In this study, stearic acid/silica phase change composites were prepared by the sol-gel method using stearic acid as phase change materials (PCMs). The effects of mass fraction of stearic acid were comprehensively investigated. The structures and thermal properties of the obtained composites were characterized by various methods, including scanning electron microscopy (SEM), differential scanning calorimetry (DSC), leakage tests, and thermogravimetry analysis (TG). The results indicated that composite containing 76% stearic acid had the best thermal properties and low mass leakage, making 76% stearic acid as the maximum content that silica matrix could protect in the composites. The latter was further confirmed by morphological analyses of the silica matrix. Silica matrix exhibited spherical particle clusters, following big–small–big–small size pattern as stearic acid rose. The composite with 76% stearic acid was at the key point of change in particle size. These findings look promising for future to prepare silica-based phase change composites with good thermal properties easily.
The behaviour of alginate gel film in response to the tensile load is analysed in this paper. The bubbles of 0.5?mm diameter were embedded in the film by the fluidic method prior to gelation, thus providing uniform voidage over the entire film. Further, the intrinsic porosity of the gel matrix around the voids was varied by removing water through either evaporation under vacuum, or employing lyophilisation. The Poisson’s ratio and the modulus of elasticity were estimated from direct measurements. The viscoelasticity of the gel matrix was characterized from stress-relaxation measurement. The transient response to tensile loading and the evolution of stress contours were studied through numerical simulation in ANSYS. The ultimate strength was studied for the gel films with embedded voids of different sizes. The numerical simulations were validated by experimental measurements.
Fiber needle felt–silica aerogel composite was successfully prepared by via sol–gel process based on water glass. The thermal conductivity show V-type variation tendency with the increase of water to Si. Thermogravimetric analysis-differential scanning calorimetry analysis revealed that the thermal stability was up to approximately 390.58?°C. It has been found that the fire hazard of the composites decreased with the increased ratio of water to Si according to the cone calorimeter test, which can be characterized by peak heat release rate, fire performance index, and fire growth rate index. The fiber needle felt/aerogels present greatly improved compressive and flexural strength (elastic modulus: 0.1–0.97?MPa; flexural modulus: 0.33–0.66?MPa) while keeping inherent properties of pure silica aerogel: low bulk density (0.166?g/cm3), low thermal conductivity of 0.0236?W/m·K, and high specific surface area (1091.62?m2/g). As a result, the as-prepared composite shows a great potential to be applied in the thermal insulation field.
Bismuth ferrite (BiFeO3) nanopowder have been successfully synthesized for the first time via a microwave-assisted sol-gel combustion method by using citric acid as fuel. The resulting nanopowder was characterized using FT-IR, TG-DTA, XRD, EDX, VSM, SEM, and UV-Vis DRS. A ferromagnetic hysteresis loop with a saturation magnetization (MS) of 0.66?emu?g?1 has been observed at room temperature in the sample. The optical properties of the nanosized BiFeO3 showed its small band gap (=2.08?eV) indicates a possibility of utilizing much visible light for photocatalysis.
Systematic studies of silica gels with covalently immobilized thiosemicarbazide and formazan groups under the conditions of competitive sorption from multicomponent systems were conducted. A methodological approach to determine the selectivity of the modified sorption material with regard to Cu(II), Ni(II), Co(II), Cd(II), and Zn(II) was proposed. Solid-phase extraction in equilibrium conditions of Cu(II), Zn(II), Co(II), Cd(II), and Ni(II) on a silica gel with covalently immobilized thiosemicarbazide and formazan groups in the conditions of competitive sorption was studied. The possibility to use the pseudo-second-order kinetic equation for assessment of mutual influence at competitive sorption has been shown. We found that sorption from multicomponent solutions proceeds as a non-additive process under the conditions of an excess of functional groups.
The mesoporous silica samples with different concentrations of phosphonic acid groups on the surface were obtained by direct template synthesis. The block-copolymer Pluronic P123 was used as a template, and sodium meta-silicate with diethylphosphatoethyltriethoxysilane as precursors. According to the SAXS diffractograms, mesoporous silica samples have a p6mm hexagonal symmetry. In addition, we used sol–gel method to synthesize xerogel with the same groups for comparison. All samples possess high values of specific surface area 615–730?m2/g and sorption pore volume. FTIR and potentiometric titration methods were used to investigate the surface layer of these samples. Sorption properties of the samples with phosphonic acid groups were studied in respect to a row of metal cations, among which we focused on lead(II), cadmium(II), and dysprosium(III) cations.
Nano noble metal coating on surface patterned mesoporous semiconductor thin film can play an important role in enhancing visible light harvesting efficiency (LHE) towards improvement in photoelectrochemical (PEC) activity of the material. In this work, one-dimensional (1D) and two-dimensional (2D) mesoscale surface patterns have been created on sol–gel-based titanium tin oxide (TSO) nanostructured thin film on pure silica/indium tin oxide-coated glass by soft lithography. The TSO film matrix is observed to be mesoporous and semicrystalline as evidenced from the structural characterization by transmission electron microscopy and measurement of atmospheric ellipso-porosimetry, respectively. The 2D patterned film exhibits maximum LHE value in visible wavelength region. Further film surface modification has been carried out by depositing nano Au coating onto the bare patterned TSO films by a low temperature solution technique. Under visible light, a significant improvement in PEC activity is found and the gold-coated patterned 2D film shows higher visible LHE as well as >2.7 times higher photocurrent density than bare 2D film. This facile fabrication strategy can create an avenue toward improvement in LHE vis-à-vis the PEC activity of mesoporous mixed metal oxide semiconductor thin film.
Two series of TiO2 thin films were prepared based on soluble precursor powders: The first run originated directly from an alcohol-based coating solution whereas for the second batch the aqueous precursor powder sol had previously undergone a hydrothermal treatment. The respective microstructures were characterized by electron microscopy, the phase evolution was monitored by X-ray diffraction. Ellipsometric porosimetry (EP) was employed to reveal changes of porosity and pore size induced by thermal treatment of the films.
Soluble TiO2 precursor powders were hydrothermally treated to yield coating solutions. Films from these sols were compared with those directly obtained by dissolving the precursor powders. Results indicate that crystallization to anatase is induced under hydrothermal conditions and the resulting films mostly maintain their porosity throughout thermal treatment. In contrast to that coatings processed from as-dissolved precursor powders undergo more extensive densification
In this study, a specific technique was used to quickly, easily, and single step, synthesize core-shell magnetite-silica nanoparticles by controlling the reaction conditions using the proper surfactant. In the first step, the magnetite nanoparticles were prepared by co-precipitation method and silica shell was immediately formed by the sol-gel process. Synthesis was performed at 80?°C with stirring at 12,000?rpm in an alkaline medium. The structural and morphological characteristics of core-shell nanoparticles were examined by XRD, TEM, SEM, and BET analyses. In addition, vibrating sample magnetometer (VSM) was used to evaluate the magnetic characteristics. XRD analysis confirmed the existence of both magnetite and silica phases in the final structure. TEM images showed the presence of nanocomposite particles with core-shell structure of 25?nm diameter. The mean core and shell size were estimated to be about 20 and 2.5?nm, respectively. A study of the magnetic characteristics showed super-paramagnetic behavior with 60?emu/g saturation magnetization (Ms). Due to the high ratio of core size to shell thickness, the magnetic saturation for the synthetized core-shell nanoparticles in this research was significant. In comparison to other multi-step synthesis techniques, the results obtained from this research confirmed the formation of magnetite-silica core-shell structures with the desired magnetic behavior in a quick and single-step process.
Nuclear magnetic resonance (NMR) spectroscopy offers an element-selective, inherently quantitative and experimentally very flexible approach for the structural elucidation of non-crystalline materials. The present review introduces the basic concepts of this technique, highlighting the use of advanced NMR methodology for characterizing short- and intermediate range order in bioactive glass systems. The current state of the literature in this field is summarized in a comprehensive manner. NMR can give clear-cut and quantitative answers about the extent of network polymerization, the spatial distribution of the network former and network modifier species, and the structural roles of Group III elements introduced into these networks. These results facilitate our understanding of the influence of bioglass compositions upon the dissolution kinetics and bioactivities of these glasses. A particular mission of this review is to highlight the utility of non-routine, more advanced experimentation, in the hope of their increased usage and circulation in future applications.
The main six nuclear isotopes used in obtaining high-resolution magic-angle spinning NMR spectra for the structural characterization of bioactive glasses
In this paper, we reported the design and preparation of a double-layer antireflective (AR) coating, which possessed relatively high transmittance at 351, 527, and 1053?nm. The refractive indices and film thicknesses of the under layer and upper layer of the simulated AR coating were determined as 1.27, 95?nm and 1.18, 106?nm, respectively. The under layer of the double-layer coating dip-coated from a mixture of base-catalyzed and acid-catalyzed silica sols had a refractive index of 1.27. The upper layer fabricated by the deposition of methylated silica nanoparticles by simply adding methyltriethoxysilane into the base-catalyzed silica sols possessed a refractive index of 1.18. The hydrophobicity of coatings could be dramatically improved with the water contact angle increasing from 23.4° to 150.0°, and the refractive indices of the pure base-catalyzed silica coatings were easily decreased from 1.20 to 1.12 through the surface treatment of silica nanoparticles. Thus, we have successfully prepared a double-layer AR coating, which had a high transmittance of 99.8%, 96.1%, and 99.7% at 351, 527, and 1053?nm, respectively.
Trimethylethoxysilane (TMES) has been recognized as a good co-precursor to increase the degree of hydrophobicity during the synthesis of a silica aerogel because of its methyl groups. Therefore, some physical properties of silica aerogels, including the contact angle and porosity, were investigated using TMES as a co-precursor at different molar ratios with the main precursor such as tetramethoxysilane (TMOS) or tetraethoxysilane (TEOS). In contrast to TMES, most silylating agents such as hexamethyldisilazane (HMDZ) and trimethylchlorosilane (TMCS) have been used for surface modification because of their ability to enhance the hydrophobicity of the aerogel surface. This work examines the silylation effect, which includes increasing hydrophobicity by TMES to determine the possibility of using it as an alternative silylating agent during ambient pressure drying in the synthesis of sodium silicate-based silica aerogel. In addition, the physical properties of sodium silicate-based silica aerogels with silylation under different TMES/TMCS volume ratio are investigated. The physical properties of sodium silicate-based aerogels can be changed by the TMES/TMCS volume ratio during the surface modification step. Aerogels with a high specific surface area (458?m2/g), pore volume (3.215?cm3/g), porosity (92.7%), and contact angle (131.8°) can be obtained TMES/TMCS volume ratio of 40/60.
Treatment of tetraethyl orthosilicate with 1,2-diisopropyl-4,4,5,5-tetra-methyl biguanide (A) as a highly strong base immediately gave silica gel by means of hydrolysis and condensation reaction at room temperature. The resulting wet gel was transparent and showed high density after dryness. From the results of gas adsorption and BET analysis, silica gel obtained by the treatment of strong base A had larger specific surface area and pore volume than silica gel that was prepared by a regular or less strong base such as tetramethylammonium hydroxide (TMAH). FTIR analysis revealed that the peak strength of Si-OH bond at 960?cm?1 of silica gel prepared by highly strong base A was smaller than that of TMAH. To understand the mechanism behind such difference, a mixture of diphenylsilandiol and dimethoxydiphenylsilane were reacted with highly strong base A, and the resulting products comprised linear-chain siloxane oligomer and octaphenylcyclotetrasiloxane. Our results indicate that silanol generated by hydrolysis of TEOS is activated by A and the activated silanol undergoes subsequent direct reaction with unhydrolyzed alkoxy silane to give condensation products in ethanol. Such a direct polycondensation between silanol and alkoxy silane brought by highly strong base A led to three-dimensional crosslinking having a higher bulk density of silica gel.
Herein, the catalytic properties of the cerium (IV) salt, cerium (IV)-sandwiched polyoxometalate (POM) and cerium (IV)-sandwiched polyoxometalate intercalated in layered double hydroxides (LDHs) in the H2O2-based green oxidation reactions have been evaluated. These cerium (IV)-based systems were applied as homogeneous and heterogeneous catalysts for the oxidation of pyridines. Despite the fact that the cerium (IV)-sandwiched polyoxometalate as a homogeneous reaction system gives good results, there are some disadvantages in recovery and reusability process. To overcome these problems, new nano catalyst was synthesized by intercalation of the Cerium (IV)-sandwiched polyoxometalate into tris(hydroxymethyl) aminomethane-modified layered double hydroxides (Tris-LDH-CO3). The as-prepared nanocomposite was characterized and used as an effective heterogeneous catalyst for the oxidation of pyridines under mild conditions in the presence of H2O2 as an oxidant. The new heterogeneous nanocomposite can be recovered and reused easily from the reaction media at least ten times without significant decrease in catalytic activity.
A modified Kendrick Mass Defect (KMD) analysis was applied to the analysis of polycyclic aromatic hydrocarbons (PAHs) and fullerenes in the diffusion flame from a handheld butane torch.
DBTL as neutral polycondensation catalyst was employed to obtain organic modified silanes (ORMOSILs), which were studied as anticorrosive films for aluminum at saline corrosion. The ORMOSILs were synthesized using TEOS as silica precursor, different alkylalkoxysilanes (trimethoxy(methyl)silane, triethoxy(octyl)silane, 3-aminopropyl(triethoxy)silane and DBTL-catalyst were employed under the free solvent sol–gel process. Results of chemical characterization of ORMOSILs coatings show that under SEM technique coatings have homogenous films, and there are a crosslinking between silica and organic modified under the Infrared spectroscopy and 29Si CPMAS-NMR techniques. On the other hand, Brinell hardness and Pull-Off adhesion tests show that all ORMOSILs increase the aluminum surface hardness between 1 and 10%, and the ORMOSILs critical forces for adhesion are in the range of 106–132?N; therefore, the ORMOSILs coatings have an excellent adhesion to aluminum surface, furthermore, the saline corrosion test shows that organic modified silica avoid the pitting aluminum corrosion; corrosion rate decreases about 60–85%; the anticorrosive behavior according to modified-silica was determined as: SiO2–NH2?>?SiO2–Me?～?SiO2–Octyl.
In this research, LiMn2O4 nanopowders were synthesized by the sol–gel method using gelatin as a chelating agent. Three categories of samples with various weight ratios of gelatin to the final product, 1:1, 2:1, and 3:1, have been synthesized. The produced gel was dried in a controllable oven with a slow slope up to 250??C and calcined at different temperatures. The results show that the amount of gelatin affects the structural properties such as the formation temperature of the spinel structure, the homogeneity of the size distribution and size of the particles. The sample with the weight ratio of 3:1 of gelatin to the final product has a lower temperature for the formation of LiMn2O4 with more homogeneity, and smaller particles with the average size of 70?nm, which is calcined at 750??C, while the samples with the weight ratios 2:1 and 1:1 have the average particle sizes of 75 and 89?nm, respectively.
Dual-network aerogels (HPSA) with improved mechanical property and thermal insulation were prepared by vacuum impregnation of HNTs/PVA aerogels (the first network aerogel, HPA) in tetraethoxysilane (TEOS). Scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, and N2 adsorption–desorption analysis were used to study micromorphology and microstructure of HPSA, while compression tests and thermal conductivity tests were used to investigate related properties. The results showed that the dual-network frame was successfully constructed, this enabled HPSA to display enhanced compressive properties with increased HNTs content. The addition of silica sol improved the mesoporous characteristics including specific surface area and pore volume and also reduced the thermal conductivities. The first network made it possible for HPSA to possess good mechanical property, while SiO2 aerogel allowed HPSA greater thermal insulation. The obtained aerogel samples exhibited a high compressive strength (i.e., 1.36?MPa) and a low thermal conductivity (i.e., 0.022?W/(m?K)). HNTs/SiO2 dual-network aerogels with improved strength and thermal insulation could show great potential in a wide variety of applications.
Natural dyes, namely, indigo carmine, cochineal carmine, curcumin and annatto, were encapsulated in silica by a sol-gel method and applied in the dyeing of different textile fibers by exhaustion. For comparative reasons, dyeing using the free (non-encapsulated) bare dyes was also carried out. The hybrid materials were analyzed by a set of techniques to investigate their elemental, structural, textural and morphological properties, and the results showed that it was possible to obtain stable natural dyes for applications in textile dyeing. The silica-structured dyes showed better affinities with the fibers (WO, PA, PAC and PET) in dyeing with cochineal carmine, while cotton (CO) showed better affinities with the encapsulated curcumin and annatto dyes. The performances of the encapsulated dyes were evaluated by color and washing fastness measurements and resulted in improved dye absorption and wash fastness properties. The color change and color transfer measurements of the encapsulated dyes were better (rated at 4–5 on a scale of 1–5) compared to the bare dyes.
An optical biosensor for the determination of catechol, a widely used yet toxic and carcinogenic molecule, is proposed using a crude extract of desert truffle (Terfezia leonis Tul.) as an enzymatic source of tyrosinase. The biosensor is constructed by the immobilization of tyrosinase crude extract in a bi-layered silica gel film prepared by dip-coating of an alkoxide/colloidal silica solution containing the enzyme on glass slide. Encapsulation has a moderate effect of the enzyme optimal pH stability but largely increases its thermal stability. Immobilized enzymes have a higher substrate affinity towards catechol but smaller maximum conversion velocity. The optical biosensor provides a linear response for catechol in the concentration range of 50–400?µM and a limit of detection was 52?µM. AFM studies show that the enzymes impact on the silica gel structure, preventing further deposition of additional layers. Comparison with similar dopamine biosensors points out that the impact of encapsulation on enzymatic activity may depend on the considered substrate.
