Russian Journal of Physical Chemistry B最新文献

This work reviews studies of the application of machine learning methods and neural network technologies in the prediction of solubility of various substances in supercritical fluids. By the example of an existing data set on the solubility of aromatic hydrocarbons in supercritical carbon dioxide, a prototype of a solubility prediction system was developed using a simple three-layer neural network. Its efficiency is shown, and further directions of research in this field are identified.

A simple method for the preparation of doped GeO₂ aerogels is proposed. At the first stage, a gel with a composition of (NH₄)₃H(Ge₇O₁₆)(H₂O)_x was obtained by dissolving germanium dioxide in aqueous ammonia with pH 8.2. The dopant ions were introduced by impregnating the hydrogels with a dimethyl sulfoxide (DMSO) solution of praseodymium nitrate. The optimum conditions of the synthesis were determined, which allow uniform distribution of the dopant ion in the matrix. The Pr/Ge ratio in the resulting aerogels was 0.1. The aerogel samples were characterized in detail by IR, inductively coupled plasma-atomic emission spectroscopy (ICP-AES), low-temperature nitrogen adsorption, etc. It was found that praseodymium affects the luminescence characteristics of GeO₂ aerogels during excitation radiation with a wavelength of 240, 255, and 390 nm.

The formation of mixed oxides in La₂O₃/MO–Al₂O₃ systems (M is a group IIA element: Mg, Ca, Sr, Ba) subjected to a high-temperature treatment and treatment in a water fluid (WF) medium is studied. It is shown that the high-temperature treatment of a group IIA element aluminate with supported lanthanum nitrate leads to the formation of LaAlO₃ only in the case of an Mg-containing system. In other cases, original aluminates do not undergo transformations, and lanthanum oxide is formed. The treatment of La/M–Al ternary systems in a WF medium leads to the formation of LaAlO₃ in all cases; in addition, in all samples, except for the Ba-containing system, phases of free oxides of group IIA metals appear. The increase in the activity and selectivity of La/M–Al ternary oxide systems in the oxidative coupling of methane compared to the respective parameters of M–Al binary systems is attributed to the presence of an individual La₂O₃ oxide phase.

The solubility isotherms of N-isopropylacrylamide monomer (NIPAM) in supercritical carbon dioxide were obtained by the synthetic visual method in the temperature range of 304.8–353.0 K and the pressures range of 0.1–40.0 MPa, and the maximal solubility of NIPAM in CO₂ at these state parameters was determined. In addition, the region of crossover of isotherms P_mix = f(x) was detected, and the nature of this phenomenon was discussed. The predictive ability of the Chrastil model was assessed for this system.

This review examines information on modern methods of separating oils and oil residues in the analysis of group composition using supercritical fluids. The features of the influence of the composition and properties of individual group components of oil samples on further processing are shown. Traditional methods of separating petroleum feedstock into group components are briefly reviewed. The results of modern studies of extraction methods for separating oil samples using supercritical fluids are shown. Information is presented on new methods for the extraction of asphaltenes and fractionation of heavy oils and oil residues using СO₂.

The effect of the extraction method and conditions on the polyphenolic composition of buckwheat Fagopyrum esculentum husk extracts and their activity in inhibiting acetylcholinesterase (AChE) was studied. The extracts were obtained both by the conventional method of water–ethanol extraction and in a subcritical water medium at 120–220°C. A direct correlation was found between the anticholinesterase activity and the content of polyphenols in the extracts. The highest activity in inhibiting AChE was shown by the extract obtained in the subcritical water medium at 220°C, which contained the maximum amounts of polyphenols and flavonoids. This indicates the decisive role of these compounds in inhibiting AChE. The obtained data allow one to consider buckwheat husk extracts as inexpensive and renewable sources of polyphenolic compounds and flavonoids with P-vitamin and neuroprotective activity.

Composites of gC₃N₄ particles immobilized in monolithic silica aerogel have been obtained, and their physicochemical photocatalytic properties were studied. The composites may be reused many times. They showed higher photocatalytic activity than free gC₃N₄ in the oxidations of alkyl aryl sulfides with molecular oxygen in supercritical carbon dioxide (SC-CO₂). The results presented in this work can serve as a basis for the development of efficient processes of organic compounds oxidation.

The dynamics of submicron gold particle formation during laser ablation in supercritical and liquid CO₂ are investigated using time-resolved Mie scattering absorption spectroscopy. It is found that a high density of CO₂ of approximately 800 kg/m³, regardless of the phase state, leads to the formation of laser-induced medium fluctuations on time scales of 10 to 1000 μs, during which the defocusing of subsequent laser pulses may occur. Under conditions of the reduced fluid density in the vicinity of the Widom region (P = 8.5 МРa, T = 310 K), it is demonstrated that nanoparticles can leave the interaction zone unhindered as evidenced by the exponential increase in integral absorption. Data from the absorption spectra allow the observation of the nanoparticle formation dynamics with an average diameter of approximately 160 nm and a log-normal size distribution, the width of which is determined by the thermodynamic conditions of CO₂.

The solubility of copper(II) hexafluoroacetylacetonate monohydrate Cu(hfa)₂⋅H₂O in carbon dioxide was studied. The solubility increases with increasing temperature in the range of 303–353 K and was observed to increase nonlinearly with increasing CO₂ density in the supercritical (SC) region. The dependence of the solubility on the parameters of state (temperature, CO₂ density) was described by the Chrastil equation. The adsorption of Cu(hfa)₂⋅H₂O from a solution in SC-CO₂ on three γ-Al₂O₃ samples differing in the presence of acidic and basic additives was investigated. The adsorption isotherms have a shape with a sharp increase in the adsorption value in the initial part, which indicates a high affinity of the complex for the surface of the substrate and/or its heterogeneity, as well as the presence of sites with high adsorption energy. An increase in the CO₂ density from 355 to 780 kg/m³ at a constant temperature (313 K) leads to a decrease in the adsorption of Cu(hfa)₂⋅H₂O on all three Al₂O₃ samples. At a constant medium density of 355 kg/m³ and an increase in temperature from 313 to 343 K, a more complex behavior of the adsorption isotherms is observed depending on the characteristics of the support and the concentration range of the adsorbed substance.

The results of joint supercritical water oxidation (SCWO) on poultry manure (PM) and brown coal (BC) mixtures continuously fed as an NaOH stabilized (0.8 wt %) slurry into a tubular reactor at 25 MPa, temperature gradient along its vertical axis of 390–600°C, varied reactant flow rate, and concentrations of PM and BC in the slurry are presented. The addition of BC leads to a reduction of the total energy consumption by ohmic heaters by factors of 1.5–1.8, depending on the content of combustible matter in the slurry. The forming gas mixture contains CO₂, N₂, and a trace amount of N₂O. Calcium and sodium carbonates, phosphates, and aluminosilicates are predominant in the composition of ash residues. The total content of phenols (17–32 μg/dm³) and polycyclic aromatic hydrocarbons (2–4 μg/dm³) in the effluent depends on the PM concentration in the slurry and does not exceed the level of their maximum permissible concentration in wastewater. The formation of HNO₃ and H₂SO₄ during the SCWO process results in the corrosion of construction materials and increases the content of chromium, copper, and nickel in the aqueous effluent. The mechanisms of the transformation of the organic and mineral components of PM and BC are discussed.