Solid state physicochemical properties and applications of organic and metallo-organic fullerene derivatives

We review the fundamental properties and main applications of organic derivatives and complexes of fullerenes in the solid-state form. We address in particular the structural properties, in terms of crystal structure, polymorphism, orientational transitions and morphology, and the electronic structure and derived properties, such as chemical activity, electrical conduction mechanisms, optical properties, heat conduction and magnetism. The last two sections of the review focus on the solid-state optoelectronic and electrochemical applications of fullerene derivatives, which range from photovoltaic cells to field-effect transistors and photodetectors on one hand, to electron-beam resists, electrolytes and energy storage on the other.Peer ReviewedPreprin

Functionalization of Surfaces in Layered Double Hydroxides and Hydroxide Salt Nanoparticles

Layered double hydroxides (LDH) and layered hydroxide salts (LHS) are widely studied as matrices to design new materials with applications in several areas of science and technology. Both LDH and LHS are composed of molecular layered units with surfaces fully covered by hydroxyl groups and positive‐charge residues within the layers; therefore, anions in the interlayer space are needed. Even though these anions are described as interlayer species without a covalent interaction with the molecular layered units, the substitution of hydroxyl groups is also possible; in other words, the functionalization of the surface could occur. This chapter reviews results previously published related to the functionalization phenomenon in LDH and LHS, which is not considered in most of the scientific reports of new materials derived from these compounds. In this text, the use of copper probes to study electron paramagnetic resonance spectra, reinforced with infrared spectroscopy to confirm functionalization, is described. The occurrence of functionalization instead of a simple anion exchange provides a change of properties in the final nanosized material

Synthesis of nanocomposites from polyaniline, polypyrrole and carbon nanotubes, and unzipping of multi-walled carbon nanotubes for the obtention of new graphitic nanomaterials

Tesis (Doctorado en Nanociencias y Nanotecnología)"La síntesis de compositos a partir de nanotubos de carbono ha tenido como principal reto el lograr una buena dispersión de los primeros en la matriz polimérica y para ello se han utilizado diversos métodos de funcionalización. Así mismo, se busca obtener una buena interacción entre ambos componentes y que el composito resultante se beneficie de las propiedades presentes en los materiales de partida. En este contexto, en la presente tesis presentamos los principales resultados concernientes a la síntesis de compositos a partir de nanotubos de carbono multicapa (MWNTs), MWNTs dopados con nitrógeno (CNx) y de polímeros conductores electrónicos, específicamente de polianilina (PAni), polianilina sulfonada (SPAni) y polipirrol (PPy). Dicho estudio surge a partir de nuestro interés en combinar las propiedades únicas de cada componente y así obtener nuevos materiales con propiedades electrónicas y mecánicas mejoradas. Por primera vez en el ámbito científico, sintetizamos estos compositos mediante la polimerización in situ de los monómeros correspondientes mediante un método de alquilación reductiva en amoníaco líquido, al cual se denomina sales de nanotubos, y que ha sido ampliamente utilizado para la funcionalización de fulerenos, nanotubos de una (SWNTs) y de varias capas (MWNTs). En este método se disuelve litio metálico en amoníaco líquido, al que se agregan los nanotubos de carbono formando entonces una sal de nanotubos. Durante la síntesis de compositos encontramos que, ocasionalmente, tanto MWNTs como CNx se exfoliaban en los extremos o en segmentos. Decidimos entonces seguir esta línea de investigación, logrando exitosamente la obtención de nanocintas de carbono a partir de MWNTs. Encontramos que los MWNTs pueden ser abiertos longitudinalmente mediante la intercalación de litio y amoníaco, seguida por exfoliación. Los mejores resultados se obtuvieron mediante intercalación en tubos cortados y abiertos en los extremos y exfoliación con tratamiento ácido y calentamiento abrupto. El material resultante consistió en: (i) estructuras grafíticas de multicapa (nanocintas), (ii) MWNTs parcialmente abiertos y (iii) hojuelas de grafeno. A los nanotubos completamente abiertos les llamamos ex-MWNTs, los cuales se caracterizan por su gran cantidad de bordes, lo cual los hace candidatos muy atractivos para muchas aplicaciones, tales como: elaboración de nanocompositos, adsorción de gases, baterías recargables, capacitores, etc.""The synthesis of composites from carbon nanotubes has its most notable challenge in the good dispersion of carbon nanotubes within the polymer matrix. Moreover, a good interaction is also desired between both components and a synergic effect in the composite as well, resulting from the properties of each component. On this respect, in this thesis we present the main results concerning the synthesis of composites from multi-walled carbon nanotubes (MWNTs), nitrogen-doped MWNTs (CNx), and electronic conducting polymers, specifically from polyaniline (PAni), sulfonated polyaniline (SPAni), and polypyrrole (PPy). This study was motivated by our interest too combine the unique properties of each component and the obtention of composites with improved electronic and mechanical properties. For first time in science, we synthesized these composites by in situ polymerization of the corresponding monomers by means of a reductive alkylation method in liquid ammonia which is called nanotube salts. This method has been widely used for functionalization of fullerenes, single- (SWNTs), and multi-walled carbon nanotubes (MWNTs). In this method, metallic lithium is dissolved in liquid ammonia, to which carbon nanotubes are added, thus forming nanotube salts. During the synthesis of these composites we occasionally observed that both MWNTs ans CNx were opened at the tips or in segments. We thus decided to follow this research line, successfully obtaining carbon nanoribbons from MWNTs. We found that these MWNTs can be opened longitudinally by intercalation of lithium and ammonia followed by exfoliation. Intercalation of open-ended tubes and exfoliation eith acid treatment and abrupt heating provided tjhe best results. The resulting material consists of: (i) multilayered flat graphitic structures (nanoribbons), (ii) partially open MWNTs, and (iii) graphene flakes. We called the completely unwrapped nanotubes ex-MWNTs, which are characterized by a large number of edges that make them very attractive for many applications such as: composites, gas adsorption, rechargeable batteries, capacitors, etc. Characterization of their morphology, vibrational, and structure properties allowed us to propose an exfoliation mechanism for MWNTs.

Thermal conductivity enhancement of graphene polymer composites through edge functionalization and expansion of graphite

In this work, we report an ultra-high enhancement of 4030% in thermal conductivity of polyetherimide/graphene nanocomposite (k = 9.5 Wm-1K-1) prepared through the use of expanded graphite (EG) with hydrogen peroxide as an intercalating agent at 10 weights% composition (k of pure polyetherimide ~ 0.23 Wm-1K-1). This value represents the highest thermal conductivity ever measured in a polymer composite at this low filler loading and is more than a factor of 2 higher relative to earlier reported results. This ultra-high thermal conductivity value is found to be due to an expanded graphite mediated interconnected graphene network throughout the composite, establishing a percolative environment that enables highly efficient thermal transport in the composite. Comparative studies were also performed using sodium chlorate as an intercalating agent. At 10 wt% composition, sodium chlorate intercalated expanded graphite was found to lead to a smaller enhancement of 2190% in k of composite. These results highlight the distinct advantage of hydrogen peroxide as an intercalating agent in enhancing thermal conductivity. Detailed characterization performed to elucidate this advantage, revealed that hydrogen peroxide led to primarily edge oxidation of graphene sheets within expanded graphite, leaving the basal plane intact, thus preserving the ultra-high in-plane thermal conductivity of ~ 2000 Wm-1K-1. Sodium chlorate, on the other hand, led to a higher degree of oxidation, with a large number of oxygen groups on basal plane of graphene, dramatically lowering its in-plane thermal conductivity. To directly shed light on the effect of intercalating agents on thermal conductivity of graphene itself, we prepared expanded graphite paper by compressing expanded graphite particles together. Thermal diffusivity of hydrogen-peroxide prepared expanded graphite paper was measured to be 9.5 mm2/s while that of sodium chlorate case measured to be 6.7 mm2/s, thus directly confirming the beneficial impact of hydrogen peroxide on k of graphene itself. This study is the first to address the role of intercalating agents on k of expanded graphite/polymer composites and has led to the discovery of hydrogen peroxide as an effective intercalating agent for achieving ultra-high thermal conductivity values. The work is also the first to address the comparison between edge and basal plane functionalization of graphene for enhancement of k of graphene-nanoplatelet /polyetherimide (GnP/PEI) composites. Graphene nanoplatelets (GnPs) comprise of multiple layers of graphene stacked parallel to each other. Edge functionalization enables the advantage of coupling the edges of all sheets of GnP with the embedding polymer, thus enabling the entire nanoplatelet to efficiently conduct heat through the composite. Basal-plane functionalization only couples the outermost layers of GnP with the polymer, thus causing only part of the nanoplatelet to be effective in conducting heat. Another very important advantage of edge-functionalization lies in leaving the basal plane of graphene intact. This preserves the ultra-high in-plane k of graphene (k~ 2000 Wm-1K-1). Basal plane functionalization, on the other hand, introduces a large number of defects in the basal plane of graphene dramatically lowering its intrinsic k value. Molecular dynamics simulations have revealed that even 5% functionalization of the basal plane can lower graphene thermal conductivity by as much as 90%. In this work, we experimentally realized the outlined advantages of edge-functionalization on the enhancement of k. Edge functionalization was achieved by oxidizing graphene with an excess of carboxyl groups through use of sulfuric acid, sodium chlorate and hydrogen peroxide. Carboxyl groups are known to preferentially attach to edges of graphene leading to edge oxidation. Basal plane oxidation was achieved through Hummer’s method by using sulfuric acid and potassium permanganate. Measurements reveal edge-oxidized graphene to enhance composite k by 18%, while basal-plane oxidized graphene reduced composite k by 57% at 10 wt% composition, clearly outlining the advantage of edge-functionalization on enhancement of thermal conductivity. Detailed characterization was performed to confirm edge versus basal plane oxidation. X-ray photoelectron spectroscopy showed greater fraction of carboxyl groups in edge-oxidized graphene, while basal plane oxidized graphene had larger fraction of hydroxyl/epoxy oxygen groups. 2D Raman mapping was used to obtain ID/IG ratios separately on edge and basal plane of GnPs. Edge oxidized graphene demonstrated higher ID/IG ratio on edge, while basal plane oxidized graphene demonstrated higher ID/IG ratio on basal plane. These studies for the first time, comprehensively demonstrate that edge functionalization can lead to superior thermal conductivity enhancement. Unique breakthroughs outlined in this thesis will lead to promising new avenues to achieve next-generation ultra-high thermal conductivity polymer-graphene nanocomposites

Chemical Modification of Graphene via A Potassium Graphite Intercalation Approach

Graphene is frequently termed a ‘wonder material’ due to its excellent properties and potential for use in a broad range of applications. Key to the realization of graphene in various applications is surface modification. The aim of the work was to investigate a facile approach to functionalize graphene with various functional groups for specific applications. To this aim, a graphite intercalation compounds (GICs) approach was introduced to activate graphene layers. In the first study, two kinds of natural graphite were used for preparation of potassium GICs. Raman spectroscopy and Powder XRD were used to investigate the quality of prepared GICs. It was found the GICs prepared from 325 mesh graphite possessed a higher order of intercalation. In the second study, potassium GIC was functionalized by various diazonium salts and benzyl bromides. Successful functionalization was confirmed by Raman spectroscopy, Thermogravimetric Analysis (TGA) and X-ray photoelectron spectroscopy (XPS). Finally, functionalized graphene was decorated with amine modified gold nanoparticles. This work provided a potential approach to functionalize graphene with various functional groups