Abstract:

The degradation rate of naproxen (NPX) can be significantly improved by activating ferrate under UV light. The effects of different process, Fe(Ⅵ) concentration, pH, phosphate, HCO{}_{\mathrm{3}}^{-}, Cl^- and humic acid (HA) were investigated. The main active species of the reaction were determined by the free radical quenching experiment and the intermediate valence iron identification experiment. In addition, the mineralization degree of NPX was determined by TOC and the possible degradation paths were proposed on the basis of the intermediates detected by liquid chromatography-mass spectrometry analysis. The results showed that after 60min of reaction, Fe(Ⅵ) alone can hardly degrade NPX. The degradation rate of NPX by UV alone was less than 26%, while the degradation rate of NPX by UV-Fe(Ⅵ) process was as high as 82%. The degradation process conformed to the pseudo-first-order kinetic law (R²>0.95) with a reaction rate constant of 0.0306min^-1, which was 6.2 times and 102 times of the degradation rates of UV alone and Fe(Ⅵ) alone, respectively. The initial pH of the solution had a significant effect on the degradation of NPX in the UV-Fe(Ⅵ) process, and the degradation was favored under acidic conditions, mainly due to the dual effect of different forms of ferrate and NPX at different pH. At the same pH, phosphate had a significant inhibitory effect on the degradation of NPX, mainly because of the complexation of phosphate and the decomposition products of ferrate resulting in a decrease in ·O{}_{\mathrm{2}}^{-}. In addition, Cl^- and HA had different degrees of inhibition on NPX degradation. However, HCO{}_{\mathrm{3}}^{-} had a promoting effect on degradation, because the addition of HCO{}_{\mathrm{3}}^{-} increased the pH of the solution and enhanced the stability of ferrate. The dominant active species in the UV-Fe(Ⅵ) process is ·O{}_{\mathrm{2}}^{-}, which decarboxylates NPX mainly through electron transfer mechanism and finally generates acids, ketones and ethers.

Key words: ferrate, ultraviolet activation, advanced oxidation, free radicals, degradation mechanism

摘要：

利用紫外线（UV）活化高铁酸盐[Fe(Ⅵ)]能显著提高萘普生（NPX）的降解率。本文考察了不同体系、 Fe(Ⅵ)投加量、溶液pH、磷酸盐、HCO{}_{\mathrm{3}}^{-}、Cl^-以及腐殖酸（HA）对NPX降解的影响，并通过自由基淬灭实验和中间价态铁鉴定实验确定了反应的主要活性物种。通过TOC去除率确定体系降解NPX的矿化程度并利用液相色谱质谱联用仪检测降解的中间产物，提出了可能的降解路径。结果表明，反应60min后，单独Fe(Ⅵ)几乎不能降解NPX，单独UV对NPX的降解率也不到26%，而UV-Fe(Ⅵ)体系对NPX的降解率高达82%，降解过程符合准一级动力学规律（R²>0.95），反应速率常数为0.0306min^-1，分别是单独UV和单独Fe(Ⅵ)降解速率的6.2倍和102倍。溶液初始pH对UV-Fe(Ⅵ)体系降解NPX有显著影响，酸性条件下有利于NPX的降解，主要是由于在不同pH下高铁酸盐和NPX的不同形态的双重作用。相同pH下，磷酸盐对NPX的降解有明显的抑制作用，主要是因为磷酸盐与Fe(Ⅵ)分解产物具有络合作用导致·O{}_{\mathrm{2}}^{-}减少。Cl^-和HA对NPX降解有不同程度的抑制作用，而HCO{}_{\mathrm{3}}^{-}对降解有促进作用，这是因为HCO{}_{\mathrm{3}}^{-}的加入使得溶液的pH升高从而增强了Fe(Ⅵ)的稳定性。较低的矿化率表明NPX的降解产物与其母体化合物相比难于在UV-Fe(Ⅵ)体系中去除。UV-Fe(Ⅵ)体系中的主要优势活性物种是·O{}_{\mathrm{2}}^{-}，NPX 与·O{}_{\mathrm{2}}^{-}主要通过电子转移机制发生脱羧反应，最终生成酸类、酮类和醚类物质。

关键词: 高铁酸盐, 紫外活化, 高级氧化, 自由基, 降解机理