Insights into the mechanism of heterogeneous activation of persulfate with a clay/iron-based catalyst under visible LED light irradiation

[Display omitted] •The inexpensive kaolinite-supported iron oxide catalyst (K-Fe) was fabricated.•Persulfate can degrade RhB via an electron transfer pathway.•The excited RhB molecules can activate persulfate to generate free radicals.•The free and surface-adsorbed radicals were responsible for the degradation of RhB.•K-Fe showed good reusability and high stability over a broad operating pH range. Activation of persulfate (PS) by ultraviolet (UV) light or metal catalysts has been extensively studied, however, little is known about the activation of persulfate by clay-based catalysts in the presence of visible light-emitting diode (LED) irradiation. Herein, a novel kaolinite-supported iron oxide (K-Fe)/PS/Vis process for the degradation of Rhodamine B (RhB) from aqueous solution is reported. It was found that although persulfate can degrade RhB via a non-radical reaction, the excited RhB molecule (RhB*) and the Fe(II) species formed on the catalyst surface can effectively activate persulfate to generate radicals which degrade RhB under visible light irradiation. On the basis of quenching experiments and electron paramagnetic resonance (EPR) studies, it is suggested that the free radicals produced from persulfate coupled with the surface-adsorbed radicals formed on the catalyst were responsible for the degradation of the dye via RhB*. Moreover, the K-Fe catalyst showed excellent reusability and stability with a low level of iron leaching. The findings of this work demonstrate a new pathway for activation of persulfate, which could effectively degrade organic pollutants and also provide some new insights into persulfate remediation of contaminated water.