Mechanistic insights into photocatalytic hydrogen evolution from crude glycerol solution over gold-decorated TiO2 nanostructures

Abstract

A series of gold-decorated titanium dioxide (Au <inf>x</inf> /HT) photocatalysts was synthesized by a sequential hydrothermal and photodeposition for the photocatalytic reforming of glycerol solution to green hydrogen (H<inf>2</inf>). The presence of metallic Au in the range of 0.25 to 1.50 wt. % had an insignificant effect on the TiO<inf>2</inf> crystallite size, phase composition, porosity, and bandgap values compared to the pristine HT. However, the Au decoration significantly enhanced the visible light response, suppressed the charge recombination, and promoted the charge carrier migration. Among all explored photocatalysts, the Au<inf>0.75</inf>/HT exhibited the highest photocatalytic H<inf>2</inf> production, attributing to its high BET surface area and optimal hemispherical surface structure. Apart the glycerol concentration and photocatalyst loading, types of glycerol feedstocks had a significant impact on the H<inf>2</inf> production. Among all the evaluated glycerol types, the refined crude glycerol achieved the highest H<inf>2</inf> output at 15 vol. % glycerol concentration and a photocatalyst loading of 3.0 g/L. This resulted in an H<inf>2</inf> production rate of 216.2 µmol/g·h (or 387.6 µmol after 3 h), approximately 1.22 and 1.59 times higher than those from commercial- and crude glycerol, respectively. Additionally, it demonstrated an outstanding long-term H<inf>2</inf> production and cost-effectiveness ($8.3 /mmol), which was comparable to that of commercial glycerol and approximately 3.41 times cheaper than that of crude glycerol.