In situ growth of gold nanoparticles onto polydopamine-encapsulated magnetic microspheres for catalytic reduction of nitrobenzene

A simple and green method for the deposition of gold nanoparticles (Au NPs) on the surface of polydopamine (PDA)-encapsulated Fe3O4 nanoparticles is proposed to fabricate a core–shell Fe3O4@PDA–Au nanocatalyst. In the current approach, Fe3O4 core, about 400 nm in diameter, is enveloped in a PDA coating with a thickness of about 45 nm on which plenty of small Au NPs are immobilized subsequently. PDA serves as a reductant as well as a stabilizer so that additional reagents and thermo treatment are not necessary. In addition, both the size of Au NPs and the thickness of PDA layer are tunable to load more Au NPs with appropriate size on the PDA coating. The Au content on Fe3O4@PDA–Au nanocomposites is about 4.3 wt.%, which endows the nanocatalyst with high catalytic performance in the reduction of o-nitroaniline to benzenediamine by NaBH4 (with a conversion of 99% in 7 min). Most importantly, the catalyst can be easily recycled by using an external magnetic field due to the high magnetization (39.6 emu g−1) and shows excellent reusability (8 cycles with a conversion of >98% for o-nitroaniline). The as-prepared catalyst also show good activity for the reduction of other nitrobenzene analogs. These facilitate the practical application of the catalyst in reduction of nitroaromatic compounds.