Potent Antibacterial Activities of Ag/TiO2 Nanocomposite Powders Synthesized by a One-Pot Sol-Gel Method

The antimicrobial properties of Ag-based materials have been actively investigated recently. In such materials, control of the size of the Ag particles is critical to their bactericidal performance. A novel one-pot sol-gel scheme is described here. It incorporates room-temperature ionic liquids (RTILs) to synthesize Ag/TiO2 nanocomposite powders. The presence of RTILs is indispensable to the control of the size of the Ag particles. Highly dispersed, metallic Ag nanoclusters are formed on the TiO2 nanoparticle surface after calcination of the gel. The average cluster size of Ag can be controlled to be below 5 nm with high Ag loading (7.4wt%). Antibacterial tests using 7.4wt% Ag/TiO2 on 10(5) CFU/mL Escherichia coli (E coli) strains incubated on Luria-Bertani (LB)/agar plates show that bacterial growth was inhibited by 98.8% at an Ag concentration of 1.2 mu g/mL. Complete inhibition was achieved at 2.4 mu g(Ag)/mL. At this concentration, a 3.9wt% Ag/TiO2 sample, with a smaller Ag cluster size (<3 nm), completely inhibited bacterial growth in a more populated E coli community (similar to 3 x 10(6) CFU/mL). In fact, 16 mu g/mL Ag suppressed bacterial growth by 99.9% with 3.9wt% Ag/TiO2. Both the small Ag cluster size and the unique structure of TiO2 nanoparticles supporting highly dispersed Ag clusters are identified to be the sources of a superior bactericidal performance of the RTILs-derived Ag/TiO2.