Journal of Sol-Gel Science and Technology

Controlling the density and the nanograin size is challenging but essential to prepare continuous alumina fibers with excellent performance. In this study, the continuous alumina fibers were prepared using the sol-gel method. The fibers calcined under different conditions were characterized to reveal the effect of calcining conditions on the fiber microstructure evolution. The results show that the phase transformation from amorphous Al2O3 to γ-Al2O3 and then to α-Al2O3 takes place during the calcining process. The fiber, prepared using a single-step calcining method, cannot obtain a fully dense and nanocrystal microstructure through optimizing the calcination conditions. Thus, a novel two-step calcining process was proposed, through which an almost fully dense α-Al2O3 fiber with an average grain size of ~150 nm was prepared and the tensile strength of fibers reaches 2.2 GPa. Based on the results, the effect mechanism of residual organics, phase transformation, densifying, and grain growth on the fiber microstructure evolution was discussed in depth.

Biological hard tissues like bone and shell show combinations of strength and toughness that are hard to duplicate with synthetic materials. These properties are attained by a composite of organic and inorganic phases with very organized microstructures. The structures are hierarchical in that several different scales of organization contribute to the final properties. Biological systems form by chemical precipitation at room temperature in contrast to synthetic processing, which usually depends on thermal solidification. In principle, chemical solidification can give much more control over composition and structure but is limited by the time taken for diffusion processes in any solid component. A family of solid freeform fabrication methods have recently been developed which allow parts to be built under the direct control of a 3-dimensional CAD drawing without the need for a mold. These methods also offer a way of building composite structures, with full control of structure and composition at the scale of 100 μm and up. Since this is a layerwise process, like biological growth, diffusion paths are short and so chemical processing of large parts is feasible. We have been developing an SFF system based on extrusion of a reactive slurry through a 300 μm needle. The needle is moved on three axes so as to build up a part. The application of this method to the formation of components from sol-gel glasses and organic-inorganic hybrids is described.

The silica coating has attracted much attention because of its superior corrosion resistance with almost no harm to human health and to the environment. In this study, a two layered silica film was tried to get an enhanced corrosion resistance. The silica film was prepared on the hairline finish 304 stainless steel surfaces by-a-spray- and subsequent-dip-coating process. The spray coating solution was prepared by mixing sodium silicate solution, silica colloid, tetraethyl orthosilicate (TEOS), methyltriethoxysilane (MTES), ethanol, and distilled water. Then the solution was sprayed onto the stainless steel surface, and was dried and heat treated. The dip coating solution was prepared by a simple mixing of TEOS and acidic water into ethanol, and the prior spray coated sample was dipped into the solution. The outer dip coated layer was intended to cover spray coated rough and porous layer and hence to enhance the corrosion resistance. A homogeneous and crack free surface was successfully obtained after the dip coating. The prepared silica film was characterized using scanning electron microscopy, potentiodynamic polarization scan, and electrochemical impedance spectroscopy. The two layered film showed an enhanced corrosion resistance. The enhancement was attributed to a protecting effect of the dip coated layer where the diffusion of ionic species was successfully impeded.

Sulfonamide Schiff bases were doped uniformly in silica sol–gels prepared from liquid precursors by a fast and easy way at room temperature and processed to form xerogels. Schiff bases are efficient chelating agents, bioactive and catalytically active compounds. The structures of the newly synthesized Schiff base doped xerogels were elucidated by their physical (morphology, surface area, porosity), spectral (FTIR) and analytical (CHNSO/Si) data. The powder X-ray diffraction studies were carried out to confirm the formation of single phase. Characterization confirmed that Schiff base molecules are entrapped inside the pores as well as physically bound onto the silica surface. All Schiff base doped xerogels are stable mesoporous materials showing hydrophilic properties. Loadings of Schiff bases from 0.10 to 0.23 g/g of xerogel were obtained resulting amorphous materials. The doping of Schiff bases with xerogel caused change in surface area, pore volume and pore diameter of xerogel without damaging the main framework of siliceous skeleton. Morphology and colour of xerogel was also changed after doping. The entrapment of Schiff bases in xerogel caused increase in their decomposition temperatures. The final Schiff base doped xerogels show remarkable thermal stability.

The surface of magnetite nanoparticles was coated with functional polysiloxane layers using reaction of hydrolytic copolycondensation of tetraethoxysilane and 3-aminopropyltriethoxysilane (or N-[3-trimethoxysilylpropyl]ethylendiamine), and also that of tetraethoxysilane, 3-aminopropyltriethoxysilane and methyltriethoxysilane (or n-propyltriethoxysilane). It was shown that these functionalized magnetically controllable particles (about 60–150 nm in size as aggregates), as opposed to magnetite, adsorb urease well from aqueous solutions (up to 1 g/g), and that the level of residual activity of adsorbed layers is up to 84 % in the case of a bifunctional sample. It was established that the activity of immobilized urease is normally gradually reduced during storage of the samples, but in the case of ethylenediamine functional group is not decreased for 45 days. The synthesized samples are promising for use as magnetically directed biocatalysts.

In this study, a low cost IL/Zeolite nanocomposite was prepared using zeolite and an environmentally friendly ionic liquid by sol-gel procedure. The IL/Zeolite nanocomposite was used as an efficient adsorbent to remove nitrate ions from water. The nanocomposite features were investigated in terms of size, structure, morphology and composition using Field Emission Scanning Electron Micrographs (FESEM), Energy Dispersive X-ray spectroscopy (XRD), and Fourier Transform Infrared (FT-IR) spectra. Moreover, the effects of solution pH, contact time, initial concentration of nitrate, and adsorbent dosage on nitrate adsorption were investigated. The optimum removal efficiency (91.29%) of IL/Zeolite occurred at an initial pH of 5 and room temperature (~25 °C) with an initial nitrate concentration of 30 mg L−1, the contact time of 30 min and IL/Zeolite adsorbent dosage of 0.04 g/20 m L−1. Based on the highest correlation coefficient (R2), the adsorption kinetics followed the pseudo-second-order equation and the isotherm followed the Freundlich equation. In addition, the adsorption process is exothermic and spontaneous. The recovery of the nanocomposite was successful in 5 times, so it can be concluded that IL/Zeolite can be used as a potential and active bio-adsorbent to remove nitrate ions from aqueous solutions.