266 research outputs found
synthesis and characterization of thermotropic liquid crystalline halide perovskites based on fluorinated imidazolium cations
No full textLAUREA MAGISTRALEAttualmente le perovskiti vengono utilizzate in numerosi campi a partire dal fotovoltaico sino a molteplici applicazioni nei dispositivi optoelettronici. Nonostante la riduzione dei costi e l’ottima efficienza dei dispositivi a base di perovskite, le problematiche di tossicità legate alla presenza del piombo e la scarsa stabilità rappresentano ancora i principali fattori limitanti per la loro commercializzazione. La presenza di difetti, sia in superficie che all’interno del materiale, è nota essere critica per la stabilità a lungo termine e considerevolmente limitante all’efficienza della perovskite. Affinché vengano superati questi limiti sono state sviluppate diverse strategie. Tra queste l’utilizzo di liquidi ionici (ILs) come additivi consente di migliorare la cristallinità della perovskite, passivare i difetti strutturali superficiali, bloccare la ricombinazione non radiativa degli eccitoni foto-generati e migliorare la stabilità contro gli agenti atmosferici. In particolare, i liquidi ionici a base di perfluoroalchil-metil-imidazolo sono stati applicati come agenti passivanti grazie alla loro capacità di auto-assemblarsi sulla superficie della perovskite, portando alla formazione di strutture ordinate con minori difetti. In questo lavoro cationi di imidazolo funzionalizzati con catene perfluoroalchil lineari o ramificate sono stati impiegati per la sintesi di nuove perovskiti a bassa dimensionalità con alogeno (LDHPs). I cationi organici florurati sono considerati un metodo innovativo per regolare le proprietà optoelettroniche delle LDHP. La presenza di frammenti molecolari saturi altamente fluorurati nelle LDHP può conferire proprietà idrorepellenti e una stabilità maggiore. Tuttavia, per sfruttare interamente i vantaggi della florurazone nelle perovskiti, è essenziale comprendere meglio come i liquidi ionici fluorurati influiscano sulla struttura e dunque sulle proprietà del materiale. In questo lavoro è stata effettuata una caratterizzazione strutturale e termica che ha permesso di studiare gli effetti delle catene perfluoroalchilche nelle proprietà delle perovskiti. Infatti è stato dimostrato che le interazioni fluoro-fluoro e la segregazione delle porzioni fluorurate inducono alla formazione di strutture ordinate lamellari nelle perovskiti, dando luogo a un comportamento termotropico liquido cristallino (LC).In recent years, perovskites have found use in numerous fields beginning with photovoltaics and expanding to light-emitting applications and other optoelectronic devices. Despite the competing costs and efficiencies of perovskite-based devices,toxicity issues related to lead-based halide perovskites together with their poor stability in air and moisture still represent the main factors limiting their marketing. It is generally accepted that the presence of defects, both at the surface or in the bulk, is critical for the long-term stability and considerably limits perovskite efficiency. Several strategies have been developed to overcome these limits. Among them, the use of ionic liquids (ILs) as additives to perovskite precursor solution allows to improve the crystallinity of the perovskite, passivate surface structural defects, block non-radiative recombination of the photogenerated ion pairs and impede atmospheric-induced degradation. In particular, perfluoroalkyl-methyl imidazolium ILs have been applied as passivating agents due to their ability to self-assemble on perovskite surface, resulting in the formation of ordered structures and higher film quality with fewer defects. In this work imidazolium cations functionalized with linear or branched perfluoroalkyl chains were applied for the synthesis of new Low Dimensional Halide Perovskites (LDHPs). Fluorination of organic cations offers an intriguing strategy to adjust the optoelectronic properties of LDHPs. In fact, the presence of highly fluorinated saturated molecular fragments in the resulting LDHPs can bestow additional water-repellent properties and superior stability compared to fully hydrocarbon-based cations previously employed. However, to completely exploit the benefits of fluorination in tailoring the physical and functional properties of perovskites, it is essential to better understand how fluorinated ionic liquids influence structure-property relationship. Here a combination of structural and thermal characterization allowed to study effects of perfluoroalkyl chains on the properties of perovskites. Indeed, fluorous-fluorous interactions and segregation of fluorinated moieties have been demonstrated to induce the formation of ordered structures in perovskite containing fluorinated imidazolium cations, resulting in a thermotropic liquid crystalline (LC) behavior
Fluorinated organic spacers in the design of new low-dimensional hybrid halide perovskites : synthesis and structural characterization
No full textLAUREA MAGISTRALELe perovskiti ibride organico-inorganiche (OIHP) sono i nuovi materiali emergenti degli
ultimi anni e vengono utilizzate per un’ampia gamma di applicazioni, tra cui nei transistor, nei diodi a emissione di luce, nelle celle solari, nei fotorivelatori e nei laser. L’utilizzo
di queste perovskiti ibride combina i vantaggi delle parti organiche altamente processabili
in soluzione e con buone proprietà ottiche, con i vantaggi dei semiconduttori cristallini
inorganici, come l’elevata mobilità delle cariche e gli ampi coefficienti di assorbimento.
Le loro eccezionali proprietà optoelettroniche, il basso costo di fabbricazione e il costo
limitato dell’elettricità sono tuttavia ostacolati dalla loro insufficiente stabilità, che porta
a una breve durata operativa e limita la loro applicazione nei dispositivi optoelettronici,
impedendone la commercializzazione su larga scala. Negli ultimi anni sono stati esplorati
molti approcci per aumentare la stabilità delle perovskiti senza sacrificare le prestazioni
dei dispositivi. Un concetto emergente consiste nell’ingegneria a bassa dimensione, ottenuta attraverso l’incorporazione di grandi cationi organici tra le lastre di perovskite ibrida. Queste parti organiche possono essere alogenate e quindi interagire con gli alogeni,
tipicamente presenti nelle perovskiti alogenate, dando origine a un tipo di interazione
non covalente alternativa, denominata legame ad alogeno (XB). In questo lavoro sono
stati selezionati diversi cationi donatori di XB per la sintesi di diverse strutture di perovskite, la cui capacità di formare legami ad alogeno è stata successivamente analizzata.
In particolare, il catione 4-iodoanilinio (IA+) è stato utilizzato per formare la perovskite
tetraiodopiombata , nella cui struttura è stata dimostrata la presenza di XB tra i domini
organici e inorganici e ne è stata studiata la forza, rivelando un’interazione relativamente
debole. Per studiare un legame ad alogeno molto più intenso, è stata applicata la strategia della sostituzione dell’idrogeno con atomi di fluoro. I cationi (4-X-2,3,5,6-tetrafluoro
anilina)-etan-1-ammonio (X-FEA+) (X=I, Br, Cl) sono stati quindi utilizzati per sintetizzare perovskiti a bassa dimensione, seguendo diverse procedure. Le perovskiti fluorurate
ottenute sono state sintetizzate, purificate e caratterizzate mediante 1H NMR, 19F NMR,
MS, XRPD e SCXRD per comprenderne le strutture cristalline finali e per indagare la
forza dei legami ad alogeno, qualora fossero presenti. Questo studio suggerisce che il
legame ad alogeno può verificarsi in condizioni di sintesi specifiche, che consentono di
accorciare la distanza alogeno-alogeno e di aumentare la linearità del legame, con il risultato di un’interazione molto più forte. La variabilità del legame alogeno-alogeno può
essere sfruttata come un potente strumento per controllare la struttura e le proprietà foto
fisiche nelle perovskiti a bassa dimensionalità, migliorando ulteriormente il potenziale di
commercializzazione dei dispositivi optoelettronici basati sulle perovskiti.Organic–inorganic hybrid perovskites (OIHPs) are the new emerging materials for the last
few years, they are used for a wide array of applications, including those in field-effect
transistors, light-emitting diodes, solar cells, photodetectors, and lasers. The utilization
of these hybrid perovskites combines the advantages of the highly solution processable and
optically tunable organic parts, together with the advantages of the inorganic crystalline
semiconductors, like high charge mobilities and large absorption coefficients. Their exceptional optoelectronic properties, lower fabrication cost and levelized cost of electricity
are, however, hampered by their insufficient stability, which leads to a short operational
lifetime and limits their application in optoelectronic devices, hindering from full-scale
commercialization. In recent years, many approaches have been explored to boost the
stability of perovskites without sacrificing their device performance. One emerging concept consists in low-dimensional engineering, achieved through the incorporation of large
organic cations between hybrid perovskite slabs. These organic moieties can be halogenated and be consequently able to interact with halide anions, typically present in
halide perovskites, giving rise to an alternative noncovalent interaction, named halogen
bonding. In this work several XB-donor cations have been selected for the synthesis
of different low-dimensional perovskite structures, whose ability to form halogen bond
was subsequently analysed. In particular, 4-iodoanilinium (IA+) cation has been used
to form bis(4-iodoanilinium) tetraiodoplumbate perovskite, in whose structure the occurrence of XB between organic and inorganic domains has been proven and its strength
has been investigated, revealing a relatively weak interaction. Aiming to study a much
stronger XB, hydrogen substitutions by fluorine atoms strategy has been applied. (4-X 2,3,5,6-tetrafluoroaniline)-ethan-1-ammonium cations (X-FEA+) (X=I, Br, Cl) have been
therefore used to synthesise low-dimensional perovskites, following different procedures.
The resulting fluorinated perovskites have been synthetised, purified, and characterised
by 1H NMR, 19F NMR, MS, XRPD and SCXRD to understand their final crystalline
structures, and to investigate the strength of their XB interactions, if there were any.
This study suggests that XB can occur under specific synthesis conditions, that allow
to shorten the halogen-halogen distance and to increase the linearity of the XB, resulting in a much stronger interaction. Tunability of halogen-halogen bond can be exploited
as a powerful tool to control structure and photophysical properties in low-dimensional
perovskites, further improving the commercialization potential of perovskite-based optoelectronic devices
Lower Bounds for Uniform Machine Scheduling Using Decision Diagrams
No full textWe propose a relaxed decision diagram (DD) formulation for obtaining lower bounds on uniform machine scheduling instances, based on separators to separate jobs on different machines. Experiments on the total tardiness for instances with tight due times show that for obtaining nontrivial bounds, it is important to partition the DD nodes on a layer based on their machine finishing time. When the number of jobs is small, DDs provide stronger bounds in less time than a time-indexed LP relaxation.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Algorithmic
Exploiting Graphene as an Efficient Catalytic Template for Organic Transformations: Synthesis, Characterization and Activity Evaluation of Graphene‐Based Catalysts
No full text
Exfoliation of graphite and chemical functionalization of graphene, and related carbon nanoforms, with substituted (ter)thiophene derivatives and other chromophores for energy conversion
No full textIn the present PhD thesis, the synthesis and characterization, in terms of spectrospopic, microspopic and electrochemical studies, of carbon nanostructured materials and specifically based on graphene (Chapters 1-3), fullerene C60 (Chapter 4) and carbon nanohorns (Chapter 5) are discussed.In Chapter 1, the synthesis and properties of graphene sheets supramolecularly decorated with linear oligothiophenes (n=3 or 9 rings) is presented. Τhe formation of the charge separated state and the electron transfer from the oligothiophenes units to the graphene sheets, contributing to the understanding of the mechanism takes place and the factors affecting the rate of the charge transfer, are exploited. In Chapter 2, the reactivity of S-doped graphene sheets non-covalently modified with a star-shaped oligothiophene is evaluated against the electrochemical oxygen reduction. Moreover, the impact of the sulfur atoms onto the grapheme sheets and the morphology of the material on the catalytic activity is discussed.In Chapter 3, the synthesis of graphene-based hybrid materials carrying either a covalently grafted fluorene-perylene copolymer or a supramolecularly interacting fluorine-perylene copolymer are described. The catalytic activity of the hybrid against the reduction of nitrophenol to nitroaniline is also presented.In Chapter 4, host-guest supramolecular interactions were applied for the fabrication of novel C60/OPV/C60 hybrid, where the OPV-Hamilton host interacts with two C60-barbiturate guests via multiple hydrogen bonds. The observed results describe for the first time the photoinduced electron transfer in a molecular architecture based on the self-organization of an OPV-Hamilton molecule with C60 and the significance of multiple hydrogen bonding in charge transfer processes.In Chapter 5, a large scale (≥1 g) exfoliation protocol for the individualization of aggregated (the so-called “Dhalia flower”) carbon nanohorns species in one step with the aid of a superacid was developed. Notably, the as prepared in-CNHs posses higher conductivity than the pristine CNHs and an intact graphitic lattice.Στην παρούσα Διδακτορική Διατριβή συντέθηκαν, χαρακτηρίστηκαν και μελετήθηκαν με φασματοσκοπικές, μικροσκοπικές και ηλεκτροχημικές μεθόδους υλικά βασισμένα σε νανοδομές του άνθρακα και συγκεκριμένα υλικά βασισμένα στο γραφένιο (Κεφάλαια 1-3), στο φουλερένιο C60 (Κεφάλαιο 4) και στα νανοκέρατα άνθρακα/CNHs (Κεφάλαιο 5). Στο Κεφάλαιο 1, παρουσιάζεται η μελέτη των ιδιοτήτων φύλλων γραφενίου υπερμοριακά τροποποιημένων με ολιγοθειοφαίνια ευθείας αλυσίδας (n=3 ή 9 δακτύλιοι). Η συγκεκριμένη μελέτη εστιάζει στην διερεύνηση του σχηματισμού της κατάστασης των διαχωρισμένων φορτίων και την μεταφορά ηλεκτρονίων από τα ολιγοθειοφαίνια προς τα γραφένιο, συμβάλλοντας στην κατανόηση του μηχανισμού που λαμβάνει χώρα και στους παράγοντες που επηρεάζουν την ταχύτητα της διεργασίας.Στο Κεφάλαιο 2, μελετάται η δράση ενός υλικού που συναπαρτίζεται από θειωμένα φύλλα γραφενίου (S-doped graphene) υπερμοριακά τροποποιημένα με ένα διακλαδισμένο ολιγοθειοφαίνιο, έναντι της ηλεκτροχημικής αντίδρασης αναγωγής του οξυγόνου. Ακόμα, περιγράφεται ο ρόλος των ατόμων θείου και της μορφολογίας του υλικού στην καταλυτική επίδοσή του.Στο Κεφάλαιο 3, περιγράφεται η σύνθεση υβριδικού υλικού που φέρει συμπολυμερές φλουορενίου-περυλενίου τόσο ομοιοπολικά προσδεδεμένου σε φύλλα γραφενίου όσο και υπερμοριακά ακινητοποιημένου και διερευνάται η δράση του ως καταλύτης για την αντίδραση αναγωγής της νιτροφαινόλης σε νιτροανιλίνη.Στο Κεφάλαιο 4, παρουσιάζεται η σύνθεση του υβριδικού υλικού C60/OPV/C60 ακολουθώντας μια στρατηγική host-guest, όπου το guest-φουλερένιο φέρει μια βαρβιτουρική ομάδα και συμπλέκεται με την host-ένωση OPV-Hamilton μέσω πολλαπλών δεσμών υδρογόνου. Μελετάται για πρώτη φορά, η φωτοεπαγόμενη μεταφορά ηλεκτρονίου σε αρχιτεκτονικές που βασίζονται στην αυτοοργάνωση ενός OPV-Hamilton παραγώγου και του C60 και περιγράφεται η σημασία τέτοιου τύπου υπερμοριακών αλληλεπιδράσεων στις διεργασίες μεταφοράς ηλεκτρονίου.Στο Κεφάλαιο 5, αναπτύχθηκε μια απλή μέθοδος αποσυσσωμάτωσης νανοκεράτων άνθρακα τύπου «λουλούδι της ντάλιας» με τη χρήση σουπεροξέος σε ένα βήμα. Τα in-CNHs εμφανίζουν αυξημένη αγωγιμότητα και το γραφιτικό πλέγμα τους δεν φέρει χημικές ή δομικές διαταραχές. Η μέθοδος αυτή μπορεί να εφαρμοστεί σε κλίμακα ≥1 γραμμαρίου
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No full textWe thank Dr Spence for his interest in the 2020 International Society of Hypertension (ISH) Global Hypertension Practice Guidelines and highlighting what he considers blind spots in the new guidelines. Specifically, the author is concerned that Liddle syndrome, one of the rare monogenic causes of hypertension is not mentioned and its treatment not appropriately addressed in the 2020 ISH guidelines. Dr Spence provides insightful comments describing the central role of the epithelial sodium channel (ENaC) in Liddle syndrome which is responsible for its clinical features including early onset of salt-sensitive hypertension, hypokalemic metabolic alkalosis, and suppression of both renin and aldosterone secretion. Importantly, Liddle syndrome is associated with increased incidence
of premature cardiovascular and cerebrovascular events and usually unresponsive to mineralocorticoid receptor antagonists
Perovskite‐Like Liquid‐Crystalline Materials Based on Polyfluorinated Imidazolium Cations
No full textHybrid Organic-Inorganic Halide Perovskites (HOIHPs) represent an emerging class of semiconducting materials, widely employed in a variety of optoelectronic applications. Despite their skyrocket growth in the last decade, a detailed understanding on their structure-property relationships is still missing. In this communication, we report two unprecedented perovskite-like materials based on polyfluorinated imidazolium cations. The two materials show thermotropic liquid crystalline behavior resulting in the emergence of stable mesophases. The manifold intermolecular F & sdot; & sdot; & sdot; F interactions are shown to be meaningful for the stabilization of both the solid- and liquid-crystalline orders of these perovskite-like materials. Moreover, the structure of the incorporated imidazolium cation was found to tune the properties of the liquid crystalline phase. Collectively, these results may pave the way for the design of a new class of halide perovskite-based soft materials.In this communication, we report two novel intrinsically liquid crystalline metal halide perovskite-like materials by utilizing fluorinated ionic liquid crystalline (FILC) mesogens based on polyfluorinated alkylimidazolium cations. Manifold intermolecular F & sdot; & sdot; & sdot; F interactions were found to be essential for the solid- and liquid-crystalline orders of the perovskite-like structures. This study may pave the way towards a new class of perovskite-based soft materials. imag
Symplectic critical models in 6+ϵ dimensions
No full textAbstractWe consider nontrivial critical models in d=6+ϵ spacetime dimensions with anticommuting scalars transforming under the symplectic group Sp(N). These models are nonunitary, but the couplings are real and all operator dimensions are positive. At large N we can take ϵ→1 consistently with the loop expansion and thus provide evidence that these theories may be used to define critical models in d=7. The relation of these theories to critical Sp(N) theories, defined similarly to the well-known critical O(N) theories, is examined, and some similarities are pointed out
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