Radiolysis of confined water:: Hydrogen production at a high dose rate

The production od molecular hydrogen in the radiolysis of dried or hydrated nanoporous controlled-pore glasses (CPG) been carefully studied using 10 MeV electron irradiation at high dose rate. In all cases, H-2 yield increases when the pore size decreases. Moreover, the yields measured in dried materials are two orders of magnitude smaller than those obtained in hydrated glasses. This proves that the part of the H-2 coming from the surface of the material is negligible in the hydrated case. Thus, themeasured yields correspond to those of nanoconfined water. Moreover, these yields are not modified by the presence of potassium bromide, which is hydroxyl radical scavenger. This experimental observations shows that the back reaction between H-2 and HO center dot does not take place in such confined environments. Therse porous materials have been characterized before and after irradiation by meansof Fourrier-transform infrared (FT-IR) spectroscopy, electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) techniques, which helps to understand the elementary processes taking place in this type of environment, especially the protective effect of water on the surface in the case of hydrated glasses.