Liquid-phase epoxidation of cyclooctene with O2 over CoOx/SiO2 catalyst prepared by sol–gel method

A series of CoO_x/SiO₂ catalysts has been prepared by the sol–gel method and characterized with XRD, N₂ adsorption/desorption, diffuse reflectance UV–vis spectroscopy, Raman spectroscopy as well as TPR techniques. This type of material is highly active and selective for the epoxidation of cyclooctene with atmospheric molecular oxygen. Although all the catalysts attained at different pH values are amorphous, their catalytic activities are remarkably different because the pH values influence not only the coordination state of Co species but also the textural structures of the prepared catalysts, in which CoO_x/SiO₂ obtained at pH below 5 is highly active and selective for the epoxidation of cyclooctene with atmospheric O₂. The prepared CoO_x/SiO₂ catalysts are highly stable and can be recycled at least four times without significant loss of activity and selectivity.     

Nano/macroporous monolithic scaffolds prepared by the sol–gel method

Development of optimal scaffolds for bone tissue engineering and regeneration is still a challenge, since many materials and structures have been proposed but few have reached clinical expectations. This work reports on the preparation and characterization of SiO₂-CaO and SiO₂-CaO-P₂O₅ sol–gel derived monoliths, with potential application as glass scaffolds for bone regeneration, exhibiting a nano/macro trimodal pore size distribution, including pores of ~100’s of micrometers (μm), several microns and just a few nanometers (nm) in size. Interconnected macropores (~20–200 μm) have been obtained in the present work by polymerization-induced spinodal phase separation along with the sol–gel transition, when a water soluble polymer [poly(ethylene oxide)] was added to the sol–gel solution; the several-micron pores are spherical and isolated and might be the result of secondary phase separation by nucleation-growth mechanism; the interconnected nanopore (~5–25 nm) structure of the macroporous gel skeleton, on the other hand, was tailored by solvent exchange procedures. The morphological and textural characterization of these materials was performed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray ultra microscopy (XuM), nitrogen adsorption and mercury intrusion porosimetry. The factors affecting the porosity exhibited by the scaffolds, such as glass composition and solvent exchange conditions, have been assessed.

Anticorrosive cerium-based coatings prepared by the sol–gel method

The development of efficient anti-corrosion and environmentally friendly coating systems are needed for the replacement of the highly toxic Cr-based conversion coatings for corrosion protection of aluminum alloys. In this study, we demonstrate that the direct application of ceramic cerium-based sol–gel coatings to AA7075-T6 substrates produces high-performance anti-corrosion layers. Electrochemical experiments and analyses of the microstructure demonstrate that the protective layers are very efficient for the passivation of the alloy surfaces operating as both passive and active barrier for corrosion protection.     

The photocatalytic properties of Ti–Mo oxides prepared by a simple sol–gel route

Powders containing mixtures of titania and molybdite in different ratios were prepared by sol–gel processing. The sols were dried and subsequently calcined at 300, 500 and 700 °C. Depending on the ratio of Ti and Mo in the initial sol and the calcination temperature, Ti-doped MoO₃, TiO₂/MoO₃ or Mo-doped TiO₂ have been formed. The as prepared samples were characterised by scanning electron microscopy with attached X-ray dispersive energy analysis, X-ray diffractometry, Raman spectroscopy, gas adsorption and optical characterisation by ultraviolet/visible spectroscopy. The latter was used for the analysis of the photocatalytic properties on the decolourisation of methylene blue solutions under visible light irradiation. The phase composition, the specific surface and the photocatalytic activity were influenced by the molybdenum content and the calcination temperature. The final molybdenum content in the samples additionally depends on the calcination temperature. The optimum photocatalytic properties were observed or Ti-doped MoO₃.     

Synthesis of SnO2 nanostructures by ultrasonic-assisted sol–gel method

Fluorine doped SnO₂ nanostructures were grown using ultrasonic assisted sol–gel method. The gel was obtained by dissolving stannous chloride in methanol with ammonium fluoride as dopant followed by irradiation with ultrasonic vibrations. Obtained samples were characterized by structural, morphological and optical studies. All the peaks in the X-ray diffractograms are identified and indexed as tetragonal cassiterite structure. Negative slope of Williamson–Hall plots indicates compressive strain. Particle size of SnO₂ nanostructures is decreases with increases in concentration of fluorine doping. Atomic force microscopy, scanning electron microscopy and transmission electron microscopy studies confirm the formation of ring like porous structures and then hollow tube like growth with increase in the fluorine concentration. Peaks in Raman spectra also indicate strong confinement in SnO₂ particles. Distinct peaks in the PL spectra make the structure suitable for photovoltaic applications.     

A novel chemical route to SiO_2 nanowires

A white substance was got by directly heating TiSi powder on Ti foil, under Ar+O2 atmosphere. ED, EDX, SEM and HRTEM studies reveal that the white substance consists of amorphous SiO2nanowires of smooth surface and uniform diameter (40-90 nm). X-ray-induced luminescent emission experiment shows that two broad peaks are at 430 and 570 nm. A one-dimensional growth mechanism, on the basis of the one-dimensional thermal flow during nanowire formation, is discussed.     

A biofriendly sol–gel route to new hybrid gels for enzyme encapsulation

New hybrid gels were prepared from the gelation of glycol-modified tetraethoxysilane (TEOS) in the presence of O-2-hydroxy-3-(trimethylammonio)propyl guar gum (HTPG), and were then used for the in situ encapsulation of papain. Different from the sol–gel process based on commonly used TEOS, the biofriendly sol–gel process developed in this study could be conducted rapidly at ambient temperature without the addition of any organic solvent or acidic catalyst. In particular, the mechanical strength and microstructure of resultant hybrid gel matrix could be modulated by HTPG amount. In comparison with free papain, the encapsulated papain is characteristic of improved enzymatic activity, thermal and storage stability as well as good reusability.     

A simple sol–gel hydrothermal method for the synthesis of defective TiO2 nanocrystals with excellent visible-light photocatalytic activity

Research on Chemical Intermediates - Defective TiO2 nanocrystals (D-TiO2) were synthesized by a simple, mild and green sol–gel hydrothermal method. The as-prepared sample possesses a high...     

Synthesis and characterization of an aliphatic monoimide-bridged polysilsesquioxane by the sol–gel route

Based on differential scanning calorimetry data, it was shown that the reaction of (3-triethoxysilylpropyl)succinic anhydride and (3-amino)propyltriethoxysilane at 110 °C resulted in the formation of polyamic acid, whereas the thermal treatment at 220 °C led to the generation of an aliphatic monoimide-bridged polysilsesquioxane as proved by FT-IR. X-ray powder diffraction studies showed a prominent reflection at 2θ = 6.66° (d = 1.32 nm) revealing that a crystalline area is formed. ²⁹Si CP-MAS-NMR and ¹³C CP-TOSS-MAS-NMR measurements proved that no cleavage of the Si–C bond occurred, and a highly condensed material was obtained.     

A simple strategy for the synthesis of Zn-IL-SBA-15 by sol–gel and the application in desulfurization

Journal of Sol-Gel Science and Technology - SBA-15 functionalized with both zinc ions and ionic liquids was simply synthesized by sol–gel method. The characterization results of Fourier...     

Polybenzoxazine–silica (PBZ–SiO2) hybrid nanocomposites through in situ sol–gel method

New type of Polybenzoxazine–silica (PBZ–SiO₂) hybrid nanocomposites was prepared through in situ sol–gel method. Benzoxazine was synthesized using bisphenol-A, trans-4-aminocyclohexanol hydrochloride and formaldehyde solution through Mannich condensation reaction and was characterized by FT-IR, ¹HNMR and ¹³CNMR spectroscopy. The methodology adopted in the present study involves to formation of hydrogen bond interaction between the benzoxazine monomer and the silica matrix, followed by the ring opening polymerization of benzoxazine monomer through thermal curing to obtain a red brown transparent PBZ–SiO₂ hybrid. The formation of hybrid nanocomposites was confirmed by FT-IR. Thermal and morphological properties of the hybrid materials were investigated by the differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA), scanning electron microscopy (SEM). The PBZ–SiO₂ hybrids show improved thermal properties and glass transition (Tg) temperature. The nitrogen porosimetry study was carried out to confirm the nanometer level integration of polybenzoxazine in the PBZ–SiO₂ hybrid nanocomposites.     

Review of mullite synthesis routes by sol–gel method

The sol–gel method for the mullite synthesis is reviewed, with particular emphasis on the characterization of monophasic and diphasic gels at low, intermediate and high temperatures and the factors that influence the hydrolysis and condensation rate of the sol–gel process, which in turn determine the properties of the final material. A wide range of studies about mullite precursors synthesized via sol–gel is discussed here.     

Low temperature transformation from γ-Fe2O3 to Ti doped α-Fe2O3 nanoparticles through an epoxide assisted sol–gel route

Maghemite and Ti doped hematite nanoparticles were synthesized through an epoxide assisted sol-gel route. Maghemite nanoparticles were prepared through the boiling of the resultant obtained by the gelation reaction of propylene oxide with FeCl₂. The production of Ti doped hematite nanoparticles follows the same preparation procedure with one difference where TiCl₃ was added to the FeCl₂ solution before reaction. The unique chemistry of the route results in the low temperature preparation of monodisperse Maghemite nanoparticles. It also minimizes the huge difference of reactivity between Ti³⁺ and Fe²⁺ ions, which guarantees the synthesis of Ti doped hematite at low temperature, resulting in the small size of the particles.