Simple Route to Enhanced Photocatalytic Activity of P25 Titanium Dioxide Nanoparticles by Silica Addition

Silica doped TiO<sub>2</sub>(P25) nanoparticles are tested for its photocatalytic activity in the degradation of bacteriophage MS2. During our studies it was found that treatment of TiO<sub>2</sub>(P25) in the glass flasks sealed with silicone grease resulted in a significant improvement in the catalytic activity of the titania. Further improvement can be made by the purposeful reaction of TiO<sub>2</sub>(P25) with 2.5 wt % silica. This non <i>in situ</i> method of incorporating silica to TiO<sub>2</sub>(P25) nanoparticles is tested for their role in killing of viruses, and it is found that the rate constant is three times higher to kill viruses with the addition of silica. BET measurements show no significant change/increase in the surface area of silica doped TiO<sub>2</sub>(P25)-SiO<sub>2</sub>, compared to the undoped TiO<sub>2</sub>(P25). Further studies show that the addition of silica increases the adsorption of viruses onto the catalyst. There is a significant difference in the activity of the TiO<sub>2</sub>(P25)-SiO<sub>2</sub> samples in the presence of methanol, supporting the notion that hydroxide radical (HO·) is responsible for the antiviral action. The TiO<sub>2</sub>(P25)-SiO<sub>2</sub> either produces more HO· than non silica-doped material, or the enhanced adsorption of MS2 to the catalyst results in greater exposure to the HO·, or both mechanisms may work in concert. XPS studies suggest the formation of silica species on the surface of the TiO<sub>2</sub>(P25), while UV−visible spectroscopy suggests that the presence of the silica results in a small increase in the measured band gap. We suggest that the enhanced catalytic activity is a result of increased adsorption and/or band bending which can occur at the interface within TiO<sub>2</sub>(P25)-SiO<sub>2</sub>. One result of this would be a reduction of the electron−hole recombination, the formation of a greater concentration of OH·, and hence an improved catalytic performance.