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.