Influence Rule of Organic Solvents Methanol from Sample Preparation on Degradation Rate and Mechanism of Atrazine in UV-based Oxidation Processes
Year: 2019
Type: article
Abstract: Stock solutions of organic micro-pollutants with low water solubility are commonly prepared using organic solvents in laboratory studies on degradation of these organic compounds.Dilution of the stock solution unavoidably introduces a small amount of organic solvent into the experimental working solutions.This could possibly affect the estimation of the degradation rate constants (k obs ) of these organic micro-pollutants by UV-based oxidation processes.To demonstrate this problem, the effect of organic solvents on the degradation rate of atrazine (ATZ) has been investigated in the sole-UV, UV/H 2 O 2 and UV/TiO 2 process at the concentration levels that would likely be derived from stock solutions.Organic solvent methanol (MeOH) commonly used for stock-solution preparation was selected.The degradation of ATZ was investigated under ultraviolet irradiation (253.7 nm).The reaction was conducted in an annular photochemical reactor, in the axis of which a low-pressure mercury lamp (LPUV) was installed.The photon flux into the solution from the LPUV was determined to be at 1.18×10 -7 Einstein/s.A magnetic stirrer was located at the bottom of the reactor to maintain homogeneity of the reacting solution.A thermostatic water recirculation system was used to control the solution temperature at 20±0.5 ℃.Prior to irradiation, the mercury lamp was ignited for 30 min for a stable output.UV photo-oxidation was performed with ultrapure water containing an initial 0.1 or 5 mg/L ATZ and different volume ratio of methanol.Solution pH value of 4.0, 7.0 and 10.0 was buffered using phosphate or borate.Determination of ATZ using ultra-performance liquid chromatography-electrospray-triple quadrupole mass spectrometry coupled with an ACQUITY™ UPLC BEH C8 separation column.The results show that the reaction rate of ATZ in UV/TiO 2 process could be affected significantly by the presence of MeOH, even at a concentration well below that possibly introduced during the preparation of working solutions from the organic solvent stock solutions (e.g.0.01%, V/V).With the increase of MeOH concentration, the k obs of ATZ in UV/TiO 2 process gradually decreases.The organic solvents having a stronger reaction activity with •OH tend to impose a greater effect on the k obs of ATZ.However, MeOH does not affect k obs of photolysis of ATZ in sole-UV process, and a small effect for the k obs of ATZ in UV/H 2 O 2 process.In addition, MeOH in the reaction system does not affect the speciation and degradation pathway of ATZ under different UV-based oxidation processes.The findings here provide a plausible explanation for the discrepancies in the reaction rate constants reported in the literature for some organic micro-pollutants during the UV-based oxidation processes.
Source: 化学学报
DOI: 10.6023/a18090365
Authors: Yucan Liu, Miaomiao Su, Yan Zhang, Jinming Duan, Wei Li
Language: English
Subfield: Water Science and Technology
Field: Environmental Science
Domain: Physical Sciences
Open Access status: bronze
OpenAlex ID: W2920198902