Kiyoaki Shinohara

Cu2O as a photocatalyst for overall water splitting under visible light irradiation

Photocatalytic decomposition of water into H2 and O2 on Cu2O under visible light irradiation is investigated; the photocatalytic water splitting on Cu2O powder proceeds without any noticeable decrease in the activity for more than 1900 h.

A highly active photocatalyst for overall water splitting with a hydrated layered perovskite structure

Photocatalytic decomposition of H2O into H2 and O2 over a novel photocatalyst, K2La2Ti3O10, was accomplished. K2La2Ti3O10, a layered perovskite-type compound with a hydrated interlayer space, exhibited a high activity for overall water splitting with Ni-loading. The highest activity was obtained over Ni(3.0 wt%)–K2La2Ti3O10 when the reaction was carried out in aqueous KOH solution (0.1 M, pH=12.8). By comparison with other Ni-loaded photocatalysts reported previously, the reaction mechanism of Ni–K2La2Ti3O10 was discussed.

Effect of the particle size for photocatalytic decomposition of water on Ni-loaded K4Nb6O17

Abstract The photocatalytic activities of water splitting by small particles (0.1–2 μm) of K 4 Nb 6 O 17 were studied. The milled catalysts were prepared by two kinds of ball-milling methods from the powder whose particles were several tens of micrometers in diameter. The surface area of the milled catalyst measured by N 2 adsorption at 77 K increased by an order of magnitude. The crystal structure was almost retained as K 4 Nb 6 O 17 , as evidenced by the results of X-ray diffraction and scanning electron micrography. The photocatalytic activity for an overall decomposition of water of the Ni-loaded K 4 Nb 6 O 17 was twice as high as that for the original catalyst.

Preparation of porous niobium oxide by the exfoliation of K 4 Nb 6 O 17 and its photocatalytic activity

A new porous material was prepared from a layered compound, K 4 Nb 6 O 17 , through the exfoliation of its layers. A composite of the niobate sheets and MgO particles were obtained by precipitating the exfoliated two-dimensional niobate sheets with MgO fine particles. Porous niobium oxide was obtained by removal of the MgO particles from the composite after thermal treatment. It had a large surface area and showed higher photocatalytic activity than the original H + /K 4 Nb 6 O 17 for H 2 evolution from various aqueous alcohol solutions.

Selective Growth of Vertically Aligned Single-, Double-, and Triple-Walled Carbon Nanotubes by Radiation-Heated Chemical Vapor Deposition

The synthesis of vertically aligned single-walled carbon nanotube (SWCNT), double-walled carbon nanotube (DWCNT), and triple-walled carbon nanotube (TWCNT) films has been achieved by a combination of radiation-heated chemical vapor deposition (RHCVD) and long-throw sputtering. The proportions of specific walled CNTs/as-grown CNTs are as follows: SWCNT/CNT ratio of 87%, DWCNT/CNT ratio of 83%, and TWCNT/CNT ratio of 62%. When the population density of vertically aligned CNTs on a substrate ranges from 1.1 ×109 to 7.1 ×1010 bundles/cm2, the selective growth of graphene walls of CNTs is achieved. As outer diameters and the number of graphene walls of CNTs increase, CNTs grow longer. It is considered that the larger the metallic catalyst diameter, the longer the catalyst lifetime.

Selective Growth of Single-, Double-, and Triple-Walled Carbon Nanotubes through Precise Control of Catalyst Diameter by Radiation-Heated Chemical Vapor Deposition

Radiation-heated chemical vapor deposition (RHCVD) is a newly developed process which enables the maintenance of narrow catalyst diameter distributions until carbon nanotubes (CNTs) start growing and the synthesis of single-walled carbon nanotube (SWCNT), double-walled carbon nanotube (DWCNT), and triple-walled carbon nanotube (TWCNT) films by changing catalyst diameters. The proportions of specific walled CNTs/as-grown CNTs are as follows: SWCNT/CNT ratio of 100%, DWCNT/CNT ratio of 88% and TWCNT/CNT ratio of 76%. It is clarified that CNT diameter and the number of graphene walls of CNTs are proportional to catalyst diameter.

Ion-exchangeable oxides with layered perovskite structures as photocatalysts for overall water splitting

A novel series of photocatalysts for an overall water splitting is reported. The catalysts have a layered perovskite type structure with a general formula of A{sub 2{minus}x}La{sub 2}Ti{sub 3{minus}x}Nb{sub x}O{sub 10} (A = K, Rb, Cs; x = 0, 0.5, 1.0). The catalysts, except for the one with x = 1.0, are spontaneously hydrated, and the band gap irradiation induced efficient evolution of H{sub 2} and O{sub 2} in a stoichiometric ratio from an aqueous alkaline solution when a proper amount of Ni loading was made. The reaction mechanism of water splitting on these catalysts is discussed on the bases of the structural study of the catalysts.

Selective Growth of Carbon Nanotubes and Their Application to Transparent Conductive Plastic Sheets and Optical Filters

Carbon nanotubes (CNTs) have incomparable physical properties and their applications in various fields have been examined. In particular, CNTs composed of a few cylindrical walls are useful for optoelectronic applications. The electronic properties of CNTs, however, significantly change depending on their chirality and the number of graphene walls. Therefore, first of all, the selective growth of graphene walls is required, and ultimately, chiral selection technology should be established. In single-walled CNTs (SWCNTs) and double-walled CNTs (DWCNTs), both semiconducting and metallic characteristics exist according to the chirality of the CNTs. On the other hand, it was predicted that all triplewalled CNTs (TWCNTs) have semimetal characteristics. Therefore, TWCNTs may be used in electronic applications without the need for chiral selection. Moreover, because TWCNTs is the finest multi-walled CNTs (MWCNTs), it is academically interesting to clarify the formation mechanism and various properties of TWCNTs. Nowadays, as-grown SWCNT films are well synthesized on substrates by several types of chemical vapor deposition (CVD) (Hata et al., 2004; Murakami et al., 2004; Zhong et al., 2005). In addition, a synthetic process of producing high-purity SWCNT powder was established at the end of the last century (Nikolaev et al., 1999). As-grown DWCNT films on substrates have also been reported (Hiramatsu et al., 2005; Yamada at al., 2006). From the viewpoint of obtaining DWCNT powder, the CVD of DWCNT powder with supporting material was reported (Muramatsu et al., 2005). The combustion removal of SWCNTs from a mixture of SWCNTs and DWCNTs was also reported (Ramesh et al., 2006). The combustion removal method required a post-treatment to obtain high-yield DWCNT powder. On the other hand, the synthesis of TWCNTs has not reported at all, regardless of the form, for example, films and powder. For the purpose of obtaining CNT films with high DWCNT and TWCNT contents, post-treatments after CNT synthesis are not suitable, because CNTs have almost same chemical properties not related to the number of graphene walls. Posttreatments are only effective for removing amorphous carbon and metallic catalysts from CNTs. Therefore, it is necessary to develop an as-grown synthetic process for DWCNT and TWCNT films.