SiO2 Precursor Research Articles

Biological influence of Ca/P ratio on calcium phosphate coatings by sol-gel processing

The objective of this work has been to develop low temperature sol-gel glass coatings to modify the substrate surface and to evaluate their bioactivity and biocompatibility. Glasses, based on SiO2·CaO·P2O5, were synthesized by the sol-gel technique using tetraethyl orthosilicate, calcium nitrate tetrahydrate and triethyl phosphate as precursors of SiO2, CaO and P2O5, respectively. Those materials, still in the sol phase, have been used to coat substrates by means of the dip-coating technique. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) has been used for characterize coatings and a microstructural analysis has been obtained using scanning electron microscopy (SEM). The potential applications of the coatings in the biomedical field were evaluated by bioactivity and biocompatibility tests. The coated substrate was immersed in simulated body fluid (SBF) for 21days and the hydroxyapatite deposition on its surface was subsequently evaluated via SEM-EDXS analysis, as an index of bone-bonding capability. In order to study the cell behavior and response to our silica based materials, prepared via the sol-gel method, with various Ca/P ratio and coating substrate, we have used the human osteoblast-like U2OS cell line.

Carbon nanofibers–SiO2 composites: Preparation and characterization

A method has been developed for preparing carbon fibers–SiO2 composites using oligomethylhydridesiloxane (OMHS) as the precursor for SiO2. The presence of active hydrogen in OMHS made it possible to attain chemical interaction between the surface of carbon nanofibers (CNFs) and the applied silicon oxide layer. The oxidation rate of CNF–SiO2 composite is found to be lower by about one order of magnitude compared to that of the as-synthesized CNF. The thermal stability of CNF–SiO2 composites has been studied. Under an inert atmosphere, CNF–SiO2 composite has thermal stability up to 1300°C. At temperatures above 1350°C, silicon carbide (SiC) fibers are formed as a result of the carbothermal reduction of silicon oxide.

Persistent Luminescent Non-Doped Layered Nanosilicate

Layered Silicates (LS) such as hectorite clays have been used as host matrices for optically functional species due to their tunable structure. Luminescence has been reported for different phosphors using LS as a host host intercalated with rare earth containing compounds. However, the LS composition has OH- ions which may result in severe luminescence quenching. In the present work, a new LS material based on the hectorite structure was synthesized by replacing OH- with F-. This LS produced without doping strong blue/green emission. Also persistent luminescence was observed for this material with the main emission lifetime about 321 ms. It is the first time that such kind of luminescence has been reported for trioctahedral smectites. The origin of the luminescence was proved to be a Ti3+ impurity - originally as TiIV in the SiO2 precursor. Both conventional and persistent luminescence mechanisms were suggested for this “non-doped” system.

Progammed synthesis of magnetic mesoporous silica coated carbon nanotubes for organic pollutant adsorption

Magnetic mesoporous silica coated carbon nanotubes were produced from hydrophilic monodisperse magnetic nanoparticles decorated carbon nanotubes using well controlled programmed synthesis method and were characterized by TEM, XRD, FTIR, TGA, N2 adsorption–desorption and VSM. The well-designed mesoporous magnetic nanotubes had a large specific area, a highly open mesoporous structure and high magnetization. Firstly, SiO2-coated maghemite/CNTs nanoparticles (CNTs/Fe3O4@SiO2 composites) were synthesized by the combination of high temperature decomposition process and an sol–gel method, in which the iron acetylacetonate as well as TEOS acted as the precursor for maghemite and SiO2, respectively. The CNTs/Fe3O4@SiO2 composites revealed a core–shell structure, Then, CNTs/Fe3O4@mSiO2 was obtained by extracting cetyltrimethylammonium bromide (CTAB) via an ion-exchange procedure. The resulting composites show not only a magnetic response to an externally applied magnetic field, but also can be a good adsorbent for the organic pollutant in the ambient temperature.

Synthesis, structural, spectroscopic and thermoanalytical study of sol–gel derived SiO2–CaO–P2O5 gel and ceramic materials

In the present work bioactive powders of the ternary SiO2·CaO·P2O5 systems, which differ in the Ca/P molar ratio, were synthesized by means of a sol–gel route, using tetraethyl orthosilicate (TEOS, Si(OC2H5)4), calcium nitrate tetrahydrate (Ca(NO3)2·4H2O) and triethyl phosphate (TEP, OP(OC2H5)3) as precursors of SiO2, CaO and P2O5, respectively. In order to investigate the influence of the relative amount of each phase (in this study: SiO2, CaO and P2O5) the thermal properties of the synthesized gel-glass materials were studied as a function of the Ca/P molar ratio using thermogravimetric and differential thermal analysis (TG/DTA). After dehydration (in a single step), described from a kinetic point of view as a simple water evaporation without rupture of chemical bonds, all gels undergo a complex multi-step decomposition with endo and exothermic effects, followed by crystallization of calcium silicate phases at about 950°C. Furthermore, Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD) and Scanning Electron Microscopy, coupled with energy dispersive spectroscopy (SEM/EDS), allowed us to detect the chemical modifications induced by modifying the Ca/P molar ratio and the sintering. This process is obtained by thermal treatment of the gel-glass precursors after analyzing their thermal behavior in the temperature range 600–1000°C, with the aim to convert them into ceramic powders, suitable for their applications. The results revealed that when temperature is up to 900°C, crystallization occurs and pseudowollastonite and wollastonite were formed. Finally, the amount of pseudowollastonite decreased with increasing the sintering temperature, while that of wollastonite increased.

Effect of pore lengths on the reduction degree and lithium storage performance of Mesoporous SiOx nanomaterials

Mesoporous SiOx nanomaterials are regarded as promising lithium storage materials due to the unique architecture consisting of ultrasmall Si nanocrystals in mesoporous SiO2 matrix where the oxygen content plays a paramount role in the lithium storage performance. Different from previous works on the extrinsic reduction conditions of SiO2 precursors, this work investigates the effect of inner structures on the reduction degree and performances for the first time. Mesoporous SBA-15 rods with tunable pore lengths are prepared as precursors for SiOx. It is found that the O/Si atomic ratios decrease from 1.31 to 0.73 as the pore lengths reduce from 3 to 0.5 μm. With the shortest pore length, SiO0.73 nanorods exhibit the best lithium storage performance. Moreover, SiO0.73 nanorods are further modified by carbon nanolayers and present a remarkably improved performance (595 mAh g−1 after 60 cycles). This study can help us further understand the role of pore lengths on the reduction degree of SiO2 and enlighten us on adopting advanced SiO2 precursors with preferable inner structures.

The structural studies of aluminosilicate gels and thin films synthesized by the sol-gel method using different Al2O3 and SiO2 precursors

AbstractAluminosilicate materials were obtained by sol-gel method, using different Al2O3 and SiO2 precursors in order to prepare sols based on water and organic solvents. As SiO2 precursors, Aerosil 200TM and tetraethoxysilane TEOS: Si(OC2H5)4 were applied, while DisperalTM and aluminium secondary butoxide ATSB: Al(OC4H9)3 were used for Al2O3 ones. Bulk samples were obtained by heating gels at 500 °C, 850 °C and at 1150 °C in air, while thin films were synthesized on carbon, steel and alundum (representing porous ceramics) substrates by the dip coating method. Thin films were annealed in air (steel and alundum) and in argon (carbon) at different temperatures, depending on the substrate type. The samples were synthesized as gels and coatings of the composition corresponding the that of 3Al2O3·2SiO2 mullite because of the specific valuable properties of this material. The structure of the annealed bulk samples and coatings was studied by FT-IR spectroscopy and XRD method (in standard and GID configurations). Additionally, the electron microscopy (SEM) together with EDS microanalysis were applied to describe the morphology and the chemical composition of thin films. The analysis of FT-IR spectra and X-ray diffraction patterns of bulk samples revealed the presence of γ-Al2O3 and δ-Al2O3 phases, together with the small amount of SiO2 in the particulate samples. This observation was confirmed by the bands due to vibrations of Al–O bonds occurring in γ-Al2O3 and δ-Al2O3 structures, in the range of 400 to 900 cm−1. The same phases (γ-Al2O3 and δ-Al2O) were observed in the deposited coatings, but the presence of particulate ones strongly depended on the type of Al2O3 and SiO2 precursor and on the heat treatment temperature. All thin films contained considerable amounts of amorphous phase.

Combined influence of titania and silica precursors on the properties of thin film humidity sensing elements prepared via a sol–gel method

The present work deals with the comparative investigations of the combined influence of precursors of TiO2 and SiO2: Tetrabutyl orthotitanate, Tetraethoxysilane and (3-Glycidyloxypropyl)trimethoxysilane in the presence of Ce-ions on the properties of the respective thin film humidity sensing elements prepared via a sol–gel method and sintered at 400°C. SEM, EDX and XRD analyses of the obtained samples have been carried out to study their surface morphology and structural composition. The electrical characteristics and parameters of the samples have been investigated by means of an impedance analyzer. It has been established that the type and proportions of the precursors substantially affect the structure of the films obtained and their humidity sensing properties. The combination of both types of precursors of TiO2 and SiO2 in all cases results in an enhancement of the sensor elements’ response to humidity compared to the use of only one of these precursors. The change in resistance of the samples reaches about four orders of magnitude within the range from 15 to 93% relative humidity at a frequency of 20Hz and at 25°C.

Effect of the carbon nanomaterials structure on silica carbothermal reduction

“Carbon nanomaterial-SiO2” composites were synthesized using carbon nanofibers (CNF) and carbon nanotubes (CNT). Oligomethylhydridesiloxane (OMHS) was used as the SiO2 precursor. The CNT–SiO2 composite was shown to be thermally stable up to 1100–1200°C. The calcination temperature increase to 1300°C resulted in segregation of the CNT–SiO2 composite into individual components: CNT and SiO2 particles. In distinction to CNT+SiO2, the CNF–SiO2 system showed stronger interaction of the amorphous silica film with the end faces of graphite terminating at the external surface of CNF. Calcination of the CNF–SiO2 composite in an inert atmosphere at 1300°C for 1h did not lead to segregation of the components. Calcination of the CNF–SiO2 composite in an argon flow at 1400°C for 1h changed the phase composition of the sample. Silicon diffused to the interplane layers of graphite. In addition, the formation of silicon carbide was observed.

Sol–gel synthesised WO3 nanoparticles supported on mesoporous silica for liquid phase nitration of aromatics

A series of WO3/SiO2 catalysts have been prepared by sol-gel method using ammonium metatungstate and ethyl silicate-40 (ES-40) as WO3 and SiO2 precursors respectively. The sol-gel method has led to the formation of WO3 nano-particles of 2–5nm well dispersed on mesoporous silica along with some WO3 agglomerates. Formation of monoclinic WO3 was seen on the catalysts above 5wt% WO3 loading by XRD analysis. Silica has shown very high surface area of 606m2/g which decreased gradually upto 368m2/g with 20wt% WO3 loading. 20wt% WO3/SiO2 catalyst has shown maximum acidity (0.56mmol NH3/g) with presence of both Lewis and Brønsted acidity. UV–vis DRS analysis showed formation of polytungstate species along with WO3 on silica surface. The prepared catalysts were used for liquid phase nitration of aromatics using 70% nitric acid as nitrating agent without using any sulfuric acid. Very high conversion (99%) was obtained for p-cresol nitration with very high selectivity (99%) for 2-nitro p-cresol. The water formed during the reaction was removed azeotropically using ethylene dichloride as solvent. In case of o-xylene 74% conversion was obtained with 54% selectivity for 4-nitro o-xylene. The effect of different WO3 precursors on nitration efficiency was studied using sodium tungstate and tungstic acid as precursors. However,ammonium metatungstate showed the highest acidity. Sodium tungstate showed formation of dimer of sodium tungstate which did not show any acidity and hence no activity for nitration. The mechanism for nitration using WO3/SiO2 has been proposed based on polarisation of water on tungsten centre generating Brønsted acidity which can further generate nitronium ion giving subsequently nitration of the aromatic ring.

Synthesis of Al–MgAl2O4 Master Alloy and its Grain Refinement Studies in Pure Aluminium

The effect of ultrasonic treatment (UT) on the synthesis of Al–MgAl2O4 master alloy has been studied by the reaction of SiO2 precursor with Al-2wt% Mg. The results show that SiO2 reaction is enhanced after UT and the corresponding mechanism is proposed. Grain refinement studies in pure Al showed that an increase in addition level of MgAl2O4 particles resulted in two to threefold reduction in grain size; whereas, UT intensified the grain size reduction by 11–12 fold. Significant grain refinement on UT is attributed to the cavitation enhanced wetting which activates MgAl2O4 particles as potent nucleating site for Al.

Enhanced thermal properties of novel shape-stabilized PEG composite phase change materials with radial mesoporous silica sphere for thermal energy storage.

Radial mesoporous silica (RMS) sphere was tailor-made for further applications in producing shape-stabilized composite phase change materials (ss-CPCMs) through a facile self-assembly process using CTAB as the main template and TEOS as SiO2 precursor. Novel ss-CPCMs composed of polyethylene glycol (PEG) and RMS were prepared through vacuum impregnating method. Various techniques were employed to characterize the structural and thermal properties of the ss-CPCMs. The DSC results indicated that the PEG/RMS ss-CPCM was a promising candidate for building thermal energy storage applications due to its large latent heat, suitable phase change temperature, good thermal reliability, as well as the excellent chemical compatibility and thermal stability. Importantly, the possible formation mechanisms of both RMS sphere and PEG/RMS composite have also been proposed. The results also indicated that the properties of the PEG/RMS ss-CPCMs are influenced by the adsorption limitation of the PEG molecule from RMS sphere with mesoporous structure and the effect of RMS, as the impurities, on the perfect crystallization of PEG.

In-situ synthesis, structural, magnetic and in vitro analysis of α-Fe2O3–SiO2 binary oxides for applications in hyperthermia

The present study aims at the development of α-Fe2O3–SiO2 (hematite–silica) binary oxides for hyperthermia applications. An in situ sol–gel process was attempted to synthesis five different α-Fe2O3–SiO2 composites in which the varied concentrations of SiO2 precursors were added to the constant Fe2O3 precursor. The characterization studies confirmed the formation of α-Fe2O3 phase at 1000°C. Heat treatments at 1200°C resulted in the formation of c-SiO2 along with the presence of α-Fe2O3 phase. The magnetic studies ensured the ferromagnetic behavior of the system, but with a decreasing trend with increasing SiO2 content. The heating ability of the system was also assessed under an AC magnetic field using an induction heating instrument. The results obtained from hemolytic activity and cytotoxity test warranted the system׳s compatibility in vitro conditions.

Synthesis of Hybrid Fe<sub>3</sub>O<sub>4</sub>–Silica–M(Zn, Cu, Ni) Submicrospheres and its Application for Adsorption on Bovine Hemoglobin

Magnetic metal silica submicrospheres were produced from silica coated on magnetic nanoparticles using well controlled hydrothermalled method and were characterized by TEM, XRD, FTIR, XPS. The well-designed mesoporous magnetic metal silciate had a large specific area, high magnetization. Firstly, SiO2-coated maghemite (Fe3O4@SiO2 composites) were synthesized by an sol-gel method, in which the iron ferrous chloride as well as TEOS acted as the precursor for maghemite and SiO2, respectively. The Fe3O4@SiO2 composites revealed a core-shell structure, Then, Fe3O4@SiO2/X3Si2O5(OH)4(X = Ni, Cu, Zn) was obtained by hydrothermalled with metal chloride. The resulting composites show not only a magnetic response to an externally applied magnetic field, but also can be a good adsorbent for bovine hemoglobin in the ambient temperature.

Silver nanoparticles embedded mesoporous SiO2 nanosphere: an effective anticandidal agent against Candida albicans 077

Candida albicans is a diploid fungus that causes common infections such as denture stomatitis, thrush, urinary tract infections, etc. Immunocompromised patients can become severely infected by this fungus. Development of an effective anticandidal agent against this pathogenic fungus, therefore, will be very useful for practical application. In this work, Ag-embedded mesoporous silica nanoparticles (mSiO2@AgNPs) have successfully been synthesized and their anticandidal activities against C. albicans have been studied. The mSiO2@AgNPs nanoparticles (d ∼ 400 nm) were designed using pre-synthesized Ag nanoparticles and tetraethyl orthosilicate (TEOS) as a precursor for SiO2 in the presence of cetyltrimethyl ammonium bromide (CTAB) as an easily removable soft template. A simple, cost-effective, and environmentally friendly approach has been adopted to synthesize silver (Ag) nanoparticles using silver nitrate and leaf extract of Azadirachta indica. The mesopores, with size-equivalent diameter of the micelles (d = 4–6 nm), were generated on the SiO2 surface by calcination after removal of the CTAB template. The morphology and surface structure of mSiO2@AgNPs were characterized through x-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), particle size analysis (PSA), atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), Brunauer–Emmett–Teller (BET) and high-resolution transmission electron microscopy (HRTEM). The HRTEM micrograph reveals the well-ordered mesoporous structure of the SiO2 sphere. The antifungal activities of mSiO2@AgNPs on the C. albicans cell have been studied through microscopy and are seen to increase with increasing dose of mSiO2@AgNPs, suggesting mSiO2@AgNPs to be a potential antifungal agent for C. albicans 077.

Facile synthesis of macroporous Li4SiO4 with remarkably enhanced CO2 adsorption kinetics

Lithium orthosilicate (Li4SiO4) has attracted extensive scientific attention due to its large CO2 adsorption capacity at high temperature (650–700°C) and low material cost. However, the conventional nonporous Li4SiO4 ceramic shows very poor CO2 adsorption performance below 600°C, which is a relevant condition for possible applications such as sorption-enhanced steam methane reforming. In the present work, in order to increase the CO2 adsorption kinetics below 600°C, Li4SiO4 was synthesized in the form of a macroporous structure by a simple solid-state transformation method using LiOH and fumed silica as a precursor for Li and SiO2, respectively. The use of LiOH substantially decreased the synthesis temperature of Li4SiO4 down to 600°C, compared with the conventional syntheses using other lithium precursors such as Li2CO3 and LiNO3 that require very high synthesis temperature (>700°C). The decrease of the material synthesis temperature circumvents undesirable sintering of initially formed small Li4SiO4 crystallites and leads to the formation of a highly macroporous (macropore volume >0.6mLg−1) Li4SiO4 framework that has a significantly higher BET surface area (15m2g−1) than conventional nonporous Li4SiO4 (<1.0m2g−1). The macroporous Li4SiO4 exhibited dramatically enhanced CO2 adsorption capacity (29.8wt%) and rate (56.1mgg−1min−1), compared with the CO2 adsorption capacities (1.40–7.79wt%) and rates (0.420–2.95mgg−1min−1) of nonporous Li4SiO4 materials. Adsorption–desorption cycles at 550°C could be repeated 10 times without a significant decrease in the adsorption capacity or the rate capability.

Influence of base inhibitor and surfactant on the electrical and physicochemical properties of PEDOT-SiO2 hybrid conductive films

This paper describes the synthesis of poly(3,4-ethylenedioxythiophene)-SiO2 hybrid conductive films possessing superior mechanical properties and improved opto-electrical properties. A mixture of a 3,4-ethylenedioxythiophene (EDOT) monomer and an optimized amount of a tetraethyl orthosilicate (TEOS) SiO2 precursor was co-vaporized and synchronously polymerized on a ferric p-toluenesulfonate (FTS)-coated poly-(ethylene terephthalate) (PET) substrate. The opto-electrical properties of the mechanically robust PEDOT-SiO2 hybrid films were improved by adding a poly(ethylene glycol)-poly(propylene glycol)-poly(ethylene glycol) (PEG-PPG-PEG) triblock copolymer surfactant and an imidazole base inhibitor to the FTS oxidant solution. These two additives served to control polymerization and prohibit crystallization, resulting in conductive thin films with smooth and homogeneous morphologies. Additionally, the additives improved the physicochemical properties of the films, as determined by their pencil hardness, solvent resistance, and scratch resistance. Finally, these additives yielded hybrid thin films that showed good electrical and optical stability over time. Open image in new window

Effect of Different TiO2-SiO2 Multilayer Coatings Applied by Sol-Gel Method on Antireflective Property

Multilayer thin films prepared using the sol-gel process have been used in many antireflection applications. In this paper, antireflective nanoscale multilayer TiO2-SiO2 coatings were formed on both sides of the glass substrates by combining sol-gel method and dip coating techniques. The coatings were carried out using tetraethyl orthosilicate as precursor for SiO2 and tetrabutyl orthotitanate as precursor for TiO2. The coatings prepared in this work were characterized using scanning electron microscope, Fourier-transformed infrared spectrophotometer and UV-Visible spectrophotometer. The SiO2 top layer coatings showed excellent antireflection in the wavelength range of 400-800 nm where the transmittance of glass substrate is significantly lower. By increasing the number of double TiO2-SiO2 layers, the transmission of the coated glasses increased due to applied multilayer coating properties. Six-layer sol-gel TiO2-SiO2 coatings showed the highest visible transmittance about 99.25% at the band of 550-650 nm.

Enhancing power conversion efficiency of DSSC by doping SiO2 in TiO2 photo anodes

A simple, less time consuming, cost ineffective sol–gel method was used to synthesis TiO2 nanoparticles (TiO2) and TiO2–SiO2 nanocomposites (TiO2–SiO2) using titanium tetra isopropoxide as TiO2 and silicic acid as SiO2 precursors respectively. The synthesized nanocomposites were characterized by XRD, SEM, TEM, UV–visible, FTIR and BET analysis. The quantum confinement effect of TiO2 and TiO2–SiO2 was confirmed by a blueshift observed in UV–visible spectra. The band observed at 950cm−1 in FTIR analysis confirmed the presence of Ti–O–Si bonds, the TEM analysis shows both the TiO2 and TiO2–SiO2 were in nanometer size. The BET (Brunauer– Emmett–Teller) specific surface areas of the samples were 65 and 75m2/g for TiO2 and TiO2–SiO2 respectively. The power conversion efficiency (PCE) of the nanocomposites were studied by using Keithely electrometer and multimeter and it was found to be 2% and 2.5% for eosin-Y sensitized TiO2 and TiO2–SiO2 nanocomposites respectively.

Synthesis of “Silica – Carbon Nanotubes” Composite and Investigation of its Properties

A new method for synthesis of CNT-SiO2 composite was developed. Oligomethylhydridesiloxane (OMHS) was used as the SiO2 precursor. The presence&lt;br /&gt;of active hydrogen in the composition of OMHS made it possible to obtain chemical&lt;br /&gt;interaction between the surface of carbon nanotubes and the deposited silica layer. The effect of the silica film on the CNT oxidizing ability was studied. It was found that the oxidation rate of the CNT-SiO2 composite decreases approximately by an order of magnitude in comparison with as-prepared CNT. The morphology and&lt;br /&gt;structure of amorphous silica obtained after oxidation of the CNT-SiO2 composite&lt;br /&gt;were studied. The thermal stability of the CNT-SiO2 composite was also studied. The CNT-SiO2 composite was found to be thermally stable up to temperatures of 1100-1200 ºC. An increase in the calcination temperature to 1300 ºC leads to segregation of the CNT-SiO2 composite into individual components: CNT and SiO2 particles.