Theoretical investigation of fullerene nanocage capacity for hydrogen storage

Fullerenes are nanocage compounds that can be used for hydrogen storage. Hydrogen is believed to be a potential alternative energy source, as the energy produced is clean. One of the most important issues in hydrogen–filled fullerene molecules is the determination of the number of hydrogen molecules that can be encapsulated inside the fullerene cage. In this study, the maximum number of hydrogen molecules that can be encapsulated inside C50, C60, C70 and C78 fullerenes was investigated by means of theoretical methods. Various density functional theory (DFT) functionals, together with Hartree–Fock (HF) and post Hartree–Fock methods were used in the computation for this study. Taking into consideration the basis set superposition error (BSSE) correction, it was found that second order Møller-Plesset perturbation theory (MP2) and dispersion corrected semiempirical hybrid density functional theory with perturbative second–order correlation (B2PLYPD), in conjunction with the triple zeta Pople–style 6-311G(d,p) basis set, provide the most reliable results in predicting the stability of nH2@Ck complexes. On the basis of complexation energy calculations, it was confirmed that encapsulation of numerous hydrogen molecules inside Ck (k = 50, 60, 70 and 78) fullerenes is unrealistic. In agreement with results of experimental works, only one hydrogen molecule can be accommodated inside C50 and C60, two inside C70 and three inside C78. Geometrical considerations of encapsulation of H2 molecule(s), host–guest interaction forces, strain energies, dispersion energies, maximum expansion of the fullerene cages that can be reached before breaking some of the C–C bonds and the bond dissociation energies (BDEs) of the cages are all in line with the calculated complexation energies

On the diverse bonding situations in nanostructures : an ab initio computational study

This computational study investigates diverse bonding situations in nanostructures (carbon nanotubes, fullerenes, metal compounds) spanning a broad range of energies. Weak, dispersive interactions and covalent metal-ligand and metal-metal bonding are examined. The results of efficient density functional calculations are compared to those of correlated wavefunction calculations on model systems. This rigorous validation is crucial in evaluating the balance between computational cost and accuracy

Optical properties of nanoclusters from time-dependent density-functional theory

The ground state properties of a quantum-mechanical many-electron system can be effectively modeled by its total electron density only, which is the key idea of the density-functional theory (DFT) methods. However, electronic excitations to higher energy states are not adequately described by the standard DFT formalism. To model the optical properties, for example, absorption and emission and response to time-dependent fields such as laser fields, the extension to time-dependent DFT (TDDFT) has become a popular method. In this Thesis, the TDDFT methods are utilized to calculate the optical properties of various nanostructures including fullerenes and fullerene derivatives, silicon nanocrystals and metal-polymer hybrid structures. The main focus is in the determination of their photoabsorption spectra using a real-space implementation of TDDFT. By these calculations we study how different structural variations and changes in the chemical environment affect the electronic and optical properties of the materials. For carbon and boron nitride fullerenes, variations in their size, geometry and doping are found to have a clear impact on their photoabsorption spectra. The results strengthen the view that optical absorption can be effectively used in the experimental characterization of such structures, for example in distinguishing between different isomers. The photoabsorption is observed to be strongly affected by the chemical environment for both silicon nanocrystals and small silver nanoclusters. When silicon nanoclusters are embedded in silica, the size dependence of their absorption edge is found to change due to major changes in the electronic structure. For the silver clusters, the presence of a polymer is found to bring the absorption edge down to the visible range in some of the studied cases. These calculations shed light to the experimental observations of unexpected absorption from such structures in the visible range

Reactividad química de nanoformas de carbono : reacciones de arilación y cicloadición 1,3-dipolar

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Químicas, Departamento de Química Orgánica I, leída el 08-05-2015La evolución de la sociedad ha estado fuertemente influenciada por el desarrollo de nuevos materiales y aplicaciones, haciendo de la Ciencia de Materiales un importante campo de investigación, donde interactúan tanto técnicas como conocimientos de diferentes aéreas científicas. En este contexto, los últimos descubrimientos en nanoformas de carbono CNF han de jugar un papel fundamental en el presente y futuro, tanto de la ciencia como de la sociedad en general. Si ya el fullereno C y los fullerenos endoédricos sorprendieron a la comunidad científica por su geometría, tamaño nanométrico y propiedades electrónicas, las últimas nanoformas de carbono descubiertas, nanotubos de carbono CNT y grafeno, han causado mayor expectación. CNT y grafeno exhiben sorprendentes propiedades electrónicas, eléctricas, mecánicas o térmicas, mejorando a algunos de los mejores materiales conocidos hasta la fecha como Cu, Ag o Si, o incluso que el kevlar o el acero. En esta tesis se describe el estudio de la reactividad química, estructura y propiedades de estas diferentes nanoestructuras de carbono nanotubos de carbono de pared simple SWNT , de pared múltiple MWNT , grafeno y fullerenos endoédricos. El trabajo se engloba en dos capítulos bien diferenciados que presentan como nexo común la utilización de reacciones de cicloadición 1,3 dipolar. EN el Capítulo 1 se describe la síntesis de nanoconjugados que contienen como nanoestructuras de carbono SWNT, MWNT y grafeno, combinados con p exTTF, mediante reacciones de arilación de tipo Tour seguidas por reacciones de cicloadición 1,3 dipolar catalizadas por cobre, también conocidas como click chemistry. Dichos nanoconjugados han sido caracterizadas mediante diferentes técnicas en ciencia de los materiales XPS, Raman, TGA, UV vis NIR, FTIR . La comunicación electrónica entre exTTF y SWNT se corroboró mediante técnicas electroquímicas y fotofísicas. Del mismo modo, la geometría cóncava del exTTF se utilizó para evaluar su comportamiento en el reconocimiento de fullereno C tanto en estado libre como ancladas sobre las diferentes CNF, demostrándose la formación del complejo receptor fullereno en ambos casos. Se realizaron valoraciones mediante UV vis NIR para evaluar la extensión de la interacción como valoraciones por RMN para desvelar los puntos de reconocimiento de los receptores con el fullereno, que fueron soportados sobre cálculos teóricos.Depto. de Química OrgánicaFac. de Ciencias QuímicasTRUEunpu

The topology of fullerenes

Fullerenes are carbon molecules that form polyhedral cages. Their bond structures are exactly the planar cubic graphs that have only pentagon and hexagon faces. Strikingly, a number of chemical properties of a fullerene can be derived from its graph structure. A rich mathematics of cubic planar graphs and fullerene graphs has grown since they were studied by Goldberg, Coxeter, and others in the early 20th century, and many mathematical properties of fullerenes have found simple and beautiful solutions. Yet many interesting chemical and mathematical problems in the field remain open. In this paper, we present a general overview of recent topological and graph theoretical developments in fullerene research over the past two decades, describing both solved and open problems. WIREs Comput Mol Sci 2015, 5:96–145. doi: 10.1002/wcms.1207 Conflict of interest: The authors have declared no conflicts of interest for this article. For further resources related to this article, please visit the WIREs website

Property screening of porous organic molecules

Porous organic molecules have internal pores readily occupied by gases, solvent or other guests. These molecules can form porous molecular materials with possible application in storage and separation. In this thesis, the properties of isolated porous organic molecules are used as a proxy to the bulk or in-solution applications. As a result, software was first developed for the automated and precise structural characterisation of porous organic molecules. This allows one to easily calculate window diameters to study the thermal window size fluctuations and predict guest diffusion in the bulk. A screening of previously reported porous organic molecules for the application of Xe/Kr separation allowed the most promising material, Noria, to be identified. This was possible with a combination of molecular modelling, electronic structure calculations and structural analysis using the developed software. The experimental Xe/Kr selectivity of Noria, not previously considered for this application, was shown to be comparable with the best performing porous materials. Next, eight synthetically realised porous organic cages were studied as possible C60 fullerene encapsulants. The relative orientation of the C60 fullerene in the pore was shown to have little to no effect on the binding energy and the encapsulation of the C60 during cage formation was determined as the likely mechanism of encapsulation. Lastly, a function-led material design approach was developed. An evolutionary algorithm was used to generate possible C60 encapsulants from a database of precursors. The resulting porous organic cages are structurally similar to some recently synthetically realised cages and some found in the literature. In summary, presented in this thesis is software, a methodology and results that can further advance the computational function-led materials discovery for specific applications.Open Acces

Environmental implications of higher order fullerenes and conjugated nanostructures

In quest of harnessing emergent properties and achieving multifunctionality in the materials realm, synthesis and manipulation at the nano-scale has moved its focus from simple passive nanomaterials (NMs) to hierarchical nanostructures. Such nanostructures include higher order fullerenes (HOFs), carbon allotropes composed of more than 60 carbon atoms per fullerene cage, and conjugated nanohybrids (NHs), prepared from materials of multiple chemical origin. The advantages in their electronic, optical, physicochemical, and magnetic properties have inspired their research and use in photovoltaics, nano-electronics, biomedical imaging and drug delivery, catalysis, energy generation and storage, and environmental remediation and sensing. Not only as research grade materials, a global market of bio-imaging and fuel-cell applications have been integrating use of HOFs, and NHs, respectively. Thus it is an exciting time for materials engineering to expand the spectrum of these ‘horizon materials’ by putting together a variety of chemical ‘building blocks’ and build a wide range of multifunctional hierarchical structures. However, such conjugation leading to complex hierarchical structures also introduces unknown environmental risks. The emergent properties of these hierarchical structures necessitate careful assessment of their environmental health and safety. This dissertation is one of the first organized efforts to identify hierarchical nanostructures and assess their environmental implications. This research, through extensive literature review of these novel nanostructures, proposes a working definition of NH from environmental perspective, classifies a wide array of NHs based on chemical origin, and identifies their emerging and altered physicochemical properties with potential to generate unprecedented environmental fate, transport, transformation, and toxicity. Furthermore, this dissertation makes an effort to address three major data gaps: i.e., a) challenges in aqueous solubilization of HOFs, b) possible correlation of carbon numbers on fullerene molecules with their aggregation behavior, and c) influence of hybridization on aggregation kinetics and antimicrobiality of an important electrocatalyst NH (metal-carbon). To address the first data gap, aqueous suspensions of nC₆₀, nC₇₀, nC₇₆, and nC₈₄ were prepared using a calorimetry-based solvent exchange method. Non-aggregating and size-specific aqueous nC₆₀ and nC₇₀ fullerene clusters also were prepared using a non-ionic polymer, pluronic acid (PA). The environmental processes section of this research assessed aggregation kinetics of nHOFs and NHs as well as antimicrobiality of TiO₂ conjugated oxidized multiwalled carbon nanotube (OMWNT-TiO₂) NH. Aqueous solubilization of C₇₀, C₇₆, and C₈₄ was performed being guided by molecular dynamics (MD) simulations. Increased energy demand reflects favorability of HOF-water interaction. The experimental findings suggest that nHOF clusters obtained via solvent-exchange solubilization method remains stabilized by electrostatic repulsion. Similarly, non-ionic triblock co-polymer PA F-127 stabilized aqueous C₆₀ and C₇₀s were prepared. Experimental results suggest that size uniformity of aqueous fullerenes increased with the increase in PA concentration, yielding optimum 58.8±5.6 and 61.8±5.6 nm nC₆₀s and nC₇₀s, respectively (0.10 %w/v PA). Fullerene aqueous suspensions also manifested colloidal stability even in presence of 1 M NaCl or in biological media, i.e., DMEM and RPMI. MD simulations results indicate encapsulation of fullerene clusters by PA molecules and subsequent steric stabilization. The results from this study may facilitate mechanistic environmental and toxicological studies with size-specific fullerenes that do not aggregate in high ionic strength biological media. Aqueous suspensions of nC₆₀ and three nHOFs (i.e., nC₇₀, nC₇₆, and nC₈₄) obtained via solvent-exchange method were systematically studied to determine their aggregation kinetics in a wide range of mono- (NaCl) and divalent (CaCl₂) electrolytes. Experimentally obtained critical coagulation concentration (CCC) values of nC₆₀ and nHOFs displayed a strong negative correlation with the carbon number in fullerenes. The aggregation mechanism was dominated by van der Waals interaction as enumerated via MD simulation and modified Derjaguin-Landau-Verwey-Overbeek (DLVO) model. Natural macromolecules profoundly stabilized all fullerene clusters, even at 100 mM NaCl concentration. The results from this study can be utilized to predict aggregation kinetics of nHOFs other than the ones studied here. To understand the aggregation behavior of carbon-metal NHs, oxidized MWNTs were hybridized sequentially with undoped or Nb-doped TiO₂ and Pt NPs. OMWNT-TiO₂, OMWNT-TiNbO₂, OMWNT-TiO₂, and OMWNT-TiNbO₂-Pt and the component materials were characterized and their aggregation behavior was studied systematically. Experimental findings show that CCC values OMWNT were reduced by TiO₂ attachment; however, Nb-doping and Pt attachment increased their colloidal stability and CCC values. The aggregation mechanism was elucidated by modified DLVO energy calculations using composition-averaged Hamaker constants for NHs. Natural macromolecules stabilized all the NHs and the component materials. Antimicrobiality of OMWNT-TiO₂ NH was studied via in vitro cell viability tests. Opportunistic pathogen Pseudomonas aeruginosa PAO1 strain was exposed to OMWNT, TiO₂, and OMWNT-TiO₂ NH at different concentrations in dark and UV-irradiated conditions. OMWNT-TiO₂ NH showed higher antimicrobial activity compared to the component materials under UV-irradiation. Extracellular reactive oxygen species (ROS) measurement by using fluorescence molecular probes for H₂O₂ identifies UV-induced enhanced ROS generation by the NH as a likely antimicrobial mechanism. The research presented in this dissertation takes the first attempt toward EHS assessment of complex and hierarchical nanostructures. The research findings present new insights into these ‘horizon materials’ and likely will spark interests on this necessary line of research to better understand the environmental fate, transport, and effects of HOFs and NHs. As nanotechnology is advancing from passive singular nanostructures to active and complex nano-systems; such undertakings become imperative to evaluate implications of material complexity at the environmental interface.Civil, Architectural, and Environmental Engineerin

Computations on Endohedral Metallofullerenes: Characterization, Properties and Growth

Els ful•lerens són caixes closes de carboni formades per un nombre parell d’àtoms. Una de les propietats mes interessants és la capacitat d’encapsular àtoms i petites molècules en la cavitat interior. El primer ful•lerè endoèdric fou proposat just després del descobriment del C60. Els metal•loful•lerens endoèdrics han atret atenció de gran part de la comunitat científica per les seves propietats i potencials aplicacions en camps com la medicina o la ciència de materials. En aquesta tesi s’hi mostra un extensiu treball combinant experiments i computació per a la caracterització i modelatge de noves especies de metal•loful•lerens endoèdrics. En la majoria dels casos, la síntesi de noves espècies necessita d’aquesta combinació d’experiments i computació per poder la identificació i caracterització de les estructures. Així doncs, aquí es presenta el treball per l’estudi de les propietats i caracterització des de sistemes petits com Ti@C2n (2n =26-50) i altres endoedres monometàl•lics (M@C2n), així com l’estudi detallat dels sistemes Sc2S@C70, Sc2S@C72, Ti2S@C78 i la modelització d’algunes de les seves propietats mes rellevants.Los fulerenos son poliedros esféricos formados por un nombre par de átomos de carbono distribuidos en pentágonos y hexágonos. Una de sus propiedades más atractiva es la capacidad de atrapar átomos y pequeñas moléculas en su interior. Estos fueron descubiertos rápidamente después del descubrimiento del C60. El Sc3N@C80 es el fulereno endoédrico más abundante, y el tercer sistema más abundante en toda la familia de fulerenos, solo por detrás de C60 y C70. Los fulerenos endoédricos han captado la atención de gran parte de la comunidad científica debido a sus propiedades y potenciales aplicaciones en campos como la medicina y la ciencia de materiales. La caracterización de nuevas especies es difícil debido al bajo rendimiento, por eso, la combinación de experimentos con trabajos computacionales es esencial para la exitosa identificación de nuevos sistemas. En esta tesis se incluye un extenso trabajo combinando estudios computacionales con varios tipos de experimentos. Entre las especies estudiadas y caracterizadas se encuentran desde los pequeños fulerenos monometálicos Ti@C2n (2n=26-50), hasta especies más grandes cómo Sc2S@C70, Sc2S@C72 y [email protected] are closed carbon cages constituted by an even number of atoms. One of the attractive properties of the hollow carbon clusters is the possibility to use them as robust containers for other species. The first proposal of an endohedral fullerene was given only a few days after the discovery of C60. Endohedral metallofullerenes have attracted the attention of the scientific community not only because their unique host-guest behaviors, but also because the properties and, thus, the applications are significantly different from those of the empty cages. The formal electron transfer that has been found to happen between the trapped unit and the carbon cages is determinant for the understanding of these new properties. Herein we report an extensive study combining computations and experiments. This combination is a powerful tool for the structural characterization of new species. The computation of the structures and the modeling of the properties, allow us to compare the experimental and computational data to identify the new systems. In this thesis the reader will find a complete study from small endohedrals, Ti@C2n (2n=26-50) and other M@C2n, to larger fullerenes as Sc2S@C70, Sc2S@C72 and Ti2S@C78