Self-assembled growth of hollow spheres with octahedron-like Co nanocrystals via one-pot solution fabrication

In this work, we report a simple one-pot approach to prepare hollow Co microspheres via self-assembly of octahedron-like nanocrystals. Uniform hollow Co spherical assemblies, prepared via a facile solvothermal reduction approach in the presence of NaCl, were composed of ordered nanooctahedra with a thickness of about 80-120 nm. The formation mechanism (NaCl-assisted Ostwald ripening) has been investigated with TEM/HRTEM/SEM/XRD methods. Surface morphologies of Co hollow spheres have been finely modulated from rough to smooth surface through altering reaction conditions (such as time, temperature, and amount of NaCl). The interior-cavity size of the Co hollow sphere has been well tunable by controlling reaction time or temperature. These materials exhibit good ferromagnetic characteristics, showing their potential applications for catalysts and other related devices. The influence of surface morphology, the interior cavity size, and surface modification upon the magnetic properties of hollow Co spheres have been systematically studied. The possible reasons for diverse magnetic properties of products obtained under different conditions are also discussed.