Won-Jin Moon

Synthesis of WO3@Graphene composite for enhanced photocatalytic oxygen evolution from water

Nano tungsten oxide (WO3) particles were synthesized on the surface of graphene (GR) sheets by using a simple sonochemical method. The obtained composite, WO3@GR, was characterized by X-ray diffraction, N2adsorption/desorption analysis, thermo-gravimetric analysis, Raman spectroscopy and UV-vis diffuse reflectance spectra measurements. It was found that chemical bonds between the nano WO3 particles and the GR sheets were formed. The average particle size of the WO3 was evidenced to be around 12 nm on the GR sheets. When used as photocatalyst for water splitting, the amount of evolved O2 from water for the WO3@GR composite with 40 wt% GR inside was twice and 1.8 times as much as that for pure WO3 and mixed-WO3/GR, respectively. The excellent photocatalytic property of the WO3@GR composite is due to the synergistic effects of the combined nano WO3 particles and GR sheets. The sensitization of WO3 by GR enhances the visible light absorption property of WO3@GR. The chemical bonding between WO3 and GR minimizes the interface defects, reducing the recombination of the photo-generated electron–hole pairs. Furthermore, the GR sheets in the WO3@GR composite enhance electrons transport by providing low resistance conduction pathways, leading to improved photo-conversion efficiency. The methodology opens up a new way of obtaining photoactive GR-semiconductor composites for photodissociating water under visible light.

Carbon-coated SnO2@C with hierarchically porous structures and graphite layers inside for a high-performance lithium-ion battery

A high-performance anode material was prepared from a hierarchically structured activated carbon which contains in situgraphene and nano-graphite. The activated carbon was immersed in a solution of SnCl2·2H2O and subjected to ultrasound. As a result, nanoparticles of SnO2 were uniformly deposited on the surface of the activated carbon. The composite material was then coated with a thin layer of carbon by soaking it in a sucrose solution, followed by carbonization of the adsorbed sucrose at 500 °C. The resulting composite showed an outstanding high-rate cycling performance that can deliver an initial discharge capacity of 1417 mAh g−1 and maintain a discharge capacity of more than 400 mAh g−1 after 100 cycles at a high current density of 1000 mA g−1. This outstanding electrochemical performance is likely to be related to a unique combination of the excellent electrical conductivity of the activated carbon with graphite layers formed inside, its hierarchical pore structure which enhances lithium-ion transportation, and the carbon coating which alleviates the effects of volume changes, shortens the distance for Li+ diffusion, facilitates the transmission of electrons, and keeps the structure stable.

3D hierarchical porous SnO2 derived from self-assembled biological systems for superior gas sensing application,

Mother Nature has always taught us lots about the arcanum of Gods creation, which primarily ties to the wonderful and complex self-assembly of biomolecules even in a mild condition. In the present work, we put forward a bio-inspired strategy, that is, directly bring in biological systems capable of self-assembly to fabricate functionalized hierarchical structures for effective gas sensing. For advanced pollination, biomolecules in pollen coats could self assemble to form bio-structures with effective mass transportablity, and herein were used to guide the self assembly of SnO2-precusors, which finally transferred to SnO2 materials by calcination. Gaining the 3D hierarchical porous structrues formed in the self-assembly of biomolecules, the as-fabricated SnO2 has high connective porous networks from macro- to micro-, and even nanoscale. The specific structures could facilite target gases to quickly transport towards, and then fully react with, the SnO2 nanoparticles, and thus endow the SnO2 with excellent gas response to both reducing gases (C2H5OH and CH3CH2CH3) and oxidising gas (Cl2). This present strategy provides a novel and facile way towards the development of functionallized hierarchical structures by learning from natural self-assembled systems. The resultant hierarchical structures can be extended to other applications in filters, adsorbents, catalysis, thermal, acoustic and electrical insulators, and so on.

Morphological Effects on Surface-Enhanced Raman Scattering from Silver Butterfly Wing Scales Synthesized via Photoreduction

Through a simple room-temperature photoreduction process, this letter conformally replicates 3D submicrometer structures of wing scales from two butterfly species into Ag to generate practical surface-enhanced Raman scattering (SERS) substrates. The Ag replicas of butterfly scales with higher structural periodicity are able to detect rhodamine 6G at a low concentration down to 10(-9) M, which is three orders of magnitude lower than the detectable concentration limit of using quasi-periodic Ag butterfly structures. This result presents a way to select suitable scale morphologies from 174,500 species of Lepidopterans to replicate, as consumable SERS substrates with low cost and high reproducibility.

Bioinspired Au/TiO2 photocatalyst derived from butterfly wing (Papilio Paris)

The reticular hierarchical structure of butterfly wings (Papilio Paris) is introduced as template for Au/TiO(2) photocatalyst by depositing the Au nanoparticles on TiO(2) matrix, which is carried out by a water-ethanol sol-gel procedure combined with subsequent calcination. The obtained Au/TiO(2) nanocomposites present the reticular hierarchical structure of butterfly wings, and Au nanoparticles with an average size of 7 nm are homogeneously dispersed in TiO(2) substrate. Benefiting from such unique reticular hierarchical structure and composition, the biomorphic Au/TiO(2) exhibits high-harvesting capability and presents superior photocatalytic activity. Especially, the biomorphic Au/TiO(2) at the nominal content of gold to titanium of 8 wt% shows the highest photocatalytic activity and can completely decompose methyl orange within 80 min, which is obviously higher than that of commercial Degussa P25 powders.

Bioinspired ultraviolet reflective photonic structures derived from butterfly wings (Euploea)

Butterfly wings have been demonstrated to have potential applications in various optical devices. For complementarily, we extend them to ultraviolet (UV) reflectors, inspired by the UV reflective photonic structures that have been evolved to satisfy UV communication systems of butterflies. UV reflective photonic structures of butterfly wings were replicated in multiscale, and thus endowed the resultant SnO2 materials with enhanced UV reflection. This biomimetic strategy provides us a universal way towards UV reflectors without changing the chemical compositions. Furthermore, the UV reflection could be potentially tuned by choosing different photonic structures of butterfly wings and other bio-species.

Well-aligned ZnO nanorod arrays derived from 2D photonic crystals within peacock feathers

Well-aligned ZnO nanorod arrays are successfully synthesized via a facile immersion and multi-step calcination process using the natural 2D photonic crystals found within peacock feathers as templates. The as-prepared ZnO nanorod arrays possess an array of melanin rods from the peacock feathers and exhibit tunable as well as enhanced photoluminescence in the visible range. The synthesis mechanism is investigated to reveal that the keratin component in peacock feathers can be activated by an EDTA–DMF suspension and provide more COO− groups, which could bind Zn2+ when immersed in the precursor solution. In the succeeding multi-step calcination process, keratin first breaks down at low temperature, so that melanin rods can act as the substrate template for the formation of the ZnO nanorod arrays.

Synthesis of Li1.6(MnM)1.6O4 (M=Cu, Ni, Co, Fe) and Their Physicochemical Properties as a New Precursor for Lithium Adsorbent

New precursors as a Li adsorbent, Li1.6(MnM)1.6O4 (M=Cu, Ni, Co, Fe), were synthesized by hydrothermal method and their physicochemical properties were discussed. XRD and HRTEM results revealed that the original spinel structure was stabilized by cobalt-doping while Cu-, Ni- and Fe-doping led to structural changes. Such a structural stabilization by Cobalt-doping was maintained after lithium leaching by acid treatment. Li absorption efficiency from seawater was significantly enhanced by using the Cobalt-doped spinel manganese oxide, Li1.6(MnCo)1.6O4, compared to the commercially available Li1.33Mn1.67O4; the adsorbed amount of Li from 1g-adsorbent was 35 and 16 mg by Li1.6(MnCo)1.6O4, and Li1.33Mn1.67O4, respectively.

An Approach to Improve the Tensile Ductility of Particle Reinforced Ultrafine-Grained Metallic Composite by Nano-Dispersion Toughening

Nano-Al2O3 dispersoids were introduced and uniformly distributed into the matrix of micron B4Cp reinforced ultrafine-grained Al composite by a “flake powder metallurgy” (flake PM). The resulting B4Cp/Al(Al2O3) hierarchical composite exhibits significant strain hardening and thus enhanced ductility and strength during tensile testing. It is evidenced that engineering the nano-dispersoids into the ultrafine-grained matrix is an effective way to enhance ductility of the ultrafine-grained metallic composites reinforced by micron ceramic particles without losing strength.