Highly efficient, stable and controllable multi-core, rattle-type Ag@SiO 2 catalyst for the reduction of 4-nitrophenol

Multi-core, rattle-type Ag@silica nanoparticles with different silver loadings were prepared via selective etching methods. A series of characterizations revealed that multiple Ag cores were uniformly distributed inside the silica shell and that the silver element was dominantly metallic silver and part silver bromide; with a ratio of about 6 : 1. Silver nanoparticles immobilized by silica nanocapsules more freely interacted with 4-nitrophenol due to the highly dispersed nanosized Ag cores, the special capsule structure, and high silver loading. Furthermore, the cationic interior of the silica capsules may serve as pools to preferentially concentrate anionic 4-nitrophenol while pumping out the 4-aminophenol. In line with these effects, Ag@silica displayed the highest efficiency of catalytic activity during 4-NP reduction. The kinetic rate constant was one or two orders of magnitude larger than those of other types of catalyst. Meanwhile, Ag@silica was stable, recyclable, and maintains its activity even after 20 reaction cycles, and is thus a candidate for 4-NP decontamination.