Borate,lithium borate,and borophosphate powders by sol–gel precipitation

Borate, lithium borate and borophosphate powders were synthesized by the sol–gel method. Triethyl borate, lithium methoxide, and orthophosphoric acid were used as precursors for B₂O_3, Li₂O, and P₂O₅, respectively. Powders were characterized by FTIR, DTA, XRD and SEM techniques. Powders from the Li₂O–B₂O₃ system exhibited glassy features while borate and borophosphate powders contained mainly crystalline B₂O₃ according to XRD analysis. However, a 500 °C heat treatment transformed these crystalline powders into glass powders. Conversely, heat treatment of Li₂O–B₂O₃ powders transformed their structure from glassy to crystalline (Li₂B₄O₇). Chemical durability studies conducted in water at 60 °C showed that minor additions of P₂O₅ into borate and lithium borate powders improved their chemical durability significantly. Furthermore, Li₂O and P₂O₅ acted synergistically on the chemical durability when added simultaneously to borate compositions.     

X-rays to study,induce, and pattern structures in sol–gel materials

X-rays investigations have been shown to reveal important information regarding material features and the formation mechanism of mesostructured materials. Small angle X-ray scattering (SAXS) analysis performed using a synchrotron source has been very important in the optimization of the organization of mesoporous coatings obtained by evaporation induced self-assembly (EISA). The interaction between X-rays and ordered mesoporous films has only recently been reported, and new knowledge has been developed to use this external radiation source to tune the local material properties. Here we discuss the recent developments in X-ray lithography combined with sol–gel synthesis to pattern mesostructured and hierarchical porous coatings including the ability to tailor functionalized surfaces.     

Sol–gel derived organic–inorganic hybrid materials: synthesis,characterizations and applications

Organic/inorganic hybrid materials prepared by the sol–gel approach have rapidly become a fascinating new field of research in materials science. The explosion of activity in this area in the past decade has made tremendous progress in both the fundamental understanding of the sol–gel process and the development and applications of new organic/inorganic hybrid materials. Polymer-inorganic nanocomposite present an interesting approach to improve the separation properties of polymer material because they possess properties of both organic and inorganic such as good permeability, selectivity, mechanical strength, and thermal and chemical stability. Composite material derived by combining the sol–gel approach and organic polymers synthesis of hybrid material were the focus area of review It has also been demonstrated in this review that a more complete understanding of their structure–property behavior can be gained by employing many of the standard tools that are utilized for developing similar structure–property relationships of organic polymers. This review article is introductory in nature and gives introduction to composite materials/nanocomposite, their applications and the methods commonly employed for their synthesis and characterization. A brief literature survey on the polysaccharide templated and polysaccharide/protein dual templated synthesis of silica composite materials is also presented in this review article.     

Synthesis and sol–gel assembly of nanophosphors

Some recent works made in our group on inorganic nanophosphors are briefly reviewed in this paper. We first present the synthesis of highly concentrated semiconductor quantum dot colloids allowing the extension of the well-known oxide sol–gel process to chalcogenide compounds. Secondly, we show the synthesis and the chemical functionalization of lanthanide-doped insulator nanoparticles. In particular, the annealing process of these particles at high temperature leads to highly bright nanocrystals, which can be used as biological luminescent labels or for integration in transparent luminescent coatings. Finally, we consider luminescent transition metal clusters, which combine the inorganic structure of nanoparticles with the monodispersity and the easy functionalization of the organic molecules. Emphasis is put on the original thermochromic luminescence properties of copper iodide clusters trapped in siloxane-based films.     

Sol–gel composite coatings from methyltriethoxysilane and polymethylhydrosiloxane

New composite coatings were prepared by mixing pre-hydrolyzed methyltriethoxysilane (MTES) sol by an acidic catalyst dibutyltin dilaurate (DBTDL) and polymethylhydrosiloxane (PMHS) in gasoline at room temperature. The gel process was thoroughly investigated regarding the use of different basic catalyst [3-aminopropyltriethoxysilane (APTES) or triethylamine (TEA)], as well as the ratios of pre-hydrolyzed MTES sol and PMHS with various content of active H. It was revealed that the composite coating from 2:1 ratio (w/w) of pre-hydrolyzed MTES sol with equimolar amounts of water and PMHS_1.55 under the catalysis of APTES demonstrated high pencil hardness, and excellent resistance against contamination and corrosion. This composite coating (MTPM21-A) was further characterized by FTIR, ²⁹Si NMR, DSC and TGA.     

Sol–gel derived mesoporous and microporous alumina membranes

Stable polymeric and colloidal boehmite sols were prepared by sol–gel process through controlled hydrolysis/condensation reactions. The particle sizes of the colloidal sols were in the 12–25 nm range depending on the process parameters and about 2 nm for polymeric sols. The presence of a significant increase in the microporosity content of the heat treated polymeric membranes relative to the mesoporous colloidal membranes might make the design of thermally stable microporous alumina membranes with controlled pore structures possible. The phase structure evolution in the 600–800 °C range had shown that the crystallization of the gamma alumina in the amorphous matrix starts at about 800 °C. This indicated that the pore structure stability may be enhanced through processing up to this relatively high temperature in polymeric alumina derived unsupported membranes. The permeance values of the two and three layered colloidal alumina membranes were observed to be independent of pressure which implies that the dominant gas transport mechanism is Knudsen diffusion in these structures. This was also supported by the 2.8 nm BJH pore sizes of the colloidal membranes. The Knudsen diffusion equation derived permeances of the polymeric alumina membranes with thicknesses of about 300 nm were determined to be very close to the experimentally determined permeance values.     

Synthesis and characterization of sol–gel alumina nanofibers

Abstract Alumina nanofibers of high aspect ratio with surface area of >300 m² g⁻¹ has been prepared successfully in bulk quantities by the sol–gel method. The synthesis parameters including the binary water–alcohol solvent system to aluminium isopropoxide ratio, pH, type of solvent and aging temperature affect the uniformity and formation of nanofibers. It is proposed that alumina nanofibers were formed by the curling of the nanosheets upon condensation after the hydrolysis. The phase evolution of alumina nanofibers from pseudoboehmite to α phase has been shown by XRD and FTIR. ²⁷Al NMR investigations show that the Al atoms are six and four coordinated. The morphology of the alumina nanofibers does not change much as the calcination temperature was increased. In addition, the average pore size increases and the BET surface area decreases as a function of calcination temperature. The thermal behavior of alumina nanofibers was investigated by TGA. Graphical Abstract      

Novel multifunctional water- and oil-repellent,antibacterial, and flame-retardant cellulose fibres created by the sol–gel process

This research aimed to prepare cotton fibres with novel multifunctional water- and oil-repellent, antibacterial, and flame-retardant properties. A three-component equimolar sol mixture, which included 1H,1H,2H,2H-perfluorooctyltriethoxysilane, 3-(trimethoxysilyl)-propyldimethyloctadecyl ammonium chloride, and P,P-diphenyl-N-(3-(trimethoxysilyl)propyl) phosphinic amide, was applied to the cotton fabric using the sol–gel process. The presence of the coating on the cotton fibres was confirmed by Fourier transform-infrared spectroscopy and X-ray photoelectron spectroscopy. The functional properties of the coated cotton fabric were determined from liquid contact angle measurements and antibacterial activity, burning behaviour, and thermo-oxidative stability studies. The results demonstrate that a unique, compatible, and uniform organic-inorganic hybrid polymer network was formed on the fabric surface, which preserved its simultaneous hydrophobic (water contact angle of 135 ± 2°), oleophobic (n-hexadecane contact angle of 117 ± 1°), and bactericidal (bacterial reduction of 100 %) properties and incorporated the enhanced thermo-oxidative stability of the modified cellulose fibres.     

Sol–gel synthesis and optical behavior of Mg–Ce–O nano-crystallites

The Mg–Ce–O powder are shown to contain periclase-type MgO and/or fluoride-type cerium oxide (CeO₂) depending upon the composition (x) defined by Ce/(Ce + Mg) atomic ratio. Lattice contraction of pariclase phase of MgO (average crystallite size ~8.8 nm) at Ce content of ‘x’ = 0.20 in comparison to pure MgO (crystallite size ~9.5 nm) has been realized due to oxygen vacancy formation. The optical band gap values of CeO₂ varies (3.0–3.2 eV) due to oxygen vacancy formation in CeO₂ phase, crystallite size and/or Ce³⁺/Ce⁴⁺ ratio. Further, the addition of Ce has shown to reduce the physisorption and chemisorption of water significantly as reflected by (1) suppression of related absorption peaks and (2) absence of magnesium hydroxide, Mg(OH)₂, bands in Fourier transform infrared spectra.     

Sol–gel development activities at IGCAR,Kalpakkam

Sol–gel based fuel fabrication processes have the potential to be the nuclear fuel fabrication processes in the future. Hence development of sol–gel technology for nuclear fuel fabrication is being the pursued in the Department of Atomic Energy in India. As a part of the efforts, a laboratory scale facility for fabrication of test fuel pins for irradiation in the Fast Breeder Reactor (FBTR), Kalpakkam has been set up at the Indira Gandhi Centre for Atomic Research, Kalpakkam, India. These fuel pins will be vibropacked with sol–gel derived microspheres or stacked with pellets obtained by compaction of sol–gel derived microspheres. The facility is aimed at demonstration of the remote operation of the fuel pin fabrication process through the sol–gel route. A capsule containing three test pins from this facility will be irradiated in FBTR. The design features of the facility and the test fuel pins are described in this paper.     

Preparation and properties of sol–gel waterborne polyurethane adhesive

Waterborne polyurethane (WBPU) sol–gel adhesives were prepared through a prepolymer process followed by a sol–gel reaction of (3-aminopropyl)triethoxysilane (APTES). The terminal amine group of APTES reacted with the NCO group of the prepolymer, and the ethoxy group created Si–O–Si branching by hydrolysis and condensation reactions in water at the dispersion step. Water swelling (%), tensile strength and Young’s modulus of the synthesized WBPU sol–gel adhesives were improved by increasing APTES content. Synthesized WBPU sol–gel adhesives were used for bonding nylon fabrics. A significant improvement in adhesive strength was recorded, and the potential for good adhesive strength under water at moderately high temperature (up to 75 °C) was observed with 6.84 mol% APTES in WBPU sol–gel adhesives.     

Sol–gel synthesis and structure of silica hybrid materials

In this work the research results on the sol–gel synthesis and structure of silica nanocomposites, containing carrageenan and their application as carriers for cell immobilization were described. The samples were prepared at room temperature by replacing different quantity of the inorganic precursor with κ-carrageenan. For studying the structure of the synthesized hybrids the following methods were used: FT-IR, XRD, BET-Analysis, SEM, AFM and Roughness Analysis. The influence of the type of silicon precursors, nature and quantity of organic component on the structure, surface area, design and size of nanostructures was established. The possibility of application of the synthesized biocatalysts in an enzyme degradation process of the toxic, carcinogenic and mutagenic substances benzonitrile, fumaronitrile, o-, m-, and p-tolunitriles was investigated at batch experiments. A two-step biodegradation process in a column bioreactor of fumaronitrile was followed. After operation of the system for 8 h at a flow rate 45 mL h^?1 and at 60 °C, the overall conversion was 89%, showing a good stability of the developed process.     

Sol–gel synthesis of sodium and lithium based materials

Sodium and lithium cobaltates are important materials for thermoelectric and battery applications due to their large thermoelectric power and ability to (de-) intercalate the alkali metal. For these applications, phase pure materials with controlled microstructure are required. We report on the sol?Cgel synthesis of sodium- and lithium-based materials by using acetate precursors. The produced Na_2/3CoO₂, Li(Ni_1/3Mn_1/3Co_1/3)O₂, and Li(Ni_1/2Co_1/2)O₂ powders are phase pure with grain sizes below 1???m. X-ray diffraction and energy-dispersive spectral analyses show that the cation stoichiometry is preserved in the lithium-based compounds. Despite the low temperatures, the sodium content is reduced by 1/3 as compared to the initial value. Chemical phases of the investigated powders are formed in the sol?Cgel route at temperatures typically 100?C200?K lower than those used in the conventional solid-state synthesis of these materials. The suggested sol?Cgel synthesis is a low temperature process suited for production of phase pure and homogeneous materials with volatile cations.     

Sol–gel synthesis and crystallization behaviour of β-spodumene

Lithium aluminum silicate powders in the form of β-spodumene were synthesized through sol–gel technique by mixing boehmite sol, silica sol and lithium salt. The gel and oxide powders were characterized by thermogravimetry, differential thermal analysis (DTA), X-ray diffraction (XRD), Fourier transformed infrared (FTIR) spectroscopy and scanning electron microscopy. DTA, XRD and FTIR results confirmed that crystallization of β-spodumene took place at about 800 °C. The tiny crystallites with average size less than 1 μm appeared when the gel powders were sintered at 800 °C. A substantial increase of the crystal grain size was observed with increasing sintering temperatures.     

Sensitivity and stability of the Fricke–gelatin–xylenol orange gel dosimeter

Spectrophotometric measurements of the Fricke–gelatin–xylenol orange (FGX) gel dosimeter demonstrated reproducible linear dose response up to 25 Gy. However, oxidation processes continue post-irradiation, affecting the response of this dosimetry system. Additional oxygenation during preparation increases the sensitivity of the gel but does not improve the auto-oxidation stability of the dosimeter post-irradiation. A suitably stable gel composition that is recommended for radiotherapy dosimetry measurements contains 0.5 mM ferrous ammonium sulphate, 50 mM sulphuric acid, 0.15 mM xylenol orange and 3.0% by weight gelatin.     

Surface properties,adherence, and photocatalytic activity of sol–gel dip-coated TiO2–ZnO films on glass plates

In this study, TiO₂–ZnO nanostructured films prepared from different Ti/water mole ratios were deposited on glass plates by a sol–gel dip-coating method. The structural and surface properties, adherence, and photoactivity of synthesized TiO₂–ZnO coatings in methylene blue degradation were investigated. Among the as-prepared TiO₂–ZnO coatings from sols with different Ti/water mole ratios (1, 0.66, 0.5, and 0.4), the highest sol concentration (Ti/water mole ratio of 1) showed the highest methylene blue photodegradation of almost 80% after 400 min of UV irradiation. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM), Energy-dispersive X-ray (EDX), and UV-vis diffuse reflectance spectra (DRS) confirmed that at high sol concentrations (Ti/water mole ratios of 1 and 0.66), a mixed phase of anatase and rutile is formed, whereas at a Ti/water mole ratio of 0.5, just pure rutile is formed. In detail, decreasing the sol concentration increases the cracks, degree of agglomeration, and the thickness of coatings. UV-vis DRS studies also confirm that decreasing the sol concentration in synthesized TiO₂–ZnO films leads to a shift in the absorption region of the coating to the UV region. Moreover, decreasing the sol concentration declines the coating adherence onto glass plates. TEM images of the TiO₂–ZnO coating synthesized from sol with a Ti/water mole ratio of 1 revealed the formation of ZnO nanorods around a spherical TiO₂, which indicates the presence of strong interaction between TiO₂ and ZnO nanoparticles. The TiO₂–ZnO coating synthesized from sol with a Ti/water mole ratio of 1 was then evaluated at different methylene blue concentrations, pH values, and number of coatings. After five consecutive runs, no significant decrease in the photodegradation efficiency was observed. Scanning electron microscopy (SEM) picture of used coating showed a smooth and stable layer without any detachment. Thermogravimetric analysis (TG) and sonication test confirmed thermal and mechanical stabilities of this coating as well.     

Sol–gel preparation of calcium titanium phosphate: viscosity,thermal properties and solubility

Calcium titanium phosphate (CTP) was prepared by the sol–gel route in order to prepare suitable coatings. This work addresses the question of how to prepare stable CTP sols. Their rheological properties as a function of process parameters like solid loading and water content are investigated. It was found that an increased solid loading as well as an increased water content lead to an increased initial viscosity as well as a more pronounced ageing induced viscosity rise. In addition, the thermal behavior of the resulting xerogels was analyzed. Furthermore, we studied the ion release behavior of the xerogels when brought in contact with water. Results suggest that calcium titanium phosphate shows a diffusion controlled ion release mode with a preferential release of Ca.     

Thermal,chemical and antimicrobial characterization of bioactive titania synthesized by sol–gel method

Journal of Thermal Analysis and Calorimetry - Chemical stability, anticorrosive properties and photocatalytic activity of titanium dioxide (TiO2) are among the most important characteristics for...     

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.