Flux Synthesis of Sillén–Aurivillius Oxyiodide for Visible Light Water Splitting Photocatalysis

Iodine-based compounds with a Sillén–Aurivillius layered perovskite structure are promising photocatalysts for visible-light-induced water splitting. However, their synthetic method has been limited to solid-state reaction (SSR), which restricts the material tunability and thus photocatalytic performance. Here, we report a liquid-phase synthesis of Sillén–Aurivillius oxyiodide Bi₄NbO₈I via the flux method. An appropriate choice of reaction conditions, including flux, precursor, and calcination atmosphere/temperature, is required for the single-phase formation due to the complex crystal growth mechanism, as revealed by in situ synchrotron X-ray diffraction measurements. The provided plate-like particles are of excellent crystallinity with size tunability. The superior charge carrier transport property of the flux sample, as shown by time-resolved microwave conductivity measurements, allows its higher photocatalytic water oxidation activity than the sample prepared via conventional SSR. An appropriate surface modification further exploits the superior bulk property of the flux sample, achieving the highest performance reported for oxyiodide photocatalysts with an apparent quantum efficiency for sacrificial O₂ evolution of 8.8% at 405 nm. This study provides a solution-based synthetic approach to the complex layered oxyiodides, broadening their potential for solar-to-energy conversion systems.