Influence of ultrasound on the instantaneous synthesis of tridimensional α-Ni(OH)2 nanostructures and derived NiO nanoparticles

Abstract

Nickel hydroxides present an extraordinary importance in the development of electrochemical devices. In contrast to the use of ammonia as a direct precipitating agent, we present herein the instantaneous precipitation of α-Ni(OH)₂ nanopowders by the addition of a nickel salt to an ammonia solution. The synthesis is based on the oversaturation of the solution in the absence of any additive or other metallic cations, where ammonia plays a role as a complexing agent for intermediate nickel compounds. The influence of ultrasound on both the microstructure and the crystalline structure is discussed and the differences are referred to a new parameter (S parameter) which quantifies the amount of power in watts per cm² that a mol of [Ni(NH₃)₆]²⁺ experiences. The description of the nucleation and growth processes of the different powders studied led to the understanding of the effect of ultrasound on the crystallography of α-Ni(OH)₂. The porosity of the samples is also evaluated and its percentage and type are also correlated to the synthesis conditions. The transformation of α-Ni(OH)₂ to NiO is also considered and their optical properties are evaluated as an initial indicator of their promising use as electrochemical devices.