Ionic liquids (ILs) are per definition salts with melting points below 100°C and might be green alternatives for the extraction of heavy metals from aqueous solutions due to their favorable environmental and physico-chemical properties. Partial solution during extraction, so-called leaching, however, limits their applicability. The present study synthesizes three novel ammonium and phosphonium ILs based on 3-hydroxy-2-naphthoic acid-trihexyltetradecylphosphonium-([P66614]), methyltrioctylphosphonium-([P1888]), and methyltrioctylammonium 3-hydroxy-2-naphthoate ([N1888][HNA])-by a deprotonation-metathesis route. The aims were to improve stability during extraction while still achieving high selectivity toward heavy metal ions, as well as to study the impact of different alkyl chains and the central atom of the cation on physico-chemical properties, extraction efficacy, and leaching. Extraction capabilities for the seven heavy metals Ag, Cd, Co, Cu, Mn, Ni, and Pb were studied in pure water at pH 8.0. Further experiments were conducted in water containing 30 g L-1 NaCl to simulate a seawater matrix and/or 30 mg L-1 humic acids, as well as metal-spiked natural water samples. All three ILs showed extraction efficacies ≥90% for Cu and Pb after 24 h. Overall, extraction efficacies for Ag, Cd, Cu, and Pb were highest for drinking water samples. Ag and Cd extraction was increased by up to 41% in (hyper-) saline samples using IL [P66614][HNA] compared with pure water samples. Leaching values were reduced down to 0.07% loss of the applied IL, which can be attributed to the hydrophobic character of 3-hydroxy-2-naphthoate. Our results represent a positive development toward a greener extraction of heavy metals from natural waters.

中文翻译：

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用于高效萃取重金属的新型 3-羟基-2-萘甲酸盐基特定任务离子液体。


离子液体 (IL) 根据定义是熔点低于 100°C 的盐，由于其有利的环境和物理化学特性，可能成为从水溶液中提取重金属的绿色替代品。然而，提取过程中的部分溶液，即所谓的浸出，限制了它们的适用性。本研究基于3-羟基-2-萘甲酸-三己基十四烷基鏻-([P66614])、甲基三辛基鏻-([P1888])和甲基三辛基铵3-羟基-2-萘甲酸盐([N1888])合成了三种新型铵和鏻离子液体。 [HNA])-通过去质子化-复分解途径。目的是提高提取过程中的稳定性，同时仍然实现对重金属离子的高选择性，以及研究不同烷基链和阳离子中心原子对物理化学性质、提取效率和浸出的影响。研究了在 pH 8.0 的纯水中对 Ag、Cd、Co、Cu、Mn、Ni 和 Pb 七种重金属的萃取能力。在含有 30 g L-1 NaCl 的水中进行了进一步的实验，以模拟海水基质和/或 30 mg L-1 腐殖酸，以及添加金属的天然水样。 24 小时后，所有三种离子液体对 Cu 和 Pb 的提取效率均≥90%。总体而言，饮用水样品中 Ag、Cd、Cu 和 Pb 的提取效率最高。与纯水样品相比，使用 IL [P66614][HNA] 将（高）盐水样品中的 Ag 和 Cd 提取率提高了 41%。所用 IL 的浸出值降低至 0.07%，这可归因于 3-羟基-2-萘甲酸酯的疏水特性。我们的结果代表了从天然水中更环保地提取重金属的积极进展。