Copper(I) Oxide Nanocrystals – One Step Synthesis, Characterization, Formation Mechanism, and Photocatalytic Properties

Abstract We report here two different simple, one‐pot, and low cost chemical synthetic routes for the preparation of Cu 2 O nanocrystals: (a) thermal decomposition of copper–organic precursors copper(II) acetate or copper(II) acetylacetonate in long chain organic solvents oleyl alcohol and trioctylamine, respectively, at 170 °C and (b) a surfactant‐free solvothermal approach involving the reaction of copper(II) acetylacetonate in acetone at 140 °C. The structure and morphology of the nanocrystals have been characterized in detail by XRD, FTIR spectroscopy, Raman spectroscopy, and high‐resolution transmission electron microscopy (HRTEM). The optical properties of the nanocrystals have been explored by diffuse‐reflectance spectroscopy (DRS) and a blueshift of the optical band gap of the nanocrystals is observed owing to size effects. Based on the FTIR, GC–MS, and 13 C{ 1 H} NMR studies of post‐reaction solutions, different formation mechanisms for the Cu 2 O nanocrystals, which depend on the synthetic approach, have been proposed. Oleyl alcohol and trioctylamine play dual roles as solvents and mild reductants and reduce Cu II species to Cu I species during the course of the thermal decomposition reactions. The solvothermal reaction of copper(II) acetylacetonate in acetone possibly proceeds by acetylacetone‐mediated reduction of Cu 2+ to Cu + in the absence of any reducing agent. The potential of Cu 2 O nanocrystals as photocatalytic materials for hydrogen generation from water/methanol (2:1) mixtures under UV/Vis irradiation has also been evaluated. The results show that all the nanocystalline Cu 2 O samples generate H 2 .