Preparation of Core–Shell Magnetic Mesoporous Silica Composite Microspheres and Drug Loading Study

Fe3O4@mSiO2 composite microspheres were synthesized via the sol–gel method, employing sodium citrate (Na3CA)-modified magnetic Fe3O4 nanoparticles as the core material, cetyltrimethylammonium bromide (CTAB) as the templating agent, and tetraethyl orthosilicate (TEOS) as the silica source. The dispersion, mesoporous structure, and spherical morphology of the composite microspheres were significantly influenced by the amount of templating agent, as evidenced by the electron microscopy and transmission electron microscopy results. Particle size and Brunauer–Emmett–Teller analyses indicated that increasing the templating agent dosage promoted larger particle sizes and enhanced the total pore capacity of composite microspheres with 20 and 50 nm Fe3O4 cores. Notably, the 50 nm Fe3O4@mSiO2-3.5 microspheres exhibited the largest total pore capacity, measuring 0.2955 cm3/g. In contrast, composite microspheres with 100 nm Fe3O4 cores exhibited opposite trends in particle size and pore capacity. All composite microspheres exhibited superparamagnetic behavior, with hysteresis loops at room temperature and maximum magnetization intensities ranging from 33.92 to 81.83 emu/g. Drug loading and release studies revealed that the 100 nm Fe3O4@mSiO2-3.0 composite microspheres achieved the highest drug loading capacity, with a rate of 18.36 ± 0.08%. Moreover, the drug-loaded microspheres exhibited faster release rates in PBS buffer at pH 6.8, while slower release was observed at pH 5.0 and pH 7.4.