Synthesis of multiple-shell porous CeO₂ hollow spheres by a hydrogel template method

CeO₂ hollow spheres with porous multiple-shell were synthesized via a simple electric-current assisted template method. Dense polyacrylamide network, as the template, plays an important role in the formation of the porous and hollow CeO₂ spheres, such as providing favorable nucleation sites for the formation of Ce(OH)₃ nanocrystals, controlling the size of the aqueous domains, and limiting crystal arrangement in the domains. Furthermore, the interaction between Ce³⁺ ions and amide groups of the polyacrylamide was the driving force for the self-assembly of the crystals, resulting in the porous Ce(OH)₃ hollow spheres. The effects of the reaction parameters on the morphology, size and number of the shells of the porous hollow structures were investigated, and the formation mechanism of the hierarchical porous CeO₂ hollow spheres was proposed.