H2 Formation from the Radiolysis of Liquid Water with Zirconia

Radiolytic Water Splitting Sensitized by Nanoscale Metal-Organic Frameworks

High-energy radiation that is compatible with renewable energy sources enables direct H₂ production from water for fuels; however, the challenge is to convert it as efficiently as possible, and the existing strategies have limited success. Herein, we report the use of Zr/Hf-based nanoscale UiO-66 metal-organic frameworks as highly effective and stable radiation sensitizers for purified and natural water splitting under γ-ray irradiation. Scavenging and pulse radiolysis experiments with Monte Carlo simulations show that the combination of 3D arrays of ultrasmall metal-oxo clusters and high porosity affords unprecedented effective scattering between secondary electrons and confined water, generating increased precursors of solvated electrons and excited states of water, which are the main species responsible for H₂ production enhancement. The use of a small quantity (<80 mmol/L) of UiO-66-Hf-OH can achieve a γ-rays-to-hydrogen conversion efficiency exceeding 10% that significantly outperforms Zr-/Hf-oxide nanoparticles and the existing radiolytic H₂ promoters. Our work highlights the feasibility and merit of MOF-assisted radiolytic water splitting and promises a competitive method for creating a green H₂ economy.

Electron-stimulated reactions in nanoscale water films adsorbed on α-Al2O3(0001)

100 eV electrons are stopped in the H₂O portion of the isotopically-layered nanoscale film on α-Al₂O₃(0001) but D₂ is produced at the D₂O/alumina interface by mobile electronic excitations and/or hydronium ions.

Reaction mechanisms in swelling clays under ionizing radiation: influence of the water amount and of the nature of the clay mineral

Picosecond pulse radiolysis experiments performed on natural swelling clays evidence a fast trapping of electrons in the layers of the material.

Radiation Effects on Materials Used in Geological Repositories for Spent Nuclear Fuel

Safe long-term storage of radioactive waste from nuclear power plants is one of the main concerns for the nuclear industry as well as for governments in countries relying on electricity produced by nuclear power. A repository for spent nuclear fuel must be safe for extremely long time periods (at least 100 000 years). In order to ascertain the long-term safety of a repository, extensive safety analysis must be performed. One of the critical issues in a safety analysis is the long-term integrity of the barrier materials used in the repository. Ionizing radiation from the spent nuclear constitutes one of the many parameters that need to be accounted for. In this paper, the effects of ionizing radiation on the integrity of different materials used in a granitic deep geological repository for spent nuclear fuel designed according to the Swedish KBS-3 model are discussed. The discussion is primarily focused on radiation-induced processes at the interface between groundwater and solid materials. The materials that are discussed are the spent nuclear fuel (based on UO2), the copper-covered iron canister, and bentonite clay. The latter two constitute the engineered barriers of the repository.

Surface species produced in the radiolysis of zirconia nanoparticles

Modifications to water-zirconia nanoparticle interfaces induced by gamma irradiation have been examined using diffuse reflection infrared Fourier transform (DRIFT), Raman scattering, and electron paramagnetic resonance (EPR) techniques. Spectroscopy with in situ heating was used to probe variations in the dissociatively bound chemisorbed water on the zirconia nanoparticles following evaporation of the physisorbed water. DRIFT spectra show that the bridged Zr-OH-Zr species decreases relative to the terminal Zr-OH species upon irradiation. No variation is observed with Raman scattering, indicating that the zirconia morphology is unchanged. EPR measurements suggest the possible formation of the superoxide ion, presumably by modification of the surface OH groups. Trapped electrons and interstitial H atoms are also observed by EPR.

Radiolysis of Confined Water: Hydrogen Production at a High Dose Rate

The production of molecular hydrogen in the radiolysis of dried or hydrated nanoporous controlled-pore glasses (CPG) has been carefully studied using 10 MeV electron irradiation at high dose rate. In all cases, the H2 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 H2 coming from the surface of the material is negligible in the hydrated case. Thus, the measured yields correspond to those of nanoconfined water. Moreover, these yields are not modified by the presence of potassium bromide, which is a hydroxyl radical scavenger. This experimental observation shows that the back reaction between H2 and HO* does not take place in such confined environments. These porous materials have been characterized before and after irradiation by means of Fourier-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.