Phenol degradation in iron-based advanced oxidation processes through ferric reduction assisted by molybdenum...

In the iron-based advanced oxidation processes (AOPs), direct use of Fe^III can be more convenient than Fe^II but the reduction of Fe^III to Fe^II is a rate-limiting step. Introducing co-catalysts with abundant reducing sites to Fe-based AOPs can be an efficient way to accelerate the Fe redox process. Herein, molybdenum disulfide (MoS₂) was used to enhance the catalytic performance of Fe³⁺/persulfate (PS) for phenol removal. In the Fe³⁺/MoS₂/PS system, 99.6 ± 0.1% of phenol was removed in 60 min, comparable to that of the Fe²⁺/PS/MoS₂ system (99.1 ± 0.3%). With the help of MoS₂, 99.3 ± 4.2% of Fe³⁺ was transformed to Fe²⁺ in 10 min, and the Fe²⁺/Fe ratio was able to be maintained at 70.0 ± 1.4% after 60 min. The rapid and complete reduction of Fe³⁺ with MoS₂ made it possible to replace Fe²⁺ by Fe³⁺, which is easier to store, transport, and use. The decrease in XPS peak area percentage of Mo(IV) and the lower valent S after reaction revealed that MoS₂ acted as an electron provider in the Fe redox cycle. Quenching experiment results indicated that the phenol removal was highly depended on the surface-bound radicals, including both SO₄^•- and ^•OH. Those results have demonstrated that ferric salts can be directly used in the Fe-based AOPs and the redox cycle could be sustained with the assistance of MoS₂.