Au/CeO(2) samples with various Au contents were prepared by the multistep (MS) photodeposition method. Their properties including Au particle size, particle dispersion, and photoabsorption were investigated and compared with properties of samples prepared by using the single-step (SS) photodeposition method. The MS- and SS-Au/CeO(2) samples were used for selective oxidation of benzyl alcohols to corresponding benzaldehydes in aqueous suspensions under irradiation by visible light from a green LED, and the correlations between reaction rates and physical properties of the MS- and SS-Au/CeO(2) samples were investigated. Difference in the two photodeposition methods was reflected in the average size and number of Au nanoparticles, for example, 92 nm and 1.3 × 10(12) (g-Au/CeO(2))(-1) for MS photodeposition and 59 nm and 4.8 × 10(12) (g-Au/CeO(2))(-1) for SS photodeposition in the case of 1.0 wt % Au samples. Fixation of larger Au particles resulted in strong photoabsorption of the MS-Au/CeO(2) samples at around 550 nm due to the surface plasmon resonance, and the Kubelka-Munk function of the photoabsorption linearly increased with increase in Au content up to 2.0 wt %, in contrast to the photoabsorption of SS-Au/CeO(2) samples, which was weak and was saturated even at around 0.5 wt %. Due to the strong photoabsorption, the MS-Au/CeO(2) samples exhibited reaction rates approximately twice larger than those of SS-Au/CeO(2) samples with the same Au contents, and apparent quantum efficiency of MS-Au/CeO(2) reached 4.9% at 0.4 mW cm(-2). Linear correlations were observed between reaction rates (r) and surface area of Au nanoparticles (S) in both MS- and SS-Au/CeO(2) samples, though the two slopes of r versus S plots were different, suggesting that oxidation of benzyl alcohol occurred on the Au surface and that S was one of the important factors controlling the reaction rate. Photocatalytic oxidation of benzyl alcohol having an amino group revealed that the Au/CeO(2) photocatalyst exhibited high chemoselectivity toward the hydroxyl group of alcohol, i.e, the Au/CeO(2) photocatalyst almost quantitatively converted aminobenzyl alcohol to aminobenzaldehyde with 99% yield.

Titanium(IV) oxide (TiO 2 ) having both small platinum (Pt) nanoparticles and large gold (Au) particles without alloying and nanoparticle coagulation was successfully prepared by the combination of traditional photodeposition of Pt in the presence of a hole scavenger (PH) and subsequent Au colloid photodeposition in the presence of a hole scavenger (CPH) onto TiO 2 −Pt. Au particles having an average diameter of 13 nm were fixed on both TiO 2 and TiO 2 − Pt samples without change in the original size of Au particles, and the Au/TiO 2 and Au/TiO 2 −Pt samples exhibited strong photoabsorption around 550 nm as a result of surface plasmon resonance (SPR) of Au to which the large size of Au particles was attributed. Bare TiO 2 , TiO 2 − Pt, Au/TiO 2 , and Au/TiO 2 −Pt samples were used for photoinduced hydrogen (H 2 ) formation from 2-propanol in aqueous solutions under irradiation of visible light. The first two samples yielded no H 2 because of no response to visible light, but the latter two formed H 2 , indicating that SPR photoabsorption of supported Au particles contributed to the H 2 evolution under irradiation of visible light. The H 2 formation rate of the Au/TiO 2 −Pt sample was ∼7-times larger than that of the Pt-free Au/TiO 2 sample, indicating that Pt nanoparticles loaded on TiO 2 acted effectively as a cocatalyst, that is, as reduction sites for H 2 evolution. The combination of the PH and CPH methods was effective for preparation of Au/TiO 2 having other metal cocatalysts (M) including Au, that is, Au/TiO 2 −Au, and H 2 evolution rates decreased in the order of M; Pt > Pd > Ru > Rh > Au > Ag > Cu > Ir. An inverse correlation between the rate and the hydrogen overvoltage (HOV) of M, that is, it was observed that the higher the HOV, the more difficult it is to reduce protons by photogenerated electrons. Since the amounts of Au and M loaded on TiO 2 were changed independently, the effects on photoabsorption and the rate of H 2 evolution were examined. A linear correlation was observed between rate and light absorption due to SPR, suggesting that SPR photoabsorption by Au particles was one of the important factors determining the rate of the H 2 evolution.

Photocatalytic H2 and O2 formations under visible light irradiation (λ > 400 nm) are demonstrated using Pt-Au nanopaticles for the reduction site and WO3 for the oxidation site in solid-state Pt/Au/WO3.

We found that plasmonic Au particles on titanium(iv) oxide (TiO2) act as a visible-light-driven photocatalyst for overall water splitting free from any additives.

Titanium(IV) oxide (TiO2) having both small platinum (Pt) nanoparticles and large gold (Au) particles without alloying and nanoparticle coagulation was successfully prepared by the combination of traditional photodeposition of Pt and subsequent Au colloid photodeposition onto TiO2–Pt. The Au/TiO2 and Au/TiO2–Pt samples exhibiting strong photoabsorption due to surface plasmon resonance (SPR) of supported Au particles were used for the reduction of hexavalent chromium (Cr6+ in Cr2O7 2–) in aqueous suspensions under irradiation of visible light from a green light emitting diode (LED). These SPR-type photocatalysts reduced Cr6+ and evolved dioxygen (O2) with O2-reduced Cr6+ ratio of 3:4 until consumption of Cr6+, indicating that these SPR-type photocatalysts had the ability to oxidize water (H2O) utilizing visible light (λ = 540 nm) and that a photocatalytic reaction (2Cr2O7 2– + 16H+ → 4Cr3+ +3O2 + 8H2O) occurred. The Au/TiO2–Pt sample exhibited a reaction rate about twice larger than that of Pt-free Au/TiO2, and the apparent quantum yield reached 1.0% at 550 nm and 0.47% even at 700 nm, indicating that functionalization of Au/TiO2 was successfully achieved by introduction of a Pt cocatalyst. This reaction can be used as a test reaction for evaluation of O2 evolution ability of photocatalysts because this reaction does not induce irreversible changes in photocatalysts.