Structural, optical and photocatalytic properties of mesoporous CuO nanoparticles with tunable size and different morphologies

Abstract

Nanomaterials with controllable particle size and shape have fascinating properties. Herein, CuO nanoparticles (NPs) with controlled particle size and morphology are obtained via a simple co-precipitation approach. Variation of the reaction medium composition steers the variation of both particle size and morphology of the CuO NPs. The reaction was performed in ethanol–water solutions with different volume to volume ratios (v/v%) i.e. 0, 25, 50, and 100%. XRD of the obtained samples revealed a drop in their particle size from ∼13 to ∼7 nm when the aqueous medium is entirely replaced by the ethanolic medium. TEM and HR-TEM investigations have pointed to the formation of CuO NPs with rod-like shapes in water (diameter = 15 nm and length = 200 nm). Whereas, spherical NPs with a diameter of 7.2 nm are obtained in ethanol. Structural analysis of CuO samples obtained in different media was done applying the Rietveld method. The volume of the monoclinic unit cell of CuO is increased to 81.869 ų when water (81.207 ų) is completely substituted by ethanol. Moreover, the internal local strain (ε) and the dislocation density (δ) values increase from 2.78 × 10⁻³ to 4.64 × 10⁻³ and 0.592 × 10⁶ to 1.93 × 10⁶ line per m², respectively by changing from aqueous to ethanolic medium. The optical band gap (E_g) determined using Tauc's equation for the direct transition is increased from 2.2 to 2.65 eV when water is totally replaced by ethanol. The feasibility of both CuO samples as photocatalysts for the degradation of Congo red was tested. CuO prepared in pure water showed remarkably high efficiency during the first 25 min of illumination. Both samples showed complete dye removal after 35 min. Ultimately, this work presents a simple and green approach for the preparation of CuO NPs with tunable particle size, varied morphological shapes, high surface area, and different structural and optical properties merely through controlling the ethanol content in water.