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 Cu₂O 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 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 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 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.