SingletOxygen Generation on Porous SuperhydrophobicSurfaces: Effect of Gas Flow and Sensitizer Wetting on Trapping Efficiency

摘要

We describe physical-organic studies of singlet oxygen generation and transport into an aqueous solution supported on superhydrophobic surfaces on which silicon–phthalocyanine (Pc) particles are immobilized. Singlet oxygen (¹O2) was trapped by a water-soluble anthracene compound and monitored in situ using a UV–vis spectrometer. When oxygen flows through the porous superhydrophobic surface, singlet oxygen generated in the plastron (i.e., the gas layer beneath the liquid) is transported into the solution within gas bubbles, thereby increasing the liquid–gas surface area over which singlet oxygen can be trapped. Higher photooxidation rates were achieved in flowing oxygen, as compared to when the gas in the plastron was static. Superhydrophobic surfaces were also synthesized so that the Pc particles were located in contact with, or isolated from, the aqueous solution to evaluate the relative effectiveness of singlet oxygen generated in solution and the gas phase, respectively; singlet oxygen generated on particles wetted by the solution was trapped more efficiently than singlet oxygen generated in the plastron, evenin the presence of flowing oxygen gas. A mechanism is proposed thatexplains how Pc particle wetting, plastron gas composition and flowrate as well as gas saturation of the aqueous solution affect singletoxygen trapping efficiency. These stable superhydrophobic surfaces,which can physically isolate the photosensitizer particles from thesolution may be of practical importance for delivering singlet oxygenfor water purification and medical devices.