Regulation of Surface Terminal Hydroxyl Coverage of FeOCl Catalyst via Crystal Facet Protection for Enhanced H₂O₂ Activation

The unique Fe coordination environment in the FeOCl catalyst confers superior reducible electronic properties, rendering them attractive Fenton-like active sites. DFT calculations reveal that the U-shaped coordinated Fe sites formed with 50% terminal hydroxyl coverage exhibit the best H₂O₂ activation performance, which allows the adsorbed H₂O₂ to form a ·OH directly with much lower activation energy. Herein, a crystal facet protection strategy induced by rapid high-temperature annealing is developed to synthesize FeOCl with high exposure of Fe atoms while regulating the surface hydroxyl coverage. The dominant expression of the (021) facet resulted in an optimized surface terminal hydroxyl coverage of 58.3%, increasing the intrinsic activity of FeOCl by 4.3 times. The d-band center of FeOCl with optimized terminal hydroxyl coverage is closer to the Fermi level, thus exhibiting higher affinity for H₂O₂, and the increased amount of U-shaped coordinated Fe sites enables sufficient ·OH generation for enhanced decontamination performance. Since the terminal hydroxyl groups can be consumed by Ca²⁺ and Mg²⁺ through coprecipitation, preremoving the hardness of actual wastewater is indispensable in the application of the FeOCl/H₂O₂ system. Our finding provides a new way to improve the intrinsic activity of FeOCl catalyst, which is helpful for its application in other environmental remediations.