A novel ZrCO composite aerogel is synthesized using zirconium oxychloride and resorcinol–formaldehyde (RF) as precursors through the sol–gel route and carbothermal reduction process. The effects of different Zr/R molar ratios and calcination temperatures on the physical chemistry properties of ZrCO aerogels are investigated. The ZrCO composite aerogel consists of the C/ZrO2/ZrC ternary aerogel. The results show that with the increase of R/Zr molar ratios, the specific surface area and bulk density increase with calcination temperature up to 1300?°C, but decrease at even temperature (1500?°C). The specific surface area is as high as 637.4?m2/g for ZrCO composite aerogel (R:Zr?=?2:1), which was higher than ever reported. As the heat-treatment temperature increases to 1500?°C, the ZrC crystalline phase occurs and the t-ZrO2 phase still appears within the composite. The thermal conductivity of the carbon fiber mat-reinforced composite aerogel is as low as 0.057?W/m/K at room temperature (25?°C).
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.
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.
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.
A facile procedure was developed for the production of Al2O3 aerogels modified with tris(8-hydroxyquinolinato)aluminum complex (AlQ3). The addition of 8-hydroxyquinoline during the stage of alumina lyogel formation was found to increase gelation duration. The translucent monolithic aerogels were obtained by supercritical drying of lyogels in CO2. The composition and properties of aerogels were analyzed using low-temperature nitrogen adsorption, helium pycnometry, IR spectroscopy, UV–visible spectroscopy, luminescence spectroscopy, powder X-ray diffraction, scanning and transmission electron microscopy, and thermogravimetry combined with mass spectrometry. The obtained aerogels had low density (0.15–0.18?g?cm?3), high specific surface area (480–550?m2/g), high porosity (90–95%), and showed bright luminescence upon excitation in the UV range.
In this study, the effective TiO2/Ag composite antibacterial aerogel powder is prepared by facile sol–gel method and ethanol supercritical technology. The surface morphology, structural properties, and chemical components are monitored by scanning electron microscopy (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and energy disperse?spectroscopy (EDS). Meanwhile, absorbance spectra and specific surface area of TiO2/Ag composite aerogel are characterized by UV-Vis spectra and Brunauer–Emmett–Teller. The TiO2/Ag composite aerogel with Ti/Ag molar ratios of 10:1, 30:1, 50:1 are measured for its antibacterial property by using Escherichia coliform (E.coli) and Staphylococcus aureus (S. aureus). The results show that the size of TiO2 and Ag nanoparticles are 40?nm and 25?nm, respectively. Simultaneously, the obtained composite aerogel with a porous structure possessed a surface area of 148?m2/g, an average pore size 11.5?nm, and a pore volume 0.39?cm3/g. With the increase of Ag content, the antibacterial properties of composite aerogel are greatly improved compared with pure TiO2 aerogel. When Ag/Ti molar ratios was 1:10, the highest antibacterial rate can up to 99%, and the inhibition bands of E. coli and S. aureus are 23?mm and 19?mm, 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.
Since the late 1960s, ceric hydrogen phosphates have attracted the attention of scientists due to remarkable ion exchange, sorption, proton-conduction and catalytic properties. In this work, through the application of various solvents, we, for the first time, have obtained monolithic aerogels based on ceric hydrogen phosphates with high porosity (~99%) and extremely low density (~10?μg/cm3). The composition and structure of aerogels were thoroughly studied with XRD, TEM, SEM, XPS, low temperature nitrogen adsorption methods, TGA/DSC, Fourier-transform infrared spectroscopy (FTIR) and small-angle neutron scattering (SANS). The aerogels were found to belong to the fibrous macroporous aerogels family.
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.
Boron Nitride (BN) particles were functionalized with vinyl-trimethoxysilane (VTMS) and incorporated into a hybrid polymer (ORMOCER®) resin. The thermal conductivity and mechanical properties of the resulting composite were compared to materials prepared using unmodified particles. Results indicate that the chemical bonding between grain surface and ORMOCER® matrix has a pronounced effect on the final performance of the respective compounds.
The surface of BN particles was functionalized prior to their incorporation into a hybrid polymer (ORMOCER®) matrix, thermal, electrical and mechanical properties of the resulting composites were characterized.
It is well known that the first step of the sol-gel method consists in obtaining of amorphous or incipient crystallized materials that could be kept in the same state or could be transformed into vitreous or crystallized materials by adequate thermal treatments. In the present study, examples regarding the relevance of the thermal analysis methods for the characterization of the sol–gel-derived oxide systems, inorganic–organic hybrids, and composite nanomaterials are discussed. For the oxide systems, case studies regarding undoped and doped monocomponent oxides and polycomponent systems are discussed. In the case of inorganic–organic hybrids, the correlation between the type of precursors and the thermal behavior is presented. For the composite nanomaterials, examples for thermal behavior of two types of nanocomposites, namely both compositionally and structurally different, as well as inorganic–organic hybrid sol-gel nanocomposites are shown. In all studied cases, the thermal analysis methods allow obtaining important information not only on thermal behavior but also on the chemical composition of the as-prepared gels and powders. Different structural investigations methods (XRD, FTIR, and Raman) sustain the results obtained by thermal investigations.
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.
Zinc oxide (ZnO) powders have been prepared by solution combustion synthesis method using conventional and microwave ignition routes. The effects of starting solution acidity on the combustion behavior, phase evolution, microstructure, optical properties and photocatalytic performance were investigated by thermal analysis, X-ray diffractometry, electron microscopy and diffuse reflectance spectrometry techniques. The chelated species in dried gels were predicted by theoretical calculations and confirmed by Fourier transform infrared spectroscopy. The combustion reaction rate increased with the increase of pH values. Single phase and well-crystalline ZnO powders were achieved by both of ignition methods regardless of pH values. The hexagonal particles (200–80?nm) formed by microwave ignition were larger than the spherical particles (60–40?nm) in conventional heating. Conventionally combusted ZnO powders exhibited higher photocatalytic activity under ultraviolet irradiation, due to their narrower band gap and smaller particle size.
C/C0 vs. irradiation time for photodegradation of MB dye under ultraviolet light irradiation by the as-combusted ZnO powders (filled symbols present conventional combusted powders and open symbols are for the microwave combusted powders)
Powders of Sm0.6Sr0.4CoO3-δ and La0.6Sr0.4CoO3-δ were synthesized using wet chemical technique. Structural and surface properties of synthesized materials were studied by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray diffraction (XRD), IR spectroscopy, and scanning electron microscopy (SEM). The influence of pH on the phase state, chemical composition, morphology, and fractal dimension of the synthesized powders were investigated. It was found that the change of pH has the influence on phase composition of synthesized powders. The increase of solution pH allows one to obtain homogeneous samples at lower temperatures down to 900–950?°C.
Thermally stable acid catalyzed mesoporous titania (TiO2) nanomatrices are obtained by sol–gel method for fiber optic pH sensing. These synthesized nanoparticles are annealed at 300?°C, at two time intervals i.e., 1?h and 2?h, characterized with several analytical techniques such as FE-SEM/EDS, AFM, XRD, FTIR, TGA, and Brunauer–Emmett–Teller (BET) analysis. Microscopic analysis shows that synthesized nanoparticles have crack-free, dense and homogeneous surface with low surface roughness (4.4–5.9?nm). EDS mapping confirms the uniform distribution of Ti in all samples. XRD findings revealed the TiO2 anatase phase. BET analysis shows that the mesoporous synthesized TiO2 nanoparticles have surface areas 169?m2/g and average pore diameter 39.2?Å. However, surface area is decreased to 113 and 102?m2/g and average pore diameter increased up to 62.36 and 68.18?Å after 1?h and 2?h heat treatment, respectively. Furthermore, the sensing activity of phenolphthalein (phph) doped mesoporous TiO2 nanoparticles/matrix is found to be high at pH 12 without any leaching/cracking.
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.
YAG:Ce and YAG:Eu sols were synthesized by a polymeric sol-gel route. The crystallization temperature of YAG was determined by X-ray diffraction as a function of the calcination temperature, revealing that YAG starts to crystallize directly from the amorphous phase at 800?°C. The effects of the thermal treatment and the dopant amount on the photoluminescent properties were studied, observing the highest emission after calcination at 1000?°C for 1?h in both cases and with a concentration of 1 and 3?mol% of Ce and Eu, respectively. Core-shell materials were prepared by dipping YAG:Ce or YAG:Eu sintered pellets into the synthesized sols and then, these materials were calcined at 1000?°C for 1?h. An effective energy transfer from Ce to Eu was observed in the sample YAG:Eu (core)–YAG:Ce (shell) when blue light (λ?=?465?nm) is used as excitation source. This wavelength excites the Ce but not the Eu; however, in the photoluminescence emission spectrum, the bands associated to both ions can be clearly detected, confirming that the core-shell strategy is a good method for the preparation of warmer white LEDs.
In this work, sol–gel-based non-stick ceramic coating formulations were prepared and coated onto aluminum panels in order to investigate their surface properties. The effect of the addition of optimal amount of fluorine-containing silane compound (FAS) on the surface and adhesion properties were also investigated. The morphology, structure, and elemental chemical composition of the coatings were characterized by scanning electron microscopy, atomic force microscopy (AFM), energy dispersion spectrum (SEM/EDAX), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS), respectively. Moreover, several properties of the coatings such as cross-cut adhesion, hardness, gloss, and contact angle (CA) were determined. When fluorine was introduced, the pencil hardness was increased to 6H. Fluorinated non-stick ceramic coatings were found to have good adhesion on the aluminum substrates.
Mixed-metal compounds, especially for the sulfides, have been investigated as a very attractive type of electroactive materials for supercapacitors. In this work, we demonstrate nickel?manganese (Ni?Mn) sulfides are very attractive for supercapacitors with promising electrochemical performance. The Ni?Mn sulfides with different Ni to Mn ratios have been synthesized via a facile one-pot hydrothermal method, which show a similar structure of interconnected particles and are very porous in microstructure. And then, the Ni?Mn sulfides are investigated by three-electrode measurements and demonstrate strong synergy between Ni and Mn. The Ni?Mn sulfide with a Ni to Mn ratio of 2:1 demonstrates superior performance of 1068?F?g?1 at 1?A?g?1. Lastly, The Ni?Mn sulfide with a Ni to Mn ratio of 2:1 are used as positive electrode for two-electrode test, and the asymmetric supercapacitor shows both high energy and power densities combined with excellent cycling stability. Our work demonstrates that the Ni?Mn sulfides are also very electrochemical active for supercapacitors and their performance can be tuned by changing the Ni to Mn ratio.
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
