Generation of Superoxide and Hydrogen Peroxide by Exposure of Stilbene-based Fluorescent Whitening Agents to UVA Radiation
Keith R. Millington
CSIRO Division of Wool Technology,
PO Box 21, Belmont, Victoria 3216, Australia
We report on the generation of hydrogen peroxide by aqueous solutions of two commercial stilbene-based fluorescent whitening agents (FWAs) in response to irradiation with UV light. A sulphonated distyryl biphenyl FWA (Uvitex NFW) produces both the superoxide anion and H2O2 on exposure to UVA radiation. The formation of superoxide suggests that the excited singlet state of Uvitex NFW undergoes ionisation producing a radical cation and a free electron which is accepted by molecular oxygen. This is consistent with previous flash photolysis work on Uvitex NFW which proposed the formation of transient radical cations. The relationship between the initial concentration of FWA and the amount of H2O2 produced appears complex. The fluorescence excitation spectrum of Uvitex NFW is also strongly dependent on its concentration, but this does not appear be due to the aggregation of FWA molecules.