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 t he transformation of recalcitrant pollutants in the atmosphere and on terre strial surfaces. Monitoring degradation on surfaces under controlled condit ions without intrusive methods, however, remains a challenge. Here, we repo rt in situ measurements of the photodegradation of 4,4'-bis(2-sulfostyryl)b iphenyl (DSBP), a fluorescent whitening agent used in laundry detergents, o n the surfaces of metal oxides under conditions of controlled humidity usin g attenuated total reflectance infrared spectroscopy (ATR-FTIR). A ZnSe ATR crystal was coated with 1-5 mu m thick layers of high specific surface are a hematite, delta-alumina, lepidocrocite, rutile, and anatase. The 0.4 mg o xide layers were spiked with 20 nmol of (E, E)-DSBP and illuminated with 36 5 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 lepido crocite, on the other hand, was slower and occurred primarily through the d irect photodegradation of adsorbed DSBP. For hematite and lepidocrocite, li ght absorption by the oxide layer reduced the degradation rate by reducing the amount of light available to DSBP. Implications for the photodegradatio n reactions,of environmental contaminants on sails are discussed.