Flux Growth of Layered Sm₂Ti₂O₅S₂ Crystal with Two Types of Simultaneously Exposed Facets

Controlling the morphology of photocatalytic crystals is crucial for enhancing overall water-splitting reactions. Sm2Ti2O5S2 (STOS) crystals are promising visible-light responsive photocatalysts; however, they do not effectively facilitate overall water-splitting. Herein, we successfully grew STOS crystals with faceted features using a CsI flux at 800 °C under varying solute concentrations. X-ray diffraction indicated that the Ruddlesden–Popper phase was consistently the primary phase regardless of the solute concentration. Plate-like STOS crystals of sizes 300–800 nm were grown at solute concentrations of 5–95 mol %, indicating efficient anisotropic crystal growth in the presence of minimal flux. The absorption edge of the STOS crystal extended to 600 nm, confirming visible light absorption. Transmission electron microscopy and selected area electron diffraction showed that the plate-like STOS crystals predominantly exhibited an exposed (100) face on the sides and a (110) face at the corners. This flux growth approach presents a new opportunity for the selective deposition of cocatalysts on STOS crystals, paving the way for realizing overall water-splitting.