Hydrothermal Synthesis of Platinum Group Metal Nanoparticles

A novel route for the synthesis of platinum group metal nanoparticles has been reported. The synthesis is based on the addition of tetramethylammonium hydroxide (TMAH) to the aqueous PtCl(4), IrCl(3) or Rh(NO(3))(3) solution followed by the hydrothermal treatment of these precipitation systems at 160 degrees C. The mean size of nanoparticles was 9.2 nm for platinum, 21 nm for iridium, and 28 nm for rhodium. The average crystallite size was estimated at 7.4 nm for platinum, 3.1 nm for iridium and 3.5 nm for rhodium. The possible mechanism of platinum group metal nanoparticles formation is briefly discussed

Formation of Magneite in Highly Alkaline Media in the Presence of Small Amounts of Ruthenium

The effect of small amounts of ruthenium on the formation of magnetite in highly alkaline media was investigated using X-ray powder diffraction (XRD), Mossbauer and FT-IR spectroscopies, field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDS). Acicular alpha-FeOOH particles precipitated in a highly alkaline medium with the addition of tetramethylammonium hydroxide (TMAH) were used as a reference material. Initial addition of small amounts of Ru(NO)(NO3)(3) to that precipitation system had a drastic effect on the formation of iron oxide phases and their properties. The addition of Ru(NO)(NO3)3 favoured the formation of stoichiometric Fe3O4. With an increase of the initial Ru(NO)(NO3)3 concentration in the precipitation systems less time was needed for the formation of Fe3O4 as a single Fe-bearing phase in the precipitates. Ruthenium ions made solid solutions alpha-(Fe,Ru)OOH; however, there was no indication of the formation of solid solutions with alpha-Fe2O3 and Fe3O4, Mossbauer and FT-IR spectroscopies supported the conclusion on the formation of solid solutions a-(Fe,Ru)OOH. FE-SEM showed the formation of octahedral Fe3O4 Particles of a mu m range size. Ruthenium particles (approximate to 20 nm in size) were deposited onto the surfaces of Fe3O4 particles. They were also present in the form of clusters containing octahedral Fe3O4 particles in the nanosize range (approximate to 100 nm or less). The formation of Fe3O4 was interpreted as a combining effect of the thermal decomposition products of TMAH under autoclaving conditions and the catalytic action of ruthenium. In such a way strong reductive conditions in the investigated precipitation system were created

57Fe mössbauer, XRD, FT-IR, FE SEM analyses of natural goethite, hematite and siderite

Natural goethite, hematite and siderite were analysed with 57Fe Mössbauer, XRD and FT-IR. FE SEM images of samples were also taken. The Mössbauer spectra of limonite (α-FeOOH · nH2O) from Budapest (Hungary), Ljubija (Bosnia and Herzegovina) and Korçё (Albania) showed the same type of spectrum, indicating low crystallinity and broad particle size distribution. All goethite particles from these three locations were one-dimensional (1D), but with different nano/microstructures. A very early precursor of limonite from Budapest and Ljubija locations was assigned to FeS2 (pyrite and/or marcasite) which oxidised upon ventilation (oxygenation) under hydrogeothermal conditions, thus producing FeSO4 and Fe2(SO4)3. In the next step limonite deposits were formed. The similarity between this limonite formation under hydrogeothermal conditions and the chemical precipitation of goethite from FeSO4 or Fe2(SO4)3 solutions at laboratory level was briefly discussed. The deposition of lateritic goethite at the Korçë location is presumed to be due to the chemical weathering (tropical conditions) of ultramafic rocks. Under the same conditions and a proper pH the transformation of goethite to hematite is possible. Alternatively, the oxidation of Fe2+ in magnetite and its transformation to hematite via maghemite (γ-Fe2O3) as an intermediate could have taken place. The Mössbauer spectrum of siderite from the Ljubija location showed a quadrupole doublet with asymmetric spectral lines. This asymmetry could be assigned to the Goldanskii-Karyagin effect, however, the contribution of the crystallite texture to this asymmetry cannot be excluded. Hematite and a small fraction of siderite at the Vareš location (Bosnia-Herzegovina) are of metasomatic origin deposited in limestone that now form a series of greatly metamorphosed sedimentary rocks. Hematite particles were deposited in the form of laminates (2D)

Microstructural Properties of Natural Allophane/Gibbsite from a White Bauxite Deposit in Montenegro

Microstructural properties of white bauxite from Montenegro were investigated. XRD analysis showed the presence of allophane (Al2O3 · 2SiO2 · 3H2O) and gibbsite (γ-Al(OH)3). The allophane phase showed very broadened diffraction lines, thus indicating poor crystallinity as well as very fine nanoparticles in this phase. Upon heating of natural allophane/gibbsite at 1000 °C mullite (Al6Si2O13) was formed, but with a lower degree of crystallinity. FT-IR spectra of allophane, gibbsite and mullite were interpreted. FE-SEM images of natural allophane/gibbsite showed a dominantly amorphous-like morphology. Upon heating of natural allophane/gibbsite two-dimensional (2D) microstructure was visible. EDS analysis showed traces of calcium, potassium, magnesium and iron. The 57Fe Mössbauer spectrum of iron traces showed a small relative intensity magnetic splitting component due to the presence of hematite and a central quadrupole doublet due to the presence of Fe3+ ions substituted for Al3+ in octahedral positions and/or a superparamagnetic fraction of hematite particles. The possible geochemical mechanism of white bauxite formation in Montenegro is discussed. This work is licensed under a Creative Commons Attribution 4.0 International License

Influence of Titanium Dioxide Preparation Method on Photocatalytic Degradation of Organic Dyes

Titanium catalysts (TiO2) were synthesized by three different methods. Their photocatalytic activity was validated through photodegradation of Reactive Red 45 (RR45) azo dye and Acid Blue 25 (AB25) anthraquinone dye in an aqueous solution under UV irradiation. TiO2 photocatalysts were characterized by FTIR, XRD and SEM. Photosensitivity and TiO2 activity range were characterized by UV/Vis spectroscopy. Photocatalytic validation has been made by way of determining the degree of RR45 and AB25 removal. TOC was determined as a measure of the mineralization of RR45 and AB25 by photocatalysis. The stability of TiO2 catalysts and a possibility of using them in consecutive photocatalysis cycles have also been studied. The results show that the photocatalytic efficiency depends on the crystal structure of TiO2. The size of crystallites depends on synthesis conditions. From the results of photocatalytic efficiency it is concluded that the chemical interaction between a catalyst and a dye strongly depends on the dye chemical structure