Aija Krūmiņa

ZnFe2O4 Containing Nanoparticles: Synthesis and Magnetic Properties

Abstract Solid solutions of Co1−xZnxFe2O4 and Ni1−xZnxFe2O4 (0 < x < 1) nanoparticles were synthesized by sol-gel self-propagating combustion method. The obtained single cubic phase product has a specific surface area 25 m2∙g−1 to 33 m2∙g−1 and crystallite size 25 nm to 40 nm. Lattice parameters change linearly from 8.371 A (CoFe2O4) and 8.337 A (NiFe2O4) to 8.431 A (ZnFe2O4). The saturation magnetization (Ms) changes non-linearly from 60.8 emu∙g−1 (CoFe2O4), respectively, from 35.6 emu∙g−1 (NiFe2O4) to 3.3 emu∙g−1 (ZnFe2O4) reaching maximal value 76.1 emu∙g−1 for Co0.8Zn0.2Fe2O4 and 64.9 emu∙g−1 – for Ni0.6Zn0.4Fe2O4.

Phase Composition and Morphology of Tungsten Oxide Nanoparticles Produced via a Pyrolytic Process

The chemical synthesis is a leading route for the purposeful design of nanomaterials, whereas the tungsten oxides are employed in a variety of special applications. The production of nanomaterials by traditional synthetic methods is still a cumbersome multistep procedure. Here we propose an improved method to produce tungsten oxide nanoparticles via a pyrolytic process. A tungsten-containing precursor was prepared by liquid extraction using n-trioctylamine (C8H17)3N solution in toluene. We have shown that the conditions of thermal treatment of the W-based precursor determine the crystalline structure and nanomorphology of the final product. Monoclinic WO3 nanocrystallites are produced conducting the pyrolysis above 450 °C. The proposed method is a facile and versatile route to produce and control the phase composition and morphology of tungsten oxide-based nanomaterials.

Influence of Technological Parameters on Thermal Properties of Cordierite Ceramics

Porous cordierite ceramic samples have been prepared by using 33% of two carbonate-containing illite clays as substitutes for the necessary synthetic ingredients. The changes of thermal (CTE) and mechanical properties (compressive strength, modulus of elasticity), as well as phase content, apparent porosity and bulk density have been investigated in regards to gradual changes in maximum sintering temperature. It can be affirmed that these properties strongly depend on the thermal parameters of sintering as well as slightly upon differences in chemical composition of composition substitutes.

Preparation of Au, Pt, Pd and Ag Doped TiO2 Nanofibers and their Photocatalytic Properties under LED Illumination

In the present work formation of active TiO2 nanofibers in microwave-assisted synthesis and their modification with Au, Pt, Pd and Ag nanoparticles were studied. Anatase nanopowder and 10M KOH solution were used as raw materials. Microwave-assisted synthesis permitted to obtain TiO2 nanofibers and nanowires with a diameter of 10nm and a specific surface area 158.5m2/g. Chemical deposition method were used to modify TiO2 nanofibers with precious metal nanoparticles. After modification, specific surface area decreased and were in range 73.1 – 74.7m2/g. Photocatalytic activity was determined by degradation of the methylene blue (MB) solution under visible light irradiation. High intensity LED lamp was used as light source. The obtained samples showed higher photocatalytic activity with respect to pure TiO2 nanofibers. The doped TiO2 nanofibers were appropriate for degradation of harmful organic compounds as well as for hydrogen production by water splitting.

Au Supported on the TiO2-nanofibers as Novel Catalysts for Glycerol Oxidation

Composites of Au supported on the TiO2-nanofibers (Au/NF-TiO2) were synthesized and tested in glycerol oxidation processes. TiO2-nanofibers were prepared by a microwave-assisted hydrothermal synthesis method. Chemical deposition method was used for nanofibers modification with Au nanoparticles. Oxidation of aqueous glycerol solutions by molecular oxygen in the presence of Au/NF-TiO2 nanocomposites was performed. It was found that Au/NF-TiO2 composites are catalytically active in alkaline glycerol water solutions. The main product of glycerol catalytic oxidation was glyceric acid, by-products were – tartronic, lactic, glycolic, oxalic, acetic and formic acid. It was shown that Au/NF-TiO2 catalysts’ activity and selectivity depend on Au weight loading, glycerol/Au molar ratio, oxygen pressure and NaOH initial concentration. The best result was achieved using the 0.5 wt%Au/NF-TiO2 catalyst: selectivity by glyceric acid was 76% with glycerol conversion 100%.

Influence of Silver on Photocatalytic Activity of Nanosized ZnO Doped with Iron Group Metals

Zinc oxide nanoparticles doped with 0.2–1.5 mol% of Fe, Ni or Co and co-doped with 1 mol% of Ag were prepared by co-precipitation method and their photocatalytic activity in degradation of MB (methylene blue) water solution under ultraviolet irradiation was determined. X-ray diffraction analysis of the samples containing up to 0.5 mol% of iron group metals showed only ZnO and Ag phases. Crystallite size of doped ZnO nanoparticles was in the range of 27–31.6 nm depending on the sample composition and additional calcination at 400 °C. The photocatalytic activity of ZnO doped with iron group metals depended on the content of metals. The highest activity was observed for ZnO doped with 0.2 mol% of nickel. The co-doped with silver samples showed enhanced photocatalytic activity and higher reaction rate constant.

Production of Nano-Sized Co3O4 by Pyrolysis of Organic Extracts

The most promising application field of materials based on nano-sized Co3O4 is catalysis. The method of production is one of the factors, which greatly affects the catalytic activity of Co3O4 catalysts. The aim of this research is to study possibilities of a new promising extractive-pyrolytic method (EPM) for the production of Co3O4 nanopowders and silica- and ceria-supported Co3O4 nanocomposites. Solutions of cobalt hexanoate in hexanoic acid and trioctylammonium tetrachlorocobaltate in toluene preliminary produced by solvent extraction were used as precursors. The precursors’ thermal stability, phase composition, morphology and the magnetic properties of the final products of pyrolysis were studied. The performed investigations have shown that the mean size of the Co3O4 crystallites in the materials produced by the EPM varies from amorphous to 55 nm due to the production conditions.

Synthesis of NiO Nanoparticles by Microwave Assisted and Molten Salts Methods

Nickel oxide nanoparticles were prepared via molten salts and microwave assisted synthesis from nickel nitrate and the parameters of obtained nanopowders were compared. NiO nanoparticles with crystallite size in the range of 6-8 nm have been prepared by combining microwave assisted treatment of Ni (NO3)2 and urea solution with calcination at 300-320 °C. Molten salts (NaNO2-NaCl) ensured direct formation of NiO from Ni (NO3)2.6H2O and salts mixture at 350 °C but crystallite size of the particles reached 51-69 nm.

Microwave Synthesis and Properties of Thin Layer Pt Modified TiO2 Nanofibers Coating

In the present work formation of macro-size TiO2 nanofiber layers in microwave synthesis were studied. Anatase nanopowder and 10M KOH solution were used as raw materials. Microwave assisted synthesis method permitted to obtain TiO2 nanofibres containing individual nanowires with a diameter of 5nm and a specific surface area up to 129m2/g. Macro size layer of TiO2 nanofibers was obtained on the surface of microwave vessel. Total surface area covered with TiO2 was about 390cm2. Modification with platinum allows to increase photocatalytical activity of TiO2 macro size fiber layer up to 94.4% in UV irradiation and up to 11.6% under visible light irradiation.

Characterization of the phase composition and structure of electrodeposited nanostructured magnetic Ni-Fe alloys for different electrodeposition processes

Thin layers of Ni-Fe alloys containing 76.0–85.0 wt.% Ni were electrodeposited from simple-salt and complex-salt electrolytes. The current density determined the Fe content of 24.0–15.0 wt.% in the layers. It was found that the electrodeposited thin Ni-Fe alloy layers approximately corresponded to FeNi3 compound with the crystal size 10–15 nm, had a globular structure, which is characteristic of amorphous layers, and the coercitivity 51–55 Oe.