Synthesis of Metallic Gold Colored alpha-Al2O3 Nanoplate-TiO2 Core-Shell Pigments with Robust and Photo-Stable Smooth TiO2 Shell

Abstract

To synthesize non-corrosive metallic gold colored alpha-Al2O3 nanoplate-TiO2 core-shell pigments with controlled roughness, we systematically checked the morphological variation of the TiO2 shell with the mole ratio of TiCl4 and NaOH from 1 : 1 to 1 : 1.5, 1 : 2, 1 : 2.5, 1 : 3, 1 : 3.5, and 1 : 4. The more increased mole ratio of TiCl4 and NaOH resulted in the smoother TiO2 shell due to the promoted formation of anatase TiO2 than that of the rutile one. By the heat-treatment of pigments at 500 degrees C, we could improve the adhesiveness between TiO2 shell and alpha-Al2O3 nanoplates without changing their topology and roughness. In addition, the alpha-Al2O3 nanoplate with the robust TiO2 by heat-treatment exhibited comparable photo-stability against photo-catalytic degradation by UV exposure compared with the commercially available alpha-Al2O3/TiO2 lustering pigment.