Catalytic Ozonation Of Acetochlor Using Magnetic Pr₆O₁₁ Catalyst And Aquatic Toxicity Of Acetochlor And The Degradation Products

Catalytic oxidation is a new advanced oxidation technology. The magnetic nano catalysts, with the advantages of easy recover, good stability and high activity, have been interested by researchers. Acetochlor is a widely used preemergence herbicide. It is persistent and can cause carcinogenesis, teratogensis and endocrine disrupting effects. In this work, we prepared the magnetic nano Pr6O11/SiO2@Fe3O4 cataly for catalytic ozonation acetochlor, and some experiments of catalytic ozonation and aquatic toxicity of reaction solution were carried out.Firstly, the magnetic nano Pr6O11/SiO2@Fe3O4 catalyst was prepared using chemical precipitation and confirmed its structure by XRD, XPS, TEM and EDX. Results showed that it had a spinel structure, and had a ternary structure with a Fe3O4 magnetic core, a SiO2 shell and a Pr6O11 outer layer. The diameters of the magnetic catalyst was about 100-200 nm.The experiment of magnetic nano Pr6O11/SiO2@Fe3O4 catalytic ozonation acetochlor was operated at temperature 30℃ and O3/O2 flow rate 60mL/min. The result was that the optimal conditions for the catalytic ozonation acetochlor was initial concentration of acetochlor 20 mg/L, catalyst dosage 1.0 g/L and calcination temperature of catalyst 600℃. Under this conditions, compared with ozonation, adding the Pr6O11/SiO2@Fe3O4 catalyst could effectively improve the acetochlor removal and mineralization. The TOC removal with Pr6O11/SiO2@Fe3O4 catalyst at 120 min could reach 37.3%, while 14.1% with ozonation alone. The mechanism was the ·OH, which produced from surface hydroxyl of catalyst contacting with O3, could react with organic compounds to form oxidized products or intermediate products. By determining the concentration of the leaching out of praseodymium ion (0.115 mg/L at 90min) and the catalyst activity after repeated use, the Pr6O11/SiO2@Fe3O4 catalyst was good at stability and repeat. The degradation process could be well described by the pseudo-first-order kinetics model. The value of kinetic constants A:was 3.92×10-3min-1 for catalytic ozonation, while 1.19 ×10-3min-1 for ozonation alone.By determining the aquatic toxicity of the reaction solution of degradation of acetochlor, it was found that reaction solution of 0 min inhibited the growth of chlorella and reaction solution of 90 min stimulated the growth. Algal cells could ingest most of the praseodymium ions dissolved in the reaction solution, so chlorella had a strong ability of enrichment rare earth elements in the water. To research the developmental toxicity of the reaction solution of degradation of acetochlor, zebrafish was used as a model organism. It was found that with the extended degradation time, the mortality and malformation rate of zebrafish embryos gradually decreased, while hatchability increased gradually.This study revealed that the Pr6O11/SiO2@Fe3O4 catalyst presented good stability, recursitivity, high efficiency and detoxification during catalytic ozonation of acetochlor. This study made sense for reach the migration, conversion of herbicides and rare earth metal, revealed part of their environmental behavior, and was important to control their biohazardous.