Microfluidic synthesis of Ag@Cu₂O core-shell nanoparticles with enhanced photocatalytic activity

A microfluidic-based method for the continuous synthesis of Ag@Cu₂O core-shell nanoparticles (NPs) has been developed. It only took 32s to obtain Ag@Cu₂O core-shell NPs, indicating a high efficiency of this microfluidic-based method. Triangular Ag nanoprisms were employed as the cores for the overgrowth of Cu₂O through the reduction of Cu(OH)₄^2- with ascorbic acid. The as-synthesized samples were characterized by XRD, TEM, SEM, HAADF-STEM, EDX, HRTEM, UV-vis spectra and N₂ adsorption-desorption. The characterization results revealed that the as-synthesized Ag@Cu₂O core-shell NPs exhibited a well-defined core-shell nanostructure with a polycrystalline shell, which was composed of numbers of Cu₂O domains epitaxially growing on the triangular Ag nanoprism. It was concluded that the synthesis parameters such as the molar ratio of trisodium citrate to AgNO₃, H₂O₂ to AgNO₃, NaOH to CuSO₄, ascorbic acid to CuSO₄ and AgNO₃ to CuSO₄ had significant effect on the synthesis of Ag@Cu₂O core-shell NPs. Moreover, Ag@Cu₂O core-shell NPs exhibited superior catalytic activity in comparison with pristine Cu₂O NPs towards the visible light-driven degradation of methyl orange. This enhanced photocatalytic activity of Ag@Cu₂O core-shell NPs was attributed to the larger BET surface area and improved charge separation efficiency. The trapping experiment indicated that holes and superoxide anion radicals were the major reactive species in the photodegradation of methyl orange over Ag@Cu₂O core-shell NPs. In addition, Ag@Cu₂O core-shell NPs showed no obvious deactivation in the cyclic test.