Effects of common inorganic anions on the rates of photocatalytic degradation of sodium dodecylbenzenesulfonate over illuminated titanium dioxide

Experiments were carried out to study the effects of several anions on the photocatalytic degradation rates of sodium dodecylbenzene sulphonate (DBS) with TiO2 as catalyst. The anions were added as Na2SO4, NaNO3, NaCl, NaHCO3, NaH2PO4 and Na3PO4, and two levels of anion content, i.e. 12 mmol/L and 36 mmol/L in terms of Na+, were studied. The results revealed that: Cl-, SO4(2-), NO3- and HCO3- retarded the rates of DBS degradation to different degrees; PO4(3-) increased the DBS degradation rate at low concentration and decreased the rate at high concentration; H2PO4- accelerated the rate of DBS degradation. The mechanism of the effects of anions on DBS degradation was concluded as the following three aspects: anions compete for the radicals; anions are absorbed on the surface of catalyst and block the active site of catalyst; anions added to the solution change the pH value and influence the formation of .OH radicals and the adsorption of DBS on catalyst.