Recyclable Au/SiO2-Shell/Fe3O4-Core Catalyst for the Reduction of Nitro Aromatic Compounds in Aqueous Solution

Highly stable gold nanoparticles immobilized on the surface of amine-functionalized nanocomposite microspheres possessing a magnetite (Fe 3 O 4 ) nanoparticle core and a silica (SiO 2 ) shell (Au/SiO 2 -shell/Fe 3 O 4 -core) were prepared. These gold nanocomposite catalysts were tested for 4-nitrophenol (4-NP) and 2-nitroaniline (2-NA) reduction in aqueous solution in the temperature range 293-323 K and in the presence of aqueous NaBH 4 reducing agent. The magnetically recyclable gold catalyst showed high stability (∼3 months), efficient recyclability (up to 10 cycles), and high activity (∼100% conversion within 225 s, ∼700 ppm 4-NP or 2-NA). The pseudo-first-order apparent reaction rate constants ( k ) of 4-NP and 2-NA reduction were 7.5 × 10 -3 and 4.1 × 10 -3 s -1 , respectively, and with an apparent catalytic activity of 4.48 × 10 -8 kmol/(m 3 s).