Synthesis, morphological control, and antibacterial properties of hollow/solid Ag2S/Ag heterodimers

Ag(2)S 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 Ag(2)S/Ag heterodimers at room temperature. Starting from monodisperse Cu(2)O solid spheres, CuS hollow spheres can be converted from Cu(2)O through a modified Kirkendall process, and the obtained CuS can then be used as a solid precursor for preparation of the Ag(2)S/Ag heterodimers through ion exchange and photo-assisted reduction. We have found that formation of the Ag(2)S/Ag heterodimers is instantaneous, and the size of Ag nanocrystals on the hollow spheres of Ag(2)S can be controlled by changing the concentration and power of reducing agents in the synthesis. The growth of Ag nanoparticles on hollow spheres of Ag(2)S 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 Ag(2)S/Ag heterodimers into dumbbell-like trimers ((Ag(2)S)(2)/Ag, linear) and triangular tetramers ((Ag(2)S)(3)/Ag, coplanar) can also be attained at 60 degrees 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 Ag(2)S/Ag heterodimers has been carried out under UV irradiation. The added Ag(2)S/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.