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 (<sup>1</sup>O<sub>2</sub>) was trapped
by a water-soluble anthracene compound and monitored <i>in situ</i> 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, even
in the presence of flowing oxygen gas. A mechanism is proposed that
explains how Pc particle wetting, plastron gas composition and flow
rate as well as gas saturation of the aqueous solution affect singlet
oxygen trapping efficiency. These stable superhydrophobic surfaces,
which can physically isolate the photosensitizer particles from the
solution may be of practical importance for delivering singlet oxygen
for water purification and medical devices
