Characterisation of synthesised nickel and cobalt nanoscale oxides

The special features of nano-structured materials have been motivating the search for new synthesis methods for these types of materials. This paper is primarily focused on the characterisation of nickel and cobalt nanoscale oxides synthesised by a method based on the dehydration of their respective metal nitrate solutions. This chemical-based synthesis route is briefly described, and basic thermodynamic arguments are presented to theoretically support the feasibility of obtaining such oxides. In addition, a very homogeneous co-formed Ni and Co oxide compound was obtained by dehydrating a water-based solution of both nitrates. Characterisation was done with by X-ray diffraction and transmission electron microscopy, which revealed, respectively, the presence of oxides and their nanoscale structures, including particle morphology and size distribution. High-resolution electron microscopy (HREM) images indicated that the average particle sizes of the obtained NiO and Co3O4 obtained were approximately 20 nm and 40 nm, respectively. In addition, some particles presented crystalline defects in their inner structure, although those smaller than 5 nm seemed to be defect-free and were spherical or faceted. In addition to being characterised as nano-particle-bearing materials, the co-formed oxides can also be used as the starting material for alloys and nano-composites preparations if they are submitted to complete or partial reduction, respectively.

► The feasibility in obtaining Ni and Co and their co-formed oxides was evaluated. ► Ni, Co and Ni and Co co-formed nanostructured oxides were synthesised by the route. ► XRD, TEM and HREM techniques were used to characterise the obtained nanostructures. ► The particles sizes of the obtained nanostructures were about 20 nm and 40 nm. ► The particles smaller than 5 nm were spherical/faceted and seems to be defect-free.