Hamid Oveisi

Unusual antibacterial property of mesoporous titania films: drastic improvement by controlling surface area and crystallinity.

One of the most urgent requirements of human life in the 21 century is development of new antibacterial materials and sterilization technologies that can improve human health. Until now, the most commonly used antibacterial agents are based on chlorine, chlorine dioxide, and organic biocide compounds. These agents are extremely toxic for humans and their residues are also not environmentally friendly. Therefore, it is very important to develop antibacterial biocompatible materials. Titanium dioxide (titania, TiO2) materials in the anatase form have attracted great interest as a new antibacterial material. Titania can work well under ultraviolet (UV) light owing to its photo-semiconductor properties. Currently, this property has been widely utilized for various applications such as water treatment, air and environmental purification, hazardous waste remediation, and deactivation of bacteria. Commercial products with titania (e.g., self-cleaning glasses and anti-fogging coatings) are well known all over the world. To date, various titania-based nanostructures including nanorods and nanoparticles have been reported. To further enhance the photocatalytic performance, many efforts have been made for doping various metal/semiconductor elements into titania materials. In this system, the electrons accumulated on the metal and holes remained on the photocatalyst surface. Therefore, a significant reduction in the recombination rate is realized owing to better charge separation between the electrons and holes. Therefore, the titania-based composites with metal/semiconductor elements can enhance the overall photocatalytic efficiency and the damage of microorganisms of the cell. In this Communication, we focused on a further simple and low-cost synthetic method and synthesized mesoporous titania films by utilizing bottom-up nanotechnology with surfactant assembly. Mesoporous materials with extremely high surface area should be good candidates for the next generation of antibacterial materials. Compared with the traditional titania materials mentioned above, the high surface area originated from mesoporous networks can provide a higher amount of hydroxyl radicals (·OH) which can increase the photoactivity. In the past few years, special attention has been paid to the synthesis of mesoporous titania powders as effective photocatalysts including an antibacterial application. However, the mesoporous titania in the powder form has some disadvantages. The powders which are not fixed on substrates are washed out easily by external treatments and then the released particles themselves may pollute the environment. Also, nanosized powders generally cause serious problems to human health. Therefore, the mesoporous titania films reported here are more applicable [a] H. Oveisi, X. Jiang, Dr. Y. Nemoto, Prof. Dr. Y. Yamauchi World Premier International (WPI) Research Center for Materials Nanoarchitectonics (MANA) National Institute for Materials Science (NIMS) 1-1 Namiki, Tsukuba, Ibaraki, 305-0044 (Japan) Fax: (+81)29-860-4706 E-mail : Yamauchi.Yusuke@nims.go.jp [b] Dr. S. Rahighi, Prof. Dr. S. Wakatsuki Structural Biology Research Center High Energy Accelerator Research Organization (KEK) 1-1 Oho, Tsukuba, Ibaraki, 305-0801 (Japan) [c] H. Oveisi, Prof. Dr. A. Beitollahi Center of Excellence in Advanced Materials and Processing Department of Metallurgy and Materials Engineering Iran University of Science and Technology (IUST) Narmak, Tehran 16844 (Iran) [d] X. Jiang, Prof. Dr. Y. Yamauchi Faculty of Science and Engineering Waseda University 3-4-1 Okubo, Shinjuku, Tokyo 169-8555 (Japan) [e] Prof. Dr. Y. Yamauchi Precursory Research for Embryonic Science and Technology (PRESTO) Japan Science and Technology Agency (JST) 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan). [] These authors contributed equally to this work. Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/asia.201000351.

A High‐Speed Passive‐Matrix Electrochromic Display Using a Mesoporous TiO2 Electrode with Vertical Porosity

Recently, the application of electronic paper (E-paper) has attracted considerable attention. Many types of reflective displays, such as reflective liquid crystal displays and electrophoretic displays, have been introduced and applied to E-paper. Among them, electrochromic materials, which change in color intensity when an appropriate potential is applied, are the subject of an increasing number of reports. Recently, polymers such as poly(3,4-ethylenedioxythiophene) (PEDOT) or catenanes were reported to show electrochromic behavior. The slow response time for coloring has been a serious problem with these kinds of polymers. As probable electrochromic materials, viologens have commonly been utilized for electrochromic displays (ECDs). Many studies have focused on viologen-modified microspheres or nanostructures to increase the switching speed. Viologens are basically blue in color, and it is thus difficult to realize a full-color display. Furthermore, these kinds of displays have a common drawback: poor background whiteness. To date, electronic displays have not been able to meet the requirements necessary for extensive practical applications. Currently, full-color reflective displays that demonstrate a fast response time are in much demand. Usually, display devices are driven by either active-matrix drive mode or passivematrix drive mode. Active-matrix drive mode is very fast, but it needs expensive thin-film transistors (TFT) for all the pixels of the display, which leads to a high price. Passive-matrix drive mode does not need such expensive electric elements, and it has a simple, low-cost structure. However, when ECD devices are driven by passive-matrix mode at high scanning speed, the drift of electrochromic materials around the electrode leads to poor resolution. That is, the display images are blurry. Herein, we aim to realize high scanning speed and high display quality. We focused on leuco dyes, which are well known as recording materials in thermal imaging systems, because the leuco dyes show a wide variety of colors and are commercially available. We demonstrated a high-speed and high-resolution electrochromic passive-matrix display using a leuco dye with a mesoporous TiO2 electrode with vertical pores (Figure 1). The vertical pores of the electrode can support effective diffusion of leuco dyes perpendicular to the electrode and can prevent the diffusion of the dye around the electrode. Since the colorless state of this kind of display is transparent, it exhibits better background whiteness, which improves readability and reduces eyestrain. Furthermore, the application of leuco dyes to ECD devices has high potential to realize a full-color reflective display with low production costs. These features are very desirable for future E-paper applications. Our device, which consists of two electrodes (working electrode and counter electrode) and electrolyte (Figure 1), was driven by the passive-matrix driving method (an addressing scheme used in earlier liquid crystal displays). Each electrode has striped indium–tin-oxide (ITO) layers 420 mm wide on a glass substrate (Figure 1b and Figure S1 in the Supporting Information). The mesoporous TiO2 film was grown only on the observation side of the working electrode. By improving the previous method, continuous TiO2 films with highly ordered mesostructure and vertical pores were uniformly prepared on the working electrodes by spin coating with a precursor solution. The film thicknesses were changed by using different spinning speeds. Thicknesses of approximately 300, 200, and 100 nm were realized by speeds of 2000, 4000, and 6000 rpm, respectively. Cross-sectional and topsurface SEM images showed that mesopores were oriented vertically with respect to the substrate (Figure S1c in the Supporting Information). The mesochannel walls are composed of periodically arranged cages with connecting necks between the neighboring cages (see the Supporting Information, in particular Figure S2, for details). The two electrodes sandwiched the electrolyte so that the striped ITO layers were orthogonally crossed (Figure 1b and Figure S3 in the Supporting Information). The electrolytic solution consisted of black leuco dye (2-(3’-trifluoromethylphenylamino)-6’[*] W. Weng, T. Higuchi, M. Suzuki, T. Fukuoka, Dr. T. Shimomura, Dr. M. Ono Funai Electric Advanced Applied Technology Research Institute Inc. 2-1-6 Sengen, Tsukuba, Ibaraki 305-0047 (Japan) E-mail: weng.w@funai-atri.co.jp

Inclusion of size controlled gallium oxide nanoparticles into highly ordered 3D mesoporous silica with tunable pore diameters and their unusual catalytic performance

Here we demonstrate for the first time a novel nanosieve approach for tuning the size, shape, dispersion and the quantity of the gallium oxide nanoparticles inside a mesoporous silica support with a three dimensional porous structure, high surface area, and large pore volume (KIT-6). It was found that the size and shape of the gallium oxide nanoparticles in the pore channels of the KIT-6 can be controlled by simply tuning the pore diameter of the support. The obtained gallium oxide/KIT-6 nanocomposites with different gallium oxide contents have been characterized by several characterization techniques such as powder XRD, SAXS, nitrogen adsorption, UV-Vis, FT-IR, HRSEM and HRTEM. XRD, HRTEM and nitrogen adsorption results reveal that the mesostructural order of the KIT-6 materials was not affected even after the encapsulation of ca. 30 wt% gallium oxide nanoparticles. UV-Vis results reveal that bandgap of the materials can be controlled by simply changing the concentration of the gallium oxide or varying the pore diameter of the support. The above catalytic materials have been also successfully employed for the benzylation of benzene and other aromatic compounds. The role of the pore diameter of the support, the loading of the metal oxide nanoparticles and other reaction parameters affecting the activity of the catalysts has been clearly demonstrated. It has been found that gallium oxide supported KIT-6 materials are highly stable and active, and show superior performance over other metal substituted mesoporous and zeolite materials with a high substrate conversion and a high product selectivity in the alkylation of benzene under the optimized reaction conditions.

A facile synthesis of alkylated nitrogen heterocycles catalysed by 3D mesoporous aluminosilicates with cage type pores in aqueous medium

Friedel–Crafts alkylation of nitrogen heterocycles such as indoles and pyrroles with epoxides has been efficiently carried out using cage-type mesoporous aluminosilicates as recyclable catalysts in water under environmentally benign and mild conditions.

Preparation of Ordered Mesoporous Alumina‐Doped Titania Films with High Thermal Stability and Their Application to High‐Speed Passive‐Matrix Electrochromic Displays

Ordered mesoporous alumina-doped titania thin films with anatase crystalline structure were prepared by using triblock copolymer Pluronic P123 as structure-directing agent. Uniform Al doping was realized by using aluminum isopropoxide as a dopant source which can be hydrolyzed together with titanium tetraisopropoxide. Aluminum doping into the titania framework can prevent rapid crystallization to the anatase phase, thereby drastically increasing thermal stability. With increasing Al content, the crystallization temperatures tend to increase gradually. Even when the Al content doped into the framework was increased to 15 mol %, a well-ordered mesoporous structure was obtained, and the mesostructural ordering was still maintained after calcination at 550 °C. During the calcination process, large uniaxial shrinkage occurred along the direction perpendicular to the substrate with retention of the horizontal mesoscale periodicity, whereby vertically oriented nanopillars were formed in the film. The resulting vertical porosity was successfully exploited to fabricate a high-speed and high-quality passive-matrix electrochromic display by using a leuco dye. The vertical nanospace in the films can effectively prevent drifting of the leuco dye.