2.1. Preparation of magnetite/silica core–shell structure
The magnetite/silica core–shell structure was prepared by
hydrolysis of tetraethoxysilane (TEOS) in the presence of core particles
under alkaline conditions. In a typical process, 0.88 g magnetite
nanoparticles were dispersed into a mixture of 120 mL water,
250 mL ethanol and 6 mL ammonia (25%) by sonication and the
mixture was kept at 35 C in a water bath. A solution of 50 mL ethanol
containing 4 mL of TEOS was slowly added into magnetite
containing mixture and then it was aged for 8 h under mechanical
stirring with a stirring speed of 120 rev./min for hydrolysis. The
resulting product was separated with magnet, and then washed
repeatedly with ethanol.