Carbon Nanodots (CNDs) are defined as carbon nanoparticles, with a characteristic size below 10 nm and a quasi-spherical morphology. They have attracted a lot of attention in material science, mainly owing to their intrinsic photoluminescence, rich-surface chemistry and high solubility. During the PhD studies different aspects of these nanoparticles were investigated. First, issues related to the bottom-up synthesis of CNDs were analyzed. Solvothermal methods have become the procedure of choice for the CND production, relying on the high-temperature treatment of small organic molecules. However, the use of high temperature conditions may trigger many simultaneous reactions in the starting mixture, often resulting in the formation of molecular side products. When these undesired compounds are not correctly removed during the material purification, they can be responsible of properties erroneously attributed to nanoparticles. In this first work, several case-studies were considered, in which it was demonstrated how a straightforward Nuclear Magnetic Resonance (NMR) analysis can be used to reveal residual molecules in CND samples. In a second work, CNDs were tested as nano-catalysts to promote organic reactions. In particular, chiral CNDs were prepared through a microwave synthesis starting from citric acid and a chiral dopant amine. The developed CNDs exhibit amino groups on their surface, interesting photophysical properties and resulted catalytically active in several transformations. Specifically, the outer-shell composition of CNDs was instrumental to carry out organocatalytic reactions in an enantioselective fashion, while their redox and light-absorbing features were used to promote photochemical processes. Finally, the photo- and organocatalytic abilities of CNDs were exploited at the same time to promote more complex transformations. Thereafter, the focus of the work was shifted from the studies of individual CNDs to their assembly into larger systems. In particular, a covalent connection of different kinds of CNDs was realized through the use of click chemistry and photophysical studies on the final assembly revealed energy transfer processes between the interconnected particles. Later on, the use of a rigid linker for the CND connection was explored, allowing to control the arrangement of particles in space along with the production of porous 3D networks. Finally, a non-covalent strategy was exploited to drive the self-assembly of chiral CNDs. In particular, upon tuning solvents and pH conditions, particles were able to assemble into different kinds of micro-sized luminescent structures, like Janus particles, carbon sheets and microtubes.
I Carbon Nanodots (CNDs) sono definiti come nanoparticelle di carbonio, con una dimensione caratteristica inferiore a 10 nm e una morfologia quasi sferica. Queste particelle hanno attirato molta attenzione nella scienza dei materiali, principalmente grazie alla loro fotoluminescenza intrinseca, alla ricca chimica di superficie e all'elevata solubilità. Durante gli studi di dottorato sono stati investigati diversi aspetti di queste nanoparticelle. Inizialmente questioni relative alla sintesi bottom-up dei CNDs sono state analizzate. I metodi solvotermici sono diventati la procedura principale per la produzione di CNDs, basandosi sul trattamento ad alta temperatura di piccole molecole organiche. Tuttavia, l’utilizzo di queste condizioni può innescare molte reazioni simultanee nella miscela di partenza, spesso portando alla formazione di sottoprodotti molecolari. Quando questi composti indesiderati non vengono correttamente rimossi durante la purificazione del materiale, possono essere responsabili di proprietà erroneamente attribuite alle nanoparticelle. In questo primo lavoro sono stati considerati diversi casi di studio, in cui è stato dimostrato come una semplice analisi di risonanza magnetica nucleare (NMR) possa essere utilizzata per rivelare molecole residue nei campioni di CNDs. In un secondo lavoro, i CNDs sono stati testati come nanocatalizzatori per promuovere reazioni organiche. In particolare, CNDs chirali sono stati sintetizzati attraverso una sintesi a microonde a partire da acido citrico e da un'ammina chirale. I CNDs sviluppati presentano gruppi amminici sulla loro superficie, interessanti proprietà fotofisiche e risultano cataliticamente attivi in numerose trasformazioni. Nello specifico, la composizione della shell esterna dei CND è stata determinante per eseguire reazioni organocatalitiche in modo enantioselettivo, mentre le loro caratteristiche redox e di assorbimento di luce sono state utilizzate per promuovere processi fotochimici. Infine, le abilità foto- e organocatalitiche dei CNDs sono state sfruttate contemporaneamente per promuovere trasformazioni più complesse. Successivamente, il focus del lavoro è stato spostato dallo studio dei singoli CNDs al loro assemblaggio in sistemi più complessi. In particolare, è stata realizzata una connessione covalente di diversi tipi di CNDs attraverso reazioni di click e studi fotofisici del network finale hanno rivelato processi di trasferimento di energia tra le particelle interconnesse. Successivamente è stato esplorato l’uso di un linker rigido per la connessione dei CNDs, consentendo di controllare la disposizione delle particelle nello spazio insieme alla produzione di network 3D porosi. Infine, interazioni non covalenti sono state esplorate per guidare il self-assembly di CNDs chirali. In particolare, scegliendo opportunamente la composizione del solvente e le condizioni di pH, le particelle sono state assemblate in diversi tipi di microstrutture luminescenti, come particelle di Giano, foglietti di carbonio e microtubi.
Carbon Nanodots: from purification strategies to multifunctional materials / Bartolomei, Beatrice. - (2024 Feb 09).
Carbon Nanodots: from purification strategies to multifunctional materials
BARTOLOMEI, BEATRICE
2024-02-09
Abstract
Carbon Nanodots (CNDs) are defined as carbon nanoparticles, with a characteristic size below 10 nm and a quasi-spherical morphology. They have attracted a lot of attention in material science, mainly owing to their intrinsic photoluminescence, rich-surface chemistry and high solubility. During the PhD studies different aspects of these nanoparticles were investigated. First, issues related to the bottom-up synthesis of CNDs were analyzed. Solvothermal methods have become the procedure of choice for the CND production, relying on the high-temperature treatment of small organic molecules. However, the use of high temperature conditions may trigger many simultaneous reactions in the starting mixture, often resulting in the formation of molecular side products. When these undesired compounds are not correctly removed during the material purification, they can be responsible of properties erroneously attributed to nanoparticles. In this first work, several case-studies were considered, in which it was demonstrated how a straightforward Nuclear Magnetic Resonance (NMR) analysis can be used to reveal residual molecules in CND samples. In a second work, CNDs were tested as nano-catalysts to promote organic reactions. In particular, chiral CNDs were prepared through a microwave synthesis starting from citric acid and a chiral dopant amine. The developed CNDs exhibit amino groups on their surface, interesting photophysical properties and resulted catalytically active in several transformations. Specifically, the outer-shell composition of CNDs was instrumental to carry out organocatalytic reactions in an enantioselective fashion, while their redox and light-absorbing features were used to promote photochemical processes. Finally, the photo- and organocatalytic abilities of CNDs were exploited at the same time to promote more complex transformations. Thereafter, the focus of the work was shifted from the studies of individual CNDs to their assembly into larger systems. In particular, a covalent connection of different kinds of CNDs was realized through the use of click chemistry and photophysical studies on the final assembly revealed energy transfer processes between the interconnected particles. Later on, the use of a rigid linker for the CND connection was explored, allowing to control the arrangement of particles in space along with the production of porous 3D networks. Finally, a non-covalent strategy was exploited to drive the self-assembly of chiral CNDs. In particular, upon tuning solvents and pH conditions, particles were able to assemble into different kinds of micro-sized luminescent structures, like Janus particles, carbon sheets and microtubes.File | Dimensione | Formato | |
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PhD thesis_Beatrice Bartolomei_REVISED.pdf
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