We study the dynamics of polydisperse dust particles in a rf post-discharge plasma. The levitation of charged particles after the discharge switching-off is found, and the velocities of their fall are measured. A model of the dynamics of particles in the afterglow plasma is proposed to estimate their size and residual charge.

Here we report, for the first time to our knowledge, the plasma modification of ZnO-based photocatalysts impregnated with silver nanoparticles (Ag NPs). Plasma-treated semiconductors have been recently proposed as effective catalysts for photodegradation of methyl orange (MO) in aqueous solution. Whereas effects of plasma treatment on activity of catalysts doped with a metal atom have been investigated, the effects of plasma treatment on the performance of catalysts doped with metal nanoparticles (NPs) have not yet been studied. In this study, ZnO microparticles were impregnated with Ag NPs. Impregnated catalysts were prepared by a wet impregnation method followed by plasma treatment. For this purpose, dielectric barrier discharge (DBD) plasma was applied. The photocatalytic degradation of methyl orange was investigated under ultraviolet (UV) light irradiation in the presence of aqueous suspension of Ag-NPs-impregnated ZnO. The catalysts were characterized by photoluminescence (PI) spectroscopy, scanning electron microscopy (SEM) combined with energy dispersive X-ray spectroscopy (EDX), infrared spectroscopy (IR), and UV-Vis spectroscopy. The presence of silver in ZnO was established by the inductively coupled plasma atomic emission spectrometry (ICP-AES) technique. A diminished catalytic activity was observed after impregnation with Ag NPs. A subsequent treatment by DBD plasma leads to the enhancement of catalysts' performance. The photocatalytic activity, expressed in terms of rate constants of photodegradation of methyl orange, was approximately 3 times higher for synthesized samples than that for untreated ZnO.

It was found that the exposure to low-temperature gas discharge plasma at atmospheric pressure is an effective way of paper cleaning from fungal spores. This effect is explained by the specific mechanisms of micro-discharges excitation and maintaining that ensure efficient (up to 90 %) reduction in the number of viable mould spores without local heating biopolymeric materials.

Институт экспериментальной ботаники имени В. Ф. Купревича НАН Беларуси, Минск, Республика Беларусь 2 Институт физики имени Б. И. Степанова НАН Беларуси, Минск,

A dielectric barrier discharge (DBD) plasma was applied to treat commercially available ZnO powders. The performance of untreated and plasma-treated ZnO photocatalysts is discussed in the light of their application for photodegradation of organic pollutants. The photocatalytic activities of plasma-treated and untreated ZnO powders were evaluated by measuring the photodegradation of methyl orange (MO) in aqueous solution exposed to ultraviolet (UV) light. The MO concentration in solution was measured spectrophotometrically (UV-Vis spectrophotometry). The photocatalytic activity, expressed in terms of the methyl orange photodegradation rate, was 2.2 times higher for the plasma-treated sample than for the untreated one. In addition, the kinetic process of photocatalytic degradation of MO was also examined, and the degradation of MO was found to follow a first-order rate law. The results imply that different mechanisms are involved in the decomposition of methyl orange on untreated and plasmatreated catalysts. The samples were also characterized by photoluminescence (PL) spectroscopy. Room temperature PL spectra of ZnO powders displayed two emission bands: excitonic UV emission, and deep level visible emission. Characterization of the ZnO powders by means of photoluminescence indicated that plasma treatment leads to an increase in the UV excitonic emission. The increasing photocatalytic activity after plasma treatment can be attributed to the increased optical quality of ZnO.

The structure and photocatalytic properties of polydisperse zinc oxide (ZnO) powder treated with a low-pressure radio-frequency (RF) plasma discharge were studied. The photocatalytic properties of ZnO before and after the treatment were studied with respect to photodegradation of organic impurities using decomposition of methyl orange in aqueous solution by UV light as an example. It was found that the photodegradation kinetics were described well by first-order equations. The photodegradation mechanisms of methyl orange over untreated and plasma-treated ZnO samples were different. It was shown that the effectiveness of the photodegradation expressed in terms of reaction constants increased by 20% after RF discharge-plasma treatment of the photocatalyst.

This paper reports the effect of radio frequency (RF) and dielectric barrier discharge (DBD) plasma on the activity of ZnO-based photocatalysts. The photocatalytic activities of plasma-modified and untreated ZnO powders were evaluated by measuring the degradation of methyl orange in water under the UV irradiation. Solutions at an initial concentration of dye of 50 mg/L (typical concentration in textile wastewaters) were used in experiments. DRIFT and SEM were used to characterize the surface changes of the ZnO powders after the treatment. The DRIFT investigations revealed a new band at around 2205 cm−1 in an RF plasma-treated sample. It has been found that the performance of a DBD plasma-treated catalyst is superior to that of RF plasma-treated and untreated catalysts.

We have studied the effect of shallow modulation of the discharge current on the burning regime and the plasma parameters of a diffusion-cooled glow discharge in CO2/N2/He laser gas mixtures. We have established that modulation of the discharge current leads to excitation in the discharge of pulsations in the acoustic pressure, the electric current, and the intensity of the generated laser radiation, with the frequency of standing acoustic waves arising in the discharge tube and also with the frequencies of the current modulation, its harmonics, and combinations of all these frequencies with the frequency of the current pulsations in the power supply. We have shown that when self-sustaining resonant oscillations in the discharge current are excited or when the current is modulated, the IR luminescence intensity from the upper laser level of the CO2 molecule and the power of the radiation generated by the laser vary because of plasma heating in the positive column of the discharge, due to its contraction in the acoustic wave field initiated by the current pulsations.

We have studied the effect of the regimes of high-frequency (radio wave) electromagnetic treatment of gauging water on the process of structurization and on the technological characteristics of portland-cement systems. It has been established that the radio wave electromagnetic activation of water leads to a reduction in its surface tension, dynamic viscosity, and shear stress, as well as intensifies the formation of coagulation structures in a portland-cement slurry and aids in increasing the mobility of cement-sand mixtures.

The change in the structure of M1 copper on exposure to a nonequilibrium low-temperature plasma produced by a high-frequency capacitive discharge in air at a pressure of about 1 Torr was investigated. The influence of the duration of plasma action on the structure and mechanical properties of copper has been studied. The increase in the dispersity of copper and in the homogeneity of its structure under the action of plasma has been established. It is shown that transformation of the copper structure is accompanied by the formation of static distortions of its crystal lattice at a level of about 0.007∙10–10 m.

We have investigated the influence of the regimes of high-frequency magnetic-impulse and acoustic action on the physicochemical properties of water solutions of polycarboxylate superplasticizers and technological indices of fine concretes plasticized by them. The dependences of technological properties of concretes on the concentration of water solutions of the superplasticizers, the content of impurity ions in the water used for dilution, and the conditions of acousto-radiowave treatment have been determined. The regimes of activation of superplasticizer solutions, which permit increasing the mobility and keeping quality of concrete and solution mixes tempered with water and the density and strength of fine concretes formed from them, have been established.

The process of decay of dust structures formed of polydisperse grains injected into an RF discharge is investigated. The dust grain velocities after switching-off of the discharge are measured. The number density, dimensions, and residual charges of dust grains are estimated from the balance of forces acting on the grains after discharge is switched off.

Local thermodynamic equilibrium (LTE), frequently used as fir t approximation in modeling of thermal plasma processes, is s ometimes unable to explain experimental results. It is particularly true near a wall and a surface impacted by the plasma jet. In this work, a 2-D custom model usin g the CFD commercial code Fluent was developed for argon-oxygen indu ctively coupled plasma (ICP) at atmospheric pressure. The assumption of the rmal equilibrium was made but not that of chemical equilibrium. The transport roperties were calculated using higher-order approximation of Chapman-E nskog theory. Reaction kinetics rates of dissociation and ionization were als o considered. The model was applied to a process torch used for carving experiments o n graphite, and the distribution of reactive species brought to the surface was analyzed in terms of reaction rate distribution: the experimental effect of diffe rent injection geometries on the distribution of the reaction rate is qualitatively re produced by the model.

Influence of complex acoustic-radio wave treatment of water on an index of activity of ions of hydrogen, rheological specifications prepared by a cement-sand mixtures and technological parameters of the obtained plasticized fine-grained concrete studied. Two methods used to reach the maximum influence on an index of activity of ions of hydrogen of water, mobility, keeping of the prepared concrete compounds, density and durability at compression of concrete. The first method four -minute complex acoustic-radio wave treatment of water (high frequency (5.28 MHz) + ultra sound (44 kHz)), with the subsequent four minute additional impact of a high-frequency field. The second used method four-minute complex treatment of water (high frequency (5.28 MHz) + ultra sound (1 MHz)) with the subsequent two-minute additional impact of a high frequency field. Assumptions about the mechanism of acoustic-radio-wave activation of water and its impact on the process of hardening and structure of Portland cement systems are stated.

The effect of the complex acoustic-radio wave treatment of water on the index of activity of the hydrogen ions, the rheological characteristics of the cement-sand mixtures tempered by this water, and the technological parameters of the obtained plasticized fine-grained concretes was studied. Two methods were used to reach the maximum effect on the index of the activity of the hydrogen ions of the water, the mobility, the storability of the prepared concrete mixes, and the density and compressive strength of the concretes. The first method was a four-minute complex acoustic-radio wave treatment of the water (high frequency (5.28MHz) + ultra sound (44 kHz)) that was followed by the four-minute additional impact of a high-frequency field. The second method used was a four-minute complex treatment of used water (high frequency (5.28 MHz) + ultra sound (1 MHz)) followed by the two-minute extra impact of a high frequency field. The assumptions concerning the mechanism of the acoustic-radio waves activation of the water and the effect of this water on the process of hardening used and the structure of the Portland cement systems are expressed.

The high-current pulsed arc discharge in vacuum used for technology of diamond-like carbon coating deposition is considered. The pulse-periodic carbon plasma flows are generated as a result of graphite cathode sputtering with the use of four-electrode arc system with self-recovering thin-film conductor of ignition device. It was found that fluctuations of plasma radiation intensity are due to formation and decay of cathode spot groups with lifetime of 5-10 mu s. Three characteristic spatial zones of discharge radiation are observed - cathode spots, diffuse radiation area of carbon ions near the cathode spots, and molecular carbon emission in the interelectrode gap near the anode attachment. The value of gas-kinetic temperature of plasma was found to be about 1000 K while the plasma electron temperature is approximately 10 eV.