Metal tetrakis(1-methylpyridinium-4-yl)porphyrins were immobilized on sulfonated SBA-15 (MTMPyP-SO3-pr-SBA-15, M = Fe, Mn, Zn) for oxidative degradation of 2,4,6-tribromophenol in the presence of humic substances. The influence of the central metal of metalloporphyrins, pH, and catalyst dosage on the 2,4,6-tribromophenol degradation was investigated. FeTMPyP-SO3-pr-SBA-15 and MnTMPyP-SO3-pr-SBA-15 showed the catalytic activities. The activity of MnTMPyP-SO3-pr-SBA-15 was more strongly inhibited by humic substances than that of FeTMPyP-SO3-pr-SBA-15. Kinetic study indicated that humic substances suppressed the generation of high valent metal-oxo species in MnTMPyP-SO3-pr-SBA-15 at slightly acid condition. There was a clear linear relationship between the content of phenolic-OH and aromatic-C in humic substances and the corresponding inhibition ability. The inhibition by humic substances is probably ascribed to the coordination of humic substances with the monopersulfate species of MnTMPyP-SO3-pr-SBA-15, which prevented the formation of the reactive Mn-oxo species.
Keywords: 2,4,6-tribromophenol; heterogeneous catalyst; humic substances; metal-oxo species; metalloporphyrins.