5 research outputs found
Fluorine-Doped SnO<sub>2</sub>@Graphene Porous Composite for High Capacity Lithium-Ion Batteries
For the first time, a composite of
fluorine-doped SnO<sub>2</sub> and reduced graphene oxide (F-SnO<sub>2</sub>@RGO) was synthesized
using a cheap F-containing Sn source, SnÂ(BF<sub>4</sub>)<sub>2</sub>, through a hydrothermal process. X-ray photoelectron spectroscopy
and X-ray diffraction results identified that F was doped in the unit
cells of the SnO<sub>2</sub> nanocrystals, instead of only on the
surfaces of the nanoparticles. F doping of SnO<sub>2</sub> led to
more uniform and higher loading of the F-SnO<sub>2</sub> nanoparticles
on the surfaces of RGO sheets, as well as enhanced electron transportation
and Li ion diffusion in the composite. As a result, the F-SnO<sub>2</sub>@RGO composite exhibited a remarkably high specific capacity
(1277 mA h g<sup>–1</sup> after 100 cycles), a long-term cycling
stability, and excellent high-rate capacity at large charge/discharge
current densities as anode material for lithium ion batteries. The
outstanding performance of the F-SnO<sub>2</sub>@RGO composite electrode
could be ascribed to the combined features of the composite electrode
that dealt with both the electrode dynamics (enhanced electron transportation
and Li ion diffusion due to F doping) and the electrode structure
(uniform decoration of the F-SnO<sub>2</sub> nanoparticles on the
surfaces of RGO sheets and the three-dimensional porous structures
of the F-SnO<sub>2</sub>@RGO composite)
Composite Films of Poly(3-hexylthiophene) Grafted Single-Walled Carbon Nanotubes for Electrochemical Detection of Metal Ions
In this study, we prepared electrochemically
active films of polyÂ(3-hexylthiophene) grafted single-walled carbon
nanotubes (SWNT-g-P3HT) by using a modified vacuum-assisted deposition
approach, in which a SWNT-g-P3HT composite layer of various thicknesses
was deposited on the top of a thin SWNT layer. Measurement of the
optical and electrical properties of the SWNT-g-P3HT composite films
demonstrated that the thickness of the SWNT-g-P3HT composite films
was controllable. The data of transmission electron microscope observation
and Raman spectroscopy indicated that the covalent grafting of P3HT
onto the surfaces of SWNTs resulted in intimate and stable connectivity
between the two components in the SWNT-g-P3HT composite. Capitalizing
on these unique features, we successfully developed a new class of
electrochemical sensors that used the SWNT-g-P3HT composite films
deposited on an indium–tin oxide substrate as an electrochemical
electrode for detection of metal ions. Significantly, such a SWNT-g-P3HT
composite electrode showed advantages in selective, quantitative,
and more sensitive detection of Ag<sup>+</sup> ions
Graphene Oxide: A Versatile Agent for Polyimide Foams with Improved Foaming Capability and Enhanced Flexibility
Close-celled aromatic polyimide (PI)/graphene
foams with low density
and improved flexibility were fabricated by thermal foaming of polyÂ(amic
ester)/graphene oxide (PAE/GO) precursor powders. The PAE/GO precursor
powders were prepared by grafting GO nanosheets with PAE chains, which
led to efficient dispersion of the GO nanosheets in PAE matrix. Incorporation
of GO resulted in an enhanced foaming capability of the precursor,
i.e., enlarged cell size and decreased foam density. Notably, a decrease
of 50% in the foam density was obtained via the addition of only 2
wt % GO in the precursor. In the foaming process, the GO nanosheets
functioned as a versatile agent that not only provided heterogeneous
nucleation sites but also produced gaseous molecules. By analyzing
the foaming mechanism, the excellent features of GO in heat transfer,
gas barrier, and strength reinforcement also facilitated to obtain
large and uniform cells in the foams. In addition, the PI/graphene
foams exhibited a prominent flexibility and enhanced flexural strength,
as an elastic-to-nonelastic conversion of the initial stage of the
compressive stress–strain curves was observed by increasing
the content of graphene in the PI matrix and an increase of 22.5%
in flexural strength was obtained by addition of 0.5 wt % GO in the
precursor
Conjunction of Conducting Polymer Nanostructures with Macroporous Structured Graphene Thin Films for High-Performance Flexible Supercapacitors
Fabrication
of hybridized structures is an effective strategy to promote the performances
of graphene-based composites for energy storage/conversion applications.
In this work, macroporous structured graphene thin films (MGTFs) are
fabricated on various substrates including flexible graphene papers
(GPs) through an ice-crystal-induced phase separation process. The
MGTFs prepared on GPs (MGTF@GPs) are recognized with remarkable features
such as interconnected macroporous configuration, sufficient exfoliation
of the conductive RGO sheets, and good mechanical flexibility. As
such, the flexible MGTF@GPs are demonstrated as a versatile conductive
platform for depositing conducting polymers (CPs), e.g., polyaniline
(PAn), polypyrrole, and polythiophene, through <i>in situ</i> electropolymerization. The contents of the CPs in the composite
films are readily controlled by varying the electropolymerization
time. Notably, electrodeposition of PAn leads to the formation of
nanostructures of PAn nanofibers on the walls of the macroporous structured
RGO framework (PAn@MGTF@GPs): thereafter, the PAn@MGTF@GPs display
a unique structural feature that combine the nanostructures of PAn
nanofibers and the macroporous structures of RGO sheets. Being used
as binder-free electrodes for flexible supercapacitors, the PAn@MGTF@GPs
exhibit excellent electrochemical performance, in particular a high
areal specific capacity (538 mF cm<sup>–2</sup>), high cycling
stability, and remarkable capacitive stability to deformation, due
to the unique electrode structures
Enhanced Photothermal Bactericidal Activity of the Reduced Graphene Oxide Modified by Cationic Water-Soluble Conjugated Polymer
Surface
modification of graphene is extremely important for applications.
Here, we report a grafting-through method for grafting water-soluble
polythiophenes onto reduced graphene oxide (RGO) sheets. As a result
of tailoring of the side chains of the polythiophenes, the modified
RGO sheets, that is, RGO-<i>g</i>-P3TOPA and RGO-<i>g</i>-P3TOPS, are positively and negatively charged, respectively.
The grafted water-soluble polythiophenes provide the modified RGO
sheets with good dispersibility in water and high photothermal conversion
efficiencies (ca. 88%). Notably, the positively charged RGO-<i>g</i>-P3TOPA exhibits unprecedentedly excellent photothermal
bactericidal activity, because the electrostatic attractions between
RGO-<i>g</i>-P3TOPA and <i>Escherichia coli</i> (<i>E. coli</i>) bind them together, facilitating direct
heat conduction through their interfaces: the minimum concentration
of RGO-<i>g</i>-P3TOPA that kills 100% of <i>E. coli</i> is 2.5 μg mL<sup>–1</sup>, which is only 1/16th of
that required for RGO-<i>g</i>-P3TOPS to exhibit a similar
bactericidal activity. The direct heat conduction mechanism is supported
by zeta-potential measurements and photothermal heating tests, in
which the achieved temperature of the RGO-<i>g</i>-P3TOPA
suspension (2.5 μg mL<sup>–1</sup>, 32 °C) that
kills 100% of <i>E. coli</i> is found to be much lower than
the thermoablation threshold of bacteria. Therefore, this research
demonstrates a novel and superior method that combines photothermal
heating effect and electrostatic attractions to efficiently kill bacteria