Zn(0)-Catalyzed Ozonation Degradation of Acid Orange 7 (AO7) in Aqueous Solution

In this paper, Zn(0)-catalyzed ozonation degradation of acid orange 7 (AO7) and its impact factors including solution pH, Zn loading, and AO7 initial concentration were investigated through a series of bath experiments. The results demonstrated that Zn could markedly accelerate the degradation of AO7 by ozone (O3) and the degradation efficiency of AO7 increased by 77 and 71 % within 30 min as compared with those in the systems of O3 alone and Zn/air, respectively. The reuse of Zn resulted in a slight decline in AO7 degradation, suggesting that a coating of ZnO on the surface of Zn particles weakened Zn catalytic activity. The optimal removal of AO7 was achieved in a wide pH range of 4 to 10, and a lower or higher pH was not conducive to the degradation of AO7. In addition, the degradation efficiency of AO7 increased with Zn loading but decreased with AO7 initial concentration. The introduction of free radical scavengers into the system of AO7/Zn/O3 confirmed that O2•−, rather than •OH, was the main free radicals responsible for the rapid removal of AO7. The degradation of AO7 by O3 assisted with Zn could be well expressed with pseudo-first-order kinetic model.