Effect of silica gel on radiation-induced reduction of dichromate ion in aqueous acidic solution

Radiation-induced reduction of dichromate ion (Cr2O72−) in aqueous acidic solution containing silica gel was studied by γ-radiolysis to seek the characteristic reactions occurring in radiolysis of water-silica coexistent system. The addition of silica gel increased the reduction yield of Cr2O72− in aqueous solution containing 0.1 mol dm−3 perchloric acid (HClO4) and 1 mmol dm−3 potassium dichromate (K2Cr2O7). However, the addition of 0.1 mol dm−3t-butanol to the aqueous solution suppressed the effect of silica gel. Also the addition of silver(I) ion (Ag+) lowered the increase in the reduction yield by the addition of silica gel. Therefore it is suggested that the increase in the reduction yield of Cr2O72− was partially due to silica gel changing the reaction scheme of the radiation-induced reduction of Cr2O72−, in addition to the energy or charge transfer from excitation and ionization in silica gel to production of reactive species in aqueous solution. The inhibition of the oxidation of chromium(III) ion (Cr3+) and/or transient chromium species by hydroxyl radical (OH radical) is especially expected, since both t-butanol and Ag+ act as a scavenger of OH radical.