Crucial factors affecting the physicochemical properties of sol–gel produced Fe₃O₄@SiO₂–NH₂ core–shell nanomaterials

Multifunctional nanomaterials with task-specific physicochemical properties, especially core–shell nanostructures with Fe₃O₄ core and NH₂-functional shells (Fe₃O₄@SiO₂–NH₂), have been extensively investigated as high-performance adsorbents, catalysts and catalyst supports; and in most cases the controllable sol–gel technique is the choice for fabrication of this kind of widely applied materials. Herein, we demonstrated that mono-dispersed and spherical Fe₃O₄@SiO₂–NH₂ nanomaterials with magnetic response core, NH₂-functional shell structure can be facilely prepared by co-condensation of TEOS with APTMS using a versatile sol–gel process. It was shown that the proper usage of APTMS and appropriate pre-hydrolysis time of TEOS were crucial and key steps for formation of highly uniform and desirable amino loading Fe₃O₄@SiO₂–NH₂ materials. The TEOS pre-hydrolysis and the critical time (around 90 min) before the addition of APTMS prove to be vital for uniform structure evolution, while the appropriate concentration of APTMS (~2.28 mmol L⁻¹ in our system) leads to well-dispersed materials with relatively high loading of amino functionality. The as-prepared Fe₃O₄@SiO₂–NH₂ magnetic nanoparticles prepared under optimum conditions possessing superparamagnetic behavior, uniform core–shell structure (~200 nm in diameter), relatively large BET surface area (~138 m²/g) and high incorporation of amino-functionality (~2.90 wt %).