Temperature- and pH-Dependence of Hydrogen Peroxide Formation from Molecular Oxygen by Gold Nanoparticle-Loaded Titanium(IV) Oxide Photocatalyst

Our preceding communication reported that UV-light irradiation (light wavelength λ > 320 nm) of gold nanoparticle-loaded TiO 2 (Au/TiO 2 ) in 4% ethanol aqueous solution reduces the oxygen (O 2 ) dissolved from the air to yield hydrogen peroxide (H 2 O 2 ) at the millimolar level, and the relation between the photocatalytic activity and mean particle size ( d ) of Au shows a unique inverse volcano-type profile ( J. Am. Chem. Soc. 2010, 132, 7850.). In this study, Au nanoparticles ( d = 3.5 and 7.7 nm) were loaded on anatase TiO 2 particles ( d = 150 nm) with the loading amount maintained at 0.24 mass% by the heating temperature-varied deposition–precipitation technique. In the reaction, the Au/TiO 2 -photocatalytic H 2 O 2 generation is accompanied by the Au/TiO 2 -thermocatalytic decomposition. The time courses for the H 2 O 2 generation under different temperature and pH of the solution are kinetically analyzed. Consequently, it has been revealed that as the temperature and pH of the solution decrease, the H 2 O 2 generation is enhanced, and conversely, the decomposition is suppressed. A photonic efficiency of 22% at λ = 355 ± 23 nm was achieved for the reaction system at 5 °C and pH 2, and the concentration of H 2 O 2 reached 17 mmol dm –3 after 23 h irradiation.