Coordination and reduction in polyol-mediated solvothermal synthesis of nickel-based materials with controllable morphology and magnetic and electrochemical properties

The coordination and reduction effects in polyol-mediated solvothermal synthesis were studied using nickel acetate as model precursor and ethylene glycol (EG)-ethanol (Et) mixture as polyol medium. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses confirmed that the morphology and phases of the nickel-based products depended on the volume ratio of EG to Et, because of their differing coordination and reduction capacities. When the Et content in the polyol mixture was low, EG dominated and the system exhibited superior coordination as well as the ability to self-assemble to produce sphere-like alpha-Ni(OH)(2). When Et was dominant, the strong reducing effect of Et and decarboxylating effect of nickel on ethanol led to formation of alpha-Ni(OH)(2) nanosheets. However, at EG:Et ratio of 1:1, polyhedral metallic nickel was produced due to the synergistic effect of coordination and reduction by EG and Et. For other EG:Et ratios, mixed products of alpha-Ni(OH)(2) and metallic nickel of different shapes were obtained, providing evidence of the coordinating and reducing abilities of the polyol mixture. The prepared alpha-Ni(OH)(2) material has potential for application in supercapacitors, while the metallic nickel displayed magnetic properties. This study demonstrates a new route for solvothermal synthesis of different nanomaterials using polyols as solvents.