Nitrogen doped carbon nanomaterials for biosensing applications

Tesis (Doctorado en Nanociencias y Nanotecnología)"The doping of carbon nanostructures with elements such as nitrogen and boron adds useful characteristics to the already remarkable features exhibited by nanocarbons. These new properties can be used for tackling several obstacles encountered for nanotechnology based applications, specially in biotechnology, where biocompatibility and sensitivity are crucial parameters for biosensing applications development. In this thesis work, we report the synthesis of nitrogendoped graphitic nanoribbons, along with their characterization by SEM and TEM. Raman and XPS spectroscopy results are also shown, and electrical characterization results are presented as well. Our results demonstrate how the presence of nitrogen produces novel morphologic, chemical and physical properties on graphitic nanoribbons, which in turn make the nanomaterial a promising candidate for bioelectronics research. Additionaly, we present results of theoretical and experimental research on interactions of doped carbon nanomaterials and biomolecules. Our theoretical findings suggest strong effects of doping on the stability of interactions between graphene and dopamine, whereas our experimental results suggest improved electrical properties for nitrogen-doped carbon nanotubes based biodevices when compared with undoped ones. This thesis shows, from theoretical and experimental studies, that doping of carbon nanostructures can be useful for sensing of biomolecules.

Calculation of the Electronic Properties and Reactivity of Nanoribbons

It has been demonstrated that matter at low dimensionality exhibits novel properties, which could be used in promising applications. An effort to understand their behavior is being through the application of computational methods providing strategies to study structures, which present greater experimental challenges. It is proven that thin and narrow carbon-based nanostructures, such as, nanoribbons show promising tunable electronic properties, particularly when they are substitutionally functionalized. This chapter is proposed as a guidance to help the readers to apply conceptual density functional theory to calculate helpful intrinsic properties, e. g., energetic, electronic and reactivity of one-dimension nanomaterial’s, such as, carbon nanoribbons. As a case of study, it is discussed the effect of boron atoms on the properties of pristine carbon nanoribbons concerning the main aspect and considerations must take into account in their computational calculations

Atomistic Modeling of Gas Adsorption in Nanocarbons

Carbon nanostructures are currently under investigation as possible ideal media for gas storage and mesoporous materials for gas sensors. The recent scientific literature concerning gas adsorption in nanocarbons, however, is affected by a significant variation in the experimental data, mainly due to the different characteristics of the investigated samples arising from the variety of the synthesis techniques used and their reproducibility. Atomistic simulations have turned out to be sometimes crucial to study the properties of these systems in order to support the experiments, to indicate the physical limits inherent in the investigated structures, and to suggest possible new routes for application purposes. In consideration of the extent of the theme, we have chosen to treat in this paper the results obtained within some of the most popular atomistic theoretical frameworks without any purpose of completeness. A significant part of this paper is dedicated to the hydrogen adsorption on C-based nanostructures for its obvious importance and the exceptional efforts devoted to it by the scientific community

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.

Electronic and Magnetic Properties of Two-dimensional Nanomaterials beyond Graphene and Their Gas Sensing Applications: Silicene, Germanene, and Boron Carbide

The popularity of graphene owing to its unique properties has triggered huge interest in other two-dimensional (2D) nanomaterials. Among them, silicene shows considerable promise for electronic devices due to the expected compatibility with silicon electronics. However, the high-end potential application of silicene in electronic devices is limited owing to the lack of an energy band gap. Hence, the principal objective of this research is to tune the electronic and magnetic properties of silicene related nanomaterials through first-principles models. I first explored the impact of edge functionalization and doping on the stabilities, electronic, and magnetic properties of silicene nanoribbons (SiNRs) and revealed that the modified structures indicate remarkable spin gapless semiconductor and half-metal behaviors. In order to open and tune a band gap in silicene, SiNRs were perforated with periodic nanoholes. It was found that the band gap varies based on the nanoribbon’s width, nanohole’s repeat periodicity, and nanohole’s position due to the quantum confinement effect. To continue to take advantage of quantum confinement, I also studied the electronic and magnetic properties of hydrogenated silicene nanoflakes (SiNFs). It was discovered that half-hydrogenated SiNFs produce a large spin moment that is directly proportional to the square of the flake’s size. Next, I studied the adsorption behavior of various gas molecules on SiNRs. Based on my results, the SiNR could serve as a highly sensitive gas sensor for CO and NH3 detection and a disposable gas sensor for NO, NO2, and SO2. I also considered adsorption behavior of toxic gas molecules on boron carbide (BC3) and found that unlike graphene, BC3 has good sensitivity to the gas molecules due to the presence of active B atoms. My findings divulged the promising potential of BC3 as a highly sensitive molecular sensor for NO and NH3 detection and a catalyst for NO2 dissociation. Finally, I scrutinized the interactions of CO2 with lithium-functionalized germanene. It was discovered that although a single CO2 molecule was weakly physisorbed on pristine germanene, a significant improvement on its adsorption energy was found by utilizing Li-functionalized germanene as the adsorbent. My results suggest that Li-functionalized germanene shows promise for CO2 capture

Inorganic Fullerene-like Nanoparticles and Inorganic Nanotubes

The subjects of the presented papers cover a wide range of challenges in the area of inorganic fullerene-like nanoparticles and nanotubes. However, it can include only a few comprehensive experimental and theoretical efforts, stepwise evaluating the rationalization of the synthesis, and elucidation of the stability, mechanical, electronic and adhesive properties of these nanostructures. We believe that this thematic issue can be helpful, not only for an advanced researcher to grasp the latest developments in this field, but also to permit a beginner to gain a deeper insight into the field of inorganic fullerene-like nanoparticles and nanotubes

Effects of doping single and double walled carbon nanotubes with nitrogen and boron

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006.Includes bibliographical references (p. 135-143).Controlling the diameter and chirality of carbon nanotubes to fine tune their electronic band gap will no longer be enough to satisfy the growing list of characteristics that future carbon nanotube applications are starting to require. Controlling their band gap, wall reactivity and mechanical properties is imperative to make them functional. The solution to these challenges is likely to lie in smart defect engineering. Defects of every kind can induce significant changes on the intrinsic properties of carbon nanotubes. In this context, this thesis analyzes the effects of doping single and double walled carbon nanotubes with nitrogen and boron. We describe the synthesis of N-doped single-walled carbon nanotubes (N-SWNTs), that agglomerate in bundles and form long strands (<10cm), via the thermal decomposition of ferrocene/ethanol/benzylamine (FEB) solutions in an Ar atmosphere at 950°C. Using Raman spectroscopy, we noted that as the N content is increased in the starting FEB solution, the growth of large diameter tubes is inhibited. We observed that the relative electrical conductivity of the strands increases with increasing nitrogen concentration. Thermogravimetric analysis (TGA) showed novel features for highly doped tubes, that are related to chemical reactions on N sites.(cont.) We also carried out resonance Raman studies of the coalescence process of double walled carbon nanotubes in conjunction with high resolution transmission electron microscope (HRTEM) experiments on the same samples, heat treated to a variety of temperatures and either undoped or Boron doped. As the heat treatment temperatures are increased (to 1300°C) a Raman mode related to carbon-carbon chains (w = 1855cm-1) is observed before DWNT coalescence occurs. These chains are expected to be 3-5 atoms long and they are established covalently between adjacent DWNTs. The sp carbon chains trigger nanotube coalescence via a zipper mechanism and the chains disappear once the tubes merge. Other features of the Raman spectra were analyzed as a function of heat treatment with special emphasis on the metallic or semiconducting nature of the layers constituting the DWNTs. DWNTs whose outer wall is metallic tend to interact more with the dopant and their outer tubes are the predominant contributors to the line shape of the G and G' bands.(cont.) The metallic or semiconducting nature of the layers of the DWNTs does not affect their coalescence temperature. All the experiments and analysis presented in this thesis are the result of a collaborative effort between Professor Dresselhaus' group at MIT and its international collaborators, including Professor Endo's group at Shinshu University, Nagano, Japan, Professors Pimenta's and Jorio's group at the Federal University of Minas Gerais, Belo Horizonte, Brazil, and Professors M. and H. Terrones' group at IPICYT, San Luis Potosi, Mexico.by Federico Villalpando Paéz.S.M

First-principles study of the electronic and magnetic properties of defective carbon nanostructures

149 p.: graf.Using ab initio calculations we habe carried out an extensive study of the electronic and magnetic propeerties of defects and impurities in graphene and carbon nanotubes. In particular, we have focused on the following topics: Electronic structure of substitutional magnetic impurities: mapping to simple models Spin-Strain phase diagram for defective graphene Magnetic order and exchange interactions between substitutional Co impurities in graphene. Effect of covalent functionalization in graphene and carbon nanotube

Growth and Doping of Carbon Nanotubes and Graphene

Single walled carbon nanotubes (SWCNTs) have been doped with nitrogen (N) by two ion-mediated approaches: directly through irradiation with N+ ions and by a novel indirect technique, creating defects through Ar+ ion irradiation which then react with nitrogen upon annealing in a N2 atmosphere. X-ray photoelectron spectroscopy (XPS) was then employed to determine the chemical environment of the nitrogen within the resulting SWCNT material. Depending upon the exact preparation conditions, nitrogen in graphitic (substitutional) pyridinic and pyrrolic configurations could be identified. Nitrogen doping through the novel method was found to introduce the largest concentration of chemisorbed nitrogen within the SWCNT films, dominated by thermodynamically unstable pyrrolic species at low process temperatures (500ºC). The maximum concentration of nitrogen in graphitic sites was achieved by direct ion bombardment, although both XPS and Raman spectroscopy indicated that this approach to doping led to the greatest damage. The ability to vary both bsolute and relative composition of chemisorbed nitrogen species is expected to be valuable for a range of fundamental studies, particularly of the catalytic behaviour of these materials. The growth of graphene on copper under atmospheric pressure using a soft solid source (nonadecane) is reported. It is found that the growth rate is best described by a model which involves the continuous supply of reactive species during the entire growth period. This observation is explained in terms of the formation of decomposition produces which reside on an otherwise clean surface after nonadecane desorption and provide a series of ‘mini carbon sources’ for graphene growth. XPS analysis indicates that, as expected, increased growth temperature leads to greater graphitisation at the surface (and hence graphene ‘quality’) which is not accompanied by any substantial change in island size and coverage. It is found that although graphene islands can be produced it is not possible to form continuous films, demonstrating the limitations of this technique. Although limited in some ways, the use of soft solid precursors for graphene growth allows the ready introduction of potential dopant materials. XPS, Raman and SEM data provide strong evidence that a PDMS precursor can be employed in atmospheric pressure solid-phase CVD to produce graphene heavily doped with silicon, which has not been previously achieved. Since silicon-doped graphene is predicted to possess a band gap related to the Si concentration, this may provide a route to produce a graphene-based material of use in digital electronics