Wan-Ting Chen

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 H2 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 ~5 nm for the Au/TiO2 photocatalysts and ~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 H2 production from ethanol-water mixtures than Ag/TiO2 photocatalysts. A 1 wt.% Au/TiO2 photocatalyst yielded the highest H2 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 H2 production.

Performance evaluation of Pd/TiO 2 and Pt/TiO 2 photocatalysts for hydrogen production from ethanol-water mixtures

This study compares the photocatalytic activity of Pd/TiO 2 and Pt/TiO 2 photocatalysts (metal loadings 0.5 wt.% and 2 wt.%) for H 2 production from ethanol-water mixtures under UV excitation. Cationic Pd(II) and Pt(IV)/Pt(II) species were deposited on Degussa P25 TiO 2 (85% anatase, 15% rutile) via the deposition-precipitation with urea method. Subsequent H 2 treatment at 350oC reduced the adsorbed cationic species to predominantly Pd 0 and Pt 0 , respectively. TEM analyses of the Pd/TiO 2 and Pt/TiO 2 photocatalysts revealed supported Pd and Pt nanoparticles of size <3 nm. XPS studies confirmed that the platinum was present primarily in metallic form, whereas palladium was present as both Pd 0 and PdO or Pd(OH) 2 . Photoluminescence measurements demonstrated that Pd and Pt nanoparticles suppress electron-hole pair recombination in TiO 2 by acting as electron acceptors. The Pt/TiO 2 and Pd/TiO 2 photocatalysts exhibited high activity and stability for H 2 production, with the optimum metal loadings being 0.5 wt.% for Pt (H 2 production rate = 41 mmol h –1 g –1 ) and 2 wt.% for Pd (H 2 production rate = 34 mmol h –1 g –1 ). Results confirm that the presence of zero valent Pd or Pt is critical for efficient H 2 production, and that both Pt/TiO 2 and Pd/TiO 2 photocatalysts are promising materials for solar H 2 production from biofuels.