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Zirconia advanced ceramic materials for functional and structural applications
No full textLa tesi di dottorato è focalizzata sullo studio e sullo sviluppo di materiali innovativi e avanzati a base di zirconia. Il progetto può essere diviso in due parti, la prima basata sullo studio dei polimorfi cristallini della zirconia in presenza di cationi aliovalenti (Y, Eu, Ta) e la seconda sulla preparazione di nanomateriali mesoporosi. Il polimorfismo della zirconia è stato indagato tramite diverse tecniche (diffrazione ai raggi X, luminescenza, catodoluminescenza, spettroscopia Raman), studiando, con approcci anche innovativi, sia strutture già note in letteratura (fasi monoclina, tetragonale e cubica), sia poco note e non approfondite (fase ortorombica), di interesse scientifico e tecnologico. Per quanto riguarda lo sviluppo di nanoparticelle mesoporose di zirconia (MZNs), preparate per applicazioni biomedicali (medicina teranostica attraverso carrier inorganici), la ricerca ha prodotto ottimi risultati, considerando la novità del tema affrontato. La realizzazione e caratterizzazione del materiale sviluppato può essere considerato come un nuovo sistema adattabile a diverse applicazioni e alternativo ai sistemi già noti in letteratura
Determining europium compositional fluctuations in partially stabilized zirconia nanopowders: a non-line-broadening-based method
No full textA method is reported for assessing the compositional fluctuations in a ceramic
sample, based only on the determination of the crystalline lattice parameters.
Pure tetragonal phase partially stabilized zirconia powders are synthesized
through the co-precipitation method by incorporating 4% Eu3+. The powder is
subjected to compression cycles to promote the tetragonal-to-monoclinic
transformation. The Rietveld analysis of the X-ray powder diffraction patterns,
recorded after each compression cycle, gives information about the lattice
parameters and monoclinic phase content. The determination of europium
content in the residual tetragonal phase is accomplished considering the unit cell
volume of t-ZrO2 using Vegard’s law. Using this information the compositional
fluctuations over the sample were determined by considering two possible
distributions of lanthanide ion content in the powders: a Gaussian and a Lognormal
one. It was found that the Gaussian distribution better fits the
experimental data. It was eventually demonstrated that these results are
physically meaningful
Low-temperature carbon monoxide oxidation over zirconia-supported CuO–CeO2 catalysts: Effect of zirconia support properties
No full textA study was conducted to investigate the effect of the preparation route of ZrO2 in CuO–CeO2/ZrO2 catalysts for the oxidation of carbon monoxide at low temperature (COX). Four ZrO2 supports were synthetized via either type sol-gel methodology or precipitation. The final Cu-Ce-Zr oxide catalysts were prepared by incipient wetness co-impregnation with copper and cerium solutions (with a loading of 6 wt% of CuO and 20 wt% of CeO2). The catalyst crystalline phases, texture and active species reducibility were determined by XRD, N2 physisorption at −196 °C and H2-TPR, respectively; meanwhile the surface composition and copper-cerium electronic states were studied by XPS. The catalytic activity was evaluated in the oxidation of CO to CO2, in the 40–215 °C temperature range. Catalytic results evidenced that the samples prepared by a sol-gel methodology showed, after the impregnation, a severe decrease of specific surface area and pore volume attributable to a wide degree of pore blockage caused by the presence of metal oxide particles and a collapse of the structure partially burying the active sites. A simple co-impregnation of a zirconia support, obtained through facile and fast precipitation, provided instead a catalyst with very good redox properties and high dispersion of the active phases, which completely oxidizes CO in the range 115–215 °C with T50 of 65 °C. This higher observed activity was ascribed to the formation of a larger fraction of highly dispersed and easily reducible Cu species and ceria nanocrystallites, mainly present as Ce(IV), with an average size of 5 nm
Mesoporous zirconia nanoparticles as drug delivery systems: drug loading, stability and release
Full text linkDrug delivery systems have been a milestone in medical research in the last twenty years, still
representing a key aspect of innovation and evolution in pharmacokinetics and pharmacodynamics. Among
several proposed solutions, inorganic mesoporous materials could be a promising vehicle. Their specific
chemical-physical properties make them ideal candidates for the adsorption and loading of active
pharmaceutical ingredients (API). Recently, mesoporous zirconia nanoparticles (MZNs) have been described
as a novel drug delivery system due to their high surface area and biocompatibility. In this work, we
investigated the loading and release efficiencies of a wide range of API on MZNs characterized by suitable
pore volume and versatility, focusing on the integrity of the released drugs investigated through solution
NMR and ESI-MS techniques. In order to explore the potentialities of MZNs for biomedical applications, we
selected ibuprofen, N-acetyl-L-cysteine, vancomycin, gentamicin, nitrofurantoin, and indomethacin as
benchmark API characterized by a wide range of polarity, molecular weight and presence of different
functional groups. MZNs showed to efficiently load and release most of the API investigated. Long time
loadings were also investigated observing that, after more than three months, no side reaction occurred on
the released drugs except for intrinsically more labile API like NTF and NAC. MZNs ensured high inertness
towards a wide range of functional groups such as aliphatic and aromatic amides, acetals of sugar residues
as well as several chiral moieties bearing tertiary stereocenter
Photoluminescence properties of YAG:Ce3+,Pr3+ phosphors synthesized via the Pechini method for white LEDs
No full textWe describe a facile route for synthesize
YAG nanophosphors via Pechini-type sol–gel process
for white light-emitting diodes technology. The wettype
synthesis was followed by a heat treatment at
1,000 C for 4 h. We carried out a study of the
luminescent properties of the YAG:Ce,Pr system
varying the concentration of praseodymium from
0.125 to 2 mol% maintaining the quantity of cerium
constant at 2 mol%. The diffractometric analysis
confirmed the purity of the YAG phase. The luminescent
analysis showed the typical Ce3? emission arising
from the 5d ! 4f transitions overlapped with the
sharper Pr3? emissions in the red region of the
spectrum. The presence of energy transfer phenomenon
was confirmed by PLE spectra of the samples
and the appearance of concentration quenching at
0.5 mol% Pr was observed thanks to the decrease both
of the intensity of praseodymium emission and mean
lifetime
Oxygen Hole States in Zirconia Lattices: Quantitative Aspects of Their Cathodoluminescence Emission
No full textSystematic assessments of cathodoluminescence
(CL) spectroscopy, Raman spectroscopy (RS), and Xray
diffraction (XRD) are presented for pure zirconia and for a
series of Y-doped zirconia powders (henceforth, simply
referred to as undoped ZrO2 and YSZ powders, respectively)
synthesized according to a coprecipitation method of Zr and Y
chlorides. Emphasis is placed here on spectral emissions
related to oxygen-vacancy sites (i.e., oxygen hole states)
equally detected from undoped and Y-doped ZrO2 samples,
either as intrinsic defects or, extrinsically induced, by means of
cathodoluminescence. Most counterintuitively, the undoped
ZrO2 sample (i.e., the one with presumably the lowest amount
of oxygen vacancies) experienced the strongest CL emission. A progressive “quenching” effect on CL emission with increasing
the fraction of Y3+ dopant could also be observed because the intrinsic vacancies present in the undoped lattice are the most
efficient since they can trap two electrons to gain electrical neutrality. However, as soon as Y3+ ions are introduced in the system,
those intrinsic vacancies migrate to Y-sites in next-nearest-neighbor locations, namely in a less efficient lattice location. This
phenomenon is tentatively referred to as “delocalization” of vacancy sites. Moreover, the fact that Y-doped zirconia series
presents quite similar CL spectra compared to the undoped zirconia could be an evidence that the radiative centers of undoped
and Y-doped ZrO2 are basically the same. A fitting procedure has been made aiming to give a rational description of the variation
of the spectra morphology, and a parameter able to describe the monoclinic to tetragonal phase transformation has been found.
This parameter and the overall set of CL data enabled us to quantitatively assess polymorphic phase fractions by CL spectroscopy
in the scanning electron microscope
Two different approaches for the synthesis of mesoporous silica nanoparticles with tunable diameter and pores size
No full textTwo combined approaches of Stöber method and supramolecular assembly of surfactant molecules, under assistance of different organic solvents, have been exploited for the synthesis of ordered MSNs with spherical morphology between 60- 200nm and pore size from 2.7 to 8nm
Ceramics of Ta-doping stabilized orthorhombic ZrO2 densified by spark plasma sintering and the effect of post-annealing in air
No full text16 mol% Ta-doped ZrO2 powders were synthesized and densified by spark-plasma sintering (SPS) in vacuum, followed by post-SPS annealing in air, thus obtaining two ultrafine-grained ceramics consisting of Ta-doping stabilized orthorhombic ZrO2. The as-SPSed ceramic is black because it is actually a suboxide essentially with reduced cations and abundant oxygen vacancies, whereas the post-annealed ceramic is white because it is an oxide without vacancies and with only partially reduced cations. Both ceramics are relatively hard and brittle, but the as-SPSed ceramic was slightly more so, attributable to crystallographic and microstructural differences. Implications of interest for the ceramics community are discussed
Structural study of a porous CuO-CeO2/ZrO2 system for the low-temperature total oxidation of carbon monoxide
No full textA promising sol-gel surfactant-assisted method for the synthesis of micro- and mesoporous zirconia with nanometric dimension and high surface area was studied. The supports were impregnated with Ce and Cu nitrates solutions (20 wt% and 6 wt%, respectively) and tested in the CO total oxidation. Correlations between catalytic activity and properties were made using XRPD, N2 physisorption, TEM, DRIFT-IR, H2-TPR, Raman spectroscopy and XPS
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