Ag/TiO₂ nanocomposites : synthesis, characterizations and applications

Nanosized noble metal (Au, Pt, Pd and Ag, etc.) particles are drawing increasing attention recently due to their widely spanned applications especially in catalytic reaction processes. Because of the much lower cost of silver than the other noble metals, development of high-performance silver-based nanomaterials is therefore of great significance. Small particle size and good dispersion of silver are the two key parameters determining its performances. To achieve these two features, deposition of silver onto less expensive supporting materials such as metal oxides has been generally practiced. Yet the major challenge is to achieve both high metal loading and good dispersion over the support surface simultaneously. A novel one-pot sol-gel synthesis method was invented in the present study to produce TiO2-supported Ag nanoparticles with excellent Ag size and dispersion control while maintaining a high Ag loading. The adopted room-temperature ionic liquids in the precursor solution inhibited the Ag particle growth, as revealed by UV/visible spectroscopy results. X-ray Photoelectron Spectrometry (XPS) investigations reveal that silver exist predominantly in the metallic state in the products. The TiO2-supported Ag nanoparticles exhibit excellent catalytic activities towards the aqueous phase reductions of methylene blue and 4-nitrophenol, which can compete with more expensive Pt, Au and Pd nanocatalysts of similar size. Potent antibacterial activity against Escherichia coli was also observed in the Ag/TiO2 nanoparticles, resulting from the small particle size and the high dispersion of silver over the TiO2 support. The Ag particles can also induce the deposition of Au, Pd and Pt on TiO2 surface via the galvanic replacement reaction scheme, which opens the possibility to synthesize other supported noble metal nanoparticles. The photocatalytic activities of TiO2 are enhanced by the Ag particles for the reduction of methyl viologen