Fluorine-Doped SnO₂@Graphene Porous Composite for High Capacity Lithium-Ion Batteries

For the first time, a composite of fluorine-doped SnO₂ and reduced graphene oxide (F-SnO₂@RGO) was synthesized using a cheap F-containing Sn source, Sn­(BF₄)₂, through a hydrothermal process. X-ray photoelectron spectroscopy and X-ray diffraction results identified that F was doped in the unit cells of the SnO₂ nanocrystals, instead of only on the surfaces of the nanoparticles. F doping of SnO₂ led to more uniform and higher loading of the F-SnO₂ 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-SnO₂@RGO composite exhibited a remarkably high specific capacity (1277 mA h g^–1 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-SnO₂@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-SnO₂ nanoparticles on the surfaces of RGO sheets and the three-dimensional porous structures of the F-SnO₂@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 poly­(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⁺ 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 poly­(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^–2), 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^–1, 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^–1, 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