F− surface modified ZnO for enhanced photocatalytic H2O2 production and its fs-TAS investigation

Pure ZnO exhibits low photocatalytic H₂O₂ production activity due to the rapid charge recombination. To realize the spatial separation of photogenerated electrons and holes, constructing an electron transfer channel on the ZnO surface is an effective approach. This study successfully modified the surface of ZnO using F^– (ZnO/F) by introducing NH₄F in an aqueous phase photocatalytic system. The F^– is adsorbed on the ZnO surface by Coulombic force and significantly improves the photocatalytic H₂O₂ production performance of ZnO, with the highest efficiency of 4137.2 μmol·g^–1·L^–1·h^–-1. The photocatalytic performance enhancement mechanism of ZnO/F is explained in terms of electron transfer dynamics by femtosecond transient absorption spectroscopy (fs-TAS) measurements. F^– surface modification constructs a new ultrafast electron transport pathway from the ZnO CB to F^–, and the optimal ZnO/F exhibits the fastest interfacial electron transfer lifetime of 5.8 ps. The F^– surface modification effectively facilitates the charge separation, thereby increasing the number of electrons available for photocatalytic H₂O₂ reaction. This study has revealed the roles of F^– surface modification in the photocatalytic H₂O₂ production by ZnO and provides guidance for ionic modification to improve photocatalytic performance.