Synthesis of Au@Cu2O Core–Shell Nanoparticles with Tunable Shell Thickness and Their Degradation Mechanism in Aqueous Solutions

Metal@semiconductor core–shell nanoparticles (NPs) are widely used in photocatalysts, sensors, and optical applications owing to their unique metal–semiconductor interface and the integration of the properties from both core and shell materials. Although many efforts have been made toward the precise synthesis of Au@Cu2O core–shell structures, the chemical stability of Au@Cu2O aqueous suspensions, which is of great significance in many related applications, is not mentioned in any published research. Herein we report the synthesis of Au@Cu2O core–shell NPs with small shell thickness from 2 to 40 nm through a wet-chemistry method. The UV–vis absorption properties are found to be tunable with Cu2O thickness in the range of 2–40 nm. Furthermore, the chemical stability of Au@Cu2O core–shell nanoparticle suspensions in water/ethanol mixed solvents is investigated. It is found that water/ethanol mixed solvents with a larger amount of water are more likely to deteriorate the stability of Au@Cu2O NPs by oxidizing Cu2O to CuO. The results from this work may provide useful information for the preparation of metal@Cu2O water-based suspensions that are expected to be used for SERS, photocatalyst, or photothermal applications.