Activation of solid grinding-derived Au/TiO2 photocatalysts for solar H2 production from water-methanol mixtures with low alcohol content

•AuPPh3Cl and titania P25 are ground together in the absence of solvent.•A thermal treatment is applied to reduce Au (I) into Au (0) nanoparticles (NP).•The best Au/TiO2 photocatalysts are obtained upon activation in air.•The highest H2 production is achieved with an economical Au loading of 0.5 wt.%.•Trends in noble metal utilization efficiency highlight the key role of NP density.

Au/TiO2 nanocomposites are prepared by the solventless solid grinding method, which consists in mechanically mixing AuPPh3Cl and titania P25 and applying a mild heat treatment to reduce Au (I) into Au (0) nanoparticles (Au NP). Given that gold oxides are not thermally stable, both air and hydrogen can be considered for such treatment. Air however leads to much more efficient photocatalysts than hydrogen, due to a more efficient degradation of the gold complex, as shown by X-ray photoelectron spectroscopy, and a more effective Au-TiO2 interface. Amongst the investigated gold loadings, the composite containing 0.5 wt.% Au 0.5Au/TiO2[air] appears as the most active, yielding about 500 μmolH2 h−1 g−1 under simulated solar light in the presence of 1 vol.% methanol. This represents a marked improvement in terms of noble metal utilization, as compared with the 2 wt.% Au/TiO2 benchmarks. The yet highest efficiency (in terms of Au-normalized H2 production) of 0.1Au/TiO2[air] (54 h−1), and the different trend observed with higher surface area titania, highlights the key role of the Au NP density in the photocatalytic process.

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