Il Tae Kim

Synthesis of polymer-decorated hydroxyapatite nanoparticles with a dispersed copolymer template

In this research, a nanoparticle synthesis method was explored in order to produce nanoparticles with different shapes and polymer-coated surfaces. Specifically, a poly(ethylene oxide)-b-poly(methacrylic acid) (PEO-b-PMAA) block copolymer was employed as a dispersed template for the controlled synthesis of hydroxyapatite (HAp) nanoparticles in water. Six different synthesis conditions were used to produce different nanoparticle shapes, and characterization of these nanoparticles was performed to understand the level of morphological control available with this synthesis method. SEM images showed that needle and spherical nanoparticles could be produced by changing the block copolymer concentration. The shape of the nanoparticles produced by this synthesis method was shown to be related to the relative concentrations of the calcium precursor and the block copolymer used. Significant quantities of the block copolymer used for synthesis remained on the particle surface, constituting a functionalized moiety and providing an opportunity to control component interactions in composites.

Magnetic Carbon Nanotubes: Synthesis, Characterization, and Anisotropic Electrical Properties

Carbon nanotubes (CNTs) have been the focus of extensive research in recent years due to their exceptional mechanical, thermal, and electrical properties (Treacy et al., 1996; Lourie et al., 1998; Yu et al., 2000; Lukic et al., 2005). As a result of their nanoscale dimensions and high surface area, CNTs could also be considered as efficient templates for the assembly and tethering of nanoparticles on their surface (Grzelczak et al., 2006). The decoration of CNTs with various compounds and various structures could increase their surface functionality and the tunability of their properties, such as their electrical and magnetic characteristics (Korneva et al., 2005; Kuang et al., 2006). Recent reports described the attachment of various inorganic nanoparticles to either the external surface of the CNTs, or to the internal surface of the CNT cavity, through several experimental methods (Han et al., 2004; Qu et al., 2006). In this context, it is important to note that the control of the size of these tethered nanoparticles is of primary importance for the purpose of tailoring the physical and chemical properties of these hierarchical materials. Iron oxide nanoparticles, such as magnetite and maghemite, have been of technological and scientific interest due to their unique electrical and magnetic properties. These nanoparticles can be used in such diverse fields as high-density information storage and electronic devices (Sun et al., 2000; Pu et al., 2005; Yi et al., 2006; Jia et al., 2007; Wan et al., 2007). Maghemite, Fe2O3, is the allotropic form of magnetite, Fe3O4 (Rockenberger et al., 1999; Pileni et al., 2003; Sun et al., 2004). These two iron oxides are crystallographically isomorphous. The main difference is the presence of ferric ions only in -Fe2O3, and both ferrous and ferric ions in Fe3O4. As a result, while the magnetic properties of Fe3O4 are superior, -Fe2O3 is more stable, since the iron cannot be further oxidized under ambient conditions. This renders Fe2O3 nanoparticles easier to work with, especially in the presence of organic solvents and organic ligands, and consequently, they have been widely used for magnetic storage in a variety of fields such as floppy disks and cassette tapes. However, maghemite-CNT nanohybrid materials have not been studied as extensively as magnetite-CNT nanohybrid materials, with the exception of several few examples (Sun et al., 2005; Youn et al., 2009).

Surfactant-assisted ammonium vanadium oxide as superior cathode for calcium-ion batteries

Ammonium vanadium oxide (NH4V4O10) was adopted as an efficient and high-capacity cathode for Ca-ion batteries. The conventional hydrothermal process allowed an NH4V4O10 cathode to exhibit an initial capacity of 125 mA h g−1 at 0.1 A g−1. However, the process led to a size range of hundreds of nanometers to a few microns, which limited the electrochemical performance. Accordingly, we created uniform rod-like NH4V4O10 particles approximately 100 nm in breadth by adding the surfactant sodium dodecylbenzenesulfonate as a soft template during the sample preparation. The addition of the surfactant not only reduced the crystal size but also generated an Na-doping effect; as a result, it increased the proportion of V4+/V5+ active sites. The Na-doped NH4V4O10 electrode delivered an initial capacity of 150 mA h g−1 and maintained the capacity by demonstrating coulombic efficiencies of 90–95% without notable fading after 100 cycles in a three-electrode system. Moreover, the material produced via the new route required less time to be activated before reaching the highest-capacity state. Ex situ X-ray diffraction analysis indicated the formation of new phases during the migration of Ca ions, and the small change in the lattice plane suggested that NH4V4O10 can exhibit stable electrochemical performance during prolonged cycling. Finally, a full-cell study demonstrated that the Na-doped NH4V4O10 electrode delivered a maximum discharging capacity of 75 mA h g−1 with both high coulombic efficiency (∼80%) and ∼100% capacity retention for 100 cycles.