| Owing to their well-defined morphology, low density, large surface area properties, hollow spheres show great advantages in many applications, such as water treatment, nanoscale reactors, catalysis, drug delivery, supercapacitors and photo-electronics. Multi-shelled hollow spheres with large specific surface area, enhanced structural stability, and multifunctionality show significant advantages in many applications over the single-shelled hollow counterparts. The synthesis approach of multi-shelled hollow spheres generally involves multistep operations and complex components, leading to difficulty in large scale production to commercially viable quantities. Consequently, how to synthesize multi-shelled hollow spheres with multi-component shells by an easy-to-efficient approach is a big challenge. In this paper, a one-step rapid aerosol process was used to synthesize magnetic double-shelled hollow spheres with different-component shells, and then the related properties of the hollow spheres were investigated.In this study, magnetic double-shelled C/SiO2 hollow spheres with an outer silica shell and an inner carbon shell were initially prepared by activating a solid silica layer of C/SiO2 aerosol particles. The magnetic substance were homogeneously distributed in the silica and carbon shells. This low-cost preparation technique included a rapid aerosol process and a subsequent dissolution-regrowth process. The activation of the solid silica layer of the aerosol particles by dissolution-regrowth resulted in large voids of～50 nm between the two layers. The large surface area (226.3 m2/g), high pore volume (0.51 cm3/g) and high mechanical stability of the spheres benefit their high adsorption capacities for methylene blue (MB) and metal ions. The novel spheres show a high adsorption capacity of 171.2 mg/g for MB, which is higher than the adsorption capacity of single-shelled silica hollow spheres (150.0 mg/g). The adsorption efficiency of the hollow spheres remains higher than 95% after five cycles of regeneration. The adsorption process on MB fits the Langmuir mode. The saturation adsorption values of Pb2+ and Ag+ions on the hollow spheres were found to be 216.5 and 283.1 mg/g, respectively, which are higher than the corresponding values of 189.8 and 213.4 mg/g on the single-shelled spheres. Moreover, the adsorption capacities of the five-times-recycled spheres for Pb2+ and Ag+ions reached as high as-180 and ～245 mg/g, respectively. Furthermore, the saturated hollow spheres could be easily recycled by an external magnetic field.Magnetic double-shelled C/SiO2 hollow spheres were then taken as a carrier for Au nanoparticles. Double-shelled C/SiO2-Au and C/Au/C hollow spheres were successfully prepared. The reduction of 4-nitrophenol (4-NP) by NaBH4 was chosen as a model reaction for evaluating the catalytic performance of the Au NPs loaded hollow spheres. It revealed that in contrast to C/SiO2-Au hollow spheres, C/Au/C hollow spheres showed a comparable catalytic activity and enhanced chemical stability even at 850℃. Moreover, C/SiO2/Au, C/Au/C microspheres can be easily recycled and reused by an external magnetic field.Double-shelled C/C hollow microspheres were also prepared based on the hollow nanostructure. C/C microspheres (482.0 m2/g,0.92cm3/g) were ideal electrode materials. The specific capacitance was 251 F/g at current density of 0.1 A/g, and the capacitance decreased by 5.4% after 5000 cycles at current density of 1 A/g, indicating good cycling stability of the C/C nanostructure as electrode materials. |
