Mechanism investigation of catalyzed ozonation of 2-methylisoborneol in drinking water over aluminum (hydroxyl) oxides: Role of surface hydroxyl group

In this investigation, the mechanism of catalyzed ozonation of MIB by aluminum oxides (gamma-AlOOH and gamma-Al2O3) was studied. It was concluded that the roles of surface hydroxyl groups in adsorption and catalyzed ozonation determined catalyzed ozonation mechanism. The removal efficiency of MIB in catalyzed ozonation by gamma-Al2O3 or gamma-AlOOH was 98.4% and 27.5%, respectively. Effect of water pH on catalyzed ozonation indicated that surface hydroxyl group, of which surface net charge was zero, was the active site of catalysts. Radical scavenger experiments results indicated that catalyzed zonation by gamma-Al2O3 followed a hydroxyl radical ((OH)-O-center dot) reaction-pathway and the reaction-pathway of catalyzed ozonation by gamma-AlOOH followed solid surface mechanism. However, both gamma-AlOOH and gamma-Al2O3 can enhance ozone decomposition to generate hydroxyl radical in catalytic ozone decomposition (without MIB). The inconsistent results between radical scavengers and catalytic ozone decomposition were mainly due to the interaction between MIB and surface hydroxyl groups. According to MIB adsorption on gamma-AlOOH or gamma-Al2O3, MIB interacted with surface hydroxyl group by chemical adsorption, and surface hydroxyl group was the main adsorption site. The adsorption capability of gamma-AlOOH was higher than that of gamma-Al2O3. The participation of surface hydroxyl group in adsorption restrained its capability of catalyzed ozone decomposition to generating (OH)-O-center dot. gamma-AlOOH that was covered with more surface hydroxyl groups, adsorbed MIB more stronger and inhibited generation of (OH)-O-center dot in catalyzed ozonation of MIB, resulting in lower removal efficiency of MIB in catalyzed ozonation. In addition, the surface texture and chemical properties of catalyst that can help to understand the catalyzed mechanism. (C) 2010 Elsevier B.V. All rights reserved.