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Ruquan Ye, Juncai Dong, Luqing Wang, Rubén Mendoza-Cruz, Yilun Li, Peng-Fei An, Miguel José Yacamán, Boris I Yakobson, Dongliang Chen, James M Tour
Heteroatom-doped metal-free graphene has been widely studied as the catalyst for the oxygen reduction reaction (ORR). Depending on the preparation method and the dopants, the ORR activity varies ranging from a two-electron to a four-electron pathway. The different literature reports are difficult to correlate due to the large variances. However, due to the potential metal contamination, the origin of the ORR activity from "metal-free" graphene remains confusing and inconclusive. Here we decipher the ORR catalytic activities of diverse architectures on graphene derived from reduced graphene oxide...
June 2018: Carbon
Irene Palacio, Gonzalo Otero-Irurueta, Concepción Alonso, José I Martínez, Elena López-Elvira, Isabel Muñoz-Ochando, Horacio J Salavagione, María F López, Mar García-Hernández, Javier Méndez, Gary J Ellis, José A Martín-Gago
While high-quality defect-free epitaxial graphene can be efficiently grown on metal substrates, strong interaction with the supporting metal quenches its outstanding properties. Thus, protocols to transfer graphene to insulating substrates are obligatory, and these often severely impair graphene properties by the introduction of structural or chemical defects. Here we describe a simple and easily scalable general methodology to structurally and electronically decouple epitaxial graphene from Pt(111) and Ir(111) metal surfaces...
April 2018: Carbon
Zhiwei Peng, Allen L Ng, Hyejin Kwon, Peng Wang, Chien-Fu Chen, Cheng S Lee, YuHuang Wang
Single-walled carbon nanotubes (SWCNTs) hold vast potential for future electronic devices due to their outstanding properties, however covalent functionalization often destroys the intrinsic properties of SWCNTs, thus limiting their full potential. Here, we demonstrate the fabrication of a functionalized graphene/semiconducting SWCNT (T@fG) heterostructured thin film transistor as a chemical sensor. In this structural configuration, graphene acts as an atom-thick, impermeable layer that can be covalently functionalized via facile diazonium chemistry to afford a high density of surface functional groups while protecting the underlying SWCNT network from chemical modification, even during a covalent chemical reaction...
December 2017: Carbon
Ajay Krishnamurthy, Donald L Hunston, Amanda L Forster, Bharath Natarajan, Andrew H Liotta, Sunny S Wicks, Paul E Stutzman, Brian L Wardle, J Alexander Liddle, Aaron M Forster
As carbon nanotube (CNT) infused hybrid composites are increasingly identified as next-generation aerospace materials, it is vital to evaluate their long-term structural performance under aging environments. In this work, the durability of hierarchical, aligned CNT grafted aluminoborosilicate microfiber-epoxy composites (CNT composites) are compared against baseline aluminoborosilicate composites (baseline composites), before and after immersion in water at 25 °C (hydro) and 60 °C (hydrothermal), for extended durations (90 d and 180 d)...
December 2017: Carbon
Duygu Ağaoğulları, Steven J Madsen, Burcu Ögüt, Ai Leen Koh, Robert Sinclair
Graphite-encapsulated Fe nanoparticles were synthesized using a combined method of high-energy ball milling and low-pressure chemical vapor deposition (LPCVD). Fe2 O3 and graphite powders were milled to increase their surface areas and obtain a more homogeneous distribution. LPCVD was performed at a pressure of ~0.57 Torr in a tube furnace under a CH4 /H2 atmosphere at 1050°C for 1 and 3 h. As-synthesized samples were purified in a 2 M HF solution. Characterization was performed using X-ray diffractometry (XRD), scanning and transmission electron microscopy (SEM and TEM) and alternating gradient magnetometry (AGM)...
November 2017: Carbon
Xiaofang Hou, Yin Hu, Ping Wang, Liju Yang, Mohamad M Al Awak, Yongan Tang, Fridah K Twara, Haijun Qian, Ya-Ping Sun
A simple yet consequential modification was made to the popular carbonization processing of citric acid - polyethylenimine precursor mixtures to produce carbon dots (CDots). The modification was primarily on pushing the carbonization processing a little harder at a higher temperature, such as the hydrothermal processing condition of around 330 °C for 6 hours. The CDots thus produced are comparable in spectroscopic and other properties to those obtained in other more controlled syntheses including the deliberate chemical functionalization of preprocessed and selected small carbon nanoparticles, demonstrating the consistency in CDots and reaffirming their general definition as carbon nanoparticles with surface passivation by organic or other species...
October 2017: Carbon
Gejo George, Suja Bhargavan Sisupal, Teenu Tomy, Bincy Akkoli Pottammal, Alaganandam Kumaran, Vemparthan Suvekbala, Rajmohan Gopimohan, Swaminathan Sivaram, Lakshminarayanan Ragupathy
Commercially useful rubber products viz. gloves, condoms, tyres, and rubber hoses used in high temperature environments, etc., require efficient thermal conductivity, which increases the lifetime of these products. Graphene can fetch this property, if it is effectively incorporated into the rubber matrix. The great challenge in preparing graphene-rubber nanocomposites is formulating a scalable method to produce defect free graphene and its homogeneous dispersion into polymer matrices through an aqueous medium...
August 2017: Carbon
J Azpeitia, G Otero-Irurueta, I Palacio, J I Martinez, N Ruiz Del Árbol, G Santoro, A Gutiérrez, L Aballe, M Foerster, M Kalbac, V Vales, F J Mompeán, M García-Hernández, J A Martín-Gago, C Munuera, M F López
We present a new protocol to grow large-area, high-quality single-layer graphene on Cu foils at relatively low temperatures. We use C60 molecules evaporated in ultra high vacuum conditions as carbon source. This clean environment results in a strong reduction of oxygen-containing groups as depicted by X-ray photoelectron spectroscopy (XPS). Unzipping of C60 is thermally promoted by annealing the substrate at 800ºC during evaporation. The graphene layer extends over areas larger than the Cu crystallite size, although it is changing its orientation with respect to the surface in the wrinkles and grain boundaries, producing a modulated ring in the low energy electron diffraction (LEED) pattern...
August 2017: Carbon
Junghyun Kim, Zhi-Xiang Luo, Yue Wu, Xiuling Lu, Michael Jay
Radionuclide therapy with nano-sized carriers is a very promising approach to treat various types of cancer. The preparation of radioactive nanocarriers can be achieved with minimum handling using a neutron-activation approach. However, the nanocarrier material must possess certain characteristics such as low density, heat-resistance, high metal adsorption, easy surface modification and low toxicity in order to be useful. Mesoporous Carbon Nanoparticles (MCNs) in which holmium oxide is formed in their pores by a wet-impregnation process are investigated as a suitable material for this application...
June 2017: Carbon
Yanfei Yang, Guangjun Cheng, Patrick Mende, Irene G Calizo, Randall M Feenstra, Chiashain Chuang, Chieh-Wen Liu, Chieh-I Liu, George R Jones, Angela R Hight Walker, Randolph E Elmquist
Quantized magnetotransport is observed in 5.6 × 5.6 mm2 epitaxial graphene devices, grown using highly constrained sublimation on the Si-face of SiC(0001) at high temperature (1900 °C). The precise quantized Hall resistance of [Formula: see text] is maintained up to record level of critical current Ixx = 0.72 mA at T = 3.1 K and 9 T in a device where Raman microscopy reveals low and homogeneous strain. Adsorption-induced molecular doping in a second device reduced the carrier concentration close to the Dirac point ( n ≈ 1010 cm-2 ), where mobility of 18760 cm2 /V is measured over an area of 10 mm2 ...
May 2017: Carbon
Joon Hyong Cho, Jason J Gorman, Seung Ryul Na, Michael Cullinan
Growth of high quality and monolayer graphene on copper thin films on silicon wafers is a promising approach to massive and direct graphene device fabrication in spite of the presence of potential dewetting issues in the copper film during graphene growth. Current work demonstrates roles of a nickel adhesion coupled with the copper film resulting in mitigation of dewetting problem as well as uniform monolayer graphene growth over 97 % coverage on films. The feasibility of monolayer graphene growth on Cu-Ni alloy films as thin as 150 nm in total is also demonstrated...
May 2017: Carbon
Tinh Nguyen, Elijah J Petersen, Bastien Pellegrin, Justin M Gorham, Thomas Lam, Minhua Zhao, Lipiin Sung
Multiwall carbon nanotubes (MWCNTs) are nanofillers used in consumer and structural polymeric products to enhance a variety of properties. Under weathering, the polymer matrix will degrade and the nanofillers may be released from the products potentially impacting ecological or human health. In this study, we investigated the degradation of a 0.72 % (by mass) MWCNT/amine-cured epoxy nanocomposite irradiated with high intensity ultraviolet (UV) light at various doses, the effects of UV exposure on the surface accumulation and potential release of MWCNTs, and possible mechanisms for the release resistance of the MWCNT surface layer formed on nanocomposites by UV irradiation...
May 2017: Carbon
Wendel Wohlleben, Christopher Kingston, Janet Carter, E Sahle-Demessie, Socorro Vázquez-Campos, Brad Acrey, Chia-Ying Chen, Ernest Walton, Heiko Egenolf, Philipp Müller, Richard Zepp
A major use of multi-walled carbon nanotubes (MWCNTs) is as functional fillers embedded in a solid matrix, such as plastics or coatings. Weathering and abrasion of the solid matrix during use can lead to environmental releases of the MWCNTs. Here we focus on a protocol to identify and quantify the primary release induced by weathering, and assess reproducibility, transferability, and sensitivity towards different materials and uses. We prepared 132 specimens of two polymer-MWCNT composites containing the same grade of MWCNTs used in earlier OECD hazard assessments but without UV stabilizer...
March 2017: Carbon
Mohindar S Seehra, Vishal Narang, Usha K Geddam, Aleksandr B Stefaniak
Structural properties of sixteen (16) commercial samples of graphene-based materials (GBM) labelled as graphene, graphene oxide or reduced graphene oxide are investigated at room temperature using X-ray diffraction (XRD) and Raman spectroscopy. Based on the observed correlation between the results obtained with these two techniques, these samples are classified into three groups: Group A of seven samples consisting of graphitic nanosheets with evaluated thickness ≃20 nm and exhibiting both the 2H and 3R phases in XRD; Group B of six samples exhibiting XRD spectra characteristic of either graphene oxides (GO) or carbons with some order; and Group C of three samples with XRD spectra characteristic of disordered carbons...
January 2017: Carbon
Yang Qiu, Samuel Moore, Robert Hurt, Indrek Külaots
Fast external heating rates in graphite oxide thermal exfoliation have been reported to be advantageous for generating high surface area graphene-based materials for a variety of applications. The study yields the surprising result that the surface area and porosity developed in reduced graphite oxide under some conditions are independent of instrument-set external heating rates. The true "total" heating rate experienced by the sample is shown to be the sum of the external rate and the local self-heating rate associated with the exothermicity of graphite oxide exfoliation, and under many conditions, the local self-heating contribution dominates...
January 2017: Carbon
Liang Mao, Chuanling Liu, Kun Lu, Yu Su, Cheng Gu, Qingguo Huang, Elijah J Petersen
While graphene has substantial commercial promise, numerous aspects regarding its ecological effects such as its potential for bioaccumulation are not well known.14 C-labeled few layer graphene (FLG) was dispersed in artificial freshwater and uptake of FLG by Limnodrilus hoffmeisteri , an oligochaete, was assessed. After exposure for 36 h to a 1 mg/L FLG suspension, the FLG body burden in the organism was nearly 60 ng/mg (on a dry mass basis). Multiple characterization results confirmed that the proteins secreted by the organisms during the exposure period coated the FLG, thus increasing its stability and decreasing its size in suspension...
November 2016: Carbon
Maria Iliut, Claudio Silva, Scott Herrick, Mark McGlothlin, Aravind Vijayaraghavan
Thin-film elastomers (elastic polymers) have a number of technologically significant applications ranging from sportswear to medical devices. In this work, we demonstrate that graphene can be used to reinforce 20 micron thin elastomer films, resulting in over 50% increase in elastic modulus at a very low loading of 0.1 wt%, while also increasing the elongation to failure. This loading is below the percolation threshold for electrical conductivity. We demonstrate composites with both graphene oxide and reduced graphene oxide, the reduction being undertaken in-situ or ex-situ using a biocompatible reducing agent in ascorbic acid...
September 2016: Carbon
Qing Zhao, Elijah J Petersen, Geert Cornelis, Xilong Wang, Xiaoying Guo, Shu Tao, Baoshan Xing
Developing methods to measure interactions of carbon nanotubes (CNTs) with soils and sediments and understanding the impact of soil and sediment properties on CNT deposition are essential for assessing CNT environmental risks. In this study, we utilized functionalized carbon-14 labeled nanotubes to systematically investigate retention of multiwall CNTs (MWCNTs) by 3 humic acids, 3 natural biopolymers, and 10 model solid-phase polymers, collectively termed macromolecules. Surface properties, rather than bulk properties of macromolecules, greatly influenced MWCNT retention...
April 2016: Carbon
Prakrit V Jena, Yosi Shamay, Janki Shah, Daniel Roxbury, Navid Paknejad, Daniel A Heller
Nanomaterials have been extensively investigated for cancer drug delivery and imaging applications. Nanoparticles that show promise in two-dimensional cell culture systems often fail in more complex environments, possibly due to the lack of penetration in dense, three-dimensional structures. Multicellular tumor spheroids are an emerging model system to investigate interactions of nanoparticles with 3D in vitro cell culture environments. Using the intrinsic near-infrared emission of semiconducting carbon nanotubes to optically reconstruct their localization within a three-dimensional volume, we resolved the relative permeability of two different multicellular tumor spheroids...
February 1, 2016: Carbon
Zhongying Wang, Daniel Tonderys, Susan E Leggett, Evelyn Kendall Williams, Mehrdad T Kiani, Ruben Spitz Steinberg, Yang Qiu, Ian Y Wong, Robert H Hurt
Textured surfaces with periodic topographical features and long-range order are highly attractive for directing cell-material interactions. They mimic physiological environments more accurately than planar surfaces and can fundamentally alter cell alignment, shape, gene expression, and cellular assembly into superstructures or microtissues. Here we demonstrate for the first time that wrinkled graphene-based surfaces are suitable as textured cell attachment substrates, and that engineered wrinkling can dramatically alter cell alignment and morphology...
February 1, 2016: Carbon
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