Sandwich Fe2O3@SiO2@PPy ellipsoidal spheres and four types of hollow capsules by hematite olivary particles

Abstract

Hematite@silica@polypyrrole (Fe₂O₃@SiO₂@PPy) ellipsoidal sandwich composite spheres as well as SiO₂, SiO₂/PPy, PPy hollow capsules and PPy ellipsoidal hollow capsules with movable hematite cores were successfully fabricated by hematite (α-Fe₂O₃) olivary particles. Monodispersed α-Fe₂O₃ olivary particles were firstly prepared via hydrolysis of ferric chloride solutions. Then Fe₂O₃@SiO₂ core–shell particles were synthesized based on base-catalysed hydrolysis of TEOS (tetraethylsiloxane) using steric agent PVP [poly(N-vinylpyrrolidone)] as anchor-molecule. Furthermore, polymerization of pyrrole monomers was preformed around as-prepared Fe₂O₃@SiO₂ composite spheres to form sandwich multilayer core–shell particles. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images show that both the middle layer silica shell and the outer layer polypyrrole sheath are uniformly coated over the hematite cores. In addition, SiO₂, SiO₂/PPy, PPy ellipsoidal hollow capsules and PPy ellipsoidal hollow capsules with movable hematite cores were obtained after the selective removal of the hematite, Fe₂O₃@SiO₂ cores or silica middle shell of the sandwich ellipsoids respectively.