NiCo2 Alloys: Controllable Synthesis, Magnetic Properties, and Catalytic Applications in Reduction of 4-Nitrophenol

Dendritic Ni33.8Co66.2 alloy microstructures with hexagonal closedpacked phase have been prepared in large-scale by a simple and facile solution phase chemical route, while flowerlike Ni33AC066.6 in size of 2.5-5.5 mu m was synthesized by solvothermal routes. Experimental results show that the reaction temperature, total concentration of [Ni2+] + [Co2+], and kinds of solvent and surfactants are key factors for controlling the morphology and crystal phase of the NiCo alloy. The possible formation mechanism for the Ni33.8Co66.2 dendrites has been discussed. Magnetic measurements revealed that both of the NiCo2 alloys obtained are ferromagnetic at room temperature. The saturation magnetization value of the Ni33.8Co66.2 dendrites (163.55 emu/g) is lower than that of the flowerlike Ni33.8Co66.2 (195.79 emu/g), but the Ni33.8Co66.2 dendritic structures exhibit an enhanced coercivity value. NiCo2 alloys with different shapes (Ni33.8Co66.2 dendrites and flowerlike Ni33.8Co66.2) have been used as reusable heterogeneous catalysts to reduce 4-nitrophenol (4-NP) into 4-aminophenol (4-AP) by NaBH4. The kinetic data indicate that Ni33.8Co66.2 dendrites are catalytically more active than the flowerlike Ni33.8Co66.2 probably due to its larger surface-to-volume ratio and surface areas, since their Brunauer Emmett -Teller surface areas are 32.68 and 20.66 m(2)/g, respectively.