2. Experimental
2.1. Synthesis of SH-mSiO2@Fe3O4
The Fe3O4 spherical particles were prepared according to the
literature [23]. The thiol-functionalized SH-mSiO2@Fe3O4 was prepared
through a modified Stöber method [24]. Typically, 0.1 g of
the prepared Fe3O4 spheres were treated with 0.1 M HCl aqueous
solution under ultrasonication for at least 10 min. After separation
and washing with deionized water, the magnetic spheres were
dispersed in a mixed solution of 80 mL ethanol, 20 mL deionized
water and 1 mL concentrated ammonia aqueous solution (28%)
under vigorous stirring. Then 0.05 g tetraethyl orthosilicate (TEOS,
Thermo Fisher Scientific) was added dropwise. After magnetically
stirred at room temperature for 6 h, the product was separated
and washed with ethanol and deionized water, and then redispersed
in a solution containing 0.3 g cetyltrimethylammonium
bromide (CTAB, Amresco), 70 mL deionized water, 70 mL absolute
ethanol and 1.1 mL concentrated ammonia aqueous solution (28%). The mixture was homogenized under ultrasonication for
30 min, followed by dropwise addition of the mixture of 3.2 g
TEOS and 0.9 g (3-mercaptopropyl)-trimethoxysilane (MPTS, Alfa
Aesar) under vigorous stirring. After 6 h stirring, the product was
collected by magnetic separation and repeatedly washed with
ethanol and deionized water to remove nonmagnetic byproducts.
The structure-directing agent CTAB was thereafter removed with
acetone reflux at 80 ◦C. The whole synthesis procedure is presented
in Fig. 1. The product was vacuum-dried at 60 ◦C overnight and
placed in a desiccator before use.