One-pot fabrication of noble-metal nanoparticles that are encapsulated in hollow silica nanospheres: dual roles of poly(acrylic acid).

An efficient and facile one-pot method was developed to fabricate noble-metal nanoparticles (NMNs; Au, Pt, PdO and Ag) that were encapsulated within hollow silica nanospheres (HSNs; NMNs@HSNs) with a size of about 100 nm. NMNs@HSNs were afforded in very high yields between 85-95 %. Poly(acrylic acid) (PAA) polyelectrolyte played a dual role in the fabrication process, both as a core template of the HSNs and as a captor of the NMNs through coordination interactions between the COO(-) groups on the ammonium polyacrylate (APA) polyanionic chains and the empty orbital of the Au atom. The amount of Au loading in Au@HSNs was easily regulated by varying the volume of the HAuCl(4) solution added. In addition, these rattle-type particles were successfully applied in the catalytic reduction of 2-nitroaniline (2-NA) as a model reaction, thus indicating that the micropores in the silica shell could achieve the transport of small species--with a size smaller than that of the micropores--into the cavity. Thus, these fabricated NMNs@HSNs have promising applications in catalysis.