Yu Horiuchi

Size-controlled synthesis of silver nanoparticles on Ti-containing mesoporous silica thin film and photoluminescence enhancement of rhodamine 6G dyes by surface plasmon resonance

Silver nanoparticles having a narrow size distribution were synthesized on Ti-containing mesoporous silica thin film (Ti-MSTF) using a simple photo-assisted deposition (PAD) method. Their particle sizes were successfully controlled by changing the photo-irradiation time during the deposition and average particle sizes at irradiation times of 1, 5 and 24 h were determined to be 2.7, 4.7 and 7.6 nm, respectively. The XPS depth profile analysis indicated that silver nanoparticles mainly exist not on the surface but in the thin film. UV–vis absorption spectra of these films showed an absorption band in the visible-wavelength region attributed to the surface plasmon resonance of silver nanoparticles. Rhodamine 6G (R6G) dye molecules were further embedded on Ti-MSTF after silver nanoparticle deposition. Photoluminescence properties of R6G dyes on these thin films were enhanced due to surface plasmon excitation from silver nanoparticles and the photoluminescence intensity reached up to 3 times as high as that achieved without silver nanoparticles. It was proven that the silver nanoparticle size had a strong influence on these enhancement effects.

Low-temperature synthesis of highly hydrophilic Ti-containing mesoporous silica thin films on polymer substrates by photocatalytic removal of structure-directing agents

This article describes a novel preparation method for highly hydrophilic porous thin films via photocatalytic removal of a structure-directing agent (SDA) under UV-light irradiation at ambient temperature. Since this technique requires no calcination process, it can effectively coat surfaces that have low thermal resistance, such as polymer substrates. In the present study, Ti-containing mesoporous silica thin films (Ti-MSTF) were prepared on polycarbonate and quartz substrates using a newly developed method involving UV-light irradiation. The film surface wettabilities were investigated by water contact angle measurements. Complete removal of the SDA was confirmed by time-dependent changes in the FT-IR spectra under UV-light irradiation, which also suggested that Ti-oxide moieties in the mesoporous silica framework play a crucial role in the removal of the SDA. XRD, UV-vis and XAFS measurements revealed that the Ti-MSTF had a mesoporous structure and isolated Ti-oxide moieties. The water contact angle measurements indicated that the Ti-MSTF exhibited highly hydrophilic property after photocatalytic removal of the SDA, and maintained this property under dark conditions for several days.

An efficient method for the creation of a superhydrophobic surface: ethylene polymerization over self-assembled colloidal silica nanoparticles incorporating single-site Cr-oxide catalysts

The present communication describes a new method for the creation of a superhydrophobic thin film, in which polyethylene is synthesized on self-assembled colloidal silica nanoparticles incorporating single-site Cr-oxide catalysts. The obtained thin film shows a static water contact angle of 162° due to the combined effect of hydrophobicity of synthesized polyethylene and microstructures formed by colloidal silica nanoparticles.

Photo-induced surface hydrophilic properties on the Ti- and V-containing mesoporous silica thin films

Using a sol-gel/spin coating method, Ti- and V-containing transparent mesoporous silica thin films (Ti- and V-MSTF) could be prepared on quartz plates. XRD, XAFS, and photoluminescence measurements demonstrated the formation of isolated and tetrahedrally-coordinated metal oxide moieties in the frameworks of the Ti- and V-MSTF. Both Ti- and V-MSTF have exhibited strong hydrophilic surface properties even before UV-light irradiation and the contact angles of water droplet became extremely lower after UV-light irradiation indicating the appearance of the photo-induced super-hydrophilic properties.