Influence of Photodeposition Sequence on the Photocatalytic Activity of Plasmonic Ag–Au/TiO₂ Nanocomposites

Bimetallic Ag–Au/TiO2 nanocomposites were synthesized by sequential
photodeposition in order to investigate the effect of surface plasmon resonance (SPR) properties on photocatalytic activity for solar water splitting and methylene blue (MB) degradation. The photodeposition times were optimized for
monometallic Ag/TiO2 and Au/TiO2 nanocomposites to yield maximum SPR absorption in the visible range. It was found that the photocatalytic activity of
bimetallic Ag–Au/TiO2 nanocomposites outperformed monometallic nanocomposites only when Au was photodeposited first on TiO2, which
was attributed to Au-core–Ag-shell nanoparticle morphology. In contrast, reversing the photodeposition order resulted in Ag–Au alloy nanoparticle morphology, which was mediated by the galvanic
replacement reaction during the second photodeposition. Alloying was not beneficial to the
photocatalytic activity. These results demonstrate alloying during sequential photodeposition providing
new insights for the synthesis of TiO2-based photocatalysts with plasmon-enhanced absorption in the
visible range.