Charge Carrier Transfer across the Silica Nanoparticle/Water Interface

We determined the yield of hydrated electrons, e - aq, in irradiated silica suspensions at very high particle concentrations. The initial concentration of e - aq, measured immediately after a pulse of high-energy electrons, increases with the silica loading, proportionately with the dose absorbed by the sample. Therefore, the yield of e - aq per unit energy absorbed remains unaltered even at 50% weight of silica. This observation holds for particles in the range of 7−22 nm in diameter. Under heavy loading of silica, a significant percentage of the energy is absorbed by the silica (essentially equal to the silica weight percent). Thus, our observations imply that energy that is originally deposited in silica crosses the solid−liquid interface and appears in the aqueous phase as solvated electrons. Possible mechanisms for this crossover process are discussed. It is proposed that either every electron that is generated in silica escapes to the water or that highly energetic secondary electrons are ejected from the silica particles and subsequently create spurs similar to those formed by primary electrons that initially are deposited in water.