Functionalization of Titanates–Silk Nanocomposites via Cation Exchange for Optical Applications

A simple and efficient method is developed to introduce plasmonic and luminescence functionalities in titanate nanosheets (TNSs)–silk nanocomposites by direct cation-exchange process. First, the cation exchange properties such as exchange kinetic and capacity are studied to verify the behavior of the material and determine the best condition of exchange. In particular, the effect of the valence on the kinetic is investigated through elemental analysis, focusing on three target cations (Ag+, Cu2+, and Eu3+) in water. It is demonstrated that the cation exchange capability of the composite is strictly dependent of the amount of TNSs. By acting on the time of ion exchange or by changing the TNSs concentration in the silk fibroin matrix it is possible to tune the metal ions doping. The process is applicable both on flexible free-standing membranes and thin films deposited on an appropriate substrate. By exposing the material to UV radiation, it is possible to synthesize in situ metallic nanoparticles, exhibiting a characteristic plasmonic peak in the visible spectrum. Furthermore, it is verified that the europium ions preserve their photoluminescence properties when introduced in the nanocomposite, showing a characteristic red emission under UV light.