Photodegradation of 4,4′-bis(2-sulfostyryl)biphenyl (DSBP) on metal glides followed by in situ ATR-FTIR spectroscopy

Photodegradation on soil and mineral surfaces is an important pathway for the transformation of recalcitrant pollutants in the atmosphere and on terrestrial surfaces. Monitoring degradation on surfaces under controlled conditions without intrusive methods, however, remains a challenge. Here, we report in situ measurements of the photodegradation of 4,4'-bis(2-sulfostyryl)biphenyl (DSBP), a fluorescent whitening agent used in laundry detergents, on the surfaces of metal oxides under conditions of controlled humidity using attenuated total reflectance infrared spectroscopy (ATR-FTIR). A ZnSe ATR crystal was coated with 1-5 mu m thick layers of high specific surface area hematite, delta-alumina, lepidocrocite, rutile, and anatase. The 0.4 mg oxide layers were spiked with 20 nmol of (E, E)-DSBP and illuminated with 365 nm light at 25 degrees C and 88% relative humidity. Extensive degradation was observed on rutile and anatase due to the photocatalytic action of the TiO2 semiconductor particles. Degradation on alumina, hematite, and lepidocrocite, on the other hand, was slower and occurred primarily through the direct photodegradation of adsorbed DSBP. For hematite and lepidocrocite, light absorption by the oxide layer reduced the degradation rate by reducing the amount of light available to DSBP. Implications for the photodegradation reactions,of environmental contaminants on sails are discussed.