Myung-Geun Jeong

Surface Modification of a ZnO Electron-Collecting Layer Using Atomic Layer Deposition to Fabricate High-Performing Inverted Organic Photovoltaics

A ripple-structured ZnO film as the electron-collecting layer (ECL) of an inverted organic photovoltaic (OPV) was modified by atomic layer deposition (ALD) to add a ZnO thin layer. Depositing a thin ZnO layer by ALD on wet-chemically prepared ZnO significantly increased the short-circuit current (Jsc) of the OPV. The highest power conversion efficiency (PCE) of 7.96% with Jsc of 17.9 mA/cm2 was observed in the inverted OPV with a 2-nm-thick ALD-ZnO layer, which quenched electron-hole recombination at surface defects of ZnO ripples. Moreover, an ALD-ZnO layer thinner than 2 nm made the distribution of electrical conductivity on the ZnO surface more uniform, enhancing OPV performance. In contrast, a thicker ALD-ZnO layer (5 nm) made the two-dimensional distribution of electrical conductivity on the ZnO surface more heterogeneous, reducing the PCE. In addition, depositing an ALD-ZnO thin layer enhanced OPV stability and initial performance. We suggest that the ALD-ZnO layer thickness should be precisely controlled to fabricate high-performing OPVs.

Transparent and superhydrophobic films prepared with polydimethylsiloxane-coated silica nanoparticles

We report a versatile and simple two-step method for fabricating superhydrophobic films with optical transparency. Silica nanoparticles were coated with a hydrophobic PDMS thin layer and subsequently fixed onto adhesive surfaces. The water contact angle on the prepared surface was over 150°, which implies that the surface is highly repellent to water. The transparent nature of the fabricated surface and its high chemical and physical stability were also demonstrated. Our method is simple, cost-effective, environment friendly and applicable on a large scale.

Hydrophobic Polydimethylsiloxane (PDMS) Coating of Mesoporous Silica and Its Use as a Preconcentrating Agent of Gas Analytes

Mesoporous silica with mean pore size of ∼14 nm was coated by polydimethylsiloxane (PDMS) using a thermal deposition method. We showed that the inner walls of pores larger than ∼8 nm can be coated by thin layers of PDMS, and the surfaces consisting of PDMS-coated silica were superhydrophobic, with water contact angles close to 170°. We used the PDMS-coated silica as adsorbents of various gas-phase chemical warfare agent (CWA) simulants. PDMS-coated silica allowed molecular desorption of various CWA simulants even after exposure under highly humid conditions and, therefore, is applicable as an agent for the preconcentration of gas-phase analytes to enhance the sensitivities of various sensors.

Fabrication of conductive, transparent and superhydrophobic thin films consisting of multi-walled carbon nanotubes

Polydimethylsiloxane (PDMS) was coated on multi-walled carbon nanotubes (MWCNTs) using a chemical vapour deposition method, and the PDMS-coated MWCNTs were well dispersed in various solvents without additional dispersants. Spin casting of the MWCNT-containing solution on a substrate pre-treated with PDMS-SiO2 nanoparticles resulted in the formation of a uniform thin film. The resulting thin film containing MWCNTs showed high optical transparency, conductivity and superhydrophobicity. We demonstrated that such multifunctional thin films can also be prepared on flexible substrates.

Superhydrophobic carbon fiber surfaces prepared by growth of carbon nanostructures and polydimethylsiloxane coating

AbstractWe prepared nanostructured carbon fiber surfaces using chemical vapor deposition in which Ni nanoparticles were used as carbon nanostructure growth catalysts. The surface of the nanostructured carbon fiber was covered by a thin polydimethylsiloxane film. This surface showed superhydrophobic behavior with a water contact angle close to 170 °C, and its superhydrophobicity was sustained in a wide pH range (1–13).

Direct hydrogenation of biomass-derived butyric acid to n-butanol over a ruthenium-tin bimetallic catalyst.

Catalytic hydrogenation of organic carboxylic acids and their esters, for example, cellulosic ethanol from fermentation of acetic acid and hydrogenation of ethyl acetate is a promising possibility for future biorefinery concepts. A hybrid conversion process based on selective hydrogenation of butyric acid combined with fermentation of glucose has been developed for producing biobutanol. ZnO-supported Ru-Sn bimetallic catalysts exhibits unprecedentedly superior performance in the vapor-phase hydrogenation of biomass-derived butyric acid to n-butanol (>98% yield) for 3500 h without deactivation.

Plasma-Assisted Non-Oxidative Conversion of Methane over Mo/HZSM-5 Catalyst in DBD Reactor

Methane utilization has been recognized as a challenging research topic because methane is very stable with strong C–H bond. Many efforts have been devoted to find an effective method for the methane activation. In this work, we examined the feasibility of decreasing the temperature of a non-oxidative methane dehydroaromatization by using DBD plasma-catalyst hybrid system. Mo/HZSM-5 catalyst was prepared and then it was used for the DBD plasma-assisted methane dehydroaromatization reaction. When the DBD plasma was applied to the Mo/HZSM-5 catalytic reactor, methane was converted at much lower temperatures than the conventional methane dehydroaromatization process. It was also confirmed that benzene selectivity could be improved by enhancing the interaction between plasma and catalyst. These results imply that the non-oxidative methane dehydroaromatization could occur effectively at milder conditions than the conventional process by using the optimized DBD plasma-catalyst hybrid system. Moreover, it was observed that the catalyst deactivation was effectively prevented when H2 gas was mixed with the reaction feed.

Use of NiO/SiO2 catalysts for toluene total oxidation: Catalytic reaction at lower temperatures and repeated regeneration

Abstract We deposited NiO via atomic layer deposition on mesoporous SiO2 particles with diameters of several hundred micrometers and a mean mesopore size of ∼14 nm. NiO was deposited within the shell region of mesoporous SiO2 particles with a shell thickness of ∼11 mm. We annealed the as-prepared NiO/SiO2 at 450 and 600 °C, respectively. These two samples were used as catalysts for the uptake of toluene molecules and their oxidative conversion to CO2. The sample annealed at 450 °C was generally more reactive in toluene uptake and its subsequent conversion to CO2. When the NiO/SiO2 annealed at 450 °C was exposed to toluene vapor at 160 °C and then heated to 450 °C, CO2 was emitted with almost no toluene desorption. We suggest that our catalysts can be used as building blocks for odor removal devices that operate below 200 °C. These catalysts can be regularly regenerated at ∼450 °C.