Structural relaxation in Ag-Ni nanoparticles: Atomistic modeling away from equilibrium

The out-of-equilibrium structural relaxation of Ag-Ni nanoparticles containing about 1000--3000 atoms was investigated computationally by means of molecular dynamics trajectories in which the temperature is decreased gradually over hundreds of nanoseconds. At low silver concentration of 10--30\%, the evolution of chemical ordering in Ni$_{\rm core}$Ag$_{\rm shell}$ nanoparticles with different surface arrangements is found to proceed spontaneously and induce some rounding of the nickel core and its partial recristallization. Fast cooling of an initially hot metal vapor mixture was also considered, and it is shown to disfavor silver aggregation at the surface. Silver impurities are also occasionally produced but remain rare events under the conditions of our simulations.

Quantum chemical study of NO reduction mechanism on Ag /Al2O3 catalysts

It was shown that N2O content among NO reduction products increases with an increase of the silver concentration in the catalyst because the nature of the catalytic centers changes and leads to a subsequent change in the mechanism of the reaction. Two reaction mechanisms were proposed and studied by means of quantum chemistry: a two-stage mechanism that proceeds via NO dimer formation on catalysts with high (above 2 wt. %) silver concentration and a parallel mechanism with isocyanates involved on catalysts with low (below 2 wt. %) silver concentration. It was demonstrated that on catalysts with high silver concentration mechanism that involves stepwise NO reduction via N2O to N2 is realised. Moreover, the final stage is complicated by the fact that formed intermediates and N2O are likely to desorb from the catalyst surface. In the case of catalysts with low silver concentration, the formation of both products (N2O and N2) proceeds in parallel and the lower activation barriers of the reaction leading to N2, as well as the thermodynamic profitability of its formation, lead to the predominance of the target product. The competition between the proposed mechanisms was studied in the case of catalytic centers represented by silver dimers. It was shown that activation barriers of reaction proceeding via NO dimer formation are lower than the corresponding barriers of the reaction with isocyanates involved, which confirms the prevalent realisation of the first process and the predominance of N2O among the final products. The obtained results explain the experimental data and are significant for further modelling of the mechanism of nitrogen oxides catalytic reduction considering the Al2O3 support.

Surface-water purification using cellulose paper impregnated with silver nanoparticles

The objective of this study is to prepare a cellulose paper that was impregnated with silver nanoparticles (AgNPs) for the purpose of water purification (disinfection and filtration). AgNP papers were prepared by chemical reduction of silver nitrate (AgNO3) with various concentrations (0.005 M, 0.015 M, 0.03 M, and 0.05 M) using sodium borohydride (NaBH4) as a reducing agent. Two ratios for NaBH4/AgNO3 of 2:1 and 10:1 were used to show the effect of reduction on the formation and removal efficiencies of AgNPs. AgNP papers were characterized using scanning electron microscopy and transmission electron microscopy. An acid digestion using HCl acid followed by analyzing the samples in an atomic absorption spectrometer (ASS) was conducted to measure the silver concentration in AgNP papers. TEM images showed that the silver nanoparticle size in the papers varied from 1.3 to 75 nm. Water samples, after filtration through AgNP papers, were analyzed using ASS to measure the silver concentration in the effluent water. AgNP paper antibacterial efficiency ranged from 99 % to 100 % for both reduction ratios. The average silver content in the effluent water for the three replicates ranged from 0 to 0.082 mg L−1, which meets the United States Environmental Protection Agency (US-EPA) guideline for drinking water of less than 0.1 mg L−1. Turbidity tests showed that these papers can be usefully used as point-of-use filters as the turbidity reduced to less than 1 NTU (Nephelometric Turbidity Units).

Study of Mechanisms Used by Algae to Decrease The Silver Toxicity in Aquatic Environment

In the study SEM, EDS, TEM and UV-vis analysis were used to investigate the biosorption, bioaccumulation and bioprecipitation/bioreduction of silver by freshwater green alga Parachlorella kessleri and to shed light on the reasons of biological silver nanoparticleproduction. When dead biomass of P. kessleri was used for silver removal, majority of silver (75%) was removed within2 min. Biosorption was probably the main mechanisms responsible for Ag+ ions removal from aqueous solutions. However, whenbehaviour of living biomass in the presence of silver ions was studied, the decrease of silver concentration was slower (68% within24 hours) with subsequent increase of silver concentration in the solution and extracellular formation of silver nanoparticles. Theformed AgNPs exhibited a lower toxicity against tested organisms. Algal cells probably used the formation of nanoparticles combinedwith rapid biosorption as detoxification mechanisms against silver toxicity. Bioaccumulation inside the cells played only aminor role in the detoxification process.

Simple Preparation of Ceramic-Like Materials Based on 1D-Agx(x=0, 5, 10, 20, 40 mM)/TiO2 Nanostructures and Their Photocatalysis Performance

Vertical Agx/TiO2 nanorods were successfully grown by a simple oxidation method of a Ti-Ag coating. The samples were grown in the phase of ceramic-like materials, which can be reusable for many cycles for photocatalysis applications. These ceramic-like Agx/TiO2 nanostructures were prepared by the spin-coating of silver nitrate onto Ti sheets. The presence of silver on the surface of the Ti sheet during the oxidation process helped in the growth of one-dimensional nanostructures. The physical properties of the fabricated ceramic-like nanostructures were studied by varying the concentration of silver on the Ti-sheet before the oxidation. One-dimensional nanostructures with an average size varying within the range of 200–500 nm were grown. The presence of silver made the nanostructure vertically directed. The nanorods were dense at the low and medium concentrations of 5, 10, and 20 mM of silver in contrary to high silver concentrations, where the nanorods were very sparse at 40 mM. Structural analysis showed the anatase and rutile structure of pure TiO2 with distinguishing diffraction lines A(101) and R(110); however, Agx/TiO2 showed a dominant orientation of A(101), confirming the 1D growth. Raman spectra confirmed the presence of TiO2 via the observation of its corresponding phonon modes. The photocatalysis properties of the fabricated ceramic-like nanostructures were performed on methylene blue (MB) as a known target dye. The low- and medium-silver-concentration samples showed a high photocatalytic activity compared to the pure and high-silver-concentration samples.

Surface Water Purification using cellulose Paper Impregnated with Silver Nanoparticles

The objective of this study is to prepare a cellulose paper was impregnated with silver nanoparticles (AgNPs) for the purpose of water purification (Disinfection (removal of Escherichia Coli, Staphylococcus Aureus, Enterococcus Faecalis, Enterobacter Aerogenes, Klebsiella Pneumoniae, and Proteus mirabilis) and filtration). AgNPs papers were prepared by chemical reduction of silver nitrate (AgNO3) with various concentrations (0.005 M, 0.015 M, 0.03 M, and 0.05 M) using sodium borohydride (NaBH4) as a reducing agent. Two ratios of NaBH4 / AgNO3 of 2 : 1 and 10 : 1 were used to show the effect of reduction on the formation and removal efficiencies of AgNPs. AgNPs papers were characterized using Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). An acid digestion using HCL acid followed by analyzing the samples in Atomic Absorption Spectrometer (ASS) was conducted to measure the silver concentration in AgNPs papers. TEM images showed that the silver nanoparticles size in the papers varies from 1.3 to 75 nm. Water samples, after filtration through AgNPs papers, were analyzed using (ASS) to measure the silver concentration in the effluent water. AgNPs paper antibacterial efficiency ranged (99 % to 100 %) for both reduction ratios. The average silver content in the effluent water for the three replicates ranged from 0 to 0.082 mg/L which meets the United States- Environmental Protection Agency (US-EPA) guideline for drinking water of less than 0.1 mg/L Turbidity tests showed that these papers can be usefully used as a point of use filters as the turbidity reduced to less than 1 NTU.

THE INFLUENCE OF NANO-SILVER ON FORMATION OF MICROBIAL BIOFILMS IN CASES OF TRAUMATIC LESION OF THE AUXILIARY APPARATUS OF THE EYE

Pyoinflammatory complications remain an acute problem in the post-operative period of traumatic lesions of the auxiliary apparatus of the eye (AAE). Silver both in the ionic form and in composition of chemical compounds is highly toxic for microorganisms, and as a result, it shows bactericidal effect to many bacterial strains, including gram-negative microorganisms. The peculiarity of AgNPs is efficiency of influence on the wide array of microorganisms, significant anti-biofilm effect and absence of resistance reaction. The aim of the research. To study the influence of the colloidal nano silver on formation of biofilms by microorganisms discharged from the wounds of patients with traumatic lesions of the auxiliary apparatus of the eye. Materials and methods. During 2018-2019, we examined 60 patients with traumatic lesions of the auxiliary apparatus of the eye. For evaluation of the influence of colloid nano silver solution on the processes of formation of the biofilm, we selected microorganisms which were cultured most frequently (Staphylococcus aureus, Acinetobacter spp., Klebsiella ozenae) from the patients. Results. The obtained data suggest that colloid nano silver inhibits efficiently formation of biofilms at the early stages (initiation, the 0 day of incubation) of their formation by all the three microorganisms, and the degree of inhibition of the biofilm formation did not depend on the silver concentration. The effect of colloid silver in the concentrations used by us at later stages of biofilm formation (the 3rd and the 7th day) with respect to К. ozenae is less efficient – the growth of cell biomass was observed (p≤0.05), and it did not depend on the silver concentration. At the same time, the effect of the colloid nano silver on S. aureus and Acinetobacter spp. on the 3rd and the 7th days was more efficient than at the early stage (p≤0.05). Conclusions. Nanoparticles of colloid silver are an efficient means to combat biofilms, as well as to prevent their formation.

Silver Ecotoxicity Estimation by the Soil State Biological Indicators

The use of silver in various spheres of life and production leads to an increase in environmental pollution, including soil. At the same time, the environmental consequences of silver pollution of soils have been studied to a much lesser extent than those of other heavy metals. The aim of this study is to estimate silver ecotoxicity using the soil state biological indicators. We studied soils that are significantly different in resistance to heavy metal pollution: ordinary chernozem (Haplic Chernozems, Loamic), sierosands (Haplic Arenosols, Eutric), and brown forest acidic soil (Haplic Cambisols, Eutric). Contamination was simulated in the laboratory. Silver was introduced into the soil in the form of nitrate in doses of 1, 10, and 100 mg/kg. Changes in biological parameters were assessed 10, 30, and 90 days after contamination. Silver pollution of soils in most cases leads to deterioration of their biological properties: the total number of bacteria, the abundance of bacteria of the genus Azotobacter, the activity of enzymes (catalase and dehydrogenases), and the phytotoxicity indicators decrease. The degree of reduction in biological properties depends on the silver concentration in the soil and the period from the contamination moment. In most cases, there is a direct relationship between the silver concentration and the degree of deterioration of the studied soil properties. The silver toxic effect was most pronounced on the 30th day after contamination. In terms of their resistance to silver pollution, the studied soils are in the following order: ordinary chernozem > sierosands ≥ brown forest soil. The light granulometric composition of sierosands and the acidic reaction of the environment of brown forest soils, as well as the low content of organic matter, contribute to high mobility and, consequently, high ecotoxicity of silver in these soils. The regional maximum permissible concentration (rMPC) of silver in ordinary chernozem (Haplic Chernozems, Loamic) is 4.4 mg/kg, in sierosands (Haplic Arenosols, Eutric) 0.9 mg/kg, and in brown forest soils (Haplic Cambisols, Eutric) 0.8 mg/kg.