Evaluation of Color and Structure of α-Fe2O3 Nanocapsules by Tuning of the SiO2 Morphology

: In this study, we synthesized a core/yolk-shell α-Fe2O3@SiO2 structure by treatment of SiO2 shell with mild basic solution. Spindle shaped α-Fe2O3 nanoparticles were initially prepared as core materials and subsequently coated with silica via sol-gel method. The yolk shell of α-Fe2O3 was produced by dissolution of silica shell from core-shell type hematite in NH4OH solution. In addition, the correlation between the density and morphology of the silica coating layer and the chromaticity according to the NH4OH concentration and the etching time was confirmed. We found that, after the conversion, the spindle shapes of the composite colloids were retained for both the hematite core and the silica shell, but the physical properties had a median value.