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

Synthesis and characterization of noel nanocomposite polymer electrolyte membranes for fuel cell applications

The polymer electrolyte membrane fuel cells (PEMFC) are the most promising of all thetypes of fuel cells due to operating in expensively in temperatures 70°C with great efficiency up to 60%. However, in this temperature face problems including poor carbon monoxide tolerance and heatrejection. These drawbacks can be overcome by increasing the operating temperature up to 120–130°C. In this temperature two opposite effects come into play: i) improved the electrocatalytickinetics and ii) decreased proton conductivity of the electrolyte. A common strategy that has beenadopted to improve the water retention capacity is to integrate fillers in the Nafion matrix.In this thesis, inorganic layered materials such as (i) clays with different structural and physicalparameters, (ii) graphene oxide, and (iii) layered double hydroxides with different compositions, weretested as 2D nanofillers in order to create Nafion nanocomposites. Hybrid nanocomposites weresynthesized in different fillers to polymer loadings. Furthermore, functionalization of clays and GOwith organo-surfactants having different terminal groups was also performed in order to increase thenumber of acid sites and consequently the water retention of the produced nanocompositesmembranes. Solution intercalation was followed for the synthesis of the above hybrid membranes.The type of solvent and the temperature for membrane preparation were examined in order todetermine the optimum conditions for the preparation of highly homogeneous nanocompositemembranes. Nafion membranes were characterized by a combination of techniques (XRD, FTIR,Raman, DTA/TG, SEM, DMA). The NMR technique was used in this work to study the watertransport mechanism on nanocomposites membranes.Results showed highly homogeneous exfoliated nanocomposites were created in most cases wherethe individual layered nanofillers are uniformly dispersed in the continuous polymeric matriximproving the thermal and mechanical properties. A remarkable behaviour at high temperature isobserved for all samples on the NMR results, where composite membranes maintain stable andunwavering diffusion for many hours and in conditions of not humidification, proving the exceptionalwater retention property of these materials. Finally, both these characteristics are highly desirable foruse in fuel cell applications.Τα κελιά καυσίμου πολυμερικών μεμβρανών ανταλλαγής πρωτονίων αποτελούν τη πιοσημαντική κατηγορία κελιών καυσίμου επειδή λειτουργούν με μεγάλη απόδοση (60%) σε χαμηλέςθερμοκρασίες (70°C). Ωστόσο, σε αυτή τη θερμοκρασιακή περιοχή παρατηρείται χαμηλή αντοχή σεμονοξείδιο του άνθρακα και απόρριψη θερμότητας. Τα προβλήματα αυτά μπορούν να ξεπεραστούνμε αύξηση της θερμοκρασίας λειτουργίας τους στους 120–130°C. Όμως, σε αυτή τη θερμοκρασίαδύο ανταγωνιστικοί παράγοντες συμβαίνουν ταυτόχρονα: α) αύξηση της κινητικότητας των μορίωντου νερού με αποτέλεσμα την αύξηση της διάχυσης τους, ενώ αντίθετα β) μειώνεται η ποσότητα τωνμορίων του νερού, και άρα η αγωγιμότητα των πρωτονίων, εξαιτίας της εξάτμισης του. Ηενσωμάτωση υδρόφιλων ενισχυτικών στη πολυμερική μάζα μπορεί να βελτιώσει την ικανότητασυγκράτησης των μορίων του νερού σε υψηλές θερμοκρασίες. Στη παρούσα διατριβή, ανόργαναφυλλόμορφα νανοϋλικά όπως φυλλόμορφοι άργιλοι με διαφορετικά φυσικοχημικά χαρακτηριστικά,οξείδιο του γραφενίου και διπλά υδροξείδια φυλλόμορφης δομής (LDHs) με διαφορετική σύσταση,αξιολογήθηκαν ως δισδιάστατα νανοενισχυτικά για τη δημιουργία νέων νανοσύνθετων μεμβρανώνNafion. Επιπλέον, πραγματοποιήθηκε τροποποίηση της επιφάνειας των αργίλων και του οξειδίου τουγραφενίου με την εισαγωγή διαφόρων ομάδων με σκοπό να αυξήσει τον αριθμό των υδρόφιλωνθέσεων στην επιφάνεια τους για τη βελτίωση τόσο της χημικής συμβατότητας με τις αλυσίδες τουNafion όσο και του συντελεστή αυτοδιάχυσης των νανοσύνθετων μεμβρανών. Nανοσύνθετεςμεμβράνες παρασκευάστηκαν με τη μέθοδο των διαλυμάτων σε διαφορετικά ποσοστά φόρτωσηςενώ μελετήθηκε η επίδραση που έχει ο διαλύτης για την παρασκευή ομοιογενών μεμβρανών. Τανανοενισχυτικά, όσο και οι τελικές νανοσύνθετες μεμβράνες χαρακτηρίστηκαν με ένα συνδυασμότεχνικών (XRD, FTIR, Raman, DTA/TGA, SEM, DMA) ενώ η αγωγιμότητα των πρωτονίων τωντελικών μεμβρανών παρακολουθήθηκε με τη φασματοσκοπία του παλμικού NMR.Από τα αποτελέσματα αποδεικνύεται η δημιουργία αποφυλλοποιημένων μεμβρανών, όπου ταφύλλα των δισδιάστατων ενισχυτικών διασπάρθηκαν ομοιογενώς στη μάζα του πολυμερούςβελτιώνοντας τις θερμικές και μηχανικές ιδιότητες της μεμβράνης. Σύμφωνα με τις μετρήσεις NMR οσυντελεστής διαχύσεως των νανοσύνθετων μεμβρανών σε συνθήκες χαμηλής ενυδάτωσηςπαραμένει σταθερός σε πολύ υψηλά επίπεδα, αποδεικνύοντας την εξαιρετική ικανότητασυγκράτησης μορίων νερού. Αυτά τα χαρακτηριστικά είναι ιδιαίτερα επιθυμητά για τη χρήση τωνμεμβρανών ως ηλεκτρολύτες σε κελιά καυσίμου

Transport Properties and Mechanical Features of Sulfonated Polyether Ether Ketone/Organosilica Layered Materials Nanocomposite Membranes for Fuel Cell Applications

In this work, we study the preparation of new sulfonated polyether ether ketone (sPEEK) nanocomposite membranes, containing highly ionic silica layered nanoadditives, as a low cost and efficient proton exchange membranes for fuel cell applications. To achieve the best compromise among mechanical strength, dimensional stability and proton conductivity, sPEEK polymers with different sulfonation degree (DS) were examined. Silica nanoplatelets, decorated with a plethora of sulfonic acid groups, were synthesized through the one-step process, and composite membranes at 1, 3 and 5 wt% of filler loadings were prepared by a simple casting procedure. The presence of ionic layered additives improves the mechanical strength, the water retention capacity and the transport properties remarkably. The nanocomposite membrane with 5% wt of nanoadditive exhibited an improvement of tensile strength almost 160% (68.32 MPa,) with respect to pristine sPEEK and a ten-times higher rate of proton conductivity (12.8 mS cm−1) under very harsh operative conditions (i.e., 90 °C and 30% RH), compared to a filler-free membrane. These findings represent a significant advance as a polymer electrolyte or a fuel cell application

Sulfonated Polyether Ether Ketone and Organosilica Layered Nanofiller for Sustainable Proton Exchange Membranes Fuel Cells (PEMFCs)

The ease and low environmental impact of its preparation, the reduced fuel crossover, and the low cost, make sulfonated polyether ether ketone (sPEEK) a potential candidate to replace the Nafion ionomer in proton exchange membrane fuel cells (PEMFCs). In this study, sPEEK was used as a polymer matrix for the preparation of nanocomposite electrolyte membranes by dispersing an organo-silica layered material properly functionalized by anchoring high phosphonated (PO3H) ionic groups (nominated PSLM). sPEEK-PSLM membranes were prepared by the solution intercalation method and the proton transport properties were investigated by NMR (diffusometry-PFG and relaxometry-T1) and EIS spectroscopies, whereas the mechanical properties of the membranes were studied by dynamic mechanical analysis (DMA). The presence of the organosilica nanoplatelets remarkably improved the mechanical strength, the water retention capacity at high temperatures, and the proton transport, in particular under harsh operative conditions (above 100 °C and 20–30% RH), usually required in PEMFCs applications

A Novel Li+-Nafion-Sulfonated Graphene Oxide Membrane as Single Lithium-Ion Conducting Polymer Electrolyte for Lithium Batteries

Single lithium-ion conducting polymer electrolytes are an innovative concept of solid-state polymer electrolytes (SPEs) for lithium-battery technology. In this work, a lithiated Nafion nanocomposite incorporating sulfonated graphene oxide (sGO-Li+), as well as a filler-free membrane, have been synthesized and characterized. Ionic conductivities and lithium transference number, evaluated by electrochemical techniques after membrane-swelling in organic aprotic solvents (ethylene carbonate-propylene carbonate mixture), display significant values, with sigma approximate to 5 x 10(-4) S cm(-1) at 25 degrees C and t(Li+) close to unity. The absence of solvent leaching on thermal cycles is also noteworthy. The description at molecular level of the lithium transport mechanism has been carefully tackled through a systematic study by Li-7 NMR spectroscopy (pulsed field gradient-PFG and relaxation times), while the mechanical properties of the film electrolytes have been evaluated by dynamic mechanical analysis (DMA) in a wide temperature range. The electrochemical performances of the graphene-based electrolyte in Li/Li symmetric cells and in secondary cells using LiFePO4 as positive electrode show good compatibility and functionality with the Li-metal anode by forming a stable interphase, as well as displaying promising performance in galvanostatic cells

Nanocomposites of Polystyrene‑<i>b</i>‑Poly(isoprene)‑<i>b</i>‑Polystyrene Triblock Copolymer with Clay–Carbon Nanotube Hybrid Nanoadditives

Polystyrene-<i>b</i>-polyisoprene-<i>b</i>-polystyrene (PS-<i>b</i>-PI-<i>b</i>-PS), a widely used linear triblock copolymer of the glassy-rubbery-glassy type, was prepared in this study by anionic polymerization and was further used for the development of novel polymer nanocomposite materials. Hybrid nanoadditives were prepared by the catalytic chemical vapor deposition (CCVD) method through which carbon nanotubes were grown on the surface of smectite clay nanolayers. Side-wall chemical organo-functionalization of the nanotubes was performed in order to enhance the chemical compatibilization of the clay–CNT hybrid nanoadditives with the hydrophobic triblock copolymer. The hybrid clay–CNT nanoadditives were incorporated in the copolymer matrix by a simple solution-precipitation method at two nanoadditive to polymer loadings (one low, i.e., 1 wt %, and one high, i.e., 5 wt %). The resulting nanocomposites were characterized by a combination of techniques and compared with more classical nanocomposites prepared using organo-modified clays as nanoadditives. FT-IR and Raman spectroscopies verified the presence of the hybrid nanoadditives in the final nanocomposites, while X-ray diffraction and transmission electron microscopy proved the formation of fully exfoliated structures. Viscometry measurements were further used to show the successful incorporation and homogeneous dispersion of the hybrid nanoadditives in the polymer mass. The so prepared nanocomposites exhibited enhanced mechanical properties compared to the pristine polymer and the nanocomposites prepared by conventional organo-clays. Both tensile stress and strain at break were improved probably due to better interfacial adhesion of the clay–CNT hybrid of the flexible rubbery PI middle blocks of the triblock copolymer matrix

Development of Effective Lipase-Hybrid Nanoflowers Enriched with Carbon and Magnetic Nanomaterials for Biocatalytic Transformations

In the present study, hybrid nanoflowers (HNFs) based on copper (II) or manganese (II) ions were prepared by a simple method and used as nanosupports for the development of effective nanobiocatalysts through the immobilization of lipase B from Pseudozyma antarctica. The hybrid nanobiocatalysts were characterized by various techniques including scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS), X-ray diffraction (XRD), Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR). The effect of the addition of carbon-based nanomaterials, namely graphene oxide and carbon nanotubes, as well as magnetic nanoparticles such as maghemite, on the structure, catalytic activity, and operational stability of the hybrid nanobiocatalysts was also investigated. In all cases, the addition of nanomaterials during the preparation of HNFs increased the catalytic activity and the operational stability of the immobilized biocatalyst. Lipase-based magnetic nanoflowers were effectively applied for the synthesis of tyrosol esters in non-aqueous media, such as organic solvents, ionic liquids, and environmental friendly deep eutectic solvents. In such media, the immobilized lipase preserved almost 100% of its initial activity after eight successive catalytic cycles, indicating that these hybrid magnetic nanoflowers can be applied for the development of efficient nanobiocatalytic systems

Shape-Memory Behavior of Polylactide/Silica Ionic Hybrids

Commercial polylactide (PLA) was converted and endowed with shape-memory properties by synthesizing ionic hybrids based on blends of PLA with imidazolium-terminated PLA and poly­[ε-caprolactone-<i>co</i>-d,l-lactide] (P­[CL-<i>co</i>-LA]) and surface-modified silica nanoparticles. The electrostatic interactions assist with the silica nanoparticle dispersion in the polymer matrix. Since nanoparticle dispersion in polymers is a perennial challenge and has prevented nanocomposites from reaching their full potential in terms of performance we expect this new design will be exploited in other polymers systems to synthesize well-dispersed nanocomposites. Rheological measurements of the ionic hybrids are consistent with the formation of a network. The ionic hybrids are also much more deformable compared to the neat PLA. More importantly, they exhibit shape-memory behavior with fixity ratio <i>R</i>_f ≈ 100% and recovery ratio <i>R</i>_r = 79%, for the blend containing 25 wt % <i>im</i>-PLA and 25 wt % <i>im</i>-P­[CL-<i>co</i>-LA] and 5 wt % of SiO₂–SO₃Na. Dielectric spectroscopy and dynamic mechanical analysis show a second, low-frequency relaxation attributed to strongly immobilized polymer chains on silica due to electrostatic interactions. Creep compliance tests further suggest that the ionic interactions prevent permanent slippage in the hybrids which is most likely responsible for the significant shape-memory behavior observed