Paolo Dolcet

Miniemulsions as chemical nanoreactors for the room temperature synthesis of inorganic crystalline nanostructures: ZnO colloids

We successfully explored, for the first time, the use of the w/o inverse miniemulsion route to prepare surfactant-functionalised nanocrystalline ZnO colloids. The adopted route exploits the micelles as nanoreactors for the precipitation of the desired oxide in a confined space. Triton X-100 (TritX-), sodium dodecyl sulfate (SDS-) and polyvinylpyrrolidone (PVP-) coated ZnO crystalline nanoparticles (NPs) have been obtained at room temperature (RT) with no need for post-treatment, by precipitation of zinc chloride with ammonium or sodium hydroxide into w/o inverse micelles. Their hydrodynamic diameter, evaluated by Dynamic Light Scattering (DLS), is about 35 nm. X-Ray Photoelectron Spectroscopy (XPS), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES), Fourier Transform Infrared (FT-IR) spectroscopy and Thermogravimetric Analysis (TGA) have been used to characterize powders separated by miniemulsions. The NP inorganic core is constituted of wurtzite ZnO, with a high degree of crystallinity, as determined by XRD. XRD data and TEM images revealed the formation, in the case of ZnOTritX, of anisotropic plate-like crystallites, with an average diameter of 72 nm and a thickness of 15–20 nm. The RT photo-luminescent (PL) spectrum of ZnOPVP NPs shows a strong UV emission band, attributed to the free exciton recombination, with a relevant tail in the Vis region due to the presence of structural defects. The morphology of these systems, investigated by SEM, corresponds to a homogeneous dispersion of globular sponge structures in a compact and fibrous matrix.

Tin(IV) oxide coatings from hybrid organotin/polymer nanoparticles.

Tin dioxide coatings are widely applied in glasses and ceramics to improve not only optical, but also mechanical properties. In this work, we report a new method to prepare SnO(2) coatings from aqueous dispersions of polymer/organotin hybrid nanoparticles. Various liquid organotin compounds were encapsulated in polymeric nanoparticles synthesized by miniemulsion polymerization. Large amounts of tetrabutyltin and bis(tributyltin) could be successfully incorporated in cross-linked and noncross-linked polystyrene nanoparticles that served as sacrificial templates for the formation of tin oxide coatings after etching with oxygen plasma or calcination. Cross-linked polystyrene particles containing bis(tributyltin)--selected for having a high boiling point--were found to be especially suited for the oxide coating formation. The content of metal in the particles was up to 12 wt %, and estimations by thermogravimetrical indicated that at least 96% of the total organotin compound was converted to SnO(2). The resulting coatings were mainly identified as tetragonal SnO(2) (cassiterite) by X-ray diffraction, although a coexistence of this phase with orthorhombic SnO(2) was observed for samples prepared with bis(tributyltin).

Room temperature crystallization of highly luminescent lanthanide-doped CaF2 in nanosized droplets: first example of the synthesis of metal halogenide in miniemulsion with effective doping and size control

In this paper, we report the first successful preparation of calcium fluoride by miniemulsion. Calcium fluoride is a widely investigated material known to be an excellent host for luminescent lanthanide ions; herein we report an easy and reproducible way to achieve the controlled doping of CaF2 nanostructures (Ca : Ln = 50 : 1, with Ln = SmIII, GdIII and TbIII) at room temperature, through the miniemulsion approach. The materials are thoroughly characterized from a structural, morphological and functional point of view, by the combined use of several techniques, i.e. X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Inductively Coupled Plasma Mass Spectrometry (ICP-MS), Scanning and Transmission Electron Microscopy (SEM and TEM respectively) and photoluminescence (PL) spectroscopy. In addition, to get further insight into the local structure around the dopants, Extended X-ray Absorption Fine Structure (EXAFS) experiments are performed.

Simple, common but functional: biocompatible and luminescent rare-earth doped magnesium and calcium hydroxides from miniemulsion†

Nanostructured (d∼ 20-35 nm) and highly luminescent Ca(OH)2:Ln and Mg(OH)2:Ln (Ln = EuIII, SmIII, TbIII, Mg(Ca)/Ln = 20 : 1 atomic) nanostructures were obtained in inverse (water in oil - w/o) miniemulsion (ME), by exploiting the nanosized compartments of the droplets to spatially confine the hydroxide precipitation in basic environment (NaOH). The functional nanostructures were prepared using different surfactants (Span80 (span) and a mixture of Igepal co-630 and Brij 52 (mix)) to optimise ME stability and hydroxide biocompatibility as well as tune the droplet sizes. X-Ray diffraction (XRD) analyses testify the achievement of a pure brucite-Mg(OH)2-phase and pure portlandite-Ca(OH)2-phase with a high degree of crystallinity. Besides structural characterisations, the products were thoroughly characterised by means of several and complementary techniques (dynamic light scattering (DLS), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), micro-Raman spectroscopy, inductively coupled plasma mass spectrometry (ICP-MS) and Fourier transform infrared spectroscopy (FT-IR)) to assess their chemico-physical properties as well as their morphological and microstructural features. The stoichiometry of the doped systems was confirmed using ICP-MS measurements. Finally, the cytotoxicity of the nanoparticles was assessed by in vitro tests using ES2 cells in order to provide preliminary data on the biocompatibility of this kind of nanoparticles. The luminescence of the Eu-doped and Tb-doped materials is clearly visible to the naked eye in the red and green regions, respectively, corroborating their employment as materials for imaging in the optical window of interest.

Sol-gel processes at the droplet interface: hydrous zirconia and hafnia nanocapsules by interfacial inorganic polycondensation

We report a simple method to prepare nanocapsules of hydrous zirconia and hafnia by interfacial precipitation in water-in-oil miniemulsions. We show that the sol–gel precipitation of transition metal hydroxides, exemplified for the cases of zirconium and hafnium, can be driven to the droplet interface by addition of an organic base. The prompt addition of triethylamine generates hydroxide ions at the interface, which initiate a polycondensation of the metal hydroxo species. Electron and X-ray diffractions indicate that the resulting materials are amorphous, but can be transformed to monoclinic ZrO2 or HfO2 upon thermolytic treatment. Mixed oxides of Hf and Zr with different compositions (HfxZr1−xO2) can also be formed by using the desired ratios of precursors. Furthermore, the ability of the hollow particles to encapsulate efficiently hydrophilic materials without leakage has been proven with the example of a water-soluble dye (fluorescein isothiocyanate).

Synthesis and Physicochemical Characterization of Ce1−xGdxO2−δ: A Case Study on the Impact of the Oxygen Storage Capacity on the HCl Oxidation Reaction

This study reports the synthesis of high‐surface‐area Ce1−xGdxO2−δ (CGO) fibers that are used as catalysts for the oxidation of HCl. Special emphasis is put on the role of the oxygen storage capacity (OSC) of the CGO fibers on the catalytic performance. An in‐depth physicochemical characterization of high‐surface‐area CGO was achieved by employing a multitude of dedicated spectroscopic techniques. The increasing OSC with Gd content is traced to the development of a space charge region with increased electron concentration as a result of the nano size of the CGO particles. The activity of CGO in the HCl oxidation reaction is shown to decrease with Gd concentration.

Hierarchically Organized Silica–Titania Monoliths Prepared under Purely Aqueous Conditions

Hierarchically organized silica-titania monoliths were synthesized under purely aqueous conditions by applying a new ethylene glycol-modified single-source precursor, such as 3-[3-{tris(2-hydroxyethoxy)silyl}propyl]acetylacetone coordinated to a titanium center. The influence of the silicon- and titanium-containing single-source precursor, the novel glycolated organofunctional silane, and the addition of tetrakis(2-hydroxyethyl)orthosilicate on the formation of the final porous network was investigated by SEM, TEM, nitrogen sorption, and SAXS/WAXS. In situ SAXS measurements were performed to obtain insight into the development of the mesoporous network during sol-gel transition. IR-ATR, UV/Vis, XPS, and XAFS measurements showed that up to a Si/Ti ratio of 35:1, well-dispersed titanium centers in a macro-/mesoporous SiO2 network with a specific surface area of up to 582 m(2)  g(-1) were obtained. An increase in Ti content resulted in a decrease in specific surface area and a loss of the cellular character of the macroporous network. With a 1:1 Si/Ti ratio, silica-titania powders with circa 100 m(2)  g(-1) and anatase domains within the SiO2 matrix were obtained.

In-depth mesocrystal formation analysis of microwave-assisted synthesis of LiMnPO4 nanostructures in organic solution

In the present work, we report on the preparation of LiMnPO4 (lithiophilite) nanorods and mesocrystals composed of self-assembled rod subunits employing microwave-assisted precipitation with processing times on the time scale of minutes. Starting from metal salt precursors and H3PO4 as phosphate source, single-phase LiMnPO4 powders with grain sizes of approx. 35 and 65 nm with varying morphologies were obtained by tailoring the synthesis conditions using rac-1-phenylethanol as solvent. The mesocrystal formation, microstructure and phase composition were determined by electron microscopy, nitrogen physisorption, X-ray diffraction (including Rietveld refinement), dynamic light scattering, X-ray absorption and X-ray photoelectron spectroscopy, and other techniques. In addition, we investigated the formed organic matter by gas chromatography coupled with mass spectrometry in order to gain a deeper understanding of the dissolution–precipitation process. Also, we demonstrate that the obtained LiMnPO4 nanocrystals can be redispersed in polar solvents such as ethanol and dimethylformamide and are suitable as building blocks for the fabrication of nanofibers via electrospinning.

Pursuing the stabilisation of crystalline nanostructured magnetic manganites through a green low temperature hydrothermal synthesis

A quick, easy and green water-based synthesis protocol involving coprecipitation of oxalates combined with hydrothermal treatment resulted in the crystallisation of nanostructured manganites at a relatively low temperature (180 °C). The subcritical hydrothermal approach was shown to play a key role in stabilising phases which are generally achieved at much higher temperatures and under harsher conditions, thus disclosing an exciting alternative for their synthesis. Through this mild wet chemistry approach, the compounds CuMnO2, ZnMn2O4 and ZnMnO3 were synthesised as nanocrystalline powders. Noticeably, the optimised route proved to be effective in stabilising the exotic polymorph cubic spinel ZnMnO3 in pure form. This is particularly notable, as very few records concerning this compound are available in the literature. The compounds were fully characterised from compositional, structural, morphological and magnetic points of view.

Transition Metal Manganites Prepared by a Green and Low-Temperature Wet Chemistry Route, Investigated by XPS

In the present contribution, three transition metal manganites, namely the copper manganite CuMnO2 and the zinc manganites ZnMnO3 and ZnMn2O4, were investigated through X-ray photoelectron spectroscopy (XPS). The chosen synthesis route involved the combination of coprecipitation of oxalates from an aqueous solution and hydrothermal processing at a mild temperature (180 °C). The precipitates were then separated and dried for 4 h at 80 °C, yielding crystalline nanostructured powders without the need for calcination. Along with survey scans of the analyzed samples, detailed spectra of the C 1s, O1s, Mn 2p, Mn 3p, Mn LMM as well as Cu 2p, Cu 3p, Cu LMM, Zn 2p and Zn LMM (depending on the sample in question) were collected. The data obtained from these analyses is discussed.