Electron transport in silver-semiconductor nanocomposite films exhibiting multicolor photochromism

Abstract

In the multicolor photochromism of TiO2 nanoporous films loaded with photocatalytically deposited Ag nanoparticles, visible light-induced electron transfer from Ag to oxygen molecules plays an essential role. Here we examined the effect of TiO2 on the electron transfer. We found that not only photocatalytically deposited Ag, but also electrodeposited Ag and commercially available Ag nanoparticles in a nanoporous TiO2 film exhibit the multicolor photochromism. The electrodeposited Ag exhibits the multicolor photochromism also in a nanoporous ZnO film, but not in nanoporous indium-tin oxide (ITO) and SiO2 matrices. Photoelectrochemical measurements for the Ag-TiO2 nanocomposite elucidated that some of the photo-excited electrons on Ag are transferred to oxygen molecules via TiO2 and non-excited Ag. Thus, an n-type semiconductor plays an important role in the charge separation between the excited electrons and Ag+. Non-excited Ag on TiO2 also plays an important role in the charge separation and/or catalysis of oxygen reduction. Replacement of the non-excited Ag with Pt accelerated the electron transport from the photo-excited Ag to oxygen molecules and the photochromic behavior.

A review on plasmonic metal⿿TiO2 composite for generation, trapping, storing and dynamic vectorial transfer of photogenerated electrons across the Schottky junction in a photocatalytic system

“…The Ag nanoparticles are photoexcited due to SPR effect and charge separation is accomplished by the transfer of photoexcited electrons from the Ag nanoparticles to the TiO 2 CB and the authors further propose simultaneous transfer of compensative electrons from donor Cl − ions to the Ag nanoparticles (Fig. 14) [191][192][193]. In another study Ag/AgCl/TiO 2 nanocomposite thin films prepared by the same method exhibited enhanced photocatalytic decomposition of 4-CP under visible light irradiation [194].…”

“…This radical ion can react with Cl − ion forming Cl 0 and Ag as shown in the equations [191][192][193]. Because of the high oxidation ability of the chlorine atoms, the 4-CP could be oxidized by the chlorine atoms and hence the Cl 0 could be reduced to chloride ions again.…”

Plasmonic Photoelectrochemistry: Functional Materials Based on Photoinduced Reversible Redox Reactions of Metal Nanoparticles

“…37 In the case of a Ag nanoparticle, the redox potential (+0.80 V vs. NHE) is in between those two potentials, and the nanoparticle is oxidized to Ag + ions and dissolves only as a result of the plasmon-induced charge separation. 38 The photodissolution results in bleaching of the plasmonic color of the Ag nanoparticles on a TiO 2 film, because Ag + ion has no color. 9 If the bleached sample is irradiated with UV light, TiO 2 is excited and the Ag + ions are reduced again to a Ag nanoparticle by the excited electrons, as a result of photocatalytic reactions of TiO 2 .…”

Contrôle optique de la croissance et de la déformation de nanoparticules métalliques au sein de matrices mésoporeuses de TiO2

“…1). Du fait d'une jonction Schottky à l'interface entre l'argent métallique et le TiO 2 , les électrons photo-excités migrent vers la bande de conduction du TiO 2 puis se stabilisent sur les molécules d'oxygène [10]. Les nanoparticules métalliques en contact avec la matrice d'oxyde de titane peuvent donc s'oxyder en présence d'oxygène sous illumination visible.…”

“…Différents travaux rapportent un comportement photochromique avec des particules d'argent réduites au sein de matrices poreuses de TiO 2 de manière photocatalytique [5,[7][8][9][10], chimique [11,12] ou thermique [12,13] tout autant qu'avec des particules d'argent déposées par pulvérisation magnétron [14,15] ou par voie électrochimique [10]. On trouve des matrices poreuses préparées à partir de NPs de TiO 2 commerciales cristallisées dans la phase anatase [5,7,8,10] ou bien élaborées par voie sol-gel sous forme de films mésoporeux de TiO 2 amorphe [9,[11][12][13]. Plusieurs expériences ont aussi été menées à la surface de substrats de TiO 2 monocristallin [16][17][18].…”