A versatile method for controlled synthesis of porous hollow spheres

A versatile method was developed to synthesize nickel silicate, silica, and silica-nickel composite porous hollow spheres by using silica spheres as templates. In the preparation, silica spheres were treated with a mixture of NiSO₄·6H₂O and NH₃·H ₂O. The nickel-based ingredient reacted with the silica to form a shell while the alkaline solution could remove the silica core, thus forming the nickel silicate hollow spheres. After these spheres were further treated with hydrogen in reduction or with HCl in etching, they became silica-nickel hollow spheres or silica hollow spheres, respectively. The sizes of these hollow spheres depended on the concentration of the precursor. Our investigation also found that their surface properties or magnetic properties could be tailored by adjusting the fabrication parameters.