Effects of pH on photochemical decomposition of perfluorooctanoic acid in different atmospheres by 185 nm vacuum ultraviolet

Perfluorooctanoic acid （PFOA）, a persistent organic pollutant, receives increasing concerns due to its worldwide occurrence and resistance to most conventional treatment processes. The photochemical decomposition by 185 nm vacuum ultraviolet （VUV） is one of the efficient methods for PFOA decomposition. The effects of pH on PFOA decomposition in nitrogen atmosphere or oxygen atmosphere were investigated. At its original pH （4.5） of PFOA aqueous solution, PFOA decomposed efficiently both in nitrogen and in oxygen atmosphere. However, when the pH increased to 12.0, PFOA decomposition was greatly inhibited in oxygen atmosphere, while it was greatly accelerated in nitrogen atmosphere with a very short half-life time （9 rain）. Furthermore, fluorine atoms originally contained in PFOA molecules were almost completely transformed into fluoride ions. Two decomposi- tion pathways have been proposed to explain the PFOA decomposition under different conditions. In acidic and neutral solutions, PFOA predominantly decomposes via the direct photolysis in both atmospheres; while in the alkaline solution and in the absence of oxygen, the decomposition of PFOA is mainly induced by hydrated electrons.

185 nm真空紫外线照射下水中抗生素的光解

185 nm真空紫外线光子具有很高的能量,不但自身具有分解有机污染物的能力,还可诱发水分子光解产生羟基自由基,氧化分解水中难降解污染物。对6种抗生素进行了185 nm真空紫外线光解,发现不但抗生素被有效降解,TOC浓度亦明显降低。重点考察了四环素的降解机理。通过对试验数据的线性回归分析,确认了四环素的降解效率是降解系数和照射时间的函数,且初始浓度越低,降解系数越高。根据静态试验数据得到,处理1 mg/L的四环素溶液时(去除率为97%)耗电量<1.833 kW·h/m^3。185 nm真空紫外线在介质中穿透率很低,水体的混合扰动对抗生素降解效果有正面影响。此外,抗生素被光解的难易程度和分子结构内的环状结构有关。

真空紫外线(185 nm)辐射测量方法与紫外灯臭氧产出特性研究

有臭氧型紫外线灯185 nm辐射输出效率直接影响其臭氧产出率。目前我国还没有185 nm紫外线照度计的标准、溯源,没有适合大众使用的成熟统一的185 nm辐射测量方法与测量仪器。本文简述了测量253.7 nm紫外线辐射通量的3种常用方法,验证了Keitz公式测量计算法测量线性紫外线灯辐射通量(辐射功率)的可靠性。采用自行设计的具有创造性的简易适用的测试系统,利用国外185 nm照度计,依据Keitz公式测量计算法测量了不同管径、不同石英玻璃的线性紫外线灯的185 nm紫外辐射参数,并利用动态臭氧测试系统测量了有臭氧紫外线灯的动态臭氧产出参数。讨论了测试系统和测量方法可能产生的误差及不确定性,对完善适合大众使用的185 nm紫外线辐射测量方法及测试系统提出建议。