Theoretical and Experimental Chemistry最新文献

It has been established that crystalline carbon nitride (CCN) in acidic solutions of C1-C4 alcohols in the presence of a palladium cocatalyst exhibits high photocatalytic activity in the process of chemoselective hydrogenation of benzaldehyde (BA) and 5-hydroxymethylfurfural (HMF) to benzyl alcohol and 2,5-dihydroxymethylfuran, respectively. The apparent quantum yield of BA conversion reaches ~90 % in ethanol under optimal conditions, while HMF reaches 30% (at λ_irr = 405 nm). A probable process scheme is proposed, which involves the initiation of transformations of substrate molecules with the participation of photogenerated charges, in particular, oxidation of alcohols by holes of the CCN valence band, reduction of carbonyl groups by photogenerated electrons, and further transformations of intermediate compounds of a radical nature with the formation of final products.

The effect of modification of nanostructured TiO₂ films with lanthanum ions on their electrocatalytic, photoelectrochemical, and sensor properties is investigated. La-TiO₂ films were prepared by sol–gel method and characterized by X-ray diffraction analysis, X-ray photoelectron spectroscopy, scanning electron microscopy and photoelectrochemical current spectroscopy. It is shown that modification with lanthanum ions leads to an increase in the photosensitivity of La-TiO₂ electrodes in the UV range and a batochromic shift in the photocurrent spectra, and also improves their catalytic activity in the reaction of oxygen reduction and sensor properties in determining the concentration of heavy metal ions in liquids.

The possibility of obtaining 2D GeH by mechanochemical treatment of bulk germanane in the presence of NaCl with subsequent sonochemical treatment and liquid-phase exfoliation has been demonstrated for the first time. It has been established that the preliminary mechanochemical nanostructuring of germanane promotes the formation of predominantly monolayer particles with a thickness of <1 nm and a lateral size of up to 200 nm, and also leads to a red shift of the E_2g mode in the Raman spectrum by 10 cm^–1. It is shown that the dispersion of mechanochemically obtained germanane has three times higher photocatalytic activity in the hydrogen evolution reaction from an aqueous solution of lactic acid than the sample obtained without mechanochemical treatment.

A functionalized nanostructure aminopropyl aerosilogel (amino-ASG) effective in the sorption of strontium ions has been synthesized using a single-stage liquid-phase chemical modification of the surface of hydroxylated mesoporous aerosilogel, which has been characterized by IR spectroscopy, low-temperature nitrogen adsorption-desorption, and chemical analysis. It is shown that amino-ASG selectively removes Sr²⁺ cations from binary solutions at pH 1.0-10.0, even under a 10-fold excess of Ca²⁺ cations, with equilibrium being reached during 5 min. It is established that the sorption kinetic for functional amino-ASG is described by a pseudo-second-order equation. The equilibrium sorption is consistent with the Langmuir adsorption equation, which proves a decisive contribution of the grafted amino groups.

The electrochemical properties of TiO_x-Pt electrodes with different platinum contents (0.3-2.0 mg/cm²), obtained by a combined method including titanium anodization, deposition of platinum, and subsequent thermal treatment, have been studied. Cyclic voltammograms were compared with data for platinum metal in 1 M of HClO₄. It is established that a decrease in the amount of platinum leads to lower currents in the oxide reduction region, which is associated with a decrease in the number of active sites. Thermal treatment causes changes in the coating morphology, a decrease in the active surface area, and the diffusion of platinum into the titanium substrate, resulting in the formation of mixed oxides. The dependences of platinum oxide reduction peak currents on the potential sweep rate indicate the irreversible electron transfer process.

The structural properties, X-ray luminescence spectra and content of active sites of the surface of nanodispersed phosphors based on terbium-doped lanthanum fluoride, lanthanum phosphate and hydroxyapatite (LaF₃:Tb³⁺, LaPO₄:Tb³⁺ and HA:Tb³⁺) have been studied. The obtained data may be useful in photopharmacology and photodynamic therapy for optimizing the conditions of adsorption immobilization of molecules of photosensitive substances and photosensitizers from physiological solution on the surface of nanodispersed phosphors at the development of targeted drug delivery and local disease therapy.

It is established that the polysaccharide glucuronoxylomannan decorated with gold nanoparticles significantly changes the spatial structuring depending on pH and temperature. A mechanism of the biopolymer conformation effect on the formation process and properties of a hybrid material is proposed. The most stable structures are formed in an alkaline medium, however, they also retain the possibility of adaptive behavior of an initial biomolecule. It has been demonstrated that biological macromolecules can be applied to form “smart” molecular hybrids with the ability to switch properties in response to external stimuli.

The optical properties (IR spectra and luminescence spectra) of polycrystalline materials based on ZnS-CeF₃ systems have been investigated. A significant change in the transmittance and luminescence spectra of the sintered samples compared to the individual components and their mechanical mixture is established. A thin-film coating, transparent in the UV, visible and IR spectral ranges (a refractive index of 1.97) has been obtained by the method of thermal evaporation in vacuum. The obtained coating is promising for interference optics.

Samples of oxygen-doped crystalline carbon nitride were synthesized by a two-step ionothermal method. The obtained materials were characterized by scanning electron microscopy, X-ray diffraction, spectrophotometry, and luminescence and IR spectroscopy. has almost no effect on the morphology and crystal structure of samples, but it leads to an increase in the absorption intensity in the visible range of the spectrum and luminescence quenching. The synthesized materials exhibit high photocatalytic activity in the simultaneous production of hydrogen and benzaldehyde upon irradiation of benzyl alcohol solutions in a water/acetonitrile mixture. The apparent quantum yields of benzaldehyde and hydrogen formation under optimal conditions reach Φ ≈ 80% at λ_irr = 405 nm.