Cation Exchange:  A Simple and Versatile Route to Inorganic Colloidal Spheres with the Same Size but Different Compositions and Properties

This paper describes a cation exchange approach to the synthesis of metal chalcogenide core−shell particles with the same size but a number of different compositions. This method begins with the preparation of colloidal spheres of amorphous Se (a-Se), followed by their reaction with Ag atoms to form Se@Ag₂Se spheres. These core−shell spheres are then converted into Se@MSe (M = Zn, Cd, and Pb) via cation exchange with Zn²⁺, Cd²⁺, and Pb²⁺. All the colloidal spheres prepared using this method are monodispersed in size and characterized by a spherical shape and a smooth surface. Starting from the same batch of Se@Ag₂Se, the resultant Se@MSe samples were essentially the same in size. Furthermore, these core−shell colloidal spheres can be easily made superparamagnetic by incorporating Fe₃O₄ nanoparticles into the a-Se cores. This synthetic approach provides a simple and versatile route to magnetoactive core−shell spheres with the same size but a range of different compositions. This study also implies that it is feasible to further increase the diversity of cations that can be used in the cation exchange of a colloidal system to produce multifunctional core−shell spheres with a variety of properties.