The roles of metal co-catalysts and reaction media in photocatalytic hydrogen production: Performance evaluation of M/TiO2 photocatalysts (M = Pd, Pt, Au) in different alcohol-water mixtures

M/TiO2 photocatalyst activity for H-2 production depends on both the metal co-catalyst (M) and the reaction medium. To quantify such effects, we compared the performance of M/TiO2 photocatalysts (M = Pd, Pt, Au) for H-2 production in different alcohol-water mixtures under UV excitation. Photocatalysts were prepared using Degussa P25 TiO2 at metal loadings of 0.5 and 1 wt.% for Pd, 1 wt.% for Pt and 1 wt.% for Au. TEM, UV-Vis, XPS and EXAFS analyses confirmed the presence of supported metal nanoparticles of size similar to 2, 1.3 and 5.4 nm for Pd/TiO2, Pt/TiO2 and Au/TiO2, respectively. Photoluminescence data established that the metal co-catalysts effectively suppressed electron-hole pair recombination in TiO2 following photo-excitation. The activities of the M/TiO2 photocatalysts for Hy production were evaluated in a wide range of alcohol-water mixtures (alcohol concentration 10 vol.%) under UV (365 nm, 5 mW cm(-2)). H-2 production rates in the alcohol-water mixtures were dependent on (i) the metal co-catalyst; (ii) the co-catalyst loading; and (iii) the alcohol type. Co-catalyst activity followed the order Pd > Pt approximate to Au. The highest Hy production rates were achieved for the 1 wt.% Pd/TiO2 photocatalyst in glycerol-water mixtures (47.5 mmol g(-1)h(-1)) and 1,2-ethanediol-water mixtures (44.5 mmol g(-1) h(-1)). H2 production rates decreased in the order glycerol > 1,2-ethanediol > 1,2-propanediol > methanol > ethanol > 2-propanol > tert-butanol >> water. For each M/TiO2 photocatalyst, correlations were established between the rate of H2 production and specific alcohol properties, especially alcohol polarity and the exponential of the alcohol oxidation potential. (C) 2015 Elsevier Inc. All rights reserved.