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

Organ specificity of template activity of mammalian chromatin

Cell differentiation is correlated with, the differential activity of genes in a given cell (and by implication in a functionally defined mixture of cell types, i.e. a tissue). One of the topics of major Importance in differentiation is concerned with the proportion of the genome which is active in RNA synthesis, i.e. the relative amount of genomic information which brings about the morphological changes characteristic of adult tissues. The template specificity of isolated chromatins in supporting RNA synthesis t/as studied in order to clarify the relationship between genomic expression and organ specificity. The molecular hybridization technique was used for RNAs transcribed vitro from several mouse chromatins. This technique provides a sensitive method for distinguishing between various populations of RNA molecules. It was found first that different populations of RNA molecules examined are not only distinguishable but also show large differences among them and second, that only a part of the genome was active in transcription. By competition experiments it was found that the RNAs produced by chromatin in a cell-free RNA system were similar to RNAs isolated from the whole homologous tissue. This provides evidence that the template specificity associated with chromosomes in vivo is retained by isolated chromatin. A particular feature of this study is the high degree of reproducibility of the hybridisation values for each tissue and the dissimilarities displayed by the different tissues. When DNA from mouse kidney was used as template in a cell free system and the RNA produced was annealed, then the amount of hybridisation was almost three times greater than the hybridization which occurred when chromatin was used as template. From these results it appears that many of the genes in animal somatic cells, which are considered as being in a completely differentiated state, are in fact inactive in supporting RNA synthesis, the inactivation pattern of the genome in such cells being distinctive for each tissue. The mechanisms which control cell division in mammalian organs are not understood. Various experimental models have been used to study this problem. The cases under investigation include in vivo models, i.e. induction by folic acid of RNA synthesis in mouse kidneys and the appearance of new species of RNA in mouse kidneys after the ligature of one ureter. Studies have been made on the effect of folio acid administration in stimulating changes in the vitro RNA synthesis such that new kinds of RNA molecules appear in mouse kidney at specific times after the treatment. The ability of kidney chromatin in supporting RNA synthesis has been studied in untreated (control) and treated animals. It was found that folic acid changes profoundly the template activity of the isolated chromatin from mouse kidneys, RNA transcribed from chromation at early stages hybridizes with twice as much DNA as RNA transcribed from normal chromatin. By competition experiments it was confirmed that the cell free system produces the same RNA species as are found vivo which indicates that the integrity of the chromatin is maintained during isolation. Furthermore, the experiments showed that new kinds of RNA molecules are transcribed from kidney chromatin after the early hours of folate. The transcriptional activity of the genome eventually falls to the control level after two days. Another method for stimulating the appearance of new species of RNA in mouse kidneys is to ligate one ureter. The template activity of chromatin from the ligated kidney has been investigated from aero hours until 48 hours. The maximum hybridization efficiency (twice the control) is exhibited at 36 hours while RNA transcribed from chromatin isolated at early stages hybridizes with as much DNA as RNA transcribed from normal chromatin. The purpose of these experiments has been to compare the template activity of chromatin isolated at various times after the ligature of one ureter with those obtained after folic acid treatment in mice and to determine if the same control mechanism operates in both phenomena. The relationship between these two systems is discussed

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

Η ενδυνάμωση της κοινωνικής συνείδησης των μαθητών μέσω των πολιτιστικών εκδηλώσεων στο Δημοτικό Σχολείο

Η σύγχρονη εκπαίδευση έχει ως βασικό σκοπό να προετοιμάσει τους μαθητές ώστε να είναι σε θέση να αντιδρούν γρήγορα και να ανταπεξέρχονται στις επιταγές των καιρών ως ενεργοί και δυναμικοί πολίτες, με δημοκρατικό ήθος, ηθική και γνωστική αυτονομία. Αντικείμενο της παρούσας εργασίας αποτελεί η διερεύνηση του τρόπου με τον οποίο η εκπαίδευση, και πιο συγκεκριμένα οι πολιτιστικές εκδηλώσεις στο σχολείο μπορούν να συμβάλλουν στην ενδυνάμωση της κοινωνικής συνείδησης των μαθητών. Οι υγιείς αλληλεπιδραστικές σχέσεις ανάμεσα στα μέλη της κοινωνίας έχουν δώσει τη θέση τους σε σχέσεις ακραίου ανταγωνισμού, οι οποίες συχνά επεκτείνονται και στο χώρο του σχολείου. Η ανάγκη για συνειδητοποίηση ότι αποτελούμε μέλη ενός αδιάσπαστου συνόλου, καθώς και η αντίληψη πως η συλλογική δράση είναι η απάντηση στα σύγχρονα κοινωνικά, πολιτικά και οικονομικά παγκόσμια προβλήματα, μας οδήγησε στην επιλογή του συγκεκριμένου θέματος. Οι σχολικές εορταστικές εκδηλώσεις, χάρη στη μεγάλη θεματολογική τους ποικιλία, την αυξημένη παιδαγωγική τους αξία, την αξιοποίηση του θεάτρου και των άλλων μορφών τέχνης, αλλά και τη συμμετοχή των μαθητών στις ομάδες εργασίας, αποδεικνύονται ισχυρό εργαλείο κοινωνικής και πολιτικής διαπαιδαγώγησης στα χέρια του εκπαιδευτικού.Modern education’s primary objective is to prepare students to be able to react effectively and respond to the actual imperatives as active and dynamic citizens with a democratic mindset, moral and cognitive autonomy. The purpose of this paper is to investigate how education, and especially cultural events in school, can help to strengthen the students' social consciousness. Healthy interactive relationships between members of a society have been replaced by extreme competition, which often extends within the school. The need of realizing that we are members of an inseparable whole, as well as the notion that collective action is the answer to current social, political and economic world problems, has led to the choice of this particular subject. The school celebrations, thanks to their increased pedagogical value, the use of theater and other forms of art, as well as the participation of pupils in working groups, prove to be powerful tools of social and political education in the hands of the teacher

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

Graphene/Carbon Dot Hybrid Thin Films Prepared by a Modified Langmuir-Schaefer Method

The special electronic, optical, thermal, and mechanical properties of graphene resulting from its 2D nature, as well as the ease of functionalizing it through a simple acid treatment, make graphene an ideal building block for the development of new hybrid nanostructures with well-defined dimensions and behavior. Such hybrids have great potential as active materials in applications such as gas storage, gas/liquid separation, photocatalysis, bioimaging, optoelectronics, and nanosensing. In this study, luminescent carbon dots (C-dots) were sandwiched between oxidized graphene sheets to form novel hybrid multilayer films. Our thin-film preparation approach combines self-assembly with the Langmuir-Schaefer deposition and uses graphene oxide nanosheets as template for grafting C-dots in a bidimensional array. Repeating the cycle results in a facile and low-cost layer-by-layer procedure for the formation of highly ordered hybrid multilayers, which were characterized by photoluminescence, UV-visible, X-ray photoelectron, and Raman spectroscopies, as well as X-ray diffraction and atomic force microscopy.</p

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