Preparation and photocatalytic activity of Ti[O.sub.2] nanocomposites coated with monolayer-protected gold clusters

We report the preparation and photocatalytic activity of Ti[O.sub.2] nanocomposites modified with monolayer-protected gold clusters (MPCs). Highly monodisperse tiopronin-coated MPCs with core diameters of 2.2 ± 0.2 nm were pre-prepared and then anchored onto a Ti[O.sub.2] surface using the bifunctional tiopronin linker. In this method, the gold core size was preserved after calcination at 260 °C as well as the anchoring process, and the gold loading on Ti[O.sub.2] could be precisely controlled by the experimental condition. The photocatalytic degradation of Rhodamine 590 (Rh-590) was carried out with thus prepared MPC-Ti[O.sub.2] composites. Mechanistic study of the photocatalytic reactions revealed that the degradation of Rh-590 occurs via the oxidative pathway by photogenerated holes. The photocatalytic activity of the MPC-Ti[O.sub.2] composites was found to increase significantly upon calcination at 260 °C, whereas the size of gold particles remained at their initial size. The photocatalytic activity of the composites, however, drastically decreased when the composites were calcined at 400 °C. X-ray photoelectron spectroscopy analysis of the calcined composites was conducted to understand the vastly different calcination results. A significant amount of oxidized sulfur remained in the composites after calcination at 400 °C, which appears to be responsible for the drastic decrease in the photocatalytic activity. Key words: monolayer-protected gold cluster, photocatalyst, Ti[O.sub.2], tiopronin, thermal activation, nanocomposite. On a prepare et determine les proprietes photocatalytiques de nanocomposites de Ti[O.sub.2] modifies par des agregats d'or proteges par une monocouche (APM). On a procede en effectuant une preparation preliminaire d'APM hautement monodisperse recouverte de tiopronine dont le diametre de la partie de coeur est de 2,2 ± 0,2 nm et on l'a ensuite ancre sur une surface de Ti[O.sub.2] faisant appel a la tiopronine, un reticulant bifonctionnel. Dans cette methode, la taille de la zone de coeur d'or est maintenue apres avoir ete soumise au processus d'ancrage et une calcination a 260 °C et la fixation de l'or sur le Ti[O.sub.2] peut etre controlee avec precision par les conditions experimentales. On a procede a la degradation photocatalytique de la Rhodamine 590 (Rh-590) a l'aide des composites APM-Ti[O.sub.2] ainsi prepares. L'etude du mecanisme des reactions photocatalytiques a permis de montrer que la degradation de la Rh-590 se produit par le biais d'une voie oxydante impliquant des trous photogeneres. On a trouve que l'activite catalytique des composites APM-Ti[O.sub.2] augmente considerablement par calcination a 260 °C alors que la taille des particules d'or maintiennent leur taille initiale. Toutefois, l'activite catalytique des composites diminuent considerablement lorsque les composites sont calcines a 400 °C. On a effectue des analyses par spectroscopie photoelectronique des rayons-X des composites calcines dans le but de comprendre les resultats si differents de ces calcinations. Il semble qu' une quantite significative residuelle de soufre oxyde dans les composites apres la calcination a 400 °C soit la cause de cette diminution drastique de l'activite catalytique. Mots-cles: agregat d'or protege par une monocouche (APM), photocatalyseur, Ti[O.sub.2], tiopronine, activation thermique, nanocomposite. [Traduit par la Redaction]
Introduction Metal-coated semiconductor nanoparticles have been the focus of numerous investigations over the last few years in photocatalysis relevant to solar energy conversion and environmental cleanup. (1-3) Contact of metal [...]