Studio per la produzione e la caratterizzazione di foglietti arrotolati di grafite (carbon nanoscrolls)

The report on research activity of this doctoral thesis is divided into two sections. In the first section the study, production and functionalization of some newly discovered carbon structures called carbon nanoscrolls (CNS) are reported. These rolled structures arises from the curling of graphene sheets to produce tubular cylinders similar to the already known carbon nanotubes. Currently, these objects are studied mainly from a theoretical point of view but are considered good candidates for hydrogen storage, nanodevice production and reinforcement in composite materials. The production of CNS is carried out through an initial stage of reaction with metallic potassium, to give a graphite intercalation compound of minimum formula KC8, characterized by alternating graphene plans and potassium atoms, pale bronze in colour and highly reactive. A direct reaction with ethanol, under inert atmosphere, produces hydrogen and heat that producethe expansion of graphene sheets. The rolling of grapheme sheets is mediated by high power ultrasounds. The application of ultrasounds overcomes the energy barrier required for the bending of the sheets so that the edges can overlap and adhere by Van der Waals forces giving CNS. It has been devised a general procedure for CNS synthesis starting from a natural Madagascar-type graphite, purified by heat treatment and commercially available in flakes. The many experiments that we carried out (intercalation, exfoliation, ultrasonication) gave some rolled sheets in the samples but in a unexpectedly low yield. We then tried to optimize the CNS synthesis by implementing a preliminary expansion of graphite. Using a mixture of concentrated H2SO4/HNO3 as intercalating agents, followed by an expansion stadium by a thermal or treatment with microwaves. In both cases, the expansion of the graphemes was very good. We also applied a mechanical demolition procedure using a high-power ball-miller. This study was implemented on the basis of SEM observations, that showed how the large slats of graphite hampered wrapping. Actually the effect was beyond expectations, excessive crushing of graphite produced too small leaflets and even the formation of amorphous carbon, thereby invalidate this step. A new and efficient CNS synthetic procedure was pursued, using ozone and fuming HNO3 as intercalating agents, followed by exfoliation with ethanol and ultrasonication. This treatment produces a considerable improvement in the production of CNS. Some funzionalization reactions were also carried out on prepared CNS through the 1,3-dipolar cycloaddition reaction of azomethine ylides and the sidewall diazotation in a similar way used for carbon nanotubes. The second part of the project has involved the production of composite materials based on graphite oxide and polithiophenes to produce a material that synergistically combine the mechanical properties of graphite with an organic semiconducting polymer, with a possible use as component in electronic devices. The graphite oxide has been obtained with permanganate oxidation in strong mineral acids; it is easily dispersable in water and can restore the starting graphite in form of carbon nanoplatelets after reduction with hydrazine. The polymer has been produced in aqueous environment using thienyl monomers such as the 3.4-etilenedioxythiophene (EDOT) and the 3-hexylthiophene (3HT), pure or blended, in the presence of graphite oxide, ammonium persulphate (APS) as polymerizing agent and a surfactant to prevent precipitaion. After evaporation of the solvent, a composite material was obtained, in the form of thin and shiny black films, with little roughness, and relatively transparent to light in water. The conductiong, composite material was used for some tests, in a transistor (FET) configuration, at the Zernike Institute for Advanced Materials of the Universityt of Groningen. It has been shown that the composite is a good candidate to prepare organic-based diodes.