205 research outputs found
Visualizing Graphene Based Sheets by Fluorescence Quenching Microscopy
Graphene based sheets have stimulated great interest due to their superior
mechanical, electrical and thermal properties. A general visualization method
that allows quick observation of these single atomic layers would be highly
desirable as it can greatly facilitate sample evaluation and manipulation, and
provide immediate feedback to improve synthesis and processing strategies. Here
we report that graphene based sheets can be made highly visible under a
fluorescence microscope by quenching the emission from a dye coating, which can
be conveniently removed afterwards by rinsing without disrupting the sheets.
Current imaging techniques for graphene based sheets rely on the use of special
substrates. In contrast, the fluorescence quenching mechanism is no longer
limited by the types of substrates. Graphene, reduced graphene oxide, or even
graphene oxide sheets deposited on arbitrary substrates can now be readily
visualized by eye with good contrast for layer counting. Direct observation of
suspended sheets in solution was also demonstrated. The fluorescence quenching
microscopy offers unprecedented imaging flexibility and could become a general
tool for characterizing graphene based materials.Comment: J. Am. Chem. Soc., Article ASA
Longitudinal unzipping of carbon nanotubes to form graphene nanoribbons.
Published versio
Computational studies for reduced graphene oxide in hydrogen-rich environment
We employ molecular dynamic simulations to study the reduction process of
graphene-oxide (GO) in a chemically active environment enriched with hydrogen.
We examine the concentration and pressure of hydrogen gas as a function of
temperature in which abstraction of oxygen is possible with minimum damage to
C-sp bonds hence preserving the integrity of the graphene sheet. Through
these studies we find chemical pathways that demonstrate beneficiary mechanisms
for the quality of graphene including formation of water as well as suppression
of carbonyl pair holes in favor of hydroxyl and epoxy formation facilitated by
hydrogen gas in the environment.Comment: 9 pages and 9 figures. Animations and movies are available at:
http://qmsimulatorgojpc.wordpress.com
Modeling of graphite oxide
Based on density functional calculations, optimized structures of graphite
oxide are found for various coverage by oxygen and hydroxyl groups, as well as
their ratio corresponding to the minimum of total energy. The model proposed
describes well known experimental results. In particular, it explains why it is
so difficult to reduce the graphite oxide up to pure graphene. Evolution of the
electronic structure of graphite oxide with the coverage change is
investigated.Comment: 12 pages, 7 figures. Discussion about reduction to pure graphene and
several references added. Methodological part expanded. Accepted to J. Am.
Chem. So
Effect of graphene-oxide enhancement on large-deflection bending performance of thermoplastic polyurethane elastomer
This paper was accepted for publication in the journal Composites Part B and the definitive published version is available at http://dx.doi.org/10.1016/j.compositesb.2015.11.033Thermoplastic polyurethane (PU) elastomers are used as shoe-sole materials due to many excellent properties but their inelastic deformation is a serious deficiency for such applications. Hence, graphene oxide (GO) was introduced into the synthesized thermoplastic PU to produce a GO/PU composite material with enhanced properties. Plastic behaviour of this composite was assessed in cyclic tensile tests, demonstrating reduction of irreversible deformations with the addition of GO. Additionally, in order to evaluate mechanical performance of PU and the GO/PU composite under conditions of large-deflection bending typical for shoe soles, finite-element simulations with Abaqus/Standard were conducted. An elastic-plastic finite-element model was developed to obtain detailed mechanical information for PU and the GO/PU composite. The numerical study demonstrated that the plastic area, final specific plastic dissipation energy and residual height for PU specimens were significantly larger than those for the GO/PU composite. Besides, the addition of GO into the PU matrix greatly delayed the onset of plastic deformation in PU in a large-deflection bending process. The average residual height and final specific plastic dissipation energy for PU were approximately 5.6 and 17.7 times as large as those for the studied GO/PU composite. The finite-element analysis provided quantification of the effect of GO enhancement on the large-deflection bending performance of PU for regimes typical for shoe soles and can be used as a basis for optimization of real composite products
Probing the Thermal Deoxygenation of Graphene Oxide using High Resolution In Situ X-Ray based Spectroscopies
Despite the recent developments in Graphene Oxide due to its importance as a
host precursor of Graphene, the detailed electronic structure and its evolution
during the thermal reduction remain largely unknown, hindering its potential
applications. We show that a combination of high resolution in situ X-ray
photoemission and X-ray absorption spectroscopies offer a powerful approach to
monitor the deoxygenation process and comprehensively evaluate the electronic
structure of Graphene Oxide thin films at different stages of the thermal
reduction process. It is established that the edge plane carboxyl groups are
highly unstable, whereas carbonyl groups are more difficult to remove. The
results consistently support the formation of phenol groups through reaction of
basal plane epoxide groups with adjacent hydroxyl groups at moderate degrees of
thermal activation (~400 {\deg}C). The phenol groups are predominant over
carbonyl groups and survive even at a temperature of 1000 {\deg}C. For the
first time a drastic increase in the density of states (DOS) near the Fermi
level at 600 {\deg}C is observed, suggesting a progressive restoration of
aromatic structure in the thermally reduced graphene oxideComment: Pagona Papakonstantinou as Corresponding author, E-mail:
[email protected]
NMR-Based Structural Modeling of Graphite Oxide Using Multidimensional 13C Solid-State NMR and ab Initio Chemical Shift Calculations
Chemically modified graphenes and other graphite-based materials have attracted growing interest for their unique potential as lightweight electronic and structural nanomaterials. It is an important challenge to construct structural models of noncrystalline graphite-based materials on the basis of NMR or other spectroscopic data. To address this challenge, a solid-state NMR (SSNMR)-based structural modeling approach is presented on graphite oxide (GO), which is a prominent precursor and interesting benchmark system of modified graphene. An experimental 2D C-13 double-quantum/single-quantum correlation SSNMR spectrum of C-13-labeled GO was compared with spectra simulated for different structural models using ab initio geometry optimization and chemical shift calculations. The results show that the spectral features of the GO sample are best reproduced by a geometry-optimized structural model that is based on the Lerf-Klinowski model (Lerf, A. et al. Phys. Chem. B 1998, 102, 4477); this model is composed of interconnected sp(2), 1,2-epoxide, and COH carbons. This study also convincingly excludes the possibility of other previously proposed models, including the highly oxidized structures involving 1,3-epoxide carbons (Szabo, I. et al. Chem. Mater. 2006, 18, 2740). C-13 chemical shift anisotropy (CSA) patterns measured by a 2D C-13 CSA/isotropic shift correlation SSNMR were well reproduced by the chemical shift tensor obtained by the ab initio calculation for the former model. The approach presented here is likely to be applicable to other chemically modified graphenes and graphite-based systems
DEBRECEN, AS AN ALGOLOGIST SEES IT = Eső után Debrecen, avagy a terresztris algák virágzása
NUCLEAR-QUADRUPOLE INTERACTION OF MO-99(BETA-)TC-99 IN VARIOUS MOLYBDENUM SULFUR CLUSTER COMPOUNDS AND THERMAL-DECOMPOSITION PRODUCTS OF (NH4)2[MO3S(S2)6].NH2O (N=0-2)
MOTTNER P, LERF A, BUTZ T, et al. NUCLEAR-QUADRUPOLE INTERACTION OF MO-99(BETA-)TC-99 IN VARIOUS MOLYBDENUM SULFUR CLUSTER COMPOUNDS AND THERMAL-DECOMPOSITION PRODUCTS OF (NH4)2[MO3S(S2)6].NH2O (N=0-2). CHEMICAL PHYSICS. 1992;160(2):327-339.The nuclear quadrupole interaction (NQI) of Mo-99(beta-)Tc-99 was measured by time differential perturbed angular correlations (TDPAC) in the following Mo-S-cluster compounds and ions: (NH4)2 [Mo3IVS(S2)6].nH2O (n = 0-2), [Mo3IVSS3(CN)9]5-, (NH4)2[Mo2V(S2)6].2H2O and [Mo2IIIS2(CN)8]6-. All compounds exhibit low NQIs with the exception of (NH4)2-[Mo3IVS(S2)6].nH2O which shows in addition to the low NQI a large fraction of a high NQI, possibly a consequence of the nuclear transmutation. In addition, we studied the thermal decomposition products of the [Mo3S(S2)6]2- cluster towards MoS2.15, which may serve as a model for technical hydrodesulfurization catalysts
Graphene oxide papers modified by divalent ions - Enhancing mechanical properties via chemical cross-linking
Significant enhancement in mechanical stiffness (10-200%) and fracture strength (similar to 50%) of graphene oxide paper, a novel paperlike material made from individual graphene oxide sheets, can be achieved upon modification with a small amount (less than 1 wt %) of Mg2+ and Ca2+. These results (an be readily rationalized in terms of the chemical interactions between the functional groups of the graphene oxide sheets and the divalent metals ions. While oxygen functional groups on the basal planes of the sheets and the carboxylate groups on the edges can both bond to Mg2+ and Ca2+, the main contribution to mechanical enhancement of the paper comes from the latter
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