Preparation of Fluorescent Thiol Group-Functionalized Silica Microspheres for the Detection and Removal of Silver Ions in Aqueous Solutions

We demonstrate that silica microspheres can act as a sensitive fluorescent sensor and adsorbent of Ag+ in aqueous media. These thiol-functionalized silica microspheres are doped with quantum dots (QDs) using organosilane chemistry in a one-step preparation. Ligand exchange takes place between the thiolated organosilane and acid-capped QDs, making the doping easy. Ag+ adsorption by the silica microspheres causes the decrease of fluorescence intensity of the QDs. The detection limit for Ag+ is found to be 10 mol/L. The abundance of thiol groups on the surface of the microspheres could effectively remove Ag+ through strong interaction. When microspheres with a diameter of 1.1 m are used as the adsorbents, the adsorption capacity for Ag+ reached 102 mg/g. This excellent adsorption ability is due to the abundance of thiol groups that act as the active sites, facilitating the adsorption of the massive metal ions on the surface of the microspheres. Furthermore, the adsorption isotherm data follows the Freundlich model. The structure and content of the silica microspheres were investigated by scanning and high-resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, and Raman analysis, and the fluorescence properties were characterized by fluorescence microscopy.