H₂ Production in the Radiolysis of Aqueous SiO₂ Suspensions and Slurries

Abstract

The production of H 2 in the radiolysis of silica suspensions in aqueous solutions and slurries has been examined. Radiation chemical yields of H 2 increase with increasing oxide weight fraction in suspensions of SiO 2 nanoparticles (7- and 22-nm diameter) probably because of the escape of electrons initially produced in the oxide to the bulk water. Reactions of H 2 with holes on the oxide surface or scavenging of precursors to H 2 in the bulk water decrease its yield at high SiO 2 loading. The production of H 2 in the radiolysis of slurries of large SiO 2 particles (8.1 m 2 /g, ∼343 nm diameter) is virtually identical to that expected in water alone suggesting little escape of electrons from the bulk oxide to the water. However, aqueous slurries of smaller SiO 2 particles (312 m 2 /g, ∼8 nm diameter) can double the H 2 production from water. Studies with varying the concentration of selenate, a good scavenger of the hydrated electron and its precursor, suggest that electron reactions on the μs time domain are responsible for the additional H 2 produced in aqueous SiO 2 mixtures. The only obvious difference between the 8-nm-particle slurry and the comparably sized suspension is the addition of additives in the latter for stability.