A nanometer-ZnO catalyst to enhance the ozonation of 2,4,6-trichlorophenol in water

Removal of 2,4,6-trichlorophenol (TCP) from water has been accomplished through zinc oxide (ZnO) catalytic ozonation. In the presence of ZnO catalyst, aqueous ozone (O₃) can be described by a two-stage behavior, first involving a short-term rapid decomposition followed by a second slow decomposition. The low reaction rate (k_d2) of second stage for O₃-ZnO systems suggested that most of O₃ was transferred into OH radical by ZnO catalyst and was rapidly consumed during the first stage. The combined use of O₃ and ZnO catalyst leads to a conspicuous 99.8% of TCP conversion in 30 min which compares favorably to the hardly 75% reached in the absence of the catalyst. The high reactivity of hydroxyl radicals that were generated by O₃-ZnO during the oxidation process effectively degraded TCP. Without regard to the O₃ dose, the catalytic–oxidation kinetics of the process depends on the concentration of ZnO catalyst and size of ZnO particles. At the same concentration of three different ZnO size in batch tests, TCP degradation rates were in the order of nanometer > submicrometer > micrometer. The effect of pore diffusion on the rate of TCP–ZnO reactions was determined by examination of the effectiveness factor using different particle sizes of ZnO. Calculations show that the rate of TCP decomposition by nano-size ZnO was strongly controlled by surface reaction with little influence of pore diffusion, as indicated by the high effectiveness factors.