Copper-Based Silica Nanotubes as Novel Catalysts for the Total Oxidation of Toluene.

Cu (10 wt%) materials on silica nanotubes were prepared via two different synthetic approaches, co-synthesis and wetness impregnation on preformed SiO2 nanotubes, both as dried or calcined materials, with Cu(NO3)2.5H2O as a material precursor. The obtained silica and the Cu samples, after calcination at 550 °C for 5 h, were characterized by several techniques, such as TEM, N2 physisorption, XRD, Raman, H2-TPR and XPS, and tested for toluene oxidation in the 20-450 °C temperature range. A reference sample, Cu(10 wt%) over commercial silica, was also prepared. The copper-based silica nanotubes exhibited the best performances with respect to toluene oxidation. The Cu-based catalyst using dried silica nanotubes has the lowest T50 (306 °C), the temperature required for 50% toluene conversion, compared with a T50 of 345 °C obtained for the reference catalyst. The excellent catalytic properties of this catalyst were ascribed to the presence of easy copper (II) species finely dispersed (crystallite size of 13 nm) on the surface of silica nanotubes. The present data underlined the impact of the synthetic method on the catalyst properties and oxidation activity.

Novel Sol-Gel Synthesis of TiO2 Spherical Porous Nanoparticles Assemblies with Photocatalytic Activity.

For this study, the synthesis of TiO2 nanomaterials was performed via a novel sol-gel method employing titanium butoxide as a metal precursor, Pluronic F127 as a templating agent, toluene as a swelling agent, and acidic water or ethanol as the reaction solvents. The method was designed by tailoring certain reaction parameters, such as the sequence of toluene addition, magnetic stirring, the type of reaction solvent, and the calcination conditions. Analysis of the specific surface area and porosity was carried out via N2 physisorption, whereas the morphological features of the solids were investigated via transmission electron microscopy. The crystalline structure of both the dried powders and the calcined materials was evaluated using X-ray diffraction analysis. It transpired that the different phase compositions of the solids are related to the specific synthesis medium employed. Under the adopted reaction conditions, ethanol, which was used as a reaction solvent, promoted the local arrangement of dispersed anatase particles, the specific arrangement of which does not lead to rutile transformation. Conversely, the use of water alone supported high-particle packing, evolving into a rutile phase. The photodegradation of Rhodamine B was used as a target reaction for testing the photocatalytic activity of the selected samples.

Adhesive and Rheological Features of Ecofriendly Coatings with Antifouling Properties.

In this work, formulations of "environmentally compatible" silicone-based antifouling, synthesized in the laboratory and based on copper and silver on silica/titania oxides, have been characterized. These formulations are capable of replacing the non-ecological antifouling paints currently available on the market. The texture properties and the morphological analysis of these powders with an antifouling action indicate that their activity is linked to the nanometric size of the particles and to the homogeneous dispersion of the metal on the substrate. The presence of two metal species on the same support limits the formation of nanometric species and, therefore, the formation of homogeneous compounds. The presence of the antifouling filler, specifically the one based on titania (TiO2) and silver (Ag), facilitates the achievement of a higher degree of cross-linking of the resin, and therefore, a better compactness and completeness of the coating than that attained with the pure resin. Thus, a high degree of adhesion to the tie-coat and, consequently, to the steel support used for the construction of the boats was achieved in the presence of the silver-titania antifouling.

Antifouling Systems Based on Copper and Silver Nanoparticles Supported on Silica, Titania, and Silica/Titania Mixed Oxides.

Silica, titania, and mixed silica-titania powders have been used as supports for loading 5 wt% Cu, 5 wt% Ag, and 2.5 wt% Cu-2.5 wt% Ag with the aim of providing a series of nanomaterials with antifouling properties. All the solids were easily prepared by the wetness-impregnation method from commercially available chemical precursors. The resulting materials were characterized by several techniques such as X-ray diffraction analysis, X-ray photoelectron spectroscopy, N2 physisorption, and temperature-programmed reduction measurements. Four selected Cu and Ag SiO2- and TiO2-supported powders were tested as fillers for the preparation of marine antifouling coatings and complex viscosity measurements. Titania-based coatings showed better adhesion than silica-based coatings and the commercial topcoat. The addition of fillers enhances the resin viscosity, suggesting better workability of titania-based coatings than silica-based ones. The ecotoxicological performance of the powders was evaluated by Microtox luminescence tests, using the marine luminescent bacterium Vibrio fisheri. Further investigations of the microbiological activity of such materials were carried out focusing on the bacterial growth of Pseudoalteromonas sp., Alteromonas sp., and Pseudomonas sp. through measurements of optical density at 600 nm (OD600nm).

Characteristics of a Cold-Adapted L-glutaminase with Potential Applications in the Food Industry.

L-glutaminases are enzymes that catalyze the hydrolysis of L-glutamine, producing L-glutamate and ammonium, and they have promising applications in pharmaceutical and food industries. Several investigations have focused on thermo-tolerant L-glutaminases; however, studies on cold-adapted L-glutaminases have not been reported. These enzymes could be useful in the food industry because they display high catalytic activity at low and room temperatures, a valuable feature in processes aimed to save energy. Besides, they can be easily inactivated by warming and are suitable to prevent decomposition of thermo-labile compounds. The objectives of this work were to characterize the L-glutaminase from the Antarctic bacterium Bizionia argentinensis and analyze its capability as flavor enhancer of protein hydrolysates. The enzyme was heterologously expressed and purified from Escherichia coli, obtaining optimum and homogeneous yields. Kinetic parameters Km and Vmax were located at the lower and upper range of values reported for L-glutaminases, suggesting high catalytic efficiency. Optimum temperature was 25 °C, and the enzyme conserved around 90% of maximum activity at 0 °C and in presence of 15% (v/v) ethanol and methanol. In saline conditions, the enzyme conserved around 80% of maximum activity in 3 M NaCl. Analysis of structural model suggested cold-adaptation features such as low Arg/(Arg+Lys) ratio and fewer intramolecular interactions than mesophilic and thermo-tolerant L-glutaminases. This work provides a novel cold-adapted L-glutaminase with promising features in the food industry.

Straightforward preparation of highly loaded MWCNT-polyamine hybrids and their application in catalysis.

Multiwalled carbon nanotubes (MWCNTs) were easily and efficiently functionalised with highly cross-linked polyamines. The radical polymerisation of two bis-vinylimidazolium salts in the presence of pristine MWCNTs and azobisisobutyronitrile (AIBN) as a radical initiator led to the formation of materials with a high functionalisation degree. The subsequent treatment with sodium borohydride gave rise to the reduction of imidazolium moieties with the concomitant formation of secondary and tertiary amino groups. The obtained materials were characterised by thermogravimetric analysis (TGA), elemental analysis, solid state 13C-NMR, Fourier-transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), potentiometric titration, and temperature programmed desorption of carbon dioxide (CO2-TPD). One of the prepared materials was tested as a heterogeneous base catalyst in C-C bond forming reactions such as the Knoevenagel condensation and Henry reaction. Furthermore, two examples concerning a sequential one-pot approach involving two consecutive reactions, namely Knoevenagel and Michael reactions, were reported.

Efficient Conversion of Carbon Dioxide by Imidazolium-Based Cross-Linked Nanostructures Containing Polyhedral Oligomeric Silsesquioxane (POSS) Building Blocks.

Polyhedral oligomeric silsesquioxanes (POSS) have been employed as molecular building blocks for the synthesis of imidazolium cross-linked networks, to be used as heterogeneous catalysts for the conversion of carbon dioxide into cyclic carbonates. Two hybrid materials with different nucleophilic species (bromide and iodide) have been prepared and characterized by means of elemental analysis, 13 C and 29 Si solid-state NMR spectroscopy, thermogravimetric analysis and IR spectroscopy. The solids were tested as the sole catalyst under metal- and solvent-free reaction conditions showing full selectivity toward the formation of cyclic carbonates. High turnover number (TON) and productivity values, up to 5502 and 1081 respectively for glycidol conversion at 100 °C and up to 4942 and 1122 for epichlorohydrin conversion at 150 °C after 3 h, were obtained. Such outstanding productivity values were ascribed to the optimal organic/inorganic (i. e., imidazolium moiety/POSS support) weight ratio. The recyclability of the materials was successfully verified for five consecutive runs allowing their consideration as promising candidates for continuous flow technologies.

Imidazolium-Functionalized Carbon Nanohorns for the Conversion of Carbon Dioxide: Unprecedented Increase of Catalytic Activity after Recycling.

Six new hybrid materials composed of carbon nanohorns (CNHs) and highly cross-linked imidazolium salts were easily synthesized using a one-step procedure based on the radical oligomerization of bis-vinylimidazolium salts (bVImiX) in the presence of pristine CNHs. The hybrid materials were characterized and employed as the sole catalysts for the conversion of carbon dioxide into cyclic carbonate by reaction with epoxides. The solids displayed excellent turnover number and productivity. Moreover, four catalysts were investigated in recycling experiments. Two catalysts containing an octyl linker between the imidazolium units and a bromide or an iodide anion showed no loss in activity after three cycles. The other two catalysts containing a p-xylyl linker and a bromide anion and different CNHs/bVImiX ratios showed an unprecedented increase of activity after recycling.

Single-Walled Carbon Nanotube-Polyamidoamine Dendrimer Hybrids for Heterogeneous Catalysis.

We report the synthesis and catalytic properties of single-walled carbon nanotube-polyamidoamine dendrimers hybrids (SWCNT-PAMAM), prepared via a convergent strategy. The direct reaction of cystamine-based PAMAM dendrimers (generations 2.5 and 3.0) with pristine SWCNTs in refluxing toluene, followed by immobilization and reduction of [PdCl4](2-), led to the formation of highly dispersed small palladium nanoparticles homogeneously confined throughout the nanotube length. One of these functional materials proved to be an efficient catalyst in Suzuki and Heck reactions, able to promote the above processes down to 0.002 mol % showing a turnover number (TON) of 48 000 and a turnover frequency (TOF) of 566 000 h(-1). In addition, the hybrid material could be recovered and recycled for up to 6 times. No leaching of the metal has been detected during the Suzuki coupling. Additional experiments carried out on the spent catalyst permitted to suggest that a "release and catch" mechanism is operative in both reactions, although during Heck reaction small catalytically active soluble Pd species are also present.