九州におけるソバ遺伝資源の諸特性の品種間差異および機能性の選抜法に関する研究

博士（農学）神戸大

Exploring the Different Roles of Particle Size in Photoelectrochemical and Photocatalytic Water Oxidation on BiVO₄

Water oxidation on visible-light-active bismuth vanadate (BiVO₄) has commonly been demonstrated to be viable in powder suspension (PS) and particulate photoelectrochemical (PEC) systems. Here, we demonstrate that particle size reduction, which is known to be efficacious in promoting charge carrier extraction and boosting surface active sites, has an opposite effect on BiVO₄’s photoactivity in the two systems. With three BiVO₄ samples of distinctive particle sizes, smaller BiVO₄ particle size is shown to be beneficial for enhancing PEC photocurrent generation, but deleterious for photocatalytic O₂ evolution on suspended BiVO₄. Such contrary effect of particle size in the PEC and PS systems is revealed to be due to the different governing factors of the systems: charge transport in the former and charge separation in the latter. Smaller particle size was found to enrich the interparticle and the particle/FTO substrate contacts which improve charge transport and charge collection efficiency in BiVO₄ particulate electrode. On the contrary, larger particle size is necessary for improved photocatalytic O₂ evolution because of increased crystallinity and greater band bending, which are essential for charge separation

Effects of Serum Adsorption on Cellular Uptake Profile and Consequent Impact of Titanium Dioxide Nanoparticles on Human Lung Cell Lines

Exposure to fetal bovine serum (FBS) is shown herein to reduce the aggregate size of titanium dioxide (TiO₂) nanoparticles, affecting uptake and consequent effect on A549 and H1299 human lung cell lines. Initially, the cellular uptake of the FBS-treated TiO₂ was lower than that of non-FBS-treated TiO₂. Expulsion of particles was then observed, followed by a second phase of uptake of FBS-treated TiO₂, resulting in an increase in the cellular content of FBS-treated TiO₂, eventually exceeding the amount by cells exposed to non-FBS-treated TiO₂. Surface adsorbed vitronectin and the clathrin-mediated endocytosis pathway were shown to regulate the uptake of TiO₂ into A549 cells, while the endocytosis mechanism responsible remains elusive for H1299. Intriguingly, nystatin treatment was shown to have the unexpected effect of increasing nanoparticle uptake into the A549 cells <i>via</i> an alternate endocytic pathway. The surface adsorbed serum components were found to provide some protection from the cytotoxic effect of endocytosed TiO₂ nanoparticles

Tuning Phase Composition of TiO₂ by Sn⁴⁺ Doping for Efficient Photocatalytic Hydrogen Generation

The anatase–rutile mixed-phase photocatalysts have attracted extensive research interest because of the superior activity compared to their single phase counterparts. In this study, doping of Sn⁴⁺ ions into the lattice of TiO₂ facilitates the phase transformation from anatase to rutile at a lower temperature while maintaining the same crystal sizes compared to the conventional annealling approach. The mass ratios between anatase and rutile phases can be easily manipulated by varying the Sn-dopant content. Characterization results reveal that the Sn⁴⁺ ions entered into the lattice of TiO₂ by substituting some of the Ti⁴⁺ ions and distributed evenly in the matrix of TiO₂. The substitution induced the distortion of the lattice structure, which realized the phase transformation from anatase to rutile at a lower temperature and the close-contact phase junctions were consequently formed between anatase and rutile, accounting for the efficient charge separations. The mixed-phase catalysts prepared by doping Sn⁴⁺ ions into the TiO₂ exhibit superior activity for photocatalytic hydrogen generation in the presence of Au nanoparticles, relatively to their counterparts prepared by the conventional annealling at higher temperatures. The band allignment between anatase and rutile phases is established based on the valence band X-ray photoelectron spectra and diffuse reflectance spectra to understand the spatial charge separation process at the heterojunction between the two phases. The study provides a new route for the synthesis of mixed-phase TiO₂ catalysts for photocatalytic applications and advances the understanding on the enhanced photocatalytic properties of anatase–rutile mixtures

Transforming Anodized WO₃ Films into Visible-Light-Active Bi₂WO₆ Photoelectrodes by Hydrothermal Treatment

We directly transformed anodized tungsten oxide film (WO₃·2H₂O) into bismuth tungstate (Bi₂WO₆) by substituting the intercalated water molecules with [Bi₂O₂]²⁺ in a hydrothermal treatment. The resultant Bi₂WO₆ was readily used as an electrode to produce anodic photocurrent in H₂ evolution on the Pt counter electrode observed under visible light irradiation

Reducing Graphene Oxide on a Visible-Light BiVO₄ Photocatalyst for an Enhanced Photoelectrochemical Water Splitting

Bismuth vanadate (BiVO₄) is incorporated with reduced graphene oxide (RGO) using a facile single-step photocatalytic reaction to improve its photoresponse in visible light. Remarkable 10-fold enhancement in photoelectrochemical water splitting reaction is observed on BiVO₄−RGO composite compared with pure BiVO₄ under visible illumination. This improvement is attributed to the longer electron lifetime of excited BiVO₄ as the electrons are injected to RGO instantly at the site of generation, leading to a minimized charge recombination. Improved contact between BiVO₄ particles with transparent conducting electrode using RGO scaffold also contributes to this photoresponse enhancement

BiVO₄ {010} and {110} Relative Exposure Extent: Governing Factor of Surface Charge Population and Photocatalytic Activity

The {010} and {110} crystal facets of monoclinic bismuth vanadate (m-BiVO₄) has been demonstrated to be the active reduction and oxidation sites, respectively. Here, we show using dual-faceted m-BiVO₄ with distinctly different dominant exposed facets, one which is {010}-dominant and the other {110}-dominant, contrary to prediction, the former m-BiVO₄ exhibits superior photooxidation activities. The population of photogenerated electrons and holes on the surface are revealed to be proportional to the respective surface areas of {010} and {110} exposed on m-BiVO₄, as evidenced by steady-state photoluminescence (PL) measurements in the presence of charge scavengers. The better photoactivity of {010}-dominant m-BiVO₄ is attributed to prompt electron transfer facilitated by the presence of more photogenerated electrons on the larger {010} surface. Additionally, the greater extent of electron trapping in {110}-dominant m-BiVO₄ also deteriorates its photoactivity by inducing electron–hole pair recombination

Exploring the Origin of Enhanced Activity and Reaction Pathway for Photocatalytic H₂ Production on Au/B-TiO₂ Catalysts

Gold-embedded boron-doped TiO₂ (Au/B-TiO₂) photocatalysts were synthesized by a sol–gel hydrothermal method. The TEM images display that the gold nanoparticles were embedded into the B-TiO₂ framework. Hydrogen evolution under light irradiation showed that doping of boron into TiO₂ enhanced the photocatalytic activity. A further remarkable improvement of the activity was observed over the Au/B-TiO₂. Evidenced by B 1s XPS and ¹¹B MAS NMR spectra, the embedment of Au nanoparticles contributes to the formation of more interstitial boron species in B-TiO₂. In turn, it gives rise to surface or near-surface states facilitating the embedment of Au nanoparticles, as demonstrated by the Au 4f XPS spectra, which indicates the strong interaction between gold and the B-TiO₂ framework. This specific synergy significantly contributes to the enhancement of photocatalytic activity. For the first time, the isotopic tracer studies using a gas chromatograph isotope ratio mass spectrometer along with a series of control experiments reveal that the produced hydrogen originated mainly from water rather than methanol, whereas the direct oxidation of methanol did not lead to hydrogen generation. Acting as a sacrificial reagent, methanol could be oxidized to formaldehyde by protons/water under oxygen-free conditions

Electrodeposited Cu₂O as Photoelectrodes with Controllable Conductivity Type for Solar Energy Conversion

Electrodeposition of copper acetate under mild acidic conditions followed by a controlled annealing process allowed the manipulation of the oxygen vacancies in the resultant Cu₂O-based electrodes. The conduction type of the Cu₂O-based semiconductor was, therefore, tunable, allowing the fabrication of n-type, p-type, and p–n junction photoelectrodes. A transformation of the original n-type conduction to the subsequent p-type nature was observed through the variation of annealing temperature and duration. The observation of anodic and cathodic photocurrents for n-type and p-type thin films confirmed their potential use as photoanodes and photocathodes, respectively, in liquid-junction photoelectrochemical systems. The high carrier densities of the electrodeposited n- and p-type Cu₂O were estimated to be 8.9 × 10¹⁹ and 1.3 × 10²⁰ cm^–3, respectively, using Mott–Schottky analysis. Furthermore, the p–n junction photoelectrodes in a device configuration also exhibited diode behavior in current–voltage measurements, indicating their potential application in solid-state photovoltaic devices

Z‑Schematic Water Splitting into H₂ and O₂ Using Metal Sulfide as a Hydrogen-Evolving Photocatalyst and Reduced Graphene Oxide as a Solid-State Electron Mediator

Z-schematic water splitting was successfully demonstrated using metal sulfide photocatalysts that were usually unsuitable for water splitting as single particulate photocatalysts due to photocorrosion. When metal sulfide photocatalysts with a p-type semiconductor character as a H₂-evolving photocatalyst were combined with reduced graphene oxide-TiO₂ composite as an O₂-evolving photocatalyst, water splitting into H₂ and O₂ in a stoichiometric amount proceeded. In this system, photogenerated electrons in the TiO₂ with an n-type semiconductor character transferred to the metal sulfide through a reduced graphene oxide to achieve water splitting. Moreover, this system was active for solar water splitting