Fabrication and characterization of TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript> composite nanoparticles and polyurethane/(TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript>) nanocomposite films

TiO₂–SiO₂ composite nanoparticles were prepared by a sol–gel process. To obtain the assembly of TiO₂–SiO₂ composite nanoparticles, different molar ratios of Ti/Si were investigated. Polyurethane (PU)/(TiO₂–SiO₂) hybrid films were synthesized using the “grafting from” technique by incorporation of modified TiO₂–SiO₂ composite nanoparticles building blocks into PU matrix. Firstly, 3-aminopropyltriethysilane was employed to encapsulate TiO₂–SiO₂ composite nanoparticles’ surface. Secondly, the PU shell was tethered to the TiO₂–SiO₂ core surface via surface functionalized reaction. The particle size of TiO₂–SiO₂ composite sol was performed on dynamic light scattering, and the microstructure was characterized by X-ray diffraction and Fourier transform infrared. Thermogravimetric analysis and transmission electron microscopy (TEM) employed to study the hybrid films. The average particle size of the TiO₂–SiO₂ composite particles is about 38 nm when the molar ratio of Ti/Si reaches to1:1. The TEM image indicates that TiO₂–SiO₂ composite nanoparticles are well dispersed in the PU matrix.     

Fabrication,characterization, and photocatalytic performance of TiO<Subscript>2</Subscript> hybridized with SiO<Subscript>2</Subscript>

Nanostructures TiO₂–SiO₂ photocatalysts were successfully synthesized using the sol-gel method, hydro-calcination, co-precipitation and room-temperature solid-phase synthesis technology. X-ray powder diffraction pattern (XRD), Fourier transform infrared spectrum (FTIR), photoluminescence (PL) spectra, thermal analyses (TG–DTA), scanning electron micrographs (SEM), X-ray photoelectron spectroscopy (XPS), and UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS) were used to characterize the as-synthesized catalysts. Photocatalytic performances of the catalysts were evaluated by the degradation of methyl orange (MO) under s imulated natural light and the degradation rate of MO is 97.2%. The composites showed a good stability: after five recycling runs there are no significant decreases in the photocatalytic activity. The photodegradation of methylene blue, rhodamine B, methyl violet, naphthol green B, basic fuchsin, malachite green, and methyl red were also tested, and the degradation rate of dyes could reach over 94.2 %. A possible mechanism for the photocatalysis with the TiO₂–SiO₂ was proposed.     

Synthesis characterization and catalytic evaluation of Ni/ZrO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> aerogels catalysts

The Ni/ZrO₂/SiO₂ aerogels catalysts were synthesized via three different routes: (i) impregnation ZrO₂–SiO₂ composite aerogels with a aqueous solution of Ni(NO₃)₂, (ii) impregnation SiO₂ aerogels with a mixed aqueous solution of Ni(NO₃)₂ and ZrO(NO₃)₂ · 2H₂O, (iii) one-pot sol–gel procedure from precursors Ni(NO₃)₂/ZrO(NO₃)₂ · 2H₂O/Si(OC₂H₅)₄. These catalysts were characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), ammonia temperature-programmed desorption (NH₃-TPD), N₂ adsorption–desorption isotherms and Fourier transform infrared (FT-IR). The Liquid-phase hydrogenation of maleic anhydride (MA) was performed over these catalysts. The results revealed that the different preparation routes result in a difference between the obtained samples, concerning the crystal structure and composition, surface acidity, mixed level of each component, texture, and catalytic selectivity.     

Permeation studies on transparent multiple hybrid SiO<Subscript>2</Subscript>-PMMA coatings-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> barriers on PEN substrates

In this work we report the performance of permeation barriers based on organic/inorganic multilayer stacks. We have used PMMA-SiO₂ (poly methyl methacrylate-silica) hybrid films synthesized through a sol–gel route as organic–inorganic components, whereas Al₂O₃ thin films were used as the inorganic component. The hybrid layers were deposited by dip coating and the Al₂O₃ by atomic layer deposition (ALD), films were prepared on polyethylene naphthalene (PEN) substrates. The permeability of the films and stacks is evaluated using helium as the diffusion gas in a custom made ultra-high vacuum system. The results show that permeability for PEN is reduced from 5 × 10⁻³ g/m²-day to about 9 × 10⁻⁵ g/m²-day for the best multiple barrier evaluated. Increased barrier properties are due to the increasing in the path and hence the lag-time of the permeating gas. In particular, we report the surface roughness of the different layers and its impact on the barrier performance. The hybrid layers reduced notably the roughness of the bare PEN substrate improving the quality of the Al₂O₃ layer in the barrier. The optical transmittance of the barriers in the visible region is higher than 80% in all the studied cases.     

Nanosized TiO<Subscript>2</Subscript> particles decorated on SiO<Subscript>2</Subscript> spheres (TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript>): synthesis and photocatalytic activities

Nanosized TiO₂ and nano-anatase TiO₂ decorated on SiO₂ spherical core shells were synthesized by using a sol–gel method. The synthesized pure TiO₂ nano particle and TiO₂ grafted on SiO₂ sphere with various ratios have been characterized for their structure and morphologies by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrophotometry (FTIR) and transmission electron microscopy (TEM). Their surface areas were measured using the BET method. The photocatalytic activity of all nanocomposites was investigated using methylene blue as a model pollutant. The synthesized TiO₂/SiO₂ particles appeared to be more efficient in the degradation of methylene blue pollutant, as compared to pure TiO₂ particles.     

Phase relationships in the SiO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript> system

Phase equilibria in a miscibility gap of the SiO₂-TiO₂ system were studied. A visual polythermal analysis and annealing of samples were performed in a Galakhov microfurnace. The microstructure and composition of the obtained samples were investigated by scanning electron microscopy and electron probe microanalysis. A critical analysis of the experimental data was made. Thermodynamically optimized based on the sub-regular solution model, a phase diagram of the SiO₂-TiO₂ system was constructed.     

SiO<Subscript>2</Subscript> and TiO<Subscript>2</Subscript> nanoparticles in Aerosol OT reverse microemulsions: Synthesis and characterization

Stable SiO₂ and TiO₂ organosols were prepared by hydrolyzing tetraethyl orthosilicate (TEOS) in the presence of 6–12 M NH₃ and titanium(IV) isopropylate (TTIP) in reverse microemulsions of 0.12–0.25 M bis(2-ethylhexyl) sulfosuccinate (Aerosol OT, AOT) in n-decane with the aqueous pseudophase content of 2–3 vol %, 0.018–0.090 M TEOS, and 0.15–0.55 vol %, 0.003–0.025 M TTIP. The degree of hydrolysis was monitored by IR spectroscopy (for TEOS) and spectrophotometry (for TTIP). Oxide nanoparticles were characterized by photon-correlation spectroscopy (PCS) (D _h = 8–100 nm) and laser electrophoresis (ζ-potential = 7.4–11.6 mV). The occurrence of surface potential made it possible to separate the oxides from the excess of surfactant by nonaqueous electrophoresis and to determine particle sizes (7–40 nm) by means of transmission electron microscopy (TEM).     

Synthesis and characterization of a new hybrid TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> filler for lithium conducting gel electrolytes

This paper describes the synthesis and properties of a new type of ceramic fillers for composite polymer gel electrolytes. Hybrid TiO₂-SiO₂ ceramic powders have been obtained by co-precipitation from titanium(IV) sulfate solution using sodium silicate as the precipitating agent. The resulting submicron-size powders have been applied as fillers for composite polymer gel electrolytes for Li-ion batteries based on poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF/HFP) copolymeric membranes. The powders, dry membranes and gel electrolytes have been examined structurally and electrochemically, showing favorable properties in terms of electrolyte uptake and electrochemical characteristics in Li-ion cells.     

FePO<Subscript>4</Subscript>/SiO<Subscript>2</Subscript> Catalysts for Propylene Glycol Oxidation

FePО₄/SiO₂ supported catalysts with a different content of iron phosphate are prepared. The properties of the catalyst are changed by the introduction of alkali metal compounds (Na or Cs) on its surface. The samples obtained are characterized by X-ray diffraction, low-temperature nitrogen adsorption, temperatureprogrammed reduction by hydrogen, and temperature-programmed desorption of ammonia. The catalytic properties are investigated in the reaction of gas-phase propylene glycol oxidation. It is shown that the selectivity of methylglyoxal formation on the unmodified catalysts is determined by the state of the supported active component and by its reduction–oxidation ability under the action of a reaction mixture.     

MgF<Subscript>2</Subscript> films prepared from solvothermally treated precursor solutions

MgF₂ coating solutions were solvothermally treated at 160?°C for different time periods, this procedure induced crystallization and particle growth. Antireflection coatings prepared on glass from these solutions were compared to films derived from untreated precursor material. Ellipsometric porosimetry (EP) was employed to characterize structural features of coatings on glass as function of annealing temperature. Based on precursor solutions that had undergone solvothermal treatment antireflective coatings with a peak transparency exceeding 99% were prepared on PMMA substrates.

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Solvothermal treatment of MgF₂ precursor solutions results in crystallization of particles that can directly be applied to PMMA substrates for λ/4 antireflective films.

     

Carbon ceramic electrodes modified with mixed oxides SiO<Subscript>2</Subscript>/SnO<Subscript>2</Subscript> for determination of levofloxacin

The preparation of a carbon ceramic electrode modified with SnO₂ (CCE/SnO₂) using tin dibutyl diacetate as precursor was optimized by a 2³ factorial design. The factors analyzed were catalyst (HCl), graphite/organic precursor ratio, and inorganic precursor (dibutyltin diacetate). The statistical treatment of the data showed that only the second-order interaction effect, catalyst × inorganic precursor, was significant at 95% confidence level, for the electrochemical response of the system. The obtained material was characterized by scanning electron microscopy (MEV), X-ray diffraction (XRD), RAMAN spectroscopy, XPS spectra, and voltammetric techniques. From the XPS spectra, it was confirmed the formation of the Si–O–Sn bond by the shift in the binding energy values referred to Sn 3d3/2 due to the interaction of Sn with SiOH species. The incorporation of SnO₂ provided an increment of the electrode response for levofloxacin, with Ipa = 147.0 μA for the ECC and Ipa = 228.8 μA for ECC/SnO₂, indicating that SnO₂ when incorporated into the silica network enhances the electron transfer process. Under the optimized working conditions, the peak current increased linearly with the levofloxacin concentration in the range from 6.21×10^?5 to 6.97×10^?4 mol L^?1 with quantification and detection limits of 3.80×10^?5 mol L^?1 (14.07 mg L^?1) and 1.13×10^?5 mol L^?1 (4.18 mg L^?1), respectively.     

Electrocatalytic activity of hemoglobin in sodium alginate/SiO<Subscript>2</Subscript> nanoparticle/ionic liquid BMIMPF<Subscript>6</Subscript> composite film

A novel biocompatible composite film containing sodium alginate (SA), room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF₆), SiO₂ nanoparticle, and hemoglobin (Hb) was fabricated and covered on the surface of a traditional carbon paste elecrode (CPE). The immobilized Hb on the electrode surface showed good direct electrochemical behaviors, and a pair of quasi-reversible redox peaks of Hb was obtained, which indicated that the direct electron transfer of Hb with the electrode surface had been achieved. The SA/nano-SiO₂/BMIMPF₆/Hb/CPE showed dramatically electrocatalytic activity to the reduction of trichloroacetic acid, hydrogen peroxide (H₂O₂), and oxygen (O₂). The kinetic parameters for the electrocatalytic reactions were evaluated. The composite film showed the potential to the biosensor and biocatalysis.     

TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> hybrid nanomaterials: synthesis and variable UV-blocking properties

Silica and core–shell structured titania/silica (TiO₂/SiO₂) nanoparticles with particles size ranging from tens to hundreds of nanometers were prepared and deposited onto cotton fabric substrates by sol–gel process. The morphologies of the nanoparticles were characterized by field-emission scanning electron microscope (FE-SEM). The photocatalytic decomposition properties as well as UV-blocking properties of the fabrics treated with SiO₂ and TiO₂/SiO₂ nanoparticles were investigated.     

Fabrication and properties of MgF<Subscript>2</Subscript> composite film modified with carbon nanotubes

Carbon nanotubes (CNTs) were used to modify magnesium fluoride (MgF₂) film via the spin coating technique. Nanoparticles of MgF₂ were in situ synthesized on surfaces of CNTs resulted in the composites (MgF₂–CNTs) by means of sol–gel technique. The sizes of the MgF₂ nanoparticles in situ synthesized on CNTs surfaces could be modulated by processing the MgF₂ sol–gel in different ways. The MgF₂–CNTs as prepared was mixed with MgF₂ sol to fabricate composite films (MgF₂–CNTs/MgF₂). Instead of adding directly CNTs, adding MgF₂–CNTs, into MgF₂ sol could effectively improve the dispersion of CNTs, avoid emergence of carbon clusters in the compsite film, decrease surface roughness of the film, and enhance the interaction between the CNTs and MgF₂ matrix. In the paper, the MgF₂ nanoparticles were in situ synthesized on the surfaces of multi-walled carbon nanotubes (MWCNTs) and single-walled carbon nanotubes (SWCNTs) respectively to prepare MgF₂–SWCNTs/MgF₂ and MgF₂–MWCNTs/MgF₂ composite films. Experimental results showed that the transparency of the MgF₂–SWCNTs/MgF₂ composite film was higher than that of the MgF₂–MWCNTs/MgF₂ film in the range of ultraviolet, visible and near-infrared wavelengths. The results showed SWCNTS could be an ideal reinforcement of MgF₂ films to get good toughness, and retain its optical transmittance at the same time.     

Stabilization of Oil-in-Water Emulsions with SiO<Subscript>2</Subscript> and Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> Nanoparticles

Stabilization of oil-in-water Pickering emulsions with SiO₂ and Fe₃O₄ nanoparticles has been studied. Emulsions containing three-dimensional gel networks formed by aggregated nanoparticles in the dispersion media have been shown to be stable with respect to flocculation, coalescence, and creaming. Concentration ranges in which emulsions are kinetically stable have been determined. Stabilization with mixed Ludox HS-30 and Ludox CL SiO₂ nanoparticles leads to the formation of stable emulsions at a weight ratio between the nanoparticles equal to 2 and pH 6.7. In the case of stabilization with Ludox CL and Fe₃O₄ nanoparticles, systems resistant to aggregation and sedimentation are obtained at pH 8. The use of mixed Ludox HS-30 and Fe₃O₄ nanoparticles has not resulted in the formation of emulsions stable with respect to creaming, with such emulsions appearing to be resistant only to coalescence at pH 2–6.     

Synthesis,characterization, and application of sol gel derived Mg<Subscript>2</Subscript>SiO<Subscript>4</Subscript> powder

This paper reports a successful preparation of a pure forsterite Mg₂SiO₄ using the sol–gel approach and its application for the removal of impurities from a Tunisian frying oil. Magnesium nitrate hexahydrate and tetraethylortho-silicate were used as magnesium and silicon precursors, respectively. The synthesis was held at different calcination temperatures for 30?min. The annealed samples were characterized by X-ray diffraction, Fourier transform infrared, scanning electron microscopy, and laser diffraction. The results revealed that the sample calcined at 500?°C was forsterite with unimodal particle size distribution (PSD) centered at 122.8?±?0.3?μm. The dispersion index I (indicator of particle size uniformity) was 1.84. With the temperature increase, well crystallized compounds were obtained. Their PSDs remain unimodal and shift towards smaller particles. A decrease of the dispersion index was also noted, indicating the formation of Mg₂SiO₄ with more uniform particle size. This study showed that 900?°C could be selected as energy saving temperature suitable for the preparation of a pure and well crystallized Mg₂SiO₄ within just 30?min of annealing time. The obtained silicate exhibited promoting results for the purification of waste frying oils.

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Pure and fine Mg₂SiO₄ powder with unimodal particle size distribution was prepared by sol gel route under energy saving conditions. The obtained magnesium orthosilicate showed excellent results for waste frying oil purification

     

Geometry and electronic structure of (SiO<Subscript>2</Subscript>)<Subscript>3</Subscript> clusters

Electronic structure of (SiO₂)₃ clusters was calculated by the density functional method. Charge states were determined using various functionals, bond lengths and total energies of clusters were estimated.     

Fabrication of gradient density SiO<Subscript>2</Subscript> aerogel

With tetraethoxysilane as the organic precursor, gradient density aerogels were fabricated by three different methods: layer-by-layer gelation, sol-co-gelation and continuous formation technics. Through layer-by-layer method, a 5-layer graded density silica aerogel whose density ranges from 50 to 200 mg/cm³ was obtained, but it existed a dense skin between adjacent layers which could result in density mutation in the interface. In order to optimize its interface character, sol-co-gelation technique was created to improve the interdiffusion and smooth out the density mutation via a self-built device. Finally, on the base of the device and sol-co-gelation technics, a continuous formation process was developed to fabricate the completely gradient density silica aerogel. Optical microscope and X-ray phase contrast method were used to characterize the samples prepared by three different technics and comparatively research their interface feature.     

Preparation and optical characterization of catalyst free SiO<Subscript>2</Subscript> sonogel hybrid materials

The synthesis of sol-gel materials induced by ultrasonic irradiation (sonolysis) is implemented as an alternative method for the fabrication of highly pure organic-inorganic composites with good monolithic, mechanical and optical properties. Ultrasonic irradiation, instead of commonly used basic- or acidic-catalyst was used to produce acoustical cavitation within the liquid H₂O/tetraethyl-ortosilicate (TEOS) reactants. This procedure forms a hydrolyzed-TEOS colloidal dispersion (sol) which produces, after drying, a highly pure SiO₂ network. The resulting SiO₂ glass exhibits high porosity and allows the inclusion of several organic compounds in the colloidal sol-state. Novel, optical active synthesized liquid crystalline (LC)-azo-compounds, bent shaped mesogens, cis- and trans-poly(1-ethynylpyrene)s, as well as fullerene (C₆₀) spheres and classical organic dyes were successfully incorporated as dopant agents within the novel catalyst free (CF) SiO₂-sonogel host matrix. Absorption and fluorescence spectroscopy studies were carried out in order to characterize the optical performance of both the CF-sonogel and several hybrid composites The pulsed laser photoacoustic technique (LPAT) was implemented to determine thermodynamic phase transitions of LC-based hybrids and laser induced damage (photo-degradation) in dye-based composites. Finally, comparative morphology studies between undoped reference samples and some doped composites were performed by Atomic Force Microscopy (AFM), where an optimal TEOS/dopant concentration ratio, to obtain good mechanical properties among the studied samples, has been found.