Gold nanoparticle loading has led to a drastic enhancement of TiO(2)-photocatalized generation of H(2)O(2) from O(2) with a unique inversed volcano-type relation between the activity and Au particle size.

The fundamentals and applications of TiO(2) photocatalysis have been extensively studied in recent decades, the central theme being increasing reaction efficiency. A guideline for achieving so-called "reasonable delivery photocatalytic reaction systems (RDPRSs)" has been presented. This tutorial review summarizes recent developments in the RDPRS-based design of highly efficient photocatalytic reactions by noble metal nanoparticle-loaded TiO(2) (M/TiO(2)). After introducing the conditions required for RDPRSs, the key factors affecting the photocatalytic activity, including Fermi energy in the photostationary state, the metal particle size effect, and solvent effects are discussed. We then describe selected applications of RDPRSs for the conversion of light energy to chemical energy, environmental purification, and low-temperature cleaning of sulfur-poisoned metal catalysts. Future applications of this idea to visible-light photocatalysts, which are currently the subject of intensive research, may lead to feasible green and efficient photocatalytic reaction systems using sunlight as an energy source.

Among various metal oxide-supported Au nanoparticles, Au/rutile TiO2 exhibits a particularly high level of visible-light activity for aerobic oxidation of amines to yield the corresponding imines on a synthetic scale with high selectivity (>99%) at 298 K. Experimental results have suggested that the reaction proceeds via the localized surface plasmon resonance-excited electron transfer from the Au nanoparticle to the TiO2.

Au nanoparticle surface plasmon resonance-induced photocatalytic chemoselective oxidation of alcohols to carbonyl compounds has been investigated. The heterosupramolecular system consisting of Au nanoparticle-loaded titanium(IV) dioxide and surfactant molecular assembly dramatically enhances the reaction. This system should evolve the photocatalyst to intelligent nanodevices.

The photocatalytic activities of Au nanoparticle-loaded anatase (Au/anatase) and rutile (Au/rutile) for green organic synthesis are compared under illumination of UV and visible light. Whereas Au/anatase shows a higher UV-light activity for the reduction of nitrobenzene than Au/rutile, the replacement of anatase by rutile greatly increases the visible-light activity of Au/TiO2 for the oxidation of alcohols to carbonyl compounds. The quantum efficiencies (molecules produced/incident photons) for the Au/rutile and Au/anatase systems for the selective oxidation of cinnamyl alcohol to cinnamaldehyde were calculated to be 1.4 × 10–3 at λ = 585 ± 15 nm and 0.33 × 10–3 at λ = 555 ± 15 nm, respectively. This superiority of rutile over anatase as the support of Au nanoparticle (NP) plasmon photocatalyst is also confirmed in the heterosupramolecular system consisting of Au/TiO2 and a cationic surfactant. In the system using Au/rutile, a quantum efficiency of 6.8 × 10–3 at λ = 585 ± 15 nm has been achieved for the cinnamyl alcohol oxidation. Also, the plot of the visible-light activity versus Au particle size (d) for the Au/rutile system shows a volcano-shaped curve with a maximum at d ≈ 5 nm, while the activity of the Au/anatase system weakly depends on d. Photoelectrochemical measurements indicate that the Au/rutile system favors the localized surface plasmon resonance (LSPR) induced interfacial electron transfer from Au to TiO2. Further, intrinsic Fano analysis for the absorption spectra of Au/TiO2 suggests that the elongation of the LSPR lifetime with the Au NP loading on rutile is primarily responsible for the enhancement of the alcohol oxidation. We concluded that the optimum d value is determined by the factors of the LSPR absorption intensity, the interfacial electron transfer efficiency, and the surface area.