Tetraethylortosilicate Research Articles

Microencapsulation of an acrylate monomer in silica particles by sol–gel process

The sol–gel synthesis strategies combined with the templated growth of organic–inorganic hybrid networks provide access to an immense new area of innovative multi-functional advanced materials. One possible way to prepare such new advanced materials is to encapsulate liquid active agents (such as monomers, dyes, catalysts and hardeners) in microcapsules. Silica microcapsules of tetraethylortosilicate (TEOS) and 3-(trimethoxysilyl)propyl methacrylate (MPTS) were prepared in a precursor-monomer/NH4OH water microemulsion system. Trimethylolpropane triacrylate (TMPTA)—a trifunctional monomer useful in manufacturing of coatings, inks and adhesives—and a corresponding photoinitiator (DAROCUR 1173) were entrapped inside the obtained microcapsules. MPTS was used to increase compatibility between TMPTA and the sol–gel precursors. As stability agent we added a “home made” product resulted from functionalization of poly (ethylene glycol) methyl ether (MPEG) with (3-isocyanatopropyl) triethoxysilane (NCOTEOS). Were obtained microcapsules containing incorporated monomer and having average particle size in range of 0.5–50 μm. Thermal analysis, morphology study and the increase of the silica microcapsules average diameter, measured by DLS technique confirm the monomer encapsulation.

Structural transformation of silane‐based zirconium‐modified sol–gel coatings

AbstractThis work is focused on a detailed analysis of silane‐based zirconium‐modified sol–gel coatings and the correlation between thermal treatment and structural transformation. To analyse the influence of the type of silane used, different sols were prepared with 3‐glycidoxypropyltrimethoxysilane (GPTMS), tetraethylortosilicate (TEOS) and tetra‐n‐propoxyzirconium (TPOZ) as precursors. The films were deposited by a dip‐coating procedure on AA2024‐T3 alloy and then submitted to several thermal treatments. Techniques, such as X‐ray photoelectron spectroscopy (XPS), Fourier‐transformed infrared spectroscopy (FTIR) and X‐ray diffraction (XRD), have been used to analyse the structural transformations. The results show that crystallisation of zirconia can be modified by the addition of silanes as co‐precursors, which induces stabilisation of the amorphous state of zirconia and an increase in the critical size for the polymorphic transformation. The type of silane used does not affect the structural transformation of ZrO2. An explanation for the stabilisation of zirconium oxide is proposed. Copyright © 2010 John Wiley & Sons, Ltd.

Immobilization in Nanomatrices of Humicola Lutea Mycelium for Alpha-Galactosidase Biosynthesis in Laboratory Air-Lift Bioreactor

ABSTRACTThe sol-gel synthesis of both hybrid nanomatrices containing tetraethylortosilicate (TEOS) as an inorganic precursor and lactic acid, or sepharose as an organic component was made. Crystal as well as surface morphology of the hybrids were investigated using different methods: X-ray diffraction, infrared spectra, BET-analysis and atomic force microscopy (AFM). The obtained nanomatrices were applicated for immobilization of the α-galactosidase producing fungal strain Humicola lutea 120–5. The semicontinuous cultivation was carried out in laboratory air-lift bioreactor. Maximal level of enzyme activity (1050–1130 U/l) that was reached in the third to fourth fermentation cycle using TEOS+40% lactic acid was higher than that obtained in the samples with TEOS+20% sepharose (660–770 U/l). The correlation between enzyme productivity and fungal development in the pore structure of the carriers was examined using scanning electron microscopy observation.

Grinding kinetics of amorphous powder obtained by sol–gel process

Pre-mullite powder has been synthesized by sol–gel process followed by calcination. Aluminium nitrate and tetraethyl ortosilicate (TEOS) were used as the starting materials. X-ray diffraction (XRD) analysis showed that calcined pre-mullite powder is completely amorphous. The powders were wet milled in planetary ball-mill within various time intervals. The particle size distribution of ground samples has been determined using particle size analyzer (PSA). The powder samples morphology was investigated with Scanning Electron Microscopy (SEM). Comminution kinetics of calcined pre-mullite gel is modeled using a classical batch grinding equation based on selection and breakage functions. The analytical solution of the batch grinding equation, as well as parameters of grinding kinetics was obtained through Nakajima and Tanaka approach. Analysis of experimental data resulted with model suitable for prediction of particle size distribution of calcined amorphous gel comminuted in planetary ball mill. Model is suitable if the duration of grinding is no longer than 128 min. Obtained product size distribution, for shorter grinding duration (≤ 128 min) is consistent with massive fracture mechanism. For longer grinding periods (≥ 256 min) changes of breakage mechanism indicated parallel fracture and attrition mechanism. The parameters of grinding kinetics obtained by the linear regression analysis were used to reproduce the product size distributions. The good agreement between experimental and calculated size distributions confirms the applicability of the applied rate equation to the description of grinding of calcined amorphous gel.

Synthesis of mesoporous silica particles with controlled pore structure

Silica particles, with controllable porosity, were synthesized using two different precursors, tetraethylortosilicate (TEOS) and sodium silicate, but without the addition of template. Characteristics of silica particles (aggregates) prepared by these two methods were compared. The pore structure was tuned only by changing the processing parameters, such as precursor concentration, base concentration, temperature and reaction time. The pore structure of prepared silica particles (aggregates) is strongly influenced by processing conditions and easy controllable in broad range of the specific surface area, pore size, size distribution and pore volume. However, the silica particles synthesized from TEOS have very low total pore volume (ranging from 0.06 to 0.2 cm 3/g) and a large portion of pores smaller than 4 nm. On the other side, the silica particles prepared from sodium silicate can be defined as a mesoporous silica with the average pore size up to ∼20 nm and much higher total pore volume (ranging from 0.8 to 1.5 cm 3/g), which are important advantages for their application in encapsulation of enzymes.

From Nanocomposite to Blend Hybrid pHEMA/SiO<sub>2</sub> Hydrogels: The Effect of Chemical Coupling on Thermal Stability, Swelling and Bioactivity

Hybrids of poly(2-hydroxyethylmethacrylate) (pHEMA), a polymer widely employed for biomedical applications, and silica gel, exhibiting a well-known bioactivity, were produced by in- situ sol-gel synthesis using two different procedures. Only Tetraethylortosilicate (TEOS) was used as inorganic precursor in the former, whereas both TEOS and methacrylate monomers bearing an alkoxysilyl unit, prepared by Michael addition of 2-hydroxyethylmethacrylate (HEMA) to 3-Aminopropyltriethoxysilane (APTS), were employed in the latter. A final concentration of 30% w/w of silica gel to the mass of polymer was obtained in both procedures. The samples prepared through the former route will be referred as T03, those obtained the latter route will be named as AT03. AT03 hybrids are optically transparent, whereas T03 samples show phase separation between the polymer and the silica gel. Synthesis procedure strongly affects hybrids structure: the silica phase mean diameter changes from 500 nm (T03) to about 50 nm when the coupling hybrid monomer is employed (AT03). Both hybrids keep swelling properties and show improved thermal stability than the as-prepared polymer, indeed AT03 exhibits the highest decomposition temperature and T03 show the highest swelling ratio. Moreover, silica gel has hydroxyapatite formed on both hybrids surface, when soaked in SBF.

Development of olefin epoxidation heterogeneous catalysts by the sol–gel and grafting methods

In this work we prepared the hybrid material (SG) by the sol–gel method through the reaction between tetraethylortosilicate (TEOS) and acetylacetonatepropyltrimethoxysilane (ACACSIL). We also immobilized the acetylacetonate on silica surface (GR) by the grafting method through the reaction between a commercial silica and ACACSIL. Infrared thermal analysis showed that these materials were thermally stable until 200 °C. SG is a microporous material and has surface area of 500 m2 g−1, average porous volume of 0.09 cm3 g−1 and organic content of 1 mmol g−1. GR is a mesoporous material and has surface area of 300 m2 g−1, average porous volume of 0.7 cm3 g−1 and organic content of 0.4 mmol g−1. Iron(III) was coordinated to SG and GR resulting in the SG–Fe and GR–Fe silicas which were tested as catalysts on the aerobic epoxidation of cis-cyclooctene. SG–Fe yielded 100% of conversion and 94% of selectivity in epoxide whereas GR–Fe silica led to a maximum conversion of 50% and 100% of selectivity.

Sol-Gel Nanomaterials with Algal Heteropolysaccharide for Immobilization of Microbial Cells, Producing A-Galactosidase and Nitrilase

ABSTRACTThe main purpose of the present work is the sol-gel synthesis and structure of the hybrid nanomaterials as matrices for two types of cells, producing hydrolytic enzymes. The effect of different percent of algal polysaccharide included in them on the hydrolytic activity of fungal and bacterial cells was investigated.The hybrid sol-gel nanomaterials were synthesized from tetraethylortosilicate (TEOS) as a silicon precursor and heteropolysaccharide (AHPS) from the red microalga Dixonella grisea as an organic part. The structure of these matrices was investigated using different methods: FT-IR, XRD, BET-Analysis, EDS, SEM and AFM. The sol-gel hybrids were used for the immobilization of fungal (Humicola lutea) and bacterial (Bacillus sp.) cells, producing α-galactosidase and nitrilase, respectively. It was established the effect of the quantity of the heteropolysaccharide in the matrices on the activity of these hydrolytic enzymes. Using 20% AHPS in the hybrid nanomaterials the α-galactosidase yield exceeded over two-fold the enzyme titre of the free cells in the third cycle of repeated batch shake flask cultivation. These results correlated with a dense growth of immobilized mycelium observed with scanning electron microscopy (SEM). The increase of the percentage of organic part in the sol-gel matrix up to 20% led to an increase in the nitrilase activity. The addition of 40% AHPS did not significantly affect the decrease of the nitrile biodegradation.

Evaluation of SiO2 Sonogels, Prepared by a New Catalyst-Free Method, as Drug Delivery System

Recently, we reported on the synthesis of catalyst-free SiO2 sonogels prepared by the sonication of a neutral distilled water/ tetraethyl ortosilicate mixture. The purpose of the present study was to evaluate the feasibility of using these sonogels as pharmaceutical delivery systems. A certified color additive (sunset yellow, SY) was used as a model compound for the release experiments. Different amounts of dye were incorporated into the gels before drying. Sonogels were characterized by scanning electron microscopy and differential scanning calorimetry. The effect of three drying temperatures (25°C, 40°C and 80°C) and two mean grain sizes (1125 and 630 μm) on release behavior was analyzed. The analysis of variance showed no significant differences between the Higuchi's constants (KH) obtained for SY-loaded sonogels dried at 80°C with different SY loads, irrespective of the mean grain size. In contrast, for SY-loaded sonogels dried at 40°C, differences were found between sonogels loaded with 2.7, 7.7, 12.2, and 18.2% of SY, and no significant differences were detected between the mean grain sizes analyzed. Considering that the preparation of sonogels by the catalyst-free method allows an easy encapsulation, sonogels may offer an interesting alternative for drug release in the pharmaceutical field.

Acid Synthesis of Luminescent Amine-functionalized or Erbium-doped Silica Spheres for Biological Applications

In this work we discuss and investigate the morphological and optical properties of luminescent silica spheres which can have interesting applications in bioimaging and biosensing. The spheres are synthesized following an acid route by the hydrolysis and condensation of tetraethylortosilicate (TEOS) and can be functionalized by incorporation of aminopropyl-triethoxysilane (APTES) during the synthesis, inducing a significant luminescence that can be attributed to a recombination mechanism from localized organic defects related to -NH(2) groups. It is shown that the acid synthesis route produces very regular spherical particles, but their diameter vary in the range of 200-4,000 nm. The luminescence properties have been investigated and optimized by variation of the annealing temperature for the functionalized spheres, obtaining the most efficient PL emission after a thermal treatment of 1 h at 600 degrees C in air. Moreover, the possibility to introduce rare earths like erbium in the spheres was also studied and the corresponding Er(3) luminescence emission at 1.53 microm is reported in terms of intensity and lifetime, pointing out that erbium can be easily and efficiently incorporated during the acid synthesis giving high PL intensity with a good lifetime of 3.9 ms.

Hybrid PDMS–Silica–Zirconia materials prepared by γ-irradiation

Hybrids are a class of materials that enable the integration of organic and inorganic characteristics at the molecular level in a single material. In this way materials with unusual optical, mechanical or even bioactive properties are obtained, which are especially suitable for applications as sensors, non-linear optical (NLO) materials, lasers, selective membranes, catalysts and protective coatings. Sol–gel processing is often used for the preparation of hybrids, usually through the alkoxides method that leads to high purity products at relatively low temperatures. The authors have developed a new method for the preparation of these materials based on gamma irradiation of the precursors mixture. The precursors used are polydimethylsiloxane (PDMS), tetraethylortosilicate (TEOS) and zirconium propoxide (PrZr). The irradiations were performed using the 60Co source at the Portuguese Gamma Irradiation Facility (UTR) located in the ITN campus at Sacavém. The materials at room temperature are macroscopically transparent, relatively flexible and amorphous. The details of the preparation of these hybrid materials by gamma irradiation are presented.

Ordered circular mesoporosity induced by phospholipids

Circular mesoporous materials with different geometries have been prepared by surfactant-templated sol–gel synthesis involving the condensation of tetraethylortosilicate (TEOS) under basic conditions. In this study, cetyltrimethylamonium bromide (CTAB) has been used as a surfactant and controlled amounts of l-α-phosphatidylcholine (lecithin) as a co-surfactant. For small concentrations of lecithin, the obtained materials retain the hexagonal pore ordering characteristic of MCM-41, as evidenced by X-ray diffraction and electron microscopy. However, the channels are no longer straight and parallel but circular and concentric. At higher concentrations of lecithin, vesicular silica was produced.

Silicon–titanium oxycarbide glasses as bimodal porous inorganic membranes

Porous oxycarbide Si–Ti–O–C glasses have been studied as potential materials for inorganic membranes. Such materials were prepared by pyrolysis of hybrid materials in nitrogen atmosphere. These hybrids were synthesized by the sol–gel process using tetraethylortosilicate (TEOS), polydimethylsiloxane (PDMS) and titanium orthotitanate (TBOT) as raw material. The influence of the TEOS/TBOT molar ratio on the pore size distribution has been studied in the range of pyrolysis temperatures between 400 and 1100 °C. The oxycarbide materials were characterized by FT-IR and NMR spectroscopies, XRD, mercury porosimetry, nitrogen adsorption and SEM. Bimodal pore size distributions showed one mode close to 0.02 μm and the other one in the range between 1 and 100 μm of pore diameter. Such pore sizes increase with the amount of TBOT. Reduced effective diffusivities were calculated by a theoretical model taking into account the mentioned pore size distributions. Diffusivities appeared in the range from 0.46 to 0.77 and increase with the titanium concentration in the oxycarbide.

Influence of Boron Concentration on the Surface Properties of TEOS-PDMS Hybrid Materials

The influence of the concentration of triethylborate (TEB) on the surface properties of hybrid materials prepared from tetraethylortosilicate (TEOS) and polydimethylsiloxane (PDMS) has been studied. TEB concentration has been varied between 0 and 30 wt.% respect to the total amount of alkoxyde whereas PDMS concentration has been set at 40 wt.% in all the hybrid samples. Pore size distributions (PSDs), specific surface areas (SSAs) and surface energies have been determined for such materials. PSDs have shown that pore size and pore volume increase with the amount of TEB forming the hybrid, whereas SSAs decrease. Surface energies have been determined by inverse gas chromatography at infinite dilution (IGC-ID) and have been divided into dispersive and specific surface energies. It was also found that TEB affects to both, dispersive and specific surface energies. Dispersive surface energy values increase from 23.23 mJ⋅m−2 for the pure TEOS-PDMS hybrid sample to 31.07 mJ⋅m−2 for the 30wt.% TEB-containing material. This increase has been attributed to the enhanced polarizability of the TEOS-PDMS hybrid when TEB is incorporated into the structure, a result which is consistent with the composition and structural characterization of the studied hybrid materials. Acid and base (kA, kB) surface constants also evidence a correlation with the TEB concentration: kA decreases and kB increases with the increase of TEB in these hybrids, a result which has been assigned to the lower acidity of boranol groups respect to that of silanols. The formation of an hybrid structure of Si–O–Si(PDMS) and B–O–Si(PDMS) bonds has been confirmed by FT-IR spectroscopy by the presence of a band at 850 cm−1 and a shoulder between 930 and 880 cm−1, respectively.

A Nonisothermal Study of the Kinetics of the Nanoporosity Elimination in Sonogels-derived Silica Xerogels

A nonisothermal study of the kinetics of the nanoporosity elimination in monolithic silica xerogels, prepared from acid and ultrasound catalyzed hydrolysis of tetraethylortosilicate (TEOS), has been carried out by means of in situ linear shrinkage measurements performed with different heating rates. The study could be applied up to almost alpha approximately 0.6 of the volume fraction alpha of eliminated pores. The activation energy was found increasing from about 3.2 x 10(2) kJ/mol for alpha approximately 0.06 up to about 4.4 x 10(2) kJ/mol for alpha approximately 0.44. The sintering process accompanying the nanopore elimination in this set of xerogels is in agreement with a viscous flux sintering process with the hydroxyl content diminishing with the volume fraction of eliminated pores. All the volume fraction of eliminated pores versus temperature (T) curves can be matched onto a unique curve with an appropriate rescaling of the T axis, independent of the heating rate. This scaling property suggests that the path of sintering seems the same, regardless of the heating rate; the difference is that the rate is faster at higher temperature.

Corrosion protective properties of nanostructured sol–gel hybrid coatings to AA2024-T3

The work aims at investigating the corrosion behavior of AA2024-T3 substrates pretreated with sol–gel derived hybrid coatings. The hybrid sols were prepared by copolymerization of 3-Glycidoxypropyltrimethoxysilane (GPTMS), tetraethylortosilicate (TEOS) and tetra- n-propoxyzirconium (TPOZ). Coatings with Zr/Si atomic ratios of 1:9 and 1:4 were also prepared. During the synthesis process, there is formation of ZrO 2 nanoparticles, which content depends on the temperature and time of the TPOZ hydrolysis/condensation reactions. The results show that the ZrO 2 nanoparticles have diameters ranging between 40 and 200 nm. These particles are amorphous and they improve the corrosion protection of the sol–gel coatings. The presence of ZrO 2 nanoparticles seems to have a pore blocking effect in the coatings with higher content of particles.

Molybdenum oxide-organosilane hybrids through sol–gel process

From reactions between tetraethylortosilicate (TEOS) and nitrogen containing organosilanes of general formula (C 2H 5O) 3Si–R; R=–(CH 3) 2NH 2, –(CH 3) 2NH(CH 2) 2NH 2 and –(CH 3) 2NH(CH 2) 2NH(CH 2) 2NH 2, with lamellar molybdenum trioxide (α-MoO 3), four hybrid matrices, named here as MoSil, MoN1, MoN2 and MoN3, respectively, were synthesized, through sol–gel process. The obtained matrices were characterized by elemental analysis, Infrared spectroscopy, thermogravimetry, scanning electron microscopy, X-ray diffraction patterns, surface area measurements and 29Si CPMAS NMR spectroscopy. The organic moiety contents are 1.7, 2.0 and 0.9 mmol g −1 for MoN1, MoN2 and MoN3 matrices, respectively. The measured surface areas are 0.61; 78.12; 1.85; 0.59 and 2.53 m 2 g −1 for MoO 3, MoSil, MoN1, MoN2 and MoN3 matrices, respectively. Molybdenum oxide exhibts a single mass loss step in TG curve, due to the sublimation of the oxide, starting at 730 °C.The MoSil matrix exhibits a similar TG curve profile, but the thermal degradation takes place at 704 °C. MoN1, MoN2 and MoN3 matrices shows mass loss steps of 20%, 30% and 23%, respectively, associated with the organic moiety. The 2 θ values for the 001 diffraction plane were 12.64, 13.20, 12.82, 12.84 and 12.90° for MoO 3, MoSil, MoN1, MoN2 and MoN3 matrices, respectively, indicating that the organic species are at the surface, and not inside the interlayer space.

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.

Adsorption of Cr(III) and Fe(III) on an inorganic–organic silicon hybrid surface

Abstract By using tetraethylortosilicate (TEOS) and n -[3(trimethoxysilyl) propyl]-ethylenediamine, a silicon inorganic–organic hybrid matrix with 4.0 mmol g −1 of pendant organic moiety was synthesized. The hybrid matrix was used as a substrate for the adsorption of chromium and iron from their chloride aqueous solutions. The matrix shows a higher affinity towards chromium, with concentrated iron solutions provoking its dissolution. The maximum adsorption capacity towards chromium and iron was 0.56 and 0.38 mmol g −1 , respectively.

Obtenção e caracterização de membranas assimétricas via sol-gel

Foram obtidas membranas de sílica via sol-gel, utilizando-se tetraetilortossilicato (TEOS) como precursor em meio ácido. A estrutura da membrana é composta de uma camada de sílica mesoporosa (raio médio de poros igual a 21,6 nm) recoberta por um filme microporoso de sílica (raio médio de poros igual a 1,1 nm). A camada suporte foi obtida utilizando-se ácido fluorídrico como catalisador, enquanto que para a fabricação do filme ativo foi utilizado ácido nítrico. A camada suporte apresenta área superficial específica de 148 m²/g e volume específico de poros de 1,60 cm³/g. O filme de sílica possui área superficial de 547 m²/g e volume específico de poros de 0,31 cm³/g. O filme microporoso de sílica apresenta uma maior quantidade de grupos silanol, conforme observado através de termogravimetria (TGA) e espectroscopia no infravermelho (FTIR). A adesão do filme ativo foi analisada por microscopia eletrônica de varredura. A resistência ao fluxo de gás através da membrana assimétrica é devida principalmente ao filme de sílica ativo.