Preparation of fluorinated Fe-MCM-48 and its mechanism for inhibiting ozone oxidation to bromate in drinking water treatment

The ozonation process in drinking water plant will generate toxic by-products such as bromate (\mathrmBrO_3^- ), which pose significant threats to human health. Heterogeneous catalytic ozonation process can inhibit the formation of \mathrmBrO_3^- . Fe-MCM-48 mesoporous molecular sieves, with their unique three-dimensional cubic pore structures, are often used as catalyst for catalytic ozonation. However, the insufficient surface acidic sites and poor mass transfer effects of Fe-MCM-48 limit its application and popularization. In this study, F-Fe-MCM-48 was prepared using FeF₃ as the iron and fluoride source via a one-step synthesis method. It was applied to inhibit \mathrmBrO_3^- production during the catalytic ozonation process. XRD, TEM and FTIR were used to study the physicochemical properties like specific surface area and acid sites. The influence of F-Fe-MCM-48, solution pH and tert-Butanol (TBA) addition on \mathrmBrO_3^- formation were investigated and the functional mechanism of catalyst was revealed by electron paramagnetic resonance (EPR). Results showed that: 1) F-Fe-MCM-48 possessed a good three-dimensional mesoporous structure and a large specific surface area (1487 m²/g). During hydrothermal reactions, iron atoms replaced silicon atoms in the siloxane tetrahedra to enter the framework of the molecular sieve, and F replaced the Si—OH on the surface to form the hydrophobic Si—F group. 2) With an ozone production of 100 mg/h and a Br⁻ addition of 1000 μg/L, the concentration of \mathrmBrO_3^- in the F-Fe-MCM-48/O₃ system after 60 min was 70.3 μg/L, with an inhibition rate of 78.9%, which was 1.4 times of that in Fe-MCM-48/O₃. Within a pH range of 5-9, the F-Fe-MCM-48/O₃ system maintained good \mathrmBrO_3^- inhibition. 3) F-Fe-MCM-48 was enriched with Lewis acid sites, which could effectively adsorb and decompose O₃, thereby reducing its concentration and inhibiting the direct oxidation of Br⁻. The active species such as \cdot \mathrmO_2^- and H₂O₂ generated during the reaction process could further reduce intermediates such as \mathrmBrO_3^- , \cdot \mathrmBr_2^- and \cdot \mathrmBr_3^- , thereby further inhibiting the formation of \mathrmBrO_3^- in F-Fe-MCM-48/O₃ process. This study can provide theoretical basis for the control of \mathrmBrO_3^- during ozonation.