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.

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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).

Design of green, safe, and sustainable process for the synthesis of hydrogen peroxide (H2 O2 ) is a very important subject. Early reported processes, however, require hydrogen (H2 ) and palladium-based catalysts. Herein we propose a photocatalytic process for H2 O2 synthesis driven by metal-free catalysts with earth-abundant water and molecular oxygen (O2 ) as resources under sunlight irradiation (λ>400 nm). We use graphitic carbon nitride (g-C3 N4 ) containing electron-deficient aromatic diimide units as catalysts. Incorporating the diimide units positively shifts the valence-band potential of the catalysts, while maintaining sufficient conduction-band potential for O2 reduction. Visible light irradiation of the catalysts in pure water with O2 successfully produces H2 O2 by oxidation of water by the photoformed valence-band holes and selective two-electron reduction of O2 by the conduction band electrons.

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