No abstract

A liquid-phase method for preparing uniform-sized silica nanospheres (SNSs) 12 nm in size and their three-dimensionally ordered arrangement upon solvent evaporation have recently been pioneered by us. The SNSs are formed in the emulsion system containing Si(OEt) 4 (TEOS), water, and basic amino acids under weakly basic conditions (pH 9-10). Here, we report the formation mechanism of the SNSs; the reasons for the uniform size and the ordered arrangement are described in detail. The formation process is monitored by FE-SEM, SAXS, and liquid-state NMR. The FE-SEM observations reveal that silica nanoparticles ca. 4 nm in size are formed in the water phase at the early stage (∼0.5 h) of the reaction. The SAXS measurements suggest that the number density of the particles remains unchanged when they are gradually grown. Liquid-state 1 H NMR analyses suggest that TEOS are slowly hydrolyzed at the oil-water interface to continuously supply silicate species into the water phase. The silicate species are immediately consumed for the growth of the parent particles without forming new particles. The size of the SNSs can be tuned from 8 to 35 nm by varying the synthesis conditions and/or the amount of TEOS. The zeta potential and pH of the dispersion of SNSs throughout the solvent evaporation process are almost constant approximately at -40 mV and 9-10, respectively; the SNSs have been well-dispersed until the final stage of the evaporation process. The critical roles of basic amino acids in the formation and regular arrangement of SNSs are discussed based on the experimental results.

No abstract

The d electron orbital is a hidden but important degree of freedom controlling novel properties of transition-metal oxides. A one-dimensional orbital system is especially intriguing due to its enhanced quantum fluctuation. We present a combined experimental and theoretical study on the Raman scattering spectra in perovskite oxides NdVO(3) and LaVO(3) to prove that the quasi-one-dimensional orbital chain described by fermionic pseudospinons bears orbital excitations exchanging occupied orbital states on the neighboring sites, termed a two-orbiton in analogy with two-magnon.

A novel method of intermediate addition of alkali ions is proposed to give phase selectivity of zeolite in crystallization stages. Location of alkali metal ions in formed zeolite A, low silica zeolite X (LSX), and their hydrogel prior to the crystallization is investigated with ion exchange isotherms in order to clarify the crystallization mechanism, where the specific alkali metal ion is required for selective growth of the zeolites. The role of potassium ion for the crystallization is found to be important to determine the final phase of crystals. Hydrated potassium ion has a function to assemble aluminosilicate precursors to form LSX by a strong salting-out effect; otherwise, sodium ion assembles the same building units into zeolite A. Intermediate addition of potassium ion into crystallizing media controls the final precipitating crystalline phase kinetically. Here our proposed method enables the building unit for zeolite A to be quenched and deposited into aluminosilicate hydrogel, resulting in the selective formation of LSX in the hydrogel phase.