Jeong Hoon Byeon

A novel polyol method to synthesize colloidal silver nanoparticles by ultrasonic irradiation.

A polyol synthesis of silver nanoparticles in the presence of ultrasonic irradiation was compared with other configurations (at ambient temperature, 120° C, and 120 °C with injected solutions) in the absence of ultrasonic irradiation in order to obtain systematic results for morphology and size distribution. For applying ultrasonic irradiation, rather fine and uniform spherical silver particles (21±3.7 nm) were obtained in a simple (at ambient temperature without mechanical stirring) and fast (within 4 min, 3.61×10(-3) mol min(-1)) manner than other cases (at ambient temperature (for 8 h, 0.03×10(-3) mol min(-1)): 86±16.8 nm, 120 °C (for 12 min, 1.16×10(-3) mol min(-1)): 64±14.9 nm, and 120 °C with injected solutions (during 12 min): 35±6.8 nm; all other cases contained anisotropic shaped particles). Even though the temperature of polyol reaction reached only at 80 °C (<120 °C) in the presence of ultrasonic irradiation, a uniform mixing (i.e. enhanced collision between silver particle and surrounding components) by ultrasonic irradiation might induce a better formation kinetics and morphological uniformity.

Removal of gaseous toluene and submicron aerosol particles using a dielectric barrier discharge reactor.

A lab-scale dielectric barrier discharge (DBD) reactor was fabricated, and gaseous and particulate contaminant removal tests were carried out under a range of DBD reactor operating conditions: applied voltage (5.0-8.5 kV), frequency (60-1000 Hz), upstream toluene concentration (50-200 ppm) and gas flow rate (1-5 L min(-1) or 0.48-0.096 s of gas residence time). The results suggested that the toluene removal efficiency (at 1 L min(-1), 100 ppm) increased (up to approximately 46%) either with increasing voltage (at 1000 Hz) or frequency (at 8.5 kV). The overall particle collection efficiency (at 1 L min(-1)) improved (up to approximately 60%) with increasing voltage (at 1000 Hz) whereas the penetration of the particles increased (up to approximately 40%) with increasing frequency (at 8.5 kV). The toluene removal efficiency (at 8.5 kV, 1000 Hz, 100 ppm) decreased (down to approximately 29%) with increasing gas flow rate while the particle collection efficiency decreased slightly (maintaining approximately 60%) regardless of the flow rate. In addition, the toluene removal efficiency (down to approximately 41%) and carbon dioxide selectivity (down to approximately 43%) decreased with increasing upstream toluene concentration (at 5 kV, 1000 Hz, 1 L min(-1)).

Aerosol-based fabrication of biocompatible organic-inorganic nanocomposites.

Several novel nanoparticle composites were conveniently obtained by appropriately reacting freshly produced aerosol metal nanoparticles with soluble organic components. A serial reactor consisting of a spark particle generator coupled to a collison atomizer was used to fabricate the new materials, which included nanomagnetosols (comprising iron nanoparticles, the drug ketoprofen, and a Eudragit shell), hybrid nanogels (comprising iron nanoparticles and an N-isopropylacrylamide, NIPAM, gel), and nanoinorganics (gold immobilized silica). A fourth hybrid material, consisting of iron-gold nanoparticles and NIPAM) was obtained via an aerosol into liquid configuration, in which aerosol iron-gold particles were collected into a NIPAM/ethanol solution and then formed into nanogels with NIPAM under ultrasonic treatment. The strategy outlined in this work is potentially generalizable as a new platform for creating biocompatible nanocomposites, using only clinically approved starting materials in a single pass and under low-temperature conditions.

Production of carbonaceous nanostructures from a silver-carbon ambient spark

Using silver-carbon ambient sparks, hollow carbon nanospheres or multiwall carbon nanotubes were produced separately from carbon encapsulated silver nanoparticles (−1,400 K s−1) during relatively slow (−800 K s−1) or fast (−2,900 K s−1) cooling process. Different cooling processes (i.e., different exposures within high temperature) caused the formation of different carbon precipitates in the process of silver mediated graphitization: for −2,900 K s−1 and <−1,400 K s−1, respectively, obtained tubelike and sphere (encapsulated and hollow)-like carbonaceous nanostructures.

Simple fabrication of a Pd-P film on a polymer membrane and its catalytic applications.

Composites were prepared by a surface activation by aerosol deposition of Pd nanoparticles (Pd nano seeds) on a poly(tetrafluoroethylene) membrane and subsequent Pd-P film formation by electroless deposition. Activation of the membrane processed by an ambient Pd spark discharge and subsequent fixation of the spark produced Pd nano seeds. Characterizations for electroless Pd-P films indicated that P entered into the crystal lattice of Pd and formed an alloy. The fabricated composites were applied to catalytic applications of formic acid oxidation (FAO) and toluene conversion (TC). The composite catalysts from the simple activation had more stable performances of FAO and TC than those from the conventional Sn-Pd activation, and their better performances might have originated from better purity due to the simple activation that only introduced pure Pd nano seeds.

Gas-phase self-assembly of highly ordered titania@graphene nanoflakes for enhancement in photocatalytic activity.

The gas-phase self-assembly of reduced graphene oxide (rGO) nanoflakes with highly ordered ultrafine titania (TiO2) particles was performed and the resultant hybrid material displayed an enhanced photocatalytic performance, both in producing hydrogen and in degrading dyes. Freshly synthesized TiO2 nanoparticles (∼35 nm in equivalent mobility diameter) were quantitatively incorporated with nanoscale rGO (∼36 nm in equivalent mobility diameter) in the form of TiO2/rGO hybrid nanoflakes (∼31 nm in equivalent mobility diameter). The TiO2/rGO hybrid flakes were finally employed to evaluate its photocatalytic activity, and it was found that the ability to achieve hydrogen production and dye degradation was greater than that of a hybridized material from commercial p25-TiO2 and large rGO. This gas-phase self-assembly also enhanced the photocatalytic activity by applying different spark configurations to prepare ZnO, Au, or Ag particles incorporated with rGO nanoflakes.

Fabrication of a pure, uniform electroless silver film using ultrafine silver aerosol particles.

To obtain evenly distributed pure Ag particles with a narrow size distribution on a polymer membrane, a novel activation procedure with an environmentally friendly, cost-effective method was utilized as a pretreatment before electroless Ag deposition. The pretreatment was first performed on an untreated membrane surface by collecting ultrafine ambient spark-generated Ag aerosol particles. After annealing, the electroless Ag film was fabricated on the collected aerosol particles in the Ag electroless bath. Experimental characterizations showed that the ultrafine Ag particles were uniformly anchored onto the membrane surface through pretreatment, resulting in a pure Ag film of closely packed particles with a narrow size distribution on the membrane, and the properties were comparable to those of an Ag film on wet Sn-Ag-activated membranes.

Morphology and structure of aerosol carbon-encapsulated metal nanoparticles from various ambient metal-carbon spark discharges.

The morphology and structure of aerosol carbon encapsulated metal nanoparticles (CEMNs) of various transition metals (anode; Ti, Cu, Zn, Mo, Pd, W, Pt, or Au) formed by ambient spark discharge at the same electrical operating specifications were analyzed. CEMNs were produced with aggregated carbon particles, and their yields and sizes varied according to the metal-to-carbon fraction of each discharge relating to the ionization potential of the electrode material. Each encapsulated metal had natural crystallinity for all discharges, but carbon graphitization for the Mo-C and W-C configurations, which have relatively small differences in melting temperature between the materials, was particularly weak. An empty zone in the carbon shell was also detected in the CEMNs because of the difference in density between the molten and solid phases of the core metal during encapsulation.

Au-TiO2 Nanoscale Heterodimers Synthesis from an Ambient Spark Discharge for Efficient Photocatalytic and Photothermal Activity

Ultrafine Au particles incorporating TiO2 heterodimers were synthesized using an ambient heterogeneous spark discharge and the resultant materials were employed both in oxidizing photocatalytically CO gas and killing photothermally cancerous cells. Ti-Au spark configuration was employed to vaporize Ti and Au components into an airflow and finally ultrafine Au particles (∼2 nm in lateral dimension) were incorporated with TiO2 nanoparticles in the form of Au-TiO2 heterodimers (∼38 nm in lateral dimension) with enhanced photocatalytic (in CO oxidation) and photothermal activity (in cancerous cell killing) under visible light. We propose that the localized surface plasmon resonance of ultrafine Au particles on TiO2 supports, induced by the visible light, would promote the adsorption-oxidation of CO and photothermal killing of HeLa cells. The present strategy may be suitable to fabricate other Au-metal oxide nanocomposites for catalytic and biomedical applications.

Silver deposition on a polymer substrate catalyzed by singly charged monodisperse copper nanoparticles.

Aerosol deposition of singly charged monodisperse copper nanoparticles was used to catalytically activate a polymer substrate for electroless silver deposition. An ambient spark discharge was used to produce aerosol copper nanoparticles, and the particles were electrostatically classified at an equivalent mobility diameter of 10 nm, using a nanodifferential mobility analyzer. Deposition of the copper particles onto the surface of the substrate was enhanced by thermophoresis. The copper-deposited substrate was then immersed in a Ag(I) solution, resulting in the electroless deposition of silver (∼17 μm line width) on the previously deposited copper (∼12 μm line width, using a shadow mask with a 100 μm in width patterned stripe). The arithmetic mean roughness and electrical resistivity of the silver pattern were 44.7 nm and 7.9 μΩ cm, respectively, which showed an enhancement compared to those from the nonclassified copper particles (roughness = 162.2 nm, resistivity = 13.3 μΩ cm), because of a more-uniform copper deposition.