Electrochemical Observation of the Plasmonic Effect in Photochromic Ag Nanoparticle Filled Mesoporous TiO₂ Films

Abstract

We report photoelectrochemical measurements from mesoporous titanium dioxide filled with silver nanoparticles under illumination. A 200 mV potential switch of silver ion reduction is observed, depending on light wavelength. An easier reduction of silver in the presence of light is linked to plasmon induced charge separation (PICS). SEM and TEM analysis before and after photoelectrochemistry have also shown an electrochemical Ostwald ripening during continuous visible irradiation, with a growth of silver particles at the sample surface. The combined use of mesoporous structures and electrochemical characterization enabled the change in silver reactivity during PICS to be quantified and emphasizes the role of plasmon in photochromism.

Fully Reversible Electrically Induced Photochromic-Like Behaviour of Ag:TiO2 Thin Films

“…All the above experimental data clearly suggest that the electrophotochromism of the Ag-TiO2 composite is due to oxidation/reduction of the Ag nanoparticles, which forms a thin layer of Ag2O on the metallic core, forming core/shell nanoparticles; the core is metallic while the outer shell is semiconducting, where the peaks agree well with those found by Kuzma et al [46]. In fact, it is suggested that the oxide thickness is about 1.5 nm when the composite absorbs at the 440 nm peak and at most 0.5 nm while the composite exhibits a peak at 413 nm.…”

“…There is also the possibility that some of the non-reduced silver ions (Ag + ) could be adsorbed on the hydroxylated TiO2 surface according to the following reaction, as suggested by other authors also in the past: Ag + + TiO2 − → Ti-O-Ag + H + [45]. The plasmon resonance in the Ag-TiO2 thin films strongly depends on the crystalline phase and dielectric constant of the TiO2 matrix [46]. In theory, the SPR peak wavelength increases with increasing dielectric constant of the matrix and depends on the refractive index.…”

“…The plasmon resonance in the Ag-TiO 2 thin films strongly depends on the crystalline phase and dielectric constant of the TiO 2 matrix [46]. In theory, the SPR peak wavelength increases with increasing dielectric constant of the matrix and depends on the refractive index.…”

“…The redox reactions are associated with Ag → Ag 2 O and Ag 2 O → Ag (oxidation and reduction peaks, respectively) [55,56]. The pair of peaks at the lower biases correspond to the reduction and oxidation of the AgNPs that have adsorbed inside the mesoporous network of the TiO 2 film and the other pair of smaller peaks most probably correspond either to small deposited AgNPs or to AgNPs adsorbed only on the outer surface of the TiO 2 film [46]. Also both re-oxidation peaks are broader and smaller to the reduction peaks due to the large band gap of the TiO 2 film.…”

Photoelectrochemical Behavior of Silver Nanoparticles inside Mesoporous Titania: Plasmon-Induced Charge Separation Effect

“…31,32 We initially studied the photoelectrochemical properties of a TiO electro-reduction potential can be modulated by light irradiation and that silver repartition within the mesoporous matrix is modified. 33 In this work, we synthesized silver NPs embedded in mesoporous TiO 2 films and characterized them through scanning electron microscopy (SEM), UV−visible absorption, and photoelectrochemistry at different wavelengths. The present study describes the specific effect of wavelength on the silver ions reduction potential and probes the chemical bonding between the silver NPs and titania matrix.…”