Anisotropic magnetic nanoparticles with a mesoporous silica shell have the combined merits of a magnetic core and a robust shell. Preparation of magnetically guidable core-shell nanostructures with a robust silica shell that contains well-defined, large, radially aligned silica pores is challenging, and hence this has rarely been described in detail. Herein, a dynamic soft-templating strategy is developed to controllably synthesize hierarchical, dual-mesoporous silica shells on diverse core nanoparticles, in terms of nanoparticle shape (i.e., spherical, chainlike, and disclike), magnetic properties (i.e., hard magnetic and superparamagnetic), and dimensions (i.e., from 3 nm to submicrometers). The developed interfacial coassembly method allows easy design of applicable silica shells containing tunable pore geometries with pore sizes ranging from below 5 nm to above 40 nm, with a specific surface area of 577 m2 g-1 and pore volume of 1.817 cm3 g-1. These are the highest values reported for magnetically guidable anisotropic nanoparticles. The versatility of the method is shown by transfer of the coating procedure to core particles as diverse as spherical superparamagnetic nanoparticles and their clusters as well as by ferromagnetic 3 nm thick hexaferrite nanoplatelets. This method can serve as a general approach for the fabrication of well-designed mesoporous silica coatings on a wide variety of core nanoparticles.
Keywords: interface assembly; iron oxide core nanoparticles; magnetic hexaferrites; mesoporous silica shell; radially aligned pores.