Quantum size effect and catalytic activity of nanosized single-crystalline spherical β-Ga2O3 particles by thermal annealing of liquid metal nanoparticles

We report on the synthesis of nanosized single-crystalline spherical beta-Ga2O3 particles (GONP) by thermal annealing of gallium nanoparticles (GaNP), which previously has been prepared under ultrasonication. GONP displayed a spherical morphology and the particle size reflected that of GaNP. The nanoparticles have been confirmed crystalline beta-Ga2O3 by powder X-ray diffraction. The selected area electron diffraction patterns obtained from a whole particle of one GONP represented production of single-crystalline nanoparticle. Furthermore, the dispersibility and stability of GONP in solvent dramatically improved through silica coating (GO@SiO2 NP). Photoluminescence spectroscopy indicated that the GO@SiO2 NP exhibited a light blue emission at 445 nm under excitation at 240 nm. Diffuse reflectance spectroscopy demonstrated that the band gap of GO@SiO2 NP (E-g = 4.89 eV) was hypsochromically shifted compared to that of bulk Ga2O3 (E-g(bulk) = 4.56 eV) due to the quantum size effect of beta-Ga2O3. Additionally, silica particle-supported GONP (GONP/MCM-41) showed catalytic activity for the benzylation of benzene with benzyl chloride. Thus, the GONP presented here will have potential applications in LED phosphors, optoelectronic devices, and supported catalysts.