a temperature of 550°C. The morphology of the samples was investigated, and the elemental mapping of the sample composition was carried out using scanning electron microscopy. It was found that the initial melamine particles have a size of more than 20 μm, and its polymerization leads to the formation of g-C₃N₄ layers up to 5 μm in size. TiO₂ particles have an average size of 150 nm, and the resulting g-C₃N₄/TiO₂ heterostructures consist of particles with a size of 20–30 nm, which form agglomerates of about 2 μm in size. It was shown that the specific surface area decreases from 67 to 41 m²/g with increasing melamine content in the initial mixture. A single-phase composition TiN_0.24O_1.88 was formed when the initial components were mixed at a ratio of 4 : 1. When the ratio of the initial melamine and titanium dioxide was increased to 8 : 1 and 10 : 1, a two-phase system was formed, which consisted of Ti_0.72O₂ in an amount from 12 to 13% and C₃N₄ in an amount from 87 to 88%. During synthesis at a ratio of 6 : 1, two phases were also formed, but the C₃N₄ content in it was significantly less, up to 5%.

Titanium dioxide (TiO₂) nanotubes array with the length of 16 μm and the outer diameter of 100 nm were synthesized by anodic oxidation of titanium foil in an electrolyte solution containing a fluorine-containing solution of ethylene glycol. The selected synthesis conditions make it possible to separate the nanotubular array from the titanium foil and study it as a homogeneous functional material. The performed scanning electron microscopy study and Brunauer--Emmett--Teller analysis allowed to get data on the morphology of the samples. X-ray diffraction, thermogravimetric, and differential scanning calorimetry analysis made it possible to determine the temperature of the phase transition of the amorphous state into crystalline anatase (sp.gr. I4/amd). Observed phase transition of first order takes place at temperature about 350^oC. Keywords: nanotubular titanium dioxide films, anodic oxidation, phase transition, anatase, TG, DSC.

Oxidative C-H/C-H coupling reactions of dipyrromethanes with azines in the presence of a heterophase oxidative photocatalytic system (O₂/TiO₂/visible light irradiation) were carried out. As a result of cyclization of obtained compounds with boron trifluoride etherate, new hetaryl-containing derivatives of 4,4-difluoro-4-boron-3a,4a-diaza-s-indacene were synthesized. For the obtained compounds, absorption and luminescence spectra, quantum yields of luminescence as well as cyclic volt-amperograms were measured.

Titanium dioxide (TiO2) nanotubes array with the length of 16 μm and the outer diameter of 100 nm were synthesized by anodic oxidation of titanium foil in an electrolyte solution containing a fluorine-containing solution of ethylene glycol. The selected synthesis conditions make it possible to separate the nanotubular array from the titanium foil and study it as a homogeneous functional material. The performed scanning electron microscopy study and Brunauer–Emmett–Teller analysis allowed to get data on the morphology of the samples. X-ray diffraction, thermogravimetric, and differential scanning calorimetry analysis made it possible to determine the temperature of the phase transition of the amorphous state into crystalline anatase (sp.gr. I4/amd). Observed phase transition of first order takes place at temperature about 350 °С.