Utilization of inorganic nanoparticles have attracted great deals of attention in material science. Liquid-phase synthesis is one of the most powerful tools so as to prepare the size- and shape-controlled inorganic particles with a specific crystal plane. Up to date, we have investigated to prepare well defined inorganic nanoparticles precisely controlled in size and shape such as α-Fe2O3, TiO2, SrTiO3, Sn-doped In2O3, Bi0.5Na0.5TiO3, BaZrO3, NaNbO3, and K0.5N0.5NbO3 with precursor gel as an intermediate under highly concentrated hydrothermal conditions. Our research interests are applying these functional nanoparticles to develop high-performance catalysts, transparent conductive oxide nano-inks, organic-inorganic hybrid liquid crystals, and liquid-crystalline organic-inorganic hybrid dendrimers.
Synthesis of novel crystalline metal oxides by assembly of polyoxometalate building blocks is presented. Polyoxometalates, anionic metal oxide clusters of early transition metals such as tungsten (W) and molybdenum (Mo) with variety of structures in controlled mater, interact or make bonds with cationic species to form crystalline metal oxides. Here, we describes our four results. 1) Formation of microporous material by assembly of in-situ produced α-Keggin-type phosphotungstate with ammonium cation. 2) Formation of molecular nanowires based crystalline metal oxides by assembly of tellurium (Te) and selenium (Se) with W and Mo. 3) Formation of Mo-vanadiuim (V) oxides by assembly of pentagonal polyoxomolybdate with other Mo and V. 4) Formation of micropores Mo-V-bithmus (Bi) oxide and Mo-M (M = manganese (Mn), zinc (Zn), iron (Fe), and cobalt (Co)) by assembly of ε-Keggin-type heteropolymolybdates with cationic elements. Applications as catalysts and adsorption materials are also presented.
Mesoporous silica nanoparticles have attracted great attention because of their potential applications as catalysts, drug/gene delivery carriers, and optical materials because of high surface area, large pore volume, transparency, biocompatibility, and high cell uptake efficiency. This review reports general preparation and applications of mesoporous silica nanoparticles, and our recent efforts on the preparation of well-dispersed mesoporous silica nanoparticles with precisely controlled particle size, pore size, functionality, and morphology.
Shape controls of primary and secondary particles, which mean the design of crystals, including atomic building, shape control, particle connection, and crystal alignment, is one of dominant factors to determine functional abilities of materials, since the material performances do not only depend on chemical compositions and structures, but also crystallographic characteristics. For improvements of advanced materials use, development of innovative morphologic-control techniques should be an important issue. We have studied crystal growths by using flux method, which is liquid-phase growth technique, to provide high crystalline, unconventional shape of functional materials. As one of strategic application of flux method for shape control, we introduced template-mediated flux crystal growths, which exhibit unique shapes in terms of their primary and secondary appearances.
The two-dimensional (2D) nucleation is the predominant growth mechanisms for colloidal crystals whose particle interaction is attractive. The colloidal crystallization in the attractive system has recently been regarded as a promising method to fabricate varieties of complex nano-structures possessing innovative functionality. In the present study, polymers are added to a colloidal suspension to generate a depletion attractive force, and the detailed 2D nucleation process on the terrace of the colloidal crystals is investigated. We first measured the nucleation rate at various area fractions of particles on the terrace, φarea. In situ observations at single-particle resolution enable us to measure the steady-state homogeneous 2D nucleation rate, J, and the critical size of nuclei, r*, and the relationship between them and φarea is found to agree well with classical nucleation theory (CNT). The step free energy, γ, derived from the nucleation theory is found to vary according to the strength of attraction, which is tuned by the concentration of the polymer as a depletant.