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

beta-Ga2O3 hexagonal nanodisks were in situ grown on the surface of gallium grain and Si substrate via a reaction of metallic gallium with NH4Cl and H2O at 650-800 degrees C for 30 min. The as-synthesized nanodisks have perfect hexagonal shape with diagonals of 0.6-4.0 mu m and thicknesses of 140-480 nm. Size of the hexagonal nanodisks increased with increasing heat treatment temperature. The formation of the Ga2O3 nanodisks results from the selective adsorption of Cl- ions on unsaturated Ga(I) and Ga(II) sites of beta-Ga2O3 (100) surface. Photoluminescence and photocatalytic activity of the hexagonal Ga2O3 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.