Polymorphous α- and β-Ni(OH)2 complex architectures: morphological and phasal evolution mechanisms and enhanced catalytic activity as non-enzymatic glucose sensors

Abstract

The morphological modulation and phase conversion of α- and β-Ni(OH)₂ complex architectures with varying subunits from nanopetals, nanocolumns, nanocones, and nanoflakes were investigated using a facile coordination homogeneous precipitation method in the Ni(NO₃)₂+ urea system. Slow growth and nucleation rates due to relatively low reaction temperatures and molar ratios of CO(NH₂)₂ to Ni(NO₃)₂ induced the formation of uniform flower-like α-Ni(OH)₂ architectures. Such flower-like architectures originated from subordinate nanopetals that grow perpendicular to the primordial nanopetal surface and are driven by minimum surface free energy effects. At relatively high reaction temperatures, flower-like α-Ni(OH)₂ can transform into β-Ni(OH)₂ microspheres assembled from nanocolumns, nanocones, and even nanoflakes by varying the reaction time. These processes could be related to the synergetic effect of the anisotropic growth and continuous increase in mass transportation along the [001] direction. Flower-like α-Ni(OH)₂ exhibited better electrochemical activity for glucose oxidation compared with β-Ni(OH)₂ microspheres consisting of nanocones because of its special flower-like morphology with high specific surface areas, well-ordered pores, and layered structures intercalated by water and anions. The approach in this study can be used to fabricate other metal hydroxide nanostructures. Flower-like Ni(OH)₂ nanoarchitectures have potential applications in rechargeable batteries, photonic catalysis, and non-enzymatic sensors for glucose.