Single-Crystalline β-Ga₂O₃ Hexagonal Nanodisks: Synthesis, Growth Mechanism, and Photocatalytic Activities

β-Ga 2 O 3 hexagonal nanodisks were in situ grown on the surface of gallium grain and Si substrate via a reaction of metallic gallium with NH 4 Cl and H 2 O at 650−800 °C for 30 min. The as-synthesized nanodisks have perfect hexagonal shape with diagonals of 0.6−4.0 μm and thicknesses of 140−480 nm. Size of the hexagonal nanodisks increased with increasing heat treatment temperature. The formation of the Ga 2 O 3 nanodisks results from the selective adsorption of Cl − ions on unsaturated Ga(I) and Ga(II) sites of β-Ga 2 O 3 (100) surface. Photoluminescence and photocatalytic activity of the hexagonal Ga 2 O 3 nanodisks were studied at room temperature. The results indicated that the hexagonal nanodisks display a stable blue-green emission band centered at 489 nm that originated from the recombination of an electron on an oxygen vacancy and a hole on a gallium−oxygen vacancy pair and high photocatalytic activity in the photodegradation of methyl orange.