Design and Study of Pillared Graphenes and Nanoporous Carbon Materials for Energy, Environmental and Catalytic Applications

Nanoporous materials have been exploited since antiquity in a plethora of applications due to their controllable pore size, diverse geometries, surface properties and their ability to interact with molecules and atoms or adsorb/release them. Being amongst the most abundant elements on earth and present in a variety of forms, carbon is an excellent candidate material for applications that can pave the way for a greener, waste-free, and less energy- and resource-demanding future and new forms of porous carbon have an important role to play in this context. Porosity in materials can be obtained in many ways; in this PhD project the focus lay on porous carbons resulting from carbonization, chemical etching, template synthesis and activation, or ‘Parthenon like’ structures. The latter were constructed through the intercalation of robust organic and/or inorganic pillars between graphene sheets in order to keep the layers apart and create interconnected void spaces with a well-defined size and chemical affinity. Towards this aim, two new composites, on where a silica network was created in the interlayer space of organically modified graphene oxide, and another one where graphene oxide was pillared with silsesquioxanes, were tested as CO2 sorbents. We also explored the ability of copper-enriched porous carbon cuboids to capture H2S gas and showed how hierarchical porous carbons with high specific surface areas and pore volumes can be produced making use of sugar and coffee wastes

Advances in fluorescent carbon dots for biomedical applications

Carbon Dots are an emerging class of carbon-based nanoparticles, which since their discovery have attracted tremendous attention because of their exceptional fluorescent, chemical and mechanical properties as well as high photostability and biocompatibility. This unique combination of outstanding characteristics, together with the ease with which they can be synthesized, qualify carbon dots as highly promising materials for applications in electronics and biology, in particular, for biosensing, bioimaging, biotherapy and drug delivery. In this review, we present some of the most recent applications of carbon dots in biology and medicine, concentrating on their fluorescence properties, biocompatibility and efficiency; we also discuss how improvements could prompt their use in human studies. We illustrate how carbon dots, prepared through several facile and cost-effective methods by either the bottom-up or the top-down route, can be used for imaging cells and bacteria and as sensing probes of metal cations. Moreover, we explain how their astonishing versatility has given rise to new biotherapy methods especially in the field of cancer theranostics

H₂S removal by copper enriched porous carbon cuboids

Hydrogen sulfide (H2S) removal by adsorption from gas streams is crucial to prevent the environmental and industrial damage it causes. Amongst the nanostructures considered excellent candidates as sorbents, porous carbon has been studied extensively over the last years. In the present work we present a synthetic procedure for three high potential sorbents based on carbon cuboids, namely a low-surface-area copper-rich structure, a highly porous aggregate without metal addition, and lastly the same porous carbon decorated with copper. The properties and performance as catalysts of these three sorbents were evaluated by powder X-ray diffraction, X-ray photoelectron spectroscopy, thermal analysis, scanning electron microscopy with energy dispersive X-ray analysis, surface area determination through N2 adsorption and desorption, as well as by H2S adsorption measurements

Highly Efficient Remediation of Chloridazon and Its Metabolites:The Case of Graphene Oxide Nanoplatelets

The contamination of aqueous environments by aromatic pollutants has become a global issue. Chloridazon, a herbicide considered as harmless to the ecosystem, has been widely used in recent decades and has accumulated, together with its degradation products desphenyl-chloridazon and methyl-desphenyl-chloridazon, to a non-negligible level in surface water and groundwater. To respond to the consequent necessity for remediation, in this work, we study the adsorption of chloridazon and its metabolites by graphene oxide and elucidate the underlying mechanism by X-ray photoelectron spectroscopy. We find a high adsorption capacity of 67 g kg-1for chloridazon and establish that bonding of chloridazon to graphene oxide is mainly due to hydrophobic interaction and hydrogen bonding. These findings demonstrate the potential of graphene-based materials for the remediation of chloridazon and its metabolites from aqueous environments

Smectite clay pillared with copper complexed polyhedral oligosilsesquioxane for adsorption of chloridazon and its metabolites

Chloridazon has been a widely used herbicide during the past decades, especially in sugar-beet cultivation. UV-induced degradation of chloridazon leads to the formation of desphenyl counterparts, i.e. desphenyl-chloridazon and methyl-desphenyl-chloridazon. Even if accumulation of these residues in natural waters is far from alarming, a low-cost effective and environmentally friendly adsorbent, capable of binding chloridazon and its degradation products is desirable to reduce their concentration in water even further below legal limits. Here we show that pillared smectite clay, prepared by cation exchange of sodium with copper complexed, cage-shaped polyhedral oligomeric silsesquioxane (Cu2+@POSS) could be a promising candidate for this purpose. X-ray diffraction and high resolution transmission electron microscopy evidenced a homogeneous layered structure where the interlayer spacing is enlarged by 7.1 ± 0.2 Å (the diameter of Cu2+@POSS) with respect to the pristine clay. Exposure of this pillared smectite clay to chloridazon and its metabolites in water showed that Cu2+@POSS intercalation significantly improved its adsorption capacity. In addition, after several thermal regeneration cycles, Cu2+@POSS_SWy-2 still exhibited excellent adsorption properties. These findings demonstrate that smectite clay pillared with copper complexed polyhedral oligosilsesquioxane is a promising environmentally friendly and relatively low cost material for herbicide waste remediation

New Porous Heterostructures Based on Organo-Modified Graphene Oxide for CO(2)Capture

In this work, we report on a facile and rapid synthetic procedure to create highly porous heterostructures with tailored properties through the silylation of organically modified graphene oxide. Three silica precursors with various structural characteristics (comprising alkyl or phenyl groups) were employed to create high-yield silica networks as pillars between the organo-modified graphene oxide layers. The removal of organic molecules through the thermal decomposition generates porous heterostructures with very high surface areas (>= 500 m(2)/g), which are very attractive for potential use in diverse applications such as catalysis, adsorption and as fillers in polymer nanocomposites. The final hybrid products were characterized by X-ray diffraction, Fourier transform infrared and X-ray photoelectron spectroscopies, thermogravimetric analysis, scanning electron microscopy and porosity measurements. As proof of principle, the porous heterostructure with the maximum surface area was chosen for investigating its CO(2)adsorption properties

A diamino-functionalized silsesquioxane pillared graphene oxide for CO2 capture

In the race for viable solutions that could slow down carbon emissions and help in meeting the climate change targets a lot of effort is being made towards the development of suitable CO2 adsorbents with high surface area, tunable pore size and surface functionalities that could enhance selective adsorption. Here, we explored the use of silsesquioxane pillared graphene oxide for CO2 capture; we modified silsesquioxane loading and processing parameters in order to obtain pillared structures with nanopores of the tailored size and surface properties to maximize the CO2 sorption capacity. Powder X-ray diffraction, XPS and FTIR spectroscopies, thermal analysis (DTA/TGA), surface area measurements and CO2 adsorption measurements were employed to characterize the materials and evaluate their performance. Through this optimisation process, materials with good CO2 storage capacities of up to 1.7/1.5 mmol g(-1) at 273 K/298 K in atmospheric pressure, were achieved

MgH2 nanoparticles confined in reduced graphene oxide pillared with organosilica: a novel type of hydrogen storage material

Hydrogen is a promising energy carrier that can push forward the energy transition because of its high energy density (142 MJ kg-1), variety of potential sources, low weight and low environmental impact, but its storage for automotive applications remains a formidable challenge. MgH2, with its high gravimetric and volumetric density, presents a compelling platform for hydrogen storage; however, its utilization is hindered by the sluggish kinetics of hydrogen uptake/release and high temperature operation. Herein we show that a novel layered heterostructure of reduced graphene oxide and organosilica with high specific surface area and narrow pore size distribution can serve as a scaffold to host MgH2 nanoparticles with a narrow diameter distribution around ~2.5 nm and superior hydrogen storage properties to bulk MgH2. Desorption studies showed that hydrogen release starts at 50 {\deg}C, with a maximum at 348 {\deg}C and kinetics dependent on particle size. Reversibility tests demonstrated that the dehydrogenation kinetics and re-hydrogenation capacity of the system remains stable at 1.62 wt.% over four cycles at 200 {\deg}C. Our results prove that MgH2 confinement in a nanoporous scaffold is an efficient way to constrain the size of the hydride particles, avoid aggregation and improve kinetics for hydrogen release and recharging

Highly Conductive Metallic State and Strong Spin-Orbit Interaction in Annealed Germanane

Similar to carbon, germanium exists in various structures such as three-dimensional crystalline germanium and germanene, a two-dimensional germanium atomic layer. Regarding the electronic properties, they are either semiconductors or Dirac semimetals. Here, we report a highly conductive metallic state in thermally annealed germanane (hydrogen-terminated germanene, GeH), which shows a resistivity of similar to 10(-7) Omega.m that is orders of magnitude lower than any other allotrope of germanium. By comparing the resistivity, Raman spectra, and thickness change measured by AFM, we suggest the highly conductive metallic state is associated with the dehydrogenation during heating, which likely transforms germanane thin flakes to multilayer germanene. In addition, weak antilocalization is observed, serving as solid evidence for strong spin-orbit interaction (SOI) in germanane/germanene. Our study opens a possible new route to investigate the electrical transport properties of germanane/germanene, and the large SOI might provide the essential ingredients to access their topological states predicted theoretically

Σχεδιασμός και μελέτη υποστηλωμένων γραφενίων και νανοπορωδών υλικών άνθρακα για ενεργειακές, περιβαλλοντικές και καταλυτικές εφαρμογές

Nanoporous materials have been exploited since antiquity in a plethora of applications due to their controllable pore size, diverse geometries, surface properties and their ability to interact with molecules and atoms or adsorb/release them. Being amongst the most abundant elements on earth and present in a variety of forms, carbon is an excellent candidate material for applications that can pave the way for a greener, waste-free, and less energy- and resource-demanding future and new forms of porous carbon have an important role to play in this context. Porosity in materials can be obtained in many ways; in this PhD project the focus lay on porous carbons resulting from carbonization, chemical etching, template synthesis and activation, or ‘Parthenon like’ structures. The latter were constructed through the intercalation of robust organic and/or inorganic pillars between graphene sheets in order to keep the layers apart and create interconnected void spaces with a well-defined size and chemical affinity. Towards this aim, two new composites, one where a silica network was created in the interlayer space of organically modified graphene oxide, and another one where graphene oxide was pillared with silsesquioxanes, were tested as carbon dioxide sorbents. The ability of copper-enriched porous carbon cuboids to capture hydrogen sulfide gas was also explored and it was shown how hierarchical porous carbons with high specific surface areas and pore volumes can be produced making use of sugar and coffee wastes.Η χρήση νανοπορωδών υλικών απαντάται από την αρχαιότητα σε μία πληθώρα εφαρμογών χάρη στη δυνατότητα ελέγχου του μεγέθους των πόρων, της ποικιλόμορφης γεωμετρίας, των επιφανειακών ιδιοτήτων και της ικανότητάς τους να αλληλοεπιδρούν με μόρια και άτομα, ή να τα απορροφούν/απελευθερώνουν. Δεδομένου ότι ο άνθρακας συγκαταλέγεται μεταξύ των πλέον άφθονων στοιχείων στη γη και ότι μπορεί να βρεθεί σε πληθώρα μορφών, τα υλικά άνθρακα αποτελούν εξαιρετικές επιλογές για εφαρμογές που μπορούν να συνεισφέρουν για ένα πιο πράσινο μέλλον, χωρίς απόβλητα, και χαμηλότερο ενεργειακό και υλικό αποτύπωμα, και οι νέες μορφές πορώδους άνθρακα έχουν να παίξουν ένα σημαντικό ρόλο σε αυτό το πλαίσιο. Το πορώδες στα υλικά μπορεί να σχηματιστεί με πολλούς τρόπους: η παρούσα διδακτορική διατριβή εστιάζει στους πορώδεις άνθρακες που προκύπτουν από την ανθρακοποίηση, τη «χημική χάραξη», τη σύνθεση με χρήση προτύπου και την ενεργοποίηση, αλλά και υποστυλωμένες δομές που προσομοιάζουν αυτή του Παρθενώνα. Τα τελευταία κατασκευάστηκαν μέσω της παρεμβολής στιβαρών οργανικών ή/και ανόργανων πυλώνων μεταξύ φύλλων γραφενίου ώστε να διαχωρίζονται τα στρώματα και να δημιουργούνται διασυνδεδεμένοι κενοί χώροι με καλοσχηματισμένους πόρους και χημική συγγένεια. Προς την επίτευξη αυτού του στόχου, δύο νέα σύνθετα υλικά, ένα στο οποίο ένα πυριτικό δίκτυο δημιουργήθηκε στον ενδοστρωματικό χώρο ενός οργανικά τροποποιημένου οξειδίου του γραφενίου, και ένα άλλο στο οποίο το οξείδιο του γραφενίου υποστυλώθηκε με σιλοξάνια, εξετάστηκαν ως υλικά αποθήκευσης διοξειδίου του άνθρακα. Επιπλέον, διερευνήθηκε η ικανότητα εμπλουτισμένου με χαλκό πορώδους κυβοειδούς άνθρακα να δεσμεύει υδρόθειο, και παρουσιάστηκε το πώς ιεραρχημένοι πορώδεις άνθρακες με υψηλή ειδική επιφάνεια και όγκους πόρων μπορούν να παραχθούν κάνοντας χρήση αποβλήτων ζάχαρης και καφέ