Synthesis of hollow microspheres of nickel using spheres of metallic zinc as templates under mild conditions

Abstract

In recent years, hollow spheres of nanometer to micrometer dimensions have attracted special interests because of their potential applications in many areas [1, 2]. For example, they can serve as extremely small container for encapsulation which may benefit the control of delivery and release process of drugs and protection of environment-sensitive materials such as enzymes [3]. When it comes to fillers in making composite materials, hollow spheres can also show some advantages over their counterparts for their relatively low densities [4]. Various approaches have been proposed for preparing hollow spheres. For example, hollow polymer, oxide and glass composite spheres in micrometer-size range can be synthesized by physical methods such as spray drying techniques [5, 6]. Chemical methods can also be used to fabricate hollow spheres and soft template synthesis is a general one [7, 8]. For example, Micrometer-sized hollow spheres of CdS have been also been synthesized through an in situ source-template interface reaction route [9]. However, so far there are few reports on the fabrication of metal hollow spheres by chemical methods [10, 11]. Fortunately, a template-engaged method has been introduced recently and presents good prospect for the synthesis of metal hollow spheres by simple chemical methods [12]. But in this approach, only noble metals were used as templates and no further experimental data were given to prove the possibility of applying this method to other metals. Here our experiment will give a strong support to the generality of this method and provide a cheap approach to fabricate hollow nickle spheres for future industrial application. In our experiment, we utilize the replacement reaction between nickel and zinc to form nickel shells on the surfaces of zinc spheres by reacting nickel salt solution with solid template of zinc under carefully controlled conditions. Hollow nickel micrometer spheres were obtained by removing the residual cores of zinc and zinc oxide via washing with NaOH aqueous solution. In a typical experiment, 0.50 g zinc powders were first dispersed into 5 ml acetone, which was then added into 100 ml distilled water. After strongly stirring for 10 min, the mixture of zinc and water were kept for 40 s to separate the few large zinc spheres from the main part of zinc spheres by gravity, and then the suspended part