Bunsho Ohtani

Hokkaido University | Hokudai · Catalysis Research Center

In this study, we explored the structural and chemical modifications of cellulose fibres subjected to chemical and mechanical treatments through an innovative analytical approach. We employed photoacoustic spectroscopy (PAS) and reversed double-beam photoacoustic spectroscopy (RDB-PAS) to examine the morphological changes and the chemical integrity...

Here, attempts to prepare octahedral-shaped anatase titanium(IV) oxide (titania) particles (OAPs) of uniform bulk structure (anatase with negligible non-crystalline components), surface structure (only exposing {101} facets) and particle size are reported as the first and sole example of a "pure" metal-oxide powder. The OAP samples were prepared by...

Oxygen vacancies (OVs) are one of the most critical factors that enhance the electrical and catalytic characteristics of metal oxide-based photo-electrodes. In this work, a simple procedure was applied to prepare reduced TiO 2 nanotube arrays (NTAs) (TiO 2−x) via a one-step reduction method using NaBH 4. A series of characterization techniques were...

Although solar-driven hydrogen production and recalcitrant pollutant degradation are appealing technologies, the photocatalytic efficiency for most reactions is limited by insufficient visible-light harvesting ability and restricted charge transfer pathways. To...

Fundamentals and important concepts for photocatalytic hydrogen evolution are interpreted from the standpoints of thermodynamics, standard electrode potential, photocatalysts, cocatalysts and role of platinum for hydrogen evolution, and anatase/rutile titania for understanding the photocatalytic hydrogen evolution and further development of efficie...

Anatase nanoparticles, exposing the majority of the {0 0 1}, {1 0 0} and {1 0 1} facets were synthesized and doped with different niobium amount to investigate the self-trapping of the excess electrons and resulting photocatalytic activity. Photocatalyst structure and presence of excess electrons inside the obtained Nb-doped anatase samples was con...

Graphitic carbon nitride/ converter slag (gCN/CS) composites were fabricated as photocatalysts by a simple co-calcination. The structural, optical, and physicochemical characteristics of graphitic carbon nitride/ artificial converter slag (gCN/artCS) composites were investigated for the photocatalytic degradation of imidacloprid under visible light...

This study fabricated tantalum (Ta)-doped titanium dioxide with a unique nanorod-assembled actinomorphic-flower-like microsphere structured film . The Ta-doped TiO2 actinomorphic-flower-like microsphere (TAFM) was fabricated via the solution immersion method in a Schott bottle with a home-made improvised clamp. The samples were characterised using...

Developing eco-friendly strategies to produce green fuel has attracted continuous and extensive attention. In this study, a novel gas-templating method was developed to prepare 2D porous S-doped g-C3N4 photocatalyst through simultaneous pyrolysis of urea (main g-C3N4 precursor) and ammonium sulfate (sulfur source and structure promoter). Different...

Five different (commercial and self-synthesized) titania samples were mixed with NaBH4 and then heated to obtain black titania samples. The change in synthesis conditions resulted in the preparation of nine different photocatalysts, most of which were black in color. The photocatalysts were characterized by various methods, including X-ray diffract...

We report easily available and highly reliable colorimetric formaldehyde analysis using only a spectrophotometer/colorimeter, which enables the evaluation of the "true" photocatalytic activity induced by photoabsorption of a "photocatalyst", compared...

Plasma processing of photocatalysts can conveniently change the surface chemistry, introducing extrinsic or intrinsic surface doping, holding promise to make photocatalysts more active without altering the bulk properties. While gas plasma has long been employed to process photocatalysts, it is hard to avoid the surface dry etching caused by the hi...

Fe/Mt./TiO2 with FeIII cation doped on montmorillonite (Mt) and, Mt./Fe-TiO2 with FeIII cation doped on TiO2 were synthesized at three temperatures. Compared with the influence from the position of FeIII, the synthesis temperature had moderate interference on the TiO2 formation as was implied by X-ray fluorescence (XRF) and X-ray diffraction (XRD)....

Photoabsorption properties of cellulose fibres under continuous and modulated irradiation were investigated in situ by the use of reversed double-beam photoacoustic spectroscopy (RDB-PAS). This photoacoustic (PA) measurement enabled observation of ultraviolet- and visible light-induced, electron trap filling, and reductive change on the surface of...

How can we design functional solid materials, such as catalysts and photocatalysts? What is the decisive structural parameters controlling their activities, performance or properties? What is obtained as structural properties by popular conventional analytical methods, such as X-ray diffraction (XRD) or nitrogen-adsorption measurement, is limited t...

The use of visible-driven photocatalysts has fascinated attention as a capable and sustainable approach for wastewater remediation. In this work, BiOBr/carbon quantum dot (CQDs)/saponite composites (CQDs/[email protected]) were fabricated via hydrothermally using two different CQDs/Clay precursors (in-situ synthesis (IS) and physical mixing (PM))....

The development of novel photocatalysts for efficient utilization of solar energy is highly essential for the most critical humanitarian challenges, i.e., energy and water crises as well as environmental pollution. Bismuth tungstate (Bi2WO6), an outstanding Aurivillius phase perovskite, has attracted intensive attention as a visible-light-responsiv...

Novel materials with a periodic structure have recently been intensively studied for various photonic and photocatalytic applications due to an efficient light harvesting ability. Here, inverse opal titania (IOT) has been investigated for possible enhancement of photocatalytic activity. The IOT films were prepared on a glass support from silica and...

Metal-doped graphitic carbon nitride (MCN) materials have shown great promise as effective photocatalysts for the conversion of acetic acid to carbon dioxide under UV–visible irradiation and are superior to pristine carbon nitride (g-C3N4 , CN). In this study, the effects of metal dopants on the physicochemical properties of metal-doped CN samples...

Photoabsorption properties of cellulose fibres under continuous and modulated irradiation were investigated in situ by the use of reversed double-beam photoacoustic spectroscopy (RDB-PAS). This photoacoustic (PA) measurement enabled observation of ultraviolet- and visible light-induced, electron trap filling, reductive change on the surface of the...

The Front Cover shows the open route for multiple oxygen reduction reaction in radial rutile TiO2‐nanorod microsphere by the surface modification with iron oxide clusters. More information can be found in the Research Article by Ryota Kojima, Bunsho Ohtani, and Hiroaki Tada.

Photocatalytic treatment is a remarkable process that is popular for the degradation of several organic contaminants in wastewater. In this work, a series of graphitic carbon nitride/ZnTi-mixed metal oxide (CN/ZnTi-MMO) composites were prepared as photocatalysts through simple calcination. The CN-MMO samples were characterized and applied for photo...

“This study shows that the surface modification of TiO2 nanorod homomesocrystal (so‐called “sea urchin‐like TiO2 microsphere”) by extremely small iron oxide (FeOx) clusters enhances the UV‐ and visible‐light activities for aerobic oxidative degradation of model organic pollutant by approximately one‐order of magnitude…” This and more about the stor...

Radial rutile TiO2 nanorod homomesocrystals (TiO2‐NR HOMCs) or the so‐called “sea urchin‐like TiO2 microspheres” were synthesized by using a hydrothermal method. TiO2‐NR HOMCs show photocatalytic activity for aerobic oxidative degradation of 2‐naphthol under irradiation of UV‐ and visible light. Furthermore, extremely small iron oxide clusters were...

Titanium(IV) oxide, titania, photocatalyst particles were prepared from titanium alkoxide in the presence of several kinds of ionic liquids, and it was clarified that a group of samples exhibited photocatalytic activity for phenol degradation under the irradiation of light of wavelength >400 nm higher than those of the other group of samples. Altho...

The Fe(III)-doped montmorillonite (Mt)/TiO2 composites were fabricated by adding Fe(III) during or after the aging of TiO2/Ti(OH)4 sol–gel in Mt, named as xFe-Mt/(1 − x)Fe-TiO2 and Fe/Mt/TiO2, respectively. In the xFe-Mt/(1 − x)Fe-TiO2, Fe(III) cations were expected to be located in the structure of TiO2, in the Mt, and in the interface between the...

Metal-free graphitic carbon nitride (GCN) is an optical semiconductor with the advantage of in situ H2O2 generation parallel to pollutant removal. The photocatalytic degradation mechanism using GCN is attributed to a series of reactions with reactive oxygen species and photogenerated holes. However, the role of each species in the photocatalytic pr...

Pollutants degradation via visible-light driven photocatalysts have attracted interest as a potentially efficient and sustainable approach for wastewater treatment. In the present study, a series of oxygen-doped hollow porous surface graphitic carbon nitride (OCN) has been prepared by one-pot thermal polycondensation of melamine with different amou...

Zn-Cr layered double oxide/fly ash (ZnCrLDO/FA) composites were synthesized using three different fly ashes (YEM, DAT, PAN) as photocatalysts for the degradation of ciprofloxacin through in situ coprecipitation followed by calcination. Ciprofloxacin (10 mg/L) was completely decomposed more than 98% within 120 min by ZnCrLDO/YEM composites in aqueou...

The effect of ion doping and the incorporation of additives on photocatalysts’ textural properties have been reviewed. Generally, it can be summarised that ion doping and additives have beneficial effects on photocatalytic efficiency and not all have an increase in the surface area. The excessive amount of dopants and additives will produce larger...

Decahedral anatase particles (DAPs) have been prepared by the gas-phase method, characterized, and analyzed for property-governed photocatalytic activity. It has been found that depending on the reaction systems, different properties control the photocatalytic activity, that is, the particle aspect ratio, the density of electron traps and the morph...

Plasmonic photocatalysis, i.e., photocatalysis with activity under visible-light (vis) irradiation due to plasmonic feature of noble metals (NMs), has been intensively studied as promising method for solar energy conversion. Although various plasmonic photocatalysts have already been investigated, the vis activity is usually low, and thus should be...

In this study, an aqueous solution containing rhodium(IV) (Rh(IV)) was prepared by oxidation of rhodium(III) (Rh(III)) with solid sodium bismuthate in nitric acid and then used as a medium for hydrothermal titania preparation to obtain rhodium-doped titania (Rh-TiO2) composite. Rh(IV) species were observed in Rh-TiO2 in XPS analysis. Effect of rhod...

It is of course necessary to study photocatalysis, but not limited to photocatalysis, based on the reliable scientific method, using correct logic, concepts, and methods, but it seems that sometimes we encounter examples of discussion in photocatalysis studies only upon empirical ways, i.e. by tracing previous studies and/or discussions without rec...

Designing of three-dimensional (3D) materials such as inverse-opal (IO) photonic crystals (PCs) has been identified as an effective pathway to enhance light harvesting to longer electromagnetic absorption regions such as visible and infrared [1]. IO PCs exhibit photonic band gap (PBG) and this band structure predicts the translation of photons with...

Different from organic molecules and metal complexes, which can be identified by chemical composition and structural characteristics such as NMR spectra, inorganic solid materials especially metal oxides cannot be identified, i.e., their purity cannot be evaluated in a strict scientific sense, because at least three structural parameters, bulk stru...

NaTaO3, a semiconductor with a perovskite structure, has long been known as a highly active photocatalyst for overall water splitting when appropriately doped with La cations. A profound understanding of the surface feature and why and how it may control the water splitting activity is critical because redox reactions take place at the surface. One...

We report a simple strategy for providing a homogenous TiO2 nanofibre host environment to stabilize Cu2O nanoparticles with an average size of ∼60 nm and high dispersibility. We found that the small fraction of Cu2O nanoparticles in direct contact/partially submerged with TiO2 nanofibre arrays (diameter ∼300 nm and length ∼650 nm) showed excellent...

The diffuse reflectance spectroelectrochemistry (SE-DRS) and reversed double-beam photoacoustic spectroscopy (RDB-PAS) provide unique, complementary information on the density of electronic states (DOS) in the vicinity of the conduction band bottom. The measurements are performed under quite different conditions, representing the solid/liquid and s...

Here, we report a novel structured material, titania inverse-opal photonic crystal with or without a single gold nanoparticle in each void, to provide a photoabsorption design strategy as enhanced photoreaction rates, only when wavelengths of photoirradiation, photoabsorption (by gold nanoparticles or titania), and photonic-bandgap edge are trebly...

Stable and enhanced UV/vis photocatalytic activity via the Z-scheme mechanism of Cu x O@TiO 2 prepared by the microemulsion method.

Here, we introduce some studies on the synthesis and photocatalysis of various kinds of titania, including anatase, rutile, amorphous titania, brookite, and TiO2(B), which are most often used in photocatalytic studies. It has often been reported that anatase has higher photocatalytic activity. However, action spectra analyses revealed that anatase...

A strange story, including a new concept of identification of inorganic solid materials and of photocatalyst design, is told here. Why is it that solid materials have not been identified,...

Changes in surface and bulk structures of rutile titania particles induced by braying up to 10 d and post calcination in air at 773 K were analyzed by reversed double-beam photoacoustic spectroscopy. The observed energy-resolved distribution of electron traps indicated that the surface was amorphized by braying to give rutile-core amorphous-shell s...

Zn-Ti layered double hydroxide/montmorillonite (ZTL/MT) and Fe-doped ZTL/MT (ZTL/[email protected]%) were prepared as photocatalyst for Cr(VI) reduction. The ZTL/[email protected]% exhibited the highest photocatalytic activity, suggesting that a combination of ZTL and Fe-bearing MT could enhance photocatalytic activity by suppressing the recombinat...

How can we design solid photocatalysts? What is the decisive factor controlling photocatalytic activities?So-called band-structure model (BSM), electrons in a valence band (VB) of a photocatalyst is photoexcited into a conduction band (CB), leaving positive holes in VB, and electrons and holes reduce and oxidize, respectively, substrates adsorbed o...

Designing of three-dimensional (3D) materials such as inverse-opal (IO) photonic crystals (PCs) has been identified as an effective pathway to enhance light harvesting to longer electromagnetic absorption regions such as visible and infrared [1]. IO PCs exhibit photonic band gap (PBG) and this band structure predicts the translation of photons with...

Different from organic molecules and metal complexes, which can be identified by chemical composition and structural characteristics such as NMR spectra, inorganic solid materials especially metal oxides cannot be identified, i.e., their purity cannot be evaluated in a strict scientific sense, because at least three structural parameters, bulk stru...

Seven commercial titania (titanium(IV) oxide; TiO2) powders with different structural properties and crystalline compositions (anatase/rutile) were modified with copper by two variants of a photodeposition method, i.e., methanol dehydrogenation and water oxidation. The samples were characterized by diffuse reflectance spectroscopy (DRS), X-ray powd...

Here, we report experimental evidence of interparticle spatial overlapping of orbitals to result in interparticle charge-transfer excitation (ICTE) at an anatase-rutile interface which is expected to be applicable to clarify the relative band position of metal-oxides and mixture homogeneity of mixture samples measured by reversed double-beam photoa...

In order to clarify the reason of often reported low photocatalytic activity of rutile titania compared to that of anatase titania and the sluggish kinetics for oxygen reduction of rutile titania, in this study, faceted copper(I) oxide (Cu2O) particles (FCPs), i.e., cube, cuboctahedron and octahedron, were deposited onto rutile particles by an in-s...

The effects of surface loading of iridium(II) oxide (IrO 2), manganese(IV) oxide (MnO 2), and cobalt(II) phosphate (CoPi) on the rate of photocatalytic oxygen evolution by anatase or rutile titania particles suspended in aqueous solutions of an electron acceptor, iodate ions, were studied by light intensity-dependence (LID) kinetic analyses. Althou...

Molecular catalyst sensitized system (MCSS), where an excited molecular catalyst adsorbed on semiconductor such as TiO2 injects electron to the conduction band of semiconductor leading to hydrogen evolution/CO2 reduction coupled with an oxidation of water on the molecular catalyst, has been one of the most probable candidates in the approach to art...

Anatase nanoparticles with a size of ca. 5 nm were prepared in mesoporous silica (SBA-15 with the pore diameter of 6 nm) by impregnation of the precursor derived from titanium tetraisopropoxide and subsequent heat treatment in air. The mesoporous structure of the anatase–silica hybrid and the size of the anatase particles were kept unchanged during...

In article number 2000204, Changhua Wang, Xintong Zhang, and co‐workers demonstrate a solution plasma strategy to introduce H dopant into oxygen vacancy type TiO2. The combination of H dopant and oxygen vacancy endows a 300 times higher conversion rate for CO2 reduction with H2O. The H dopant is believed to bridge the gap between oxygen vacancy and...

Noble metal (NM)-modified wide-bandgap semiconductors with activity under visible light (Vis) irradiation, due to localized surface plasmon resonance (LSPR), known as plasmonic photocatalysts, have been intensively studied over the last few years. Despite the novelty of the topic, a large number of reports have already been published, discussing th...

Heterojunctions of small CuO nanoclusters (synthesized by radiolysis) with TiO2 (commercial P25) induced a photocatalytic activity under visible light irradiation in a wide range of wavelengths due to the narrow bandgap of CuO nanoclusters of around 1.7 eV. The optical, chemical, and electrical properties of these composite nanomaterials were studi...

Titania-supported nickel catalysts (3, 6, 12 and 20 wt% Ni/TiO2) were prepared by a sol–gel method. The results showed that the CO2 conversion increased with increasing Ni content and 20 wt% Ni/TiO2 exhibited the highest CO2 conversion and CH4 yield. The results on XRD and EXAFS revealed unit cell expansion and lattice distortion, which indicated t...

Understanding the science behind highly active materials is essential to advance the field of photocatalytic water splitting for solar energy harvesting. Sodium tantalate (NaTaO3) doped with La cations is one of the best engineered materials for efficient water splitting to evolve hydrogen. In this study, physical insights into the sensitivity of w...

Colored wide‐bandgap semiconductor oxides with abundant mid‐gap states have long been regarded as promising visible light responsive photocatalysts. However, their catalytic activities are hampered by charge recombination at deep level defects, which constitutes the critical challenge to practical applications of these oxide photocatalysts. To addr...

Surface modification of titania with noble and semi-noble metals resulted in significant enhancement of photocatalytic activity. Presented data, showing the photocatalytic properties of TiO2-M (where M is Pt and/or Cu) photocatalysts were further used as Fe3O4@SiO2/TiO2-M magnetic nanocomposites shells in "Mono- and bimetallic (Pt/Cu) titanium(IV)...

A clear understanding of the electron energy structure of TiO2(B)/anatase is needed to study the related catalytic reactions and design new composite photocatalysts. In this study, the electron energy structures of TiO2(B) and anatase were estimated by analyzing the energy-resolved distribution of electron traps measured by reversed double-beam pho...

Different from organic molecules and metal complexes, which can be identified by chemical composition and structural characteristics such as NMR spectra, inorganic solid materials especially metal oxides cannot be identified, i.e., their purity cannot be evaluated in a strict scientific sense, because at least three structural parameters, bulk stru...

How can we design solid photocatalysts? What is the decisive factor controlling photocatalytic activities? So-called band-structure model (BSM), electrons in a valence band (VB) of a photocatalyst is photoexcited into a conduction band (CB), leaving positive holes in VB, and electrons and holes reduce and oxidize, respectively, substrates adsorbed...

Designing of three-dimensional (3D) materials such as inverse-opal (IO) photonic crystals (PCs) has been identified as an effective pathway to enhance light harvesting to longer electromagnetic absorption regions such as visible and infrared [1]. IO PCs exhibit photonic band gap (PBG) and this band structure predicts the translation of photons with...

Titanium(IV) oxide is one of the most widely investigated photocatalysts. However, separation of nano-sized particulate titania might result in profitless technologies for commercial applications. Additionally, bare titania is almost inactive under the Vis range of solar spectrum due to its wide bandgap. Therefore, the present study aims to prepare...

The development of high-quality photocatalytic materials for the degradation of organic pollutants under visible light irradiation is a vital field of research. In the present study, a composite of natural sepiolite clay and synthetic graphitic carbon nitride (CN) mixed with dispersed palladium nanoparticles was developed for the efficient photocat...

We report on the first time the identification of heteroatom-doped and undoped C 3 N 4 with the energy-resolved distribution of electron traps (ERDT) near the conduction band bottom position (CBB) using reversed...

In this study, ZnTi-mixed metal oxides (ZTM), such as ZnTiO3, were synthesized from ZnTi layered double hydroxides by varying the molar ratio of Zn/Ti, calcination temperatures and synthesis methods (hydrothermal or reflux). The surface electronic characteristics of ZTM were investigated by the energy-resolved distribution of electron traps (ERDTs)...

Octahedral anatase particles (OAPs) belonging to faceted titania photocatalysts exhibit one of the highest photocatalytic activities among various titania photocatalysts, probably due to hindered recombination of charge carriers resulting from low content of defects (recombination centers). In this study, OAPs have been examined for oxidative decom...