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首页> 外文期刊>RSC Advances >Water sorption properties of room-temperature ionic liquids over the whole range of water activity and molecular states of water in these media
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Water sorption properties of room-temperature ionic liquids over the whole range of water activity and molecular states of water in these media

机译：在这些介质中，在整个水活度和水分子状态的整个范围内，室温离子液体的吸水特性

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摘要

The water sorption behavior for various RTILs ([C(4)C(1)im][BF4], [C(4)C(1)im][PF6], [C(6)C(1)im][PF6], [C(4)im][DBP], [C(4)im][BEHP] and [Et3HN][CF3SO3]) was studied over the whole range of water activity using a continuous gravimetric method. Analysis of the water sorption isotherms using the non-random two-liquid model (NRTL) and the combination of a dual-mode sorption (Henry-clustering) allowed a better understanding of the RTIL-water interactions. It is noticed that the sorption of water by RTILs is mainly controlled by the anion's nature. Anions interact with water molecules by hydrogen bonds that promotes the formation of a hydrogen bond network between the water molecules. The water uptake by RTILs increases in the following order (up to 0.8 in the water activity a): [C(6)C(1)im][PF6] <= [C(4)C(1)im][PF6] < [C(4)C(1)im][BF4] approximate to [C(4)im][BEHP] < [Et3HN][CF3SO3] <= [C(4)im][DBP]. The [PF6]-based RTILs show the lowest water uptake (low affinity with water; water-immiscible RTILs), whereas [C(4)C(1)im][BF4] and [C(4)im][BEHP] and especially [C(4)im][DBP] and [Et3HN][CF3SO3] exhibit high water uptake (high affinity with water; water-miscible RTILs). At high activity (a > 0.8), water molecules are aggregated only in water-miscible RTILs (case of [C(4)im][DBP] and [Et3HN][CF3SO3]) because of their stronger anion basicity. To complete the sorption study, the molecular state of water dissolved in RTILs was studied by the infrared spectroscopy. The water molecules dissolved in water-immiscible RTIL such as [C(4)C(1)im][PF6] are not self-associated independently of the water content and, thus, can be defined as "free" water molecules interacting via H-bonding with the anions in the symmetric complex: anion/HOH/anion. On the contrary, the water molecules sorbed in water-miscible RTILs such as [C(4)im][DBP] or [Et3HN][CF3SO3] are strongly associated by H-bonds and also with the anions even at low water activity, and are easily aggregated when the water content reaches the critical concentration at high activity.
机译：各种RTIL（[C（4）C（1）im] [BF4]，[C（4）C（1）im] [PF6]，[C（6）C（1）im] [ [PF6]，[C（4）im] [DBP]，[C（4）im] [BEHP]和[Et3HN] [CF3SO3]）使用连续重量法研究了整个水分活度范围。使用非随机两液模型（NRTL）和双模式吸附（亨利聚类）的组合对水吸附等温线进行分析，可以更好地理解RTIL与水的相互作用。注意到RTILs对水的吸附主要受阴离子的性质控制。阴离子通过氢键与水分子相互作用，从而促进水分子之间形成氢键网络。 RTIL的吸水量按以下顺序增加（在水活度a中最高为0.8）：[C（6）C（1）im] [PF6] <= [C（4）C（1）im] [PF6 ] <[C（4）C（1）im] [BF4]近似于[C（4）im] [BEHP] <[Et3HN] [CF3SO3] <= [C（4）im] [DBP]。基于[PF6]的RTIL显示出最低的吸水率（与水的亲和力低;与水不混溶的RTIL），而[C（4）C（1）im] [BF4]和[C（4）im] [BEHP]特别是[C（4）im] [DBP]和[Et3HN] [CF3SO3]表现出高吸水率（与水具有高亲和力;与水混溶的RTIL）。在高活性下（a> 0.8），水分子仅在与水混溶的RTIL（[C（4）im] [DBP]和[Et3HN] [CF3SO3]的情况下）聚集，因为它们具有更强的阴离子碱性。为了完成吸附研究，通过红外光谱研究了溶解在RTILs中的水的分子状态。溶解在与水不混溶的RTIL中的水分子，例如[C（4）C（1）im] [PF6]，不与水含量无关地自缔合，因此可以定义为“自由”水分子通过与对称络合物中的阴离子进行氢键结合：阴离子/ HOH /阴离子。相反，吸附在与水混溶的RTIL中的水分子，例如[C（4）im] [DBP]或[Et3HN] [CF3SO3]，即使在低水活度下也通过氢键强烈地与阴离子缔合，当水分在高活性下达到临界浓度时，容易聚集。

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