Ionizing radiation induced catalysis on metal oxide particles. 1997 annual progress report

'This project focuses on a novel approach for destroying organics found in high-level mixed waste prevalent at DOE sites. In this project the authors propose that organics can be destroyed by utilizing reduction/oxidation (redox) chemistry resulting from electron-hole (e{sup -}/h{sup +}) pairs generated in stable, wide bandgap semiconductors via interactions with ionizing radiation ({alpha}, {beta}, {gamma}). Conceptually this process is an extension of visible and near-UV photocatalytic processes known to occur at the interfaces of narrow bandgap semiconductors in both solution and gas phases. In these processes, an electron is excited across the energy gap between the filled and empty states in the semiconductor. The excited electron does reductive chemistry and the hole (the point from which the electron was excited) does oxidative chemistry. The energy separation between the hole and the excited electron reflects the redox capability of the e{sup -}/h{sup +} pair, and is dictated by the energy of the absorbed photon and the bandgap of the material. The use of ionizing radiation has advantages in that it (1) overcomes optical transparency limitations associated with visible and near-UV illumination (y-rays penetrate much farther into a solution than UV/Vis light), and (2) permits the use of wider bandgap materials (such as ZrO{sub 2}), which possess potentially greater redox capabilities than those with narrow bandgap materials. Planned experiments are aimed at extending the body of knowledge about e{sup -}/h{sup +} pair chemistry of semiconducting metal oxide (MO) materials by examining the influence of surface structure, defects, and dopants on the photocatalytic activity of narrow bandgap materials (TiO{sub 2}), and by expanding these studies to wider bandgap materials (ZrO{sub 2}) that are virtually unexplored in terms of their e{sup -}/h{sup +} pair chemistry. Experiments are being conducted in three areas: (1) g-radiocatalysis of reactant-colloidal metal oxide solutions, (2) photoelectrochemical studies at-model MO electrodes, and (3) photochemical studies in ultra-high vacuum (UHV) and high pressures on model MO surfaces. An outcome of this proposed work will be a more thorough evaluation of the use of ionizing radiation in the catalytic remediation of organics (and other problem species) in high-level mixed waste.