Eunwoo Lee

Synthesis of TiO2 nanorod-decorated graphene sheets and their highly efficient photocatalytic activities under visible-light irradiation.

The titanium dioxide (TiO(2)) nanorod-decorated graphene sheets photocatalysts with different TiO(2) nanorods population have been synthesized by a simple non-hydrolytic sol-gel approach. Electron microscopy and X-ray diffraction analysis indicated that the TiO(2) nanorods are well-dispersed and successfully anchored on the graphene sheet surface through the formation of covalent bonds between Ti and C atoms. The photocatalytic activities are evaluated in terms of the efficiencies of photodecomposition and adsorption of methylene blue (MB) in aqueous solution under visible-light irradiation. The as-synthesized TiO(2) nanorod-decorated graphene sheets showed unprecedented photodecomposition efficiency compared to the pristine TiO(2) nanorods and the commercial TiO(2) (P-25, Degussa) under visible-light. It is believed that this predominant photocatalytic activity is due to the synergistic contribution of both a retarded charge recombination rate caused by a high electronic mobility of graphene and an increased surface area originated from nanometer-sized TiO(2) nanorods. Furthermore, photoelectrochemical study is performed to give deep insights into the primary roles of graphene that determines the photocatalytic activity.

Enhanced antigen‐presenting activity and tumour necrosis factor‐α‐independent activation of dendritic cells following treatment with Mycobacterium bovis bacillus Calmette–Guérin

Dendritic cells (DCs) are most potent among the antigen‐presenting cells and are believed to be crucial for the initiation of a primary T‐cell response to foreign antigens. Mycobacterial infection within macrophages is controlled by cell‐mediated immunity. To elucidate the stimulation of immune response by Mycobacterium bovis bacillus Calmette–Guérin (BCG), we purified DCs from precursor cells in human peripheral blood mononuclear cells (PBMC) by culturing them with granulocyte–macrophage colony‐stimulating factor (GM‐CSF) and interleukin‐4 (IL‐4) and characterized their surface antigen expression. The interaction of cultured DCs with BCG resulted in increased surface expression of several DC‐related marker antigens. BCG also induced reduction of endocytosis, enhancement of CD83 expression as well as B7 costimulatory molecules and IL‐12 production, suggesting that BCG treatment directly induces DCs to mature. BCG‐treated DCs were much more potent antigen‐presenting cells in allogeneic immune response than untreated DCs. Moreover, while the neutralization of tumour necrosis factor‐α (TNF‐α) significantly blocked the DC maturation induced by lipopolysaccharide (LPS), it could not inhibit the induction of DC maturation by the BCG treatment, indicating that TNF‐α production plays a minor role in the BCG‐induced DC maturation. However, the neutralization of TNF‐α resulted in decreased IL‐12 production by activated DCs. These results suggest that infection with BCG might evoke direct activation and maturation of DC and the general immune stimulant effect of BCG might be related with the activation of DCs.

Electro-responsive and dielectric characteristics of graphene sheets decorated with TiO2 nanorods

Titanium dioxide (TiO2) nanorod-decorated graphene sheets have been synthesized by a simple non-hydrolytic sol–gel approach and demonstrated to be a highly effective dispersing material for electrorheological fluids. Electron microscopy and X-ray diffraction analysis indicated that the TiO2 nanorods with a high crystallinity are well-dispersed and successfully anchored on the graphene sheet surface through the formation of covalent bonds between Ti and C atoms. Furthermore, electro-responsive properties of graphene sheets decorated with TiO2 nanorods are investigated on the basis of the dielectric loss model. The dielectric property analysis based on the dielectric loss model clarifies that an introduction of TiO2 nanorods has been coupled with the larger achievable polarizability and short relaxation time of interfacial polarization. Consequently, the TiO2 nanorod-decorated graphene sheets exhibit consistently higher ER efficiency than that of GO sheets and show unprecedented electro-responsive performance in extremely low concentration ER materials (<0.2 wt%).

High-Performance Förster Resonance Energy Transfer (FRET)-Based Dye-Sensitized Solar Cells: Rational Design of Quantum Dots for Wide Solar-Spectrum Utilization

High-performance Förster resonance energy transfer (FRET)-based dye-sensitized solar cells (DSSCs) have been successfully fabricated through the optimized design of a CdSe/CdS quantum-dot (QD) donor and a dye acceptor. This simple approach enables quantum dots and dyes to simultaneously utilize the wide solar spectrum, thereby resulting in high conversion efficiency over a wide wavelength range. In addition, major parameters that affect the FRET interaction between donor and acceptor have been investigated including the fluorescent emission spectrum of QD, and the content of deposited QDs into the TiO2 matrix. By judicious control of these parameters, the FRET interaction can be readily optimized for high photovoltaic performance. In addition, the as-synthesized water-soluble quantum dots were highly dispersed in a nanoporous TiO2 matrix, thereby resulting in excellent contact between donors and acceptors. Importantly, high-performance FRET-based DSSCs can be prepared without any infrared (IR) dye synthetic procedures. This novel strategy offers great potential for applications of dye-sensitized solar cells.

A graphene quantum dots based fluorescent sensor for anthrax biomarker detection and its size dependence

Graphene quantum dots (GQDs) with two different diameters were modified with a EuIII-macromolecule complex and applied in dual emission fluorescent sensors for detection of Bacillus anthracis spores. The Eu-GQD sensors exhibited a morphology of ultrafine particles, increased surface-to-volume ratio, enhanced dispersibility, and extraordinary sensitivity. The 3 nm Eu-GQDs showed three emission bands, which are ascribed to the emission from the blue GQDs (435 nm) and the red [(Eu)-(DPA)] complex (593 nm and 616 nm). Accordingly, incorporation of the GQDs as a non-interfering internal calibration makes it possible for use as a ratiometric sensor. The time dependent fluorescence response study revealed that the reaction was complete within 8 s, thus enabling rapid detection of B. anthracis spores. It is noteworthy that the Eu-GQD sensors exhibited an extraordinary limit of detection (LOD) of ca. 10 pM towards B. anthracis, which is six orders of magnitude smaller than the infectious dose of the spores (60 μM). Furthermore, the selectivity study indicates that Eu-GQD sensors have an outstanding selectivity of 103-fold for DPA over competing aromatic ligands.

Self-Assembled Poly(3,4-ethylene dioxythiophene):Poly(styrenesulfonate)/Graphene Quantum Dot Organogels for Efficient Charge Transport in Photovoltaic Devices

UNLABELLED We report the self-assembly of poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) ( PEDOT PSS) organogel films incorporating graphene quantum dots (GQDs). Because of the electrostatic interaction between the GQDs and the PEDOT chains, GQD@PEDOT core-shell nanostructures are readily formed. We demonstrate that the GQDs affect the reorientation of PEDOT chains and the formation of interconnected structure of PEDOT-rich domains, improving the charge transport pathway. The power conversion efficiency of the organic photovoltaic device containing the self-assembled organogel as the hole extraction layer (HEL) was 26% higher than the device with pristine PEDOT-PSS as the HEL.

Large anomalous Hall current induced by topological nodal lines in a ferromagnetic van der Waals semimetal

Topological semimetals host electronic structures with several band-contact points or lines and are generally expected to exhibit strong topological responses. Up to now, most work has been limited to non-magnetic materials and the interplay between topology and magnetism in this class of quantum materials has been largely unexplored. Here we utilize theoretical calculations, magnetotransport and angle-resolved photoemission spectroscopy to propose Fe3GeTe2, a van der Waals material, as a candidate ferromagnetic (FM) nodal line semimetal. We find that the spin degree of freedom is fully quenched by the large FM polarization, but the line degeneracy is protected by crystalline symmetries that connect two orbitals in adjacent layers. This orbital-driven nodal line is tunable by spin orientation due to spin–orbit coupling and produces a large Berry curvature, which leads to a large anomalous Hall current, angle and factor. These results demonstrate that FM topological semimetals hold significant potential for spin- and orbital-dependent electronic functionalities.A combined experimental and theoretical approach identifies the van der Waals material Fe3GeTe2 as a candidate ferromagnetic nodal line semimetal. These results extend the connections between topology and magnetism.