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

Nanocomposites consisting of Au and TiO2 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/TiO2 network gels were calcined at 500 degrees C for 4 h, leading to Au/TiO2 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/TiO2 reveal that the TiO2 particles are quite uniform in size and shape. The particle sizes of TiO2 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/TiO2 was shown to be more effective as compared with pure TiO2 and with Degussa P25, respectively. The increased photocatalytic activity of Au/TiO2 with interparticle mesopores is attributed to a higher intrinsic activity of the Au/TiO2 and improved intrinsic electron diffusion. The latter effect is explained by considering the mesoporous TiO2 network to behave like an antenna system for the photogenerated electrons, enabling them to reach the respective TiO2/Au contacts with high probability. Thus, a few Au particles in electronic contact with the entire TiO2 structure are sufficient to act as efficient electron relays, enabling the charge transfer to the solutes. The sample 0.5 wt % Au/TiO2 nanocrystals with smaller Au nanoparticles is therefore more photoactive than those composed of larger Au particles and hence less semiconductor/metal contacts.