Ultrathin nickel oxide nanosheets: Highly exposed Ni³⁺-doped high-energy {110} facets

Ultrathin NiO nanosheets with high surface-energy facets are gaining attention, owing to their excellent catalytic property. Two-dimensional NiO nanocrystals generally possess a large lateral size and thickness exhibit a lack of coordinatively unsaturated active/reactive edge and corner sites, which can adversely affect their properties. In this study, round-ultrathin NiO nanosheets (diameter ≈ 60–300 nm, thickness <10 nm) were synthesized using a hydrothermal method followed by calcination. Upon increasing the concentration of NaOH in the medium, the sizes of these nanosheets increased without any change in their thickness. The nanosheets were characterized via powder-XRD, field-emission scanning electron microscopy, high-resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED) analysis. HRTEM and SAED revealed that these NiO nanosheets mainly comprised an exposed high-energy {110} surface. XPS analysis revealed that an unsaturated Ni³⁺ site was present in the NiO nanosheets. The NiO nanosheet exhibited high-catalytic activity for the aromatic-aldehyde reduction reaction.