Green synthesis of Fe3O4/bentonite-supported Ag and Pd nanoparticles and investigation of their catalytic activities for the reduction of azo dyes

In this work, the biosynthesis of Ag or Pd nanoparticles (NPs) supported on Fe3O4/bentonite using an aqueous Salix aegyptiaca leave extract in the role of reducing and stabilizing agent was reported. Techniques of fourier transform infra-red spectroscopy, X-ray diffraction, field emission scanning electron microscope (FESEM), X-ray spectroscopy (EDX), and vibrating sample magnetometer were used for characterization of structures or properties of the prepared nanocomposites. The average particle sizes of well-dispersed spherical Ag and Pd NPs supported on the surface of Fe3O4/bentonite obtained from FESEM were below 70 nm. The magnetically recoverable Ag or Pd NPs/Fe3O4/bentonite nanocomposites exhibited remarkable catalytic activity for the reduction reaction of rhodamine B (RhB), methylene blue (MB), and methyl orange (MO) azo dyes in the presence of aqueous NaBH4 with good reusability. The obtained nanocomposites showed the dyes reduction rates in an order of Pd/Fe3O4/bentonite > Ag/Fe3O4/bentonite > Fe3O4/bentonite. The reduced form of MO under the reduction process cannot be converted to the original oxidized form; nevertheless, the products of the reduction reactions of RhB and MB can be oxidized again to the original form.