The effect of pH on the synthesis of stable Cu₂O/CuO nanoparticles by sol–gel method in a glycolic medium

Abstract

In this work, we demonstrate that using a glycolic medium, both stable CuO and Cu₂O nanoparticles can be elaborated from Cu colloidal particles by adjusting their chemical environment, in particular the acido-basicity of the solution. In this context, the effect of pH on the sol–gel synthesis of Cu₂O/CuO NPs was investigated. XRD results confirmed the formation of pure Cu₂O with a cubic structure at lower pH (pH ≤ 6), whereas the pure monoclinic CuO was formed at higher pH (pH ≥ 12). TEM image indicates that the as-formed CuO NPs in basic pH are spherical in shape and their average size is found to be in the range of 4.5 nm. However, the as-obtained Cu₂O NPs in acid pH are cubical, with an average diameter of about 3 nm, and agglomerated into large spherical particles under the effect of ethylene glycol. Using the UV–Vis spectroscopy, the measured band gap energies of the prepared Cu₂O and CuO NPs are 2.07 and 4.08 eV respectively. FTIR results confirm the purity of the synthesized CuO and Cu₂O nanoparticles.