Naflon perfluorinated membranes treated in Fenton media: radical species detected by ESR spectroscopy
Naflon perfluorinated membranes treated in Fenton media: radical species detected by ESR spectroscopy
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DOI：
10.1021/jp037519c
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发表时间：
2004-04-08
影响因子：
3.3
通讯作者：
Schlick, S
中科院分区：
文献类型：
--
作者：
Bosnjakovic, A;Schlick, S
采用ESR波谱法检测和鉴定了全氟磺酸全氟膜在基于Ti 3+（TiCl 3 + H2 O2）的芬顿试剂作用下的自由基。该方法允许监测反应期间来自Ti 3+的ESR信号的消失。最初形成的自由基是HOO。在200 K时，磁参数g（1）= 2.0261，g（2）= 2.0088，g（3）= 2.0031（g（iso）= 2.0127），a（1）= 5 G。在220 K以上，这个自由基的消失伴随着过氧自由基TiOO的混合物的出现。和超氧自由基O-2（-）。在300 K时，g张量分量为g（1）= 2.0190 '，g（2）= 2.0092，g（3）= 2.0036（g（iso）= 2.0106）。在被过氧化氢溶液溶胀的样品中，来自TiOO的信号。在200 K时，g-张量分量g（1）= 2.0228，g（2）= 2.0092，g（3）= 2.0046（g（iso）= 2.0122）。一个动力学过程导致平均的g各向异性的TiO O。自由基的温度范围为220-320 K。动力学机制被确定为“立方跳跃”模型：O-O片段绕着一个与g张量的主方向倾斜相等的轴旋转。大约14天后，在稍微干燥的样品中出现宽信号（线宽约为84 G，g = 2.0023），并且在92天后强度增加;该信号被认为代表氟化烷基自由基，其通过氧自由基攻击聚合物链而形成。在芬顿试剂（在不存在Nafion的情况下）中，仅对高浓度的过氧化氢（30%w/v）检测到自由基。形成的自由基不太稳定，过氧自由基TiOO。是唯一在200 K及以上温度下检测到的物种。Nafion膜的存在对形成的自由基的类型和它们的热稳定性都有重要影响。
ESR spectroscopy was used to detect and identify radicals in Nafion perfluorinated membranes exposed to the Fenton reagent based on Ti3+ (TiCl3 + H2O2). This method allowed monitoring the disappearance of the ESR signal from Ti3+ during reaction. The initially formed radical was HOO., with magnetic parameters g(1) = 2.0261, g(2) = 2.0088, g(3) = 2.0031 (g(iso) = 2.0127), and a(1) = 5 G at 200 K. The disappearance of this radical above 220 K was accompanied by the appearance of a mixture of peroxy radicals TiOO. and superoxide radicals O-2(-). The O-2(-) radicals were observed only in the dry Nafion after treatment and were stable up to 370 K, the g-tensor components are g(1) = 2.0190', g(2) = 2.0092, and g(3) = 2.0036 (g(iso) = 2.0106) at 300 K. In samples swollen by the hydrogen peroxide solution, signals from the TiOO. radicals predominated, with g-tensor components g(1) = 2.0228, g(2) = 2.0092, and g(3) = 2.0046 (g(iso) = 2.0122) at 200 K. A dynamical process lead to averaging of the g anisotropy of TiOO. radicals in the temperature range 220-320 K. The dynamics mechanism was identified with the "cubic jump" model: rotation of the O-O fragment about an axis equally inclined to the principal directions of the g tensor. A broad signal (line width approximate to 84 G, g = 2.0023) appeared in slightly dried samples after approximate to 14 days and increased in intensity after 92 days; this signal is thought to represent fluorinated alkyl radicals, formed by attack of oxygen radicals on the polymer chain. In the Fenton reagent (in the absence of Nafion) radicals are detected only for high concentrations of hydrogen peroxide, 30% w/v. In addition, the HOO. radicals formed are less stable, and the peroxy radicals TiOO. are the only species detected at and above 200 K. The presence of the Nafion membranes has important effects on both the type of radicals formed and their thermal stability.