Composite Silica Particles Using a Mixture of Organosilane Monomers

Composite silica particles were synthesized by a two-step (acid-base) process in an aqueous solution with a mixture of organoalkoxysilane monomers. The two-step process separates the hydrolysis and condensation procedures to easily control condensation rate. In this study, the silane monomers used were phenyltrimethoxysilane (PTMS), vinyltrimethoxysilane (VTMS), methyltrimethoxysilane (MTMS), and tetraethyl-orthosilicate (TEOS). The physical properties of the resultant composite particles were investigated with the change in the molar ratio of monomers. The size of the particles increased with increasing the molar ratio of R_aSi(OR)₃/R_bSi(OR)₃ or R_aSi(OR)₃/TEOS (R_a: phenyl; R_b: vinyl, methyl).     

Optical biosensor for the determination of BOD in seawater

An automatic sensing system was developed using an optical BOD sensing film. The sensing film consists of an organically modified silicate (ORMOSIL) film embedded with an oxygen-sensitive Ru complex. A multi-microorganisms immobilization method was developed for the BOD sensing film preparation. Three different kinds of microorganisms, Bacillus licheniformis, Dietzia maris and Marinobacter marinus from seawater, were immobilized on a polyvinyl alcohol ORMOSILs. After preconditioning, the BOD biosensor could steadily perform well up to 10 months. The linear fluctuant coefficients (R²) in the range of 0.3-40 mg L⁻¹ was 0.985 when a glucose/glutamate BOD standard was applied. The reproducible response for the BOD sensing film could be obtained within ±2.3% of the mean value in a series of 10 samples in 5.0 mg L⁻¹ BOD standard GGA solution. The effects of temperature, pH and sodium chloride concentration on the two microbial films were studied as well. The BOD sensing system was tested and applied for the BOD determination of seawater.     

X-Ray Diffraction Studies of Sol-Gel Derived ORMOSILs Based on Combinations of Tetramethoxysilane and Trimethoxysilane

ORMOSILs have been prepared in the series TMOSx·MTMS(100 – x) (where TMOS is tetramethoxysilane; MTMS is methyltrimethoxysilane; x is mol% silane with respect to total silane for 0 x 100) by means of acid catalyzed, sol-gel processing. After drying at 60°C, small bulk samples were obtained of excellent optical clarity. Powder X-ray diffraction (XRD) patterns, in the range of 5 to 60°2, were compared with that of fused silica. All the prepared samples were amorphous. Fused silica exhibits one broad peak, d2 centered at d-spacing 4.12 Å. For the TMOS100 silica xerogel, the analogous broad peak had shifted slightly, to be centered at 3.88 Å; and remained in about the same position as x was decreased for the series TMOSx·MTMS(100 – x). In addition, a second, broad peak, d1, was observed for the ORMOSIL series centered at the d-spacing 8.7 Å for MTMS100 (i.e., x = 0) and increasing smoothly as x was increased, reaching 11.3 Å for x = 70, and >11.3 Å for x > 70. The intensity of d1 was found to have trebled, relative to the intensity of d2, on increasing the organic character of the matrix from TMOS70·MTMS30 to MTMS100.The d2 peak appearing at about 4 Å for both fused silica and the ORMOSILs is assumed to be associated with the spacing between silicon atoms connected by means of an oxygen bridge. The Si–O–Si angle for silica xerogels is known to depend upon the nature of the sol-gel processing and is bigger than that of fused silica.The d1 peak may be associated with the spacing between silicons attached to methyl groups and indicative of channels of methyl groups in the structure. Alternatively, the d1 peak may have its origin in a preferred, discrete structural unit in the matrix for instance cubane based on a octameric silicon arrangement.     

A fiber-optic evanescent wave sensor for dissolved oxygen detection based on novel hybrid fluorinated xerogels immobilized with [Ru(bpy)3]2+

We have prepared a novel fiber-optic evanescent wave sensor (FEWS) for dissolved oxygen (DO) detection. The sensor fabrication was based on coating a decladded portion of an optical fiber with a microporous coating, which was prepared from 3,3,3-trifluoropropyltrimethoxysilane and n-propyltrimethoxysilane. The fluorophores were immobilized in the porous coating and excited by the evanescent wave field produced on the core surface of the optical fiber. The sensitivity of the sensor was quantified by the ratio of the fluorescence intensities in pure deoxygenated (I ₀) and in pure oxygenated environments (I). Results show that the quenching response of DO is increased with the enhancement of the coating surface hydrophobicity using the presented hybrid fluorinated ORMOSILs. The calibration curve of I ₀/I to [O₂] is linear from 0 to 40 ppm and the detection limit is 0.05 ppm (3σ) with a short response time of 15 s for DO detection. Figure       

Fast sol–gel technology: from fabrication to applications

A novel method to prepare crack-free sol–gel materials without shrinkage is reviewed. The method allows fabrication of a viscous sol–gel resin in a few minutes followed by either thermal-curing or UV-curing requiring several hours or several minutes, respectively. The method is distinguished by the short time required to achieve a solid monolith. The fast sol–gel method uses a combination of organically modified alkoxides with traditional alkoxides as precursors, to produce a final product which is an organic-inorganic hybrid with properties that vary from silicone rubbers to silica glass. Optical and physical properties, such as refractive index and thermal expansion, can be engineered by controlling the ratio between the precursors. This class of materials is a promising candidate for preparation of optical elements such as waveguides and submicron structured replicas and can also be used as an optical bonding material. This paper reviews the fast sol–gel technology, as well as methods to characterize the process and its final products. Various applications of fast sol–gel materials are presented.     

Luminescence and oxygen sensing properties of ORMOSILs covalently grafted with a novel ruthenium(II) complex

A series of VTES/TEOS composite xerogels covalently grafted with a novel complex Ru(phen)₂(Dppz-Si)Cl₂ were prepared, using the alkoxysilane-modified dipyrido[3,2-a:2′,3′-c]phenazine compound (denoted as Dppz-Si) as the second ligand of the Ru(phen)₂Cl₂ (phen = 1,10-phenanthroline) complex and a precursor of the sol–gel process. Bulk xerogels were obtained by co-hydrolyzing and co-condensation from a mixture of triethoxysilane (TEOS), Ru(phen)₂(Dppz-Si)Cl₂ and Vinyltriethoxysilane (VTES). The luminescence intensity of composite xerogels is enhanced by 18.2 times, and the sensitivity is improved from 1.1 to 3.1 by optimizing the molar ratio of VTES to TEOS. The composite xerogel containing 80% VTES in precursor was optimal, exhibiting the maximum luminescence intensity and sensitivity. These results indicate that the complex Ru(phen)₂(Dppz-Si)Cl₂ is sensitive to oxygen concentration, VTES is a kind of excellent organic modifier and can greatly improved photoluminescent (PL) and oxygen sensing performances.     

Electrochemiluminescent behaviors of alkaloids and tris(2,2'-bipyridine) ruthenium in organically modified silicate film

Electrogenerated chemiluminescences (ECLs) of alkaloids, such as berberine, trigonelline, allantoin and betaine, were studied in an aqueous alkaline buffer solution (pH 9.5), based on tris(2,2′-bipyridine)ruthenium(II) [Ru(bpy)₃²⁺] immobilized in organically modified silicates (ORMOSILs) film on a glassy carbon electrode (GCE). The immobilized Ru(bpy)₃²⁺ showed good electrochemical and photochemical activities. In a flow system, the eluted alkaloids were oxidized on the modified GCE, and reacted with immobilized Ru(bpy)₃²⁺ at the potential of +1.50 V (versus Ag/AgCl). The luminescence with λ_max 610 nm was caused by a reaction of electrolytically formed Ru(bpy)₃³⁺ with an oxidized amine group to generate Ru(bpy)₃^2+*. The determination limit was 5 × 10⁻⁶ mol L⁻¹, 8 × 10⁻⁶ mol L⁻¹, 2.0 × 10⁻⁵ mol L⁻¹ and 5.0 × 10⁻⁵ mol L⁻¹ for berberine, trigonelline, allantoin and betaine at S/N 3, respectively. In addition, the factors affecting the determination of the four alkaloids were also studied.