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

We report here two different simple, one-pot, and low cost chemical synthetic routes for the preparation of Cu2O nanocrystals: (a) thermal decomposition of copperorganic precursors copper(II) acetate or copper(II) acetylacetonate in long chain organic solvents oleyl alcohol and trioctylamine, respectively, at 170 degrees C and (b) a surfactant-free solvothermal approach involving the reaction of copper(II) acetylacetonate in acetone at 140 degrees 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, GCMS, and 13C{1H} NMR studies of post-reaction solutions, different formation mechanisms for the Cu2O nanocrystals, which depend on the synthetic approach, have been proposed. Oleyl alcohol and trioctylamine play dual roles as solvents and mild reductants and reduce CuII species to CuI 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 Cu2+ to Cu+ in the absence of any reducing agent. The potential of Cu2O 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 Cu2O samples generate H2.