Precious metal-like oxide-free copper nanoparticles: high oxidation resistance and geometric structure

Abstract

Cu nanoparticles have attracted much attention as an alternative to precious metal Au- and Pt-based materials. However, they have a problem with stability and get oxidized easily. Moreover, their synthesis is carried out with hazardous chemicals and in conditions, which is not environmentally friendly. Thus, both improvement in oxidation resistance and establishment of a novel synthesis method under mild conditions are desired for further applications. To solve these problems, we synthesized Cu nanoparticles from copper(II) acetate by photoreduction at room temperature in the presence of kaolinite, a layered clay mineral with high gas barrier properties. We obtained disk-like metallic Cu nanoparticles adsorbed on kaolinite without oxides. The nanoparticles showed high oxidation resistance in the solid phase. The powder sample was stable and did not get oxidized at all even after 6 months on exposure to fresh air in spite of no apparent protectants, which was revealed by infrared spectroscopy. Namely, the obtained Cu nanoparticles showed a precious metal-like property. On the other hand, the as-prepared Cu nanoparticles still showed the reactivity with fresh air in the suspension. This indicates that the adsorption on kaolinite did not spoil the reactivity of the Cu nanoparticles. Therefore, the present study revealed that the combination of photoreduction and addition of a layered clay mineral would be a promising environmentally friendly way to synthesize oxidation–resistant metal nanoparticles.