A. Reum Park

Green Synthesis of Biphasic TiO2–Reduced Graphene Oxide Nanocomposites with Highly Enhanced Photocatalytic Activity

A series of TiO(2)-reduced graphene oxide (RGO) nanocomposites were prepared by simple one-step hydrothermal reactions using the titania precursor, TiCl(4) and graphene oxide (GO) without reducing agents. Hydrolysis of TiCl(4) and mild reduction of GO were simultaneously carried out under hydrothermal conditions. While conventional approaches mostly utilize multistep chemical methods wherein strong reducing agents, such as hydrazine, hydroquinone, and sodium borohydride are employed, our method provides the notable advantages of a single step reaction without employing toxic solvents or reducing agents, thereby providing a novel green synthetic route to produce the nanocomposites of RGO and TiO(2). The as-synthesized nanocomposites were characterized by several crystallographic, microscopic, and spectroscopic characterization methods, which enabled confrimation of the robustness of the suggested reaction scheme. Notably, X-ray diffraction and transmission electron micrograph proved that TiO(2) contained both anatase and rutile phases. In addition, the photocatalytic activities of the synthesized composites were measured for the degradation of rhodamine B dye. The catalyst also can degrade a colorless dye such as benzoic acid under visible light. The synthesized nanocomposites of biphasic TiO(2) with RGO showed enhanced catalytic activity compared to conventional TiO(2) photocatalyst, P25. The photocatalytic activity is strongly affected by the concentration of RGO in the nanocomposites, with the best photocatalytic activity observed for the composite of 2.0 wt % RGO. Since the synthesized biphasic TiO(2)-RGO nanocomposites have been shown to effectively reduce the electron-hole recombination rate, it is anticipated that they will be utilized as anode materials in lithium ion batteries.

Single-step solvothermal synthesis of mesoporous Ag–TiO2–reduced graphene oxide ternary composites with enhanced photocatalytic activity

With growing interest in the photocatalytic performance of TiO2-graphene composite systems, the ternary phase of TiO2, graphene, and Ag is expected to exhibit improved photocatalytic characteristics because of the improved recombination rate of photogenerated charge carriers and potential contribution of the generation of localized surface plasmon resonance at Ag sites on a surface of the TiO2-graphene binary matrix. In this work, Ag-TiO2-reduced graphene oxide ternary nanocomposites were successfully synthesized by a simple solvothermal process. In a single-step synthetic procedure, the reduction of AgNO3 and graphene oxide and the hydrolysis of titanium tetraisopropoxide were spontaneously performed in a mixed solvent system of ethylene glycol, N,N-dimethylformamide and a stoichiometric amount of water without resorting to the use of typical reducing agents. The nanocomposites were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, along with different microscopic and spectroscopic techniques, enabling us to confirm the successful reduction of AgNO3 and graphite oxide to metallic Ag and reduced graphene oxide, respectively. Due to the highly facilitated electron transport of well distributed Ag nanoparticles, the synthesized ternary nanocomposite showed enhanced photocatalytic activity for degradation of rhodamine B dye under visible light irradiation.

Nanomesh‐Structured Ultrathin Membranes Harnessing the Unidirectional Alignment of Viruses on a Graphene‐Oxide Film

DOI: 10.1002/adma.201305862 However, strong van der Waals interactions and subsequent irreversible aggregation of the nanomaterials makes it unlikely for the assembled system to exhibit unidirectional alignment. This limitation can be overcome by employing “intelligent” (i.e., responsive) and fl exible one-dimensionally structured biomaterials. [ 11,12 ] The self-assembled structures of M13 viruses are an example; their mechanical stiffness and structural characteristics are readily controlled by manipulating the environmental pH or the type of bonding with the underlying substrate. [ 13,14 ]

Ag Nanoparticle/Polydopamine-Coated Inverse Opals as Highly Efficient Catalytic Membranes

Polymeric three-dimensional inverse-opal (IO) structures provide unique structural properties useful for various applications ranging from optics to separation technologies. Despite vast needs for IO functionalization to impart additional chemical properties, this task has been seriously challenged by the intrinsic limitation of polymeric porous materials that do not allow for the easy penetration of waterborne moieties or precursors. To overcome this restriction, we present a robust and straightforward method of employing a dipping-based surface modification with polydopamine (PDA) inside the IO structures, and demonstrate their application to catalytic membranes via synthetic incorporation of Ag nanoparticles. The PDA coating offers simultaneous advantages of achieving the improved hydrophilicity required for the facilitated infiltration of aqueous precursors and successful creation of nucleation sites for a reduction of growth of the Ag nanoparticles. The resulting Ag nanoparticle-incorporated IO structures are utilized as catalytic membranes for the reduction of 4-nitrophenol to its amino derivatives in the presence of NaBH4. Synergistically combined characteristics of high reactivity of Ag nanoparticles along with a greatly enhanced internal surface area of IO structures enable the implementation of remarkably improved catalytic performance, exhibiting a good conversion efficiency greater than 99% while minimizing loss in the membrane permeability.

Si–Mn/Reduced Graphene Oxide Nanocomposite Anodes with Enhanced Capacity and Stability for Lithium-Ion Batteries

Although Si is a promising high-capacity anode material for Li-ion batteries (LIB), it suffers from capacity fading due to excessively large volumetric changes upon Li insertion. Nanocarbon materials have been used to enhance the cyclic stability of LIB anodes, but they have an inherently low specific capacity. To address these issues, we present a novel ternary nanocomposite of Si, Mn, and reduced graphene oxide (rGO) for LIB anodes, in which the Si-Mn alloy offers high capacity characteristics and embedded rGO nanosheets confer structural stability. Si-Mn/rGO ternary nanocomposites were synthesized by mechanical complexation and subsequent thermal reduction of mixtures of Si nanoparticles, MnO2 nanorods, and rGO nanosheets. Resulting ternary nanocomposite anodes displayed a specific capacity of 600 mAh/g with ∼90% capacity retention after 50 cycles at a current density of 100 mA/g. The enhanced performance is attributed to facilitated Li-ion reactions with the MnSi alloy phase and the formation of a structurally reinforced electroconductive matrix of rGO nanosheets. The ternary nanocomposite design paradigm presented in this study can be exploited for the development of high-capacity and long-life anode materials for versatile LIB applications.

Si/Ti2O3/Reduced Graphene Oxide Nanocomposite Anodes for Lithium-Ion Batteries with Highly Enhanced Cyclic Stability

Silicon (Si) has attracted tremendous attention as a high-capacity anode material for next generation Li-ion batteries (LIBs); unfortunately, it suffers from poor cyclic stability due to excessive volume expansion and reduced electrical conductivity after repeated cycles. To circumvent these issues, we propose that Si can be complexed with electrically conductive Ti2O3 to significantly enhance the reversible capacity and cyclic stability of Si-based anodes. We prepared a ternary nanocomposite of Si/Ti2O3/reduced graphene oxide (rGO) using mechanical blending and subsequent thermal reduction of the Si, TiO2 nanoparticles, and rGO nanosheets. As a result, the obtained ternary nanocomposite exhibited a specific capacity of 985 mAh/g and a Coulombic efficiency of 98.4% after 100 cycles at a current density of 100 mA/g. Furthermore, these ternary nanocomposite anodes exhibited outstanding rate capability characteristics, even with an increased current density of 10 A/g. This excellent electrochemical performance can be ascribed to the improved electron and ion transport provided by the Ti2O3 phase within the Si domains and the structurally reinforced conductive framework comprised of the rGO nanosheets. Therefore, it is expected that our approach can also be applied to other anode materials to enable large reversible capacity, excellent cyclic stability, and good rate capability for high-performance LIBs.

Multiscale Porous Interconnected Nanocolander Network with Tunable Transport Properties

A nanocolander network is developed by embedding mesoporous block copolymers inside the structural frame of a macroporous inverse-opal structure. Spontaneously formed macroconduits interconnecting the macropores are utilized as internal bypasses for enhancing the bulk transport properties. A demonstrative application for the membrane of the nanocolander network is of perfect size-selectivity for nanoparticle separation without compromising the high permeability of the transporting medium.

Porous MoS2@C heteroshell with a Si yolk structure with improved lithium transport properties and superior cycle stability

To solve the problems of the Si anode such as excessive volume expansion and the corresponding destruction of the solid electrolyte interface (SEI) film, we propose a porous MoS2@C heteroshell with a Si yolk structure. We prepared a porous MoS2@C heteroshell with a Si yolk structure using polydopamine (PDA) polymerization and a hydrothermal method using sodium molybdate and L-cysteine. In particular, the PDA layer on the Si yolk plays a role as a medium in growing the MoS2 shell as a MoS2@C heteroshell. We proposed Si@C@MoS2 (SCM) structures having different MoS2 shell thicknesses (SCM1, SCM3, SCM5 in the order of shell thickness) and measured various electrochemical properties. When the MoS2 shell was thin (SCM1), it exhibited a high specific capacity of 1451 mA h g−1 with a coulombic efficiency of 86.6% after 100 cycles at a current density of 100 mA g−1 (1st cycle), 200 mA g−1 (2nd cycle), and 500 mA g−1 (3rd cycle and following cycles). Furthermore, it shows excellent rate capability even at high current density compared to the Si@C electrode. When the MoS2 shell was thick (SCM5), ultrahigh electrochemical output properties and rate capability were exhibited although it shows low absolute capacity because of the high MoS2 weight ratio. From the results, we found that the thin MoS2 coating on the carbon shell had advantages compared to only the carbon shell because of the remarkable Li ion transport properties of MoS2. It was also found that there is a trade-off between the MoS2@C heteroshell thickness and the participation of Si in electrochemical reactions. In addition, the initial coulombic efficiency depended on the MoS2 shell thickness. This excellent electrochemical phenomenon was attributed to the high specific surface area and high ion conductivity of MoS2. Therefore, it is expected that these phenomena can also be applied to other anode materials to enable excellent cyclic stability and good rate capability for high performance Li ion batteries.