Speakers
Description
A surfactant-free, precursor-modulated nanoscale engineering approach for the synthesis of self-assembled flower-like 3D NiO nanostructures is reported. The method utilizes two distinct intermediate phases: ordered β-Ni(OH)₂ and turbostratic Ni₃(OH)₄(NO₃)₂ nanoplates. Through a combination of structural and spectroscopic techniques (XRD, SAED, TEM, HRTEM, SEM, AFM, UV–Vis, and DSC), the transformation mechanisms from intermediates to NiO nanoparticles are elucidated.
The resulting NiO nanoparticles exhibit distinct morphologies, optical, electrical, and surface properties depending on the precursor used. β-Ni(OH)₂ and Ni₃(OH)₄(NO₃)₂ intermediates form self-assembled nanoflake-like flower morphologies. While the β-Ni(OH)₂ intermediates are highly ordered, the Ni₃(OH)₄(NO₃)₂ counterparts exhibit a turbostratic structure. DSC analysis reveals that the Ni₃(OH)₄(NO₃)₂-to-NiO transformation proceeds via two distinct thermal events (306 °C and 326 °C), corresponding to loss of interlayer H₂O and ions, followed by the removal of chemically bonded OH⁻ and NO₃⁻ species. In contrast, the ammonia-derived NiO NPs undergo a single phase transition at 298 °C.
Ammonia-derived NiO NPs retain the flower-like nanomorphology due to water-mediated adhesion on the neutral {100} surfaces. In contrast, structural transformation of turbostratic Ni₃(OH)₄(NO₃)₂ nanoplates yields NiO NPs dominated by polar OH-terminated (111) surfaces, disrupting the original 3D self-assembled structure. Carbamide-derived NiO NPs are three times larger, possess wider band gaps, higher concentration of nickel vacancies, enhanced p-type conductivity, and more pronounced polar surfaces than those prepared with ammonia.
These findings highlight the critical role of precursor chemistry in controlling the morphology and surface characteristics of NiO nanostructures, offering tunable routes toward p-type materials for catalytic and electronic applications.
