An environmentally friendly route to synthesize Cu micro/nanomaterials with “sustainable oxidation resistance” and promising catalytic performance

Abstract

Practical application of nanostructured Cu has long been limited by the surface oxidation. Although conventional surface modification can slow down the oxidation rate, the formation of a surface oxide shell cannot completely be prevented. Here, we report an effective approach to achieve “sustainable oxidation resistance” for Cu micro/nanomaterials. Once the Cu is oxidized by the external environment, an ageing treatment would not only convert the oxidized sample back to an unoxidized state but also enhance the oxidation resistance. This approach takes advantage of the dual functions of the citrate group: one is its complexation with the Cu²⁺, which can facilitate the oxidative etching of Cu₂O; the other is its interaction with the Cu surface, which can effectively enhance the Cu oxidation resistance. In the ageing process, the oxide layer was etched by the oxygen, whereas the formed Cu⁰ was protected by the citrate group. Since there is no long-chain or hydrophobic molecule capped on the surface, the adsorption and desorption of the reactant on the Cu surface could proceed smoothly, enabling Cu to be a preferable catalyst. In the reduction of 4-nitro-phenol (4-NP), the rate constant of the reaction catalyzed by the Cu particles is estimated to be 3.85 × 10⁻² s⁻¹. By comparison, rate constants for Ag and Au particles are much lower, which are 1.03 × 10⁻² s⁻¹ and 2.73 × 10⁻³ s⁻¹, respectively. Since the Cu is significantly cheaper, this work provides a promising platform for the development of non-noble metal catalysts.