Preparation of Single-Crystalline AgIn<sub>5</sub>S<sub>8</sub> Octahedrons with Exposed {111} Facets and Its Visible-Light-Responsive Photocatalytic H<sub>2</sub> Production Activity

Although AgIn<sub>5</sub>S<sub>8</sub> as one kind of ternary chalcogenides has been extensively investigated due to its band-edge positions meeting the thermodynamic requirement for water photosplitting, very little attention has been focused on the crystallinity and facet effects of AgIn<sub>5</sub>S<sub>8</sub> on its photocatalytic activity. Herein, a facile hydrothermal route was developed to fabricate regular single-crystalline AgIn<sub>5</sub>S<sub>8</sub> octahedrons with only {111} facets exposed. Also, the effects of the hydrothermal reaction conditions on the composition, crystal phase, crystallinity, and morphology of the obtained Ag<sub><i>x</i></sub>In<sub><i>y</i></sub>S<sub>(<i>x</i>+3<i>y</i>/2)</sub> products (hereafter denoted as AIS-<i>x</i>, where <i>x</i> represents the pH value of the reaction solution) were investigated, and it was found that the accurately released S<sup>2–</sup> ions from the thermal decomposition of thioacetamide (TAA) is the central factor for the nucleation and growth of the AgIn<sub>5</sub>S<sub>8</sub> octahedrons. The experimental results indicate that the resultant regular AgIn<sub>5</sub>S<sub>8</sub> octahedrons (AIS-10.6) exhibit the best photocatalytic activity for H<sub>2</sub> production among those Ag<sub><i>x</i></sub>In<sub><i>y</i></sub>S<sub>(<i>x</i>+3<i>y</i>/2)</sub> products, and the higher crystallinity and fewer defects of the AgIn<sub>5</sub>S<sub>8</sub> octahedrons compared to the other Ag<sub><i>x</i></sub>In<sub><i>y</i></sub>S<sub>(<i>x</i>+3<i>y</i>/2)</sub> products can retard the photogenerated charge recombination, while those indium atoms with higher density in the exposed {111} facets might be beneficial for the photocatalytic H<sub>2</sub> production reaction by acting as active sites to promote the charge separation and transfer processes. The results presented here provide new insights into the significance of crystallinity and exposed facets in the visible-light-responsive activity of AgIn<sub>5</sub>S<sub>8</sub>, thus paving new ways into the design and synthesis of high-performance, cost-effective AgIn<sub>5</sub>S<sub>8</sub> photocatalysts for H<sub>2</sub> production.