A new approach to synthesize uniform metal oxide hollow nanospheres via controlled precipitation

Uniform NiO, α-Fe₂O₃, ZnO, CuO and Ga ₂O₃ hollow nanospheres consisting of a shell of closely packed nanoparticles with a shell wall thickness of a few tens of nanometers have been successfully synthesized on a large scale by controlled precipitation of metal cations with urea in the presence of carbonaceous saccharide nanospheres as hard templates. In addition, it is interesting to find that the single-phase transition metal oxides of NiO and α-Fe₂O ₃ can form ball-in-ball hollow nanoarchitectures by this simple approach. Furthermore, it is demonstrated that direct size control of the oxide hollow nanospheres can be achieved by using carbon templates of different diameters. This method could be extended to the synthesis of many other metal oxide hollow nanospheres. The hollow nanostructured metal oxides might be found to have potential applications in many fields such as catalyst supports, catalysis, drug delivery, chemical/biological separation, sensing, etc.