Effect of TiO2 polymorph and alcohol sacrificial agent on the activity of Au/TiO2 photocatalysts for H2 production in alcohol–water mixtures

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This study compares the performance of 5 different Au/TiO2 photocatalysts for H2 production in alcohol–water mixtures under UV excitation, placing particular emphasis on the role of the TiO2 support and alcohol sacrificial reagent. 1.5wt.% Au/TiO2 photocatalysts were prepared by the deposition–precipitation with urea method, using P25 TiO2 (85% anatase and 15% rutile, 49m2g−1), sol–gel anatase (39m2g−1), hydrothermally synthesised anatase (115m2g−1), commercial brookite (33m2g−1) and hydrothermally synthesised rutile (29m2g−1) as supports. UV–Vis, TEM, XRD, XPS and Au L3-edge EXAFS characterisation studies confirmed the presence of gold nanoparticles of mean size 5–10nm on all the Au/TiO2 photocatalysts, which generated intense localised surface plasmon resonances (LSPRs) centred between 560 and 590nm. Gold nanoparticle deposition suppressed electron–hole pair recombination in each TiO2 support following UV excitation, and created cathodic sites on TiO2 for H2 evolution. Photocatalytic H2 production tests were conducted in water, methanol–water, ethanol–water, ethylene glycol–water and glycerol–water mixtures (alcohol concentration 10vol.%) at a UV flux of 6.5mWcm−2. H2 production rates decreased in the order Au/P25>Au/anatase SG≈Au/brookite>Au/anatase HT≫Au/rutile HT when the rates were normalised against photocatalyst surface area. For each Au/TiO2 photocatalyst, the rates decreased in the order glycerol>ethylene glycol>methanol>ethanol. Good correlations were established between H2 production rates and the number of hydroxyl groups, polarity and relative hole scavenging ability of the alcohols. Results improve knowledge about the role of sacrificial reagents in photocatalytic hydrogen production.