Advanced Engineering Forum Vol. 38

Abstract: Gallium oxide (Ga₂O₃) nanowires were grown on fused quartz and Si substrates by a vapor transport method of heating gallium metal at 750−1100 °C in a tube of the horizontal furnace. The obtained white colored product has shown to be the Ga₂O₃ nanowires with average diameters ranging from 30 to 80 nm. The optical transmittance spectra indicated that the bandgap energy of Ga₂O₃ nanowire increases as the diameter of nanowire decreases.

Abstract: Optical absorption and photoluminescence (PL) spectra were measured on defect-stannite-type semiconductor ZnGa₂Se₄ at temperatures T from 11 to 300 K. The square of the absorption coefficient spectra showed distinct two absorption edges, which were E_0A,B and E_0C,D transitions at Γ point in the Brillouin zone. The temperature dependence of the direct-gap energies, E_0A,B and E_0C,D, of ZnGa₂Se₄ were determined and fit using the analytical four-parameter expression developed for the explanation of the band-gap shrinkage effect in semiconductors. The PL emissions at near band-edge and at higher energy than band-edge were also observed at T ≤ 150 K.

Abstract: Titania-modified zirconias with different Ti/Zr ratios were synthesized via thermal treatment of zirconium (IV) tetra-n-propoxide and titanium (IV) tetra-iso-propoxide in 1,4-butanediol at 300 °C. The obtained products were spherical particles composed of nanocrystals with the tetragonal ZrO₂ structure. The products had large specific surface areas, large pore volumes, and relatively narrow pore size distributions in the mesopore region. After calcination at high temperatures, the obtained TiO₂-modified ZrO₂ samples preserved large surface areas and pore structure. Having these superior thermal stability and pore structure, the obtained TiO₂-modified ZrO₂ particles are expected to show high performance as catalytic materials.

Abstract: Nanocrystalline rutile TiO₂ particles were prepared via hydrothermal treatment of Ti-containing precursors obtained by low-temperature aging for a transparent diluted HCl solution of amorphous TiO₂. The products were modified with FeO_x and phosphoric acid, and the photocatalytic activities of the obtained catalysts under visible-light irradiation were examined. By the addition of FeO_x or phosphoric acid, the photocatalytic activity of the rutile TiO₂ was slightly increased. On the contrary, by the FeO_x loading and subsequent addition of phosphoric acid, significant increases in the photocatalytic activity were attained. Results of UV-vis suggest that the iron oxides formed on the surface of rutile TiO₂ were changed into highly dispersed iron phosphate species by the addition of phosphoric acid. It was presumed that these species effectively suppress the recombination reaction between the photogenerated electrons and holes and contribute to the high photocatalytic activity of the rutile TiO₂ photocatalysts modified with FeO_x and phosphoric acid.

Abstract: One of the technical issues of vanadium redox flow batteries with a carbon paper electrode and interdigitated flow channel is the relatively low current density due to insufficient active material transport downstream in the electrode and low reaction interface area. In this study, we propose a new composite electrode structure, i.e., a porous carbon nanofiber layer that is partially added on the carbon paper. The current density of the composite electrode was higher than that of the unloaded carbon paper electrode due to the lower internal resistances of the battery. In addition, the discharge capacity and voltage efficiency during the charge-discharge operation were improved by the composite structure.

Abstract: With the aim of developing an active catalyst for a direct methanol fuel cell and its preparation process, PtRu supported on reduced graphene oxide (RGO), PtRu/RGO, was prepared by three different processes using RGO with different sizes, i.e., large and small. The first process (A) involves the drying of RGO, the second one (B) does not involve the drying, and the third one (P) also does goes not involve the drying but goes through a polydopamine modification. (A) results in large agglomerates of RGO due to stacking and PtRu also formed agglomerates of nanoparticles on the outer surface of the RGO agglomerates. (B) resulted in a low Pt utilization due to the stacking of RGO. (P) improved its ECSA, Pt utilization and mass activity due to the modification that allows a homogeneous and small size PtRu deposition on the RGO. However, a problem with the modification that reduce the positive interaction between PtRu and RGO was also suggested. A smaller RGO was preferred in (P), but not in (A) and (B).

Abstract: β-AgI thin films with thicknesses of 0.09–8.9 µm were prepared on polyethylene terephthalate (PET) substrate. Dependence of ionic conductivity on the thickness of the β-AgI thin film was measured via impedance spectroscopy in the temperature range of 300–330 K. It has been confirmed that the ionic conductivity of the b-AgI thin film is several hundred times higher than the b-AgI bulk. The enhancement of ionic conductivity is considered to be due to the formation of a high ion-conducting region near the hetero-interface region of b-AgI and PET. Furthermore, it has been suggested that the activation energy and carrier density may change depending on the distance from the interface, and the thickness dependence of enhancement in ionic conductivity may be related to the film thickness dependence of crystal orientation and structural disorder of β-AgI thin films.

Abstract: Antigene technology is the one strategy for the artificial regulation of gene expression by the formation of triple structure on triplex forming oligonucleotide (TFO) with dsDNA. For the enhancement of the thermal stability of triplex structure, photo-crosslinking reaction is attractive by the covalent bond formation between TFO and dsDNA. In this paper, we designed the novel TFOs containing benzophenone moiety as a photo-crosslinkable agent. Several types of glycol nucleoside analogs having glycol scaffold and benzophenone residues with different linker length were prepared, and the these were incorporated into TFOs. The thermal stability of triplex and the photo-crosslinking reaction efficiency of TFOs toward dsDNA was systematically evaluated.

Abstract: Malaria caused by Plasmodium falciparum continues to be a major public health problem especially in tropical and sub-tropical regions of the world. Considering the growing resistance of parasites to anti-malarial drugs and of vector mosquitoes to insecticides, there is no doubt that the effective vaccine is the most awaiting tool to reduce the risk of malaria. Our synthetic studies have shown that a loop region (AD22 = ²⁵⁶ASEFYNSENKTYDLDFKTPNND²⁷⁷) of Plsmodium falciparum enolase has antigenic reactivity against patients’ sera and AD22 can produce inhibitory antibodies against in vitro parasite growth. In this paper, we will briefly present our ongoing research of malaria vaccine development and related model studies.