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

In the iron-based advanced oxidation processes (AOPs), direct use of FeIII can be more convenient than FeII but the reduction of FeIII to FeII 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.