Takuya Kitaoka

Capturing of bisphenol A photodecomposition intermediates by composite TiO2–zeolite sheets

Abstract Two types of powders, titanium dioxide (TiO 2 ) photocatalyst and zeolite adsorbent, were made into a paper-like composite by a papermaking technique using a dual polyelectrolyte system. The photodegradation behavior of bisphenol A (2,2-bis(4-hydroxyphenyl)propane, BPA) in water was investigated under UV irradiation. It was found that TiO 2 sheets could photocatalytically decompose BPA in an aqueous medium. Composite TiO 2 –zeolite sheets, however, demonstrated a higher efficiency for BPA removal from water than did zeolite-free TiO 2 sheets owing to the synergistic effect obtained through the combined use of TiO 2 and zeolite, as reported in our previous study. Furthermore, the total organic carbon (TOC) content of the system was reduced, evidently through the use of composite sheets, rather than a TiO 2 powder suspension or zeolite-free TiO 2 sheets. Trace amounts of intermediates resulting from BPA degradation were detected in the water treated with the composite sheets. In general, various intermediates are formed during the TiO 2 photodecomposition of organic compounds, which can potentially cause a secondary pollution because the degradation products sometimes turn out to be more hazardous than the parent compound. The composite TiO 2 –zeolite sheets prepared in the present study helped to overcome this problem by allowing the elimination of BPA without the release of hazardous intermediates into water: most of the intermediates were temporarily captured by the zeolite adsorbent contained in the composite sheets, and eventually decomposed through TiO 2 photocatalysis. Paper-like TiO 2 –zeolite composites clearly offer great advantages in efficacy and safety for the aqueous decomposition of BPA.

Transparent, Conductive, and Printable Composites Consisting of TEMPO-Oxidized Nanocellulose and Carbon Nanotube

Ultrastrong, transparent, conductive and printable nanocomposites were successfully prepared by mixing single-walled carbon nanotubes (CNTs) with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibrils (TOCNs) with abundant sodium carboxyl groups on the crystalline nanocellulose surfaces. The surface-anionic cellulose nanofibrils had reinforcing and nanodispersing effects on the CNTs both in water used as the dispersed medium and in the dried composite film, providing highly conductive and printable nanocomposites with a small amount of CNTs. TOCNs are therefore expected as an effective flexible matrix that can be used as an alternative to conventional polymers for various electrical materials, when nanocomposited with CNTs and also graphene. Our findings provide a promising route to realize green and flexible electronics.

Removal of indoor pollutants under UV irradiation by a composite TiO2–zeolite sheet prepared using a papermaking technique

Toluene and formaldehyde are malodorous and cause indoor pollution. These materials have received much attention as hazardous and malodorous substances. It is well known that long-term exposure to even fairly low levels of toluene and formaldehyde brings about the risk of asthma and eczema. In this study, a composite TiO2-zeolite (ZE) sheet prepared using a papermaking technique was applied to remove toluene and formaldehyde under UV irradiation. The optimum composition of the TiO2 (Ti)-ZE sheet was studied in detail with regard to the effective removal of various indoor pollutants. Gaseous toluene and formaldehyde were removed by a composite TiO2-ZE sheet with different efficiencies depending upon the ratio of Ti/ZE in the composite sheet. The composite sheets could decompose formaldehyde and toluene repeatedly after being recharged. It was shown that the sheets are potentially applicable as highly functional materials to be placed on walls and ceilings of houses for the removal of various indoor pollutants.

Photocatalytic oxidation of NOx using composite sheets containing TiO2 and a metal compound

The photocatalytic oxidation of nitrogen oxides (NO(x)) over titanium dioxide (TiO(2)) sheets containing metal compounds (MCs) had been studied. Calcium oxide (CaO), magnesium oxide (MgO), calcium carbonate (CaCO(3)), aluminium oxide (Al(2)O(3)) and ferric oxide (Fe(2)O(3)) were used as MCs. Al(2)O(3) and Fe(2)O(3) added to the TiO(2) sheet did not affect the photooxidation of nitrogen oxides (NO(x)). The CaO sheet treated with TiO(2) sol had the greatest efficiency as a NO(x) remover under UV irradiation. It is believed that CaO has a high adsorptivity for nitrogen dioxide (NO(2)) and nitric acid (HNO(3)). The amount of NO(x) removed by a TiO(2) sheet including MC showed a tendency to increase with increasing pH of the MC suspension, i.e. there is a good correlation between the alkalinity of the MC and the retention of NO(2) and HNO(3).

In situ synthesis of silver nanoparticles on zinc oxide whiskers incorporated in a paper matrix for antibacterial applications

Silver nanoparticles (AgNPs) were successfully synthesized in situ on a paper matrix composed of ceramic fibers as the main framework and zinc oxide (ZnO) whiskers as a selective support for AgNPs. Paper-like ceramic fiber/ZnO whisker composites were prepared in advance using a high-speed, low-cost papermaking technique, then immersed in an aqueous solution of silver nitrate for 6 h. AgNPs with particle size 5–20 nm were spontaneously formed on the ZnO whiskers through selective ion-exchange between Ag and Zn species, and simultaneous ZnO-mediated photo-reduction under natural light irradiation. As-prepared material (AgNPs@ZnO paper) was subjected to antibacterial assay by the disk diffusion method using Escherichia coli. The AgNPs@ZnO paper exhibited excellent antibacterial activity and durability for repeated use, as compared with paper composites containing either ionic Ag components or commercial crystalline Ag microparticles. The facile and direct synthesis of AgNPs on a paper-like matrix is a unique approach for the immobilization of highly active metal NPs onto easy-to-handle support materials, and the AgNPs@ZnO paper is expected to be a promising bioactive material having both antibacterial function and paper-like utility.

Preparation and characteristics of high performance paper containing titanium dioxide photocatalyst supported on inorganic fiber matrix

A novel paper-based material containing titanium dioxide (TiO(2)) photocatalyst was successfully prepared by a papermaking technique with the internal addition of inorganic fibers on which TiO(2) particles were supported. Photodegradation performance of acetaldehyde gas, an indoor pollutant, and the durability of the TiO(2)-containing papers were investigated under UV irradiation. Ceramic fiber suspension and polydiallyldimethylammonium chloride as a cationic flocculant were mixed, followed by the addition of TiO(2) suspension and anionic polyacrylamide. Subsequently, the inorganic mixture was poured into a pulp suspension, and TiO(2) handsheets then prepared by a papermaking method. The tensile strength of TiO(2)-containing paper without a ceramic carrier decreased by more than 30% after 240-h UV irradiation (2 mW/cm(2)), although the strength of the TiO(2) sheet with ceramic fibers remained reasonably stable. The efficiency of acetaldehyde decomposition by the TiO(2) paper containing an inorganic carrier was nearly equal to that of the carrier-free TiO(2) paper. Scanning electron microscopic observation suggested that most TiO(2) particles were predominantly supported on the inorganic fiber matrix, and were mostly out of contact with organic pulp fibers. The TiO(2) paper with an inorganic carrier demonstrated both excellent photocatalytic performance and durability, which before had been mutually incompatible for organic materials containing TiO(2) photocatalyst. The two-stage mixing procedure for TiO(2) sheet-making is promising for the simple manufacture of high performance paper with photocatalytic ability.

Cellulose Nanofiber Paper as an Ultra Flexible Nonvolatile Memory

On the development of flexible electronics, a highly flexible nonvolatile memory, which is an important circuit component for the portability, is necessary. However, the flexibility of existing nonvolatile memory has been limited, e.g. the smallest radius into which can be bent has been millimeters range, due to the difficulty in maintaining memory properties while bending. Here we propose the ultra flexible resistive nonvolatile memory using Ag-decorated cellulose nanofiber paper (CNP). The Ag-decorated CNP devices showed the stable nonvolatile memory effects with 6 orders of ON/OFF resistance ratio and the small standard deviation of switching voltage distribution. The memory performance of CNP devices can be maintained without any degradation when being bent down to the radius of 350 μm, which is the smallest value compared to those of existing any flexible nonvolatile memories. Thus the present device using abundant and mechanically flexible CNP offers a highly flexible nonvolatile memory for portable flexible electronics.

Helical Assembly of Azobenzene-Conjugated Carbohydrate Hydrogelators with Specific Affinity for Lectins

Carbohydrate-mediated interactions are involved in various biological processes via specific molecular assembly and recognition. Such interactions are enhanced by multivalent effects of the sugar moieties, and thus supramolecular sugar-assembly, i.e., spontaneous association of glycoamphiphiles, is a promising approach to tailor glycocluster formation. In this study, novel sugar-decorated nanofibers were successfully prepared by self-assembly of low molecular weight hydrogelators composed of azobenzene and disaccharide lactones. Circular dichroism measurement of the as-prepared hydrogels indicated that the azobenzene amphiphile containing a lactose moiety possessed (R)-chirality, while the maltose-azobenzene conjugate exhibited (S)-chirality, even though the cellobiose-conjugated azobenzene existed in an achiral form. This suggests that the chiral orientation of the chromophoric azobenzene depended on both the glycosidic linkages and the steric arrangement of hydroxyl groups in the conjugated carbohydrates. Lectin-binding and cell adhesion assays revealed that the nonreducing ends of the conjugated sugar moieties were exposed on the surfaces of self-assembled nanofibrous hydrogels, allowing them to be effectively recognized by the corresponding lectins. In addition, photoisomerization of azobenzene under ultraviolet irradiation induced the sol-gel transitions of the hydrogels. These results demonstrate that the reversibly transformed fibrous glycohydrogels show potential for application as carbohydrate-decorated scaffolds for cell culture engineering.

Preparation of composite TiO2-zeolite sheets using a papermaking technique and their application to environmental improvement. Part I. Removal of acetaldehyde with and without UV irradiation

Composite titanium dioxide (TiO2)-zeolite sheets were prepared using a papermaking technique and were tested with regard to their ability to remove acetaldehyde, which is often used as a typical volatile organic compound. It was demonstrated that the composite TiO2-zeolite sheet could remove acetaldehyde much more effectively under UV irradiation than a sheet of TiO2 alone. Acetaldehyde removal by a composite TiO2-zeolite sheet with a TiO2/zeolite ratio of 1 : 4 was particularly effective under the conditions adopted in this work although the composite sheet contained only one fifth of the amount of TiO2 in the TiO2 sheet. Additionally, the combination of TiO2 and zeolite was a useful method to solve the disadvantage of adsorbents, which were the decrease of the performance when the material was saturated or equilibrated with the adsorbates. Consequently, a composite TiO2-zeolite sheet can be utilized as a high functional material to prevent environmental pollution.

Synthesis of Gold Nanoparticles for In Situ Conjugation with Structural Carbohydrates

Gold nanoparticles (GNPs) have recently attracted much attention as innovative nanomaterials with unique properties in the fields of physicochemistry and biomedicine, 2] because of their quantum-size effects. Surface modification of GNPs is essential for enhancing their functionality and versatility, hence extensive efforts have been devoted to methodological studies toward the synthesis of GNPs and modification of their surfaces with a variety of functional molecules. Of the various substances used for surface modification of GNPs, carbohydrates have become a major target because of their specific molecular characteristics and actions in living systems. Many types of carbohydrate-related molecules have been used for conjugation with GNPs. However, there have been few reports on the related uses of structural carbohydrates because of their poor solubility and the considerable difficulties in their reaction with GNPs. Cellulose, a b-1,4-linked d-glucopyranose polymer that is the major constituent of plant cell walls, is a typical structural polysaccharide. It has unique amphipathic and self-assembling properties because of the formation of regular intra and intermolecular hydrogen bonds. Such molecular features are expected to provide a high potential for gathering the functional carbohydrate moieties on GNP surfaces. However, cellulose that has a degree of polymerization (DP) greater than six is insoluble in both common aqueous and organic media because of its inherent, strong molecular interactions. 11] Consequently, it is extremely difficult to apply to the glycomodification of GNP surfaces by using conventional approaches. Herein we present the first preparation of GNPs that uses an ideal solvent for structural carbohydrates such as cellulose, namely hot 80% N-methylmorpholine-N-oxide (NMMO)/ H2O, and the in situ conjugation of the GNPs with thiolabeled cellulose through spontaneous chemisorption. We have previously reported the successful formation and resulting biofunctionality of cellulose nanolayers from cellulose thiosemicarbazones (cellulose-TSCs, Figure 1a). These nanolayers, which are formed through self-assembling S–Au chemisorption on a gold plate, have a parallel-chain alignment.