A Nanoreactor of Gold Nanoparticle Encapsulated Hollow Silica Nanosphere: Synthesis and Catalytic Applications

In recent years, hollow nanostructures have been reported of their unique properties such as high surface-to-volume ratio and the large fraction of void space in hollow structure. Those materials could be used in various applications including catalysis, drug delivery, hydrogen storage, and rechargeable batteries. In general, the as-synthesized materials are prepared through coating the target materials on the templates. Then, hollow structures are obtained by removal of the templates. However, the synthetic procedures were complicated and involved numerous steps. It was difficult to reduce the particle size to 100 nm. Thus, those methods restricted the development of hollow nanostructure in the biomedical applications.
Herein, we synthesized hollow silica nanospheres (HSNs) with tunable sizes from 25 nm to 170 nm by a one-step water in oil reverse microemulsion (W/O) method. The size of HSNs could be adjusted via three approaches: (1) changing the oil phase in the reverse microemulsion, (2) adjusting the volume of co-surfactant, and (3) varying the ratio of surfactant CA-520 to Triton X-100. The compositions and structures were characterized by different characterization techniques, such as transmission electron microscope (TEM), and nitrogen adsorption-desorption isotherms. Furthermore, the functional materials such as metal, metal oxide, drug, and protein could be encapsulated in the hollow silica nanospheres through this novel method. Hollow silica nanospheres have potential applications in catalysis, cell-labeling and drug delivery. Herein, we demonstrate its application in catalysis.
The gold nanoparticle encapsulated in hollow silica nanospheres (Au@HSNs) were examined on p-nitrophenol reduction and CO oxidation reaction. The silica shell of hollow silica sphere protected the gold nanoparticle from sintering during calcination and reaction. In p-nitrophenol reduction, the Au@HSNs displayed high catalytic activity and resistance to DMSA (meso-2,3-dimercaptosuccinic acid) poisoning. In CO oxidation reaction, the catalyst performed amazingly at low-temperature CO oxidation even at -20℃, and displayed high stability after many catalytic cycles. Furthermore, the water vapor could not only enhance the catalytic activity but also be a switch to turn on/off the nanoreactor.