Effect of gold loading and TiO₂ support composition on the activity of Au/TiO₂ photocatalysts for H₂ production from ethanol–water mixtures

This paper systematically compares the activity of Au/TiO₂ photocatalysts (Au loadings 0–10wt.%) for H₂ production from ethanol–water mixtures under UV excitation. Degussa P25 TiO₂ was used as the support phase. TEM analyses revealed that the average Au nanoparticle size at all loadings was 5±2nm, with the Au nanoparticles preferentially located at the interfacial sites between TiO₂ crystallites. XRD, XRF, XPS, and UV–Vis measurements established that metallic Au was the only gold species on the surface of the photocatalysts. The Au/TiO₂ photocatalysts showed an intense absorption maximum centred around 560–570nm due to the localised surface plasmon resonance (LSPR) of the supported gold nanoparticles. Photoluminescence measurements revealed that gold nanoparticles effectively suppress electron–hole pair recombination in TiO₂, even at low Au loadings. All of the Au/TiO₂ photocatalysts displayed high activity for H₂ production from ethanol–water mixtures under UV irradiation, with the highest activities observed in the Au loading range 0.5–2wt.% (H₂ production rate 31–34mmolg⁻¹h⁻¹). In order to deconvolute the role of the P25 TiO₂ support in promoting H₂ production, anatase and rutile nanoparticles were isolated from P25 TiO₂ by selective chemical dissolution and then functionalised with gold nanoparticles (3wt.% loading, size 5±2nm). The H₂ production activity of the resulting Au/anatase and Au/rutile photocatalysts was 22 and 10mmolg⁻¹h⁻¹, respectively, and substantially lower than the corresponding Au/P25 TiO₂ photocatalyst (32mmolg⁻¹h⁻¹). The data provide strong evidence that synergistic electron transfer between the TiO₂ polymorphs and supported Au nanoparticles is responsible for the high rates of H₂ production observed in the Au/P25 TiO₂ system. The interface between anatase and rutile crystallites, where gold nanoparticles preferentially deposit, is identified as a photocatalytic ‘hot spot’ for H₂ production. High Au loadings reduce the efficiency of such ‘hot spots’.