Formation of β-nickel hydroxide plate-like structures under mild conditions and their optical properties

Nanostructural β-nickel hydroxide (β-Ni(OH)2) plates were prepared using the microwave–hydrothermal (MH) method at a low temperature and short reaction times. An ammonia solution was employed as the coordinating agent, which reacts with [Ni(H2O)6]2+ to control the growth of β-Ni(OH)2 nuclei. A trigonal β-Ni(OH)2 single phase was observed by X-ray diffraction (XRD) analyses, and the crystal cell was constructed with structural parameters and atomic coordinates obtained from Rietveld refinement. Field emission scanning electron microscopy (FE-SEM) images revealed that the samples consisted of hexagonal-shaped nanoplates with a different particle size distribution. Broad absorption bands assigned as transitions of Ni2+ in oxygen octahedral sites were revealed by UV–vis spectra. Photoluminescence (PL) properties observed with a maximum peak centered in the blue-green region were attributed to different defects, which were produced during the nucleation process. We present a growth process scheme of the β-Ni(OH)2 nanoplates.

Nanostructural β-Ni(OH)2 crystalline powders were prepared by rapid microwave–hydrothermal method for 1, 8 and 32 min. The hexagonal-shaped nanoplates obtained presented PL emission in the blue-green region and each decomposed component represents a different type of electronic transition, which can be linked to the structural arrangement or surface defects.Figure optionsDownload as PowerPoint slideHighlights
► Ammonia solution to control the growth of β-Ni(OH)2 nuclei.
► Regular plates-shape related to crystallization–dissolution–recrystallization.
► The surface states and lattice defects generated in growth mechanism of crystals.
► Different defects produced in the growth process responsible by photoluminescence.
► Each component of photoluminescence curve linked to structural arrangement or surface defects.