Photocatalytic H2 production from ethanol over Au/TiO2 and Ag/TiO2

This paper compares the photocatalytic activities of Au/TiO2 (Au loadings 0-4 wt.%) and Ag/TiO2 photocatalysts (Ag loadings 0-4 wt.%) for H-2 production from ethanol-water mixtures under UV irradiation. Au and Ag nanoparticles were deposited on commercially available Degussa P25 TiO2 (85% anatase, 15% rutile) using deposition-precipitation and liquid impregnation methods, respectively. TEM analyses showed the average noble metal nanoparticle size to be similar to 5 nm for the Au/TiO2 photocatalysts and similar to 3 nm for the Ag/TiO2 photocatalysts. Au/TiO2 photocatalysts showed a strong localised surface plasmon resonance (LSPR) at 570 nm characteristic for nanocrystalline Au. Complementary XRD studies confirmed that Au and Ag nanoparticles were present in metallic form. Photoluminescence measurements revealed that Au and Ag nanoparticles effectively suppress electron-hole recombination in TiO2, thereby enhancing the photocatalytic activity of TiO2 for hydrogen production. Au/TiO2 photocatalysts were far more active for H-2 production from ethanol-water mixtures than Ag/TiO2 photocatalysts. A 1 wt.% Au/TiO2 photocatalyst yielded the highest H-2 production rate (34 mmol g(-1) h(-1)). Amongst the Ag/TiO2 photocatalysts, the 2 wt.% Ag/TiO2 sample was the most active (3.7 mmol g(-1) h(-1)). Results are rationalised in terms of differences in the electronic properties of supported Au and Ag nanoparticles, with the former being near ideal for H-2 production.