Molar Ratio Of Tetraethoxysilane Research Articles

Glycerol valorization through production of di-glyceryl butyl ether with sulfonic acid functionalized KIT-6 catalyst

In this work, the etherification of glycerol with n-butanol catalyzed by sulfonic acid functionalized on KIT-6 mesoporous silica (SO3H-KIT-6) was investigated for the production of valuable fuel additives. The SO3H-KIT-6 catalyst was synthesized by co-condensation with different molar ratios of tetraethoxysilane and 3-mercaptopropyl(methyl)di-methoxy silane. The etherification reaction was systematically examined to determine the optimal reaction temperature, reaction time, catalyst loading, and glycerol to n-butanol ratio under autogenous pressure. The maximum glycerol conversion and di-glyceryl n-butyl ether (di-GNBE) selectivity were 59.09 and 51.50%, respectively, when the SO3H-KIT-6 catalyst with the highest acidity was applied. Interestingly, the presence of a methyl group on the catalyst surface prevented glycerol adsorption during the reaction process, leading to the inhibition of undesired product formation. The SO3H-KIT-6 catalyst could be reused up to three times, with only a 13% decrease in glycerol conversion being found. Moreover, the superior performance of the SO3H-KIT-6 catalyst for di-GNBE production was also demonstrated compared with conventional solid acid catalysts including HZSM-5, H-beta zeolite, Amberlyst-35, and Amberlyst-36.

Comparative studies of Laser induced plasma in TEOS and MTMS based aerogels and solid quartz

Abstract:The interaction of laser radiation with low density aerogels is of crucial importance in areas such as the creation of coherent radiation sources in the X-ray range, simulation of astrophysical as well as nuclear fusion phenomena in laboratory and fundamental studies of the properties of soft condensed matter under dynamic pressure in the Mbar range. In the present paper, the experimental results on the X-ray emission of laser induced plasma in TEOS based, MTMS based aerogels and solid quartz targets, are reported. The aerogels were produced by the sol-gel processing of tetraethoxysilane (TEOS) and methyltrimethoxysilane (MTMS) followed by supercritical drying. Silica alcogels were produced using 0.001 M oxalic acid (C2H4O4), 0.5 M ammonium hydroxide (NH4OH) catalysts. Different densities of aerogels varying from 0.02 to 0.06 g/cm3 have been obtained using different molar ratios of TEOS, MTMS, ethanol and catalysts. The laser, with intensity up to 2 x 1014 W/m2, interaction with TEOS and MTMS based aerogels have been conducted using 30J/500 ps Nd : glass laser system. The resulting soft (0.8 – 1.56 Kev) and hard (>4 Kev) X-ray emissions have been measured using semiconductor photodiodes. It has been observed that the soft X-ray yield increases by a factor of two for the silica aerogel targets compared to the X-ray emission from the solid quartz target, whereas the hard X-ray yield reduces. The enhanced soft X-ray yield in silica aerogel targets is attributed to the large volume heating.

Development of hydrophobic and optically transparent monolithic silica aerogels for window panel applications

In the present paper, highly transparent, monolithic and hydrophobic silica aerogel monoliths were prepared by using tetraethoxysilane (TEOS) as precursor and methyltriethoxysilane (MTES) as co-precursor with different MTES/TEOS molar ratios (M) by two-step acid–base catalyzed sol–gel process followed by supercritical alcohol drying. The molar ratio of TEOS, ethanol (EtOH), water (0.001 M oxalic acid catalyst) and ammonium hydroxide (1 M NH4OH) was kept constant at 1:5:3.5:3.5 respectively, while the molar ratio of MTES/TEOS (M) was varied from 0 to 0.75. It has been observed that as the M value increases, the gelation time increases. It has been found that lower (0.25) M values resulted in highly transparent (optical transmission >90 % for a 10 mm thick sample at 700 nm wavelength) and negligible volume shrinkage ( 10 % volume shrinkage but excellent hydrophobicity. A good compromise of acceptable optical transmittance (~87 % optical transmission at 700 nm wavelength for a 10 mm thick sample) with negligible volume shrinkage (6 %) were obtained at M = 0.50. The hydrophobicity of the aerogels was tested by measuring the contact angle between a water droplet and silica aerogel surface. The hydrophobicity was confirmed by Fourier transform infra-red spectroscopy and contact angle measurements. the aerogels have been characterized by percentage of volume shrinkage, optical transmittance, scanning electron microscopy, thermal conductivity measurements and thermogravimetric analysis and differential thermal analysis.

Preparation of ordered and oriented mesoporous silica thin films bearing octyl or hexadecyl groups by electrochemically assisted self-assembly and evaluation of their transport properties

Well-organized octyl- and hexadecyl-functionalized mesoporous silica thin films are generated onto indium-tin oxide electrodes by combining the electrochemically assisted self-assembly technique and the sol–gel co-condensation route. The electrodeposition is carried out under potential control from mixtures containing various molar ratios of tetraethoxysilane and octyltrimethoxysilane (O-TES) or hexadecyltrimethoxysilane (HD-TES), using cetyltrimethylammonium bromide as surfactant template. Films with hexagonally packed functionalized mesochannels oriented perpendicular to the underlying support are obtained up to, respectively, 20 % O-TES and 5 % HD-TES introduced in the starting sol. Electrochemical investigations using various redox probes demonstrate that the films remain porous despite the presence of long carbon chains inside the mesochannels and that, in the presence of such long chain alkyl groups, the physical diffusion through the pores is not sufficient to describe the mass transport issues, which can also imply accumulation effects owing to the hydrophobic character of the medium.

Synthesis and characterization of SiO2–CrO3, SiO2–MoO3, and SiO2–WO3 mixed oxides produced using the non-hydrolytic sol–gel process

Silica-based mixed oxide xerogels, namely SiO2–CrO3, SiO2–MoO3, and SiO2–WO3, were prepared using the non-hydrolytic sol–gel process. The materials were synthesized using metal chloride:tetraethoxysilane (TEOS) molar ratios of 0.1:2; 0.2:2 and 0.4:2 for each metal chloride and 1:2 SiCl4:TEOS molar ratio. All of the xerogels containing Cr, Mo or W had considerably greater surface areas than that of SiO2. The small angle X-ray scattering experiments suggest that the surface roughness of the aggregates in SiO2–CrO3 is less than that of SiO2–MoO3 and SiO2–WO3. The morphological characteristics of the silica-based mixed oxide xerogels were not affected by the nature and amount of metal chloride employed in the synthesis. An irregular morphology was observed for SiO2–CrO3, SiO2–MoO3 and SiO2–WO3, but a lamellar structure was observed for SiO2. X-ray photoelectron spectroscopy analysis suggests that tungsten species were preferentially distributed on the outmost part of the grain. The resulting particle diameter was shown to be lower for the mixed oxides compared to that of bare silica. Furthermore, the presence of metals (Cr, Mo and W) on silica caused a decrease in the size of the particles as the atomic radii of these metals increased. According to the Fourier transform infrared spectroscopy and Raman, Cr, Mo and W were incorporated within the silica framework.

Preparation and Characterization of Transparent Hydrophilic Photocatalytic TiO2/SiO2 Thin Films on Polycarbonate

Transparent hydrophilic photocatalytic TiO2 coatings have been widely applied to endow the surfaces self-cleaning properties. A mixed metal oxide (TiO2/SiO2) can enhance the photocatalytic performance improving the ability of surface adsorption and increasing the amount of hydroxyl surface groups. The present work introduces a systematic study concerning the effect of the SiO2 addition to TiO2 films on the wettability, the photocatalytic activity, the adhesion strength, and the mechanical stability of the films. Transparent hydrophilic photocatalytic TiO2/SiO2 thin films were used to coat the polycarbonate (PC) substrate which was precoated by an intermediate SiO2 layer. The TiO2/SiO2 thin film was prepared employing a bulk TiO2 powder (Sachtleben Hombikat UV 100) and different molar ratios of tetraethoxysilane in acidic ethanol. A dip-coating process was used to deposit the films onto the polycarbonate substrate. The films were characterized by UV/vis spectrophotometry, FTIR spectroscopy, ellipsometry, BET, AFM, XRD, and water contact angle measurements. The mechanical stability and the UV resistance were examined. The photocatalytic activity of the coated surface was calculated from the kinetic analysis of methylene blue photodegradation measurements and compared with the photocatalytic activity of Pilkington Activ sheet glass. The coated surfaces displayed considerable photocatalytic activity and superhydrophilicity after exposure to UV light. The addition of SiO2 results in an improvement of the photocatalytic activity of the TiO2 film reaching the highest value at molar ratio TiO2/SiO2 equal to 1:0.9. The prepared films exhibit a good stability against UV(A) irradiation.

Effect of acid-catalyzed sol-gel silica coating on the properties of cotton fabric

Silica sols, used as carriers to incorporate functional ingredients into textiles for obtaining desired functions, could also affect the properties of textiles. Thus, the effects of silica content, coating composition, and coating processes on the mechanical properties, wicking effect, water vapor transmission (WVT), moisture desorption, and handle of the coated cotton fabric were examined. The results indicated that coating cotton fabric using the tetraethoxysilane (TEOS)-derived silica sol with weak acidity was advantageous to the improvement of the tensile strength, especially at a higher curing temperature or longer curing time. Tearing strength, wicking height, and WVT rate of the coated cotton fabric all reduced in relation to the uncoated one, especially at a higher curing temperature, or longer curing time, or higher silica content, whereas the addition of (3-glycidyloxypropyl)-trimethoxysilane (GPTMS) weakened the negative effect, especially at lower molar ratios of TEOS to GPTMS. Bending length of the coated cotton fabric increased, especially at higher curing temperatures, or longer curing time, or higher silica content, whereas the addition of GPTMS reduced the negative effect, especially at lower molar ratios of TEOS to GPTMS. The moisture desorption rate of the coated cotton fabric decreased, especially at lower curing temperatures, or shorter curing time, or lower silica content, but the addition of GPTMS in this case did not have a remarkable effect.

Self-cleaning silica coatings on glass by single step sol–gel route

Considerable efforts have been made over the last few decades for developing self-cleaning surfaces exhibiting high water contact angles. We prepared TEOS based hydrophobic, self-cleaning silica coatings on a glass substrate by single step sol–gel process with methyltrimethoxysilane (MTMS) as a co-precursor. The coating sol was prepared by keeping the molar ratio of tetraethoxysilane (TEOS), methanol (MeOH) and water (H 2O) constant at 1:33.15:6.06 respectively, throughout the experiments with NH 4F (0.1 M) as a catalyst. The molar ratio (M) of the MTMS/TEOS was varied from 0 to 7.84 and its influence on the hydrophobicity was studied by static contact angle and sliding angle measurements. It was observed that, with increase in the M value from 0 to 1.57, the contact angle increased from 30° to 135°, respectively and with further increase in M value, the contact angle reduced and remained nearly constant thereafter. For coatings prepared with M values 0.78, 1.18 and 1.57, petal effect (water sticking) was observed. The sliding angle for the coatings was reduced with further increase in M values, leading to self-cleaning surface. The hydrophobicity of the silica coatings was sustained up to a temperature of 270 °C and the optical transmission observed was above 80%. The silica coatings were characterized by surface roughness measurement, field emission scanning electron microscopy (FESEM), Fourier transform infrared (FTIR) spectroscopy, percentage of optical transmission, self-cleaning test and static contact angle and sliding angle measurements.

Effect of Different Reaction Solvents on the Hydrophobic and Structural Properties of Silica Cryogels

The experimental results on the microstructural and physical properties of the TEOS-based silica cryogels have been reported. The cryogels were produced by two-step sol-gel process followed by vacuum freeze drying. The wet gels were synthesized via acid-base catalysis using tetraethoxysilane (TEOS) as a silica precursor, the different solvents containing ethanol (EtOH), methanol (MeOH) and tert-butanol (TBA), the molar ratio of TEOS / solvent were varied from 1:6 to 1:13. Further, the microstructure and specific surface area of the cryogels were analysed by Scanning Electron Microscopy (SEM) and nitrogen absorption/desorption isotherms. The hydrophobicity of the cryogels was studied by contact angle. It was found that the highest specific surface area (1040.17 m2 / g) was obtained with the solvent of MeOH. The lowest density (0.074 g/cm3) was acquired with the solvent of EtOH.

Transparent water repellent silica films by sol–gel process

Non-wettable surfaces with high contact angles and facile sliding angle of water droplets have received tremendous attention in recent years. The present paper describes the room temperature (∼27 °C) synthesis of dip coated water repellent silica coatings on glass substrates using iso-butyltrimethoxysilane (iso-BTMS) as a co-precursor. Emphasis is given to the influence of the hydrophobic reagent (iso-BTMS) on the water repellent properties of the silica films. Silica sol was prepared by keeping the molar ratio of tetraethoxysilane (TEOS) precursor, methanol (MeOH) solvent, water (H 2O) constant at 1:16.53:8.26 respectively, with 0.01 M NH 4F throughout the experiment and the molar ratio of iso-BTMS/TEOS ( M) was varied from 0 to 0.965. The effect of M on the surface structure and hydrophobicity has been researched. The static water contact angle values of the silica films increased from 65° to 140° and water sliding angle values decreased from 42° to 16° with an increase in the M value from 0 to 0.965. The water repellent silica films are thermally stable up to a temperature of 280 °C and above this temperature the film shows hydrophilic behavior. The water repellent silica films were characterized by the Fourier Transform Infrared (FT-IR) Spectroscopy, Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), % of optical transmission, thermal and chemical aging tests, humidity tests, static and dynamic water contact angle measurements.

Structural and magnetic properties of γ- and ε-Fe 2O 3 nanoparticles dispersed in silica matrix

Fabrication of composite materials by in situ generation of γ- and ε-Fe 2O 3 nanoparticles in a SiO 2 matrix through sol–gel process is reported. The process involves the hydrolysis and condensation of 1:3:10: x ( x = 0.05, 0.1 and 0.2) molar ratios of tetraethoxysilane, absolute ethanol, nitric acid (0.16 N) and ferric nitrate, respectively, and subsequent thermal-treatment at temperatures ranging from 110 to 1000 °C. The in situ generation and growth of γ- and ε-Fe 2O 3 nanoparticles, and their distribution in SiO 2 matrix strongly depend on the concentration of Fe 3+ ions and thermal-treatment temperatures. The restricted growth of Fe 2O 3 in SiO 2 matrix seems to stabilize the metastable ε-Fe 2O 3 phase and prevent the formation of α-Fe 2O 3 even at 1000 °C. Further, the presence of Fe 2O 3 nanoparticles in SiO 2 matrix modified the gel morphology on thermal-treatment, leading to strong structural and chemical changes which influence the magnetic properties to a large extent. The concentration of individual magnetic phase (γ- and ε-Fe 2O 3) in the samples, the particle size and distribution, and thermal-treatment temperature determine the net magnetic moment, shape of the hysteresis loop (symmetric or concentric), coercivity and magnetic phase transition.

Porous superhydrophobic silica films by sol–gel process

Wettability of solid surfaces is a crucial concern in our daily life as well as in engineering and science. The present research work describes the room temperature synthesis of adherent and porous superhydrophobic silica films on glass substrates using methyltriethoxysilane (MTES) as hydrophobic reagent by sol–gel process. The coating sol was prepared by keeping the molar ratio of tetraethoxysilane (TEOS), methanol (MeOH), water (H 2O) constant at 1:22.09:6.25, respectively, with 0.01 M NH 4F catalyst throughout the experiments and the MTES/TEOS molar ratio ( M) was varied from 0 to 0.43. The static water contact angle as high as 160° and water sliding angle as low as 3° was obtained for silica film prepared from M = 0.43. The surface morphological study showed the porous structure with pore sizes ranging from 250 to 300 nm. The superhydrophobic silica films retained their superhydrophobicity up to a temperature of 290 °C and above this temperature the films became superhydrophilic. The prepared silica films were characterized by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), Fourier Transform Infrared (FT-IR) spectroscopy, percentage of optical transmission, humidity test and static and dynamic water contact angle measurements.

Ultrahydrophobic silica films by sol–gel process

Wettability of solid surfaces is a crucial concern in our daily life as well as in engineering and science. The present research work describes the room temperature (27 °C) synthesis of adherent and water repellent silica films on glass substrates using vinyltrimethoxysilane (VTMS) as a hydrophobic reagent by a single step sol–gel process. The silica sol was prepared by keeping the molar ratio of tetraethoxysilane (TEOS), methanol (MeOH), water (H2O) constant at 1:14.69:5, respectively, with 0.01 M NH4F throughout the experiments and the VTMS/TEOS molar ratio (M) was varied from 0 to 0.97. The effects of M on the surface structure and hydrophobicity have been researched. The static water contact angle as high as 144° and water sliding angle as low as 14° was obtained for silica film prepared from M = 0.97. The hydrophobic silica films retained their hydrophobicity up to a temperature of 255 °C and above this temperature the films became superhydrophilic. The prepared silica films were characterized by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), Fourier Transform Infrared (FT-IR) spectroscopy, humidity test and static and dynamic water contact angle measurements.

Superhydrophobic silica films by sol–gel co-precursor method

Wetting phenomena of water droplets on solid are of crucial concern in our daily life as well as in engineering and science. The present paper describes the room temperature synthesis of superhydrophobic silica films on glass substrates using trimethylethoxysilane (TMES) as a co-precursor. The coating sol was prepared by keeping the molar ratio of tetraethoxysilane (TEOS) precursor, methanol (MeOH) solvent, water (H 2O) constant at 1:38.6:8.68, respectively, with 2 M NH 4OH throughout the experiments and the TMES/TEOS molar ratio ( M) was varied from 0 to 1.1. It was found that with an increase in M value, the hydrophobicity of the films increased, however the optical transmission decreased from 88% to 82% in the visible range. The hydrophobic silica films retained their hydrophobicity up to a temperature of 275 °C and above this temperature the films became superhydrophilic. The hydrophobic silica films were characterized by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), Fourier Transform Infrared (FT-IR) spectroscopy, percentage of optical transmission, humidity test and static and dynamic contact angle measurements.

Influence of the molar ratio of tetraethoxysilane and glycidoxypropyltriethoxysilane on the properties of anhydride-cured epoxy-siloxane composites

The topological structure of epoxy-siloxane composites prepared by anhydride curing was studied in relation to the molar ratio of glycidoxypropyltriethoxysilane and tetraethoxysilane and to the total content of siloxane components of the system. The optical characteristics, glass transition point, sol fraction yield, concentration of internodal chains, and maximal rate of oxygen uptake by the hybrid materials were determined.

Silica Films Having Zigzag Mesoporous Structures with Fixed Kink Angles

Mesoporous silica films with a highly controlled unique zigzag porous structure are prepared on a rubbing-treated polyimide film. The honeycomb-packed tubular pores in the films have two distinct in-plane alignment directions with respect to the rubbing direction; that is, the films have an in-plane zigzag mesoporous structure with a fixed kink angle. The kink angle is controllable by the molar ratio of tetraethoxysilane as a silica source to surfactant in the reactant solution, and the increase of the ratio results in larger kink angles. The zigzag structure is found to be formed through the formation of an initial immature mesostructured film with uniaxially aligned rodlike surfactant assemblies. It is highly probable that the observed in-plane bending of the pores is caused by the translational shift of the positions of the adsorbed surfactant molecules along the polyimide chains on the surface and that the shift is caused by the steric effects between the adjacent hydrophilic components consisting of surfactant head groups and silica oligomers. The present results show that a unique nanoscale structure, which can hardly be obtained through a reaction under homogeneous conditions, can be formed under the heterogeneous conditions in which the reaction takes place within a restricted environment.

Electrical Insulating and Heat-Resistive Properties of PDMS-TEOS Hybrid with Different Molar Ratio of TEOS to PDMS

The hybrids prepared from polydimethylsiloxane (PDMS) and tetraethoxysilane (TEOS) have been well known to be rubbery hybrid materials. In this report, the authors have investigated the electrical insulating and heat resistive properties of the hybrids by changing the molar ratio of TEOS to PDMS. The electrical insulating properties are evaluated by volume resistivity and AC breakdown strength at room temperature. The resistivity is about 1013 Ω · m and AC breakdown strength is about 25 kV/mm irrespective of the molar ratio. Heat-resistive properties are evaluated by the weight loss after keeping for 480 h at 200°C in air. The weight loss becomes smaller as the TEOS content increases, and it is less than 3%. It has been clarified that the hybrids have good electrical insulating and heat-resistive properties.

Two step sol-gel processing of TEOS based hydrophobic silica aerogels using trimethylethoxysilane as a co-precursor

The experimental results on the surface modification of tetraethoxysilane (TEOS) based silica aerogels using trimethylethoxysilane (TMES) as a co-precursor by two step sol-gel process are reported. The molar ratio of MeOH/TEOS was fixed at 17 and TMES/TEOS ratio was varied from 0.38 to 1.14. The concentration and quantity of acidic water (oxalic acid) added in the first step and base water (ammonium hydroxide) in the second step were also varied. The best quality superhydrophobic aerogels could be obtained with only distilled water (without any acid catalyst) in the first stage and the basic water in the second step of the sol-gel process. The molar ratio of TEOS: TMES: MeOH: distilled water: basic water was optimized at 1:0.86:17:4.9:4.9, respectively. The surface modification has been confirmed from the Fourier transform infrared spectroscopy measurements while the hydrophobicity was quantified in terms of the contact angle measurements. The TMES/TEOS based aerogel powder could be used to transport micro-liters of water in the form of water marbles. The aerogels have been characterized by the bulk density, porosity, thermal conductivity, contact angle measurements and the transmission electron microscopy (TEM).

Surfactant-assisted synthesis of helical silica

Amorphous helical silica was synthesized at room temperature from tetraethoxysilane (TEOS) under the presence of cetyltrimethylammonium bromide (CTAB) in acidic conditions. The formation conditions of the silica helices were studied carefully. It was found that the reaction time and temperature, molar ratio of TEOS and CTAB and types of acids are crucial to the formation of helices.

In Vitro Bioactivity of Bi-Structured Nano-Hybrids in the CaO-SiO<sub>2</sub>-PTMO System

Synthetic model of a large transparent crack-free monolithic ceramic-polymer hybrid, which was synthesized using triethoxysilane end-capped poly(tetramethylene oxide) (Si-PTMO) and tetraethoxysilane (TEOS), was examined in the CaO-SiO2-PTMO sol-gel system. Bulk precursor with nominal mass ratio of PTMO: TEOS = 80: 20 and surface precursor with nominal molar ratio of TEOS: Ca(NO3)2 = 1: 0.3 were subjected to hybridization through hydrolysis and condensation process, producing a bi-structured hybrid in which polymeric bulk was molecular hybridized with bioactive silicate surface. Spectroscopic and microscopic characterizations revealed that the surface of hybrid was typical bioactive silicate. In vitro study using a simulated body fluid (SBF) revealed that the hybrid formed an apatite on its surface within 6 hours in SBF, suggesting bioactive materials with high capability of tissue integration as well as polymeric physical properties.