Self-Assembled Heterosupramolecular Visible Light Photocatalyst Consisting of Gold Nanoparticle-Loaded Titanium(IV) Dioxide and Surfactant

摘要

“Heterosupramolecules” represented by dye-sensitized TiO2nnanocrystalline films is a key material in intelligent nanodevicesnfor the conversion of solar energy to electric and chemicalnenergy.n1,2nWe have previously reported a self-assembled het-nerosupramolecular photocatalyst consisting of TiO2 and a cationicnsurfactant bilayer formed on the surface, the so-called admicelle,nwith a high level of activity for the degradation of 2-naphtholnunder UV light irradiation.n3nSimilar enhancing effects by thenaddition of surfactants have also been reported in some othernTiO2-photocatalyzed decompositions of organic substances fornwater purification.n4 7nHowever, there is no report on thenapplication of the surfactant/TiO2 system to oxidations as organicnsynthesis. This is mainly because the valence band holes of TiO2npossess extremely strong oxidizing power,n8nand hence partiallynoxidized products are difficult to obtain selectively.n9nThe greaternfundamental drawback to the TiO2 photocatalyst is that visiblenlight is hardly utilized because of its wide band gap. Recently,nthe visible light excitation of the surface plasmon resonancen(SPR) of Au nanoparticles (NPs) loaded on TiO2 (Au/TiO2) hasnbeen found to cause the electron injection from Au to TiO2,n10nand the applications to the photovoltaic cell and biosensor havenbeen reported.n11nThe visible light-induced electron transfernendows Au NPs with mild oxidizing ability, allowing us tonexpect the application to oxidative organic synthesis. Suchnresearch has just begun with the oxidations of isopropanol tonacetone12nand thiol to disulfide;n13nhowever, the photocatalyticnactivity is low.