Polymer assisted synthesis of chain-like cobalt-nickel alloy nanostructures: Magnetically recoverable and reusable catalysts with high activities

We present a simple wet chemical reduction method to synthesize chain-like bimetallic cobalt-nickel (CoNi) alloy nanostructures of varying compositions in the presence of a thermoresponsive polymer, poly(vinyl methyl ether) (PVME). We also synthesize monometallic Co and Ni nanostructures by this method for comparison of their properties with that of CoNi nanoalloys. Transmission electron microscopic (TEM) study reveals that the formed CoNi nanoalloys exhibit a chain-like assembled nanostructure encompassed with some hairy structure. The chain-like assembled alloy nanostructures are composed of spherical CoNi alloy nanoparticles. CoNi nanoalloys prepared without PVME do not show such chain-like structures indicating that PVME-assisted growth is needed for preparation of such patterned self-assembled nanostructures. The combined X-ray diffraction and selected area electron diffraction (SAED) studies confirm that this method produces polycrystalline chain-like CoNi nanoalloys. SAED study further reveals that the hairy structures are amorphous in nature. The synthesized CoNi alloy/pure Co/pure Ni nanostructures show soft ferromagnetic behaviour. The formed nanostructured bimetallic CoNi alloys and monometallic Co and Ni are excellent catalysts for both organic and inorganic reactions in aqueous phase. The obtained CoNi alloy nanochain also successfully catalyzes the cross coupling reaction between iodobenzene and 4-chlorothiophenol in the organic phase (DMF). The magnetically recovered chain-like CoNi alloy nanocatalyst is reusable at least for eight times without much loss of its initial activity.