Catalytic ozonation of p-chlorobenzoic acid in aqueous solution using Fe-MCM-41 as catalyst

MCM-41and iron-substituted MCM-41 (Fe-MCM-41) were synthesized successfully and characterized using X-ray diffraction (XRD), nitrogen adsorption–desorption and transmission electron microscopy (TEM). The mesopores of the sample remained well ordering and of hexagonal structure. Fe-MCM-41 samples possessed high BET surface areas, high pore volumes and narrowed pore size distribution. Their catalytic activities were compared in terms of p-chlorobenzoic acid (p-CBA) and TOC removal. Ozonation catalyzed by Fe-MCM-41 exhibited extraordinarily high catalytic performance over other studied processes. 100% conversion of p-CBA and 91.3% TOC were achieved in 10 min and 60 min, respectively. Fe-MCM-41 as a novel heterogeneous catalyst in ozonation process was addressed. The presence of tert-butanol (TBA) inhibiting the degradation of p-CBA in the Fe-MCM-41/O3 process verified that the hydroxyl radicals derived from ozone decomposition were responsible for the improvement of catalytic ozonation. The mechanism explaining the formation of hydroxyl radicals on Fe-MCM-41 surface was proposed. Negative centers or Brönsted acid sites developed by the substitution of trivalent iron into the walls of MCM-41 and the hydroxyl groups formed as a result of coordinative unsaturation were found to be the active sites enhancing catalytic performance. The superior stability of iron ions in Fe-MCM-41 catalyst during the ozonation process was also examined.

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► Fe-MCM-41 was first used as a heterogeneous catalyst for ozonation process.
► Fe leaching of Fe-MCM-41 was greatly reduced compared with that of Fe/MCM-41.
► Brönsted acid sites on the Fe-MCM-41 catalyst were thought to be the active sites.
► Generation mechanism of hydroxyl radicals was proposed.