Sol–gel technology and template synthesis in thin gelatin films

Processes of sol–gel technology of template synthesis of 3d-element metal macrocyclic complexes that occurs in thin films of metalhexacyanoferrate(II) gelatin-immobilized matrix implants under their contact with water solutions containing various (N,O,S)-donor atomic and (C=O) containing organic compounds, have been discussed. It was noted that, in a series of cases, sol–gel technology of template synthesis in the given specific conditions allows to realize such metal macrocyclic complexes formation processes that are not typical at the complexing in solutions or solid phase.     

Sol–gel combustion synthesis and characterization of nanostructure copper chromite spinel

Nanocomposite copper chromite spinel was fabricated by sol–gel process using copper nitrate trihydrate, chromium nitrate nonahydrate, ethylene glycol, diethyl ether, and citric acid. The thermoanalytical measurements (TG–DTG), X-ray powder diffractometry (XRD), field emission scanning electron microscopy (FESEM), and energy dispersive X-ray analysis were used to characterize the structural and the chemical features of the nanocomposites. TG–DTG results showed that the major mass loss for copper(II) nitrate, chromium(III) nitrate as precursors occur at 258 and 140 °C, respectively. The major mass loss for dried gel of copper chromite occurs at 310 °C. XRD data revealed the formation of pure copper chromite after thermal decomposition at 1,000 °C for 2 h. The observation of XRD patterns reveals the presence of single-phase tetragonal spinel CuCr₂O₄. FESEM analysis of calcined composite was found to be in the range of 20–30 nm.     

Sol–gel synthesis,optical and structural characterization of ZrOS nanopowder

In this paper, we report the synthesis of tetragonal zirconium oxysulfide t-ZrOS nanopowder by the sol–gel method using water solution of a precursor containing thiourea [CS(NH₂)₂] and zirconium in the form of an anionic oxalate complex [Zr(C₂O₄)]^4?. The tetragonal t-ZrOS structure with space group P4/nmm revealed by X-ray patterns showed preferred orientation along (101) plane. For surface morphology, compositional and optical absorption studies, scanning electron microscopy, energy dispersive X-ray and ultraviolet–visible spectroscopy were employed for characterization of the powder respectively. A nearly constant value of the refractive index at higher wavelength λ ≥ 1,100 nm was found to be 2.19. High indirect and direct optical band gap of ~2.0 and 2.50 eV with absorbance <40 % were obtained for the powder.     

Sol–gel synthesis and characterization of titania monolith with bimodal porosity

Monolithic titania materials with macro-mesoporosity bimodal texture have been prepared through a template-free sol–gel approach, based on the reaction of hydrolysis and polycondensation of titanium isopropoxide promoted by the slow released water from esterification between acetic acid and methanol under a strong acidic condition. With the coarsening of the titania oligomers, phase separation and sol–gel transition processes take place so as to form a homogeneous gel system that will change into a monolith after aging, drying and heat treatment. The synthesized titania monolith possesses a specific surface area of 77 m² g⁻¹ (calcined at 350 °C), an anatase with partly rutile crystallite structure and great mechanical strength. The synthesis method applied here is simple and easy to implement as no extra chemical modifier such as poly(ethylene oxide) (PEO) and formamide is needed to control the process. The properties of biomodal porous structure, satisfactory surface area and high mechanical strength will enable the monolith to be served as a chromatography column to separate phosphorus organo-compounds.     

Sol–gel synthesis and characterization of SiO2–Tac nanocomposites with controlled volume fraction

Nanocrystalline tantalum carbide (TaC) particles of average size ~15 nm dispersed in silica matrix, have been synthesized by the carbothermal reduction of Ta₂O₅ over a range of temperature 1,100–1,360 °C in Ar atmosphere. Investigation of the stability diagram of carbon saturated Ta–O–N system suggests that the TaC phase can be successfully synthesized within the SiO₂ matrix when the partial pressure of O₂ and N₂ are restricted to approximately lower than 1.25 and 0.0001 atm. respectively. Two different synthesis routes are investigated in the present study which differ fundamentally in the order of addition of the precursors, tetraethyl orthosilicate (TEOS) and tantalum isopropoxide (Ta-iso). Rietveld refinement analyses of the powder X-ray diffraction data are carried out for the quantitative estimation of the two phases in the samples. The yield of TaC increases from 18 to 52 % when both TEOS and Ta-iso are added simultaneously to the water compared to the process where TEOS is added first to the water followed by the delayed addition of Ta-iso. Samples are further characterized by field emission scanning electron microscopy and high resolution transmission electron microscopy.     

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 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 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.     

Sol–gel combustion synthesis of BNBT powders

Ba-modified bismuth sodium titanate with composition 0.94[(Bi_0.5Na_0.5)TiO₃]-0.06BaTiO₃ (BNBT) was prepared by a citrate nitrate sol–gel combustion method. The sol was obtained using barium acetate, bismuth nitrate, sodium nitrate and a peroxo-citrate complex of titanium isopropoxide as starting precursors. Various molar ratios of citrate/nitrate (C/N) were considered for the sol production. The corresponding gels were fired at different temperatures (300, 400, 500 °C) in order to evaluate the conditions necessary to obtain the decomposition of the precursors and the formation of the pure BNBT perovskitic phase in a single step. The best conditions to obtain the desired phase are: (C/N) = 0.2, and combustion temperature of 500 °C. Ball milled powders were densified at a temperature 100 °C lower than the one generally used for powder produced with the conventional mixed oxide route. The electrical properties are comparable to those reported for conventionally prepared materials.     

Sol–gel preparation and characterization of ceria stabilized zirconia minispheres

A novel processing technique based on sol–gel drop generation method has been developed to prepare fine zirconia minispheres for use as grinding media. Zirconium oxalate gel formation from the prepared sol was obtained in proper synthesis condition using Zirconium oxy-chloride octahydrate(ZrOCl₂·8H₂O) as starting material. The transparent oxalate gel was then added dropwise into the setting solution for the formation minispheres. To obtain the required fluidity and viscosity a suitable binder was mixed to the sol and stabilizing agent of required mol% was added to stabilize the phase formation. The addition of stabilizing agent transformation toughened the minispheres, with a complete retention of the tetragonal phase in the final product sintered at 1500 °C. Thermogravimetric analysis indicated the removal of most of the volatiles by 600 °C. Density and Crystallite size were found to be increasing linearly with sintering temperature. The phase identification, density variation, chemical decomposition, functional group specification and microstructural features for the dried and sintered final product were studied.     

Sol–gel synthesis, characterization and catalytic activity of γ-alumina with bimodal mesopore distribution

In this study, boehmite sols were used for preparation of mesoporous γ-alumina with bimodal mesopore distribution. Superfine nanospheres of poly(methyl methacrylate) (PMMA) prepared by water based emulsion polymerization method were used as a template. Nitrogen sorption revealed that aluminas prepared using this approach demonstrated bimodal mesopore size distribution with maxima at 3.8 and 25.7 nm, respectively. Catalytic tests showed that bimodal mesopore distribution within γ-Al₂O₃ prepared with PMMA nanospheres as a template provides improved catalytic activity in the methanol dehydration reaction.     

Sol–gel synthesis of silica composited flower-like microspheres using trivalent europium tartrate as a template

Journal of Sol-Gel Science and Technology - Silica composited flower-like microspheres were synthesized by a facile sol–gel synthesis method using trivalent europium tartrate (Eu3+-TTA) as...     

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.