Gas Production from the Radiolysis of Water Adsorbed on ZnO Nanoparticles

The presence of a metal oxide surface can significantly alter the product yield distribution during the radiolysis of water with some metal oxides such as ZrO2 or CeO2, increasing the yield of H2 during the irradiation of water adsorbed on the oxide as compared to liquid water, while other oxides such as PuO2 decrease H2 yields. In this study, the γ-ray radiolysis of the ZnO/H2O system was investigated. Surprisingly, both O2 and H2 were produced in similar quantities. The production of O2 is unexpected as no, or negligible, amounts of O2 have been observed for the radiolysis of water adsorbed on other oxides. Molecular oxygen production is observed during the radiolysis of both wet and dry ZnO, indicating that the source of at least some of the O2 is the bulk oxide. The production of H2 due to the radiolysis of water adsorbed on ZnO is an order of magnitude greater than for pure water. This increase is likely due to an energy-transfer process from the oxide to the adsorbed water molecules. However, the radiolysis of aqueous suspensions of ZnO resulted in lower radiolytic H2 yields than for pure water.