Aivaras Kareiva

On the synthesis of yttria-stabilized zirconia: a comparative study

Yttria-stabilized zirconia (YSZ) has been studied as a promising material for application as an electrolyte in solid oxide fuel cells. In this work, YSZ powders ((xY2O3xa0−xa0(1xa0−xa0x)ZrO2), xxa0=xa05, 8 and 10xa0mol%) were synthesized by three different methods: co-precipitation, sol–gel combustion and sol–gel. The precursor solution obtained by sol–gel method was successfully applied for chemical solution deposition of YSZ thin films on Si(100)/SiO2 substrates. The thermal behavior of Y–Zr–O precursor gels and precipitated Y–Zr oxalates were investigated by TG-DSC measurements. X-ray diffraction analysis was utilized for the characterization of phase purity and crystallinity. Scanning electron microscopy was employed for the estimation of surface morphology features. The quality of obtained ceramic samples strongly depends on the morphology of initial powders. Electrical properties of synthesized ceramics were studied by means of impedance spectroscopy. The highest ionic conductivity was observed for samples prepared by sol–gel combustion synthesis route.Graphical Abstract

Structure and charge density of Ce doped gadolinium gallium garnet (GGG)

Nanocrystalline powders of cerium doped gadolinium gallium garnet (Gd3Ga5O12, GGG) powders were prepared by an aqueous sol–gel method. Effects of Ce doping on the microstructure, band gap energy and electron density distributions of the grown Gd3−xCexGa5O12 (xxa0=xa00.5, 1 and 3) have been studied by means of scanning electron microscopy, diffuse reflectance spectroscopy, X-ray diffraction techniques and the maximum entropy method (MEM). The mid bond densities between different atoms of Gd3−xCexGa5O12 (xxa0=xa00.5, 1 and 3) obtained from 1D electron density profiles are analyzed.

Surface functionalization of ceramic membranes with 3-aminopropyl groups using the sol-gel method

Planar ceramic Al2O3 membranes were functionalized with polysiloxane and polysilsesquioxane layers containing 3-aminopropyl groups using the sol-gel method. SEM images show the formation of polysiloxane or polysilsesquioxane layers on the membrane surfaces with the thickness of 0.35 and 4.4 nm, respectively. Infrared spectroscopy data confirmed the presence of the polysiloxane network and functional groups introduced during the synthesis. Measurements of the contact angles on the membrane surfaces showed that the hydrophilicity of the active layer is practically independent of the type of the structuring agent (tetraethoxysilane or 1,2-bis(triethoxysilyl)ethane), and the introduction of the methyl groups increases the hydrophobicity of the surface layer. According to the filtration studies, all functionalized membranes are capable of retaining Cu(II) ions during filtration of diluted solutions due to the complexation of the amino groups in the selective layer with these ions.

Environmentally benign fabrication of calcium hydroxyapatite using seashells collected in Baltic Sea countries: A comparative study

GRAPHICAL ABSTRACT ABSTRACT In this study, high purity crystalline calcium hydroxyapatite (Ca10(PO4)6(OH)2; CHAp) was fabricated from seashells collected in different regions of the Baltic Sea using an environment-friendly water-based sol-gel synthesis route. The phase composition of the synthesized CHAp powders was studied by X-ray diffraction analysis and Fourier transform infrared spectroscopy. The surface morphologies of the precursors and synthesized samples were examined by scanning electron microscopy. A single shell type, Macoma balthica (L.), was collected from various locations around the Baltic Sea. Nevertheless, the resulting CHAp powders had surprisingly large variations in the surface morphology of sol-gel-derived CHAp bioceramics.

Sol-Gel Synthesis and Characterization of Lanthanide-Substituted Nanostructured Calcium Hydroxyapatite

In this study, nanostructured Ce- and Sm-substituted Ca10(PO4)6(OH)2 samples have been synthesized using an aqueous sol-gel chemistry route. For the characterization of obtained specimens, the XRD, SEM, UV-visible reflection and IR spectroscopy and luminescence measurements were recorded. It was shown that phase purity of the end products highly depends on the amount of lanthanide element. The reflectance of lanthanide-substituted calcium hydroxyapatite samples is wavelength independent in the wavelength range of 450-800 nm and equal almost 100%. The cerium-substituted samples show a significant decrease of transmission at ~300 nm. The characteristic samarium absorption line (~430 nm) is evident in the UV-vis reflection spectra of samarium-substituted hydroxyapatites.

The Antimicrobial Action of Silver Halides in Calcium Phosphate

Silver halides represent a yet unexplored avenue for imparting antimicrobial activity in calcium phosphates. Silver halide colloids were added to calcium phosphate. Concurrent melting of silver halides and crystallization of carbonated apatite was achieved by heating to increase the silver halide surface area available to bacteria.Pseudomonas aeruginosa were more sensitive to silver iodide and silver bromide than Staphylococcus aureus. Silver iodide demonstrated greater activity than silver bromide. Silver chloride did not produce an antibacterial response. Both amorphous calcium phosphate and carbonated apatite displayed similar antibacterial activity when accompanied by silver halides. It is thought that amorphous calcium phosphate dissolves more readily and increases the bioavailability of the silver halide particles. Silver iodide displays a greater antibacterial response of all silver halides, with a response that is improved in a more resorbable matrix.

Synthesis of Bio-Cation-Substituted Ca-Apatites by Precipitation

Nanosize Mg2+, Zn2+, Sr2+, and Na+ mono- and di-substituted calcium hydroxyapatites were synthesized using an aqueous precipitation route under controlled conditions. The chemical composition and the micro-structural features of the polycrystalline samples were characterized by chemical analysis, thermal analysis (TG/DTA) combined with MS for evolved gas analysis, FTIR and XRD spectroscopy as well as SEM. The correlations between chemical composition and the crystal morphology were elucidated.

Synthesis and Characterization of Lanthanide Metal-Organic Frameworks with Perfluorinated Linkers

In this study, lanthanide elements (Ln3+) and 2,3,5,6-tetrafluoro-1,4-benzenedicarboxylic acid (TFBDC) based metal-organic frameworks (MOFs) were synthesized by precipitation and diffusion-controlled precipitation methods. Powders insoluble in aqueous media and polar solvents were obtained. The microstructure and properties of Ln3+ MOFs were evaluated and discussed. X-ray diffraction (XRD) analysis, infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and fluorescence spectroscopy (FLS) were carried out to characterize Ln3+ MOFs crystallinity, the microstructure, chemical composition and optical properties.