Hierarchical magnetite/silica nanoassemblies as magnetically recoverable catalyst-supports

We report the synthesis of magnetically responsive hierarchical assemblies of silica colloids that can be used as recoverable supports for nanocatalysts. Each assembly is composed of a central magnetite/silica composite core and many small satellite silica spheres. The two regions are held together as a stable unit by a polymer network of poly(N-isopropylacrylamide). The central magnetite particles are superparamagnetic at room temperature with strong magnetic response to external fields, thus providing a convenient means for separating the entire assembly from the solution. The satellite silica particles provide large surface areas for loading nanocatalysts through the well-developed silane chemistry. As an example, we demonstrate the use of such magnetically responsive hierarchical assemblies as recoverable supports for Au nanocatalysts for the reduction of 4-nitrophenol with NaBH ₄.