Visible-light irradiation (λ > 450 nm) of gold nanoparticles loaded on a mixture of anatase/rutile TiO(2) particles (Degussa, P25) promotes efficient aerobic oxidation at room temperature. The photocatalytic activity critically depends on the catalyst architecture: Au particles with <5 nm diameter located at the interface of anatase/rutile TiO(2) particles behave as the active sites for reaction. This photocatalysis is promoted via plasmon activation of the Au particles by visible light followed by consecutive electron transfer in the Au/rutile/anatase contact site. The activated Au particles transfer their conduction electrons to rutile and then to adjacent anatase TiO(2). This catalyzes the oxidation of substrates by the positively charged Au particles along with reduction of O(2) by the conduction band electrons on the surface of anatase TiO(2). This plasmonic photocatalysis is successfully promoted by sunlight exposure and enables efficient and selective aerobic oxidation of alcohols at ambient temperature.

Photocatalytic production of hydrogen peroxide (H 2 O 2 ) on semiconductor catalysts with alcohol as a hydrogen source and molecular oxygen (O 2 ) as an oxygen source is a potential method for safe H 2 O 2 synthesis because the reaction can be carried out without the use of explosive H 2 /O 2 mixed gases. Early reported photocatalytic systems, however, produce H 2 O 2 with significantly low selectivity (∼1%). We found that visible light irradiation (λ > 420 nm) of graphitic carbon nitride (g-C 3 N 4 ), a polymeric semiconductor, in an alcohol/water mixture with O 2 efficiently produces H 2 O 2 with very high selectivity (∼90%). Raman spectroscopy and electron spin resonance analysis revealed that the high H 2 O 2 selectivity is due to the efficient formation of 1,4-endoperoxide species on the g-C 3 N 4 surface. This suppresses one-electron reduction of O 2 (superoxide radical formation), resulting in selective promotion of two-electron reduction of O 2 (H 2 O 2 formation).

TiO2 loaded with Au–Ag bimetallic alloy particles efficiently produces H2O2 from an O2-saturated ethanol/water mixture under UV irradiation. This is achieved via the double effects created by the alloy particles. One is the efficient photocatalytic reduction of O2 on the Au atoms promoting enhanced H2O2 formation, due to the efficient separation of photoformed electron–hole pairs at the alloy/TiO2 heterojunction. Second is the suppressed photocatalytic decomposition of formed H2O2 due to the decreased adsorption of H2O2 onto the Au atoms.

Rejuvenating sunlight: Supported Au–Cu bimetallic alloy nanoparticles promote aerobic oxidation at room temperature under visible light (λ>450 nm) irradiation with little deactivation by the oxidation of surface Cu atoms by oxygen. This is achieved through the reduction of oxidized surface Cu atoms by the surface Au atoms, a process which is activated by visible‐light irradiation, even by sunlight.

We report that photoactivated rutile titanium dioxide (TiO 2 ) catalyzes a highly efficient and selective hydrogenation of nitroaromatics with alcohol as a hydrogen source. Photoirradiation (λ >300 nm) of rutile TiO 2 suspended in alcohol containing nitroaromatics at room temperature and atmospheric pressure produces the corresponding anilines with almost quantitative yields, whereas common anatase and P25 TiO 2 show poor activity and selectivity. The Ti 3+ atoms located at the oxygen vacancies on the rutile surface behave as the adsorption site for nitroaromatics and the trapping site for photoformed conduction band electrons. These effects facilitate rapid and selective nitro-toamine hydrogenation of the adsorbed nitroaromatics by the surface-trapped electrons, enabling aniline formation with significantly high quantum yields (>25% at <370 nm). The rutile TiO 2 system also facilitates chemoselective hydrogenation of nitroaromatics with reducible substituents; several kinds of functionalized anilines are successfully produced with >94% yields.