Simone Mascotto

Ordered mesoporous α-Fe2O3 (hematite) thin-film electrodes for application in high rate rechargeable lithium batteries.

Herein is reported the synthesis of ordered mesoporous α-Fe(2)O(3) thin films produced through coassembly strategies using a poly(ethylene-co-butylene)-block-poly(ethylene oxide) diblock copolymer as the structure-directing agent and hydrated ferric nitrate as the molecular precursor. The sol-gel derived α-Fe(2)O(3) materials are highly crystalline after removal of the organic template and the nanoscale porosity can be retained up to annealing temperatures of 600 °C. While this paper focuses on the characterization of these materials using various state-of-the-art techniques, including grazing-incidence small-angle X-ray scattering, time-of-flight secondary ion mass spectrometry, X-ray photoelectron spectroscopy, and UV-vis and Raman spectroscopy, the electrochemical properties are also examined and it is demonstrated that mesoporous α-Fe(2)O(3) thin-film electrodes not only exhibit enhanced lithium-ion storage capabilities compared to bulk materials but also show excellent cycling stabilities by suppressing the irreversible phase transformations that are observed in microcrystalline α-Fe(2)O(3).

Diffusion in hierarchical mesoporous materials: applicability and generalization of the fast-exchange diffusion model.

Transport properties of cyclohexane confined to a silica material with an ordered, bimodal pore structure have been studied by means of pulsed field gradient nuclear magnetic resonance. A particular organization of the well-defined pore structure, composed of a collection of spatially ordered, spherical mesopores interconnected via narrow worm-like pores, allowed for a quantitative analysis of the diffusion process in a medium with spatially ordered distribution of the fluid density for a broad range of the gas-liquid equilibria. The measured diffusion data were interpreted in terms of effective diffusivities, which were determined within a microscopic model considering long-range molecular trajectories constructed by assembling the alternating pieces of displacement in the two constituting pore spaces. It has further been found that for the system under study, in particular, and for mesoporous materials with multiple porosities, in general, this generalized model simplifies to the conventional fast-exchange model used in the literature. Thus, not only was justification of the applicability of the fast-exchange model to a diversity of mesoporous materials provided, but the diffusion parameters entering the fast-exchange model were also exactly defined. The equation resulting in this way was found to nicely reproduce the experimentally determined diffusivities, establishing a methodology for targeted fine-tuning of transport properties of fluids in hierarchical materials with multiple porosities.

The effect of hydrothermal treatment on column performance for monolithic silica capillary columns.

Monolithic silica capillary columns with i.d. 100 μm and monolithic silica rods were prepared with tetramethoxysilane (TMOS) or a mixture of TMOS and metyltrimethoxysilane (MTMS) using different hydrothermal treatments at T=80 °C or 120 °C. Nitrogen physisorption was applied for the pore characterization of the rods and inverse size exclusion chromatography (ISEC) for that of the capillary columns. Using nitrogen physisorption, it was shown change of pore size and surface area corresponds to that of hydrothermal treatment and silica precursor. The results from ISEC agreed well with those from nitrogen physisorption regarding the pore size distribution (PSD). In addition, the retention factors for hexylbenzene with the ODS-modified capillary columns in methanol/water=80/20 at T=30 °C could also support the results from nitrogen physisorption. Furthermore, column efficiency for the columns was evaluated with alkylbenzenes and three kinds of peptides, leucine-enkephalin, angiotensin II, and insulin. Column efficiency for alkylbenzenes was similar independently of the hydrothermal treatment at T=120 °C. Even for TMOS columns, there was no significant difference in column efficiency for the peptides despite the difference in hydrothermal treatment. In contrast, for hybrid columns, it was possible to confirm the effect on hydrothermal treatment at T=120 °C resulting in a different column efficiency, especially for insulin. This difference supports the results from both nitrogen physisorption and ISEC, showing the presence of more small pores of ca. 3-6 nm for a hybrid silica without hydrothermal treatment at T=120 °C. Consequently, the results suggest that hydrothermal treatment for a hybrid column with higher temperature or longer time is necessary, compared to that for a TMOS column, to provide higher column efficiency with increase in molecular size of solute.

Adsorption in periodically ordered mesoporous organosilica materials studied by in situ small-angle X-ray scattering and small-angle neutron scattering.

Modified periodically ordered mesoporous organosilica materials were prepared starting from a recently introduced type of sol-gel precursor, containing both organic moieties and hydrolyzable Si-OR groups. In order to thoroughly characterize the mesoporosity and its accessibility, different probe gases were used in conventional gas adsorption experiments. Furthermore, in situ small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS) were applied to study the mesoporosity and the sorption processes, taking advantage of scattering contrast matching conditions. Thereby, the materials were characterized not only by different probe molecules but also at different temperatures (nitrogen at 77 K, dibromomethane at 290 K and perfluoropentane at 276 K). The comparison between the standard and in situ SAXS/SANS adsorption experiments revealed valuable information about the porosity and microstructure of the materials. It is demonstrated that the organic moieties are homogeneously distributed; that is, they do not phase-separate from silica on the nanometer scale.

Effect of microwave assisted and conventional thermal heating on the evolution of nanostructured inorganic–organic hybrid materials to binary ZrO2–SiO2 oxides

The effect of microwave assisted and conventional thermal heating on the morphological, microstructural and compositional evolution upon annealing of inorganic–organic Si–Zr based hybrid materials and on their conversion to mixed oxides (consisting of host silica with variable amounts of zirconia) was systematically studied. Samples with different compositions (Si : Zr = 2.5 : 1; 5 : 1; 10 : 1; 20 : 1), annealed at different temperatures (RT, 600, 800, 900 °C, 1000 °C) by using either a microwave oven or a conventional muffle were analysed to clarify the role of microwave heating on the final molecular features of the materials. The composition of the hybrid, as well as of the final oxidic materials was determined by X-ray photoelectron spectroscopy (XPS) and elemental analysis (EA), whereas FT-IR and multinuclear solid-state NMR spectroscopies shed light on the changes occurring in the composition upon thermal heating and the degree of condensation of the silica network. Interesting differences in the morphology and in the microstructure of the hybrids and of the oxides as a function of the type of annealing were pointed out by nitrogen sorption and scanning electron microscopy (SEM). X-Ray diffraction (XRD) and transmission electron microscopy (TEM) were used to follow the conversion of the amorphous oxides to partially crystalline materials consisting of crystalline zirconia nanoclusters homogeneously dispersed in the amorphous silica matrix. Interesting microstructural and morphological differences were revealed between samples annealed in muffle and those heated in the presence of microwaves.

Distribution of Sulfur in Carbon/Sulfur Nanocomposites Analyzed by Small-Angle X-ray Scattering.

The analysis of sulfur distribution in porous carbon/sulfur nanocomposites using small-angle X-ray scattering (SAXS) is presented. Ordered porous CMK-8 carbon was used as the host matrix and gradually filled with sulfur (20-50 wt %) via melt impregnation. Owing to the almost complete match between the electron densities of carbon and sulfur, the porous nanocomposites present in essence a two-phase system and the filling of the host material can be precisely followed by this method. The absolute scattering intensities normalized per unit of mass were corrected accounting for the scattering contribution of the turbostratic microstructure of carbon and amorphous sulfur. The analysis using the Porod parameter and the chord-length distribution (CLD) approach determined the specific surface areas and filling mechanism of the nanocomposite materials, respectively. Thus, SAXS provides comprehensive characterization of the sulfur distribution in porous carbon and valuable information for a deeper understanding of cathode materials of lithium-sulfur batteries.

Combined use of XAFS, XRD and TEM to unravel the microstructural evolution of nanostructured ZrO2–SiO2 binary oxides: from nanometres down to the molecular domain

In this paper, the detailed study of the microstructural evolution under annealing of zirconium-based inorganic–organic hybrid materials to give silica–zirconia mixed oxides was addressed by X-ray absorption fine structure (XAFS) spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). The silica materials embedding different amounts of ZrO2 nanoparticles were prepared by copolymerisation of the organically modified oxozirconium cluster (Zr4O2(OMc)12 (OMc = methacrylate)) with methacryloxypropyltrimethoxysilane (MAPTMS). By the free radical copolymerisation of the oxoclusters bearing 12 methacrylate groups with the methacrylate-functionalised siloxanes, a stable anchoring of the clusters to the silica network was achieved. The thermal treatment of these hybrids at high (≥500 °C) temperatures yielded the SiO2–ZrO2 mixed oxides. The microstructural evolution upon heating was studied at increasing temperatures, namely 500, 600, 700, 900, 1000 and 1300 °C. Furthermore, different samples characterised by different Zr : Si atomic ratios and annealed at 1000 °C were comparatively analysed to study the effect of the composition on the evolution of the hybrids to give the mixed oxides. In a third experiment, samples characterised by the same composition were annealed at the same temperature by using either a conventional muffle or a microwave oven in order to evidence whether the different processing could also affect the microstructural features of the final oxide materials. Through XRD and XAFS it was demonstrated that at temperatures above 800 °C, crystallisation of tetragonal zirconia occurs in the samples of high zirconium concentration treated in muffle, whereas amorphous oxide materials form upon annealing in microwave oven. The presence of zirconia nanoclusters having an average size of 5–10 nm was evidenced by TEM.

Alkyl chain grafting on silica–zirconia mixed oxides: preparation and characterization

Silica–zirconia mixed oxide substrates were prepared and grafted with C18 alkyl chains using n-octadecyltrichlorosilane. Si : Zr molar ratios in the mixed oxide samples before and after alkyl chain modification were determined by X-ray photoelectron spectroscopy (XPS). Nitrogen sorption measurements provided the porous features of these materials. By means of solid-state 29Si nuclear magnetic resonance (NMR) the amounts of the silanol groups present in the as-prepared, humidified and grafted mixed oxide systems as well as the degree of cross-linking of the silanes were obtained. 13C NMR spectroscopy was used to examine the conformational order of the n-octadecyl chains grafted on the silica–zirconia mixed oxide substrates. Similar information was available from variable temperature Fourier transform infrared (FTIR) investigations. Scanning electron microscopy (SEM) measurements and energy dispersive X-ray (EDX) analyses yielded the morphological features of the solid substrates and information about the distribution of the alkyl chains on the oxide surfaces. The annealing temperature for the preparation of the mixed oxides and the elemental composition of the samples, i.e. relative amount of the oxide components, were found to determine the surface properties and in turn the alkyl chain assembly on the mixed oxide surfaces. FTIR and solid-state 13C NMR data gave evidence for an unusual high conformational order of the grafted C18 alkyl chains in all samples, irrespective of the low surface coverage, which exceeds comparable C18 and C30 grafted silica and metal oxide systems. This finding was attributed to the formation of island structures with aggregated octadecyl chains of high conformational order due to strong intermolecular interactions. Differences in the conformational order of the various samples most likely arise from vertical polymerization which varies with the actual sample.

Cooperative assembly synthesis of mesoporous SrTiO3 with enhanced photocatalytic properties

The synthesis of mesoporous SrTiO3 by using the cooperative assembly of metal chelate complexes and alkoxysilanes is here presented. The high affinity and intimate mixing between the two precursors fostered the formation, via polycondensation, of interpentrating organic and inorganic polymers. Hence, after calcination and removal of the siliceous phase, aggregates of mesoporous, polycrystalline SrTiO3 with interconnected pores of ca. 10 nm and surface areas as high as 240 m2 g−1 were obtained. Systems using different SrTiO3 : SiO2 molar ratios were prepared to vary the porosity and microstructure. The templating action of the silica and its effect on the physicochemical properties of the final porous materials were addressed by a multi-technique approach. Finally, the activity of the bulk mesoporous SrTiO3 systems was exemplarily demonstrated by photodegradation tests of methylene blue under UV light. The dye conversion progressively increased with the content of silica template, proving the higher activity of the proposed mesoporous materials.

Pore geometry effect on the synthesis of silica supported perovskite oxides

The formation of perovskite oxide nanoparticles supported on ordered mesoporous silica with different pore geometry is here presented. Systematic study was performed varying both pore shape (gyroidal, cylindrical, spherical) and size (7.5, 12, 17nm) of the hosts. LaFeO3, PrFeO3 and LaCoO3 were chosen as target guest structures. The distribution of the oxide nanoparticles on silica was comprehensively assessed using a multi-technique approach. It could be shown that the pore geometry plays a determining role in the conversion of the infiltrated metal nitrates to metal oxide. In particular, slow degradation kinetic was observed in highly curved pores, which fostered nucleation and crystallization of the guest species. In spherical pore systems the enhancement of pore size caused a remarkable delay of the decomposition of the metal salts, but at the same time improved the homogeneous distribution of the oxide particles in the matrix.