Activation of persulfate for degradation of sodium dodecyl sulfate by a hybrid catalyst hematite/cuprous sulfide with enhanced FeIII/FeII redox cycling.

Surfactants are recalcitrant compounds that require advanced treatment for their degradation. Heterogeneous advanced oxidation processes (AOPs) using iron-based catalysts can be a promising method for surfactant degradation. The acceleration of the FeIII/FeII redox cycling is the key to enhance the catalytic degradation. Herein, a hybrid catalyst composed of α-Fe2O3 and Cu2S was synthesized to improve the reduction of FeIII in a heterogeneous persulfate-AOP system. The results of XRD, Raman and TEM demonstrated the successful preparation of the hybrid catalyst. Because of the optimized FeII regeneration, the AOP containing the catalyst FC75 achieved 100.0% removal of sodium dodecyl sulfate (SDS) in a neutral aquatic environment, significantly higher than 22.9 ± 2.4% with pure α-Fe2O3 or 39.6 ± 2.5% with pure Cu2S. The catalyst FC75 demonstrated effective SDS removal in the recycling test (82.7 ± 7.0% after six recycling test) and in actual wastewater (84.4 ± 4.5%). The regeneration of FeII was confirmed by the increased proportion of FeII from 39.5% in the fresh catalyst to 42.6% in the used catalyst. The main active species was revealed to be sulfate radicals under an acidic condition and shifted to hydroxyl radicals under a basic condition. In the hybrid catalyst, α-Fe2O3 provided FeII to activate persulfate to radicals, with an oxidation product of FeIII, which was then reduced to FeII by CuI provided by Cu2S, coupling with the oxidation of CuI to CuII. The S element in Cu2S could directly or indirectly facilitate the FeIII/FeII redox cycling as an electron donor. Those results have demonstrated that the developed hybrid catalyst is able to promote FeII regeneration for effective SDS removal.