Browsing by Author "Vajtai, Robert"

Now showing 1 - 20 of 48
  • Thumbnail Image
    Item
    3D Macroporous Solids from Chemically Cross-linked Carbon Nanotubes
    (Wiley, 2014) Ozden, Sehmus; Narayanan, Tharangattu N.; Tiwary, Chandra S.; Dong, Pei; Hart, Amelia H.C.; Vajtai, Robert; Ajayan, Pulickel M.
    Suzuki reaction for covalently interconnected 3D carbon nanotube (CNT) architectures is reported. The synthesis of 3D macroscopic solids made of CNTs covalently connected via Suzuki cross-coupling, a well-known carbon-carbon covalent bond forming reaction in organic chemistry, is scalable. The resulting solid has a highly porous, interconnected structure of chemically cross-linked CNTs. Its use for the removal of oil from contaminated water is demonstrated.
  • Thumbnail Image
    Item
    Ambient solid-state mechano-chemical reactions between functionalized carbon nanotubes
    (Nature Publishing Group, 2015) Kabbani, Mohamad A.; Tiwary, Chandra Sekhar; Autreto, Pedro A.S.; Brunetto, Gustavo; Som, Anirban; Krishnadas, K.R.; Ozden, Sehmus; Hackenberg, Ken P.; Gong, Yongi; Galvao, Douglas S.; Vajtai, Robert; Kabbani, Ahmad T.; Pradeep, Thalappil; Ajayan, Pulickel M.
    Carbon nanotubes can be chemically modified by attaching various functionalities to their surfaces, although harsh chemical treatments can lead to their break-up into graphene nanostructures. On the other hand, direct coupling between functionalities bound on individual nanotubes could lead to, as yet unexplored, spontaneous chemical reactions. Here we report an ambient mechano-chemical reaction between two varieties of nanotubes, carrying predominantly carboxyl and hydroxyl functionalities, respectively, facilitated by simple mechanical grinding of the reactants. The purely solid-state reaction between the chemically differentiated nanotube species produces condensation products and unzipping of nanotubes due to local energy release, as confirmed by spectroscopic measurements, thermal analysis and molecular dynamic simulations.
  • Thumbnail Image
    ItemEmbargo
    An Approach Towards Sustainable Synthesis of MXene and High-Performance Cementitious Composites
    (2024-04-19) Jayanthi Harikrishnan, VJ; Ajayan, Pulickel M; Vajtai, Robert
    This thesis investigates innovative methods for synthesizing MXenes and enhancing cementitious materials to meet the critical need for sustainable manufacturing and improved mechanical properties in structural materials. Central to this research is the advancement in material science across two key areas: the development of environmentally friendly synthesis methods and the adoption of efficient manufacturing strategies to create advanced cement structures. A significant emphasis is placed on pushing the boundaries of material performance, sustainability, and synthesis techniques. For example, we explore modified approaches to MXene synthesis and the development of reinforced cementitious composites through the integration of nanotechnology and cutting-edge 3D printing technologies. The initial three chapters primarily concentrate on sustainable synthesis strategies for MXenes, including the exploration of alternatives to traditional hydrofluoric acid (HF) for removing aluminum (Al) from the MAX-phase. Due to HF's high toxicity and associated health and safety risks, we investigate the use of ammonium fluoride (NH4F) as a safe alternative. Our findings, supported by various analytical techniques, confirm NH4F's effectiveness in Al removal and in the production of 2D MXene flakes. Additionally, we explore a novel non-fluoride-based chemical method using iron chloride (FeCl2) as an etchant, which plays a dual role in etching and intercalating, leading to the production of high-quality Fe intercalated MXene flakes. Through detailed analysis, we evaluate the crystallinity, chemical composition, surface morphology, and defects of the MXene flakes produced by these new techniques. This part of the thesis not only aims to mitigate the environmental impact associated with MXene production due to HF use, but also to enhance their surface chemistry adaptability, broadening their application potential. Furthermore, the thesis chapters provide fundamental and an in-depth analysis of MXenes, in addition to highlighting the efficacy of these innovative synthesis techniques in maintaining the structural integrity and desired features of MXenes. The latter chapters, specifically chapters four and five, focus on enhancing the mechanical properties of cementitious materials by leveraging the unique properties of nanoparticles and the advancements in multi-material 3D printing. This section demonstrates significant improvements in compressive strength, toughness, and thermal management by incorporating hexagonal boron nitride (h-BN) into cement matrices. Additionally, it examines the application of direct ink writing (DIW) in creating reinforced cement and polyvinyl alcohol (PVA) structures, aiming to boost their impact resistance and energy absorption capabilities. Overall, this thesis offers a comprehensive overview of the synthesis, chemistry, and technologies involved in developing advanced materials with wide-ranging applications. For instance, the synthesized MXenes could be applied in electromagnetic interference shielding, catalysis, sensors, and flexible electronics. Conversely, the nanofiller and polymer-reinforced cement structures have potential applications in environments subjected to extreme thermal and mechanical stresses
  • Thumbnail Image
    Item
    Atomically thin gallium layers from solid-melt exfoliation
    (AAAS, 2018) Kochat, Vidya; Samanta, Atanu; Zhang, Yuan; Bhowmick, Sanjit; Manimunda, Praveena; Asif, Syed Asif S.; Stender, Anthony S.; Vajtai, Robert; Singh, Abhishek K.; Tiwary, Chandra S.; Ajayan, Pulickel M.
    Among the large number of promising two-dimensional (2D) atomic layer crystals, true metallic layers are rare. Using combined theoretical and experimental approaches, we report on the stability and successful exfoliation of atomically thin “gallenene” sheets on a silicon substrate, which has two distinct atomic arrangements along crystallographic twin directions of the parent α-gallium. With a weak interface between solid and molten phases of gallium, a solid-melt interface exfoliation technique is developed to extract these layers. Phonon dispersion calculations show that gallenene can be stabilized with bulk gallium lattice parameters. The electronic band structure of gallenene shows a combination of partially filled Dirac cone and the nonlinear dispersive band near the Fermi level, suggesting that gallenene should behave as a metallic layer. Furthermore, it is observed that the strong interaction of gallenene with other 2D semiconductors induces semiconducting to metallic phase transitions in the latter, paving the way for using gallenene as promising metallic contacts in 2D devices.
  • Thumbnail Image
    Item
    Bacteria as Bio-Template for 3D Carbon Nanotube Architectures
    (Springer Nature, 2017) Ozden, Sehmus; Macwan, Isaac G.; Owuor, Peter S.; Kosolwattana, Suppanat; Autreto, Pedro A.S.; Silwal, Sushila; Vajtai, Robert; Tiwary, Chandra S.; Mohite, Aditya D.; Patra, Prabir K.; Ajayan, Pulickel M.
    It is one of the most important needs to develop renewable, scalable and multifunctional methods for the fabrication of 3D carbon architectures. Even though a lot of methods have been developed to create porous and mechanically stable 3D scaffolds, the fabrication and control over the synthesis of such architectures still remain a challenge. Here, we used Magnetospirillum magneticum (AMB-1) bacteria as a bio-template to fabricate light-weight 3D solid structure of carbon nanotubes (CNTs) with interconnected porosity. The resulting porous scaffold showed good mechanical stability and large surface area because of the excellent pore interconnection and high porosity. Steered molecular dynamics simulations were used to quantify the interactions between nanotubes and AMB-1 via the cell surface protein MSP-1 and flagellin. The 3D CNTs-AMB1 nanocomposite scaffold is further demonstrated as a potential substrate for electrodes in supercapacitor applications.
  • Thumbnail Image
    Item
    Bifunctional Luminomagnetic Rare-Earth Nanorods for High-Contrast Bioimaging Nanoprobes
    (Springer Nature, 2016) Gupta, Bipin Kumar; Singh, Satbir; Kumar, Pawan; Lee, Yean; Kedawat, Garima; Narayanan, Tharangattu N.; Vithayathil, Sajna Antony; Ge, Liehui; Zhan, Xiaobo; Gupta, Sarika; Martí, Angel A.; Vajtai, Robert; Ajayan, Pulickel M.; Kaipparettu, Benny Abraham
    Nanoparticles exhibiting both magnetic and luminescent properties are need of the hour for many biological applications. A single compound exhibiting this combination of properties is uncommon. Herein, we report a strategy to synthesize a bifunctional luminomagnetic Gd2−xEuxO3 (x = 0.05 to 0.5) nanorod, with a diameter of ~20 nm and length in ~0.6 μm, using hydrothermal method. Gd2O3:Eu3+ nanorods have been characterized by studying its structural, optical and magnetic properties. The advantage offered by photoluminescent imaging with Gd2O3:Eu3+ nanorods is that this ultrafine nanorod material exhibits hypersensitive intense red emission (610 nm) with good brightness (quantum yield more than 90%), which is an essential parameter for high-contrast bioimaging, especially for overcoming auto fluorescent background. The utility of luminomagnetic nanorods for biological applications in high-contrast cell imaging capability and cell toxicity to image two human breast cancer cell lines T47D and MDA-MB-231 are also evaluated. Additionally, to understand the significance of shape of the nanostructure, the photoluminescence and paramagnetic characteristic of Gd2O3:Eu3+ nanorods were compared with the spherical nanoparticles of Gd2O3:Eu3+.
  • Thumbnail Image
    Item
    Carbon and Silicon Nanomaterials for Medical Nanotechnology Applications
    (2015-05-18) Gizzatov, Ayrat; Wilson, Lon J.; Tour, James M; Vajtai, Robert; Decuzzi, Paolo
    This dissertation focuses on the development of sp2-carbon- and silicon-based nanomaterials for medical diagnostics and in vivo magnetic field-guided delivery applications. To realize these applications, especially for the development of new in vivo Magnetic Resonance Imaging (MRI) contrast agents (CAs), high solubility in aqueous media is required. Therefore, this work first details development of a new non-covalent method for the preparation of stable aqueous colloidal solution of surfactant-free sp2-carbon nanostructures, as well as a second rapid covalent functionalization procedure to produce highly-water-dispersible honey-comb carbon nanostructures (ca. 50 mg/mL). Next, highly-water-dispersible graphene nanoribbons and Gd3+ ions were together used to produce a high-performance MRI CA for T1- and T2- weighted imaging. In terms of its relaxivity (r1,2) values, this new CA material outperforms currently-available clinical CAs by up to 16 times for r1 and 21 times for r2. Finally, sub-micrometer discoidal magnetic nanoconstructs have been produced and studied for applications for in vivo magnetic-field-guided delivery into cancerous tumors. The nanoconstructs were produced by confining ultra-small superparamagnetic iron oxide nanoparticles (USPIOs) within mesoporous silicon which produced T2-weighted MRI CA performance 2.5 times greater than for the free USPIOs themselves. Moreover, these nanoconstructs, under the influence of an external magnetic field, collectively cooperated via a new mechanism to amplify accumulation in melanoma tumors of mice. Overall, the results of this dissertation could aid in the rapid translation of these nanotechnologies into the clinic, while, hopefully, also serving as an inspiration for continued research into the field of Medical Nanotechnology.
  • Thumbnail Image
    Item
    Carbon nanotube micropillars trigger guided growth of complex human neural stem cells networks
    (Springer, 2019) Lorite, Gabriela S.; Ylä-Outinen, Laura; Janssen, Lauriane; Pitkänen, Olli; Joki, Tiina; Koivisto, Janne T.; Kellomäki, Minna; Vajtai, Robert; Narkilahti, Susanna; Kordas, Krisztian
    New strategies for spatially controlled growth of human neurons may provide viable solutions to treat and recover peripheral or spinal cord injuries. While topography cues are known to promote attachment and direct proliferation of many cell types, guided outgrowth of human neurites has been found difficult to achieve so far. Here, three-dimensional (3D) micropatterned carbon nanotube (CNT) templates are used to effectively direct human neurite stem cell growth. By exploiting the mechanical flexibility, electrically conductivity and texture of the 3D CNT micropillars, a perfect environment is created to achieve specific guidance of human neurites, which may lead to enhanced therapeutic effects within the injured spinal cord or peripheral nerves. It is found that the 3D CNT micropillars grant excellent anchoring for adjacent neurites to form seamless neuronal networks that can be grown to any arbitrary shape and size. Apart from clear practical relevance in regenerative medicine, these results using the CNT based templates on Si chips also can pave the road for new types of microelectrode arrays to study cell network electrophysiology.
  • Thumbnail Image
    Item
    Carbon-based Nanoparticles: Synthesis, Characterization and Applications
    (2014-09-05) Ceriotti Rona, Gabriel; Tour, James M.; Engel, Paul S; Vajtai, Robert
    The research detailed in this thesis is an investigation of the chemistry, applications, and methods for the synthesis of graphene oxide (GO), GO derivatives, graphite derivatives, carbon black derivatives, and activated charcoal derivatives, with an emphasis on applications relevant to the oil and gas industry. More particularly, the research involves a method for the rapid purification of GO; the use of GO and GO derivatives in oil-drilling fluids; the use of activated charcoal and carbon black for asphaltene inhibition; and the synthesis of nanoplatelets from an H2SO4/SO3/SO5- graphite intercalation compound and their application as conductivity enhancers in oil-based drilling fluids. Although many applications for GO have been reported in the literature, development of these applications on an industrial scale is held back by the lack of scalable procedures for the purification of GO after synthesis. A scheme for scalable purification is presented in Chapter 1. Suspensions of the resulting GO were tested for rheology and radionuclide uptake. One of the many possible industrial applications of GO and GO-derived products are their use in oil-drilling formulations also known as “drilling muds”. In Chapter 2, the performance of GO and chemically converted graphene as fluid loss control (FLC) agents and rheological modifiers in water-based mud (WBM) is investigated. Large-flake GO was found to be the best FLC additive in fresh-water mud (FWM), and five times more efficient as a rheological modifier than materials used in current FWM formulations. When WBM cannot be used for drilling, and oil-based mud (OBM) needs to be used instead, the reduced performance of resistivity-based imaging tools is of concern. In order to improve their performance, the electrical permittivity of the oil-based medium needs to be improved without disrupting the chemical equilibrium of the drilling formulation. For this purpose, a new method for the synthesis of graphite-derived nanoplatelets was studied (Chapter 3), and their performance as conductivity enhancers in OBM was investigated (Chapter 4). As an additional application of carbonaceous nanoparticles to the oilfield, the use of carbon black and activated charcoal particles for the inhibition, prevention or remediation of asphaltene deposition was investigated (Chapter 5). It was found that these nanoparticles can help stabilize, or controllably precipitate, asphaltenes by virtue of their high surface area, and by being a thermodynamically preferable surface for asphaltene deposition. Early collaborative works with a significant contribution by the author are included in Chapter 6 and Chapter 7. The work included in Chapter 6 pertains to the background of Chapter 2, and the work included in Chapter 7 pertains to the background of Chapter 3.
  • Thumbnail Image
    Item
    Charge coupled device based on atomically layered van der waals solid state film for opto-electronic memory and image capture
    (2016-08-30) Lei, Sidong; Ge, Liehui; George, Antony; Li, Bo; Vajtai, Robert; Ajayan, Pulickel M.; Rice University; United States Patent and Trademark Office
    An opto-electronic sensor may provide one or more layers of atomically layered photo-sensitive materials. The sensor may include a gate electrode layer, a dielectric layer in contact with the gate electrode layer, and a working media layer that is photo-sensitive deposited on the dielectric layer. The working media layer may provide one or more layers of one or more materials where each of the one or more layers is an atomic layer. The sensor may also include side electrodes in contact with the working media layer.
  • Thumbnail Image
    Item
    Cryo-mediated exfoliation and fracturing of layered materials into 2D quantum dots
    (AAAS, 2017) Wang, Yan; Liu, Yang; Zhang, Jianfang; Wu, Jingjie; Xu, Hui; Wen, Xiewen; Zhang, Xiang; Tiwary, Chandra Sekhar; Yang, Wei; Vajtai, Robert; Zhang, Yong; Chopra, Nitin; Odeh, Ihab Nizar; Wu, Yucheng; Ajayan, Pulickel M.
    Atomically thin quantum dots from layered materials promise new science and applications, but their scalable synthesis and separation have been challenging. We demonstrate a universal approach for the preparation of quantum dots from a series of materials, such as graphite, MoS2, WS2, h-BN, TiS2, NbS2, Bi2Se3, MoTe2, Sb2Te3, etc., using a cryo-mediated liquid-phase exfoliation and fracturing process. The method relies on liquid nitrogen pretreatment of bulk layered materials before exfoliation and breakdown into atomically thin two-dimensional quantum dots of few-nanometer lateral dimensions, exhibiting size-confined optical properties. This process is efficient for a variety of common solvents with a wide range of surface tension parameters and eliminates the use of surfactants, resulting in pristine quantum dots without surfactant covering or chemical modification.
  • Thumbnail Image
    Item
    CVD Grown Graphene-Based Materials: Synthesis, Characterization and Applications
    (2015-04-22) Ma, Lulu; Ajayan, Pulickel M; Lou, Jun; Zheng, Junrong; Vajtai, Robert
    Graphene draws a lot of attention due to its exceptional electrical, mechanical, thermal, optical and chemical properties. However, its zero bandgap is a limitation for electronics applications and its two-dimensional (2D) nature is a limitation for large scale, volumetric and macroscopic applications. Doping graphene with heteroatoms and creating graphene hetero-structures are two approaches herewith suggested to sidestep the above limitations. The illustration of thus approaches begins with the chemical vapor deposition (CVD) growth of graphene in the form of either atomically thin films or 3D porous structures; which involves the synthesis of several structures such as nitrogen-doped graphene, graphene-carbon nanotube hybrids, in-plane graphene-boron nitride heterostructures, and graphene-molybdenum carbide hybrids. The analysis of impurities in CVD grown graphene at the atomic scale and the measurement of fracture toughness of graphene will then follow. Furthermore, the potential applications of as-synthesized materials like field emitters, supercapacitors, and catalysts for water splitting are discussed.
  • Thumbnail Image
    Item
    Damage-tolerant 3D-printed ceramics via conformal coating
    (AAAS, 2021) Sajadi, Seyed Mohammad; Vásárhelyi, Lívia; Mousavi, Reza; Rahmati, Amir Hossein; Kónya, Zoltán; Kukovecz, Ákos; Arif, Taib; Filleter, Tobin; Vajtai, Robert; Boul, Peter; Pang, Zhenqian; Li, Teng; Tiwary, Chandra Sekhar; Rahman, Muhammad M.; Ajayan, Pulickel M.
    Ceramic materials, despite their high strength and modulus, are limited in many structural applications due to inherent brittleness and low toughness. Nevertheless, ceramic-based structures, in nature, overcome this limitation using bottom-up complex hierarchical assembly of hard ceramic and soft polymer, where ceramics are packaged with tiny fraction of polymers in an internalized fashion. Here, we propose a far simpler approach of entirely externalizing the soft phase via conformal polymer coating over architected ceramic structures, leading to damage tolerance. Architected structures are printed using silica-filled preceramic polymer, pyrolyzed to stabilize the ceramic scaffolds, and then dip-coated conformally with a thin, flexible epoxy polymer. The polymer-coated architected structures show multifold improvement in compressive strength and toughness while resisting catastrophic failure through a considerable delay of the damage propagation. This surface modification approach allows a simple strategy to build complex ceramic parts that are far more damage-tolerant than their traditional counterparts. Conformal polymer coating leads to damage-tolerant architected ceramic structures with high strength and toughness. Conformal polymer coating leads to damage-tolerant architected ceramic structures with high strength and toughness.
  • Thumbnail Image
    Item
    Design and development process for application-oriented supercapacitors
    (2020-08-07) Baburaj, Abhijit; Pulickel, Ajayan; Vajtai, Robert
    Increasing demand for clean and sustainable energy, with a rise in technology, has pushed us to investigate clean energy sources and their storage. Batteries and supercapacitors are electrochemical storage devices that have applications both in the industry as well as in portable electronics. Supercapacitors are energy storage devices that store electrical energy through an adsorption/desorption of ions or pseudo-capacitive faradaic reactions at the electrode-electrolyte interfaces. Supercapacitors can be a replacement for batteries during high power output events and can have a near indefinite cycling life. High-power density, high-rate capability, and performance at high-frequency are the most desirable properties for a supercapacitor. Hence, my research focused on engineering the supercapacitor electrodes as well as designing the supercapacitor of desired form factors for various applications.
  • Thumbnail Image
    Item
    Efficient Modulation of 1.55 μm Radiation with Gated Graphene on a Silicon Microring Resonator
    (American Chemical Society, 2014) Qiu, Ciyuan; Gao, Weilu; Vajtai, Robert; Ajayan, Pulickel M.; Kono, Junichiro; Xu, Qianfan
    The gate-controllability of the Fermi-edge onset of interband absorption in graphene can be utilized to modulate near-infrared radiation in the telecommunication band. However, a high modulation efficiency has not been demonstrated to date, because of the small amount of light absorption in graphene. Here, we demonstrate a ~40% amplitude modulation of 1.55 μm radiation with gated single-layer graphene that is coupled with a silicon microring resonator. Both the quality factor and resonance wavelength of the silicon microring resonator were strongly modulated through gate tuning of the Fermi level in graphene. These results promise an efficient electro-optic modulator, ideal for applications in large-scale on-chip optical interconnects that are compatible with complementary metal-oxide-semiconductor technology
  • Thumbnail Image
    Item
    Electric Double Layer Field-Effect Transistors Using Two-Dimensional (2D) Layers of Copper Indium Selenide (CuIn7Se11)
    (MDPI, 2019) Patil, Prasanna D.; Ghosh, Sujoy; Wasala, Milinda; Lei, Sidong; Vajtai, Robert; Ajayan, Pulickel M.; Talapatra, Saikat
    Innovations in the design of field-effect transistor (FET) devices will be the key to future application development related to ultrathin and low-power device technologies. In order to boost the current semiconductor device industry, new device architectures based on novel materials and system need to be envisioned. Here we report the fabrication of electric double layer field-effect transistors (EDL-FET) with two-dimensional (2D) layers of copper indium selenide (CuIn7Se11) as the channel material and an ionic liquid electrolyte (1-Butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6)) as the gate terminal. We found one order of magnitude improvement in the on-off ratio, a five- to six-times increase in the field-effect mobility, and two orders of magnitude in the improvement in the subthreshold swing for ionic liquid gated devices as compared to silicon dioxide (SiO2) back gates. We also show that the performance of EDL-FETs can be enhanced by operating them under dual (top and back) gate conditions. Our investigations suggest that the performance of CuIn7Se11 FETs can be significantly improved when BMIM-PF6 is used as a top gate material (in both single and dual gate geometry) instead of the conventional dielectric layer of the SiO2 gate. These investigations show the potential of 2D material-based EDL-FETs in developing active components of future electronics needed for low-power applications.
  • Thumbnail Image
    Item
    Electrically tunable hot-silicon terahertz attenuator
    (AIP Publishing LLC, 2014) Wang, Minjie; Vajtai, Robert; Ajayan, Pulickel M.; Kono, Junichiro
    We have developed a continuously tunable, broadband terahertz attenuator with a transmission tuning range greater than 103. Attenuation tuning is achieved electrically, by simply changing the DC voltage applied to a heating wire attached to a bulk silicon wafer, which controls its temperature between room temperature and ~550 K, with the corresponding free-carrier density adjusted between ~1011 cm−3 and ~1017 cm−3. This “hot-silicon”-based terahertz attenuator works most effectively at 450–550 K (corresponding to a DC voltage variation of only ~7 V) and completely shields terahertz radiation above 550 K in a frequency range of 0.1–2.5 THz. Both intrinsic and doped silicon wafers were tested and demonstrated to work well as a continuously tunable attenuator. All behaviors can be understood quantitatively via the free-carrier Drude model taking into account thermally activated intrinsic carriers.
  • Thumbnail Image
    Item
    Engineered Nanomaterials for Energy Harvesting and Storage Applications
    (2014-11-03) Gullapalli, Hemtej; Ajayan, Pulickel M; Vajtai, Robert; Biswal, Sibani L; Arava, Leela Mohana Reddy
    Energy harvesting and storage are independent mechanisms, each having their own significance in the energy cycle. Energy is generally harvested from temperature variations, mechanical vibrations and other phenomena which are inherently sporadic in nature, harvested energy stands a better chance of efficient utilization if it can be stored and used later, depending on the demand. In essence a comprehensive device that can harness power from surrounding environment and provide a steady and reliable source of energy would be ideal. Towards realizing such a system, for the harvesting component, a piezoelectric nano-composite material consisting of ZnO nanostructures embedded into the matrix of ‘Paper’ has been developed. Providing a flexible backbone to a brittle material makes it a robust architecture. Energy harvesting by scavenging both mechanical and thermal fluctuations using this flexible nano-composite is discussed in this thesis. On the energy storage front, Graphene based materials developed with a focus towards realizing ultra-thin lithium ion batteries and supercapacitors are introduced. Efforts for enhancing the energy storage performance of such graphitic carbon are detailed. Increasing the rate capability by direct CVD synthesis of graphene on current collectors, enhancing its electrochemical capacity through doping and engineering 3D metallic structures to increase the areal energy density have been studied.
  • Thumbnail Image
    Item
    Flexible planar supercapacitors by straightforward filtration and laser processing steps
    (IOP, 2020) Pitkänen, Olli; Eraslan, Toprak; Sebők, Dániel; Szenti, Imre; Kukovecz, Ákos; Vajtai, Robert; Kordas, Krisztian
    There is ever increasing demand for flexible energy storage devices due to the development of wearable electronics and other small electronic devices. The electrode flexibility is best provided by a special set of nanomaterials, but the required methodology typically consists of multiple steps and are designed just for the specific materials. Here, a facile and scalable method of making flexible and mechanically robust planar supercapacitors with interdigital electrode structure made of commercial carbon nanomaterials and silver nanowires is presented. The capacitor structure is achieved with vacuum filtration through a micropatterned contact mask and finished with simple laser processing steps. A maximum specific capacitance of 4 F cm−3 was measured with cyclic voltammetry at scan rate of 5 mV s−1. The reliability and charge transfer properties of devices were further investigated with galvanostatic charge-discharge measurements and electrochemical impedance spectroscopy, respectively. Furthermore, mechanical bending tests confirmed the devices have excellent mechanical integrity, and the deformations have no adverse effects on the electrochemical charge-discharge behavior and stability.
  • Thumbnail Image
    Item
    Fluorinated Graphene Oxide: structure, morphology and its potential use in biological applications
    (2014-04-25) Romero Aburto, Rebeca; Ajayan, Pulickel M.; Vajtai, Robert; Grande-Allen, K. Jane; West, Jennifer L.; Mani, Sendurai A
    The main objective of this work is to report a novel carbon nanomaterial that can serve as a theranostic agent. This thesis will elaborate on the structure, chemical functionalization, morphology, size distribution and biological applications of this material. Then, this thesis will discuss the limitations of this material and propose an optimization for these drawbacks. Fluorinated Graphene Oxide (FGO) is reported for the first time as a potential multimodal contrast agent, drug carrier as well as a photothermal therapy. FGO is a sheet like material with oxygen and fluorine functional groups present in the structure, a complete characterization of the material is offered in the following pages. Non-cytotoxic FGO exhibited paramagnetic behavior and was able to confer Magnetic Resonance Imaging (MRI) contrast. When irradiated with a Near Infra Red (NIR)-laser, FGO was able to exhibit photoacoustic contrast and serve as a photothermal therapy being able to ablate cancer cells in vitro. The limitation of FGO is its size (500-1000nm). Therefore, density gradient ultracentrifugation was successfully used to size select this material, resulting in a fraction containing sheet sizes around 200nm. Additionally, Fluorinated Graphene Oxide Nanoribbons (FGONRs) will be synthesized, characterized and evaluated as a possible optimization of FGO. However, after the systematic FGONRs, did not result in an optimization with respect to FGO. The ribbons exhibit a diamagnetic behavior and their length is comparable to the length of FGO.