Direct Solvothermal Synthesis of Phase-Pure Colloidal NiO Nanocrystals

Nickel(II) oxide (NiO) nanocrystals have potential applications in catalysis and photocatalysis and as precursors for nanostructured thin films of NiO used as photocathodes in p-type dye-sensitized solar cells. Previously reported methods for synthesizing NiO nanocrystals typically produce Ni(OH)2 or Ni as an intermediate phase that is subsequently converted to NiO via calcination or oxidation. Here, we report a reproducible solvothermal method to access colloidal, monodisperse NiO nanocrystals of high optical quality from aminated nickel carboxylate precursor complexes in a single synthetic step at a low reaction temperature (180 °C). The use of a tertiary alcohol, such as tert-butanol or tert-amyl alcohol, as a solvent and the presence of amines and a trace amount of water are all necessary for the formation of NiO. The high optical quality of these nanocrystals combined with the reproducibility and scalability of the synthesis will enable future spectroscopic and reactivity studies of colloidal NiO nanocrystals in the context of their optoelectronic and catalytic applications.