Hydrothermal self-assembly of hierarchical cobalt hyperbranches by a sodium tartrate-assisted route

Abstract

Three-dimensional (3D) hierarchical cobalt (Co) hyperbranches are synthesized by a sodium tartrate-assisted hydrothermal self-assembly route. The route includes the fabrication of the Co hyperbranches in a solution of cobalt chloride (CoCl₂·6H₂O) and sodium hydroxide (NaOH) at 110 °C for 24 h using sodium tartrate (Na₂C₄H₄O₆·2H₂O) as the complex reagent and sodium hypophosphite (NaH₂PO₂·H₂O) as the reducing agent. Each Co hyperbranch is 50–100 μm in length and consists of a main branch with several secondary branches and leaves. The adjustments of the molar ratio of Na₂C₄H₄O₆ to CoCl₂ and the concentration of NaOH in the solution lead to the formation of the Co products with different morphologies. A possible growth mechanism for the Co hyperbranches is proposed based on the characterization results of X-ray diffraction and scanning electron microscopy. The magnetic hysteresis loops at room temperature of the resulting Co products with different morphologies show ferromagnetic characteristics with high dependence on their sizes and morphologies. An increased coercivity (H_c) of 231 Oe and a reduced saturation magnetization (M_s) of 152 emu/g are observed in the Co hyperbranches compared to their bulk counterpart. This relatively simple, efficient, and morphologically controllable route can be applied to the synthesis of complex 3D micro/nanoarchitectures of other materials.