Development of two new approaches for preparation of zirconium silicate systems at low temperature

Homogeneous and stable zirconium silicate sols and gels were prepared via the sol-gel process. Two synthesis procedures were explored based on using acetylacetone (acac) and acetic acid (HOAc) as modifying agents. The homogeneous sols were characterized by small angle x-ray scattering (SAXS) and ²⁹Si NMR in the early stages of polymerization. Zr addition to the Si sols caused significant modification of the extent of condensation of the Si species as determined by ²⁹Si NMR. TGA and DTA of the two types of xerogels revealed differences attributed to the modifying agents. Fourier Transform Infrared (FTIR) spectroscopy of acac xerogels showed a band at 1600 cm^–1, assigned to acac bonded to Zr. FTIR spectra of the HOAc xerogels were consistent with OAc bidentate ligands bonded to Zr. UV-Vis spectroscopy results of the HOAc2.3 thin film presented a band assigned to OAc singly coordinated to Zr.     

Synthesis of polysilisiquioxane used as core layer material of optical waveguide

Colorless and transparent polysilisiquioxane was synthesized using non-hydrolytic sol–gel process. A high degree of poly-condensation and a lower remnant ratio of Si–OCH₃ were calculated by ²⁹Si NMR and ¹H NMR, respectively. After spin-coating, subsequently UV and thermal curing, free-cracked thin films were obtained. The properties of the free-cracked thin films were measured by a prism coupler and thermal analysis system. The refractive index increased to 1.5495 (1,310 nm TE) and 1.5468 (1,550 nm TE), respectively, with the increasing of phenyltrimethoxysilane content to 20 mol%. Birefringence was below 0.0005. The thermo-optic coefficient was about −2.8 × 10⁻⁴ °C⁻¹. The optical loss was 0.20 dB cm⁻¹ at 1,310 nm and 0.75 dB cm⁻¹ at 1,550 nm, which was very important for core layer material of optical waveguide. The results of Thermo-Gravimetric Analysis indicated an excellent thermal stability. All of these properties imply that it will be a promising core layer material of optical waveguide.     

Evolution of the Si-condensed species in a multicomponent polymeric system

Alcoholic sol-gel systems were prepared using a pre-hydrolyzed tetraethyl orthosilicate (TEOS) sol as the main component. Ti and Zr alkoxides were also introduced in order to provide properties of technological interesttowards producing the final ceramics. The molar ratios Si:Ti:Zr were 82:7:11, respectively. Six potential chelating molecules were used as modifying agents in order to control the reactivity of Ti and Zr, avoiding precipitation. The products were characterized by spectroscopic techniques including Small Angle X-ray Scattering (SAXS), ²⁹Si NMR, UV-Vis and Fourier Transform Infrared (FTIR) spectroscopies. The radial distribution functions (RDF) of the gels and calcined solids were obtained; in addition, the porosimetry study of the solids calcined at 873 K in air was performed. The results are mainly discussed in terms of the condensation of the Si species; however, the influence of Ti, Zr and the modifying agent structures is also considered.     

The Role of 2-(Methacryloyloxy) Ethyl Acetoacetate in the Polymerization of Hybrid Multicomponent (Si, Ti, Zr) Sols

2-(Methacryloyloxy) ethylacetoacetate (MEEAH) was used as stabilyzing agent to control the chemical reactivity of Ti and Zr monomeric alkoxides in a Si—Ti—Zr sol. The organic and inorganic polymerizations were carried out simultaneously. The organic polymerization was performed using benzoyl peroxide as the initiator. The inorganic polymerization was done via the sol-gel process. The polymerization was studied by several spectroscopic techniques, including Fourier Transform Infrared (FTIR), UV-Vis, ²⁹Si NMR, Small Angle X-ray Scattering (SAXS) and X-ray diffraction (XRD). Theoretical calculation and experimental results showed that MEEAH acted as a monodentate ligand, mainly. This led to a high condensation extent of the Si species in the sol. A short range order gel was obtained, according to the SAXS results. The Si—O—Ti and Si—O—Zr bonds were detected by FTIR. The bonds remained stable, because a sample calcined at 1173 K was amorphous according to the XRD results, indicating structural homogeneity.     

Surface Modification of Colloidal Silica by Sulfonation Route for Super-Hydrophilicity

Colloidal silica was chemically modified by a two-step method including an olefin sulfonation route as a preliminary study for super-hydrophilic applications. The hydrophobic vinyl groups were initially bonded chemically to the hydroxylated silica surface using the trichlorosilane coupling agents. The vinyl-terminated silica was then sulfonated by addition reaction with chlorosulfonic acid. The modified silica was investigated using DRIFT, TGA, element analysis, solid-state ²⁹Si- and ¹³C CP-MAS NMR. The vinyl-terminated specimen showed a characteristic IR absorption band at 1600 cm^–1 and a weight loss of approximately 3% starting at 350°C while the ²⁹Si NMR peaks at 70.9 and 79.8 ppm and ¹³C NMR at 136 ppm and 129.8 ppm were assigned to a vinyl group bonded to silica. Elemental analysis of the sulfonated silica indicated the presence of sulfur, carbon and hydrogen. Thermal decomposition in range 150–600°C was due to the presence of sulfonated organics and unreacted vinyl groups while the new signals on ¹³C NMR, which were in the range 70–15 ppm, were assigned to sulfonated carbons.     

Organic-inorganic hybrid materials based on N=C=O functionalised silan modified with titanium and zirconium

This work investigates the influence of the precursor trimethylsilil isocyanate on the sol-gel synthesis of hybrid materials. The obtained Si−O−C−N network is additionally modified by titanium and zirconium alcoxypropoxides in the range of 10 to 30 wt. %. The structure of the obtained hybrid materials before and after pyrolysis up to 1100°C was investigated by methods of XRD, FTIR and ²⁹Si MAS NMR. We established that the hybrid structure was stable up to 600°C based on IR study. The structural transformation of the hybrid materials into oxycarbonitrogen system started at 800°C. The network of the hybrids modified by titanium remained stable and amorphous up to the final temperature of the pyrolysis (1100°C) compared to the gels modified by more than 10 wt.% Zr. It was confirmed by XRD analysis that the last mentioned are nanocomposite materials, built from carbooxynitrogen vitreous matrix and ZrO₂-nanocrystals (tetragonal). The NMR method verified the presence of heterometallic bonds (Si−O−Ti and Si−O−Zr) and Q₄, ZrQ₃ or TiQ₃, NSiO₃ and D structural units in the gels.     

Amorphous sol-gel titania modified with heteropolyacids

Samples of amorphous sol-gel titania were prepared at 50%wt with tungstophosphoric or molybdophosphoric acid. The resulting gels were dried and annealed at 100, 150 and 200°C and studied by FT-IR, UV-Vis, EPR, TGA and Raman spectroscopy. By FT-IR the evolution of the stretching vibration of the OH groups (3450–3700 cm⁻¹) was followed. The intensity of this band decreased as the annealing temperature increased. With UV-Vis spectroscopy the band gap was determined for each sample, and the Eg was found between 2.72 and 3.38 eV. Raman spectroscopy revealed the formation of Mo—O—Ti and W—O—Ti—O bonds. An intense EPR signal at g = 1.998 was observed during annealing of the samples. Amorphous solids with a significant number of vacancies and promising photocatalytic properties were obtained.     

Complexation of Silicic Acid with Tiron in Aqueous Solution Under near Natural Condition

The formation of a silicic acid–tiron (a derivative of catechol) complex was investigated in aqueous solution with various molar ratios of tiron to silicic acid (tiron/Si) or with various pH using ²⁹Si NMR. Only the 1:3 silicic acid–tiron complex was detected in despite of the range of tiron/Si molar ratios. This complex is stable in the pH range from 6 to 10. This indicates that the formation of a hydrogen bond (SiOH⋅⋅⋅O− in tiron), due to dissociation of H⁺ from hydroxy groups of tiron, may be a trigger for the formation of the complex. Around pH=6, the formation of the complex occurs when the tiron/Si molar ratio is larger than 3 and most of silicic acid is converted to the complex when the ratio is larger than 25. Based on the temperature dependence of the ²⁹Si NMR spectra for the complex, the existence of two possible meridional and facial isomers was confirmed. The conditional formation constant for the 1:3 silicic acid–tiron complex was defined as Eq. 8 and estimated to be 2.0 mol⁻¹⋅dm³ for the facial complex and 4.1 mol⁻¹⋅dm³ for the meridional complex, respectively.     

An ultra-low hydrolysis sol-gel route for titanosilicate xerogels and their characterization

In this work TiO₂-SiO₂ xerogels were prepared through an ultra low hydrolysis method using titanium and silicon alkoxide. The samples were heat treated to 500°C. The xerogels were characterized using TGA/DTA, FTIR, XRD and TEM. The samples showed the formation of Si–O–Ti bridges by its characteristic vibration within 925–960 cm⁻¹ range. Si–O–Si bond angles were calculated using the central force network model. The TiO₂ in all the samples crystallized on heat treatment to 500°C. The crystallite size calculated using the Scherer formula from the XRD was verified from the Transmission Electron Micrograph. Samples heat treated to 350°C remained amorphous and hence could be used as hosts for biomaterials and organic optical materials.     

Formation of borosilicate glasses from silicon alkoxides and metaborate esters in dry non-aqueous solvents

The reaction of metaborate esters (RO)₃B₃O₃ [R = Me, Et, ClCH₂CH₂–, Cl₃CCH₂–, ClCH₂CH₂CH₂–, (ClCH₂)₂CH–] with Si(OR)₄ (R = Me, Et), either neat or in dry propan-2-one or dry THF at room temperature, led to gels which when dried and heated in air for 20 mins at 600°C afforded borosilicate glasses in high ceramic yields. The dried gels and glasses were characterized by elemental analysis, TGA, IR, and powder XRD, and solid-state MAS ²⁹Si and ¹¹B NMR. The gelling reaction was investigated by solution ¹¹B and ²⁹Si NMR. These NMR studies indicated B–O–Si reaction intermediates and a mechanism involving alkoxy exchange and various condensation/elimination reactions of the borosilicate esters have been proposed.     

Hydrolysis behavior of a precursor for bridged polysilsesquioxane 1,4-bis(triethoxysilyl)benzene: a <Superscript>29</Superscript>Si NMR study

The hydrolysis behavior of 1,4-bis(triethoxysilyl)benzene (BTB), a precursor of bridged polysilsesquioxane, was investigated with high-resolution ²⁹Si nuclear magnetic resonance (²⁹Si NMR) spectroscopy at ambient temperature in a system with BTB:ethanol:water:HCl = 1:10:x:0.8 × 10⁻⁴ (x = 3, 6 or 9). Signals due to hydrolyzed triethoxysilyl groups as well as unhydrolyzed triethoxysilyl groups [−Si(OEt)₃, −Si(OEt)₂(OH), −Si(OEt)(OH)₂ and −Si(OH)₃ (OEt = OCH₂CH₃)] formed four sub-regions based on the number of hydroxyl groups bound to a silicon atom. In addition, one silicon environment influenced the other silicon environment by an intra-molecular interaction between two silicon atoms, and each sub-region for monomeric species thus contained four signals. Based on the development of signal intensity, it is revealed that one of the two triethoxysilyl groups in BTB is hydrolyzed preferentially. Thus, when a triethoxysilyl group is hydrolyzed, the −Si(OH) _x (OEt)_3−x (x = 1, 2) groups formed undergo further hydrolysis, which is opposite to the tendency expected from the hydrolysis behavior of organotrialkoxysilanes under acidic conditions.     

Large electric polarization in BiFeO3 film prepared via a simple sol–gel process

BiFeO₃ film has been deposited on Pt/Ti/SiO₂/Si substrate by a simple sol–gel process annealed at 500 °C. X-ray diffraction analysis revealed that the film was fully crystallized and no impure phase was observed. Cross-section scanning electric microscopy results indicated that the thickness was about 600 nm. Large remanent polarization was observed. The double remanent polarization is 95.8 μC/cm² at an applied field of 800 kV/cm. Intense dielectric dispersion was observed above 100 kHz. At a biased electric field of 167 kV/cm, the leakage current densities were identified as ∼10⁻⁵ to 10⁻⁴ A/cm².     

Determination of paracetamol (acetaminophen) by HPLC with post-column enzymatic derivatization and fluorescence detection

Summary A novel method is described for the determination of paracetamol (acetaminophen;N-acetyl-4-aminophenol) in urine. After reversed-phase HPLC separation, paracetamol is oxidized by H₂O₂ with horseradish peroxidase catalysis. Detection is performed fluorimetrically at an excitation wavelength of 329 nm and an emission wavelength of 435 nm. Urine samples were spiked with paracetamol, diluted, and injected directly without further pretreatment. Under these conditions, the limit of detection was 2×10⁻⁸ molL⁻¹, and the limit of quantification was 7×10⁻⁸ molL⁻¹. The method was validated by two different approaches based on HPLC with UV-Vis detection.     

Synthesis and characterization of inclusion complexes of aliphatic-aromatic poly(Schiff base)s with β-cyclodextrin (highlight)

This paper describes the formation of polymer inclusion complexes(polymer-CD-ICs) between β-cyclodextrin(β-CD) and aliphatic-aromatic poly(Schiff base)s. Fourier transform infrared(FTIR) spectroscopy, ¹H nuclear magnetic resonance spectroscopy(¹H-NMR), thermogravimetric analysis(TGA) and X-ray diffraction(XRD) have been used to observe the formation of polymer-CD-ICs. In FTIR spectra, the characteristic peaks of β-CD at 3391 cm⁻¹ shifted to 3418 cm⁻¹ and the intense peak at 1602 cm⁻¹ due to the –C = N– stretching vibration diminished after formation of inclusion complexes. Compared the ¹H-NMR of polymer-CD-ICs with β-CD, the chemical shift of the protons H-3, H-5 have shifted to higher field after the formation of inclusion complexes, which is perhaps due to the interaction of these protons with polymers. The TGA analysis revealed that the polymer-CD-ICs had better thermal stability than β-CD, suggesting that the polymer increased the stability of β-CD. The X-ray diffraction patterns displayed that the strong peak for both polymer-CD-ICs at approximately 20.0° (2θ) may confirm their IC formation.     

Synthesis, charge-separated state characterization of N-methyl-2-(4′-N-ethylcarbozole)-3-fulleropyrrolidine and its derivatives

N-Methyl-2-(N-ethylcarbozole)-fulleropyrro lidine and N-methyl-2-(4′-N,N-diphenylaminophenyl)-fulleropyrrolidine were synthesized by 1,3-dipolar cycloaddition under microwave irradiation, which were characterized by MS, ¹H NMR, IR and UV-Vis. Photoinduced intramolecular electron transfer process from C₆₀ moiety to carbazole moiety has been studied by nanosecond laser flash photolysis. The charge-separated state C₆₀ ^•−-Cz^•+ was observed in the near-IR region with a lifetime of 0.28 μs. The electronic spectrum of the C₆₀-TPA was studied by using ZINDO method on the basis of the optimized geometrics with B3LYP/6-31G* program. The results show that the calculated absorption was beyond 440nm, essentially consistent with the experimental value 433 nm. __________ Translated from Acta Chimica Sinica, 2005,63(17)(in Chinese)     

The synthesis and characterisation of novel dimethyl- and diphenyl-silanediolates

Dimethyl- and diphenylsilanediolates are key intermediates in the preparation of dimethyl- and diphenyl-siloxane polymers. Both dimethyl- and diphenylsilanediolates R₂Si(OM)₂, where R = Me or Ph, and M = Li, Na and K were synthesised by the reaction between dimethyl- and diphenylsilanediol and a metal or metal hydride (M/MH where M = Li, Na and K). The silanediolates were characterised by ²⁹Si, ¹³C and ¹H NMR, FTIR and mass spectroscopy.     

Thermodynamic Model for ThO<Subscript>2</Subscript>(am) Solubility in Alkaline Silica Solutions

No thermodynamic data for Th complexes with aqueous Si are available. To obtain such data, extensive studies on ThO₂(am) solubility were carried out as functions of: (1) a wide range of aqueous silica concentrations (0.0004 to 0.14 mol⋅L⁻¹) at fixed pH values of about 10, 11, 12, and 13; and (2) and variable pH (ranging from 10 to 13.3) at fixed aqueous Si concentrations of about 0.006 mol⋅L⁻¹ or 0.018 mol⋅L⁻¹. The samples were equilibrated over long periods (ranging up to 487 days), and the data showed that steady-state concentrations were reached in < 29 days. X-ray diffraction, FTIR, and Raman analyses of the equilibrated solid phases showed that the Th solids were amorphous ThO₂(am) containing some adsorbed Si. The solubility of ThO₂(am) at pH values ranging from 10 to 13.3 at fixed 0.018 mol⋅L⁻¹ aqueous Si concentrations decreases rapidly with an increase in pH, and increases dramatically with an increase in Si concentrations beyond about 0.003 mol⋅L⁻¹ at fixed pH values > 10. The data were interpreted using both the Pitzer and SIT models, and required only the inclusion of one mixed-hydroxy-silica complex of Th [Th(OH)₃(H₃SiO₄)₃²⁻]. Both models provided similar complexation constant values for the formation of this species. Density functional theory calculations predict complexes of this stoichiometry, having six-fold coordination of the Th cation, to be structurally stable. Predictions based on the fitted value of log ₁₀ K ⁰=−18.5±0.7 for the ThO₂(am) solubility reaction involving Th(OH)₃(H₃SiO₄)₃²⁻[ThO₂(am)+3H₄SiO₄+H₂O↔Th(OH)₃(H₃SiO₄)₃²⁻+2H⁺], along with the thermodynamic data for aqueous Si species reported in the literature, agreed closely with the extensive experimental data and showed that under alkaline conditions aqueous Si makes very strong complexes with Th.     

Synthesis and characterization of oligosalicylaldehyde-based epoxy resins

The synthesis of a new epoxy resin of oligosalicylaldehyde by the reaction with epichlorohydrin is reported. New resin’s epoxy value and chlorine content were determined and found to be 25% and 1%, respectively. The characterization of the new resin was instrumented by FTIR, ¹H NMR, scanning electron microscopy, and thermal gravimetric analyses. TGA results showed that the cured epoxy resin has a good resistance to thermal decomposition. The mass losses of cured epoxy resin were found to be 5%, 10%, 50% at 175°C, 240°C, and 400°C, respectively. On the curing procedure the resin was cured with polyethylenepolyamine at 25 °C for 8 h and 100°C for 1.5 h. The FTIR spectrum of new epoxy resin gave the peak of oxirane ring at ṽ = 918 cm⁻¹. In memory of Professor Dr. Adalet R. Vilayetoğlu     

Sol–gel preparation of aminopropyl-silica-magnesia hybrid materials

A series of aminopropyl-silica-magnesia hybrid materials has been prepared by the sol–gel method from tetraethoxysilane (TEOS), magnesium chloride (MgCl₂) and aminopropyltriethoxysilane (APTES) under acid conditions. The APTES:TEOS ratio was varied between 0:1 and 1:0. The aminopropyl coverage concentrations for APTES-silica-Mg samples were in the range of 0.3–2.3 mmol g⁻¹. The hybrid materials were characterized by numerous techniques, including X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), Fourier transform Raman spectroscopy (FT-Raman), solid-state ¹³C and ²⁹Si nuclear magnetic resonance (¹³C- and ²⁹Si-NMR), thermogravimetry (TGA), N₂ adsorption–desorption, small-angle X-ray scattering (SAXS), and scanning electron microscopy (SEM). The increase of APTES content in the silica network resulted in the increase of six-membered siloxane rings. The hybrid systems were shown to be formed from fully-condensed, trifunctional APTES species. The porosity and morphology of the hybrid materials were influenced by the initial TEOS/APTES ratio. The radius of gyration of the primary particles, determined by SAXS, was between 1.1 and 2.9 nm.     

Synthesis and luminescence behavior of inorganic–organic hybrid materials covalently bound with pyran-containing dyes

A DCM derivative, namely 4-Dicyanomethylene-2-methyl-6-{[4′-(N-hydroxyethyl-N-methyl)amino]styryl}-4H-pyran (DCMH), has been synthesized and covalently incorporated into the inorganic silica network as pendants via a sol–gel process. Molecular structures of the resultants are confirmed by elemental analysis, ¹H NMR, DSC, TGA, FTIR and UV–Vis spectroscopy. Photoluminescence (PL) spectra shows that the emission of DCMH peaked at 625 nm is almost completely quenched in DMF solution with a concentration of 1 × 10⁻⁴ mol/L, however, in hybrid films, the PL intensity enhances obviously with increasing DCMH concentration even at the high loading content of 40 mol%. All the hybrid films exhibit PL emission around 646–650 nm and the peak position reveal little dependence on the concentration of dye, suggesting they can be used as red emissive materials in light-emitting diodes. The relationship between fluorescence lifetime and dye concentration is also investigated by time-resolved PL measurements.