Solar production of singlet oxygen from crude oil films on water

• Sunlight exposed oil films produced singlet oxygen.
• ∼2 × 10−5 moles 1O2 were produced in 1 h from sunlight irradiated 100 mg oil films.
• [1O2] = 1.4–1.6 × 10−12 M in water under 100 mg irradiated oil films.
• TiO2 nanoparticles did not affect singlet oxygen formation rates.

Photochemical production of singlet oxygen from thin oil films over seawater and pure water was measured with furfuryl alcohol as a selective chemical probe. Oil was collected from the surface of the Gulf of Mexico following the deepwater horizon spill and from other sources. The loss of furfuryl alcohol and the formation of 6-hydroxy(2H)pyran-3(6H)-one were monitored. Total singlet oxygen formation was studied using high furfuryl alcohol concentrations and varying exposure time. The total amount of singlet oxygen produced in 1 h irradiations of thin oil films (100 mg, 60 microns thick) over Gulf of Mexico water and pure water were 1.9 ± 0.4 × 10−5 and 1.6 ± 0.3 × 10−5 mol, respectively. After initial tests were performed, titanium dioxide (TiO2) nanomaterials were added to the system in two different concentrations to study the effects of singlet oxygen formation in the presence of a photocatalyst. The addition of TiO2 nanoparticles did not significantly change the observed formation rate of singlet oxygen. Steady state concentrations of photoproduced singlet oxygen were also determined and found to be near 1 × 10−12 M in water under thin films of oil, which is considerably greater than values previously observed for pure seawater. This study illustrates that oil is a source of singlet oxygen when exposed to sunlight. The fate of oil and other dissolved species will be heavily dependent on the formation and reaction of singlet oxygen in thin oil films on water.

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