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Sol-Gel chemistry is a “bottom-up” synthesis route that starting from simple molecules allows to obtain films, particles (also nano), fibers, gels and bulk materials both glassy than crystalline. Silicatic materials are generally obtained from the following Si precursors: tetramethoxysilane (TMOS) or tetraethoxysilane (TEOS). The chemistry is based on the very well-known hydrolysis and polycondensation reactions. In alkaline environment monodisperse silica particles may be easily obtained with sizes from a few nanometers till micron (“Stöber” method). The above reminded reactions occur at room temperature allowing matching their formation with polymer chemistry. In the “in situ” strategy, nanoparticles are produced in the presence of a monomer before polymerization is promoted. In this communication a series of innovative self-responsive materials for aeronautical applications produced by the research group using the Sol-Gel chemistry will be shown.

Different spectroscopic techniques have been applied to fluorine doped ZnO powders prepared through hydrothermal synthesis, to discern the effective capability of F atoms to improve ZnO conductivity. From XRD analysis, no lattice distortion was observed up to F doping at 5 at. % concentration. Photoluminescence measurements and electron paramagnetic resonance data show that F atoms tend to occupy oxygen vacancies, inducing the onset of luminescence centers. The resulting doping effect consists into the increment of localized charge, as also proved via THz spectroscopy, where the Drude-Smith model has been applied to extract quantitative information on the electrodynamic parameters of ZnO:F samples. Results show that F doping does not produce any substantial change of plasma frequency but only the enhancement of scattering rate due to an increase of grain boundary density. Our measurements are in agreement with theoretical calculations asserting that the energy required to excite donor levels is on the order of 0.7 eV, and therefore, the doping mechanism is ineffective at room temperature.

The generation and stabilization of reactive oxygen species (ROS), including the superoxide radical anion (O2-), have a huge potential in environmental remediation and industrial chemical processes, but they still remain a challenge. Here, we elucidate the formation, stability and reactivity of superoxide radicals spontaneously produced on the surface of a hybrid TiO2-acetylacetonate material exposed to air. EPR spectra reveal an exceptional lifetime (up to three years, in air at room temperature) of the adsorbed O2-, which can also be easily regenerated after its decay. The performances of this material in the degradation of organic pollutants in aqueous solution without any light irradiation indicate a heterogeneous catalytic mechanism, mediated by superoxide radicals, with a synergistic homogeneous action of hydroxyl radicals (OH), which are released in solution, as detected by the EPR spin trapping method. The regeneration ability of the adsorbed superoxide radicals by simple exposure to air counteracts the partial instability in aqueous environment of the organic component of the hybrid structure allowing the catalyst reuse. These structural and functional features joined to the simple preparation route open a new perspective in the field of advanced oxidation processes for hybrid TiO2 materials.

The search for efficient routes for the production of sorbitol from starch-derived glucose is of great interest and importance because sorbitol is a highly attractive chemical for different applications, such as a building block for the synthesis of fine chemicals, additives in food, and the cosmetic and paper industries. In this study, the (RuO2)0.038·(SiO2)0.962 nanomaterial was prepared by a one-pot sol–gel route. The performances of the gel-derived catalyst in the glucose hydrogenation reaction, in the aqueous phase and mild conditions, are reported and compared with those of a commercial Ru/C catalyst. When the commercial Ru/C catalyst was used, a high activity and no selectivity loss were observed, but the activity dramatically dropped soon after the first cycle; on the contrary, the gel-derived catalyst activity increased during the first three cycles. The different catalytic behavior was ascribed to the morphological distribution of the Ru active phase in the gel-derived catalyst. Actually, the adopted synthesis procedure leads to a multimodal size distribution of the Ru nanoparticles, which are fairly stabilized by a combined interaction with the SiO2 support and the reaction environment, which proved to be active in obtaining a self-activating catalyst.

Matrix Assisted Pulsed Laser Evaporation (MAPLE) is a thin film deposition technique which uses a pulsed laser beam impinging, inside a high vacuum chamber, on a frozen target containing the guest molecules in a volatile matrix to induce fast “evaporation” of the matrix, and ejection of the guest molecules. Lipase, an enzyme acting as a catalyst in hydrolysis of lipids, is widely used in biosensors for detection of triglycerides in blood serum. A key action to this purpose is lipase immobilization on a substrate. In a recent paper, we have shown that MAPLE technique is able to deposit lipase on a substrate in an active form. Here we show that addition to the guest/matrix target of a small amount of m-DOPA (3-(3,4-dihydroxyphenyl)-2-methyl-l-alanine) in order to improve adhesion and protect lipase secondary structure, also allows the lowering the laser pulse energy required for matrix evaporation and therefore the risk of damaging the enzyme. Keywords: MAPLE, Lipase, m-DOPA, Biosensors

The catalytic activity of niobium oxide-based materials, containing the same amount of Nb 2 O 5 (∼15 wt%) and prepared by different methods, with that of pure Nb 2 O 5 in the epoxidation of methyl oleate with hydrogen peroxide was compared. The catalytic performances of the catalyst prepared by impregnation do not differ substantially from the ones of Nb 2 O 5 . The performances of Nb-supported catalysts prepared by sol–gel can be modulated by controlling the process parameters. The high dispersion of the active NbO x species obtained by this preparation method gives very higher selectivity than in the case of pure Nb 2 O 5 . Morphologic and structural characterization of the catalysts helped justifying the obtained catalytic results in terms of activity and selectivity.

The hybrid sol-gel zirconia-acetylacetonate amorphous material (HSGZ) shows high catalytic activity in oxidative degradation reactions without light or thermal pretreatment. This peculiar HSGZ ability derives from the generation of highly reactive oxygen radical species (ROS) upon exposure to air at room conditions. We disclose the origin of such unique feature by combining EPR and DRUV measurements with first-principles calculations. The organic ligand acetylacetonate (acac) plays a pivotal role in generating and stabilizing the superoxide radical species at the HSGZ-air interfaces. Our results lead the path toward further development of HSGZ and related hybrid materials for ROS-based energy and environmental applications.

Co/SiO2 catalysts with two Co contents of 10 and 30 mol% were prepared and used in ethanol steam reforming. With the aim of tailoring the materials features by varying the synthesis parameters, two different sol-gel procedures were designed, namely a modified hydrolytic alkoxide sol-gel synthesis and a (non-ionic) surfactant assisted one. Effect of the synthesis procedure on the physico-chemical properties of the prepared catalysts is in the focus of the present investigation. The obtained Co/SiO2 catalysts were characterized by means of X-rays powder diffraction, diffuse reflectance UV-Vis spectroscopy, N-2 adsorption/desorption isotherms at 196 degrees C, field emission scanning electron microscopy equipped with energy dispersive X-ray probe, temperature-programmed reduction and CO adsorption at nominal 196 degrees C as followed by IR spectroscopy. The oxidation state of Co species within the SiO2 matrix was affected by the synthesis method. In particular, the non-ionic surfactant, acting both as pores template and as chelating agent of Co ions during the synthesis, prevented the formation of Co3O4 phase leading to a higher dispersion and higher temperature reducibility of Co species with respect to samples with same Co content synthesized without surfactant. The fine balance between Co dispersion and reducibility was the fundamental parameter governing the activity of the Co/SiO2 catalysts in terms of H-2 production, CO/CO2 ratio and C balance during ethanol steam reforming.

Glucosidase (BG) was immobilized by adsorption on wrinkled silica nanoparticles (WSNs) giving an active and stable biocatalyst for the hydrolysis of cellobiose. WSNs exhibiting both a central-radial pore structure and a hierarchical trimodal micro-/mesoporous pore size distribution were synthesized. They were used as a matrix to immobilize BG, obtaining a biocatalyst (BG/WSNs) containing 150 mg of enzyme per gram of matrix. A complete textural and morphological characterization of BG/WSNs performed by the Brunauer-Emmett-Teller (BET) method, thermogravimetric (TG), Fourier transform infrared (FT-IR), and transmission electron microscopy (TEM) analyses showed that this matrix can generate a microenvironment particularly suitable for this enzyme. The immobilization procedure used allowed preserving most of the secondary structure of the enzyme and, consequently, its catalytic activity. The kinetic parameters of the cellobiose hydrolysis performed with the biocatalyst were determined and compared with those of the free enzyme. It was found that the apparent KM value of the biocatalyst was slightly lower than that of the free enzyme, indicating that the enzyme-substrate affinity was increased. A complete hydrolysis of cellobiose was observed for four consecutive runs, showing a high operational stability of the biocatalyst

Candida rugosa lipase (CRL) was deposited by matrix assisted pulsed laser evaporation (MAPLE) in order to immobilize the enzyme with a preserved native conformation, which ensures its catalytic functionality. For this purpose, the composition of the MAPLE target was optimized by adding the oil phase pentane to a water solution of the amino acid 3-(3,4-dihydroxyphenyl)-2-methyl-l-alanine (m-DOPA), giving a target formed by a frozen water-lipase-pentane microemulsion. Fourier transform infrared (FTIR) spectroscopy and atomic force microscopy (AFM) were used to investigate the structure of MAPLE deposited lipase films. FTIR deconvolution of amide I band indicated a reduction of unfolding and aggregation, i.e., a better preserved lipase secondary structure in the sample deposited from the frozen microemulsion target. AFM images highlighted the absence of big aggregates on the surface of the sample. The functionality of the immobilized enzyme to promote transesterification was determined by thin layer chromatography, resulting in a modified specificity.

The oxidative degradation of 2-methyl-4-chlorophenoxyacetic acid (MCPA), 4-(4-chloro-2-methylphenoxy)butanoic acid (MCPB), 4-chlorophenoxyacetic acid (4-CPA) and 2,4-dichlorophenoxyacetic acid (2,4 D) by ZrO2-acetylacetonate hybrid catalyst (HSGZ) without light irradiation was assessed. The thermal stability of the catalyst was investigated by thermogravimetry, differential thermal analysis, and Fourier transform infrared spectroscopy. For each herbicide, a virtually complete removal in about 3 days without light irradiation at room temperature was achieved. The removal kinetics of the herbicides has been satisfactorily characterized by a double-stage physico-mathematical model, in the hypothesis that a first-order adsorption on HSGZ surface is followed by the herbicide degradation, catalytically driven by HSGZ surface groups. The long-term use of the HSGZ catalyst was assessed by repeated-batch tests. The specific cost for unit-volume removal of herbicide was evaluated by a detailed cost analysis showing that it is comparable with those pertaining to alternative methods.

A method is developed for rapid preparation of titania substrates using a sol–gel preparation route in combination with an amphiphilic block copolymer (BCP) template, acting as structure directing agent. The method consists in performing the spin coating of an initial solutions of BCP and titania species in a controlled atmosphere using a flux of solvent vapors (Rapid-Flux-Solvent-Atmosphere, RFSA method). The method is demonstrated in the case of thin films of polystyrene-b-poly(oxyethylene) BCP (PS-PEO) with cylindrical morphology of PEO domains in the PS matrix, characterized by the selective inclusion of titanium species inside the PEO cylinders. Upon removal of the organic matrix by heat treatment at 600 °C, titania substrates of different morphology are obtained depending on the concentration of titania precursor and processing conditions. The method allows preventing the negative effect of hydrolysis and condensation reactions of Ti species and titania substrates with morphology reminiscent of that one achieved in the hybrid nanostructured thin films are obtained. The RFSA method is simple, direct, and it is of particular interest for systems that require a short processing time to eliminate the solvent and to obtain regular nanostructured thin-films over large area. Merit figures such as the degree of hexagonal order and the degree of coverage of the surface with titania motifs are identified to characterize the hybrid composites and titania substrates.

Manganese oxide catalysts supported on monolithic yttria stabilized zirconia honeycombs were studied for H 2 O 2 decomposition in view of space propulsion applications. The materials were prepared by impregnation (IM), precipitation (PR) and sol–gel (SG) methods and characterized by N 2 adsorption, SEM and H 2 temperature programmed reduction (TPR). The catalytic activity for H 2 O 2 decomposition was studied under vapour phase conditions. The tests were carried out in a flow apparatus at T = 200 °C, gas hourly space velocity (GHSV) = 2.00 and 2.67 s −1 , H 2 O 2 concentrations of 11.3 mol%. The redox properties of the catalysts were markedly influenced by the preparation method. In the SG catalyst, a large fraction of Mn was not reducible in the TPR tests differently from the PR and IM materials. Despite this effect, the SG catalyst showed an activity comparable or higher than that of PR and IM, due to a more effective dispersion of Mn species. A too strong effect of space velocity on H 2 O 2 conversion was attributed to an autocatalytic effect. A radical mechanism was hypothesized: it was assumed that a reaction between O 2 and Mn species produced radicals that promoted the overall reaction.

Here, we report the structural characteristics, the surface properties, and the catalytic performances of a Nb–P–Si ternary oxide material (2.5Nb2O5·2.5P2O5·95SiO2, 2.5NbP) in two reactions of importance for biomass valorisation and green industrial production: hydrolysis of inulin and esterification of oleic acid with polyalcohol for biolubricant production. High dispersion of the Nb centers, ascertained by UV–vis–DRS, 29Si, 31P, and 1H solid-state NMR spectroscopy, is the key point for the successful activity of 2.5NbP. Intrinsic and effective acidities of the sample were studied by FT-IR of adsorbed pyridine in the absence and presence of water and by volumetric titrations of the acid sites in cyclohexane and in water, to enlighten the nature and amount of acid sites in different environments. For both studied reactions, 2.5NbP catalyst exhibits water-tolerant acidic sites, mainly Brønsted ones, giving higher activity and better stability in the reaction medium than well-known niobium oxophosphate catalyst, which is considered one of the best water-tolerant acid catalysts.

Factors tuning the functional performances of the various TiO2-based materials in the wide range of their possible applications are poorly understood. Here the electronic structure of TiO2-based materials characterized by Ti3+ self-doping, obtained by a sol–gel route wholly performed in air at room temperature, is reported. In the amorphous hybrid TiO2–acetylacetonate (HSGT) material the formation of the Ti(IV)–acac complex makes it photoresponsive to visible light and allows us to obtain by means of a simple annealing in air at 400 °C a very stable black Ti3+ self-doped anatase TiO2 nanomaterial (HSGT-400), characterized by an extraordinary high concentration of Ti atoms with oxidation states lower than IV (about 26%), which absorbs light in the entire visible range. The very high stability of HSGT-400 is mainly related to the process, which does not require the use of harsh conditions nor external reducing agents. The electronic structure of HSGT, owing to the presence of the Ti(IV)–acac complex, allows the stabilization of superoxide anion radicals on its surface for a very long time (months) at room temperature. The extraordinary low recombination rate of electron–hole pairs gives to HSGT unusual catalytic performances at room temperature allowing the complete removal of 2,4-dichlorophenol from water in about one hour without any light irradiation. Our results clearly highlight the connection among the production process of TiO2-based materials, their electronic structure and, finally, their functional behaviour., RSC Advances, 7 (4), ISSN:2046-2069

A TiO2–based hybrid material (HSGT), obtained by a sol–gel route wholly performed in air at room temperature, was used as catalyst for the oxidative degradation of 2,4-dichlorophenol (2,4-DCP), 4- chlorophenoxyacetic acid (4-CPA) and phenanthrene (PHE). Acetylacetonate ligands, used as complexing/sensitizing molecules, was added directly to the solution containing the precursors of titanium. In the presence of air, the acetylacetonate ligands on the HSGT surface were able to generate stable superoxide radicals, as demonstrated by EPR measurements. The presence of superoxide radicals correlated to the catalytic activity of HSGT. ThDue to the stability of the free radicals, HSGT can be considered a promising catalyst for the degradation of organic pollutants.

The crystallization behavior of two new stable glasses belonging to the BaO−K2O−Na2O−Nb2O5−SiO2 system, synthesized by the melt-quenching technique, was studied with the aim to obtain nanostructured glasses based on tungsten−bronze phases. Nanostructured samples with valuable second harmonic generation (SHG) activity were obtained starting from 8BaO·15Na2O·27Nb2O5·50SiO2 glass after suitable heat treatments performed in the glass transition range, by means of the bulk nucleation mechanism. The influence of the devitrification mechanism on the SHG efficiency was clarified with particular reference to the effect of structural modifications on the transparency of the nanostructured glasses. These samples are formed by Ba2NaNb5O15 nanocrystals (about 15 nm in size) randomly dispersed in a phase-separated amorphous matrix. Their SHG efficiency is partially impaired by the Rayleigh scattering originated by the nanocrystals. These nanostructured glasses can be useful when the generation efficiency is not an issue, as in the diagnostics for ultrafast lasers, due to the independence of the second harmonic generation from the polarization state of the laser light and no need for preferential material orientation.

The main aspects of the sol–gel synthesis of ZnO thin films were critically examined with particular reference to the optimization of the process parameters that influence specific properties of the films, such as the transparency, the crystallization behavior and the electrical resistivity. Starting from zinc acetate dihydrate, anhydrous ethanol and triethanolamine, a valuable sol–gel route was set. This route allowed the preparation of transparent ZnO thin films by dip-coating. Triethanolamine, thanks to its high chelating efficiency towards Zn2+, permitted to prepare stable zinc acetate dihydrate solutions wholly at room temperature. The structural, optical and morphological characteristics of the films were examined by glancing incidence X-ray diffraction, UV–vis spectroscopy and atomic force microscopy. Single layer films, with a thickness of about 120 nm, characterized by a high adhesion force (about 140 Kg cm−2), were obtained. The crystallization behavior of dip-coated amorphous films was explored in the 500–600 °C range; polycrystalline films, formed by randomly oriented ZnO nanocrystals (about 20 nm), with an average transmittance higher than 90% in the visible region, were obtained. Finally, a strong influence of annealing environment on electrical resistivity was observed.

A class II hybrid sol-gel material was prepared starting from zirconium(IV) propoxide and 2,4-pentanedione and its catalytic activity in the removal of the herbicide 4-chloro-2-methylphenoxyacetic acid (MCPA) was revealed. The thermal and structural characterization, performed by thermogravimetry, differential thermal analysis, and diffuse reflectance Fourier transform infrared spectroscopy, demonstrated the hybrid nature of the material. The structure of the material can be described as a polymeric network of zirconium oxo clusters, on the surface of which large part of Zr(4+) ions are involved in strong complexation equilibria with acetylacetonate (acac) ligands. The incubation of MCPA in the presence of this material yielded an herbicide removal fraction up to 98%. A two-step mechanism was proposed for the MCPA removal, in which a reversible first-order adsorption of the herbicide is followed by its catalytic degradation. The nature of the products of the MCPA catalytic degradation as well as the reaction conditions adopted do not support typical oxidation pathways involving radicals, suggesting the existence of a different mechanism in which the Zr(4+):acac enol-type complex can act as Lewis acid catalyst.

The performances of Nb2O5–SiO2 catalysts prepared by sol–gel technique in the epoxidation of soybean oil with hydrogen peroxide have been investigated. The most active catalyst showed a good activity in epoxidation reaction but also a low selectivity to epoxide. The low selectivity has been attributed to the presence on the surface besides the Lewis acid sites, that promote the epoxidation, also of strong Bronsted acid sites, that promote the reaction of ring epoxide opening by hydrolysis.

Second harmonic generation properties have been studied in 23 K2O · 27Nb2O5 · 50 SiO2 glass subjected to thermal poling. The poling-induced optical nonlinearity, with χ(2) = 3.8 pm/V, has been related to structural modifications within a surface layer of a few microns on the anode side, as evidenced by means of confocal micro-Raman mapping along the sample thickness. The data indicate that the structural changes result from a charge transport process that causes network modifications in an alkali depleted layer whose thickness is comparable with that of the non-linear region. The Raman data also indicate that in the alkali depleted layer the network polymerization degree increases as a consequence of ion migration. The origin of the nonlinearity and the mechanisms activated by poling are discussed. The mechanism of non-bridging-oxygen to bridging-oxygen bond switching is proposed to explain ion migration and the subsequent structural changes in the glass. © 2009 Elsevier B.V. All rights reserved.

Transparent glasses having molar composition (23-x)K{sub 2}O.xNa{sub 2}O.27Nb{sub 2}O{sub 5}.50SiO{sub 2} (x=0, 5, 10, 15 and 23) have been synthesized by the melt-quenching technique and their devitrification behaviour has been investigated by DTA and XRD. Depending on the composition, the glasses showed a glass transition temperature in the range 660-680 deg. C and devitrified in several steps. XRD measurements showed that the replacement of K{sub 2}O by Na{sub 2}O strongly affects the crystallization behaviour. Particularly, in the glasses with only potassium or low sodium content the first devitrification step is related to the crystallization of an unidentified phase, while in the glass containing only sodium, NaNbO{sub 3} crystallizes. For an intermediate sodium content (x=10 and 15) a potassium sodium niobate crystalline phase, belonging to the tungsten-bronze family, is formed by bulk nucleation. This system looks promising to produce active nanostructured glasses as the tungsten-bronze type crystals have ferroelectric, electro-optical and non-linear optical properties. Preliminary measurements evidenced SHG activity in the crystallized glasses containing this phase. - Graphical abstract: Synthesis of glasses (23-x)K{sub 2}O.xNa{sub 2}O.27Nb{sub 2}O{sub 5}.50SiO{sub 2} (x=0, 5, 10, 15 and 23) from which SHG active phases crystallize by bulk nucleation for non-linear optical nanostructured glasses.

Amorphous nanoheterogeneities of the size less than 100 A have been formed in glasses of the Li2O–Nb2O5–SiO2 (LNS) and Li2O–ZnO–Nb2O5–SiO2 (LZNS) systems at the initial stage of phase separation and examined by transmission electron microscopy, small-angle X-ray and neutron scattering. Both LNS and LZNS nanoheterogeneous glasses exhibit second harmonic generation (SHG) even when they are characterized by fully amorphous X-ray diffraction (XRD) patterns. Chemical differentiation and ordering of glass structure during heat treatments at appropriate temperatures higher Tg lead to drastic increase of SHG efficiency of LNS glasses contrary to LZNS ones in the frame of amorphous state of samples. Following heat treatments of nanostructured glasses result in crystallization of ferroelectric LiNbO3 and non-polar LiZnNbO4 in the LNS and LZNS glasses, respectively. Taking into account similar polarizability of atoms in LNS and LZNS glasses, the origin of the principal difference in the second-order optical non-linearity of amorphous LNS and LZNS samples is proposed to connect predominantly with the internal structure of formed nanoheterogeneities and with their polarity. Most probably, amorphous nanoheterogeneities in glasses may be characterized with crystal-like structure of polar (LiNbO3) phase initiating remarkable SHG efficiency or non-polar (LiZnNbO4) phase, which do not initiate SHG activity. It gives an opportunity to vary SHG efficiency of glasses in a wide rage without remarkable change of their transparency by chemical differentiation process at the initial stage of phase separation when growth of nanoheterogeneities is ‘frozen’. At higher temperatures, LiNbO3 crystals identified by XRD precipitate in LNS glasses initiating even more increase of SHG efficiency but visually observable transparency is impaired.

Two synthetic strategies were developed for in-situ modification of a silica sol gel matrix in a PEEK tubing, to obtain a hybrid monolith with entrapped lipases. A suitable combination of the sol-gel precursors (tetramethoxysilane, methyltrimethoxysilane and n-propyltrimethoxysilane) was found, for the simultaneous improvement of the monolith adhesion to the tubing internal surfaces and of the catalytic properties of the entrapped enzyme. The effects of the immobilization procedure were characterized as regards both the catalytic properties of the enzyme, as well as the secondary structure of lipases by FTIR. The catalytic efficiency of the entrapped enzyme was better preserved in more hydrophobic microenvironment. The improved stability of the biocatalysts allows further industrial applications.

The submicroscopic structure of lithium niobium silicate glasses of the compositions 2xLiNbO3 · (1 − x)(Li2O · 2SiO2) (x = 0.40, 0.45, 0.50) and 30Li2O · 25Nb2O5 · 45SiO2 in the initial state and after heat treatment for different times at temperatures in the vicinity of the glass transition point T g are investigated using X-ray powder diffraction, small-angle neutron scattering (SANS), synchrotron small-angle X-ray scattering (SAXS), and electron microscopy. A nanostructure with inhomogeneities ∼40 A in size is formed in glasses at the initial stages of phase separation at temperatures in the range 600–670°C. This structure is responsible for the appearance of the second-order optical nonlinearity. The SANS, SAXS, and electron microscopic data on the inhomogeneity size are in good agreement with each other. According to the X-ray diffraction, SANS, and SAXS data, the ordering of the glass structure and the difference between the density of inhomogeneities and the density of the matrix increase in the course of heat treatment. At the initial stage of amorphous phase separation, the glass decomposes into regions enriched in SiO2 and regions with an increased content of lithium and niobium. An increase in the temperature or time of heat treatment results in the precipitation of LiNbO3 ferroelectric crystals. The results obtained allow us, for the first time, to make the inference that nanoscale changes in the glass structure lead to considerable changes (by one order of magnitude and more) in the quadratic optical nonlinearity, which can be controlled by heat treatment. The origin of the second-order optical nonlinearity is associated with both the nanosized modulations of the polarizability due to the inhomogeneous glass structure and the polarity of structural nanoinhomogeneities from which the LiNbO3 phase precipitates at the later stages of phase separation.

The structure and crystallization behavior of glasses with 25La2O3 · 25B2O3 · 50GeO2 composition, melted in platinum (P glass) and corundum (A glass) crucibles, were studied by DTA, X-ray diffraction and FTIR spectroscopy. The Al2O3 dissolved from corundum crucible in the A glass was estimated to be in the range 5–7 wt%. This alumina content had almost no influence on glass transition temperature but strongly affected the structure and crystallization behavior of the A glass. In fact, the P glass showed good texture-forming ability: high quality textured glass-ceramic plates based on stillwellite-like LaBGeO5 crystals were easily obtained. On the contrary, the presence of alumina stabilized the A glass from which binary phases crystallize first, and only afterwards they are transformed in stillwellite by secondary crystallization: so in this glass texturing is hindered. Crystallization and texturing behavior of P and A glasses were well related to FTIR data. P glass contained both threefold and fourfold coordinated boron while in the A glass the presence of aluminum forced boron to assume almost exclusively threefold co-ordination. Hence the easier crystallization of stillwellite phase and the good textures obtained from the P glass contrary to the A glass, can be well understood since all boron atoms have tetrahedral co-ordination in stillwellite LaBGeO5 crystal.

High surface area phosphosilicate glasses were synthesized by a new sol-gel method and characterized for structural, textural and acid properties by XRD, TG/DTA, infrared spectroscopy (FTIR and DRIFT), solid state 31P and 29Si NMR spectroscopy, N2 adsorption and NH3 temperature programmed desorption (TPD). The glasses were synthesized by a sol-gel route hydrolyzing the precursors in an almost solely aqueous environment. Microstructural changes occurring during the conversion of the gels into the corresponding glasses were investigated. For all dried gels (383 K) the elimination of organic residues was complete at 673 K. After this heat treatment ca. 80% of the phosphorus was present as free phosphoric acid except for the sample with the highest P content for which the percentage dropped to ca. 47%. Textural properties of samples treated at 673 K were greatly influenced by the composition. Surface area decreased and pore dimension increased with increasing phosphorus content, indicating a gradual transformation of the siloxane matrix from microporous to mesoporous. Brønsted acid sites of differing strength, mainly related to the presence of phosphoric acids, were found. The surface concentration and strength of acid sites increased with phosphorus content. Key words: sol-gel; phosphosilicate glasses; IR spectroscopy; NMR; N2 adsorption isotherms; surface acidity

Glasses from which the ferroelectrics phase KTiOPO 4 can crystallise have been prepared and studied. Namely, two glasses having the 92(K 2 O·2TiO 2 ·P 2 O 5 )·8SiO 2 (KTP-8Si) and the 88(K 2 O·2TiO 2 ·P 2 O 5 )·12SiO 2 (KTP-12Si) molar compositions have been synthesised by the melt quenching technique. They were examined by differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The KTP-8Si glass devitrifies in a single step forming KTiOPO 4 phase, whereas the KTP-12Si glass firstly crystallises in an unknown phase and then, at higher temperatures, KTiOPO 4 crystallites grow. Proper heat treatments performed on the KTP-8Si glass at temperatures just below the glass transition range produce transparent samples the glassy matrix of which contains crystalline nanostructure of the KTP phase.

The first nonlinear optic nanocomposite based on a low-melting vitreous matrix and a ferrielectric crystal has been obtained. The matrix consists of lead-borate glass and the filler is single-phase powder of ferrielectric KNbSi2O7. The quadratic optical nonlinearity of composites was studied depending on temperature and time of dissolution of crystals in the glass matrix. Conditions for producing transparent nanocomposites that generate the second optic harmonic are identified.

For the first time niobium-phosphorus-silicon mixed oxide gels xNb2O5·xP2O5·(100 - 2x)SiO2, with x = 2.5 (2.5PNb), 5 (5PNb), 7.5 (7.5PNb) and 10 (10PNb), were synthesized at room temperature by an innovative sol-gel route from phosphoryl chloride, niobium chloride and tetraethoxysilane. Thermogravimetry/differential thermal analysis, X-ray diffraction, solid state 29Si and 31P NMR, Raman and Fourier transform infrared spectroscopy were used to examine the structure of dried and heat-treated (1 h at 500 °C) gels. The synthesis procedure developed in this work allowed obtaining, for each studied composition, transparent chemical gels by means of careful control of the precursor reactivity. Amorphous dried gels were obtained which were characterized by a very high degree of silicon cross-linking. Moreover, Si-O-Nb bridges were formed which allowed phosphorus to be anchored stably through Nb-O-P bonds within the gel. All heat-treated gels retain their amorphous nature with a high content of OH groups that are mainly linked to phosphorus, making them strong acidic solids.

Lipase is an enzyme that finds application in biodiesel production and for detection of esters and triglycerides in biosensors. Matrix Assisted Pulsed Laser Evaporation (MAPLE), a technique derived from Pulsed Laser Deposition (PLD) for deposition of undamaged biomolecules or polymers, is characterized by the use of a frozen target obtained from a solution/suspension of the guest material (to be deposited) in a volatile matrix (solvent). The presence of the solvent avoids or at least reduces the potential damage of guest molecules by laser radiation but only the guest material reaches the substrate in an essentially solvent-free deposition. MAPLE can be used for enzymes immobilization, essential for industrial application, allowing the development of continuous processes, an easier separation of products, the reuse of the catalyst and, in some cases, enhancing enzyme properties (pH, temperature stability, etc.) and catalytic activity in non-aqueous media. Here we show that MAPLE technique can be used to deposit undamaged lipase and that the complex structure (due to droplets generated during extraction from target) of the deposited material can be controlled by changing the laser beam fluence.

Hybrid sol–gel TiO2–acetylacetonate (HSGT) material has been synthesized via a sol–gel route. The as dried HSGT can be described as an amorphous polymeric network of titanium oxo-clusters on which surface part of Ti4+ ions are involved in strong complexation with acetylacetonate (acac) ligands. In this material a ligand-to-metal charge transfer (LMCT) is active giving light absorption in the visible region indicating a band gap of 2.5 eV, lower than crystalline TiO2. In the HSGT gel derived material the LMCT mechanism results much more active respect to ligands on crystalline nanoparticles. In presence of air, the acac ligands on the HSGT surface are able to generate and stabilize superoxide radical as resulting by EPR measurements. The ˙O2− radicals were stably adsorbed on the HSGT at room temperature for very long time. The presence of these free radicals makes HSGT material a useful catalyst in degradation of organic pollutants. Its catalytic activity has been tested in the oxidative degradation of phenanthrene resulting in a fast degradation rate in absence of any light irradiation.

Potassium niobium silicate (KNS) glasses xK2OxNb2O5(1−2x)SiO2 with x=0.167; 0.182; 0.200; 0.220 and 0.250 have been subjected to prolonged heat treatments in a wide temperature range above Tg. As a result, glasses exhibiting liquid-type phase separation phenomena have been isolated. Moreover for each glass composition, the temperature zones have been determined to produce transparent, opalescent or opaque materials which have been studied by X-ray diffraction (XRD), small-angle neutron scattering (SANS) and second harmonic generation (SHG) techniques. SANS data unambiguously point at nanostructuring of KNS glasses in the scale of 5–20 nm under appropriate heat treatments near Tg. In contrast to initial KNS glasses, nanostructured glasses exhibit SHG activity. For earliest stages of phase separation SHG-active glasses are characterized by fully amorphous XRD patterns. Further development of phase separation in glasses with increasing of their opalescence leads to diminishing SHG, and subsequently partial crystallization takes place giving opaque materials. Since relative maximum of SHG efficiency corresponds to non-crystalline nanostructured glasses, such new transparent second-order non-linear media may be of both scientific and practical interest. With regard to non-crystalline structure of nano-inhomogeneities, SHG mechanism in the glasses is supposed to be due to a combination of third-order non-linearity with a spatial modulation of linear polarizability.

In this study room temperature X-ray diffraction patterns and FTIR spectra of zeolite A in its Na form, Ba-exchanged zeolite A, hexacelsian, monoclinic celsian and Ba-exchanged zeolite A samples thermally treated at temperatures ranging from 200 to 1000 °C are reported. The combined inspection of room temperature X-ray diffraction patterns and FTIR spectra reveals the following points. 1) The thermal collapse of the microporous zeolite structure goes to completion upon thermal treatment at 200–300 °C; in the resulting amorphous phase the presence of the secondary building units of the zeolite A structure may be detected. 2) Thermal treatment in the temperature range 200–400 °C results in a middle-range order which favours the crystallisation of small crystallites of monoclinic celsian at 500 °C. 3) The further evolution of the amorphous phase in the 500–800 °C temperature range of thermal treatment instead of promoting the crystalline growth of monoclinic celsian, creates a middle-range order favourable to the crystallisation of hexacelsian which occurs at 1000 °C.

Lead germanate glasses of the xPbO(1 - x)GeO2 compositions with x ranging from 0.200 to 0.625 have been synthesised and their crystallisation behaviour and vibrational properties studied by differential thermal analysis (DTA) and Raman spectroscopy. Raman spectra of the Pb5Ge3O11 ceramics also have been measured and compared to lead germanate glass spectra and literature data on beta -PbO, Ge atoms in low lead glasses are supposed to be surrounded by four to six oxygen atoms, while the high-lead glass (x = 0.625) corresponding to stoichiometry of the Pb5Ge3O11 ferroelectrics contains predominantly fourfold coordinated germanium. Structural resemblence of high-lead germanate glasses to the Pb5Ge3O11 crystal is proposed rather than to beta -PbO. The 'boson' peak range in the spectra of lead germanate glasses is discussed taking into account the similarities of the spectra of glassy and crystalline Pb5Ge3O11. (C) 2001 Elsevier Science B.V. All rights reserved.

The crystallization of the K2O . Nb2O5. 2SiO2 (KNS-50) glass has been studied by DTA, XRD, SEM and FTIR. The as-quenched glass crystallizes in two steps during a DTA run. In the first step only potassium niobates crystallize while at the higher temperature step KNbSi207 ferroelectric crystallizes. Heat treatments of the bulk glass at temperatures not far from T-g produce a nanocrystalline structure penetrating the whole volume of the glass and clearly observed by high resolution SEM as isometric nuclei. The observed nanostructure is the result of two processes occurring during the heat treatment amorphous phase separation followed by the crystallization of the high alkali and niobium content glassy phase. The heat-treated glass, in which the nanostructure is grown, shows an additional DTA peak at about 900 degrees C related to the crystallization of an unknown crystalline phase, nor obtained in the as-quenched glass. The existence of the nanostructure clarifies the origin of SHG discovered recently in potassium niobium silicate glasses. (C) 2000 Elsevier Science B.V. All rights reserved.

The structure and the devitrification behavior of barium aluminoborate glasses, examined by Fourier transform infrared spectroscopy, differential thermal analysis and X-ray diffraction are reported. The glass compositions are expressed by the general formula: (50 - x/2)BaO .(50 - x/2)B2O3. xAl(2)O(3) with x = 2, 4 and 8. All the as-quenched glasses were phase separated. Aluminum acting as glass former gives a more polymerized structure increasing the glass stability with respect to the devitrification process. Surface crystallization was found to be dominant for all glasses, forming beta BaB2O4 nanocrystals as the main crystalline phase. (C) 1999 Elsevier Science B.V. All rights reserved.

The intrinsic catalytic activity of a hybrid gel-derived ZrO2-acetylacetonate (HSGZ) material towards the oxidative degradation of phenanthrene (PHE), in aqueous solution and in the dark, was revealed for the first time. The HSGZ catalyst is a polymeric network of zirconium oxo-clusters on the surface of which part of Zr4+ ions are involved in strong complexation with acetylacetonate (acac) ligands. The HSGZ gave significant PHE degradation rates acting as radicals initiator without any light irradiation at 30 °C. Free radicals were formed on the solid surface by the coexistence of Zr(IV)-acac and Zr(III)-acac• complexes in equilibrium at a given temperature, from which reactive oxygen species were produced in the presence of molecular O2. A direct evidence of radical's presence on HSGZ solid surface was obtained by EPR spectroscopy. The analysis of the degradation products confirmed that the reaction goes on through the formation of intermediate free radicals, leading to the first ring-opening and to the formation of phthalates as main intermediates. Subsequently, low molecular weight alkanes are produced. Finally, a deep oxidation of the intermediates occurs completing the mineralization process. The HSGZ catalyst showed a good stability under the reaction conditions, retaining its catalytic activity after repeated tests.

A fast method to direct the self-assembly of block copolymers loaded with metal oxide precursors in specific domains is demonstrated. It consists of performing spin-coating in a controlled atmosphere under a flux of solvent vapors (rapid-flux-vapor-atmosphere). Nanostructured thin films of hybrid composites and regular titania substrates, well oriented over a large area, are rapidly obtained.

The sol-gel synthesis of undoped and B- or Al-doped ZnO thin films were critically examined with particular reference to the influence of the pH of the reaction medium on some of their specific characteristics, such as thickness, morphology, doping level and optical properties, in view of their application in the photovoltaic field. Using triethanolamine (TEA) as chelating agent, a range of basic pH from 7.66 to 8.76 was explored starting from a very concentrated zinc acetate dehydrate (ZAD) solution in ethanol, [Zn2+] = 1.0 M, and keeping the ZAD/TEA = 1. A more basic environment gives more porous films whose thickness and crystallinity are higher than those achieved at lower pH. It was found that the morphology, as well as the sheet resistance (Rs) of films, depends on both pH and doping. Increasing the pH the Rs decreases for both undoped and doped films. At a certain pH undoped films exhibit a granular microstructure and lower Rs than B- or Al-doped films which exhibit a finer texture, characterized by a lower porosity. Optical properties strongly depend on the pH as well. Increasing the pH, a noticeable blue shift effect was observed, that was attributed mainly to structural changes and to a lesser extent to the Burnstein-Moss effect. © 2014 Elsevier B.V.