Photocatalytic Degradation of Surfactants. XX. Photooxidation of Sodium Butylnaphthalenesulfonates

Abstract

The photocatalyzed degradation of surface-active and surface-inactive naphthalene-sulfonate derivatives has been investigated in UV-irradiated air-equilibrated heterogeneous TiO2 dispersions. The dynamics for the photodegradation of sodium butylnaphthhalene-1-sulfonate (B-1-NS) and sodium naphthalene-1-sulfonate (1-NS) are compared to those of sodium dodecylbenzenesulfonate (DBS) and sodium benzenesulfonate (BS). The adsorption behavior of the surfactants on the TiO2 catalyst, cleavage of the aromatic ring, mineralization to carbon dioxide, formation of sulfate ions, and the temporal changes of the surface activity (surface tension) against UV irradiation time were probed experimentally to provide inferences on the photoinitiated mechanism. The position(s) of ·OH and/or ·OOH radicals attack on the surfactant structure was inferred from theoretical considerations on the basis of molecular orbital calculations of frontier electron densities; similarly, the adsorption behavior of the surfactants on the TiO2 catalyst surface was deduced from calculations of point charges of each of the atoms in the surfactant structure.