Preparazione e caratterizzazione di nanocompositi strutturali costituiti da poliammide e carbonio nanostrutturato

L’obiettivo della presente tesi di dottorato è stato la preparazione e la caratterizzazione di nanocompositi a matrice polimerica contenenti forme allotropiche del carbonio nanostrutturato; tali materiali, grazie alle particolari caratteristiche meccaniche e di rinforzo, trovano applicazione nella fabbricazione di speciali dispositivi individuali come guanti, elmetti, corpetti, etc... Sono state preparate fibre di poliammide (PA) contenenti carbon black (CB), nanoplacchette di grafite (GNP) e nanotubi di carbonio (CNT); per questi ultimi sono stati valutati, inoltre, gli effetti delle loro dimensioni e della funzionalizzazione della loro superficie sulle proprietà di rinforzo dei nanocompositi. Il CB ed i CNT utilizzati sono stati di origine commerciale, mentre le GNP sono state ottenute a partire da grafite intercalata attraverso due tecniche di preparazione differenti. I materiali ottenuti sono stati caratterizzati mediante indagini morfologiche (Microscopia Elettronica a Scansione e a Trasmissione), strutturali (Risonanza Magnetica Nucleare), e meccaniche (modulo elastico, resistenza a rottura e allungamento a rottura) allo scopo di interconnettere le proprietà su scala micro e su scala macro. Per lo studio di alcune caratteristiche microscopico-strutturali, inoltre, sonostate sviluppate delle metodiche di indagine basate sull’utilizzo di tecniche innovative come l’EELS (Energy Electron Loss Spectroscopy) e la SAED (Selected Area Electron Diffraction). Sebbene in tutti i materiali studiati siano state riscontrate interazioni filler-matrice che ne hanno migliorato le caratteristiche, è stato dimostrato come la filatura delle fibre giochi un particolare ruolo sulle proprietà morfologiche, strutturali e meccaniche dei nanocompositi. La tesi si suddivide in quattro capitoli il cui contenuto può essere così riassunto: 1. Nel primo capitolo è riportata un’introduzione sui nanocompositi polimerici, con particolare riferimento a quelli contenenti il carbonio nanostrutturato. Per tutti vengono forniti alcuni esempi di preparazione e le applicazioni più significative. 2. Nel secondo capitolo sono fornite le caratteristiche commerciali dei materiali utilizzati ed i dettagli sulle metodologie di preparazione sia delle GNP che dei nanocompositi. Sono riportati, inoltre, i parametri sperimentali delle tecniche di caratterizzazione utilizzate in questa tesi. 3. Nel terzo capitolo sono presentati i risultati ottenuti per ciascun sistema, la correlazione tra le proprietà e le conclusioni intra-sistema. Sono anche riportare le conclusioni inter-sistema che evidenziano i punti di somiglianza e le differenze tra i tre sistemi studiati. 4. Infine, nel quarto capitolo, sono riportate le conclusioni generali riferite ai tre sistemi studiati e correlate agli obiettivi iniziali

Streptomyces coelicolor Vesicles: Many Molecules To Be Delivered

Streptomyces coelicolor is a model organism for the study of Streptomyces, a genus of Gram-positive bacteria that undergoes a complex life cycle and produces a broad repertoire of bioactive metabolites and extracellular enzymes. This study investigated the production and characterization of membrane vesicles (MVs) in liquid cultures of S. coelicolor M145 from a structural and biochemical point of view; this was achieved by combining microscopic, physical and -omits analyses. Two main populations of MVs, with different sizes and cargos, were isolated and purified. S. coelicolor MV cargo was determined to be complex, containing different kinds of proteins and metabolites. In particular, a total of 166 proteins involved in cell metabolism/differentiation, molecular processing/transport, and stress response were identified in MVs, the latter functional class also being important for bacterial morpho-physiological differentiation. A subset of these proteins was protected from degradation following treatment of MVs with proteinase K, indicating their localization inside the vesicles. Moreover, S. coelicolor MVs contained an array of metabolites, such as antibiotics, vitamins, amino acids, and components of carbon metabolism. In conclusion, this analysis provides detailed information on S. coelicolor MVs under basal conditions and on their corresponding content, which may be useful in the near future to elucidate vesicle biogenesis and functions.IMPORTANCE Streptomycetes are widely distributed in nature and characterized by a complex life cycle that involves morphological differentiation. They are very relevant in industry because they produce about half of all clinically used antibiotics, as well as other important pharmaceutical products of natural origin. Streptomyces coelicolor is a model organism for the study of bacterial differentiation and bioactive molecule production. S. coelicolor produces extracellular vesicles that carry many molecules, such as proteins and metabolites, including antibiotics. The elucidation of S. coelicolor extracellular vesicle cargo will help us to understand different aspects of streptomycete physiology, such as cell communication during differentiation and response to environmental stimuli. Moreover, the capability of these vesicles for carrying different kinds of biomolecules opens up new biotechnological possibilities related to drug delivery. Indeed, decoding the molecular mechanisms involved in cargo selection may lead to the customization of extracellular vesicle content

Catalytic performance of CoAlZn and NiAlZn mixed oxides in hydrogen production by bio-ethanol partial oxidation

CoAlZn and NiAlZn mixed oxides were prepared by sol-gel method and tested in partial oxidation of bio-ethanol (POE). At lower temperatures, CoAlZn showed higher ethanol conversion and higher selectivity to H2 and CO than NiAlZn. At higher temperatures, ethanol conversion on both catalysts reached 100%, while selectivity (S) to H2 and CO became higher on NiAlZn. At 750 C, NiAlZn showed S(H2) of 95%, S(CO) of 90%, while for CoAlZn these values were 90% and 83% respectively. Both catalysts were resistant to coking, but the amount of carbon deposits was still lower on NiAlZn. During 50 h on-stream, ethanol conversion and selectivity to H2 and CO on NiAlZn remained unchanged demonstrating stable performance of the catalyst. The difference in catalytic behavior was ascribed to different reducibility and lattice oxygen mobility in the mixed oxides. TPR and DRIFT-monitored pyridine desorption tests revealed that in the respective materials, NiO particles were reduced easier than Co3O4 and NiAlZn had more mobile lattice oxygen with higher capacity to form vacancies than CoAlZn. Higher concentration of metallic Ni species coupled with more abundant mobile oxygen afforded correspondingly higher rates of C-H bond cleavage and carbon removal as CO on NiAlZn than on CoAlZn. Copyright © 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved

Synthesis of Nd:YAG nanopowder using the citrate method with microwave irradiation

Nd:YAG nanopowders were prepared using the Pechini process with microwave irradiation (MWs). A reference sample was also prepared using conventional heating. XRD pattern analysis showed that nanopowder obtained by means of conventional heating and calcination for 1 h at 900 ◦ C has a structure made up of the garnet phase together with the hexagonal phase that disappeared after two additional hours of thermal treatment. The MWs powder calcined for 1 h con- sists of the single garnet phase. SAXS data analysis indicated that nanoparticles are characterized by a sharp interface. TEM investigation showed crystalline particles with remarkable agglomeration in both samples, although a more homogeneous size of particles was evident in the MWs sample as compared to the reference sample. The rate, the calcination time and the quality of the powder obtained make the Pechini process with microwave irradiation an attractive alternative procedure to conventional YAG preparation methods

H3PW12O40 supported on mesoporous MCM-41 and Al-MCM-41 materials: preparation and characterisation

MCM-41 and Al–MCM-41 has been synthesized using cetyl-trimethylammonium bromide (CTAB) surfactant as template and adding the silica precursor to aqueous solutions containing CTAB. The obtained solids were calcined at 600 C for 4 h. HPW heteropolyacid supported on the mesoporous were prepared using the incipient wetness method. The characterization of materials was performed by X-ray diffraction, Transmission Electron Microscopy, N2 adsorption, 29Si Cross Polarization– Magic Angle Spinning and 27Al MAS NMR. Results showed that the hexagonal structure is obtained in both cases. The Aluminium species are located inside an extraframework. The impregnation reduces the surface area of the mesoporous materials especially of the Al–MCM-41 suggesting a participation of aluminium during the impregnation. HPW is well dispersed in the mesoporous materials and is located inside the pores interacting with the silanol group of the pores wall. 27Al MAS NMR measurements have showed that the impregnation causes the removal of the non-framework aluminium

Synthesis, Characterization and Catalytic Activity of mesoporous Mn-MCM-41 materials

MCM-41 has been synthesized at two different pH using cetyl-trimethylammonium bromide (CTAB) surfactant as template and adding the silica precursor to aqueous solutions containing CTAB. The obtained solids were calcined at 600 ◦C for 4 h. Mn-MCM-41 powders with different Mn/Si molar ratios were prepared using the incipient wetness method, followed by calcination at 550 ◦C for 5 h. At the end of the impregnation process the powders colour changed from white to brown whose intensity depends on manganese quantity. The materials characterization was performed by X-ray diffraction, N2 adsorption, 29Si Cross Polarization–Magic Angle Spinning NMR, and X-ray Photoelectron Spectroscopy. The effects of the manganese quantity and of the structural characteristic of the MCM-41 support were studied. The catalytic activity of the prepared systems was evaluated in a complete n-hexane oxidation

MCM-41-CdS nanoparticles composite material: preparation and characterization

The preparation and characterization of a hierarchical material constituted by a mesoporous silica MCM-41 whose mesochannels contain CdS nanoparticles capped with both bis(2-ethylhexyl) amine and bis(2-ethylhexyl) sodium sulfosuccinate is reported. MCM-41 powder was synthesized by using the LCT methodology. CdS nanoparticles were obtained within the inversed micelle core of a water/ AOT/n-heptane microemulsion. Nanoparticles growth was followed by means of UV–Vis spectroscopy and was inhibited by BEA addition. The CdS-capped nanoparticles were separated by centrifugation, washed with water and ethanol and finally dispersed in n-heptane. The insertion of CdS nanoparticles into MCM-41 mesochannels was obtained by adding mesoporous silica into the n-heptane nanoparticles dispersion. The yellow MCM-41-CdS nanoparticles composite was characterized by using different structural (X-ray diffraction, nitrogen adsorption–desorption isotherm and small angle neutron scattering coupled with the contrast variation method), spectroscopic (diffuse reflection UV–Vis, attenuated total reflection and diffuse reflectance Fourier transform infrared) and morphological techniques (high resolution transmission electron microscopy). The CdS nanoparticles, significantly capped by both the amine and the surfactant molecules, were found to be localized inside the cylindrical silica pores. The mesoporous material loses its long-range order while the incorporation process does not affect the size and electronic structure of CdS nanoparticles

On the role of extensional flow in morphology and property modifications of MWCNT/polyamide-based fibres

Unfilled and MWCNT-filled PA fibers are prepared and the effect of the extensional flow on their mechanical performance and morphological variations is investigated. Morphological analyses using SEM, TEM, and SAXS suggest a stronger orientation of the MWCNTs along the fiber direction with increasing extensional flow. A particular MWCNT bundle formation in the PA drawn nanocomposite fibers is observed for the first time, and a pull-out of the central nanotube in some bundles is noted. The maintenance of the “shish-kebab” structure upon extensional flow is responsible for the mechanical improvements and dimensional stability in MWCNT-filled PA fibers

Ce:YAG nanoparticles embedded in a PMMA matrix: preparation and characterization

A Ce:YAG-poly(methyl methacrylate) composite was prepared using in situ polymerization by embedding the Ce: YAG nanopowder in a blend of methyl methacrylate (MMA) and 2-methacrylic acid (MAA) monomers and activating the photopolymerization using a radical initiator. The obtained nanocomposite was yellow and transparent. Its characterization was performed using transmission electron microscopy, small angle X-ray scattering, 13C crosspolarization magic-angle spinning nuclear magnetic resonance, and photoluminescence spectroscopy. Results showed that Ce:YAG nanoparticles are well dispersed in the polymeric matrix whose structure is organized in a lamellar shape. The luminescence properties of the nanocomposite do not show quenching or a significant spectral shift, indicating that the nanocomposite can be useful for advanced applications such as white LED construction