Synthesis, Characterization and Photocatalytic Behavior of SiO2 @nitrized-TiO2 Nanocomposites Obtained by a Straightforward Novel Approach.

We report on the facile synthesis of SiO2 @nitrized-TiO2 nanocomposite (NST) by calcination of TiO2 xerogel with OctaAmmonium POSS® (N-POSS; POSS=polyhedral oligomeric silsesquioxanes). The as-obtained nanoporous mixed oxide is constituted by uniformly distributed SiO2 and nitrized-TiO2 , where the silica component is present in an amorphous state and TiO2 in an anatase/rutile mixed phase (92.1 % vs. 7.9 %, respectively) with very small anatase crystallites (3.7 nm). The TiO2 lattice is nitrized both at interstitial and substitutional positions. NST features a negatively charged surface with a remarkable surface area (406 m2 g-1 ), endowed with special adsorption capabilities towards cationic dyes. Its photocatalytic behavior was tested by following the degradation of standard aqueous methylene blue and methyl orange solutions under UV and visible light irradiation, according to ISO 10678:2010. For comparison, analogous investigations were carried out on a silica-free N-TiO2 , obtained by using NH4 Cl as nitrogen source.

Analytical assessment to develop innovative nanostructured BPA-free epoxy-silica resins as multifunctional stone conservation materials.

Bisphenol A (BPA)-free epoxy resins, synthesized from low molecular weight cycloaliphatic compounds, may represents promising materials for stone conservation due to their very appealing and tunable physico-chemical properties, such as viscosity, curing rate and penetration ability, being also easy to apply and handle. Furthermore, alkoxysilanes have been widely employed as inorganic strengtheners since they are easily hydrolysed inside lithic substrates affording SiO linkages with the stone matrix. Taking into account the advantages of these two classes of materials, this work has been focused on the development of innovative conservation materials, based on hybrid epoxy-silica BPA-free resins obtained by reaction of 1,4-cycloexanedimethanol diglycidylether (CHDM-DGE) with various siloxane precursors, i.e. glycidoxypropylmethyldiethoxysilane (GPTMS), tetraethyl orthosilicate (TEOS) and isobutyltrimethoxysilane (iBuTMS), using the 1,8-diaminooctane (DAO) as epoxy hardener. Thanks to Raman spectroscopy the synthesis processes have been successfully monitored, allowing the identification of oxirane rings opening as well as the formation of the cross-linked organic-inorganic networks. In accordance with the spectroscopic data, the thermal studies carried out by TGA and DSC techniques have pointed that GPTMS is a suitable siloxane precursor to synthesize the most stable samples against temperature degradation. GPTMS-containing resins have also shown good performances in the dynamic mechanical analysis (DMA) and in contact angle investigations, with values indicating considerable hydrophobic properties. SEM analyses have highlighted a great homogeneity over the entire observed areas, without formations of clusters and/or aggregates bigger than 45 µm, for the cited materials, confirming the efficiency of GPTMS as coupling agent to enhance the organic/inorganic interphase bonding. The variations provided by the incorporation of nanostructured titania, specifically synthesized, inside the epoxy-silica hybrids have been also evaluated. According to all the collected results, the hybrid materials here reported have proven to be promising multifunctional products for potential application in the field of stone conservation.

Novel Luminescent Ionic Adducts Based on Pyrene-1-sulfonate.

The potential of pyrene-1-sulfonate to act as an emitting anion for the development of ionic liquids is explored here. Amphiphilic trimethylpropylammonium hepta(isooctyl)octasilsesquioxane and conventional imidazolium, namely, 1-vinyl-3-hexyl-, 1-vinyl-3-decyl-, and 1-methyl-3-decyl-imidazolium, featuring moderate alkyl chain length substituents, have been chosen as countercations. The new species have been synthesized via simple metathesis reactions involving pyrene-1-sulfonate sodium salt and the appropriate halide cation precursors. Their thermal behavior has been investigated by thermogravimetric and differential scanning calorimetry at different scanning rates. According to this latter technique, only the trimethylpropylammonium hepta(isooctyl)octasilsesquioxane pyrenesulfonate adduct, displaying a reversible glass transition at -4.2 °C, may be classified as an ionic liquid. All pyrene-1-sulfonate imidazolium-based ion pairs are crystalline solids with the melting point just above 100 °C that produce very complex, nonreversible, and scanning rate-dependent thermograms, very likely arising from polymorphism phenomena. Such a behavior may be attributed to the pyrene-1-sulfonate polycyclic system, which in solution, as confirmed through spectroscopic characterization, displays a general attitude in promoting supramolecular structures via cation interactions. Emission lifetime measurements on the emitting fluorophore reveal that there are at least two different active species, whereas light scattering measurements show the presence of aggregates with hydrodynamic radii depending on the medium and adduct concentration. Tests aimed at investigating the potential of these novel pyrene-1-sulfonate salts in functionalization/exfoliation of graphite flakes are also reported here.

Selective monitoring of parts per million levels of CO by covalently immobilized metal complexes on glass.

Optical detection of parts-per-million (ppm) levels of CO by a structurally well-defined monolayer consisting of bimetallic rhodium complexes on glass substrates has been demonstrated.

Redox-active dirhodium(II,II) species covalently entrapped into a methylmethacrylate backbone.

A novel class of polymers was obtained by insertion of dirhodium(II,II) metal systems into a methacrylate backbone; the synthesis was realized by free radical polymerization of an appropriate methacrylate-functionalized dirhodium polymer precursor, namely [Rh2(form)2(MA-COO)2](form =N,N'-di-p-tolylformamidinate)(MA-COO = 2-(methacroyloxy)ethyl-phthalate), with methylmethacrylate (MMA); the new copolymers, in solution, show reversible CO-absorption, connected to the axial reactivity of dirhodium(II,II) species.

In situ polymerization of 3-glycidoxypropyl trimethoxysilane (GLYTS) as a new tool for stone conservation.

The effectiveness, as stone restoration materials, of a series of polymers obtained by "in situ polymerization" of the epoxy derivative 3-glycidoxypropyltrimethoxysilane (GLYTS) with the primary amine 3-aminopropyltriethoxysilane (ATS), at various molar ratios and concentrations, has been explored through selected preliminary tests. The experiments carried on a low-porosity quartzite show that, independently from concentration and molar ratio, all of the mixtures fail to significantly affect the porosimetric and hydric properties of this stone while inducing not negligible chromatic alterations. As it concerns high porosity stones, such as Comiso calcarenite, the 2:1 15% mixture only has been selected for further experiments since preliminary tests show that it acts as an excellent barrier against water penetration either by capillarity as by total immersion while showing only negligible chromatic alterations.

Trimethoxysilylpolymethacrylate as new material for stone conservation. Porosimetric and colorimetric investigations.

Aimed to obtain new materials for the conservation of stone substrates, we report here on the synthesis of a polymer which has been obtained by inducing polymerization on a methacrylate monomer functionalized by alchoxysilane groups. Two lithotypes, the Comiso calcarenite and Mistretta quartzite, stones largely used in artworks of north-eastern Sicily, were treated with the above polymer and its conserving efficacy evaluated in terms of porosimetric features, hydric properties and appearance. The collected data were compared to those provided, under the same experimental conditions, by an ethylmethacrylate/methylmethacrylate copolymer and an alkylalchoxysilane, products widely employed in the protection of stones. Experiments aimed to test the durability of the above polymer against UV artificial ageing are also reported.

New Adducts of Dirhodium(II) Formamidinate Complexes with Polycyano Acceptor Molecules. X-ray Crystal Structure of the Tricyanomethanide Complex Rh(2)(form)(4)[C(CN)(3)] (form = N,N'-Di-p-tolylformamidinate).

The dirhodium(II) formamidinate complexes Rh(2)(form)(2)(O(2)CCF(3))(2)(H(2)O)(2) (I) and Rh(2)(form)(4) (II, form = N,N'-di-p-tolylformamidinate) react with the polycyano acceptor molecules tetracyanoethylene (TCNE), tetracyano-p-quinodimethane (TCNQ), 2,5-dimethyl-N,N'-dicyano-p-quinonediimine (2,5-DMDCNQI), and N,N'-naphthocyano-p-quinonediimine (NCNQI) giving species whose nature is critically dependent on the redox potentials of the two parent complexes. Complex I reacts via axial coordination with negligible charge transfer (CT) from the dimetal unit to the ligand. With TCNE, it gives the labile monoaxial adduct Rh(2)(form)(2)(O(2)CCF(3))(2)(TCNE) (1), which easily loses the cyano ligand restoring the parent complex. TCNQ, 2,5-DMDCNQI, and NCNQI react with I giving polymeric materials of composition {[Rh(2)(form)(2)(O(2)CCF(3))(2)](2)TCNQ)}(n)() (2) and [Rh(2)(form)(2)(O(2)CCF(3))(2)X](n)() (X = 2,5-DMDCNQI (3), NCNQI (4)). The reaction of II with TCNE, TCNQ, and 2,5-DMDCNQI proceeds via a single electron transfer from the dimetal unit to the cyano ligand to form the CT species [Rh(2)(form)(4)X] (X = TCNE (5), TCNQ (6), 2,5-DMDCNQI (7)). Electrochemical and EPR measurements suggest a different extent of coordination between the polycyano fragment and the dirhodium unit, depending upon the polarity of the solvents. Attempts to crystallize complex 5 from acetonitrile unexpectedly led to the formation of the tricyanomethanide complex Rh(2)(form)(4)[C(CN)(3)] (5A), arising from the unprecedented transformation of the tetracyanoethylenide ion into the tricyanomethanide anion. The complex crystallizes in the tetragonal P4/ncc space group with a = 14.169(6) Å, c = 29.20(2) Å, V = 5863(5) Å(3), and Z = 4. The molecule consists of a dirhodium unit symmetrically bridged by four formamidinate ligands and one tricyanomethanide anion N-coordinated at the axial position of Rh(2).