Magnetically retrievable nanocomposite adorned with Pd nanocatalysts: efficient reduction of nitroaromatics in aqueous media

Herein, we describe the fabrication of a magnetically retrievable nanocomposite adorned with highly active Pd nanoparticles (NPs) (MRN-Pd), which is useful for the efficient reduction of nitroaromatics in aqueous solution. The polymerization of pyrrole as the monomer in the presence of Pd salt and iron nanopowder generates Pd nanocatalysts and localizes the resultant Pd NPs discretely and uniformly on the polypyrrole framework comprising strongly magnetic MRN-Pd catalyst without the need for any reducing agent. The nitrogen-containing polymer enhances the interaction between the decorated Pd nanocatalysts and the polymer scaffold, endowing stability to the Pd NPs and maintaining their monodispersity. This prevents the possible aggregation of the MRN-Pd catalyst and promotes its reactivity for fast reduction processes. The unique features exhibited by the MRN-Pd catalyst result in excellent catalytic activity for the expeditious reduction of nitroaromatics under green reaction conditions at room temperature. Furthermore, the pronounced magnetic characteristics of the MRN-Pd catalyst allow its convenient separation and recycling from the reaction mixture. In addition, the MRN-Pd catalyst can be completely separated and recycled using a small magnet and reused for seven consecutive cycles of high-yield reduction of nitrobenzene (99-95%) in water, thus affording a highly retrievable and sustainable magnetic nanocomposite catalyst suitable for environmentally friendly processes. The MRN-Pd catalyst also presents high catalytic activity in other typical catalytic transformations requiring Pd nanocatalysts, such as the Suzuki and Heck cross-coupling reactions.