Investigation of Factors Influencing the Precipitation of Iron Oxides from Fe(II) Containing Solutions

Factors that influence the precipitation of iron oxides from Fe(II) containing solutions were investigated by X-ray powder diffraction, 57Fe Mössbauer and FT-IR spectroscopies, FE SEM and EDS techniques. Near spherical aggregates of spindle-shape goethite particles were obtained by oxidation of 0.1 mol dm–3 FeSO4 solution (suspension) with pure oxygen at 90 °C. Wide and thin goethite particles elongated along the crystallographic c-axis were formed in parallel. With the addition of tetramethylammonium hydroxide to 0.1 mol dm–3 FeSO4 solution (suspension) substoichiometric magnetite (Fe3-xO4) particles were additionally formed. They were dominant at pH > 12.5. Mössbauer spectroscopy was used to calculate the stoichiometries of Fe3-xO4 particles. Very small magnetite particles ( 20–100 nm) showed a tendency to aggregate. The twinning effect of octahedral magnetite particles (> 200 nm) was observed. A drastic effect on the properties of iron oxide precipitates was achieved by adding H3PO4 to the precipitation system containing 0.1 mol dm–3 FeSO4 + 0.01 mol dm–3 H2SO4 solution at the start. In dependence on the concentration of the added H3PO4, nanosize goethite particles about 15–25 nm in size, or poor crystalline ferrihydrite particles (two-line ferrihydrite) were obtained. The EDS analyses of the precipitates did not show any significant change in the sulphur content, whereas the phosphorous content gradually increased in the precipitates with an increase in the added H3PO4. In high concentrations phosphates completely suppressed the formation of goethite under given experimental conditions, and phosphated ferrihydrite was formed instead

Formation and Characterization of NiFe2O4

Synthesis of nickel ferrite, NiFe204, was performed applying the thermal treatment of the corresponding mixed metal hydroxides or the solid state reaction between NiO and a-Fe203. The samples were studied by X-ray diffraction, Fourier transform IR spectroscopy and 57Fe Mčssbauer spectroscopy. Ball-milling of NiFe204 caused a decrease of hyperfine magnetic fields corresponding to Fe3+ ions in tetrahedral and octahedral sites, an increase of the Mossbauer spectral line widths, as well as a slight increase of isomer shifts. It was supposed that the ball-milling of NiFe204 had more influence on the degree of inversion than on other structural properties of the spinel. It was found that the heating temperature, and not the heating time, had the ultimate effect on NiFe204 microstructure. Samples heated up to 500 °C showed a pronounced size-correlated diffraction line broadening, corresponding to the coherent domain size of about 13 nm, and rather small crystalline disorder. Samples heated at temperature s above "" 1000 °C had much larger crystallites, exhibiting very small disorder

Formation and Characterization of NiFe2O4

Synthesis of nickel ferrite, NiFe204, was performed applying the thermal treatment of the corresponding mixed metal hydroxides or the solid state reaction between NiO and a-Fe203. The samples were studied by X-ray diffraction, Fourier transform IR spectroscopy and 57Fe Mčssbauer spectroscopy. Ball-milling of NiFe204 caused a decrease of hyperfine magnetic fields corresponding to Fe3+ ions in tetrahedral and octahedral sites, an increase of the Mossbauer spectral line widths, as well as a slight increase of isomer shifts. It was supposed that the ball-milling of NiFe204 had more influence on the degree of inversion than on other structural properties of the spinel. It was found that the heating temperature, and not the heating time, had the ultimate effect on NiFe204 microstructure. Samples heated up to 500 °C showed a pronounced size-correlated diffraction line broadening, corresponding to the coherent domain size of about 13 nm, and rather small crystalline disorder. Samples heated at temperature s above "" 1000 °C had much larger crystallites, exhibiting very small disorder

Studij nanofaznog TiO2 elektronskom mikroskopijom, difrakcijom x-zračenja i Ramanovim raspršenjem

Dye-sensitized solar cells differ from conventional semiconductor devices in that they separate the function of light absorption from charge-carrier transport. The device is based on a 10-mm-thick optically transparent film of titanium dioxide (TiO2) particles of a few nanometers in size, coated with a monolayer of charge-transfer dye to sensitize the film for light harvesting. In the present authors\u27 review, the principal role of the TiO2 photoanode is emphasized by a detailed presentation of its characterization by different experimental methods, while the photoelectric responses of the cells, a work which is still in progress, are indicated in the references cited. Hydrolysis of Ti(IV)-isopropoxide in isopropanol by the addition of water is a suitable chemical reaction for the production of nanosized TiO2. The properties of nanosized TiO2 can be modified by the hydrolysis catalyst, pH of the solution, temperature, presence of complexing ligand and the colloidal state of TiO2 precursor. In the present work, the microstructural properties of nanosized TiO2 were studied by HREM, ED, XRD, SAXS and Raman spectroscopy. HREM was used to determine both grain and pore sizes. Electron diffraction and X-ray diffraction provided evidence of nanocrystalline anatase and brookite phases. The grain sizes of the anatase and brookite phases changed from (5±1) to (12±3) nm with an increase of the treating temperature up to 773 K, as shown by XRD. An method of determining nanosized TiO2 grain size based on low-frequency Raman scattering, is presented.Solarne ćelije senzitizirane bojom razlikuju se od klasičnih poluvodičkih uređaja u tome da imaju odvojenu funkciju apsorpcije svjetla od transporta nositelja naboja. Nov tip solarne ćelije osniva se na 10-µm-debelom, optički prozirnom filmu titanovog dioksida (TiO2) čija su zrna veličine nekoliko nm. Oksidni film je prekriven monoslojem boje za prenošenje naboja kojom se izvodi senzitacija filma za sakupljanje svjetla. U ovom se radu istražuju mikrostrukturna svojstva TiO2 nanoveličine primjenom visokorezolucijske elektronske mikroskopije, elektroske difrakcije, difrakcije X-zracenja, raspršenjem rentgenskog zračenja pod malim kutom i Ramanovog raspršenja. U zrnima TiO2 detektirani su anatas i brukit primjenom elektronske difrakcije i difrakcije X zračenja. Veličina zrna anatasa i brukita su bile od (5 $1) do (12$ 3) nm s odgovarajućim povećanjem temperature do 773 K, što je određeno difrakcijom X-zračenja. Prikazana je nova metoda određivanja veličine zrna TiO2 nanoveličine primjenom niskofrekvencijskog Ramanovog raspršenja. Postignuto je dobro slaganje rezultata pri određivanju nanoveličine zrna TiO2 navedenim instrumentalnim tehnikama

Transmission electron microscopy, x-ray diffraction and Raman scattering studies of nanophase TiO_2

Dye-sensitized solar cells differ from conventional semiconductor devices in that they separate the function of light absorption from charge-carrier transport. The device is based on a 10-µm-thick optically transparent film of titanium dioxide (TiO_2) particles of a few nanometers in size, coated with a monolayer of charge-transfer dye to sensitize the film for light harvesting. In the present authors' review, the principal role of the TiO_2 photoanode is emphasized by a detailed presentation of its characterization by different experimental methods, while the photoelectric responses of the cells, a work which is still in progress, are indicated in the references cited. Hydrolysis of Ti(IV)-isopropoxide in isopropanol by the addition of water is a suitable chemical reaction for the production of nanosized TiO_2. The properties of nanosized TiO_2 can be modified by the hydrolysis catalyst, pH of the solution, temperature, presence of complexing ligand and the colloidal state of TiO_2 precursor. In the present work, the microstructural properties of nanosized TiO_2 were studied by HREM, ED, XRD, SAXS and Raman spectroscopy. HREM was used to determine both grain and pore sizes. Electron diffraction and X-ray diffraction provided evidence of nanocrystalline anatase and brookite phases. The grain sizes of the anatase and brookite phases changed from (5±1) to (12±3) nm with an increase of the treating temperature up to 773 K, as shown by XRD. An method of determining nanosized TiO_2 grain size based on low-frequency Raman scattering, is presented

Deposition of Thin Alumina Films Containing 3D Ordered Network of Nanopores on Porous Substrates

Self-supporting thin films containing nanopores are very promising materials for use for multiple applications, especially in nanofiltration. Here, we present a method for the production of nanomembranes containing a 3D ordered network of nanopores in an alumina matrix, with a diameter of about 1 nm and a body centered tetragonal structure of the network nodes. The material is produced by the magnetron sputtering deposition of a 3D ordered network of Ge nanowires in an alumina matrix, followed by a specific annealing process resulting in the evaporation of Ge. We demonstrate that the films can be easily grown on commercially available alumina substrates containing larger pores with diameters between 20 and 400 nm. We have determined the minimal film thickness needed to entirely cover the larger pores. We believe that these films have the potential for applications in the fields of filtration, separation and sensin