Bromate Inhibition during Ozonation of Bromide-Containing Water by the Presence of Mn Incorporated MCM-41

The mesoporous Mn incorporated MCM-41 was employed to inhibit bromate formation during catalytic ozonation of bromide-containing water, Mn-MCM-41 was synthesized via hydrothermal method and the influences of temperature ramping rate (0.5, 1 and 2 K min-1) during calcination were investigated. It was characterized by XRD, TEM, SEM, XPS and H2-TPR, indicating that temperature ramping rate could affect the valence states of active Mn species, the dispersion of Mn on the surface of catalyst and the formation of oxygen vacancies, which could increase surface hydroxyl groups on Mn-MCM-41 and accelerated ozone decomposition to generate oxygen species. Compared with 0.5 K min-1 and 2 K min-1, Mn-MCM-41 with 1 K min-1 showed much better performance in bromate inhibition process, Mn100-MCM-41 (molar ratio of Si/Mn=100) achieved 96.7% inhibition efficiency at pH 6.5, which was attributed to higher fraction of Mn(II)/Mn(III) and oxygen vacancies. The influence of pH, TBA and intermediate HOBr/OBr- were explored to investigate the mechanism. The results showed that more H2O2 generation and decreased O3 exposure to Br- in Mn-MCM-41 catalytic ozonation process, the oxidative transformation from Br- to HOBr/OBr- was blocked, resulting to less bromate formation. Highlights: • Temperature ramping rate during calcination of Mn-MCM-41 was crucial. • Oxygen vacancy and variation Mn state are responsible for catalytic performance. • Mn-MCM-41 achieved high bromate inhibition efficiency (96.7%) at pH 6.5. • Mn-MCM-41 inhibited BrO3 - by reducing HOBr/OBr-.