Functionalization of Tailored Porous Carbon Monolith for Decontamination of Radioactive Substances.

As the control over radioactive species becomes critical for the contemporary human life, the development of functional materials for decontamination of radioactive substances has also become important. In this work, a three-dimensional (3D) porous carbon monolith functionalized with Prussian blue particles was prepared through removal of colloidal silica particles from exfoliated graphene/silica composite precursors. The colloidal silica particles with a narrow size distribution were used to act a role of hard template and provide a sufficient surface area that could accommodate potentially hazardous radioactive substances by adsorption. The unique surface and pore structure of the functionalized porous carbon monolith was examined using electron microscopy and energy-dispersive X-ray analysis (EDS). The effective incorporation of PB nanoparticles was confirmed using diverse instrumentations such as X-ray diffraction (XRD), Fourier-transform infrared (FT-IR), and X-ray photoelectron spectroscopy (XPS). A nitrogen adsorption/desorption study showed that surface area and pore volume increased significantly compared with the starting precursor. Adsorption tests were performed with 133Cs ions to examine adsorption isotherms using both Langmuir and Freundlich isotherms. In addition, adsorption kinetics were also investigated and parameters were calculated. The functionalized porous carbon monolith showed a relatively higher adsorption capacity than that of pristine porous carbon monolith and the bulk PB to most radioactive ions such as 133Cs, 85Rb, 138Ba, 88Sr, 140Ce, and 205Tl. This material can be used for decontamination in expanded application fields.

Revealing molecular-level surface redox sites of controllably oxidized black phosphorus nanosheets.

Bulk and two-dimensional black phosphorus are considered to be promising battery materials due to their high theoretical capacities of 2,600 mAh g-1. However, their rate and cycling capabilities are limited by the intrinsic (de-)alloying mechanism. Here, we demonstrate a unique surface redox molecular-level mechanism of P sites on oxidized black phosphorus nanosheets that are strongly coupled with graphene via strong interlayer bonding. These redox-active sites of the oxidized black phosphorus are confined at the amorphorized heterointerface, revealing truly reversible pseudocapacitance (99% of total stored charge at 2,000 mV s-1). Moreover, oxidized black-phosphorus-based electrodes exhibit a capacitance of 478 F g-1 (four times greater than black phosphorus) with a rate capability of ~72% (compared to 21.2% for black phosphorus) and retention of ~91% over 50,000 cycles. In situ spectroelectrochemical and theoretical analyses reveal a reversible change in the surface electronic structure and chemical environment of the surface-exposed P redox sites.

Hot Electron Transistor with van der Waals Base-Collector Heterojunction and High-Performance GaN Emitter.

Single layer graphene is an ideal material for the base layer of hot electron transistors (HETs) for potential terahertz (THz) applications. The ultrathin body and exceptionally long mean free path maximizes the probability for ballistic transport across the base of the HET. We demonstrate for the first time the operation of a high-performance HET using a graphene/WSe2 van der Waals (vdW) heterostructure as a base-collector barrier. The resulting device with a GaN/AlN heterojunction as emitter, exhibits a current density of 50 A/cm2, direct current gain above 3 and 75% injection efficiency, which are record values among graphene-base HETs. These results not only provide a scheme to overcome the limitations of graphene-base HETs toward THz operation but are also the first demonstration of a GaN/vdW heterostructure in HETs, revealing the potential for novel electronic and optoelectronic applications.

Distortion of DNA Origami on Graphene Imaged with Advanced TEM Techniques.

While graphene may appear to be the ultimate support membrane for transmission electron microscopy (TEM) imaging of DNA nanostructures, very little is known if it poses an advantage over conventional carbon supports in terms of resolution and contrast. Microscopic investigations are carried out on DNA origami nanoplates that are supported onto freestanding graphene, using advanced TEM techniques, including a new dark-field technique that is recently developed in our lab. TEM images of stained and unstained DNA origami are presented with high contrast on both graphene and amorphous carbon membranes. On graphene, the images of the origami plates show severe unwanted distortions, where the rectangular shape of the nanoplates is significantly distorted. From a number of comparative control experiments, it is demonstrated that neither staining agents, nor screening ions, nor the level of electron-beam irradiation cause this distortion. Instead, it is suggested that origami nanoplates are distorted due to hydrophobic interaction of the DNA bases with graphene upon adsorption of the DNA origami nanoplates.

A Comparative Study on Optical, Electrical, and Mechanical Properties of Conducting Polymer-Based Electrodes.

Transparent, free-standing, conducting polypyrrole (PPy) film is successfully fabricated by a simple method using the spin-coating technique. The free-standing PPy film exhibits high transparency, flexibility, electrical conductivity, and stable mechanical properties because the PPy film is composed of densely packed and highly ordered PPy nanoparticles. This approach provides feasible candidate for applications requiring flexible and conducting materials.

Chemical modification of graphene aerogels for electrochemical capacitor applications.

Graphene aerogel is a relatively new type of aerogel that is ideal for energy storage applications because of its large surface area, high electrical conductivity and good chemical stability. Also, three dimensional interconnected macropores offer many advantages such as low density, fast ion and mass transfer, and easy access to storage sites. Such features allow graphene aerogels to be intensively applied for electrochemical capacitor applications. Despite the growing interest in graphene aerogel-based electrochemical capacitors, however, the graphene aerogels still suffer from their low capacitive performances and high fragility. Both relatively low capacitance and brittleness of physically crosslinked graphene aerogels remain a critical challenge. Until now, a number of alternative attempts have been devoted to overcome these shortcomings. In this perspective, we summarize the recent research progress towards the development of advanced graphene aerogel-based electrochemical capacitors according to the different approaches (e.g. porosity, composition and structure controls). Then, the recently proposed chemical strategies to improve the capacitive performances and mechanical durability of graphene aerogels for practical applications are highlighted. Finally, the current challenges and perspectives in this emerging material are also discussed.

[Influence of Tumor Microenvironment of Hepatocellular Carcinoma on the Proliferation of Vascular Endothelial Cells and Vascular Angiogenesis Ability].

To study the potential molecular mechanism of tumor angiogenesis in its microenvironment, we investigated the effects of HepG2 conditioned medium on the proliferation of vascular endothelial cell and vascular angiogenesis in our laboratory. Human umbilical vein endothelial EA. hy926 cells were co-cultured with HepG2 conditioned medium in vitro. The proliferation and the tubulogenesis of EA. hy926 cells were detected by teramethylazo salt azole (MTT) and tube formation assay, respectively. The results showed that the survival rate of the EA. hy926 cells was significantly increased under the co-culture condition. HepG2 conditioned medium also enhanced the angiogenesis ability of EA. hy926 cells. In addition, the expressions of intracellular VEGF and extracellular VEGFR (Flk-1) were regulated upward in a time-dependent manner. In conclusion, the proliferation of vascular endothelial cells and Vascula angiogenesis were improved under the condition of indirect co-culture.

[Effect of Gold (Au) Nanoparticles Modified by Surface Chemistry on the Proliferation and Migration of Hepatocellular Carcinoma Cells in Vitro].

Due to the good tumor-targeting and excellent biocompatibility, the drug-loading nanoparticles (NPs) has been widely applied in the diagnosis and treatment of cancer. However, after the NPs are recognized and internalized by cancer cells, the effects of NPs on cell migration behavior were unclear. In the present study, the self-assembly techniques (SAMs) was used to modify gold (Au) nanoparticles (Au NPs) with different chemical functional groups (CH3, OH, COOH and NH2) as model NPs. The dispersion of these groups in solution and the distribution in cells were studied by transmission electron microscope (TEM), respectively, and the proliferation was examined by MTT assay in vitro. The wound-healing and the Transwell assay were used to examine the effect of internalized Au-NPs on HepG2 cells migration. The results showed that different Au-NPs mainly distributed at the edge of the vesicle membrane and the gap between cells. The Au-NPs resulted in decreased cell viability in a concentration-depended manner. In addition, the results of wound-healing and Transwells assay indicated that the internalization of the NH2-NPs and OH-NPs would inhibit cell migration compared with those in the control group.

[Effect of fluid shear stress on the cellular morphology and tight junction of laryngeal squamous carcinoma Hep2 cells].

This paper is aimed to investigate the effect of fluid shear stress on the tight junction of laryngeal squamous carcinoma (Hep2) cells and to explore the potential molecular mechanism. Hep2 cells were selected and subjected to the fluid shear stress of 1.4 dyn/cm2 for different time, respectively. The morphological changes of Hep2 cells under shear stress were observed using inverted microscope. The cell-cell junctions were examined by transmission electron microscope (TEM). The expressions of tight junction proteins (including Occludin, Claudin-5 and ZO-1) and the distribution of Claudin-5 were examined by Western blot assay and laser scanning confocal microscope, respectively. The results indicated that Hep2 cells turned to spindle-like shapes after exposed to shear stress, and showed the trend of the recovering to original shapes when the shear stress was cancelled. The cell-cell junctions were tight under the shear flow condition, and the permeability was reduced under the condition of 1.4 dyn/cm shear flow. The expressions of tight junction proteins were enhanced with increased duration of shear flow, but reduced after removing shear flow. The result of Claudin-5 expression by immufluorescence assay was consistent with that by Western blot. The Claudin-5 mainly distributed in the cytoplasm under static condition, while it located at the intercellular after shear flow stimulation, and it appeared intercellular and cytoplasm after stopping shear flow stimulation. Therefore, it can be concluded that shear stress changes the morphology of laryngeal squamous carcinoma Hep2 cells, and upregulates the tight junction.

Spatially controlled graphitization of reduced graphene oxide films via a green mechanical approach.

An effective approach to fabricate micropatterned reduced graphene oxide sheets is explored on the basis of the pressure-assisted thermal graphitization as a concept of eco-friendly method. The high pressure can considerably reduce the graphitization temperature and substantially accelerate the kinetics of phase transformation of non-crystalline graphene domain, leading to enhance the degree of graphitization.

Fabrication of Wearable Transistor with All-Graphene Electrodes via Hot Pressing.

Textile electronics are ideal for novel electronic devices owing to their flexibility, light weight, and wearability. In this work, wearable organic field-effect transistors (OFETs) with all-graphene electrodes, fabricated using hot pressing, are described. First, highly conductive and flexible electrodes consisting of a cotton textile substrate and electrochemically exfoliated graphene (EEG) were prepared via hot pressing. The EEG/textile electrodes exhibited a low sheet resistance of 1.3 Ω sq-1 and high flexibility; these were used as gate electrodes in the wearable OFETs. In addition, spray-coated EEG was also used as the source/drain (S/D) electrodes of the wearable OFETs, which recorded a sheet resistance of 14.8 Ω sq-1 after hot pressing. The wearable OFETs exhibited stable electrical performance, a field-effect mobility of 13.8 cm2 V-1 s-1, and an on-off current ratio of ~103 during 1000 cycles of bending. Consequently, the fabrication method for wearable transistors developed using textiles and hot-pressed graphene electrodes has potential applications in next-generation wearable devices.

Comparison of Surface Modification Methods for Improving the Compatibility of Recycled Plastic Film-Based Aggregates.

The surface modification of recycled plastic film-based aggregates was investigated to improve the compatibility between the aggregates and a cement paste. Surface modification was performed using ultraviolet-ozone treatment (UV-O3), a silane coupling agent, O2 atmospheric pressure plasma, and acrylic binder coating methods. The surface properties of the modified aggregates were analyzed using a contact angle measuring instrument. The results revealed that for all surface modification methods, the contact angle decreased with an increase in the treatment time. According to the comparative evaluation results of the changes in the surface characteristics of the aggregates through various surface modification methods, the contact angle reduction rates were 58.9%, 51.4%, 25.5%, and 24.5% for the O2 atmospheric pressure plasma, the acrylic binder coating, the silane coupling agent, and the UV-O3 method, respectively. After 48 h, the contact angle had increased by 110.9%, 29.9%, 16.4%, and 5.9% for the O2 atmospheric pressure plasma, UV-O3, the silane coupling agent, and the acrylic binder coating, respectively. Namely, the surface modification using the acrylic binder coating method was found to be the most effective method in terms of the wettability increase effect and the long-term storage stability.

Development of the Functionalized Nanocomposite Materials for Adsorption/Decontamination of Radioactive Pollutants.

A polymer-based nanofiber membrane with a high specific surface area, high porosity and abundant adsorption sites is demonstrated for selective trapping of radionuclides. The Prussian blue (PB)/poly(methyl methacrylate) (PMMA) nanofiber composites were successfully prepared through a one-step, single-nozzle electrospinning method. Various analytical techniques were used to examine the physical and chemical properties of PB nanoparticles and electrospun nanofibers. It is possible to enhance binding affinity and selectivity to radionuclide targets by incorporation of the PB nanoparticles into the polymer matrix. It is noteworthy that the maximum 133Cs adsorption capacity of hte PB/PMMA nanofiber filter is approximately 28 times higher than that of bulk PB, and the removal efficiency is measured to be 95% at 1 ppm of 133Cs. In addition, adsorption kinetics shows that the PB/PMMA nanofiber has a homogenous surface for adsorption, and all sites on the surface have equal adsorption energies in terms of ion-exchange between cyano groups of the introduced PB nanoparticles and radionuclides.

A Review of Polymer Composites Based on Carbon Fillers for Thermal Management Applications: Design, Preparation, and Properties.

With the development of microelectronic devices having miniaturized and integrated electronic components, an efficient thermal management system with lightweight materials, which have outstanding thermal conductivity and processability, is becoming increasingly important. Recently, the use of polymer-based thermal management systems has attracted much interest due to the intrinsic excellent properties of the polymer, such as the high flexibility, low cost, electrical insulation, and excellent processability. However, most polymers possess low thermal conductivity, which limits the thermal management applications of them. To address the low thermal conduction of the polymer materials, many kinds of thermally conductive fillers have been studied, and the carbon-based polymer composite is regarded as one of the most promising materials for the thermal management of the electric and electronic devices. In addition, the next generation electronic devices require composite materials with various additional functions such as flexibility, low density, electrical insulation, and oriented heat conduction, as well as ultrahigh thermal conductivity. In this review, we introduce the latest papers on thermally conductive polymer composites based on carbon fillers with sophisticated structures to meet the above requirements. The topic of this review paper consists of the following four contents. First, we introduce the design of a continuous three-dimensional network structure of carbon fillers to reduce the thermal resistance between the filler-matrix interface and individual filler particles. Second, we discuss various methods of suppressing the electrical conductivity of carbon fillers in order to manufacture the polymer composites that meet both the electrical insulation and thermal conductivity. Third, we describe a strategy for the vertical alignment of carbon fillers to improve the through-plane thermal conductivity of the polymer composite. Finally, we briefly mention the durability of the thermal conductivity performance of the carbon-based composites. This review presents key technologies for a thermal management system of next-generation electronic devices.

Giant enhancement of third-harmonic generation in graphene-metal heterostructures.

Nonlinear nanophotonics leverages engineered nanostructures to funnel light into small volumes and intensify nonlinear optical processes with spectral and spatial control. Owing to its intrinsically large and electrically tunable nonlinear optical response, graphene is an especially promising nanomaterial for nonlinear optoelectronic applications. Here we report on exceptionally strong optical nonlinearities in graphene-insulator-metal heterostructures, which demonstrate an enhancement by three orders of magnitude in the third-harmonic signal compared with that of bare graphene. Furthermore, by increasing the graphene Fermi energy through an external gate voltage, we find that graphene plasmons mediate the optical nonlinearity and modify the third-harmonic signal. Our findings show that graphene-insulator-metal is a promising heterostructure for optically controlled and electrically tunable nano-optoelectronic components.

Kinetic study of the formation of polypyrrole nanoparticles in water-soluble polymer/metal cation systems: a light-scattering analysis.

A facile way to synthesize nanometer-sized polymer (polypyrrole, PPy) particles is explored on the basis of the formation of complexes between water-soluble polymers and metal cations in aqueous solution. The metal cation is used as an oxidizing agent to initiate the chemical oxidation polymerization of the corresponding monomer, and the water-soluble polymer effectively provides a steric stability for the growth of polymer nanoparticles during the polymerization process. Light-scattering analyses are performed to give insight into the behavior of the complexes in aqueous solution. In addition, major physical parameters affecting the formation of polymer nanoparticles are investigated, including hydrodynamic radius, radius of gyration, shape factor, and viscosity. By judicious control of these parameters, PPy nanoparticles with narrow size distribution can be readily fabricated in large quantities. It is also possible to control the diameter of the nanoparticles by changing critical synthetic variables. Importantly, PPy nanoparticles of approximately 20-60 nm in diameter can be prepared without using any surfactants or specific templates; this novel strategy offers great possibility for mass production of polymer nanoparticles.

Preparation of Porous Carbon Nanofibers with Tailored Porosity for Electrochemical Capacitor Electrodes.

Porous carbon electrodes that accumulate charges at the electrode/electrolyte interface have been extensively investigated for use as electrochemical capacitor (EC) electrodes because of their great attributes for driving high-performance energy storage. Here, we report porous carbon nanofibers (p-CNFs) for EC electrodes made by the formation of a composite of monodisperse silica nanoparticles and polyacrylonitrile (PAN), oxidation/carbonization of the composite, and then silica etching. The pore features are controlled by changing the weight ratio of PAN to silica nanoparticles. The electrochemical performances of p-CNF as an electrode are estimated by measuring cyclic voltammetry and galvanostatic charge/discharge. Particularly, the p-CNF electrode shows exceptional areal capacitance (13 mF cm-2 at a current of 0.5 mA cm-2), good rate-retention capability (~98% retention of low-current capacitance), and long-term cycle stability for at least 5000 charge/discharge cycles. Based on the results, we believe that this electrode has potential for use as high-performance EC electrodes.

Far-field excitation of single graphene plasmon cavities with ultracompressed mode volumes.

Acoustic graphene plasmons are highly confined electromagnetic modes carrying large momentum and low loss in the mid-infrared and terahertz spectra. However, until now they have been restricted to micrometer-scale areas, reducing their confinement potential by several orders of magnitude. Using a graphene-based magnetic resonator, we realized single, nanometer-scale acoustic graphene plasmon cavities, reaching mode volume confinement factors of ~5 × 1010 Such a cavity acts as a mid-infrared nanoantenna, which is efficiently excited from the far field and is electrically tunable over an extremely large broadband spectrum. Our approach provides a platform for studying ultrastrong-coupling phenomena, such as chemical manipulation via vibrational strong coupling, as well as a path to efficient detectors and sensors operating in this long-wavelength spectral range.

Integrin-Induced Signal Event Contributes to Self-Assembled Monolayers on Au-Nanoparticle-Regulated Cancer Cell Migration and Invasion.

Gold nanoparticles (Au NPs) have received much attention because of their distinct physicochemical properties. The surface terminal functional groups of Au NPs can facilitate easy conjugation with biological molecules for targeting cancer cells and controlling drugs/genes release. However, little is known regarding molecular mechanisms involved in their regulation of cancer cell migration and invasion. In the present study, Au NPs were successfully conjugated with functional groups (CH3, NH2, OH and COOH) by self-assembled monolayer (SAM) technique. The endocytosis of SAM-Au NPs mediating HepG2 cell migration and invasion in integrin-induced cascaded events were examined. Our results showed that the combination of integrins-Caveolin-1 together contributed to the internalization of SAM-Au NPs. The CH3-Au NPs showed fast cell motility than COOH- and OH- groups by upregulating PI3K expression, but reducing FAK phosphorylation level. Additionally, CH3-Au NPs showed the strongest activated GTP-bound Rac1 and RhoA. Taken together, these results concluded that internalization of SAM-Au NPs inhibited cancer cell migration via FAK/PI3K and downstream Rho-GTPase signaling pathway in a time-dependent manner. This work provides a further understanding of SAM-Au NPs regulating cancer cell migration, which might be helpful to functionalize the Au NP surface in drug delivery system.

Correction: All-solution-processed, flexible thin-film transistor based on PANI/PETA as gate/gate insulator.

[This corrects the article DOI: 10.1039/C5RA23848J.].