A mesoporous SiO2/dense SiO2/Fe3O4 multiply coated hollow microsphere: Synthesis and application on papain immobilization

Abstract

The mesoporous SiO2/dense SiO2/Fe3O4 multiply coated hollow microspheres were prepared by a multistep coating technique. At first, the dense SiO2 layers with the thickness of 4.2nm were coated on the Fe3O4 nanorods to prevent them from being corroded in acidic system. Then, the mesoporous SiO2 was coated on the composite microspheres via a sol-gel and hydrothermal synthesis process by using TEOS as silicon source, P123 in combination with co-surfactant CTAB as template in acidic system. The mesoporous SiO2/dense SiO2/Fe3O4 multiply coated hollow microsphere has a narrow pore size distribution around 3.74nm, a large surface area of 505m2g−1, and a pore volume of 0.47cm3g−1. The composite microspheres had a high papain immobilization (222mg/g) since the hollow cavity in the composite microsphere is a natural warehouse storing papain molecules effectively. The pH stabilities and temperature stabilities of the immobilized papain activity were much higher than that of the free papain activity.