An environment-benign solvothermal method for the synthesis of flower-like hierarchical nickel and zinc compounds and their transformation to nanoporous NiO and ZnO

Abstract

Flower-like hierarchical Ni₃(NO₃)₂(OH)₄ and Zn₅(OH)₈(NO₃)₂(H₂O)₂ compounds were synthesized by a simple solvothermal method. Absolute ethanol was adopted as solvent, and the precursor is the corresponding nitrate. The as-prepared products were studied by XRD, SEM, TEM, and SAED. It is noted that compared to the conventional oil–water surfactant system, this biosafe alcohol system is simpler and environmentally more benign. Through calcination of the as-synthesized nickel and zinc compounds, nanoporous NiO and ZnO were generated. The optical properties of the nanoporous NiO and ZnO microcrystals have been discussed in terms of photoluminescence (PL) at room temperature. An emission band centered at ca. 2.3 eV that could only be found by cathodoluminescence was observed for the NiO microcrystals. We tentatively assign the peak to the magnetic exciton state 3d⁸2p and relate it to the unique nanostructure of the nanoporous NiO microcrystals.