Theoretical insight into hydroxyl production via H 2 O 2 decomposition over the Fe 3 O 4 (311) surface.

Fenton's reagent provides a method to produce active hydroxyl radicals (˙OH) for chemical oxidation by mixing iron oxide and hydrogen peroxide, which divides into homogeneous and heterogeneous Fenton's reagent. Heterogeneous Fenton's reagent is fabricated from H 2 O 2 and various iron oxide solid materials, such as α-FeOOH, α-Fe 2 O 3 , and Fe 3 O 4 . Fe 3 O 4 possesses the Fe 2+ /Fe 3+ mixed valence oxidational state and has been reported to have good catalytic activity. However, the reaction mechanism of H 2 O 2 decomposition on Fe 3 O 4 surfaces is still unclear. In this work, we performed DFT calculations to investigate the H 2 O 2 decomposition mechanisms over the Fe 3 O 4 (311) surface. There are two iron environments for H 2 O 2 adsorption and decomposition on the Fe 3 O 4 (311) surface, a Fe 2+ /Fe 3+ environment and a Fe 3+ /Fe 3+ environment. We found that the H 2 O 2 can adsorb on the Fe 2+ /Fe 3+ environment by molecular adsorption but by dissociative adsorption on the Fe 3+ /Fe 3+ environment. Our results show that both adsorption structures can produce two OH groups on the Fe 3 O 4 (311) surface thermodynamically. In addition, based on the electronic property analysis, H 2 O 2 on the Fe 2+ /Fe 3+ environment follows the Haber-Weiss mechanism to form one OH anion and one OH radical. On the other hand, H 2 O 2 on the Fe 3+ /Fe 3+ environment follows the radical mechanism to form two OH radicals. In particular, the OH radical formed on Fe 2+ /Fe 3+ has energy levels on both sides of the Fermi energy level. It can be expected that this OH radical has good redox activity.