Synthesis, Morphological Control, and Antibacterial Properties of Hollow/Solid Ag2S/Ag Heterodimers

Abstract

Ag₂S and Ag are important functional materials that have received considerable research interest in recent years. In this work, we develop a solution-based synthetic method to combine these two materials into hollow/solid Ag₂S/Ag heterodimers at room temperature. Starting from monodisperse Cu₂O solid spheres, CuS hollow spheres can be converted from Cu₂O through a modified Kirkendall process, and the obtained CuS can then be used as a solid precursor for preparation of the Ag₂S/Ag heterodimers through ion exchange and photo-assisted reduction. We have found that formation of the Ag₂S/Ag heterodimers is instantaneous, and the size of Ag nanocrystals on the hollow spheres of Ag₂S can be controlled by changing the concentration and power of reducing agents in the synthesis. The growth of Ag nanoparticles on hollow spheres of Ag₂S in the dimers is along the [111] direction of the silver crystal; the light absorption properties have also been investigated. Furthermore, coupling or tripling of Ag₂S/Ag heterodimers into dumbbell-like trimers ((Ag₂S)₂/Ag, linear) and triangular tetramers ((Ag₂S)₃/Ag, coplanar) can also be attained at 60 °C by adding the bidentate ligand ethylenediamine as a cross-linking agent. To test the applicability of this highly asymmetric dipolar composite, photocatalytic inactivation of Escherichia coli K-12 in the presence of the as-prepared Ag₂S/Ag heterodimers has been carried out under UV irradiation. The added Ag₂S/Ag heterodimers show good chemical stability under prolonged UV irradiation, and no appreciable solid dissolution is found. Possible mechanisms regarding the enhanced antibacterial activity have also been addressed.