Two-step Sol Gel Research Articles

APS-silane modification of silica nanoparticles: effect of treatment’s variables on the grafting content and colloidal stability of the nanoparticles

Silica nanoparticles, Aerosil 200, with an average primary particle size of 12 nm were chemically modified by γ-aminopropyltriethoxy silane (APS) via a two-step sol–gel process. Effects of the treatment variables including reaction temperature, water content, and silane concentration on the colloidal stability and the amount of APS grafting on the surface of nanoparticles were studied using thermal gravimetric analysis, diffuse reflectance infrared spectroscopy, and by monitoring the sedimentation behavior of the dispersion of nanoparticles in distilled water as a polar media. Furthermore, the effect of surface modification on the dispersibility of silica nanoparticles in an epoxy novolac coating was evaluated by means of scanning electron microscopy. The results showed chemical interactions between APS and SiO2 nanoparticles. Also, parameters including treatment at ambient temperature, low level of water, and moderate concentration of silane compound, have a considerable effect on the APS grafting content due to the increase of silane hydrolysis and higher silylation coverage of the nanoparticles.

Investigating the role of a Schiff-base ligand in the characteristics of TiO2 nano-particles: Particle size, optical properties, and photo-voltaic performance of dye-sensitised solar cells

A Schiff base ligand was employed to synthesise TiO2 nano-particles by a two-step sol–gel method. The effect of the ligand on purity, particle size, optical properties and photo-voltaic performance of dye-sensitised solar cells was investigated. Various concentrations of the ligand were applied and each sample was characterised. Changing the ligand content had an effective role on the optical and photo-voltaic properties of the final product. The obtained products were characterised through powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectra, energy-dispersive X-ray spectrometry and ultraviolet–visible spectroscopy.

Room temperature ferromagnetism and diamagnetism of Co-doped ZnO microspheres synthesized by sol–gel method

We have prepared Zn1−xCoxO (x=0%, 1%, 2%, 3% and 4%) microspheres via a two-step sol–gel method without grinding and investigated their composition, morphology and magnetic properties by means of X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer, respectively. The X-ray diffraction result demonstrates that Co has been successfully doped into hexagonal ZnO. The scanning electron microscope images of Zn0.98Co0.02O reveal an average particle size around 200nm, which is larger than that of as-prepared ZnO nanoparticles (60nm). Magnetic properties measurement indicates that room temperature ferromagnetism and diamagnetism were obtained in Co-doped ZnO at the same time.

Preparation of Ion Implanted Porous Silica Thin Film

The porous silica thin film was selected as thermal insulation thin film of uncooled infrared detector in order to reduce device thermal conduction loss. A new ion implantation manufacture method of porous silica thin film was studied in this paper. The porous silica thin films were prepared by ion implanted method and acid/alkali two-step catalytic sol-gel method respectively for comparison purpose. H+ and N+ ion mixing implantation technique adopted makes the gas bubble in the depth and shallow of silica thin film respectively, and one setting power can form porous structure with porous rate between 17% and 29%. By properly control the heat dealing process, gas bubble will format, expand, but not abrupt in the silica thin film. Sol-gel derived silica thin film has porous rate of 62.8%, but it cannot be used as substrate of electrode film and infrared thermal sensing film because of its irregular surface. The surface of ion implanted silica thin film is even and can be used as substrate, and its insulating performance could be further enhanced by etch off the thick silica substrate from back, after pyroelectric infrared sensing layer formed.

Facile preparation of transparent and dense CdS–silica gel glass nanocomposites for optical limiting applications

To realize their practical and operable applications as a potential optical limiting (OL) material, quantum dots (QDs) need to have good processability by incorporating them into optical-quality matrices. This work reports a facile route for the room-temperature preparation of large, stable transparent monolithic CdS nanocomposites which can be easily extended to allow the introduction of acid-sensitive functional molecules/nanoparticles into a silica network by sol-gel chemistry. Our strategy involves a two-step sol-gel process (acid-catalyst hydrolysis and basic-catalyst condensation) and the co-condensation of the resulting alkoxysilane-capped CdS QDs with other alkoxysilanes, which allows the CdS QDs to become part of the silica covalent network. The degradation and agglomeration of CdS QDs were thereby effectively restrained, and large monolithic transparent CdS-silica gel glass was obtained. Using Z-scan theory and the resulting open-aperture Z-scan curves, the nonlinear extinction coefficient of the CdS-silica nanocomposite gel glass was calculated to be 1.02 × 10(-14) cm W(-1), comparable to that of the parent CdS QD dispersion, indicating their promise for OL applications.

Preparation of SiO<sub>2</sub> Antireflective Film by a Base/Acid Two-Step Catalyzed Sol-Gel Process

SiO2 antireflective films were prepared by two-step catalyzed sol-gel method with TEOS as the raw materials, acid and ammonia as catalyst. Effects of the ratio of acid-catalyzed and base-catalyzed silica sols on the transmittance and stability of SiO2 film were investigated. The transmittance can be adjusted by change the ratio of base-catalyzed sols, and a higher transmittance can be obtained in the higher ratio of base-catalyzed coatings. A higher stability of SiO2 film in salt spray can be obtained in higher ratio of acid-catalyzed AR coatings. AR coatings with excellent transmittance and stability can be obtained by adjusting the ratio of acid/base catalyzed silica sols.

Yellow emission of SiO2/Zn2SiO4:Mn nanocomposite synthesized by sol–gel method

A two-step sol–gel process was used for the preparation of Mn doped β-Zn2SiO4 nanoparticles embedded in silica host matrix after the incorporation of ZnO:Mn nanoparticles in silica monolith. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to characterize the phase purity, particle size and morphology. XRD results indicate that pure phase of β-Zn2SiO4 with triclinic structure was obtained after thermal treatment at 1500°C. However, photoluminescence (PL) technique was investigated for optical study. It was illustrated that the Mn doping content influenced the degree of aggregation and luminescence of the nanocomposite. This manganese doped zinc silica phase in silica host matrix, exhibit yellow emission centred at about 575nm driven by 4T1 to 6A1 relaxation in Mn2+. The crystallinity and luminescent property of nanocomposite were investigated.

Electrochemical performance and stability of LiMn0.6Fe0.4PO4/C composite

Abstract Fe-substituted lithium manganese phosphate (LiMn0.6Fe0.4PO4/C), with a small particle size of 50 nm in diameter, is successfully prepared using a two-step sol–gel method. TEM analysis reveals that LiMn0.6Fe0.4PO4 particles are embedded in a porous carbon matrix, and carbon interconnected particles to form a secondary spherical-like morphology. The composite prepared in this study exhibits excellent electrochemical behavior in terms of specific capacities and rate cycling ability. Furthermore, the XPS spectral studies before and after aging test reflect the much lower surface reactivity of the LiMn0.6Fe0.4PO4/C towards 1.5 M LiPF6 solutions. And the results also reveal the good stability of electrolyte/carbon interface.

Synthesis of paramagnetic iron incorporated silica aerogels by ambient pressure drying

The iron incorporated silica aerogels were prepared under ambient pressure drying through a two-step sol-gel route by using tetraethoxysilane (TEOS), methyltriethoxysilane (MTES) and ferric nitrate as co-precursors, and hexamethyldisilazane (HMDZ) as a surface modification reagent. Compared with the silica aerogels modified by trimethylchlorosilane (TMCS) or HMDZ, the iron incorporated silica aerogels exhibited good integrity, paramagnetic behavior, and highly hydrophobicity which could be maintained up to 650 °C. However, the introduction of iron into silica aerogels resulted in more apparent volume shrinkage, higher density, lower porosity, and smaller pore diameter. It was found that a large amount of water was retained in the silica network, accordingly, the water containing iron oxides (Fe–OH) were more readily formed than water free iron oxides (Fe–O), which adversely affected the physical properties of iron incorporated silica aerogels.

Synthesis and characterization improvement of gradient density aerogels for hypervelocity particle capture through co-gelation of binary sols

In this paper, we reported the preparation technics and details of gradient density aerogels (GA) via continuous formation technics, and introduced an effective and facile method to analyze its physical properties and microstructure correctly, since these properties are density dependent. With tetramethoxysilane as precursor and two-step sol–gel process, high transparence and crack-free of GA were fabricated, the density ranges from 0.02 to 0.2 g/cm3. The linear shrinkage of GA increases continuously with density increases from top to bottom. Base on systematically analyze the formation mechanism of GA, the co-gelation of binary sols with different concentrations method was developed to prepare mixed aerogels, which possessed a similar internal skeleton structure compare with GA. The internal skeleton structure of these aerogels is cross-linked by distinct sizes silica particles from two concentrations of silica-sols. Four mixed aerogels corresponding to different density positions of GA (a—0.15, b—0.12, c—0.09, and d—0.05 g/cm3) were selected to test. X-ray phase contrast method was used to shown the density distribution of GA. BET observation, SEM analysis, and TEM study, DMA and UV–vis results shown that GA are with excellent performance in physical properties, such as high optical transmittance, and good mechanical strength, which are critical characteristics for practical applications of GA, particularly in capture particle areas, for easy observation and lossless capture.

Effect of Schiff base ligand on the size and the optical properties of TiO2 nanoparticles

The effect of a Schiff-base ligand (N,N′-ethylenebis(acetylacetone iminato)dianion=acacen) on size and optical properties of TiO2 nanoparticles in a two-step sol–gel method was investigated. Different amounts of Schiff-base ligand were applied and the as-prepared products were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectrum, Electron Dispersive X-ray spectroscopy (EDX) and ultraviolet–visible (UV–Vis) spectroscopy. Molecular orbital structure of acacen was calculated by density functional theory (DFT) in order to determine the exact orbital energies and electron transfer pathways. The results demonstrated that applying the appropriate amount of Schiff-base ligand could be effective in particle size control.

Effect of tertiary amines on the synthesis and photovoltaic properties of TiO2 nanoparticles in dye sensitized solar cells

Two different amines as complexing agents were used in a two-step sol–gel method to prepare TiO2 nanoparticles. The effect of amines on the size of the TiO2 nanocrystals and its influence on the performance of corresponding dye-sensitized solar cell (DSSC) were investigated. It is shown that using a tertiary long chained monoamine as a complexing agent is beneficial in two ways; one is producing the particles with smaller size and the other is slightly sticking the particles in order to have a film with higher reflectivity which both is beneficial to photovoltaic performance. The obtained products were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectra, and ultraviolet-visible (UV–vis) spectroscopy. The overall conversion efficiency of the long-chain-based DSSC (5.04%) appeared to be 45% higher than that obtained for the tertiary short-chain diamine.

Effect of silica nanoparticles surface treatment on in situ polymerization of styrene–butyl acrylate latex

In this study, silica nanoparticles were treated by γ-methacryloxypropyltrimethoxy silane (MPS), via a two-step sol–gel route. The effects of treatment conditions; such as: pH, time, silane and water amounts on the surface modification of silica nanoparticles were evaluated. MPS grafting on the surface of nanoparticles was characterized using FTIR, TGA and TEM techniques. The un-treated and MPS-treated silica nanoparticles were used for in situ preparation of silica/styrene:butyl acrylate latex nanocomposites. The synthesized latex samples were characterized using; FTIR, dynamic light scattering (DLS) and field emission-SEM (FESEM) techniques. Mechanical properties of nanocomposite latex samples were evaluated using DMTA and Taber abrasion test method.The results showed the chemical interactions between MPS and silica nanoparticles. The treatment conditions such as; silane and water contents, reaction time and pH, have significant effect on the MPS grafting of nanoparticles as a result of increase in the rate of silane hydrolysis. FTIR and DLS studies indicated successfully performing of in situ polymerization of silica/acrylate nanocomposites. The latex particles size was affected by inclusion of either un-treated or MPS-treated nanoparticles. The average diameter of latex containing MPS-treated nanoparticles (129nm) was larger than that of neat latex (98nm). The FESEM study revealed a better distribution of the treated nanoparticles compared with their untreated counterparts. Eventually, the results revealed that addition of either un-treated or MPS treated nanoparticles significantly enhanced mechanical properties of acrylate latex samples.

The Performance Investigation of BaFe<sub>12</sub>O<sub>19-</sub>ZnFe<sub>2</sub>O<sub>4</sub> which is a Composite Nano Powder

The nanoscale magnetic composite powders BaFe12O19-ZnFe2O4 were prepared by two-step citrate sol-gel, with analytically pure Fe(NO3)3、Zn(NO3)2 and Ba(NO3)2 as the main materials. The XRD, TEM and VSM were used to analyze the structure, feature and magnetic property of the nano-powder. The results show that the same presoma is calcined in 600°C、650°Cand 700°C obtained BaFe12O19-ZnFe2O4，XRD display for both pure phase, do not contain any mixed phase。The higher the temperature, the content of magnetoplumbite phase increased, corresponding the content of spinel phase low。By hysteresis loop of composite powde BaFe12O19- ZnFe2O4 can see, simple substance BaFe12O19 magnetoplumbite phase has the wasp waist shaped hysteresis loop，simple substance ZnFe2O4 spinel phase has superparamagnetism，but the nanoscale composite powders BaFe12O19-ZnFe2O4 has rectangular hysteresis loop。

Preparation of TiO2 nanoparticles by using tripodal tetraamine ligands as complexing agent via two-step sol–gel method and their application in dye-sensitized solar cells

The effect of different tripodal tetraamine ligands was investigated on the particle size, agglomeration level, optical and photovoltaic properties of TiO2 nanoparticle prepared via a two-step sol–gel method. The products were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron spectroscopy (TEM), scanning electron microscopy (SEM), and UV–vis spectroscopy. The results showed that the symmetry of ligands has a crucial effect on the size and agglomeration level of the products. The optical and photovoltaic properties of the products were studied, as well. The reflectivity property of the samples due to different agglomeration sizes is shown to be very important factor in increasing conversion efficiency of DSSC.

Optically transparent silica aerogels based on sodium silicate by a two step sol–gel process and ambient pressure drying

Interest in improving the optical transmission of sodium silicate-based aerogels by ambient pressure drying led to the synthesis of aerogels using a two-step sol–gel process. To produce optically transparent silica aerogel granules, NH4F (1 M) and HCl (4 M) were used as hydrolyzing and condensation catalysts, respectively. The silica aerogels were characterized by their bulk density, porosity (%), contact angle and thermal conductivity. Optical transmission of as synthesized aerogels was studied by comparing the photos of aerogel granules. Scanning electron microscopic study showed the presence of fractal structures in these aerogels. The degree of transparency in two step sol–gel process-based aerogels is higher than the conventional single step aerogels. The N2 adsorption–desorption analysis depicts that the two step sol–gel based aerogels have large surface areas. Optically transparent silica aerogels with a low density of ∼0.125 g/cc, low thermal conductivity of ∼0.128 W/mK and higher Brunauer, Emmett, and Teller surface area of ∼425 m2/g were obtained by using NH4F (1 M), HCl (4 M), and a molar ratio of Na2SiO3::H2O::trimethylchlorosilane of 1::146.67::9.46. The aerogels retained their hydrophobicity up to 500 °C.

Flexible hybrid aerogels prepared under subcritical conditions

A new flexible insulator was developed, consisting of a silica–latex-fiber nanocomposite aerogel that combines the lightness and insulating properties of silica aerogels with the mechanical properties of silica–latex hybrids and the flexibility of fibers. This was accomplished by coating selected insulating fibers (polyester and glass) with a silica–polymer hybrid aerogel, synthesized in situ by a two-step sol–gel process, consisting of the acidic co-hydrolysis of TEOS and trimethoxysilyl-grafted latex nanoparticles in excess water, followed by basic co-condensation. The hybrid coating has improved mechanical properties that allow its drying under subcritical conditions. The outstanding properties of the insulating blankets produced render them extremely attractive for high-technology applications, and, due to the low energy consumption process, they may even displace the commonly used mineral wool, by presenting a best value-for-money compromise.

Tat peptide-decorated gelatin-siloxane nanoparticles for delivery of CGRP transgene in treatment of cerebral vasospasm

BackgroundGene transfer using a nanoparticle vector is a promising new approach for the safe delivery of therapeutic genes in human disease. The Tat peptide-decorated gelatin-siloxane (Tat-GS) nanoparticle has been demonstrated to be biocompatible as a vector, and to have enhanced gene transfection efficiency compared with the commercial reagent. This study investigated whether intracisternal administration of Tat-GS nanoparticles carrying the calcitonin gene-related peptide (CGRP) gene can attenuate cerebral vasospasm and improve neurological outcomes in a rat model of subarachnoid hemorrhage.MethodA series of gelatin-siloxane nanoparticles with controlled size and surface charge was synthesized by a two-step sol-gel process, and then modified with the Tat peptide. The efficiency of Tat-GS nanoparticle-mediated gene transfer of pLXSN-CGRP was investigated in vitro using brain capillary endothelial cells and in vivo using a double-hemorrhage rat model. For in vivo analysis, we delivered Tat-GS nanoparticles encapsulating pLXSN-CGRP intracisternally using a double-hemorrhage rat model.ResultsIn vitro, Tat-GS nanoparticles encapsulating pLXSN-CGRP showed 1.71 times higher sustained CGRP expression in endothelial cells than gelatin-siloxane nanoparticles encapsulating pLXSN-CGRP, and 6.92 times higher CGRP expression than naked pLXSN-CGRP. However, there were no significant differences in pLXSN-CGRP entrapment efficiency and cellular uptake between the Tat-GS nanoparticles and gelatin-siloxane nanoparticles. On day 7 of the in vivo experiment, the data indicated better neurological outcomes and reduced vasospasm in the subarachnoid hemorrhage group that received Tat-GS nanoparticles encapsulating pLXSN-CGRP than in the group receiving Tat-GS nanoparticles encapsulating pLXSN alone because of enhanced vasodilatory CGRP expression in cerebrospinal fluid.ConclusionOverexpression of CGRP attenuated vasospasm and improved neurological outcomes in an experimental rat model of subarachnoid hemorrhage. Tat-GS nanoparticle-mediated CGRP gene delivery could be an innovative strategy for treatment of cerebral vasospasm after subarachnoid hemorrhage.

Sol–gel preparation of PTMS modified hydrophobic and transparent silica coatings

Wettability of solid surfaces is an important property, which depends on both the surface chemistry and surface roughness. The present paper describes the room temperature synthesis of dip coated water repellent silica coatings on glass substrates using phenyltrimethoxysilane (PTMS) as a co-precursor with two-step sol–gel process. Silica sol was prepared by keeping the molar ratio of tetraethylorthosilicate precursor, methanol solvent, acidic water (0.001 M oxalic acid) and basic water (12 M NH4OH) constant at 1:11.03:0.17:0.58 respectively, throughout the experiments and the PTMS weight percentage was varied from 0 to 15 %. It was found that with an increase in wt% of PTMS, the roughness and hydrophobicity of the films increased. However, the optical transmission decreased from 93 to 82 % in the visible range. The hydrophobic silica films retained their hydrophobicity up to a temperature of 386 °C and above this temperature the films became hydrophilic. The hydrophobic silica thin films were characterized by taking into consideration the surface roughness studies, Fourier transform infrared spectroscopy, percentage of optical transmission, scanning electron microscopy, thermogravimetric–differential thermal analysis and contact angle measurements.

Photovoltaic properties of corresponding dye sensitized solar cells: Effect of active sites of growth controller on TiO2 nanostructures

A two-step sol–gel method was applied to prepare TiO2 nanoparticles using two different primary amines as shape controller. The effect of active sites of amines on the shape of the TiO2 nanocrystals and its effect on the performance of dye-sensitized solar cells were investigated. The results showed that using the diaminodioxaoctane ligand results in well-dispersed 1D TiO2 nanostructures while the diaminooctane ligand gave rise to sheet-like structures. Photovoltaic measurements showed higher conversion efficiency when TiO2 films were prepared using the diaminodioxaoctane ligand (SDADO) than in the case of the diaminooctane ligand (SDAO) which is mainly due to the increased light scattering for SDADO.