Abstract
This study presents an investigation into the surfactant-free synthesis of copper oxide nanoparticles (CuONPs) via a precipitation method, focusing on how various experimental parameters influence nanoparticle characteristics. By varying key parameters, such as precursor type and concentration, pH, and reaction temperature, the work reveals their impact on nanoparticle size, morphology, and crystallinity. The results highlight that the precursor's counter-ion and Cu/OH ratio play key roles in directing the particle shape, while an increased copper concentration favored rod-like structures through an oriented attachment phenomenon. A temperature-dependent phase transition was observed for the first time, illustrating a metastable flake-like intermediate that transforms into spherical nanoparticles at high temperatures. This study proposes a detailed growth mechanism, identifying two temperature-dependent pathways, slow CuO condensation at low temperatures and competing oxolation/olation reactions at high temperatures. Overall, this work establishes a reproducible framework for tailoring the morphology of CuONPs under mild conditions.