Estudos de absorção e emissão de UV/Vis em xerogéis de sílica dopados com cromo obtidos por processo Sol-Gel

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Desenvolvimento de eletrodos de pasta de carbono modificada com 2-aminotiazol sílica gel para a determinação de metais em etanol combustível

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

High fluorescence quantum efficiency of CdSe/ZnS quantum dots embedded in GPTS/TEOS-derived organic/silica hybrid colloids

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Effect of colloidal silica on the mechanical properties of fiber-cement reinforced with cellulosic fibers

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Preparation and characterization of PEG-coated silica nanoparticles for oral insulin delivery

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Unusual broadening of the NIR luminescence of Er3+-doped Nb2O5 nanocrystals embedded in silica host: Preparation and their structural and spectroscopic study for photonics applications

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Application of mesoporous SBA-15 silica functionalized with 4-amino-2-mercaptopyrimidine for the adsorption of Cu(II), Zn(II), Cd(II), Ni(II), and Pb(II) from water

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effect of mucoadhesive polymers on the in vitro performance of insulin-loaded silica nanoparticles: Interactions with mucin and biomembrane models

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Propriedades ópticas e elétricas de materiais híbridos de sílica/orgânico à base de GPTS:TEOS preparados pelo método sol-gel

Fabrication of optoelectronic devices requires the employment of at least one transparent electrode. Usually, commercially transparent electrodes have been made by deposition of indium tin oxide (ITO) films by RF-Sputtering technique. These commercial electrodes have sheet resistance of about 100 Ω/sq and optical transmittance of 77% at the wavelength of 550 nm. The poly(3,4-ethylenedioxythiophene):polystyrene-sulfonate (PEDOT:PSS) is an alternative material to fabricate transparent electrodes due to its high conductivity (about 600 S/cm) and solubility in water. Soluble conductive materials exhibits advantages for processing of electrode layers, however there is a disadvantage during devices fabrication once materials with the same solvent of the electrode material cannot be coated one over the other. Alternatively, organic/Silica hybrid materials prepared by sol-gel process allow producing bulks and films with high chemical durability. In order to obtain transparent electrodes with high chemical durability, we introduced a blended material comprising the high UV-VIS transparency of organic/Silica sol-gel material and a high conductivity polymer PEDOT:PSS. The organic/Silica sol was obtained using two different molar concentrations (1:1 and 4:1), of tetraethylorthosilicate (TEOS) and 3-glycidoxypropyltrimethoxysilane (GPTS). Amounts of PEDOT:PSS solutions were added to the sol material, resulting in different weight fractions of sol and polymer. G:T/P:P were deposit onto glass substrates by spray-coating. In order to perform electrical characterization of the blended material, gold electrodes were thermally evaporated onto the films. The electrical characterization was performed using a Keithley 2410 source/meter unity and the optical characterization, using a Cary50 UV-Vis spectrophotometer. The absorption coefficient and electric conductivity of the different compositions blends, as function of the PEDOT:PSS concentration, were...

Preparação e caracterização de híbridos orgânico-inorgânicos à base de epoxí-silica

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Preparação e caracterização de híbridos orgânico-inorgânicos à base de epoxí-silica

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Influence of the use of Aliquat 336 in the immobilization procedure in sol-gel of lipase from Bacillus sp ITP-001

Aliquat 336, a liquid hydrophobic material, was used at different concentrations (0.5-3.0%, w/v) as an additive in the preparation of encapsulated lipase from Bacillus sp. ITP-001 on sol-gel silica matrices using tetraethoxysilane (TEOS) as the precursor. The resulting hydrophobic matrices and immobilized lipases were characterized with regard to specific surface area (BET method), adsorption-desorption isotherms, pore volume (Vp) and size (dp) by nitrogen adsorption (BJH method) and scanning electron microscopy (SEM). The catalytic activities and the corresponding coupling yields were assayed in the hydrolysis of olive oil. In comparison with pure silica matrices, the immobilization process in the presence of Aliquat 336 decreased the values for specific surface area and increased the values for pore specific volume (Vp) and mean pore diameter (dp). This behavior may be related to the partial adsorption of the enzyme on the external surface of the hydrophobic matrix as indicated by scanning electron microscopy. Aliquat 336 concentrations in the range from 0.5 to 1.5% (w/v) provided immobilized derivatives with higher coupling yields and better substrate affinity. The highest coupling yield (Y-A = 71%) was obtained for the immobilized enzyme prepared in the presence of 1.5% Aliquat which gave the following morphological properties: specific surface area = 183 m(2)/g, pore specific volume (Vp) = 0.36 cc/g and mean pore diameter (dp)= 91 angstrom. (c) 2012 Elsevier B.V. All rights reserved.

Structural and Luminescence Properties of Silica-Based Hybrids Containing New Silylated-Diketonato Europium(III) Complex

A new betadiketonate ligand displaying a trimethoxysilyl group as grafting function and a diketone moiety as complexing site (TTA-Si = 4,4,4-trifluoro-2-(3-trimethoxysilyl)propyl)-1-3-butanedione (C4H3S)COCH[(CH2)(3)Si(OCH3)(3)]COCF3) and its highly luminescent europium(III) complex [Eu(TTA-Si)(3)] have been synthesized and fully characterized. Luminescent silica-based hybrids have been prepared as well with this new complex grafted on the surface of dense silica nanoparticles (28 +/- 3 nm) or on mesoporous silica particles. The covalent bonding of Eu(TTA-Si)(3) inside the core of uniform silica nanoparticles (40 +/- 5 nm) was also achieved. Luminescence properties are discussed in relation to the europium chemical environment involved in each of the three hybrids. The general methodology proposed allowed high grafting ratios and overcame chelate release and tendency to agglomeration, and it could be applied to any silica matrix (in the core or at the surface, nanosized or not, dense or mesoporous) and therefore numerous applications such as luminescent markers and luminophors could be foreseen.

Development and characterization of fluorescent pH sensors based on porous silica and hydrogel support matrices

The hydrogen ion activity (pH) is a very important parameter in environment monitoring, biomedical research and other applications. Optical pH sensors have several advantages over traditional potentiometric pH measurement, such as high sensitivity, no need of constant calibration, easy for miniaturization and possibility for remote sensing. Several pH indicators has been successfully immobilized in three different solid porous materials to use as pH sensing probes. The fluorescent pH indicator fluorescein-5-isothiocyanate (FITC) was covalently bound onto the internal surface of porous silica (pore size ~10 nm) and retained its pH sensitivity. The excited state pK* a of FITC in porous silica (5.58) was slightly smaller than in solution (5.68) due to the free silanol groups (Si-OH) on the silica surface. The pH sensitive range for this probe is pH 4.5 - 7.0 with an error less than 0.1 pH units. The probe response was reproducible and stable for at least four month, stored in DI water, but exhibit a long equilibrium of up to 100 minutes. Sol-gel based pH sensors were developed with immobilization of two fluorescent pH indicators fluorescein-5-(and-6)-sulfonic acid, trisodium salt (FS) and 8-hydroxypyrene- 1,3,6-trisulfonic acid (HPTS) through physical entrapment. Prior to immobilization, the indicators were ion-paired with a common surfactant hexadecyltrimethylammonium bromide (CTAB) in order to prevent leaching. The sol-gel films were synthesized through the hydrolysis of two different precursors, ethyltriethoxysilane (ETEOS) and 3- glycidoxypropyltrimethoxysilane (GPTMS) and deposited on a quartz slide through spin coating. The pK a of the indicators immobilized in sol-gel films was much smaller than in solutions due to silanol groups on the inner surface of the sol-gel films and ammonium groups from the surrounding surfactants. Unlike in solution, the apparent pK a of the indicators in sol-gel films increased with increasing ionic strength. The equilibrium time for these sensors was within 5 minutes (with film thickness of ~470 nm). Polyethylene glycol (PEG) hydrogel was of interest for optical pH sensor development because it is highly proton permeable, transparent and easy to synthesize. pH indicators can be immobilized in hydrogel through physical entrapment and copolymerization. FS and HPTS ion-pairs were physically entrapped in hydrogel matrix synthesized via free radical initiation. For covalent immobilization, three indicators, 6,8-dihydroxypyrene-1,3- disulfonic acid (DHPDS), 2,7-dihydroxynaphthalene-3,6-disulfonic acid (DHNDS) and cresol red were first reacted with methacrylic anhydride (MA) to form methacryloylanalogs for copolymerization. These hydrogels were synthesized in aqueous solution with a redox initiation system. The thickness of the hydrogel film is controlled as ~ 0.5 cm and the porosity can be adjusted with the percentage of polyethylene glycol in the precursor solutions. The pK a of the indicators immobilized in the hydrogel both physically and covalently were higher than in solution due to the medium effect. The sensors are stable and reproducible with a short equilibrium time (less than 4 minutes). In addition, the color change of cresol red immobilized hydrogel is vivid from yellow (acidic condition) to purple (basic condition). Due to covalently binding, cresol red was not leaching out from the hydrogel, making it a good candidate of reusable "pH paper".

Quinine doped hybrid sol-gel coatings for wave guiding and optical applications

Pure and quinine doped silica coatings have been prepared over sodalime glasses. The coatings were consolidated at low temperature (range 60-180 A degrees C) preserving optical activity of quinine molecule. We designed a device to test the guiding properties of the coatings. We confirmed with this device that light injected in pure silica coatings is guided over distances of meters while quinine presence induces isotropic photoluminescence. With the combined use of both type of coatings, it is possible to design light guiding devices and illuminate regions in glass elements without electronic circuits.