Effects of ultrasound irradiation on Au nanoparticles deposition on carbon-coated LiNi0.5Mn1.5O4 and its performance as a cathode material for Li ion batteries.

LiNi0.5Mn1.5O4 (LMNO) has attracted considerable attention as a Li-ion battery cathode material, owing to its high discharge voltage of 4.7 V (vs. Li/Li+) and high energy density. However, the electronic conductivity of LMNO is low, resulting in a low discharge capacity at high current density. To overcome this limitation, we deposited Au nanoparticles (NPs), which have a high conductivity and chemical stability at high battery voltages, on carbon-coated LMNO (LMNO/C) using ultrasound irradiation. Consequently, Au NPs that are ∼16 nm in size were deposited on LMNO/C, and ultrasound irradiation was reported to disperse the NPs on LMNO/C more effectively than stirring. Furthermore, the deposition of Au NPs on LMNO/C using ultrasound irradiation improved its electronic conductivity, which is related to an increase in the discharge capacity due to the reduction of Ni4+ to Ni2+ in LMNO/C at a high current density.

Low-Temperature Synthesis of Aluminum Nitride by Addition of Ammonium Chloride.

Aluminum nitride (AlN) is highly insulating and has a high thermal conductivity. AlN also has the advantages of being nontoxic and chemically stable. Therefore, it is a suitable sealing material for electric devices. Previous studies have shown that the addition of NH4Cl has a large influence on the formation of AlN and can effectively be used in its low-temperature synthesis without the use of special equipment. However, it has not been clarified whether NH4Cl simply promotes the reaction between Al and nitrogen or directly contributes to the nitridation reaction. In this study, which was part of a series of studies on the development of low-temperature synthesis methods for AlN, the nitridation behaviors of Al in Al-N2, Al-NH4Cl-N2, and Al-NH4Cl-He systems were determined, and the effects of the heating temperature and amount of NH4Cl on the nitridation behavior were examined in detail. When NH4Cl was added, AlN began to form at 600 °C, a formation temperature that was approximately 200 °C lower than that when only Al powder was heated under a nitrogen stream. The fact that the formation of AlN was also observed when the NH4Cl-added Al powder was heated under a helium gas stream confirmed that nitrogen derived from NH4Cl contributed to the formation of the AlN. Furthermore, based on the experimental results, the reaction mechanism was clarified, and the kinetic parameters for the nitridation of Al were determined.

Effect of reaction temperature on the size and morphology of scorodite synthesized using ultrasound irradiation.

Synthesis of scorodite (FeAsO4·2H2O) using dynamic action agglomeration and the oxidation effect from ultrasound irradiation was investigated. The effect of different reaction temperatures (90, 70, 50, and 30°C) on the size and morphology of scorodite particles synthesized under O2 gas flow and ultrasound irradiation was explored because the generation of fine bubbles depends on the solution temperature. At 90°C, the size of scorodite particles was non-homogeneous (from fine particles (<1µm) to large particles (>10µm)). The oxidation-reduction potential (ORP) and yield at 90°C showed lower values than those at 70°C. The scorodite particles, including fine and non-homogeneous particles, were generated by a decrease in the oxidation of Fe(II) to Fe(III) and promotion of dissolution caused by the generation of radicals and jet flow from ultrasound irradiation. Using ultrasound irradiation in the synthesis of scorodite at low temperature (30°C) resulted in the appearance of scorodite peaks in the X-ray diffraction (XRD) pattern after a reaction time of 3h. The peaks became more intense with a reaction temperature of 50°C and crystalline scorodite was obtained. Therefore, ultrasound irradiation can enable the synthesis of scorodite at 30°C as well as the synthesis of large particles (>10µm) at higher temperature. Oxide radicals and jet flow generated by ultrasound irradiation contributed significantly to the synthesis and crystal growth of scorodite.

Synthesis of temperature-responsive anion exchanger via click reaction.

The temperature-responsive anion exchanger was synthesized by immobilizing the poly(N-isopropylacrylamide) (PNIPAM), a kind of the temperature-responsive polymer, on the external surface of mesoporous silica via click reaction. The structure of this synthesized composite was characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), elemental analysis, and nitrogen adsorption experiment. The amount of PNIPAM immobilized on the external surface of mesoporous silica, which was calculated from the weight loss measured by thermogravimetry, increased from 5.3 wt.% to 12.9 wt.% (dry) depending on the amount of PNIPAM added in the click reaction. The adsorption-desorption behavior of methyl orange (MO) ions in this synthesized anion exchanger was affected by the temperature of aqueous solution: the MO ions were adsorbed and desorbed reversibly and repeatedly with changing the pH of the solution at 25 °C, while the amount of adsorbed MO ions remained nearly constant at about 0.05 mmol/g independent of the pH of the solution at 40 °C. Also, the amount of PNIPAM immobilized on the mesoporous silica influenced the adsorption rate of MO ions, suggesting that the adsorption rate in this composite is controlled by the diffusion of MO ions through the PNIPAM layer.

Synthesis of thermosensitive polymer/mesoporous silica composite and its temperature dependence of anion exchange property.

An anion exchanger consisting of amino-functionalized MCM-41 type mesoporous silica coated with temperature-responsive polymer, poly(N-isopropylacrylamide) (PNIPAM), was synthesized in this study. The structure of this composite was characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and elemental analysis. The XRD pattern showed that the synthesized composite had the ordered hexagonal structure and the interplanar spacing, d(100), was around 40Å. The amount of surface-grafted thermosensitive polymer was estimated to be about 0.8wt.% by elemental analysis. The adsorption-desorption behavior of methyl orange in this synthesized material depended on the temperature of aqueous solution: at 25°C, the reversible adsorption-desorption of methyl orange was repeated with changing pH of the solution; at 40°C, the methyl orange was not adsorbed and desorbed independent of pH of the solution.

Solid-liquid separation by sonochemistry: a new approach for the separation of mineral suspensions.

The effect of sonochemistry to acidify solutions was applied for the solid-liquid separation of three kinds of mineral suspensions. At first, the relationship was measured between zeta-potential and pH in these suspensions to find pH levels correspondent to the isoelectric points. Then sonication (200 kHz or 28 kHz) was applied to adjust pH to the isoelectric points and separated particles from solutions by still-standing and spontaneous precipitation. Compared to the conventional methods using filters and chemical agents, the advantage of this sonochemical separation is two-fold. First, it does not require the maintenance of filters. Second, separated particles are easy to use since they are not mixed with pH adjusters and chemical flocculants. Isoelectric zone (ion strength 0.01, concentration 0.001 wt.%) of green tuff, andesite and titanium dioxide suspensions tested in this study were pH 1.1-3.7, 0.8-3.4, 2.7-5.7, respectively. The sonication of green tuff and andesite suspensions at 200 kHz changed the pH to the isoelectric zone despite the pH buffering effect of eluted alkali earth metals, and successfully precipitated the particles. On the contrary, the sonication of these suspensions at 28 kHz failed to adjust pH to the isoelectric zone, and the particles did not precipitate. In addition, the degradation of particles was observed in the SEM photographs of particles sonicated at 28 kHz, whereas no significant change was detected in particles sonicated at 200 kHz. Thus, it is concluded that the optimal frequency is about 200 kHz because its strong chemical effect can easily adjust the pH while its relatively weak physical effect prevents the degradation of particles.

Heavy metal removal from aqueous solution using carbonaceous K2S-impregnated adsorbent.

A novel carbonaceous adsorbent for heavy metal removal was prepared from raw coal by one-step simple sulfur impregnation using K2S. Raw coal was mixed with K2S powder and then heated at 800 degrees C for 30 min in nitrogen to produce K2S char. The sulfur content and form in K2S char were determined, and the ability of K2S char to adsorb Zn2+, Cd2+ and Pb2+ was examined. The K2S impregnation was effective at impregnating sulfur into coal, especially in the form of elemental, thiophenic and sulfatic sulfur. The sulfur content of K2S char was higher than those of raw coal and pyrolysis char. The Zn2+ removal in 2.4 mmol/L of Zn2+ solution by K2S char was higher than raw coal with the removal rate of 100%. K2S char adsorbed Pb2+ and Cd2+ in 24 mmol/L of Pb2+ and Cd2+ solution with the removal rate of 97% and 35%, respectively. The elution extents of adsorbed Pb2+ and Cd2+ were zero in distilled water and 27% in 0.1 mol/L HCl solution. These results indicated that an effective adsorbent for heavy metal ions was prepared from coal using K2S sulfur impregnation, and that the adsorbed metals were strongly retained in K2S char.