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330 results on '"Joo, Ji Bong"'

143. Synthesis of tailored Au@TiO2 core–shell nanoparticles for photocatalytic reforming of ethanol.

Author

Goebl, James, Joo, Ji Bong, Dahl, Michael, and Yin, Yadong

Subjects
*TITANIUM dioxide, *GOLD compound synthesis, *STRUCTURAL shells, *METAL nanoparticles, *PHOTOCATALYSIS, *CATALYTIC reforming, *ETHANOL, *CATALYTIC activity
Abstract

Highlights: [•] We have developed a technique for coating TiO2 shells on Au nanoparticles. [•] We can tune the shell thickness over a wide range with minimal coating steps. [•] Catalytic properties were studied under UV irradiation. [•] Catalytic activity is optimal at a weight percent of 0.731%. [•] Catalytic activity is optimal when the sample is processed at 600°C. [ABSTRACT FROM AUTHOR]

Published
2014
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144. Nitridation and Layered Assembly of Hollow TiO2 Shells for Electrochemical Energy Storage.

Author

Moon, Geon Dae, Joo, Ji Bong, Dahl, Michael, Jung, Heejung, and Yin, Yadong

Subjects
*NITRIDATION, *TITANIUM dioxide, *ELECTROCHEMISTRY, *ENERGY storage, *ELECTRODES, *MOLECULAR self-assembly, *SUPERCAPACITORS
Abstract

The nitridation of hollow TiO2 nanoshells and their layered assembly into electrodes for electrochemical energy storage are reported. The nitridated hollow shells are prepared by annealing TiO2 shells, produced initially using a sol-gel process, under an NH3 environment at different temperatures ranging from 700 to 900 °C, then assembled to form a robust monolayer film on a water surface through a quick and simple assembly process without any surface modification to the samples. This approach facilitates supercapacitor cell design by simplifying the electrochemical electrode structure by removing the need to use any organic binder or carbon-based conducting materials. The areal capacitance of the as-prepared electrode is observed to be ≈180 times greater than that of a bare TiO2 electrode, mainly due to the enhanced electrical conductivity of the TiN phase produced through the nitridation process. Furthermore, the electrochemical capacitance can be enhanced linearly by constructing an electrode with multilayered shell films through a repeated transfer process (0.8 to 7.1 mF cm-2, from one monolayer to 9 layers). Additionally, the high electrical conductivity of the shell film makes it an excellent scaffold for supporting other psuedocapacitive materials (e.g., MnO2), producing composite electrodes with a specific capacitance of 743.9 F g-1 at a scan rate of 10 mV s-1 (based on the mass of MnO2) and a good cyclic stability up to 1000 cycles. [ABSTRACT FROM AUTHOR]

Published
2014
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145. Controllable Synthesis of Mesoporous TiO2 Hollow Shells: Toward an Efficient Photocatalyst.

Author

Joo, Ji Bong, Lee, Ilkeun, Dahl, Michael, Moon, Geon Dae, Zaera, Francisco, and Yin, Yadong

Subjects
*CRYSTALLINITY, *MESOPOROUS materials, *PHOTOCATALYSTS, *ORGANIC dyes, *BIOCHEMICAL substrates
Abstract

TiO2 hollow shells with well-controlled crystallinity, phase, and porosity are desirable in many applications. In photocatalysis in particular, they can provide high active surface area, reduced diffusion resistance, and improved accessibility to reactants. Here, the results from studies of the causes for the failure of a prior etching and calcination scheme to make such shells and on a newly-developed simple yet robust process for producing uniform mesoporous TiO2 shells with precisely controllable crystallinity and phase are reported. The key finding is that base etching of the SiO2@TiO2 core-shell particles leads to the formation of sodium titanate species, which, if not removed, promote substantial crystal growth during calcination and destroy the structural integrity of the TiO2 shells. A simple acid treatment of the base-etched samples may convert the sodium titanates into protonated titanates, which not only prevent the formation of the impurity phases, but also help to maintain the structural integrity of the shell and allow precise control of the TiO2 phase and crystallinity. This new development affords convenient optimization of the structure of the hollow TiO2 shells toward efficient photocatalysts, which outperform the commercial P25-TiO2 in the photocatalytic decomposition of organic dye molecules. [ABSTRACT FROM AUTHOR]

Published
2014
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146. Graphene derivatives supported nanocatalysts for oxygen reduction reaction

Author

Lee, Ilkeun, Joo, Ji Bong, and Shokouhimehr, Mohammadreza

Abstract

Very recent progress on the graphene derivatives supported variable nanocatalysts for oxygen reduction reaction (ORR) in fuel cell is reviewed. First, common electrochemical techniques to characterize graphene-based electrocatalysts are mentioned. Second, recent updates on graphene-derived electrocatalysts are introduced. In this part, both electrochemical activity and stability of Pt catalysts can be improved when they are supported by reduced graphene oxide (RGO). Other noble-metal catalysts including Pd, Au, and Ag showing comparable performance have been investigated. The stability of Pd catalyst is enhanced by RGO or few-layered graphene support. Synthetic approaches for Au or Ag catalysts supported on graphene oxide are discussed. In addition, non-noble transition metals in N4-chelate complexes can reduce oxygen electrochemically. Fe and Co are cheap alternative catalysts for ORR. In most cases, the stability and tolerance issues are overcome well, but their overall performances don't seem to surpass Pt/C catalyst yet.

Published
2015
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147. A Sulfated ZrO2 Hollow Nanostructure as an Acid Catalyst in the Dehydration of Fructose to 5-Hydroxymethylfurfural.

Author

Joo, Ji Bong, Vu, Austin, Zhang, Qiao, Dahl, Michael, Gu, Minfen, Zaera, Francisco, and Yin, Yadong

Subjects
MESOPOROUS materials, METAL clusters, CATALYSIS, DIFFUSION, NANOPARTICLES
Abstract

Mesoporous hollow colloidal particles with well-defined characteristics have potential use in many applications. In liquid-phase catalysis, in particular, they can provide a large active surface area, reduced diffusion resistance, improved accessibility to reactants, and excellent dispersity in reaction media. Herein, we report the tailored synthesis of sulfated ZrO2 hollow nanostructures and their catalytic applications in the dehydration of fructose. ZrO2 hollow nanoshells with controllable thickness were first synthesized through a robust sol-gel process. Acidic functional groups were further introduced to the surface of hollow ZrO2 shells by sulfuric acid treatment followed by calcination. The resulting sulfated ZrO2 hollow particles showed advantageous properties for liquid-phase catalysis, such as well-maintained structural integrity, good dispersity, favorable mesoporosity, and a strongly acidic surface. By controlling the synthesis and calcination conditions and optimizing the properties of sulfated ZrO2 hollow shells, we have been able to design superacid catalysts with superior performance in the dehydration of fructose to 5-hydroxymethyfurfural than the solid sulfated ZrO2 nanocatalyst. [ABSTRACT FROM AUTHOR]

Published
2013
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