Rapid preparation of size-tunable Fe3O4@SiO2 nanoparticles to construct magnetically responsive photonic crystals

Superparamagnetic Fe3O4@SiO2 with regular core–shell structure, controllable size, and high saturation magnetization (Ms) were prepared as the building blocks to construct magnetically responsive photonic crystals (MRPCs). A simple, rapid, and feasible procedure to self-assemble the core of Fe3O4 colloidal nanoclusters (CNCs) was accomplished through miniemulsification and evaporation. Subsequently, the shell of SiO2 was prepared by a modified Stober method. The sizes of Fe3O4 CNCs could be controlled easily by tuning emulsifier SDS concentrations, the phase ratio of oil to water, and the amount of OA-Fe3O4. The size of Fe3O4 CNCs could be tuned from 76.8 to 151.8 nm expediently. The Fe3O4 CNC with a size of 99.1 nm was chosen as the magnetic core for the fabrication of Fe3O4@SiO2 nanoparticles because of a strong saturation magnetization and an appropriate size. Moreover, the amount of TEOS added in Stober system was also an important parameter, which influenced SiO2 shell thickness and Ms. TEM images and hysteresis loops showed that as the amount of TEOS ranged from 0.3 to 1.5 mL, the thickness of SiO2 shell increased from 14.72 to 22.31 nm, and the Ms decreased from 47.01 to 35.2 emu·g−1. Obviously, the increase of shell thickness also resulted in a red shift of the structural color of Fe3O4@SiO2 colloidal photonic crystals. This work provided a quick and gentle approach to prepare Fe3O4 CNCs with a high Ms and a controllable size, which makes regulation of the structure color of MRPCs simplified.