Radiolytic hydrogen yields in aqueous suspensions of gold particles

The effect of high concentrations of large gold particles, in the hundreds of nanometer size regime, on the yields of molecular hydrogen, G(H(2)), produced in the radiolysis of several aqueous solutions was determined. In particular we look for direct effect of radiation absorbed by the solid particles on the yield of water products. These particles, however, are catalytically active in the conversion of reducing radicals to molecular hydrogen as well. A very small increase in G(H(2)) observed in bromide solutions upon addition of 50 wt % of gold particles indicates that the radiolysis of the solid particles does not affect the yields in the aqueous phase. Very little exchange of charge carriers or energy between the two phases occurs in these large particle suspensions. On the other hand, efficient catalytic conversion of (CH(3))(2)C(*)OH radicals to H(2) is shown to occur. The efficiency of the presently studied suspensions in the redox-catalytic process is similar to that of suspensions of small particles of similar total surface area. In the presence of radicals from hydrogen atom abstraction from tert-butyl alcohol the yield decreases significantly, again similar to the behavior in suspensions of small particles. We conclude that the redox catalysis does not depend on the size of the particles when their size exceeds a few nanometers.