Template-free Synthesis and Characterization of Nickel Oxide Nanocrystal with High-energy Facets in Deep Eutectic Solvent

Abstract

In this study, nickel oxide (NiO) nanocrystals with high-energy facets were synthesized in a nonaqueous choline chloride-urea deep eutectic solvents (DES). The NiO nanocrystals were obtained without the aid of stabilizing or templating agent. FT-IR and FE-SEM results indicate that approximately 100 nm sized NiO nanocrystals with truncated hexagonal bipyramidal structure were obtained. Further structural investigation of HR-TEM results reveal that the faceted NiO nanocrystals were formed with each face of crystal compose of sharp and defined edges. We believed that the "supramolecular" moiety formed in DES through the extensive hydrogen bonding in conjugation with solvent viscosity operates as soft template for directed growth of NiO nanocrystals. The urea molecules in DES play a vital role in governing the final morphology of the NiO nanocrystal. With the virtue of their well-defined three-dimension structure, NiO crystals would have the potential advantageous in the field of energy as well as catalysis.