Gas-Phase Condensation of Nanoparticles and Nanocomposites for Energy Applications

Nanomaterials are not simply miniaturized materials. In this world halfway between the atomic and the bulk scale, high density of interfaces and surfaces, elemental composition, unique geometries and interactions constitute a virtually infinite set of parameters that allows to tailor material properties at the nanoscale. The aim of this Thesis is to contribute to the development of strategies for the growth of nanomaterials featuring complex morphologies and tailorable structures by careful design of Gas Phases Condensation (GPC) experiment. The proposed strategies are demonstrated for the growth of nanomaterials with applications in the energy storage field. The co-evaporation of Mg and Ti in a H enriched atmosphere is the key to grow small Mg-Ti-H nanoparticles (NPs), in which TiH2 and Mg/MgH2 coexist at the single NP level, despite the bulk immiscibility of Mg and Ti. The high density of MgH2/TiH2 interfaces gives rise to outstanding H-absorption and desorption kinetics in the 373-423 K temperature range. Moreover, a theoretical model is proposed to explain the altered thermodynamics induced by interface energetics. Thermal GPC and Pulsed Laser GPC were employed to grow Fe-Co alloy nanoparticles. The influence of the two techniques over the morphology of the nanoparticles is discussed and an application in the catalysis of CO2 reduction is presented. Finally, a novel strategy for the one-step synthesis of Fe-Co alloy nanoparticles supported on Ti oxide nanoparticles via Thermal GPC is presented. This new approach relies on the independent evaporation of two metallic precursors with strongly different oxidation enthalpies in an O2 enriched atmosphere. TEM and XRD morphological and structural characterizations clearly show that less negative enthalpy gives birth to metallic NPs, while the other to oxide NPs

Hydrogen Desorption below 150 °c in MgH2-TiH2 Composite Nanoparticles: Equilibrium and Kinetic Properties

Reversible hydrogen sorption coupled with the MgH2 <-> Mg phase transformation was achieved in the remarkably low 340-425 K temperature range using MgH2-TiH2 composite nanoparticles obtained by reactive gas-phase condensation of Mg Ti vapors under He/H-2 atmosphere. The equilibrium pressures determined by in situ measurements at low temperature were slightly above those predicted using enthalpy Delta H and entropy Delta S of bulk magnesium. A single van't Hoff fit over a range extended up to 550 K yields the thermodynamic parameters Delta H = 68.1 0.9 kJ/molH(2) and Delta S = 119 2 J/(Kmo1H2) for hydride decomposition. A desorption rate of 0.18 wt % H-2/min was measured at T = 423 K and p(H-2) approximate to 1 mbar, i.e., close to equilibrium, without using a Pd catalysts. The nanoparticles displayed a small absorption desorption pressure hysteresis even at low temperatures. We critically discuss the influence exerted by nanostructural features such as interface free energy, elastic clamping, and phase mixing at the single nanopartide level on equilibrium and kinetic properties of hydrogen sorption

Endosperm structure and Glycemic Index of Japonica Italian rice varieties

Introduction: Given that rice serves as a crucial staple food for a significant portion of the global population and with the increasing number of individuals being diagnosed with diabetes, a primary objective in genetic improvement is to identify and cultivate low Glycemic Index (GI) varieties. This must be done while ensuring the preservation of grain quality. Methods: 25 Italian rice genotypes were characterized calculating their GI "in vivo" and, together with other 29 Italian and non-Italian genotypes they were studied to evaluate the grain inner structure through Field Emission Scanning Electron Microscopy (FESEM) technique. Using an ad-hoc developed algorithm, morphological features were extracted from the FESEM images, to be then inspected by means of multivariate data analysis methods. Results and discussion: Large variability was observed in GI values (49 to 92 with respect to glucose), as well as in endosperm morphological features. According to the percentage of porosity is possible to distinguish approximately among rice varieties having a crystalline grain ( 5%), and a third group having intermediate characteristics. Waxy rice varieties were not united by a certain porosity level, but they shared a low starch granules eccentricity. With reference to morphological features, rice varieties with low GI (<55) seem to be characterized by large starch granules and low porosity values. Our data testify the wide variability of Italian rice cultivation giving interesting information for future breeding programs, finding that the structure of the endosperm can be regarded as a specific characteristic of each variety

Apparato volumetrico per misure di assorbimento di idrogeno nei solidi

L’obiettivo che ci si pone con la presente tesi è quello di descrivere la realizzazione e il funzionamento di un apparato per l’analisi volumetrica delle proprietà di immagazzinamento di idrogeno da parte di metalli. Dopo aver presentato le motivazioni che stanno ridirezionando l’attenzione della ricerca nel campo energetico verso l’idrogeno e aver dato una breve panoramica delle tecnologie di immagazzinamento e trasporto di questo potenziale vettore di energia alternativa e pulita, viene posta al centro dell’attenzione la tecnica di immagazzinamento allo stato solido dell’idrogeno (Solid State Hydrogen Storage), della quale vengono descritti i meccanismi fisico/chimici. In seguito viene presentato il metodo di analisi volumetrica per la caratterizzazione delle proprietà di immagazzinamento di idrogeno nei metalli e viene data una descrizione delle accortezze e delle considerazioni sperimentali fatte in fase di progettazione dello strumento. In conclusione, dopo avere mostrato la procedura di analisi dei campioni utilizzando lo strumento realizzato e il suo significato, vengono mostrati alcuni risultati ottenuti su un campione di idruro di magnesio e uno di palladio

Sintesi di nanoparticelle composite con morfologia avanzata mediante condensazione in atmosfera inerte o reattiva

Uno dei concetti chiave dell'impiego della nanotecnologia è quello dell'ingegnerizzazione dei materiali alla nano-scala. Si procede così alla realizzazione di materiali aventi morfologia, struttura e composizione ottimizzate per migliorarne specifiche proprietà in maniera controllata. In questo lavoro sono stati realizzati campioni nanoparticellari a base di magnesio con la tecnica (R-)IGC (Reactive or Inert Gas Condensation) allo scopo di studiare come l'atmosfera nella quale vengono sintetizzati ne influenzi le proprietà morfologiche e strutturali, al fine di poterne controllare la crescita per impieghi specifici. In particolare, si sono voluti analizzare i risultati ottenuti in diverse situazioni: nel caso in cui la sintesi avvenga in un'atmosfera contenente una piccola concentrazione di ossigeno e nel caso della coevaporazione di magnesio e titanio in atmosfera inerte o contenente idrogeno. I campioni sono poi stati analizzati dal punto di vista morfologico, composizionale e strutturale mediante microscopia a scansione elettronica e diffrazione a raggi X. E' stato mostrato che la presenza controllata di ossigeno durante la sintesi permette di realizzare strutture core-shell di dimensione media 40nm e che la co-evaporazione di magnesio e titanio permette la sintesi di nanoparticelle di dimensioni medie anche inferiori ai 12nm. La presenza di idrogeno durante l'evaporazione permette inoltre di crescere nanoparticelle contenenti idruro di titanio senza dover ricorrere ad una idrurazione successiva. Le proprietà termodinamiche e cinetiche di (de)-idrurazione dei campioni sintetizzati sono state misurate utilizzando sia un apparato barometrico Sievert, sia effettuando un'analisi direttamente nel sito di crescita. I campioni realizzati non mostrano una termodinamica significativamente diversa da quella del magnesio bulk, mentre le cinetiche dei processi di assorbimento e desorbimento risultano notevolmente più rapide

The Cuban Cure: Culture and identity in global science

The thesis explores the paradigms that inform the design of the New Headquarters for the Cuban Pharmaceutical Industry

Interface Enthalpy-Entropy Competition in Nanoscale Metal Hydrides

We analyzed the effect of the interfacial free energy on the thermodynamics of hydrogen sorption in nano-scaled materials. When the enthalpy and entropy terms are the same for all interfaces, as in an isotropic bi-phasic system, one obtains a compensation temperature, which does not depend on the system size nor on the relative phase abundance. The situation is different and more complex in a system with three or more phases, where the interfaces have different enthalpy and entropy. We also consider the possible effect of elastic strains on the stability of the hydride phase and on hysteresis. We compare a simple model with experimental data obtained on two different systems: (1) bi-phasic nanocomposites where ultrafine TiH2 crystallite are dispersed within a Mg nanoparticle and (2) Mg nanodots encapsulated by different phases

Interface Enthalpy-Entropy Competition in Nanoscale Metal Hydrides

We analyzed the effect of the interfacial free energy on the thermodynamics of hydrogen sorption in nano-scaled materials. When the enthalpy and entropy terms are the same for all interfaces, as in an isotropic bi-phasic system, one obtains a compensation temperature, which does not depend on the system size nor on the relative phase abundance. The situation is different and more complex in a system with three or more phases, where the interfaces have different enthalpy and entropy. We also consider the possible effect of elastic strains on the stability of the hydride phase and on hysteresis. We compare a simple model with experimental data obtained on two different systems: (1) bi-phasic nanocomposites where ultrafine TiH2 crystallite are dispersed within a Mg nanoparticle and (2) Mg nanodots encapsulated by different phases

One-Step Synthesis of Metal/Oxide Nanocomposites by Gas Phase Condensation

Metallic nanoparticles (NPs), either supported on a porous oxide framework or finely dispersed within an oxide matrix, find applications in catalysis, plasmonics, nanomagnetism and energy conversion, among others. The development of synthetic routes that enable to control the morphology, chemical composition, crystal structure and mutual interaction of metallic and oxide phases is necessary in order to tailor the properties of this class of nanomaterials. With this work, we aim at developing a novel method for the synthesis of metal/oxide nanocomposites based on the assembly of NPs formed by gas phase condensation of metal vapors in a He/O2 atmosphere. This new approach relies on the independent evaporation of two metallic precursors with strongly different oxidation enthalpies. Our goal is to show that the precursor with less negative enthalpy gives birth to metallic NPs, while the other to oxide NPs. The selected case study for this work is the synthesis of a Fe-Co/TiOx nanocomposite, a system of great interest for its catalytic and magnetic properties. By exploiting the new concept, we achieve the desired target, i.e., a nanoscale dispersion of metallic alloy NPs within titanium oxide NPs, the structure of which can be tailored into TiO1-&#948; or TiO2 by controlling the synthesis and processing atmosphere. The proposed synthesis technique is versatile and scalable for the production of many NPs-assembled metal/oxide nanocomposites

Structure and magnetic properties of Fe-Co alloy nanoparticles synthesized by pulsed-laser inert gas condensation

Fe-Co alloy nanoparticles of different compositions (Fe content of 76, 51, and 30 at%), along with pure Fe and Co nanoparticles, were prepared by pulsed-laser inert gas condensation, consisting in laser ablation of Fe-Co alloy targets under helium atmosphere. From the morphological point of view, the obtained nanoparticles have nearly spherical shape, follow a lognormal size distribution and exhibit little aggregation. X-ray diffraction and highresolution electron microscopy coupled with electron energy loss spectroscopy show that the Fe-Co nanoparticles are single crystals with body-centered cubic structure. Furthermore, in the majority of nanoparticles the composition is highly uniform across the whole diameter and there is little variation in composition from one nanoparticle to another. Exposure to non-inert atmosphere leads to the formation of a core@shell metal@oxide morphology characterized by a spinel oxide shell of 2–3 nm around the metallic alloy core. All samples display a ferromagnetic behavior, characterized by a hysteretic magnetization loop. The saturation magnetization attains a maximum value of 2.43 Bohr magnetons per atom for Fe content of 76 at%, in agreement with the Slater- Pauling curve for alloys of 3d elements. Instead, the coercive field, ranging from 29 to 60 kA m−1, is much larger than the reported values for polycrystalline bulk Fe-Co compounds and monotonically increases from pure Fe to pure Co. These results demonstrate that pulsed-laser inert gas condensation allows to prepare high-quality nanoalloys with tailorable magnetic properties, overcoming the limitations of thermal evaporation methods with respect to compositional control