Silica hybrid nanocomposites

In this work we present experimental results about the formation, properties and structure of sol — gel silica based biocomposite containing Calcium alginate as an organic compound. Two different types of silicon precursors have been used in the synthesis: tetramethylortosilicate (TMOS) and ethyltrimethoxysilane (ETMS). The samples have been prepared at room temperature. The hybrids have been synthesized by replacing different quantitis of the inorganic precursor with alginate. The structure of the obtained hybrid materials has been studied by XRD, IR Spectroscopy, EDS, BET and AFM. The results proved that all samples are amorphous possessing a surface area from 70 to 290 m²/g. It has also been established by FT IR spectra that the hybrids containing TMOS display Van der Walls and Hydrogen bonding or electrostatic interactions between the organic and inorganic components. Strong chemical bonds between the inorganic and organic components in the samples with ETMS are present. A self-organized nanostructure has been observed by AFM. In the obtained hybrids the nanobuilding blocks average in size at about 8–14 nm for the particles.     

Microstructure of Gel-Glasses in the SiO2-Nd2O3 System

The microstructure of thermally treated neodymium containing silica gels is investigated by transmission electron microscopy and electron diffraction. Microheterogeneities with amorphous nature are found. Information for the short range order is obtained by the Radial Distribution Functions: SiO₄ tetrahedra and NdO₆ groups are formed and transition from four-fold to six-fold ring structure is observed with increasing of the heat treatment temperature.     

Characterization of superparamagnetic Mg x Zn1−x Fe2O4 powders

Structural and magnetic properties of Mg _x Zn_1−x Fe₂O₄ powders have been studied with respect to the application for thermal cancer therapy (magnetic hyperthermia). Mg _x Zn_1−x Fe₂O₄ (x=0.1–0.5) powders with particle sizes between 5 and 8 nm were produced by citrate method. The X-ray diffraction patterns of the samples correspond to a spinel phase. The lattice constant and the volume of the elementary cell increase when x changes from 0.1 to 0.5. The FTIR-spectra ascertain the spinel phase formation. The Mossbauer studies reveal the presence of extremely small particles, which undergo superparamagnetic relaxation at room temperature. The core-shell model has been applied to explain quadruple doublets. The quadruple splitting at “shells” is bigger than those at “cores” whereas the isomer shifts remain close. Magnetic studies confirm the presence of extremely small particles that behave as superparamagnetic ones.      

Sol-gel bioactive glass-ceramics Part II: Glass-ceramics in the CaO-SiO2-P2O5-MgO system

Ceramics, with basic composition based on the CaO-SiO₂-P₂O₅-MgO system with different Ca+ Mg/P+Si molar ratio (R), were prepared via polystep sol-gel technique. The structure of the obtained ceramic materials has been studied by XRD, FTIR spectroscopy, and SEM. X-ray diffraction showed the presence of akermanite and HA for the sample with R = 1.68 and Mg substituted β-TCP and silicocarnotite for the sample with R = 2.16, after thermal treatment at 1200°C/2 h. The obtained results are in good agreement with FTIR. In vitro test for bioactivity in static condition proved that the carbonate containing hydroxyapatite (CO₃HA) can be formed on the surface of the synthesized samples. CO₃HA consisted of both A- and B-type CO₃²⁻ ions. SEM micrographs depicted different forms of HA particles, precipitated on the surface after soaking in 1.5 simulated body fluid (SBF).      

Crystallization of Gels in the Apatite-Mullite System

Crystallization processes in gels of the apatite-mullite system were studied to obtain information for the synthesis of bioglass-ceramics and composite materials. SiO2-sol, Al(NO3)3·9H2O, Ca(NO3)2·4H2O, (NH4)3PO4·3H2O and CaF2 were used as precursors. CaF2 was added before and after gelation. Mixtures of mullite gel-glass and fluorapatite in the range 10 to 90 mol% were investigated for synthesis of composites. All the samples were heat treated at different temperatures in the range 950–1250°C and the structural changes were established using X-ray diffraction and IR-spectroscopy. When the gels were treated at 1050°C and at 1150°C, the main crystalline phases found were fluorapatite and mullite independent of the CaF2 content and the manner of its addition. At 1250°C the relative amounts of fluorapatite and mullite decrease and gehlenite appears. Composite materials containing fluorapatite and mullite as main crystalline phases can be obtained only when the content of mullite gel-glass in the initial mixture is more than 60 mol%.     

Bioactive ceramics in the CaO-Al2O3-P2O5-ZnO system prepared by the sol-gel technology

The sol-gel method was applied to the synthesis of porous bioactive glass-ceramic materials in the Ca-Al₂O₃-P₂O₅-ZnO system when compositions were chosen in the glass formation range. Aluminium sol and soluble inorganic salts of the other components have been used as starting materials. The sol-gel transition was achieved by controlling the pH value of the medium. After drying the gel products were thermally treated up to 800°C, Phase formation was studied by X-ray diffraction, IR spectroscopy and electron microscopy.It was found that the main crystalline phases in the glass ceramics were C(PO₃)₂ and Ca₂P₂O₇. The amorphous powder was sintered to form ceramic materials with average pore size distribution of 150–200 µm by isostatic pressing and heat treatment at 500–600°C. This glass ceramic is more bioactive than hydroxylapatite in the initial stage after implantation.     

Formation of gels and gel-glasses in the VO2(V2O5)-SiO2 systems

Blue-coloured gels have been prepared in the VO₂-SiO₂ system up to 80 mol% VO₂ by sol-gel technology using TEOS and aqueous solutions of VOSO₄·5H₂O. It is established by means of VIS and ESR spectra that at low temperatures VO²⁺ complexes are formed. An oxidation of V⁴⁺ has taken place with increasing temperature, and V₂O₅ and cristobalite have been separated. Silica gel glasses stable up to 800°C have been obtained from gels containing 1–3 mol% VO₂.     

Crystallization Processes in Composite Biomaterials

The crystallization processes in composite biomaterials containing fluorapatite (FA) and gel glasses (GG) have been investigated. Using the sol-gel method three gel-glasses have been synthesized: ZnO·SiO₂, ZnO·Al₂O₃·2SiO₂ and ZnO·CaO·2SiO₂. The composites have been prepared from GG and FA in different mole ratios and each of them treated at 950°C, 1050°C, 1150°C and 1250°C. From the XRD analysis of the composites it has been established that fluorapatite is present as a major crystalline phase. The XRD patterns and the IR spectra of the pure GG systems have been studied at 200°C, 600°C and 800°C. The surface of the samples has been analyzed before and after the in vitro experiments using SEM. An amorphous layer has been observed on the surface of each of the treated samples. The element concentration and the solubility of the samples have been analyzed after the in vitro experiments by Atomic Absorption Spectroscopy (AAS).     

Composite Glass-Ceramics in the Systems MgO-SiO2, MgO-Al2O3-SiO2 and Fluorapatite Obtained by Sol-Gel Technology

The crystallization processes in the synthesis of composite glass-ceramics in the systems fluorapatite (FA)-MgO·SiO₂ gel-glass (GG) and FA-MgO·Al₂O₃·SiO₂ (GG) have been studied. The composites were prepared by mixing of MgO·SiO₂ and MgO·Al₂O₃·2SiO₂ gel-glasses with FA (from 20 mol% to 80 mol%). The obtained samples were thermally treated at 950°C, 1050°C, 1150°C and 1250°C for 2 hours and the structural changes were investigated, applying XRD-analysis, IR-spectroscopy, Raman spectroscopy and SEM. It has been proved that depending on the chemical composition of the gel-glass and the temperature of treatment, composite glass-ceramics may be prepared consisting only FA, FA and a silicate phase or FA, other phosphate phases and a silicate phase. Because of the absence of calcium or aluminum ions in the composition of the GG, FA is easily decomposed and phases as 7CaO·2MgO·3P₂O₅ and MgO·2P₂O₅ are formed.     

Sol–gel synthesis and structure of silica hybrid materials

In this work the research results on the sol–gel synthesis and structure of silica nanocomposites, containing carrageenan and their application as carriers for cell immobilization were described. The samples were prepared at room temperature by replacing different quantity of the inorganic precursor with κ-carrageenan. For studying the structure of the synthesized hybrids the following methods were used: FT-IR, XRD, BET-Analysis, SEM, AFM and Roughness Analysis. The influence of the type of silicon precursors, nature and quantity of organic component on the structure, surface area, design and size of nanostructures was established. The possibility of application of the synthesized biocatalysts in an enzyme degradation process of the toxic, carcinogenic and mutagenic substances benzonitrile, fumaronitrile, o-, m-, and p-tolunitriles was investigated at batch experiments. A two-step biodegradation process in a column bioreactor of fumaronitrile was followed. After operation of the system for 8 h at a flow rate 45 mL h^?1 and at 60 °C, the overall conversion was 89%, showing a good stability of the developed process.