Synthesis and catalysis properties of NiO flower-like spheres and nanosheets: Water-induced phase transformation of nickel hydroxides

An oleylamine-assisted solvothermal approach has been developed for the synthesis of nickel hydroxide nanomaterials. α-Ni(OH)2flower-like spheres and β-Ni(OH)2hexagonal sheets were obtained by tuning the water volume in the synthesis system. The water-induced phase and morphology evolution from α-Ni(OH)2spheres to β-Ni(OH)2sheets were investigated in detail by controlled experiments based on their crystal structures. Moreover, NiO spheres and sheets were obtained by direct thermal decomposition of corresponding nickel hydroxides. N2adsorption/desorption, temperature-programmed reduction with H2, and catalytic activity tests reveal that NiO spheres exhibit higher surface area, larger pore volume, higher reducibility, and better catalysis activities for CO oxidation than NiO sheets.