Microwave discharge electrodeless lamps (MDELs). VI. Performance evaluation of a novel microwave discharge granulated electrodeless lamp (MDGEL)-Photoassisted defluorination of perfluoroalkoxy acids in aqueous media
Microwave discharge electrodeless lamps (MDELs). VI. Performance evaluation of a novel microwave discharge granulated electrodeless lamp (MDGEL)-Photoassisted defluorination of perfluoroalkoxy acids in aqueous media
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DOI：
10.1016/j.jphotochem.2011.05.007
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发表时间：
2011-07-05
影响因子：
4.3
通讯作者：
Serpone, Nick
中科院分区：
文献类型：
--
作者：
Horikoshi, Satoshi;Tsuchida, Akihiro;Serpone, Nick
新型微波放电颗粒状无电极灯（MDGEL：5毫米× 10毫米），制造真空紫外线（VUV）透明石英信封，已被检查用于处理模型污染的废水。这些MDGEL的评价是通过在低微波功率水平的灯的自燃和光辅助的分解和脱氟的三氟乙酸（TFA），七氟丁酸（HFBA）和全氟辛酸（PFOA）的水溶液中的流通式微波光反应器（MW/光）包含20个这样的MDGEL。一个传统的单棒状微波放电无极灯（MDEL）和低压电极汞灯也被用来比较这些新的MDGEL的性能。MDGEL的主要性能通过浸没在溶液中的光源的单位表面积的去电动力学和灯的施加电功率来确定。在pH 10时，动力学与碳链长度和与在三个氟化酸中的C-F键的数目相关。在初始pH = 4.7-5.2的条件下，单棒状MDEL装置的微波辐射对于溶液的240分钟VUV/UV辐射实现了51%（TFA）、67%（HFBA）和37%（PFOA）的脱附水平，而在pH = 10的条件下，TFA和HFBA的脱附在120-135分钟的辐射内100%完成：PFOA的脱附约为100%。使用20 MDGEL系统，在105 min后实现了TFA和HFBA的100%脱附，而PFOA的100%脱附需要约10 min。照射400分钟。一个分解/脱氟途径的基础上确定的中间体的LC-MS技术，涉及最初的VUV/UV照射（185 nm和254 nm）的全氟辛酸污染物，随后损失的CO2和-CF2单位，以完成脱氟和降解。(C)2011爱思唯尔有限公司版权所有。
Novel microwave discharge granulated electrodeless lamps (MDGELs: 5 mm x 10 mm), fabricated using vacuum-UV (VUV) transparent quartz envelopes, have been examined for the treatment of model contaminated wastewaters. Evaluation of these MDGELs was performed through the self-ignition of the lamps at low microwave power levels and by the photoassisted decomposition and defluorination of trifluoroacetic acid (TFA), heptafluorobutyric acid (HFBA) and perfluorooctanoic acid (PFOA) in aqueous solutions in a flow-through microwave photoreactor (MW/Photo) containing 20 such MDGELs. A conventional single rod-shaped microwave discharge electrodeless lamp (MDEL) and a low-pressure electrode Hg lamp were also used to compare the performance of these novel MDGELs. The dominant performance of the MDGELs was established by the defluorination kinetics per surface area of the light source immersed in the solutions and by the applied electric power of the lamps. At pH 10, the kinetics correlated with the carbon chain length and with the number of C-F bonds in the three fluorinated acids. Microwave irradiation of the single rod-shaped MDEL device achieved a defluorination level of 51% (TFA), 67% (HFBA), and 37% (PFOA) for a 240-min VUV/UV irradiation of solutions at initial pHs = 4.7-5.2, whereas at pH = 10 defluorination of TFA and HFBA was 100% complete within 120-135 min of irradiation: defluorination of PFOA was ca. 80% complete after 200 min. With the 20 MDGEL system, 100% defluorination of TFA and HFBA was achieved after 105 min, whereas 100% defluorination of PFOA required ca. 400 min of irradiation. A decomposition/defluorination pathway is described for PFOA on the basis of intermediates identified by LC-MS techniques that involved initial VUV/UV irradiation (185 nm and 254 nm) of the PFOA contaminant followed by subsequent losses of CO2 and -CF2 units to complete defluorination and degradation. (C) 2011 Elsevier B.V. All rights reserved.