SiO2 nanoparticles were firstly prepared following the well known modified St ¨ober method [25].The core–shell mesoporous
silica was prepared according to the previous report with some modifications [26]. 0.5 g SiO2 was well dispersed in the mixture solution of 0.15 g cetyltrimethylammonium bromide (CTAB), 40 mL deioned water, 0.5 g concentrated ammonia aqueous solu-tion (28wt%), and 30 mL ethanol. After the solution was stirred for 0.5 h, 0.40 g TEOS was added dropwise to the solution with vigorous stirring.