Rubia F. S. Lenza

Preparation of silica by sol-gel method using formamide

In this work we obtained microporous and mesoporous silica gels by sol-gel processing. Tetraethylortosilicate (TEOS) was used as precursor. Nitric acid and hydrofluoric acid were used as catalysts. In order to study the affect of formamide as drying additive, we used a molar ratio alkoxide/formamide of 1/1. The performance of formamide in obtaining crack-free gels was evaluated through monolithicity measurements. The structural evolution occurring in the interconnected network of the gels during thermal treatment was monitored by Fourier transform infrared spectroscopy (FTIR), shrinkage and density measurements and nitrogen gas sorption. We noted that in the presence of formamide, the Si-O-Si bonds are stronger and belong to a more cross-linked structure. The samples obtained in the presence of formamide have larger pore volume and its pore structure is in the range of mesoporosity. The samples obtained without additive are microporous. Formamide allowed the preparation of crack-free silica gels stabilized at high temperatures.

Sol-gel silica based networks with controlled chemical properties

Abstract In this work, different chemical functionalities, both organic and inorganic, were inserted in a silica glass based sol–gel derived network to create specific chemical activities. Modified silica glass networks were prepared by reacting alkoxysilanes with different chemical functionalities, such as tetraethoxysilane (TEOS), aminopropyl triethoxysilane (APS) and mercaptopropyl triethoxysilane (MPTS), among others. The obtained gels were evaluated by using infrared spectroscopy, mercury picnometry and electron microscopy. The chemical activity of the created multifunctional surfaces was evaluated by the ability of the incorporated proteins to remain adsorbed onto the different gels. Porcine insulin (PI) and bovine serum albumin (BSA) were impregnated into modified networks and desorption of those proteins was monitored. Results showed that gels with multifunctionalities regularly dispersed can be successfully produced by optimizing some of the processing parameters of the gels, such as pH and concentration of reactants. Results also revealed that the type and concentration of chemical functionalities within the gels regulate the ability of incorporated proteins to remain adsorbed on them, suggesting that chemically patterned surfaces and interfaces can be prepared which regulate protein–substrate interactions.

Structural Evolution of Silica Sols Modified with Formamide

In this work we investigated the influence of formamide on the acid-catalyzed sol-gel process by Fourier transform infrared spectroscopy (FTIR). Three silica sols were studied: Sol catalyzed with nitric acid without formamide, sol catalyzed with nitric acid containing formamide and sol catalyzed with a mixture of nitric acid and hydrofluoric acid and modified with formamide. Following the time evolution of both the Si-(OH) stretching vibration at around 950 cm-1 and the Si-O-(Si) vibration between 1040 cm-1 and 1200 cm-1 we were able to describe the structural evolution of each sol. The curve of evolution of Si-(OH) stretching vibration corresponding to sol A has a simple asymptotic evolution. In the case of formamide containing sol, we observed a two-step structural evolution indicating that for the system containing formamide the polymerization goes through a temporary stabilization of oligomers, which can explain the non-variation of the Si-O(H) bond wavenumber for a certain time. Gelation times were of several days for gels without formamide and few hours for gels containing additive. The presence of additive resulted in a highly interconnected gel.

Surface-modified 3D scaffolds for tissue engineering

The aim of this work was to use sol–gel processing to develop bioactive materials to serve as scaffolds for tissue engineering that will allow the incorporation and release of proteins to stimulate cell function and tissue growth. We obtained organofunctionalized silica with large content of amine and mercaptan groups (up to 25%). The developed method can allow the incorporation and delivery of proteins at a controlled rate. We also produced bioactive foams with binary SiO2–CaO and ternary SiO2–CaO–P2O5 compositions. In order to enhance peptide–material surface properties, the bioactive foams were modified with amine and mercaptan groups. These materials exhibit a highly interconnected macroporous network and high surface area. These textural features together with the incorporation of organic functionally groups may enable them to be used as scaffolds for the engineering of soft tissue.

Synthesis of Titania-Silica Materials by Sol-Gel

In this work TiO2-SiO2 glasses containing as much as 20 mol % of TiO2 were prepared via sol-gel process using titanium and silicon alkoxides, in the presence of chlorine, in the form of titanium tetrachloride or HCl. The gels were heat-treated until 800 °C. X-ray diffraction and Fourier transform infrared spectroscopy were used to understand the structural properties of TiO2-SiO2 oxides calcined at different temperatures and to evaluate the homogeneity of these materials. The degree of the compactness of the silica network is inferred from the frequency of the asymmetric stretching vibrations of Si-O-Si bonds. Formation of Si-O-Ti bridges, as monitored by the intensity of characteristic 945 cm-1 ¾ 960 cm-1 vibration, is particularly prominent if the method of basic two-step prehydrolysis of silicon alkoxide, addition of titanium alkoxide and completion of hydrolysis was used.

Synthesis and properties of microporous sol-gel silica membranes

Abstract Unsupported silica membranes were prepared via sol–gel processing through acid-catalyzed hydrolysis and condensation of tetraethyl orthosilicate (TEOS). The possibility of controlling the pore sizes and porosities of silica membranes were investigated by varying processing parameters. The effect of the type and concentration of the acid catalyst and molar ratio water/alkoxide on the structure of the membranes was determined by measuring their structural properties. The membranes catalyzed only with nitric acid have a smaller pore structure, with larger pore-solid surface areas and solid densities than the membranes catalyzed with a combination of nitric acid and hydrofluoric acid. The average pore size increases for larger hydrofluoric acid concentrations, in a range from 1.1±0.1 to 22±0.9 nm. Silica membrane obtained with molar ratio water/alkoxide equal to 2 has a pore structure differing from the pore structures of the other membranes. The connectivity (ca. 1019 cm−3) and the diffusion coefficients (ca. 1.6±0.2×10−6 to 2.8±0.3×10 −5 cm 2 / s ) of the Cu in the pore structure of these silica membranes indicate the feasibility of using these materials in impregnation and separation processes.

Evaluation of the Influence of Microwaves in the Structure of Silica Gels

In this work we studied the influence of microwaves in the pore structure of silica gels obtained via sol-gel polymerization process. We analised the feasibility of replacing conventional heating by microwave heating during drying. Structural parameters such as specific volume of pores (Vp), specific surface area (Sp), average pore size (rp) and the bulk and true densities were measured. X-ray diffraction confirmed the obtention of a completely amorphous structure for the gels. Some characteristics of silica gels were evaluated by thermogravimetric analyses (TGA), differential thermal analyses (DTA) and Fourier transform infrared spectroscopy (FTIR). We observed that microwave drying is a feasible process to yield controlled pore nanostructures. The gels obtained via microwave heating presented average pore size of 1.2 nm, specific surface area of 112 m2/g and specific volume of pores of 0.06 cm3/g. The gels obtained via conventional heating presented average pore size of 1.3 nm, specific surface area of 748 m2/g and specific volume of pores of 0.49 cm3/g.

The Effect of 58S Bioactive Sol-Gel Derived Foams on the Growth of Murine Lung Epithelial Cells

Bioactive 58S sol-gel derived foams were tested for their abilit y to promote the growth and proliferation of murine lung epithelial cells. Foams were modified with an amine or mercaptan functional group and/or coated with laminin. Routine histologic staining w ith haematoxylin and eosin (H&E) determined qualitatively that cells do grow into foams an d their proliferation was evaluated quantitatively with the WST-1 assay. 58S foams promote the growth of MLE-12 cells with the amine modified, laminin coated foam being the most effec tive. SEM confirmed the above observations and showed that laminin encouraged the growth, attachment and m igration of cells into foams and the type of surface modification affects the patter n of growth of cells on the foams. These results provide a foundation for use of biomaterials as bioactive scaffolds promoting differentiation of stem cells into mature pneumocytes.

Síntese de membranas cerâmicas via método sol-gel utilizando TEOS e N,N-dimetilformamida

In this work we obtained microporous and mesoporous silica membranes by sol-gel processing. Tetraethylortosilicate (TEOS) was used as precursor. Nitric acid was used as catalyst. In order to study the affect of N,N-dimethylformamide (NDF) as drying additive, we used a molar ratio TEOS/NDF of 1/3. The performance of N,N-dimethylformamide was evaluated through monolithicity measurements. The structural evolutions occurring during the sol-gel transition and in the interconnected network of the membranes during thermal treatment were monitored by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analyses and nitrogen sorption. We noted that in the presence of N,N-dimethylformamide, polymerization goes through a temporary stabilization of oligomers. The Si-O(H) bonds are stronger and belong to a more cross-linked structure for the N,N-dimethylformamide containing sol. The membranes obtained in the presence of N,N-dimethylformamide have larger surface area and its pore structure is in the range of mesoporous. The membranes obtained without additive have pore structure in the range of microporous.