Synthesis and characterization of nanocomposites based on polylactide/silver nanoparticles, obtained by thermochemical reduction of Ag+ ions by natural or synthetic polymers

The addition of silver ions or nanoparticles to impart antimicrobial properties to polymeric or other materials is a widely used method. However, it should be noted that the antiviral and antimicrobial effect of silver nanoparticles that come into contact with the environment, associated with their size, with a decrease in the size of nanoparticles, their effectiveness increases sharply. In the present work, we used a biodegradable polymer polylactide (PLA), which is obtained by condensation of lactic acid or ring-opening polymerization of lactide. These studies will further contribute to the development of new safe materials, in particular for food packaging, which is undoubtedly an urgent problem. The work aims is to obtain the silver-containing polymer composites based on polylactide by thermochemical reduction of Ag+ ions using natural (chitosan) and synthetic (polyethyleneimine (PEI)) polymers and to study the structure, morphology, thermomechanical and antimicrobial properties of the obtained nanocomposites. Thermochemical reduction of Ag+ ions in the bulk of polymer films, containing PLA, silver palmitate as a precursor of Ag NP and reducing agent (PEI or chitosan), has been performed by keeping them at 100–170 °C within 5 minutes. The polymeric film composites, cast from chloroform solution, were heated in an oven using precise thermal regulator VRT-3. As a result of reduction, the films get attained silver color, the Ag content in the bulk of films varied from 1 to 4 wt. %, and the thickness of the films was 110 μm. Structure, morphology, thermomechanical and antimicrobial properties of two types of nanocomposites – PLA-Ag-PEI and PLA-Ag-chitosan, formed by the thermochemical reduction of Ag+ in polymer films have been studied using wide-angle X-ray scattering (WAXS) (a DRON-4-07 diffractometer), a transmission electron microscope (TEM) (JEM-1230 JEOL, Japan), and thermomechanical analysis (a UIP-70M device). Antimicrobial activity of the obtained nanocomposites was investigated applying reference strains of opportunistic bacteria Staphylococcus aureus and Escherichia coli. It has been found that thermochemical reduction of Ag+ ions in the bulk of polymer films, when using synthetic or natural polymers (PEI or chitosan) as a reducing and stabilizing agent of silver nanoparticles occurs at 160 °C during 5 minutes. It has been found that the average size of Ag nanoparticles in the polymeric matrix is equal to ~ 7 and ~ 4 nm for PEI and chitosan, respectively. It has been shown that PLA-Ag-chitosan nanocomposites have much higher antimicrobial activity against S. aureus and E. coli strains as compared to PLA-Ag-PEI nanocomposites.

Compositional and operational impacts on the thermochemical reduction of CO2 to CO by iron oxide/yttria-stabilized zirconia

The versatile redox chemistry of ferrites makes them useful as active materials for the solar-thermochemical production of synthetic fuels. Optimization of the distribution of iron in a YSZ matrix allows the performance of ferrites to be enhanced.

Facile Synthesis of Single-Phase Alpha-Tungsten Nanopowders from Ammonium Paratungstate by RF Induction Thermal Plasma and Thermochemical Reduction

Facile, economic methods of preparing tungsten (W) nanopowder are critically needed to meet industrial demand. Herein, we report a method of preparing single-phase alpha-W (α-W) nanopowders using ammonium paratungstate (APT) as a starting material and the optimum synthesis conditions. The process involves two stages: i) the radio-frequency (RF) induction thermal plasma treatment of APT, followed by ii) thermochemical reduction at 600-900 ^oC. The crystallographic phase and morphological evolution of all products were systematically investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM), and the effects of the annealing temperature on the phase and particle size of the obtained powders were also evaluated. When the RF induction thermal plasma treatment was conducted with and without H₂, the XRD and FESEM results showed the formation of mixed-phase α- and beta-W (β-W) nanopowder and WO₃ nanopowder, respectively. Single-phase α-W nanopowder was achieved by annealing the WO₃ nanopowder in an H₂ reductive atmosphere at 700 ^oC for 10 min, resulting in homogenous nanoparticles with a small particle size (d50) of 21.16 nm without any aggregation.

Using iron formations during exploration for c. 1.9 Ga Zn-Pb-Ag sulphide deposits, Jugansbo area, Bergslagen, Sweden

<p>Oxide- and silicate-dominated, stratiform iron formations are abundant in the northern part of the Sala inlier, Bergslagen, Sweden. The iron formations are commonly laminated and are associated with fine-grained siliciclastic and felsic volcaniclastic rocks in a 1.91-1.89 Ga succession dominated by pumiceous and lithic-bearing rhyolitic volcaniclastic rocks. Depositional features are consistent with a volcanically active, submarine environment, in which the iron formations and fine-grained host strata to sulphide mineralization accumulated during pauses in volcanism. At c. 1.87-1.81 Ga, the succession underwent polyphase folding and shearing under lower amphibolite facies conditions, followed by polyphase faulting under more brittle conditions.</p><p>The iron formations are locally directly stratigraphically overlain by  stratiform Zn-Pb-Ag sulphide mineralization. Detailed geological mapping has demonstrated that sulphide-bearing (proximal) iron formation is gradational into sulphide-poor (distal) iron formation along a strike extent of more than 7 km. Proximal iron formation is dominated by magnetite, grunerite, tremolite, quartz, almandine-rich garnet (Alm<sub>54</sub>Sps<sub>35</sub>Grs<sub>8</sub>), muscovite, and chlorite, whereas distal iron formation is characterized by hematite, magnetite, epidote, actinolite, spessartine-rich garnet (Sps<sub>53</sub>Adr<sub>29</sub>Grs<sub>15</sub>) and locally calcite. </p><p>Elevated contents of Mn, Zn and Co are observed in both distal and proximal iron formation, whereby these elements help pinpoint the favorable horizon, but are of less use for vectoring along strike. Whole-rock lithogeochemistry samples of proximal iron formation differ from distal iron formation in: (1) Eu/Eu*>1, (2) Ce/Ce*<1, (3) suprachondritic Y/Ho, (4) elevated Tl, Cs, Cd, Sn, S, Cu, Pb, Sb and Au (5) lower volcaniclastic/siliciclastic content based on lower Al, Ti and Zr. Collectively, these features are indicative of Fe mineralization following interaction of a hot, acid and reduced hydrothermal fluid with oxidized seawater in a vent proximal position which was deprived of clastic or volcaniclastic input.</p><p>Sulphide mineralization, ranging from banded, to disseminated and fracture-hosted, is associated with chlorite-rich, locally graphitic mudstone immediately overlying proximal iron formation. Multi-grain δ<sup>34</sup>S<sub>V-CDT</sub> of sphalerite, pyrite and pyrrhotite are exclusively negative, ranging from -10.6 to -0.25 with no clear mode. The δ<sup>34</sup>S<sub>V-CDT</sub> distribution is unusual for Bergslagen deposits, and is indicative of a significant contribution of sulphur via bacteriogenic or thermochemical reduction of seawater SO<sub>4</sub><sup>2-</sup>.</p><p>Stratigraphic analysis suggest that proximally, the mineralizing event followed a sudden deepening of the basin, and progressed from Fe oxide to polymetallic sulphide mineralization. The temporal zonation probably reflect a decrease in the redox potential of the basin, possibly due to venting and ponding of reduced hydrothermal fluids. Ore textures and host facies are consistent with of an exhalative mode of formation for both deposit types, albeit an importance of subseafloor mineralization processes is implied by lateral variability in both sulphide and chlorite content. In relation to the local stratigraphic evolution in the area, the mineralizing event can be directly linked to an event of basin deepening following a caldera-forming volcanic eruption. The results from stratigraphic analysis along with aforementioned proxies for redox and vent-proximity present first order vectors to stratiform Zn-Pb-Ag mineralization in the Jugansbo area, Bergslagen.</p>