Kyong-Hoon Choi

Self-Assembly of Nanosized 0D Clusters: CdS Quantum Dot–Polyoxotungstate Nanohybrids with Strongly Coupled Electronic Structures and Visible-Light-Active Photofunctions

Nanohybrids of CdS-polyoxotungstate with strongly coupled electronic structures and visible-light-active photofunctions can be synthesized by electrostatically derived self-assembly of very small CdS quantum dots, or QDs, (particle size ≈ 2.5 nm) and polyoxotungstate nanoclusters (cluster size ≈1 nm). The formation of CdS-polyoxotungstate nanohybrids is confirmed by high-resolution transmission electron microscopy, elemental mapping, and powder X-ray diffraction analysis. Due to the strong electronic coupling between two semiconductors, the CdS-polyoxotungstate nanohybrids show a narrow bandgap energy of around 1.9-2.7 eV, thus reflecting their ability to harvest visible light. Time-resolved photoluminescence experiments indicate that the self-assembly between nanosized CdS and polyoxotungstate is very effective in increasing the lifetime of holes and electrons, thus indicating an efficient electron transfer between two-component semiconductors. The hybridization results not only in a significant improvement in the photostability of CdS QD but also in the creation of visible-light-induced photochromism. Of particular importance is that the present nanohybrids show visible-light-driven photocatalytic activity to produce H(2) and O(2) , which is superior to those of the unhybridized CdS and polyoxotungstate. The self-assembly of nanometer-level semiconductor clusters can provide a powerful way of optimizing the photoinduced functionalities of each component (i.e., visible-induced photochromism and photocatalysis) by means of strong electronic coupling.

Synthesis and characterization of Ni magnetic nanoparticles in AlMCM41 host

Superparamagnetic nickel nanoparticles were prepared by incorporating nickel ion into AlMCM41 as a nanoreactor and then reduced with sodium borohydride or H2 gas. Products were characterized by elemental analysis, transmission electron microscopy, X-ray powder diffraction, and magnetic susceptibility. The nickel particle size and blocking temperature depend on the reduction method. q 2002 Elsevier Science Ltd. All rights reserved.

Directional random lasing in dye-TiO2 doped polymer nanowire array embedded in porous alumina membrane

We have demonstrated the lasing in the porous alumina membrane filled with hybrid polymer nanowires which consisted of poly(N-vinylcarvazole), rhodamine 6G, and TiO2 nanoparticles. The angle-resolved photoluminescence measurement suggested that lasing had a strong directionality along the hybrid polymer nanowires which were embedded within the nanochannels of the membrane. Although wavelengths of the lasing peaks were not affected by excitation and detection angles, lasing behavior strongly depended on the pore diameters of the membranes utilized. It is suggested that the closed loops for lasing are formed via multiple scattering induced by TiO2 nanoparticles embedded in the hybrid polymer nanowires.

A Facile Fabrication of Fe

Monodispersed superparamagnetic magnetite submicron particles were synthesized by using a one-step solvothermal method. Increasing the volume ratio of ethylene glycol/diethylene glycol (EG/DEG) shows a gradual increase in the size of primary nanograin and secondary Fe3O4 submicroparticles. To induce the photo-magnetic functionality, we have successfully synthesized the multifunctional core-shell (Fe3O4/ZnO) submicron particles by atomic layer deposition (ALD) method. Microstructure and magnetic properties of the multifunctional core/shell submicron particles are investigated by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), and photoluminescence spectroscopy.

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For the photooxidative reaction of olefin, colloidal CdS nanoparticles (NPs) show enhanced efficiency of photocatalytic activity compared to bulk CdS. We find that the enhanced activity is due to the enlarged surface area of the colloidal CdS NPs as well as enhanced energetic coupling between the colloidal CdS NPs and the olefin molecules. Photocatalytic activity is reduced in the case that CdS NPs are encapsulated in mesoporous silica nanopores.

O

We report a novel zinc oxide (ZnO) nanoparticle with antioxidant properties, prepared by immobilizing the antioxidant 3-(3,4-dihydroxyphenyl)-2-propenoic acid (caffeic acid, CA) on the surfaces of micro-dielectric barrier discharge (DBD) plasma-treated ZnO nanoparticles. The microstructure and physical properties of ZnO@CA nanoparticles were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), infrared spectroscopy, and steady state spectroscopic methods. The antioxidant activity of ZnO@CA nanoparticles was evaluated using an ABTS (3-ethyl-benzothiazoline-6-sulfonic acid) radical cation decolorization assay. ZnO@CA nanoparticles exhibited robust antioxidant activity. Moreover, ZnO@CA nanoparticles showed strong antibacterial activity against Gram-positive bacteria (Staphylococcus aureus) including resistant bacteria such as methicillin-resistant S. aureus and against Gram-negative bacteria (Escherichia coli). Although Gram-negative bacteria appeared to be more resistant to ZnO@CA nanoparticles than Gram-positive bacteria, the antibacterial activity of ZnO@CA nanoparticles was dependent on particle concentration. The antioxidant and antibacterial activity of ZnO@CA may be useful for various biomedical and nanoindustrial applications.

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Multifunctional Fe3O4@TiO2 core-shell submicron particles were fabricated by a simple surface modification process that induces the magnetic submicron particles to be coated with a TiO2 shell. As characterized by field emission scanning electron microscopy, (FESEM), the as-synthesized Fe3O4@TiO2 particles exhibit a narrow size distribution with a typical size of 248 ± 19 nm and 8 nm in shell thickness. Magnetic measurement indicates that the as-synthesized Fe3O4@TiO2 core-shell particles are superparamagnetic at room temperature. Photocatalytic experiment is demonstrated by utilizing the oxidation reaction of 2,4,6-trichlorophenol (2,4,6-TCP) with the photofunctional magnetic nanoparticles.

/ZnO Core-Shell Submicron Particles With Controlled Size

In this study, we report a new multifunctional nanoparticle with antioxidative and antibacterial activities in vitro. ZnO@GA nanoparticles were fabricated by coordinated covalent bonding of the antioxidant gallic acid (GA) on the surface of ZnO nanoparticles. This addition imparts both antioxidant activity and high affinity for the bacterial cell membrane. Antioxidative activities at various concentrations were evaluated using a 2,2′-azino-bis(ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical scavenging method. Antibacterial activities were evaluated against Gram-positive bacteria (Staphylococcus aureus: S. aureus), including several strains of methicillin-resistant S. aureus (MRSA), and Gram-negative bacteria (Escherichia coli). The functionalized ZnO@GA nanoparticles showed good antioxidative activity (69.71%), and the bactericidal activity of these nanoparticles was also increased compared to that of non-functionalized ZnO nanoparticles, with particularly effective inhibition and high selectivity for MRSA strains. The results indicate that multifunctional ZnO nanoparticles conjugated to GA molecules via a simple surface modification process displaying both antioxidant and antibacterial activity, suggesting a possibility to use it as an antibacterial agent for removing MRSA.

Photocatalytic Efficiency Analysis of CdS Nanoparticles with Modified Electronic States

Photodynamic therapy (PDT) has been adopted as a minimally invasive approach for the localized treatment of superficial tumors, representing an improvement in the care of cancer patients. To improve the efficacy of PDT, it is important to first select an optimized nanocarrier and determine the influence of light parameters on the photosensitizing agent. In particular, much more knowledge concerning the importance of fluence and exposure time is required to gain a better understanding of the photodynamic efficacy. In the present study, we synthesized novel folic acid-(FA) and hematoporphyrin (HP)-conjugated multifunctional magnetic nanoparticles (CoFe2O4-HPs-FAs), which were characterized as effective anticancer reagents for PDT, and evaluated the influence of incubation time and light exposure time on the photodynamic anticancer activities of CoFe2O4-HPs-FAs in prostate cancer cells (PC-3 cells). The results indicated that the same fluence at different exposure times resulted in changes in the anticancer activities on PC-3 cells as well as in reactive oxygen species formation. In addition, an increase of the fluence showed an improvement for cell photo-inactivation. Therefore, we have established optimized conditions for new multifunctional magnetic nanoparticles with direct application for improving PDT for cancer patients.

Antioxidant Potential and Antibacterial Efficiency of Caffeic Acid-Functionalized ZnO Nanoparticles

Photodynamic therapy (PDT) is a promising alternative to conventional cancer treatment methods. Nonetheless, improvement of in vivo light penetration and cancer cell-targeting efficiency remain major challenges in clinical photodynamic therapy. This study aimed to develop multifunctional magnetic nanoparticles conjugated with a photosensitizer (PS) and cancer-targeting molecules via a simple surface modification process for PDT. To selectively target cancer cells and PDT functionality, core magnetic (Fe3O4) nanoparticles were covalently bound with chlorin e6 (Ce6) as a PS and folic acid (FA). When irradiated with a 660-nm long-wavelength light source, the Fe3O4-Ce6-FA nanoparticles with good biocompatibility exerted marked anticancer effects via apoptosis, as confirmed by analyzing the translocation of the plasma membrane, nuclear fragmentation, activities of caspase-3/7 in prostate (PC-3) and breast (MCF-7) cancer cells. Ce6, used herein as a PS, is thus more useful for PDT because of its ability to produce a high singlet oxygen quantum yield, which is owed to deep penetration by virtue of its long-wavelength absorption band; however, further in vivo studies are required to verify its biological effects for clinical applications.