Controlled and stepwise generation of Cu2O, Cu2O@Cu and Cu nanoparticles inside the transparent alumina films and their catalytic activity

Abstract

A stepwise generation of Cu₂O, Cu₂O@Cu core-shell and Cu nanoparticles (NPs) inside the alumina films has been accomplished. First, CuO–Al₂O₃ films were prepared on glass substrates by dip-coating method using alumina sol derived from partially acetylacetonate (acac) chelated aluminium-tri-sec-butoxide doped with copper(II) chloride, followed by heat-treatment at 450 °C in air. Heat-treatment of CuO–Al₂O₃ films at 450–500 °C in reducing atmosphere resulted in the formation of stable Cu₂O NPs which can be subsequently converted to Cu₂O@Cu core-shell NPs with tunable Cu-shell thickness, and followed by pure Cu NPs by further heat-treatment at 550–700 °C. UV–visible, transmission electron microscopy (TEM) and grazing incidence X-ray diffraction (GIXRD) studies of the films in different stages confirmed the generation of Cu₂O, Cu₂O@Cu core-shell and Cu NPs. It has been understood that the chemical structure and property of matrix alumina facilitated the stabilization of Cu₂O NPs inside the films. As a result, the formation of Cu₂O@Cu NPs can be achieved easily by controlled heat-treatment in reducing atmosphere. The catalytic properties of Cu₂O, Cu₂O@Cu and Cu NPs incorporated alumina films were studied by monitoring the degradation of an azo dye congo-red. All films showed very good catalytic activities; among these Cu₂O NPs doped films showed excellent stability, reusability and high rate constant values.