Sintesi e caratterizzazione di nanoparticelle bimetalliche Pd/Au E Pd/Cu

I nanomateriali presentano proprietà molto differenti dai corrispondenti materiali bulk; per questo motivo, negli ultimi anni, se ne è sempre più diffuso l’utilizzo. In particolare, recentemente ha suscitato grande interesse l’impiego di nanoparticelle bimetalliche, le cui proprietà ottiche, morfologiche e dimensionali possono essere modulate sulla base della composizione. L’interesse del mondo industriale allo studio di materiali con dimensioni nano-metriche deriva principalmente dalle loro possibili applicazioni su grande scala ed è quindi di fondamentale importanza la messa a punto di metodologie di sintesi versatili, facilmente scalabili ed a basso impatto ambientale. L’ottimizzazione della sintesi è un aspetto molto importante in quanto deve assicurare un accurato controllo di forma, dimensioni e composizione. A tale scopo è stata sviluppata una sintesi a basso impatto ambientale, in acqua, basata sull’azione riducente del sistema glucosio – NaOH, che permette di ottenere nanoparticelle stabili e con dimensioni omogenee. Nel corso dello studio il riscaldamento è stato effettuato mediante un sistema a microonde: una tecnologia affidabile e sicura che permette un riscaldamento rapido ed omogeneo. La tesi ha come scopo:• l’ottimizzazione e la caratterizzazione di nanosospensioni monometalliche di Pd mediante la sintesi già ottimizzata in lavori precedenti per i metalli: Au, Ag e Cu; •lo studio di sistemi bimetallici Pd/Cu e Pd/Au con morfologia di lega, ottenuti per co-riduzione dei sali precursori; •lo studio dell’attività catalitica delle nanoparticelle sintetizzate nella reazione di riduzione del 4-nitrofenolo a 4-amminofenolo mediante NaBH4; •lo studio della supportazione su carbone di Pd/Au per applicazioni elettrocatalitiche. Per poter studiare e valutare l’eventuale presenza di effetti sinergici tra i metalli coinvolti nella sintesi sono stati confrontati sistemi monometallici con sistemi bimetallici a differenti composizioni (Pd/Cu e Pd/Au). In particolare è stato possibile apprezzare un miglioramento delle prestazioni catalitiche per i sistemi bimetallici Pd/Au rispetto ai metalli di partenza, al contrario i sistemi bimetallici Pd/Cu mostrano un peggioramento dell’attività catalitica all’aumentare del contenuto di rame. La nanosospensione Pd/Au risultata con le maggiori prestazioni catalitiche, è stata supportata su carbone per applicazioni nel campo dell’elettrocatalisi. Da uno studio preliminare sulle tecniche di supportazione è emerso che il metodo migliore per depositare le nanoparticelle sul carbone è l’impregnazione fisica.

Theoretical studies of microfluidics: "walking" drops and "melting" snowflakes.

The present PhD thesis summarizes two examples of research in microfluidics. Both times water was the subject of interest, once in the liquid state (droplets adsorbed on chemically functionalized surfaces), the other time in the solid state (ice snowflakes and their fractal behaviour). The first problem deals with a slipping nano-droplet of water adsorbed on a surface with photo-switchable wettability characteristics. Main focus was on identifying the underlying driving forces and mechanical principles at the molecular level of detail. Molecular Dynamics simulation was employed as investigative tool owing to its record of successfully describing the microscopic behaviour of liquids at interfaces. To reproduce the specialized surface on which a water droplet can effectively “walk”, a new implicit surface potential was developed. Applying this new method the experimentally observed droplet slippage could be reproduced successfully. Next the movement of the droplet was analyzed at various conditions emphasizing on the behaviour of the water molecules in contact with the surface. The main objective was to identify driving forces and molecular mechanisms underlying the slippage process. The second part of this thesis is concerned with theoretical studies of snowflake melting. In the present work snowflakes are represented by filled von Koch-like fractals of mesoscopic beads. A new algorithm has been developed from scratch to simulate the thermal collapse of fractal structures based on Monte Carlo and Random Walk Simulations (MCRWS). The developed method was applied and compared to Molecular Dynamics simulations regarding the melting of ice snowflake crystals and new parameters were derived from this comparison. Bigger snow-fractals were then studied looking at the time evolution at different temperatures again making use of the developed MCRWS method. This was accompanied by an in-depth analysis of fractal properties (border length and gyration radius) in order to shed light on the dynamics of the melting process.

Oxodiperoxomolybdenum catalyzed olefin epoxidation: the role of Ionic Liquids

Ionic Liquids (ILs) constituted by organic cations and inorganic anions are particular salts with a melting point below 100°C. Their physical properties such as melting point and solubility can be tuned by altering the combination of their anions and cations. In the last years the interest in ILs has been centered mostly on their possible use as “green” alternatives to the traditional volatile organic solvents (VOCs) thanks to their low vapour pressure and the efficient ability in catalyst immobilization. In this regard, the subject of the present thesis is the study of the oxodiperoxomolybdenum catalyzed epoxidation of olefins in ILs media with hydrogen peroxide as the oxidant. In particular N-functionalized imidazolium salts, such as 1-(2-t-Butoxycarbonylamino-ethyl)-3-methylimidazolium (1), were synthesized with different counterions [I]-, [PF6]-, [NO3]-, [NTf2]- and [ClO4]– and tested as reaction solvents. The counterion exchange with [Cl]-, [NTf2]- and [NO3]- was also performed in unfuctionalized imidazolium salts such as 3-butyl-1-methylimidazol-3-ium (3). All the prepared ILs were tested in catalytic epoxidation of olefins exploiting oxodiperoxomolybdenum complexes [MoO(O2)2(C4H6N2)2] (4) and [MoO(O2)2(C5H8N2)2] (5) as catalysts. The IL 3[NTf2] and the catalysts 5 give rise to the best results leading to the selective formation of the epoxide of cis-cyclooctene avoiding hydrolysis side reaction. A preliminary study on the synthesis of novel NHC oxodiperoxomolybdenum complexes starting from imidazolium salts was also developed.

Defects in thermosensitive colloidal crystals

Poly-N-Isopropylacrylamide (PNIPAM) colloidal particles form crystal phases that show a thermosensitive behaviour and can be used as atomic model systems. This polymer has both hydrophilic and hydrophobic character and has interesting stimuli-responsive properties in aqueous solution, of which the most important is the temperature response. Above a certain temperature, called Lower Critical Solution Temperature (LCST), the system undergoes a volume phase transition (VPT). Above the LCST, the water is expelled from the polymer network and the swollen state at low temperature transforms into a shrunken state at high temperature. The thermoresponsive behaviour of PNIPAM can be influenced by pH and ionic strength, as well as by the presence of copolymers, such as acrylic acid. In a system formed both by particles of PNIPAM and PNIPAM doped with acrylic acid, one can control the size ratio of the two components by changing the temperature of the mixture, while keeping particle interactions relatively the same. It is therefore possible to obtain thermoresponsive colloidal crystal in which temperature changes induce defects whose formation processes and dynamics can be analysed in an optical microscope at a convenient spatial and temporal scale. The goal of this thesis project was to find the conditions in which such a system could be formed, by using characterization techniques such as Static Light Scattering, Dynamic Light Scattering and Confocal Laser Scanning Microscopy. Two PNIPAM-AAc systems were available, and after characterization it was possible to select a suitable one, on the basis of its low polydispersity and the lack of a VPT, regardless of the external conditions (system JPN_7). The synthesis of a PNIPAM system was attempted, with particles of dimensions matching the JPN_7 system and, unlike JPN_7, displaying a VPT, and one suitable candidate for the mixed system was finally found (system CB_5). The best conditions to obtain thermoresponsive crystal were selected, and the formation and healing of defects were investigated with CLSM temperature scans. The obtained results show that the approach is the correct one and that the present report could represent a useful start for future developments in defect analysis and defect dynamics studies.

α-ossidazione asimmetrica organocatalizzata di aldeidi ramificate con dibenzoil perossido

In this thesis, the development of an enantioselective oxidation of α-branched aldehydes using covalent organocatalysis is described. At state of the art, the asymmetric organocatalysis approach, gave often serous difficulties for these kind of substrate respect “classic” aldehydes. We have used a primary cinchona alkaloid derived amine (specially the 9-epi-NH2-CDA) to develop the reaction in combinations with additives. With benzoyl peroxide as oxidant and 2-phenylpropionaldehyde as reference substrate, we have tried to optimize this system but we not found great results about enantiomeric excess.

Produzione di idrogeno mediante reforming ciclico dell'etanolo

This work deals with a study on the feasibility of a new process, aimed at the production of hydrogen from water and ethanol (a compound obtained starting from biomasses), with inherent separation of hydrogen from C-containing products. The strategy of the process includes a first step, during which a metal oxide is contacted with ethanol at high temperature; during this step, the metal oxide is reduced and the corresponding metallic form develops. During the second step, the reduced metal compound is contacted at high temperature with water, to produce molecular hydrogen and with formation of the original metal oxide. In overall, the combination of the two steps within the cycle process corresponds to ethanol reforming, where however COx and H2 are produced separately. Various mixed metal oxides were used as electrons and ionic oxygen carriers, all of them being characterized by the spinel (inverse) structure typical of Me ferrites: MeFe2O4 (Me=Co, Ni, Fe or Cu). The first step was investigated in depth; it was found that besides the generation of the expected CO, CO2 and H2O, the products of ethanol anaerobic oxidation, also a large amount of H2 and coke were produced. The latter is highly undesired, since it affects the second step, during which water is fed over the pre-reduced spinel at high temperature. The behavior of the different spinels was affected by the nature of the divalent metal cation; magnetite was the oxide showing the slower rate of reduction by ethanol, but on the other hand it was that one which could perform the entire cycle of the process more efficiently. Still the problem of coke formation remains the greater challenge to solve.

Sintesi di catalizzatori supportati su silice mesoporosa e loro utilizzo per l'idrodeclorurazione di molecole clorofluorurate

La necessità di raggiungere la sostenibilità ambientale delle produzioni industriali rappresenta un motore di sviluppo per innovative tecnologie impiantistiche e nuove filosofie produttive. Ad esempio, la necessità di promuovere lo smaltimento dei clorofluorocarburi, causa i loro dimostrati effetti dannosi sullo strato di ozono stratosferico, ha promosso lo sviluppo di nuovi processi industriali. In questo ambito ha acquisito sempre maggior importanza la reazione di idrodeclorurazione di clorofluorocarburi (CFC), in particolare rivolta alla produzione di idrocarburi fluorurati insaturi che mostrano caratteristiche interessanti per la produzione di polimeri con specifiche proprietà di resistenza meccanica, termica e chimica. In questo lavoro di tesi, svolto in collaborazione con SOLVAY SPECIALTY POLYMERS ITALY, sono stati studiati catalizzatori innovativi per la reazione di idrodeclorurazione del 1,2-dicloro-1,2,2-trifluoro-1-(triflurometossi)etano (AM) a 1,2,2-trifluoro-1-(trifluorometossi)etene (MVE).

Trasformazioni asimmetriche indotte da cristallizzazione di miscele diastereoisomeriche di aldeidi alpha-epimerizzabili

In the last few years organic chemistry has focused attention on enantiomeric resolution. Among the several techiniques, crystallization-induced diastereoisomeric transformation (CIDT) aroused the interest because of high yields, as well as to meet the criteria of green chemistry. The process is applied in the specific way for a racemic mixtures of α- epimerizable aldehydes, in order to obtain enatiomerically enrichment mixtures. This technique involves the transformation of a racemic mixture of enantiomers into a diasteroisomeric one by a reaction with a enantiopure auxiliary (Betti’s base). Then, to mixture of diastereoisomers is applied the acid-catalyzed enrichment process: in solution, the epimerization of more soluble diastereoisomer occurs, accompanied by precipitation and hence the removal of the less soluble one from the equilibrium. Finally, through the hydrolysis reaction, it was possible to recover the enantiomerically enriched aldehydes.

α-alchilazione di aldeidi, via organocatalisi: un approccio sintetico e computazionale

During this internship, the α-alkylation of branched aldehydes was taken into consideration. An enantiopure Betti’s base derivative was used as catalyst, applying a new concept in catalysis: organocatalysis. The Betti’s base may be of particular interest for organic chemists working in the field of “reactions catalysed by enantiopure small organic molecules”, in particular for the ones interested in enantiopure primary amines. The potential of secondary amines as catalysts has certainly been known for years. It is indeed more innovative to conduct reactions using primary amine derivatives as catalyst. In this work, the efficacy of the primary amine was checked first. Then, the focus was set on finding optimal reaction conditions. Finally, to have a more complete picture of the structure of the compounds used in the project, experimental and computational IR spectra were compared, after the method was validated. Durante il periodo di tirocinio è stata presa in esame la reazione di α-alchilazione di aldeidi branched, utilizzando un derivato dell’ammina di Betti come catalizzatore enantiopuro ed applicando un nuovo tipo di catalisi: l’organocatalisi. Questi composti possono essere di particolare interesse per lavori in chimica organica, nel campo delle reazioni catalizzate da “piccole” molecole organiche, in particolare da ammine primarie a chiralità definita; la potenzialità delle ammine secondarie chirali come catalizzatori è certamente nota da anni, ma innovativo è condurre il tutto con l’impiego di un derivato amminico primario. Altri aspetti significativi sono gli apparenti e innumerevoli vantaggi, dal punto di vista economico ed ambientale, oltre che operativo e sintetico, derivanti dal nuovo tipo di catalisi. In un primo momento è stata verificata l’efficacia dell’ammina primaria sintetizzata nella reazione in progetto, quindi sono state individuate le condizioni di reazione ottimali. Infine, per un’analisi più completa di alcune molecole organiche e dopo un’opportuna validazione del metodo utilizzato, sono stati ottenuti a livello computazionale gli spettri IR delle molecole di sintesi prodotto e catalizzatore.

Metalli nel particolato atmosferico: distribuzione granulometrica e valutazione del contributo della combustione di biomasse

La tossicità delle polveri atmosferiche è associata sia alla natura granulometrica sia al carico di contaminanti, da qui la necessità di investigare oltre la concentrazione delle PM in atmosfera anche la loro composizione chimica. In questo studio è stata effettuata una prima caratterizzazione da un punto di vista sia granulometrico che chimico del particolato atmosferico campionato in una zona suburbana di Riccione (Castello degli Agolanti). In particolare sono state determinate le concentrazioni di metalli quali Pb, Cd, Ni, Zn, Cu, Fe e Al nel PM 2,5 PM 10 e PM totale. Inoltre, dato che uno degli scopi dello studio è quello di verificare il contributo della combustione di biomasse sul carico complessivo di contaminanti, il periodo di campionamento comprende il giorno delle Fogheracce, festa popolare in cui vengono accesi diversi falò all’aperto. Complessivamente sono stati prelevati 13 campioni di 48 ore per ogni frazione granulometrica dal 9 Marzo all’8 Aprile 2011. Dallo studio emerge che nel periodo di campionamento, mediamente il contributo antropogenico è dominante per Pb, Cd, Ni Cu e Zn dovuto principalmente al traffico veicolare. Tali metalli, ad eccezione del Cu infatti si concentrano nel particolato più fine. Al e Fe invece sono principalmente marker delle emissioni crostali e si concentrano nella frazione grossolana. Interessante quanto registrato nella giornata delle Fogheracce. Oltre ad una variazione nel contenuto relativo dei metalli con un forte arricchimento di Pb e Al, per quest’ultimo si nota anche un forte incremento della sua concentrazione nella frazione PM2.5 ad indicare una diversa sorgente emissiva. Si evidenzia in questo studio un importante contributo nel carico di inquinanti da parte di combustioni di biomasse all’aperto.

Isoxazolidines and oxazines: preliminary studies for the synthesis of N,O-heterocyclic systems via an organocatalyzed 1,3-Dipolar Cycloaddiction and a tandem reaction mediated by TEMPO salts

This thesis is the result of the study of two reactions leading to the formation of important heterocyclic compounds of potential pharmaceutical interest. The first study concerns the reaction of (1,3)-dipolar cycloaddition between nitrones and activated olefins by hydrogen bond catalysis of thioureas derivatives leading to the formation of a five-membered cyclic adducts, an interesting and strategic synthetic intermediate, for the synthesis of benzoazepine. The second project wants to explore the direct oxidative C(sp3)-H α-alkylation of simple amides with subsequent addition of an olefin and cyclization in order to obtain the corresponding oxazine. Both reactions are still under development.

Addizione viniloga enantioselettiva di Michael di alchilidenossindoli a nitroolefine

Questo lavoro di tesi è frutto di uno studio sull’addizione viniloga enenantioselettiva di sistemi 3-alchilidenossindolici a nitrotrirene utilizzando un catalizzatore bifunzionale in grado di attivare la posizione gamma del suddetto ossindolo, per mezzo di una reazione acidobase, e di attivare il nitrostirene attraverso interazione via legame a idrogeno. Questo progetto nasce come novità assoluta nel mondo dell’organocatalisi.