Synthesis And Characterization Of Ag@TiO₂ Core-shell Nanoparticles

Metal/oxide nanoparticles with a core-shell structure are of essential importance in theoretical sense and practical application in light of easiness of avoiding agglomeration of metal nanoparticles when transferred from one solution to another. Besides their well-known catalytic performance, they exhibit remarkable nonlinear optical limiting property as well. In addition to the proper optical limiting to nano-second pulse laser, high damage threshold and swift response enable them to be good candidates for optical limiters.In this work, Ag/TiO₂ was opted, the synthesis and UV-Vis. spectral property of nanoparticles with titanium dioxide as the covering shell and silver as the inner core were discussed.With silver nitrate (AgNO₃) and titanium iso-propoxide as the starting materials and dimethylformamide (DMF) as the reducing agent, Ag@TiO₂ core-shell nanoparticles were successfully fabricated. TEM (Transmission Electron Microscope) observation showed that most particles were 20-40nm in diameter and the shell thickness averaged 2-4nm. XRD (X-Ray Diffraction) and XPS (X-Ray Photoelectron Spectroscopy) indicated that the inner core was metallic silver. Ti-O-Ti stretching mode and Ti-O band were observed in IR (Infrared Spectroscopy) and RAS (Raman Absoprtion Spectroscopy) respectively, proving the presence of amorphous titanium dioxide.The as-prepared nanoparticles were dispersed in a solution containing DMF and 2-propanol with the volume ratio of 1:1 before UV-Vis. spectral study with regard to the peak position and band width. It is discovered that the oxide thickness increases as the starting titanium iso-propoxide increases while other parameters are kept exactly unchanged, and accordingly, the peak redshifts initially and then blueshifts; Moreover, as the mass of silver nitrate increases, the peak redshifts and the absorption band goes wider; the synthetic temperature exerts no effect on the final shape and size of the prepared nanoparticles, only tolengthen the needed reaction time.It is found as well that the protecting titanium dioxide is porous, making it possible for Cl^- to diffuse through the thin outer layer and to react with the silver core. The produced AgCl runs out of the thin layer likewise, hence the nanobubble shaped titanium dioxide is procured. TEM observation showed the wall thickness as thin as 2-3nm. XRD and UV-Vis. spectrum verify the reaction mechanism involved. Residual NaCl and produced AgCl are present; No characteristic peak belonging to silver particles are observed. The novel way by NaCl solution has been proved successful and effective in obtaining TiO₂ nanobubbles.