Photocatalytic decomposition of the sodium dodecylbenzene sulfonate surfactant in aqueous titania suspensions exposed to highly concentrated solar radiation and effects of additives

The sodium dodecylbenzene sulfonate (DBS) surfactant photodegrades in aqueous titanium dioxide (TiO2) dispersions under highly concentrated solar light exposure (ca. 70 suns) via apparent first-order kinetics with accumulated light energy as the experimental variable. The choice of optimal experimental parameters for the photodegradation of DBS with a concentrated solar illumination device is explored: optimal circulation flow rate, 8.3 l min−1; pH, 5.0; and TiO2 loading, 5 g l−1. Foaming action of the DBS–TiO2 suspension increased with increase in increments of the flow rate. The foam produced at the higher TiO2 loadings exhibited greater stability than in the absence of TiO2. The increase in surface tension is faster than the temporal decrease of the concentration of DBS, which followed the typical. Langmuir–Hinshelwood (LH) model: LH apparent rate constant, kLH=0.184 mM kJ−1; LH adsorption constant, KLH=0.527 mM−1. The relative photonic efficiency, ξrel; against phenol; kapp) of DBS is 0.53. The rate of removal of total organic carbon (TOC) of DBS was improved by a combination of TiO2 loading and added K2S2O8 additive; i.e. at pH 5.0 and TiO2 loading of 0.2 g l−1, or pH 8.4 and TiO2 loading of 5.0 g l−1. However, at pH 5.0 and TiO2 loading 5.0 g l−1, the rate of TOC removal was not enhanced in the presence of K2S2O8 as the oxidizing agent and electron scavenger. The results are explained by contributions from the photochemical oxidation with K2S2O8 and from the K2S2O8-assisted photocatalytic oxidation of DBS.