12 research outputs found
Guidelines for Tailored Chemical Functionalization of Graphene
Graphene oxide (GO) has been synthesized by the Hummers method with modification of experimental condition by different research groups, but there is no guideline to prepare tailored GO for targeted applications. In this research, we suggest a guideline for tailor-fittable functionalization of graphene on the basis of the scope of our previous report on the two-step oxidation of GO. We describe a detailed procedure for synthesis of GO, effects of degree of step I oxidation on characteristics of GO and comparing them with effects of degree of step II oxidation. Characteristic changes of GO occurring during step I oxidation and those occurring during step II oxidation are different in species of oxygen functional groups, interlayer spacing, thermal stability, size distribution, and yield of GO. On the basis of the results, three types of tailor-fitted GO for a fiber, transparent conducting film, and hydrogen storage material are synthesized by controlling the degree of step I and step II oxidation. Compared to the reference GO synthesized by conventional modified Hummers method, the tailor-fitted GO showed 33.5%, 117%, and 104% enhanced performance in strength of the fiber, figure of merits of transparent conducting film, and hydrogen storage, respectively. Our results show that the performance of GO based application is significantly influenced by the synthesis condition of GO, and optimized performance of the applications can be obtained by the tailor-fitted functionalization of GO. We anticipate that this study would be helpful for a variety of researches, both synthesis and application of GO
Effects of morphological characteristics of Pt nanoparticles supported on poly(acrylic acid)-wrapped multiwalled carbon nanotubes on electrochemical performance of direct methanol fuel cells
Preparation and Exceptional Mechanical Properties of Bone-Mimicking Size-Tuned Graphene Oxide@Carbon Nanotube Hybrid Paper
The self-assembled nanostructures
of carbon nanomaterials possess
a damage-tolerable architecture crucial for the inherent mechanical
properties at both micro- and macroscopic levels. Bone, or “natural
composite,” has been known to have superior energy dissipation
and fracture resistance abilities due to its unique load-bearing hybrid
structure. However, few approaches have emulated the desirable structure
using carbon nanomaterials. In this paper, we present an approach
in fabricating a hybrid composite paper based on graphene oxide (GO)
and carbon nanotube (CNT) that mimicks the natural bone structure.
The size-tuning strategy enables smaller GO sheets to have more cross-linking
reactions with CNTs and be homogeneously incorporated into CNT-assembled
paper, which is advantageous for effective stress transfer. The resultant
hybrid composite film has enhanced mechanical strength, modulus, toughness,
and even electrical conductivity compared to previously reported CNT-GO
based composites. We further demonstrate the usefulness of the size-tuned
GOs as the “stress transfer medium” by performing in
situ Raman spectroscopy during the tensile test
MOF-Derived Hierarchically Porous Carbon with Exceptional Porosity and Hydrogen Storage Capacity
Highly porous carbon has played an important role in
tackling down the energy and environmental problems due to their attractive
features such as high specific surface area (SSA), stability, and
mass productivity. Especially, the desirable characteristics of the
highly porous carbon such as lightweight, fast adsorption/desorption
kinetics, and high SSA have attracted extensive attention in the “hydrogen
storage” application which is a main bottleneck for the realization
of on-board hydrogen fuel cell vehicles. We herein presented porous
carbon with hierarchical pore structure derived from highly crystalline
metal organic frameworks (denoted as MOF-derived carbon: MDC) without
any carbon source and showed it as a promising hydrogen storage adsorbent.
MDCs can be fabricated by a simple heat adjustment of MOFs without
complicated process and environmental burden. The MDC displayed hierarchical
pore structures with high ultramicroporosity, high SSA, and very high
total pore volume. Due to its exceptional porosity, MDCs exhibited
reversible H<sub>2</sub> storage capacities at certain conditions
that were better than those of previously reported porous carbons
and MOFs
Highly Reproducible Thermocontrolled Electrospun Fiber Based Organic Photovoltaic Devices
In
this work, we examined the reasons underlying the humidity-induced
morphological changes of electrospun fibers and suggest a method of
controlling the electrospun fiber morphology under high humidity conditions.
We fabricated OPV devices composed of electrospun fibers, and the
performance of the OPV devices depends significantly on the fiber
morphology. The evaporation rate of a solvent at various relative
humidity was measured to investigate the effects of the relative humidity
during electrospinning process. The beaded nanofiber morphology of
electrospun fibers was originated due to slow solvent evaporation
rate under high humidity conditions. To increase the evaporation rate
under high humidity conditions, warm air was applied to the electrospinning
system. The beads that would have formed on the electrospun fibers
were completely avoided, and the power conversion efficiencies of
OPV devices fabricated under high humidity conditions could be restored.
These results highlight the simplicity and effectiveness of the proposed
method for improving the reproducibility of electrospun nanofibers
and performances of devices consisting of the electrospun nanofibers,
regardless of the relative humidity
Easy Preparation of Self-Assembled High-Density Buckypaper with Enhanced Mechanical Properties
A controlled
assembly and alignment of carbon nanotubes (CNTs) in a high-packing
density with a scalable way remains challenging. This paper focuses
on the preparation of self-assembled and well-aligned CNTs with a
densely packed nanostructure in the form of buckypaper via a simple
filtration method. The CNT suspension concentration is strongly reflected
in the alignment and assembly behavior of CNT buckypaper. We further
demonstrated that the horizontally aligned CNT domain gradually increases
in size when increasing the deposited CNT quantity. The resultant
aligned buckypaper exhibited notably enhanced packing density, strength,
modulus, and hardness compared to previously reported buckypapers
Crucial Role of Oxidation Debris of Carbon Nanotubes in Subsequent End-Use Applications of Carbon Nanotubes
A facile
purification method for oxidized carbon nanotubes (CNTs) is developed
to preserve acidic carbon compounds (ACCs) for achieving high-quality
dispersion of CNTs. The remaining ACCs, which originated from the
surface destruction of CNTs during the oxidation process, are considered
to play a crucial role in the dispersion of CNTs in water and various
polar protic solvents. To elucidate the concrete role of ACCs, a direct
titration method is applied to quantitatively investigate the degree
of ionization of both CNTs and ACCs in their aqueous dispersions.
While ACCs with strong carboxylic groups (p<i>K</i><sub>a</sub> of around 2.9) are easily removed by the neutral or base
washing of oxidized CNTs, which is common in the purification process,
ACC-selective purification using acid washing preserves the ACCs attached
to CNTs, thereby effectively stabilizing CNT dispersions in aqueous
solutions. Additionally, the Hansen solubility parameters of ACC-preserved
and ACC-removed CNTs were determined by the inverse gas chromatography
method to estimate their miscibility in various solvents. The preserved
ACCs significantly influenced the dispersibility of CNTs in polar
protic solvents, which may widen the possible application of CNTs.
Specifically, the ACC-preserved high-quality CNT dispersion produces
high-performance CNT buckypaper with densely packed nanostructures.
The Young’s modulus and tensile strength of these buckypapers
reach up to 12.0 and 91.0 MPa, respectively, which exceed those of
ACC-removed CNTs in previous reports
Hidden Second Oxidation Step of Hummers Method
Hummers
method has been used for 50 years to prepare graphene oxide
(GO) by oxidizing graphite using Mn<sub>2</sub>O<sub>7</sub>. In this
work, a new angle on Hummers method is described. The oxidation procedure
before the addition of water, which has been respected as the main
oxidation step of Hummers method, is named <i>step I oxidation</i>, and the widely ignored further oxidation step after the addition
of water is named <i>step II oxidation</i>. The chemical
and structural evolutions during step II oxidation was demonstrated
for the first time using various techniques including atomic force
microscopy (AFM), dynamic light scattering (DLS), X-ray photoelectron
spectroscopy (XPS), ultraviolet–visible light (UV–vis)
spectroscopy, Fourier-transform infrared spectroscopy (FT-IR), <sup>13</sup>C nuclear magnetic resonance (NMR), and zeta-potentiometry.
Step II oxidation influences the size of GO, defects within the layers,
and functional groups on the surface, which affect the thermal stability
of GO and the properties of resultant thermally reduced GO. This work
provides new chemical insights into GO and guidelines for preparation
of tailor-fitted GO
Carbon science in 2016: Status, challenges and perspectives
cited By 66International audienceSeveral researchers share their perspective on the status and challenges faced by the carbon science in 2016. In addition to chemical vapor deposition (CVD) and hydrosolvo/thermal processes, alternative innovative growth techniques of these hypothetical 3D solids should now be a focus for carbon researchers. Recently, it has been demonstrated that graphene nanoribbons with specific diameters and nanotubes with desired helicity could be synthesized by careful polymerization of aromatic molecules. New theoretical studies using the nanotube/catalyst interface thermodynamics and the kinetic growth theories have widened the understanding of chirality selectivity towards near-armchair tubes. In 2013, a novel method based on aqueous-two polymer phase separation has emerged as an easily accessible and versatile approach for sorting nanotubes which is promising for low-cost scalable production of high-purity SWCNTs. Gel chromatograph based separation methods have also yielded high-purity single chirality optical isomers. New carbon materials are key components in alternative energy technologies that include electrodes for batteries, supercapacitors, fuel cells, and electrolytic cells for hydrogen production from water. They are also of interest as transparent conductors in solar cells, bipolar plates in fuel cells, lightweight materials that save energy in aircraft and automotive operations, and catalysts or catalyst supports for energy transformations that include carbon dioxide reduction into fuels and commercial chemicals