Highly stable molecular layers on nanocrystalline anatase TiO2 through photochemical grafting.

Well-defined molecular layers can be formed on the surface of nanocrystalline anatase TiO2 by photochemically grafting organic molecules bearing a terminal vinyl group. The molecular layers produced are shown to have minimal oxidation and are able to be patterned and uniformly grafted through optically thick nanocrystalline films. Stability tests show that the layers have excellent stability in deionized water at 80 degrees C, aqueous solutions at pH=1.0 and pH=10.3 at 65 degrees C, and acetonitrile for time scales approaching 1200 h. Degradation of the films in deionized water occurs using a AM1.5 full-spectrum solar simulator as an illumination source but is partially suppressed by filtering with a 400 nm UV blocking filter which blocks the above-bandgap light. A mechanism is proposed for the grafting reaction in which the surface hydroxyl groups trap photoexcited holes, facilitating reaction with the vinyl group.