The radiation chemistry of aqueous sodium terephthalate solutions

Abstract

The radiation chemistry of cobalt-60 gamma-irradiated aqueous sodium terephthalate solutions has been studied. In aerated 4x10-4 M sodium hydroxide solutions, the main products are hydroterephthalate (HTA) (G = 0.99 + 0.01), carbonate (G = 1.31 + 0.08), and peroxides (G = 2.84 + 0.04). The HTA and carbonate species are both formed as a result of hydroxyl radical attack and account for approximately 90 per cent of hydroxyl radical reactions. Oxygen needs to be present for efficient conversion of the terephthalate-OH radical adduct to HTA and oxygenation increases G(HTA) above the aerated solution value. G(HTA) is unaffected by changes in terephthalate concentration between 1 x 10-4 M and 1 x 10-2 M in sodium hydroxide solutions at pH 10. Decreasing the solution pH does however affect G(HTA). In phosphate buffered solutions at pH 6.85, G(HTA) is 0.93 + 0.01 and lower values are obtained with further decrease in solution pH. The lowering of teh G(HTA) value is attributed to recombination reactions between the terephthalate-OH radical products and reducing radical products. Experimental evidence supporting the recombination postulate was obtained from the measurement of a parallel decrease in the peroxide yield and the observation of a dose rate effect on G(HTA). Competition kinetic studies with the added solutes carbonate and biocarbonate gave the rate ratios k(OH + TA=) : k(OH + CO3=) : k(OH + HCO3-) = 1 : 0.105 : 0.0036.