The photocatalytic oxidation of dibenzothiophene (DBT)

TiO2/UV solar light degradation of dibenzothiophene (DBT) aqueous solutions readily occurs in neutral and acid media. For instance, at neutral pH, t1/2 = 30min are found for DBT degradation and mineralization. In neutral and acid media the rate limiting step for mineralization is the same as for degradation and corresponds to the DBT sulfone formation. Benzaldehyde is the major reaction product. In addition, it also acts as an intermediate in the mineralization to CO2 + water+sulfate. The results support the Langmuir-Hinshelwood degradation mechanism. Therefore, instead of pseudo-first-order rate constants, apparent rate constants that depend on concentration are obtained. Only at basic pH these apparent rate constant are independent of the [DBT]o. The solubility of DBT in water is increased by one-order of magnitude when solutions of the surfactant Triton X-100 is used at [Triton X-100] >CMC (critical micelle concentration). Under these conditions DBT is readily degraded without degrading Triton X-100 at t1/2 ca. 120min. DBT is solubilized into Triton X-100 micelles from where it exchanges with water and becomes available for degradation. Triton X-100 monomers slightly compete with DBT for the TiO2 catalytic site. The degradation method established in this work might be used, for instance, to decontaminate soil contaminated with sulphur-rich heavy oil following a pre-treatment consisting of washing out the solid with Triton X-100 solutions, prior to photolysis.