Sol–gel research in Italy

A short story of the research on sol–gel in Italy is given, and the evolution is presented and compared with the rest of the world in terms of number of publications, citations and patents. It is shown that both basic and applied research are active and effective in Italy.     

Click approaches in sol–gel chemistry

The combination of the copper-catalyzed alkyne-azide cycloaddition (CuAAC) reaction with sol–gel processing enables the versatile preparation of sol–gel materials under different shapes with targeted functionalities through a diversity-oriented approach. In this account, the development of the CuAAC reaction under anhydrous conditions for the synthesis of sol–gel precursors and for the assembling of magnetic nanoparticles on self-assembled monolayers is related, as well as the use of the classical CuAAC methodologies for the functionalization of mesoporous silica nanoparticles and microdots arrays. Coupling CuAAC and Sol–Gel will result in simplified preparations of multifunctional materials with controlled morphologies.     

Die UV-Absorption von gelöstem Kohlenoxysulfid

Zusammenfassung Anknüpfend an durchgeführte Absorptionsmessungen im Quarz-UV an Lösungen von COS und CS₂ — deren Absorptionskurven wiedergegeben werden — und älteren eigenen Arbeiten über Schwefelverbindungen werden einerseits die Unterschiede zwischen der chromophoren Carbonyl- und Thiocarbonylgruppe, anderseits die Absorptionskurven der anders absorbierenden linearen Moleküle COS, CS₂ und CO₂ diskutiert, bei denen die C=S- bzw. C=O-Gruppe sich nicht im (Thio-) Carbonylzustand befindet.Mit 2 Abbildungen.     

Sol–gel derived ion imprinted thiocyanato-functionalized silica gel as selective adsorbent of cadmium(II)

A Cd(II)-imprinted thiocyanato-functionalized silica gel adsorbent with high adsorption capacity was prepared by surface imprinting technique combined with sol–gel process for the selective adsorption of Cd(II) ion in aqueous solution, and was characterized by Fourier-transform infrared spectroscopy, nitrogen gas sorption and thermogravimetric analysis. The influences of different conditions (such as the pH of solutions, the contact time and the initial concentrations of Cd(II) ions) on the adsorption capacity of Cd(II) were investigated. The optimum pH of adsorption was in the range of 4–8.5. The adsorption equilibrium could be reached in 20 min. The relatively selectivity coefficients of the imprinted silica were higher than those of the non-imprinted adsorbents. Ho’s pseudo-second-order model well described the kinetics of the adsorption reaction. The adsorption process of metals followed Redlich–Peterson isotherm model, and the experimental value of maximum adsorption capacity for Cd(II) was 72.8 mg·g^?1. The positive value of ΔH ^o suggested endothermic nature of Cd(II) adsorption on the imprinted silica adsorbent. Increase in entropy of adsorption reaction was shown by the positive value of ΔS ^o and the negative value of ΔG ^o indicating that the adsorption was spontaneous in nature.     

Preparation of hollow titania and strontium titanate spheres using sol–gel derived silica gel particles as templates

A facile approach, based on polyelectrolyte-mediated electrostatic adsorption of a water-soluble titanium complex on colloidal templates and hydrothermal treatment, is presented for the formation of hollow titania (TiO₂) and strontium titanate (SrTiO₃) spheres. Monodispersed silica gel particles were prepared by the sol?Cgel method and adopted as core templates. Deposition of a water-soluble titanium complex, titanium (IV) bis(ammoniumlactato)dihydroxide (TALH), on the silica gel particles was carried out via the layer-by-layer assembly technique. Hollow spheres were successfully formed from the core?Cshell particles. The silica gel particles used as core templates dissolved during hydrothermal treatment because of the particles?? undeveloped siloxane network. In addition, the hydrothermal treatment induced crystallization of the hollow shells. Therefore, the hydrothermal treatment played two roles; removal of the silica templates and crystallization of the hollow shells. When deionized water was used, hollow TiO₂ spheres were obtained. Hollow SrTiO₃ spheres could also be formed when an aqueous solution of Sr(OH)₂ was used. The approach presented here could be exploited as a novel and sustainable approach for the fabrication of a range of different inorganic hollow spheres.     

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.     

Microwave-assisted sol–gel synthesis for molecular imprinting

Molecularly imprinted polymers have been the subject of intense research for several decades in both academic and industrial settings. In this paper, we introduce a novel microwave-assisted sol–gel method for molecular imprinting of silica microspheres. The microspheres were characterized, and their adsorption of imprint and non-imprint molecules was investigated. The dye molecules methyl orange and ethyl orange were used as templates. Good molecular imprinting was observed as evaluated by the re-adsorption of dye into the silica matrix followed by the removal of dye from the supernatant solution.     

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.     

Photochromic hybrid sol–gel films containing naphthopyrans

Abstract  

Several photochromic benzo- and naphthopyrans were embedded in hybrid organic–inorganic ureasilicate based films obtained by a sol–gel process. The resulting films, containing 0.1% (w/w) of the photochromic compound, were transparent and flexible and for naphthopyrans they were colourless or presented just a slight colouration. Under UV continuous irradiation the films developed a significant absorption in the visible region that fades in the dark with variable kinetics depending on the naphthopyran structure. 2,2-Diphenyl-3H-naphtho[2,1-b]pyran films showed a very fast colouration under UV light giving rise to coloured open forms, containing mainly the TC isomer (98%) along with a very small amount of the more stable TT isomer (2%), that practically returned to the initial absorbance in 1 min.     

Proteins conjugation with ZnO sol–gel nanopowders

The conjugation between probe biomolecules and inorganic nanoparticles has been studied. Three different and biologically relevant proteins, bovine serum albumin (BSA), lysozyme (LSZ) and Ribonuclease A (RNAseA), have been selected as model systems because of their difference in size and isoelectric point. Zinc oxide nanoparticles, synthesized via sol–gel, have been thoroughly characterized by X-ray Photoelectron Spectroscopy, Scanning Electron Microscopy and X-ray Diffraction, and subsequently used as platforms for immobilization of the biomolecules. The interaction of the three proteins with the ZnO surface was performed in phosphate buffer solutions at pH 7.2 in order to mimic physiological fluids and was investigated through fluorescence experiments. The obtained results indicate that conjugation of BSA, LZS and RNAseA on the oxide nanoparticles was mostly dictated by the overall charge of the different proteins. Electrostatic bonds dominate the formation of the protein/ZnO conjugates, whereas the size of the proteins seems to play a negligible role under the adopted experimental conditions.     

Die Mikro-Molekulargewichtsbestimmung gelöster Substanzen durch Dampfdruckmessung

Zusammenfassung Die bereits beschriebene Methode zur Molekulargewichtsbestimmung durch Dampfdruckmessung konnte in apparativer Hinsicht weiter verbessert werden. Durch Anwendung eines verkürzten, nur Dampfdruckdifferenzen anzeigenden Manometers ergab sich eine einfachere und leichter zu handhabende Apparatur. Die Genauigkeit der Bestimmung und der Anwendungsbereich der Methode haben sich nicht geändert. Die Dauer einer Bestimmung im Serienbetrieb beträgt zirka 20 Minuten.

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Summary The method previously described for determining the molecular weight through the vapor pressure was further improved from the apparative side. By using a shortened manometer, which indicates merely differences in vapor pressure, there resulted an apparatus which was more simple and easier to manipulate. The accuracy of the determination and the range of application were not affected. If series determinations are run, a single determination consumes around 20 minutes.

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Résumé La méthode antérieurement décrite pour la détermination des masses moléculaires par mesure de tension de vapeur a été améliorée quant à l'appareillage correspondant. L'emploi d'un manomètre plus court n'indiquant que les différences de tensions de vapeur a permis de réaliser un appareil plus simple et plus facile à manipuler. La précision de la méthode et son domaine d'emploi n'ont pas varié. La durée d'une détermination incluse dans une série est d'environ 20 minutes.

     

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.     

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      

Ionic liquid-mediated sol–gel coatings for capillary microextraction

Ionic liquid (IL)-mediated sol–gel hybrid organic–inorganic materials present enormous potential for effective use in analytical microextraction. This opportunity, however, has not yet been explored. One obstacle to materializing this prospect arises from high viscosity of ILs significantly slowing down sol–gel reactions. In this work, we developed a method that overcomes this hurdle and provides IL-mediated advanced sol–gel materials for capillary microextraction (CME). We examined two different ILs: (a) a phosphonium-based IL, trihexyltetradecylphosphonium tetrafluoroborate, and (b) a pyridinium-based ionic liquid, N-butyl-4-methylpyridinium tetrafluoroborate. These ILs were evaluated in conjunction with two types of hydroxy-terminated polymers: (a) two Si–OH terminated polymers (PDMS and BMPO), and (b) two C–OH terminated polymers (PEG and polyTHF) that differ in their sol–gel reactivity. Scanning electron microscopy results demonstrate that ILs can serve as porogenic agents in sol–gel reactions. The IL-mediated sol–gel coatings prepared with silanol-terminated polymers provided up to 28 times higher extractions in off-line CME-GC compared to analogous sol–gel coatings prepared without any IL in the sol solution. Contrary to this, the IL-mediated sol–gel coatings prepared with C–OH terminated polymers provided lower extraction efficiencies compared to their IL-free counterparts. These observations were explained by (a) lower sol–gel reactivity of C–OH groups in PEG and polyTHF compared to Si–OH groups in PDMS and in hydrolyzed alkoxysilane precursors and (b) extremely high viscosity of ionic liquids. This study shows that IL-generated porous morphology alone is not enough to provide effective extraction media: careful choice of the organic polymer and the precursor with close sol–gel reactivity must be made to ensure effective chemical bonding of the organic polymer to the created sol–gel material to be able to provide the desired sorbent characteristics. Additionally, IL-mediated sol–gel PDMS coatings provided run-to-run RSD values of 4.2–5.0% and detection limits ranging from 3.2 ng/L to 17.4 ng/L. PDMS sol–gels prepared without ILs provided RSD values of 2.8–14.1%, and detection limits ranging from 4.9 ng/L to 487.0 ng/L.     

Um in Mineral?l gel?ste Cellulosederivate

Ohne Zusammenfassung     

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.     

Zur Bestimmung von gel?stem Sauerstoff in Kohlenwasserstoffen

Ohne Zusammenfassung     

Non-aqueous sol–gel preparation of carbon-supported nickel nanoparticles

This work addresses the novel non-aqueous sol–gel process preparation of carbon-supported nickel nanoparticles. In the sol–gel process, ethanol, nickel nitrate or nickel (П) acetylacetonate, and citric acid were used as solvent, source of metallic element, and chelating agent, respectively. Hexadecylamine (HDA), oleic acid and oleylamine were used as surfactants. The calcination process was performed under protecting Ar or N₂ flowing. Carbon supported nickel nanoparticles can be prepared by this sol–gel process. Moreover, no grain growth occurs in a temperature range of 200 K, meaning that the grain size of the nickel nanoparticles can be controlled in this sol–gel process. The nickel nanoparticles can display typical superparamagnetic behavior at room temperature when HDA has been used. This novel method is expected to have wide applications in the field of metallic nanoparticles.