Carbon nanostructures derived through hypergolic reaction of conductive polymers with fuming nitric acid at ambient conditions

Hypergolic systems rely on organic fuel and a powerful oxidizer that spontaneously ignites upon contact without any external ignition source. Although their main utilization pertains to rocket fuels and propellants, it is only recently that hypergolics has been established from our group as a new general method for the synthesis of different morphologies of carbon nanostructures depending on the hypergolic pair (organic fuel-oxidizer). In search of new pairs, the hypergolic mixture described here contains polyaniline as the organic source of carbon and fuming nitric acid as strong oxidizer. Specifically, the two reagents react rapidly and spontaneously upon contact at ambient conditions to afford carbon nanosheets. Further liquid-phase exfoliation of the nanosheets in dimethylformamide results in dispersed single layers exhibiting strong Tyndall effect. The method can be extended to other conductive polymers, such as polythiophene and polypyrrole, leading to the formation of different type carbon nanostructures (e.g., photolumincent carbon dots). Apart from being a new synthesis pathway towards carbon nanomaterials and a new type of reaction for conductive polymers, the present hypergolic pairs also provide a novel set of rocket bipropellants based on conductive polymers.Web of Science266art. no. 159

Microwave synthesis, characterization and perspectives of wood pencil-derived carbon

More than 14 billion pencils are manufactured and used globally every year. On average, a pencil is discarded after 60% of its original length has been depleted. In the present work we propose a simple and affordable way of converting this non-neglectable amount of waste into added value carbon product. In particular, we demonstrate the microwave synthesis of carbon from the wood pencil with and without chemical activation. This could be a process stage before the final recycling of the expensive graphite core. In the latter case, irradiation of the wood pencil in a domestic microwave oven heats up the pencil's graphite core, thus inducing carbonization of its wood casing. The carbonized product consists of amorphous carbon nanosheets having relatively low surface area. However, if the wood pencil is soaked in 50% KOH aqueous solution prior to microwave irradiation, a significantly higher surface area of carbon is obtained, consisting of irregular-shaped porous particles. Consequently, the obtained carbon can easily decolorize a methylene blue aqueous solution, can be used to make pocket warmers or gunpowder, and lastly, serves as an excellent adsorbent towards Cr(VI) removal from water, showing a maximum adsorption capacity of 70-75 mg/g within 24 h at 23 degrees C, pH = 3.Web of Science121art. no. 41

Alternating Gyroid Network Structure in an ABC Miktoarm Terpolymer Comprised of Polystyrene and Two Polydienes

The synthesis, molecular and morphological characterization of a 3-miktoarm star terpolymer of polystyrene (PS, M¯¯¯¯n = 61.0 kg/mol), polybutadiene (PB, M¯¯¯¯n = 38.2 kg/mol) and polyisoprene (PI, M¯¯¯¯n = 29.2 kg/mol), corresponding to volume fractions (φ) of 0.46, 0.31 and 0.23 respectively, was studied. The major difference of the present material from previous ABC miktoarm stars (which is a star architecture bearing three different segments, all connected to a single junction point) with the same block components is the high 3,4-microstructure (55%) of the PI chains. The interaction parameter and the degree of polymerization of the two polydienes is sufficiently positive to create a three-phase microdomain structure as evidenced by differential scanning calorimetry and transmission electron microscopy (TEM). These results in combination with small-angle X-ray scattering (SAXS) and birefringence experiments suggest a cubic tricontinuous network structure, based on the I4132 space group never reported previously for such an architecture

Surface modification with polymer chains prepared by the ‘grafting to’ method and characterization

The goal of the present dissertation has been the fabrication of polymer brushes on plenar and curved surfaces (nanoparticles). Using the “grafting to” method a V-shaped polymer brush consisting of a diblock copolymer system of PS and P2VP, which has been prefabricated via anionic synthesis polymerization was attached on the surface of Si wafers and of iron oxide nanoparticlesSubsequently, the resulting polymer brushes were characterized with the use of XPS, FTIR, ellipsometry, contact angle measurements, AFM and DLS in order to verify the attachments of the polymner chains on the modified surfaces. The results of the characterization proved inadvertently that the formation of mixed polymer brushes upon the modified surfaces has been successful and that “smart” materials able to adapt on different externa stimuli such as pH and the presence of water, through switching hydrophilic and hydrophobic behavior.Η παρούσα διατριβή έχει ως κύριο στόχο την δημιουργία νέων τροποποιημένων επιφανειών προσκολλημένες με πολυμερικές αλυσίδες σε επίπεδα υποστρώματα πυριτίου και μαγνητικών νανοσωματιδίων οξειδίων του σιδήρου (μαγκεμίτης γ-Fe2O3) χρησιμοποιώντας τη μέθοδο ‘εμβολιασμού σε’. Οι πολυμερικές βούρτσες που προσδέθηκαν στις επιφάνειες αποτελούνταν από τις συστάδες πολυστυρενίου (PS) και πολύ(2-βινυλοπυριδίνης) (P2VP) και ήταν του τύπου V-σχήματος που συντέθηκαν με ανιοντικό πολυμερισμό (κάτι εντελώς καινούργιο έως τώρα). Η επιλογή των συγκεκριμένων συστάδων PS και P2VP επετεύχθη με σκοπό να προσδοθούν οι αντίστοιχες ιδιότητές τους με έκθεση σε περιβαλλοντικά εξωτερικά ερεθίσματα (διαλύτες και pH).Η παρούσα εργασία διαχωρίστηκε σε τρία (3) διαφορετικά στάδια σε σχέση με τον τρόπο σύνθεσης που ακολουθήθηκε. Αρχικώς πραγματοποιήθηκε η σύνθεση των τριών συμπολυμερών (PS-SiCl2-P2VP) με διαφορετικά κλάσματα μάζας που συντέθηκαν με την τεχνική του ανιοντικού πολυμερισμού όπου συγκεκριμένα χρησιμοποιήθηκε η χημεία χλωροσιλανίων. Από τα αποτελέσματα τους πιστοποιήθηκαν τα μοριακά χαρακτηριστικά, η δομή, η σύσταση, οι θερμοκρασίες υαλώδους μετάπτωσης, οι χαρακτηριστικές κορυφές των δραστικών ομάδων και η θερμική τους ανάλυση καθώς και η μελέτη της απώλειας μάζας σε σχέση με τη θερμοκρασία. Οι τεχνικές χαρακτηρισμού που χρησιμοποιήθηκαν ήταν οι εξής: Χρωματογραφία Αποκλεισμού Μεγεθών (SEC), Φασματοσκοπία Πυρηνικού Μαγνητικού Συντονισμού Πρωτονίου (1H-NMR), Διαφορική Θερμιδομετρία Σάρωσης (DSC), Θερμική Σταθμική Ανάλυση (TGA), Φασματοσκοπία Υπερύθρου (IR).Στο επόμενο στάδιο ακολούθησε η σύνθεση των τροποποιημένων επιφανειών πυριτίου με κατάλληλες πυριτικές ενώσεις προς το σχηματισμό αυτοοργανωμένων μονοστρωμάτων (SAMs) και έπειτα ακολούθησε η πρόσδεση των πολυμερικών αλυσίδων με τη μέθοδο ‘εμβολιασμός σε’ στο ειδικά διαμορφωμένο υπόστρωμα SAM. Οι τεχνικές χαρακτηρισμού που χρειάστηκαν για να μελετηθούν οι παραπάνω επιφάνειες ήταν: φωτοηλεκτρονιακή φασματοσκοπία ακτινών-Χ (XPS), μικροσκοπία ατομικών δυνάμεων (AFM), φασματοσκοπική ελλειψομετρία και μέτρηση γωνίας επαφής (contact angle) προκειμένου να πιστοποιηθούν σημαντικά μεγέθη όπως το πάχος της πολυμερικής βούρτσας, η δομή της και η τιμή της γωνίας επαφής έπειτα από έκθεση των τροποποιημένων υποστρωμάτων με τις αλυσίδες πολυμερούς σε αντίστοιχους εκλεκτικούς διαλύτες για την κάθε συστάδα. Tα αποτελέσματα που εξήχθησαν από τις μετρήσεις AFM επιτευχθεί σύγκριση των πειραματικών αποτελεσματων με τα θεωρητικά μοντέλα για την πιστοποίηση της μορφολογίας της επιφάνειας έπειτα από εξωτερικά περιβαλλοντικά ερεθίσματα (διαλύτη, pH).Στο τρίτο και τελευταίο στάδιο παρουσιάστηκε εκτενώς η σύνθεση των μαγνητικών νανοσωματιδίων οξειδίων του σιδήρου (μαγγεμίτης) καθώς και η προσκόλληση των πολυμερικών αλυσίδων του συμπολυμερούς PS-SiCl2-P2VP στην επιφάνειά του. Η διαδικασία αυτή εκπονείται σε διαφορετικές συνθήκες όπου εν τέλει τα τροποποιημένα νανοσωματίδια εκτίθενται σε εκλεκτικούς διαλύτες για την κάθε συστάδα. Η πιστοποίηση της κρυσταλλικής δομής, του μεγέθους, του σχήματος, των χαρακτηριστικών κορυφών των δραστικών ομάδων και της θερμική τους ανάλυση όσον αφορά την απώλεια μάζας του καθαρού νανοσωματιδίου και του τροποποιημένου με τις πολυμερικές αλυσίδες ακολουθήθηκαν οι παρακάτω τεχνικές: Φασματοσκοπία Υπερύθρου (IR), Περίθλαση ακτίνων-Χ (XRD), Θερμική Σταθμική Ανάλυση (TGA), Ηλεκτρονική Μικροσκοπία Διέλευσης (TEM), Ηλεκτρονική μικροσκοπία σάρωσης (SEM), Δυναμική Σκέδαση Φωτός (Dynamic Light Scattering-DLS). Τέλος η δυνατότητα των εμβολιασμένων πολυμερικών ‘βουρτσών’ σε επίπεδες επιφάνειες Si και NPs να μεταβάλλουν τις επιφανειακές τους ιδιότητες ανάλογα με το περιβάλλον τους, φέρουν ως αποτέλεσμα να ονομάζονται ως ‘έξυπνες’ επιφάνειες

Microstructural features, physicο-mechanical properties, and wear behavior of dental translucent polychromic multilayer zirconia of hybrid composition prepared by milling technology

Objective: The present study determined the mechanical properties and the wearbehavior, as results of the micro(nano)structure, of the enamel, transition, and den-tine layers, which comprise the polychromic multilayer zirconia materials of hybridcomposition fabricated by milling technology.Materials and Methods:Prismatic blocks were fabricated from two commercialpre-sintered dental polychromic multilayer zirconia materials of hybrid composi-tion, IPS e.max ZirCAD Prime (medium andhigh translucency, from the dentineto the incisal layer) and 3D Pro ML (translucency gradient, from the dentine tothe incisal layer) by milling technique, and then, cut into 3 distinct parts to sepa-rate the enamel, transition, and dentine layers. The samples were sintered, ther-mally treated (similarly to the glazing procedure), and polished forcharacterization. Their microstructure, mechanical properties (determined bynanoindentation and microhardness), andwear behavior (evaluated by scratchtest), were examined.Results:The produced materials had a homogeneous and dense nanostructure,where the grain size decreased from the enamel to dentine layer. The mechanicalproperties also decreased from the enamel to dentine layer. However, the threelayers manifested similar dynamic friction coefficient.Conclusion:The differences in the above properties in the three layers negligiblyinfluenced the wear behavior of the entire multilayer zirconia material.Clinical Significance:The properties of dental restorations produced from poly-chromic multilayer zirconia of hybrid composition by milling technology(i.e., strong, non-fragile, and esthetic materials), anticipate good performance inoral cavit

Development of 3D Printed Enzymatic Microreactors for Lipase-Catalyzed Reactions in Deep Eutectic Solvent-Based Media

In this study, 3D printing technology was exploited for the development of immobilized enzyme microreactors that could be used for biocatalytic processes in Deep Eutectic Solvent (DES)-based media. 3D-printed polylactic acid (PLA) microwell plates or tubular microfluidic reactors were modified with polyethylenimine (PEI) and lipase from Candida antarctica (CALB) was covalently immobilized in the interior of each structure. DESs were found to have a negligible effect on the activity and stability of CALB, and the system proved highly stable and reusable in the presence of DESs for the hydrolysis of p-nitrophenyl butyrate (p-NPB). A kinetic study under flow conditions revealed an enhancement of substrate accessibility in the presence of Betaine: Glycerol (Bet:Gly) DES, while the system was not severely affected by diffusion limitations. Incubation of microreactors in 100% Bet:Gly preserved the enzyme activity by 53% for 30 days of storage at 60 °C, while the buffer-stored sample had already been deactivated. The microfluidic enzyme reactor was efficiently used for the trans-esterification of ethyl ferulate (EF) with glycerol towards the production of glyceryl ferulate (GF), known for its antioxidant potential. The biocatalytic process under continuous flow conditions exhibited 23 times higher productivity than the batch reaction system. This study featured an effective and robust biocatalytic system with immobilized lipase that can be used both in hydrolytic and synthetic applications, while further optimization is expected to upgrade the microreactor system performance

Structure/Properties Relationship of Anionically Synthesized Diblock Copolymers “Grafted to” Chemically Modified Graphene

International audiencenovel approach to obtaining nanocomposite materials using anionic sequential polymerization and post-synthetic esterification reactions with chemically modified graphene sheets (CMGs) is reported. The anionically synthesized diblock copolymer precursors of the PS-b-PI-OH type were grafted to the chemically modified –COOH groups of the CMGs, giving rise to the final composite materials, namely polystyrene-b-poly(isoprene)-g-CMGs, which exhibited enhanced physicochemical properties. The successful synthesis was determined through multiple molecular characterization techniques together with thermogravimetric analysis for the verification of increased thermal stability, and the structure/properties relationship was justified through transmission electron microscopy. Furthermore, the arrangement of CMGs utilizing lamellar and cylindrical morphologies was studied in order to determine the effect of the loaded CMGs in the adopted topologie

Functional Carbon Materials Derived through Hypergolic Reactions at Ambient Conditions

Carbon formation from organic precursors is an energy-consuming process that often requires the heating of a precursor in an oven at elevated temperature. In this paper, we present a conceptually different synthesis pathway for functional carbon materials based on hypergolic mixtures, i.e., mixtures that spontaneously ignite at ambient conditions once its ingredients contact each other. The reactions involved in such mixtures are highly exothermic, giving-off sizeable amounts of energy; hence, no any external heat source is required for carbonization, thus making the whole process more energy-liberating than energy-consuming. The hypergolic mixtures described here contain a combustible organic solid, such as nitrile rubber or a hydrazide derivative, and fuming nitric acid (100% HNO3) as a strong oxidizer. In the case of the nitrile rubber, carbon nanosheets are obtained, whereas in the case of the hydrazide derivative, photoluminescent carbon dots are formed. We also demonstrate that the energy released from these hypergolic reactions can serve as a heat source for the thermal conversion of certain triazine-based precursors into graphitic carbon nitride. Finally, certain aspects of the derived functional carbons in waste removal are also discussed

Green Synthesized Magnetic Nanoparticles as Effective Nanosupport for the Immobilization of Lipase: Application for the Synthesis of Lipophenols

In this work, hybrid zinc oxide–iron oxide (ZnOFe) magnetic nanoparticles were synthesized employing Olea europaea leaf aqueous extract as a reducing/chelating and capping medium. The resulting magnetic nanoparticles were characterized by basic spectroscopic and microscopic techniques, namely, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), fourier-transform infrared (FTIR) and atomic force microscopy (AFM), exhibiting a spherical shape, average size of 15–17 nm, and a functionalized surface. Lipase from Thermomyces lanuginosus (TLL) was efficiently immobilized on the surface of ZnOFe nanoparticles through physical absorption. The activity of immobilized lipase was found to directly depend on the enzyme to support the mass ratio, and also demonstrated improved pH and temperature activity range compared to free lipase. Furthermore, the novel magnetic nanobiocatalyst (ZnOFe-TLL) was applied to the preparation of hydroxytyrosyl fatty acid esters, including derivatives with omega-3 fatty acids, in non-aqueous media. Conversion yields up to 90% were observed in non-polar solvents, including hydrophobic ionic liquids. Different factors affecting the biocatalyst performance were studied. ZnOFe-TLL was reutilized for eight subsequent cycles, exhibiting 90% remaining esterification activity (720 h of total operation at 50 °C). The green synthesized magnetic nanoparticles, reported here for the first time, are excellent candidates as nanosupports for the immobilization of enzymes with industrial interest, giving rise to nanobiocatalysts with elevated features