Microstructure Control of Nanoporous Silica Thin Film Prepared by Sol-gel Process

Nanoporous silica films were prepared by sol-gel process with base, acid and base/acid two-step catalysis.Transmission electron microscope （TEM） and particle size analyzer were used to characterize the microstructure and the particle size distribution of the sols. Scanning electron microscopy （SEM）, atomic force microscopy （AFM） and spectroscopic ellipsometer were used to characterize the surface microstructure and the optical properties of the silica films. Stability of the sols during long-term storage was investigated. Moreover,the dispersion relation of the optical constants of the silica films, and the control of the microstructure and properties of the films by changing the catalysis conditions during sol-gel process were also discussed.

A comparative study of drying techniques on the morphology of porous silica gels synthesized via sol-gel process

The effect of drying techniques on the microstructure,morphology and pore structure of porous silica gels was studied in the paper.The gels were prepared by using sol-gel process and different drying routes:freeze-drying (FD),low pressure drying (LPD),high temperature drying (HTD) and chemical modification & ambient drying (CMD) techniques.Observation under pore distribution and structural properties showed that CMD technique leads to homogenous mesoporous silica material with specific surface area of 745 m2/g,and the average pore size around 20 nm,while LPD and HTD result in loosely packed particles with non-isotropic aggregation pattern.The specific surface areas of LPD and HTD samples are 419 and 513 m2/g respectively,and the pore size distribution of the samples are observed distributing widely in range of 10-100 nm.Freeze drying method is a new but prospective way to prepare mesoporous silica.The specific area of FD sample is around 500 m2/g.By the comparison for the properties of the gels,this paper wants to induce a further interest in finding a proper method to synthesize the porous silica gels for low price use.

RHEOLOGICAL MODIFICATION OF EPOXY RESINS WITH NANO SILICA PREPARED BY THE SOL-GEL PROCESS

Nano silica-modified epoxy resins were synthesized by the sol-gel process, The materials have the morphological structure of nano particales dispersed in the epoxy matrix. The dispersed phase formed a physical network in the resin and thus influenced the rheological behavior greatly. However, the nano silica did not show a significant influence on the mechanical properties of the cured resins.

Preparation of Scratch-Resistant Nano-Porous Silica Films Derived by Sol-Gel Process and Their Anti-reflective Properties

Structural strengthening of the nano porous silica films has been reported. The films were prepared with a base/acid two-step catalyzed TEOS-based sol-gel processing and dip-coating, and then baked in the mixed gas of ammonia and water vapor. The silica films were characterized with TEM, AFM, FTIR, spectrophotometer, ellipsometer, and abrasion test, respectively. The experimental results have shown that the films have a nanostructure with a low refractive index and can form an excellent scratch-resistant broadband anti-reflectance. The two-step catalysis noticeably strengthens the films, and the mixed gas treatment further improves mechanical strength of the silica network. Finally the strengthening mechanism has been discussed.

Sol-Gel Preparation of Zn2 SiO4 :Mn Phosphor Layers on Silica Spheres and Their Luminescent Properties

The synthesis and luminescence properties of Zn2 SiO4: Mn phosphor layers on spherical silica spheres, i.e.,a kind of core-shell complex phosphor, Zn2SiO4: Mn@ SiO2 were described.Firstly, monodisperse silica spheres were obtained via the Stober method by the hydrolysis of tetraethoxysilane(TEOS) Si ( OC2H5 ) 4 under base condition ( using NH4 OH as the catalyst).Secondly, the silica spheres were coated with a Zn2 SiO4: Mn phosphor layer by a Pechini solgel process.X-ray diffraction ( XRD), scanning electron microscope ( SEM), energy-dispersive X-ray spectrum ( EDS )and photoluminescence (PL) were employed to characterize the resulting complex phosphor.The results confirm that1000 ℃ annealed sample consists of crystalline Zn2SiO4: Mn shells and amorphous SiO2 cores.The phosphor show the green emission of Mn2+ at 521 nm corresponding 4T1 (4G) - 6 A1 (6S) transition, and the possible luminescence mechanism is proposed.

Sol-gel Synthesis and Photoluminescence of InP Nanocrystals Embedded in Silica Glasses

III-Vsemiconductor nanocrystals rarely exist as spherical inclusions inside glasses, due to difficulties during their preparation, such as high toxic reagents or fast oxidation under usual glass technology temperatures. In this article a sol-gel method for synthesis of InP nanocrystals embedded in silica glasses was described. Gels were synthesized by hydrolysis of a complex solution of Si(OC 2 H 5 ) 4 , InCl 3 4H 2 O and PO(OC 2 H 5 ) 3 . Then, the gels were heated at 600 o C in the presence of H 2 gas to form fine cubic InP crystallites. Raman spectrum showed InP longitudinal-optic mode (342cm -1 ) and transverse-optic mode (303cm -1 ). The size of InP nanocrystals was found to be from 2 to 8 nm in diameter by transmission electron microscopy. A strong photoluminescence with peaks at, 606, 730nm 856 nm was observed from 3InP/100SiO 2 nanocompositions. The temperature-and excitation power-dependent PL spectra from the nanocomposition are measured in order to confirm the origin of the PL spectra. These behaviors of the three peaks emissions suggest that 606, 733, and 856 nm emissions do not have the same origin. The PL with peak at 856nm arise from the cubic InP nanocrystallites embedded in the SiO 2 gel glasses. The 605 and 732 nm emissions may arise from the SiO 2 gel glass matrix or the interface between the InP crystallite core and SiO2 glass matrix.

Study and Characterization of Organically Modified Silica-Zirconia Anti-Graffiti Coatings Obtained by Sol-Gel

In this work, it is presented the synthesis and characterization of transparent and colorless organic-inorganic hybrid anti-graffiti protective materials obtained by sol-gel method. This type of materials is based on MTES （methyltriethoxysilane）, TPOZ （tetrapropoxide of zirconium） and PDMS （polydimethylsiloxane）. The synthesis has been carried out at 25, 35 and 45 ℃ in order to evaluate the role of temperature in the structure, microstructure and anti-graffiti behavior as well. The incorporation of zirconium within the organic modified silica network, of sols after being gelled and dried, is evident by a shoulder which increased with temperature situated at 950 cml （Si-O-Zr bonds）, and it is homogenously dispersed inside the matrix avoiding the formation of large ZrO2 precipitates. As the temperature increases, the hydrolysis and condensation reactions occur in more extension and thus, the obtained sols are more cross-linked and present more Si-O-Zr linkages. The promising anti-graffiti beha＇4ior of the protectNe hybrids was qualitatively determined being the spot removal higher than 90%.

Facile and Controlled Synthesis of Silica Sol Nanospheres Through a Modifi ed Sol-Gel Process

An effective and reproducible preparation of silica sol nanospheres via a modified sol-gel process has been described. Monodisperse and stable silica sol nanospheres with uniformsize were successfully obtained through the optimized synthesis in which the mixture of tetraethyl orthosilicate （TEOS） and ethanol was followed by the addition of water and ammonium hydroxide （NH3） separately, and the size of silica sol spheres was strictly controlled in the range of 25-119 nm with a narrow size distribution by fine adjustment of several reaction parameters. Results showed that in the presence of low concentration of TEOS, spheres size rose first and reached maximum when H2O concentration was up to 66 g/L. However, the diameter of silica sol spheres decreased above 66 g/L of H2O concentration. Furthermore, it was also found that the size and size distribution of silica sol nanospheres were affected by NH3 concentration. As NH3 concentration increased from 15 to 35 g/L, the diameter declined from 83 to 64 nm. Nevertheless, higher NH3 concentration would result in relatively broad size distribution, and gelation occurred when NH3 concentration reached 44 g/L. In addition, the effect of the different feed rates ofNH3 on the size growth of silica sol nanospheres was also discussed.

Immobilization of Functionalized Ionic Liquid on Sol-Gel Derived Silica for Efficient Removal of H_2S

An innovative approach to H2 S capture has been developed using several metal-based ionic liquids([Bmim]Cl·CuCl_2, [Bmim]Cl·FeCl_3, [Bmim]Cl·ZnCl_2, [Bmim]Br·CuCl_2, and [Bmim]Br·FeCl_3) immobilized on the sol-gel derived silica, which is superior to purely viscous ionic liquid with a crucial limit of high temperature, low mass transfer rate,and mass loss. The adsorbents were characterized by the Fourier transform infrared spectrometer, transmission electron microscope, N_2 adsorption/desorption, X-ray photoelectron spectroscopy, and thermal analysis techniques. The effects of the metal and halogen in IL, the loading amount of IL, and the adsorption temperature were studied by dynamic adsorption experiments at a gas flow rate of 100 mL/min. The H2 S adsorption results have showed that the optimal adsorbent and adsorption temperature are 5% [Bmim]Cl·CuCl_2/silica gel and 20—50 ℃, respectively. H_2 S can be captured and oxidized to elemental sulfur, and [Bmim]Cl·CuCl_2/silica gel can be readily regenerated by air. The excellent efficiency of H2 S removal may be attributed to the formation of nano-scaled and high-concentration [Bmim]Cl·CuCl_2 confined in silica gel, indicating that the immobilization of [Bmim]Cl·CuCl_2 on the sol-gel derived silica can be used for H2 S removal promisingly.

In-Situ Synthesis of Terbium Complex with Salicylic Acid in Silica Matrix by a Two-Step Sol-Gel Process

A process for in situ synthesis of terbium complex with salicylic acid by a two-step solgel method in silica matrix has been proposed. The luminescence properties of the silica gelscodoped with terbium and salicylic acid have also been discussed with respect to that of the geldoped with terbium and that of pure terbium complex with salicylic acid.

Formation of macroporous gel morphology by phase separation in the silica sol-gel system containing nonionic surfactant

The phase separation and gel formation behavior in an alkoxy-derived silica sol-gel system containing C16EO15 has been investigated. Various gel morphologies similar to other sol-gel systems containing organic additives were obtained by changing the preparation conditions. Micrometer-range interconnected porous gels were obtained by freezing transitional structures of phase separation in the sol-gel process. The dependence of the resulting gel morphology on several important reaction parameters such as the starting composition, reaction temperature and acid catalyst concentration was studied in detail. The experimental results indicate that the gel morphology is mainly determined by the time relation between the onset of phase separation and gel formation.

Preparation and Characterization of Silica and Clay-Silica Core-Shell Nanoparticles Using Sol-Gel Method

Silica and montmorillonite-supported silica nanoparticles were prepared via an acid one step sol-gel process. The synthesized solids were characterized using XRD, FTIR, TEM and N2 adsorption. The effect of preparing temperatures on the structure and properties of the silica nanoparticles were studied. The results show that the increase of annealing temperature from 25 to 200℃, don’t change amorphous state of silica. While for montmorillonite-supported silica the clay platelets are delaminated during the sol-gel process. TEM results showed that the average particle size of silica is increased by increasing temperature due to the particle sintering and the clay-silica nanoparticles possessed core–shell morphology with diameter of 29 nm. The surface area measurements showed that by increasing annealing temperature the surface area was decreased due to aggregation of particle. The clay-silica sample showed lower average pore width than that of the silica prepared at 200℃ indicating that it has a macropores structure. The adsorption efficiency of the prepared samples was tested by adsorption of protoporphyrin IX. The highest adsorption efficiency was found for SiO2 prepared at 200℃. Temkin model describe the equilibrium of adsorption of protoporphyrin IX on caly-silica nanoparticles under different conditions.

Mesoporous Silica Materials Synthesized via Sol-Gel Methods Modified with Ionic Liquid and Surfactant Molecules

Mesoporous silica materials were synthesized via a sol-gel method employing a room temperature ionic liquid （1-butyl-3-methylimidazolium tetrafiuoroborate, [bmim][BF4]） as a new solvent medium and further modified with surfactant （hexadecyl-trimethyl-ammonium bromide, CTAB） as a pore templating material. The synthesized samples were characterized by the transmission electron microscopy, X-ray diffraction, and N2 adsorption-desorption techniques. The results indicated that the mesoporous silica synthesized by using [bmim][BF4] and CTAB as mixed templates showed better mesostructural order and smaller pore size, compared with mesoporous silica materials synthesized by using single [bmim][BF4] as template under the same conditions. This indicates that the presence of surfactant can affect the microstructures of silica prepared by＇the present synthesis method.

Preparation and luminescence properties of europium complex with α-naphthylacetic acid incorporated in silica matrix by sol-gel method

Europium ternary complex of Eu(NNA) 3(NNA=α-naphthylacetic acid) was embedded in silica matrix at different ratios by sol-gel method. The luminescence properties of silica composites were studied by comparing them with those of corresponding pure complex by means of excitation, emission spectra and lifetimes. The fluorescence lifetime was prolonged when the pure complex was incorporated in silica matrix. The relative fluorescence intensity and fluorescence lifetimes increased simultaneously with the increase of (Eu(NNA) 3.)

Sol-Gel Synthesis and Luminescent Characteristic of Doped Eu~ 3+ Silicate-Silica Phosphor

Eu-doped silicate complex gel nano-particles was obtained by sol-gel process and characterized with TEM, XRD, PL, etc. The well dispersed particles have particle size about 60 - 70 nm with specific surface area 98.3 m^2· g^- 1 The complex gel phosphor gives a broad and strong luminescent emission originating from Eu^2＋ ions centered at 425 nm. The emission band shifts to shorter wavelengths with the increase of the ion radius of the alkali earth metals, but the band becomes red-shifted gradually with the increase of the ion radius of the alkali metals（except Li ^＋ ）. These divalent Eu^2＋ ions originate in inequivalent substitution of the alkaline earth ions. The presence of alkaline ions is favorable for the increasing emission intensity of the Eu^2 ＋ and lowering crystalline temperature of the silicate complex gel.

Sol-Gel Processing of Silica Nuclear Waste Glasses

A complex Sol-Gel process has been used for synthesis of silica glasses designed to contain high-level nuclear wastes. Cs, Sr, Co, and Nd (generically denoted Me) were used, the last as surrogate for actinides. Gels in the form of powders and sintered compacts were prepared by hydrolysis and polycondensation of tetraethoxide/Me nitrate solutions, which contained ascorbic acid as a catalyst. Thermal treatment studies were conducted on the resulting gels. Transformation to final products was studied by thermogravimetric analysis, infrared spectroscopy, and X-ray diffraction. Preliminary testing of Me leaching was also completed in quiescent water. Only a single dense form was resistant to

Influence of pH on the Property of Apatite-type Lanthanum Silicates Prepared by Sol-gel Process

The apatite-type lanthanum silicates with formula La9.33Si6O26 are prepared by sol-gel process. The homogeneity of the sol affected by pH value of the solution is investigated. The viscosity of the sols slightly increases first and then increases abruptly because the predominant reaction mechanism changes from hydrolysis reaction to condensation reaction. In addition, the onset time of the increase for the viscosity shortens from pH 1 to pH 4. The gelation time decreases with increasing pH of the solution. Therefore, the pH of the sols should be less than 4 to form gel. The sol with initial pH 2 shows maximum value of zeta potential and maximum stability. For the sample with initial pH 2, pure apatite-type lanthanum silicates La9.33Si6O26 have been successfully prepared after the dried gel is calcined at 1 000 ℃. In addition, this sample sintered at 1 550 ℃ exhibits the highest ionic conductivity. The activation energies are all less than 0.90 eV.

Sol-Gel Silica Matrix as Reservoir for Controlled Release of Paracetamol: Characterization and Kinetic Analysis

Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) are usually suitable candidates for the development of drug delivery devices. Sol-gel chemistry represents an easy method to obtain porous silica nanoparticles. Mesoporous silica nanomaterials have been widely used for drug delivery purposes. In this work we synthesized silica based materials using two molar alkoxide:water ratios 1:4 and 1:8, incorporating paracetamol to develop a nano-sized matrix for controlled release purposes. The samples exhibited different values for surface area, porosity, particle size and distinct punctual defects. Infrared and UV-visible spectroscopic studies were carried out to demonstrate the effect of water concentration and the adequate incorporation of paracetamol molecules. Nitrogen adsorption characterization was realized and the estimated BET surface values were from 532 to 825 m2/g. Kinetic analysis of drug release profiles was performed using the hyperbola model. Transmission electron micrographs showed that all the materials formed aggregates of small particles with size between 10 - 60 nm. Mesoporous SiO2 materials were proved to be a suitable system for controlled release of paracetamol.

Preparation and characterization of silica microcapsules containing butyl-stearate via sol-gel method

For thermal energy storage application in energy-saving building materials,silica microcapsules containing phase change material were prepared using sol-gel method in O/W emulsion system. In the system droplets in microns are formed by emulsifying an organic phase consisting of butyl-stearate as core material. The silica shell was formed via hydrolysis and condensation from tetraethyl silicate with acetate as catalyst. The SEM photographs show the particles possess spherical morphology and core-shell structure. The as-prepared silica microcapsules mainly consist of microsphere in the diameter of 3-7 μm and the median diameter of these microcapsules equals to 5.2 μm. The differential scanning calorimetry(DSC) curves indicate that the latent heat and the melting point of microcapsules are 86 J/g and 22.6 ℃,respectively. The results of DSC and TG further testify the microcapsules with core-shell structure.

Effect of Catalyst on the Formation of Silica Coating on Nickel Substrate by Sol-Gel Processing

In this research work silica coating was produced on nickel substrates by a sol-gel process. In order to increase the rate of hydrolysis and to reduce the rate of polymerization several acid catalysts including nitric acid-hydrochloric acid, acetic acid, hydrochloric acid and nitric acid were add to silica sol. Conversely, in order to control the rate of hydrolysis and to increase the rate of polymerization, basic catalyst of ammonia and ammonia hydroxyl were introduced in to the solution. Nickel specimens of known surface roughness were chemically cleaned and prepared by dipping in the sols. In order to produce a suitable silica coating the drying and firing cycles were optimized on these substrates. The structure and uniformity of the coatings produced were examined by scanning electron microscopy. Coatings composition was determined using glow discharge optical spectroscopy and EDAX microanalysis. Experimental result showed that hydrochloric acid, acetic acid, ammonia and acetic acid - ammonia are suitable catalytic agents for silica coating formation on nickel type substrate.