Myeong-Heon Um

Synthesis and catalytic performance on methanol conversion of NiAPSO-34 crystals (I): effect of preparation factors on the gel formation

Abstract In order to synthesize the NiAPSO-34 crystal with a pure CHA structure having a uniform size and stable catalytic activity, factors having influence on the crystallization at gel preparation were investigated. The results showed that the mixing order of starting materials influences on the crystallization rate. The concentration of the template was related to the morphology of crystals and the crystallinity, while the particle size obtained was controlled by the silica source and the amount of nickel. Moreover, it was elucidated that the mixing orders of starting materials influences on the crystal growth rate. Seed crystal addition (SAPO-34; 0.8 μm) and ultrasonic-wave treatment after the gel formation were effective in decreasing smaller particle size and in narrowing the size distribution.

High-Efficiently Photoelectrochemical Hydrogen Production over Zn-Incorporated TiO2 Nanotubes

To investigate the Zn dopant and nanotube morphology effects of TiO2 in electrochemical hydrogen production from the photo-splitting of methanol/water solution, we have designed a Zn-incorporated TiO2 nanotube (Zn-TNT) photocatalyst. The TNT and Zn-TNT materials had a width of 70~100 nm. The hydrogen production over the Zn-TNT photocatalysts was higher than that over the TNT; specifically, 10.2 mL of H2 gas was produced after 9 hours when 0.5 g of 0.01 mol% Zn-TNT was used. The zeta-potential values in aqueous solution determined by electrophoretic light scattering (ELS) had negative surface charges, which was related to the surface stability, and the absolute value was the largest in 0.01 mol% Zn-TNT. On the basis of UV-visible and photoluminescence (PL) spectra results, the high photoactivity of Zn-TNT was attributed to the shift toward the visible region and increase of PL intensity due to the increased number of excited electrons and holes.

Preparation of Nanosized -Al2O3 Particles Using a Microwave Pretreatment at Mild Temperature

This study investigated the effect of microwave pretreatment to reduce the growth temperature of α-Al2O3. The microwave pre-treating of the synthesized powders at 1,000∘C produced rhombohedral structured α-Al2O3 with high specific surface area and dispersion; however the structure accumulated among the particles was seen above 1,200∘C when the microwave did not pretreated.