Activation Mechanism of a Peroxymonosulfate-based Fenton-like System with Birnessite and Cu²⁺ Modified Birnessite

The peroxymonosulfate (PMS) activation mechanism is closely related to the structure/configuration of the "active site" of the Fenton-like catalysts. In this paper, it is shown that Cu²⁺ chemically bonds the surface of birnessite at the Mn vacancy site to form triple-corner-sharing inner-sphere surface complexes (Cu-Bir), which regulates the PMS activation mechanism. Birnessite/PMS Fenton-like system degrades phenol via a non-radical mechanism, which involves high valent Mn(V)=O generated from the surface reaction of Mn(III) with adsorbed PMS. While Cu-Bir initiates an additional radical mechanism that involves reactive oxygen species of ⋅O₂ ^- and ¹ O₂ , and the k value of 5Cu-Bir is 1.9 times higher than that of Bir. The Fenton-like reaction mechanism of the Cu-Bir/PMS system is thus proposed as a radical and non-radical cooccurrence mechanism, which involves a synergistic effect that the radical pathway accelerates the regeneration of Mn(III) for the non-radical pathway, and the non-radical pathway assists to produce ¹ O₂ for the radical pathway.