Sustainable anti-oxidation of metallic copper in aqueous solution endowed by ultra-small nanobubbles

Copper (Cu) is prized for its exceptional conductivity and catalytic properties. However, its susceptibility to oxidation, particularly in the presence of water, poses a significant challenge, potentially compromising its inherent properties. Despite numerous efforts to address Cu oxidation, effective remedies remain elusive. Herein, we present the identification of nanobubbles (NBs) as a novel strategy to sustain Cu in a metallic state for extended durations within aqueous environments. The Cu foils immersed in pure water undergo rapid oxidation within a mere 4-hour timeframe, while ultra-small NBs maintain the metallic state for a prolonged 72-hour immersion period. During this process, the immersion treatment with ultra-small NBs induces nanocavity formation on Cu foils, accompanied by the detection of zero-valent Cu clusters in the bulk solution. This suggests a process wherein a fraction of metallic copper ionizes, enters the solution and undergoes reduction to form metallic copper clusters. This finding recovers a spatially separated redox process, with the NBs interface playing a pivotal role. The significance of this work extends beyond proposing a simple method to sustain Cu in a metallic state. It also unravels the anti-oxidant mechanism by using spatially separated redox reactions, which hold great potential for broad applications.