Tesi di Dottorato
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Item Adsorption properties of carbon nanotubes and application of thermal desoprtion spectroscopy to ammonia and methane ices and zoisite(2010-12-14) Vasta, Roberta; Bonanno, Assunta; Falcone, GiovanniIn this work we wanted to underline the importance of Thermal Desorption Spectroscopy and its applications to several branches of Physics. Temperature-programmed desorption techniques (TPD) are important to determinate kinetic and thermodynamic parameters of desorption processes and decomposition reactions. Knowledge of the nature of the desorption process is fundamental to understand the nature of the elementary chemical processes of adsorbates, as the energetics of bonding, the specification of the chemical nature of the bound species and the nature and magnitude of interactional effect between adsorbed species. We focused our attention on the applications of Thermal Desorption Spectroscopy (TDS) to High-Energies Physics, Astrophysics and Geophysics; in fact this technique was used, respectively, to investigate the molecular hydrogen adsorption on carbon nanotubes, the effects of electron bombardment on ammonia and methane ices and changes of zoisite mineral after heating. The molecular hydrogen adsorption on carbon nanotubes was studied to find a possible solution to vacuum system problems of Large Hadron Collider (LHC); in fact, the circular path of photon beams produces synchrotron radiation which deteriorates LHC vacuum desorbing gas molecules from the ring walls. Among the desorbed species the most problematic to pump out is H2. Since LHC elements operate at low temperatures, a possible solution to vacuum problem is the installation of cryosorbent materials on the LHC walls. In this work we study the possibility to use carbon nanotubes as criosorbers in future accelerators. Our sample, furnished by Prof. Nagy group of Chemical Engineering Department of Calabria University, is constituted by MWNTs synthesized by chemical vapor deposition using C2H4 and subsequently purified. Our investigations confirm that the carbon nanotubes have a great adsorption capacity also at low temperatures both for H2 and noble gases as Kr; then we observed that H2 adsorption on CNT is described by a first kinetic-order, while Kr adsorption is characterized by a zero kinetic-order. By means of TDS we calculate the activation energy for H2 adsorption on carbon nanotubes and we found a value of about 3KJ/mol, perfectly coherent with theoretic one. Moreover, from a comparison between nanotubes and other carbon-based material (as charcoal), we noted that adsorption efficiency for CNT is almost an order of magnitude higher then charcoal. So carbon nanotubes are good candidates to cryosorbers in future accelerators. 2 As Thermal Desorption Spectroscopy application to Astrophysics we studied the effect of electron bombardment on ammonia and methane ices. The interstellar medium is composed for 99% by gas; molecules, atoms and radicals at gas state condense on dust grains surface of molecular clouds (at 10 K) creating an icy mantle with a thickness of 0.1 μm. The presence of ices is confirmed by IR spectroscopy of obscured stellar sources and in interstellar grains are localized solid mixture containing H2O, CO, CH4 and NH3. In these environments ices are subjected to chemical and physical processes, specifically to bombardment of photons and cosmic rays, with the consequent synthesis of new organic species In this work we conducted an investigation of the chemical processing of ammonia and methane ices subjected to energetic electrons. By Thermal Desorption Spectroscopy we verify the production of new organic species, after energetic irradiation in interstellar ices, as diazene (N2H2), ethane (C2H6) and acetylene (C2H2). Finally, in Geophysics and Petrology Thermal Desorption Spectroscopy can be used to study minerals chemical composition. Our interest was focused on zoisite and the sample investigated was furnished by prof. Ajò from “Institute of Inorganic Chemistry and Surfaces” of CNR, in Padova. In this work we used TDS to investigate zoisite behaviour during heating form room temperature to 650oC and to understand if its modification into tanzanite variety after heating is due to structural changes or to a dehydration mechanism.Item Modelling of nanostructured membranes for wasterwater purification(2013-11-29) Bisignano, Federica; Bartolino, Roberto; De Luca, GiorgioThe removal of pollutants as well as the recovery of high added value molecules with low molecular weight is a current challenge in the wastewater treatment. Membrane processes can be considered as a viable option to solve these issues. In separations based membranes, high rejection of organic matter and water high permeability are two very important aspects that must be optimised. In general, the increase of the former comes at the expense of the latter because high rejection is cause of membrane fouling which in turns reduces dramatically the water permeability. Thus, membrane fouling constitutes one of the major limitations in membrane separation processes. The design of innovative materials which show high water permeability and at same time molecular rejection but with a low propensity to fouling is of fundamental relevance in this area. Mixed-matrix composite membranes where nanostructures such as Carbon Nano Tubes (CNTs) or Nano particles (NPs) are added, are receiving a huge focus since the properties of these nanostructures can confer an increase of the membrane efficiency in terms of permeability, selectivity, resistance and finally antifouling. The choice of the right nanomaterial can be highly accelerated by computational modelling. Thus, in this thesis an ab-initio modelling study in the frame of the Density Functional Theory (DFT) is carried out in order to investigate the structure-property relationships of nanostructures like CNTs and polyoxometalates NPs (POM). These nanostructures are used in the preparation of composite membranes in the frame of BioNexGen project [1] with the aim to propose novel membranes to be used in bioreactor for industrial waste water treatment. In particular, the rejection of CNTs towards organic solutes with low molecular weight coming from industrial waste water such as cosmetic, textile and oil olive was analysed in conjunction to the optimization of water permeability in CNTs. Also, the adsorption of POMs on polymeric membrane surface was analysed in order to understand if an efficient antifouling property can be imparted to the membranes by adding these NPs which possess excellent antibacterial and oxidants properties. While nanotube permeability has been extensively studied in both experimental and modelling works resulting in orders of magnitude water flow enhancements for tube diameters in the reverse osmosis and nanofiltration range [2], less work has been done on CNT selectivity of small organic solutes. Precise control of the CNTs synthesis allows for fine-tuning of the outer and inner diameters in the case of single- and multi-wall carbon nanotubes (SWNTs and MWNTs, respectively), offering the possibility of controlling their selectivity toward small solutes. In this thesis a modelling study was, therefore, addressed to define the optimal CNT internal diameter that should be used in order to achieve a total rejection of several target compounds very difficult to separate. Three novel algorithms [3, 4] were implemented during the thesis for reach the aforementioned objective. These algorithms do not make use of any adjustable parameters (i.e. fitting parameters) being based on geometry optimizations carried out in the frame of high level of quantum approach (DFT) and topological analysis of the considered systems. In addition, the CNTs geometrical characteristics should be optimized in order to get the best compromise between permeability and rejection. The functionalizing of the nanotubes tip with specific functional groups capable of hindering the passage of solutes while allowing water molecules to flow has been suggested as a solution to this problem [5, 6]. Thus, a theoretical study of CNT-composite membranes was carried out in this work with the aim of optimizing the CNTs tip, through their functionalization, to maximise both water permeability and solutes selectivity. This study is the basis of the third implemented algorithm [7]. Concerning the membrane fouling, the analysis of the adsorption of antibacterial anionic NPs (i.e. POM) on the surface of polymeric membranes was carried out in this thesis in order to achieve an optimal adsorption of these NPs. Noncovalent interactions between POM and commercial surfactants, used in polymer membrane preparations, were evaluated. Anionic POMs are in fact promising antibacterial agents [8], therefore, an efficient exchange with the bromide ions, used to counterbalance the positive charge of the commercial surfactants, would allow to increase the efficiency of the membrane by reducing the organic and bio fouling. In order to achieve this result, besides the aforementioned POM-surfactants noncovalent interactions the electronic hydration energy of POM and bromide anions was also evaluated in order to predict the probable exchange of these anions on the polymer surface. The conclusions of this thesis are achieved by using only ab-initio methods thus the results can be considered quite generals and homogeneous, free from empirical or fitting parameters. A validation of the theoretically prediction is provided concerning the POM-bromide exchange by means of an ad hoc designed experiment. The experimental results are in agreement with the theoretically predictionsItem Eco-friendly functionalization of carbon-carbon double bonds through epoxidation and cycloaddition reactions(2008-10-07) Tocci, Amedeo; Bartolo, Gabriele; Bortolini, OlgaItem Nanotubi di carbonio multiparete: ottimizzazione dei parametri di sintesi per la produzione su larga scala(2010-11-12) Perri, Caterina; Molinari, Raffaele; Nagy, Jànos B.Questo lavoro di tesi è dedicato allo studio sperimentale della produzione di nanotubi di carbonio su larga scala. La tecnica utilizzata per la sintesi dei nanotubi è la CCVD (Catalytic Chemical Vapour Deposition). La sperimentazione verte sulla preparazione del catalizzatore, la sintesi vera e propria e la caratterizzazione dei prodotti ottenuti. Lo studio e l’ottimizzazione della produzione di nanotubi di carbonio è particolarmente interessante per la loro vasta gamma di applicazioni in campi quali la nano-elettronica, bio e gas sensoristica, materiali nano-compositi, catalisi. I principali obiettivi del lavoro di tesi sono stati innanzitutto progettare e realizzare l’impianto per la sintesi, trovare il catalizzatore più attivo, la quantità ottimale dello stesso da utilizzare nel reattore e sperimentare la migliore miscela idrocarburo/gas portante al fine di ottenere elevate rese nonché buona qualità dei prodotti, cioè una buona grafitizzazione dei nanotubi. Tutto ciò è correlato all’idea di passare, una volta trovate le condizioni ottimali, da scala di laboratorio a scala industriale. Il primo passo è quello di preparare il catalizzatore. Si sceglie così un supporto (zeolite, ossido, argilla) adeguato all’inserimento di metalli di transizione (Fe, Ni, Co, Mo), centri attivi nella sintesi. Anche il metodo di preparazione risulta di fondamentale importanza per il raggiungimento degli obiettivi prefissati. In seconda battuta avviene la sintesi e, in questo caso, la fase importante è la scelta dell’idrocarburo utilizzato e la quantità che viene inviata al reattore. C. Perri - Nanotubi di carbonio multiparete: ottimizzazione dei parametri di sintesi per la produzione su larga scala Nella terza fase, la caratterizzazione del prodotto (attraverso tecniche quali SEM, TEM) conduce all’eventuale miglioramento delle fasi precedenti per l’ottenimento di prodotti di qualità e rese elevate, fermo restando che nel passaggio alla produzione industriale non è nient’affatto trascurabile l’aspetto economico. L’utilizzo di un catalizzatore bi-metallico preparato per impregnazione, l’etilene come idrocarburo, una ben determinata miscela etilene-azoto hanno influenzato positivamente la crescita dei nanotubi di carbonio in grande quantità e con un elevato grado di purezza. La Microscopia Elettronica a Trasmissione ha messo in evidenza l’elevata qualità dei nanotubi prodotti (buona grafitizzazione, nanotubi multiparete ben strutturati) e la non necessaria purificazione degli stessi dopo la sintesi.Item Chemical and morphological influence on nanostructures: synthesis and characterization of Carbon-based materials(2014-05-15) Policicchio, Alfonso; Agostino, G.; Falcone, GiovanniItem Adsorption properties of carbon nanotubes and application of thermal desoprtion spectroscopy to ammonia and methane ices and zoisite(2014-05-15) Vasta, Roberta; Bonanno, Assunta; Falcone, GiovanniIn this work we wanted to underline the importance of Thermal Desorption Spectroscopy and its applications to several branches of Physics. Temperature-programmed desorption techniques (TPD) are important to determinate kinetic and thermodynamic parameters of desorption processes and decomposition reactions. Knowledge of the nature of the desorption process is fundamental to understand the nature of the elementary chemical processes of adsorbates, as the energetics of bonding, the specification of the chemical nature of the bound species and the nature and magnitude of interactional effect between adsorbed species. We focused our attention on the applications of Thermal Desorption Spectroscopy (TDS) to High-Energies Physics, Astrophysics and Geophysics; in fact this technique was used, respectively, to investigate the molecular hydrogen adsorption on carbon nanotubes, the effects of electron bombardment on ammonia and methane ices and changes of zoisite mineral after heating. The molecular hydrogen adsorption on carbon nanotubes was studied to find a possible solution to vacuum system problems of Large Hadron Collider (LHC); in fact, the circular path of photon beams produces synchrotron radiation which deteriorates LHC vacuum desorbing gas molecules from the ring walls. Among the desorbed species the most problematic to pump out is H2. Since LHC elements operate at low temperatures, a possible solution to vacuum problem is the installation of cryosorbent materials on the LHC walls. In this work we study the possibility to use carbon nanotubes as criosorbers in future accelerators. Our sample, furnished by Prof. Nagy group of Chemical Engineering Department of Calabria University, is constituted by MWNTs synthesized by chemical vapor deposition using C2H4 and subsequently purified. Our investigations confirm that the carbon nanotubes have a great adsorption capacity also at low temperatures both for H2 and noble gases as Kr; then we observed that H2 adsorption on CNT is described by a first kinetic-order, while Kr adsorption is characterized by a zero kinetic-order. By means of TDS we calculate the activation energy for H2 adsorption on carbon nanotubes and we found a value of about 3KJ/mol, perfectly coherent with theoretic one. Moreover, from a comparison between nanotubes and other carbon-based material (as charcoal), we noted that adsorption efficiency for CNT is almost an order of magnitude higher then charcoal. So carbon nanotubes are good candidates to cryosorbers in future accelerators. 2 As Thermal Desorption Spectroscopy application to Astrophysics we studied the effect of electron bombardment on ammonia and methane ices. The interstellar medium is composed for 99% by gas; molecules, atoms and radicals at gas state condense on dust grains surface of molecular clouds (at 10 K) creating an icy mantle with a thickness of 0.1 μm. The presence of ices is confirmed by IR spectroscopy of obscured stellar sources and in interstellar grains are localized solid mixture containing H2O, CO, CH4 and NH3. In these environments ices are subjected to chemical and physical processes, specifically to bombardment of photons and cosmic rays, with the consequent synthesis of new organic species In this work we conducted an investigation of the chemical processing of ammonia and methane ices subjected to energetic electrons. By Thermal Desorption Spectroscopy we verify the production of new organic species, after energetic irradiation in interstellar ices, as diazene (N2H2), ethane (C2H6) and acetylene (C2H2). Finally, in Geophysics and Petrology Thermal Desorption Spectroscopy can be used to study minerals chemical composition. Our interest was focused on zoisite and the sample investigated was furnished by prof. Ajò from “Institute of Inorganic Chemistry and Surfaces” of CNR, in Padova. In this work we used TDS to investigate zoisite behaviour during heating form room temperature to 650oC and to understand if its modification into tanzanite variety after heating is due to structural changes or to a dehydration mechanism.