Novel Au/TiO2 photocatalysts for hydrogen production in alcohol–water mixtures based on hydrogen titanate nanotube precursors

Abstract

In this study, a series of titania nanorods with different phase compositions and surface areas were prepared by calcination of hydrogen titanate (H2Ti3O7) nanotubes at temperatures up to 1000°C. Gold nanoparticles were subsequently deposited on the obtained TiNTx (x=calcination temperature) nanorod supports at loadings between 0.5 and 2.0wt.%, and also onto a commercially available mixed-phase titania support (Degussa P25). TEM, XRF, UV–Vis, XPS and photoluminescence measurements confirmed the presence of gold nanoparticles of mean size 4–7nm on the surface of the Au/TiNTx (x=350–800) and Au/P25 photocatalysts, which suppressed electron–hole pair recombination in TiO2 under UV and created cathodic sites for hydrogen evolution. Hydrogen production tests were conducted on the Au/TiNTx and Au/P25 photocatalysts in various alcohol–water mixtures under UV excitation (6.5mWcm−2) with no external bias applied. The impact of the gold loading and the calcination temperatures on the structural, physico-chemical and photocatalytic properties of the TiNTx nanorods was investigated, and a comparison to P25 was made. A 0.5wt.% Au/TiNT600 photocatalyst demonstrated excellent H2 production activity in all the alcohol–water systems, performing similarly to a 1.5wt.% Au/P25 reference photocatalyst. For both the 0.5wt.% Au/TiNT600 and 1.5wt.% Au/P25 photocatalysts, H2 production rates decreased in the order triol (glycerol)>diol (1,2-ethanediol≈1,2-propanediol)>ethanol>1-propanol. Good correlations were found between the H2 production rates and alcohol properties such as the number of hydroxyl groups, polarity or standard oxidation potential.