Gold Nanoparticles on Mesoporous Interparticle Networks of Titanium Dioxide Nanocrystals for Enhanced Photonic Efficiencies

Abstract

Nanocomposites consisting of Au and TiO 2 nanocrystals have been synthesized through simple one-step sol−gel reactions of titanium tetraisopropoxide with hydrogen tetrachloroaurate in the presence of an F127 triblock copolymer as the template to direct the formation of nanostructured photocatalysts. The thus formed Au/TiO 2 network gels were calcined at 500 °C for 4 h, leading to Au/TiO 2 nanocomposites with high interparticle mesoporosity, pore diameters of around 10 nm, and BET surface areas of about 100 m 2 /g. TEM investigations of 0.5 wt % Au/TiO 2 reveal that the TiO 2 particles are quite uniform in size and shape. The particle sizes of TiO 2 and Au are in the range of 5−10 and 20−120 nm, respectively. The photocatalytic methanol oxidation to formaldehyde chosen as the test reaction to examine the photocatalytic activity of the Au/TiO 2 was shown to be more effective as compared with pure TiO 2 and with Degussa P25, respectively. The increased photocatalytic activity of Au/TiO 2 with interparticle mesopores is attributed to a higher intrinsic activity of the Au/TiO 2 and improved intrinsic electron diffusion. The latter effect is explained by considering the mesoporous TiO 2 network to behave like an antenna system for the photogenerated electrons, enabling them to reach the respective TiO 2 /Au contacts with high probability. Thus, a few Au particles in electronic contact with the entire TiO 2 structure are sufficient to act as efficient electron relays, enabling the charge transfer to the solutes. The sample 0.5 wt % Au/TiO 2 nanocrystals with smaller Au nanoparticles is therefore more photoactive than those composed of larger Au particles and hence less semiconductor/metal contacts.