Heavy Metal Extraction under Environmentally Relevant Conditions Using 3-Hydroxy-2-Naphthoate- Based Ionic Liquids: Extraction Capabilities vs. Acute Algal Toxicity

We investigated the applicability of three task-specific ionic liquids (ILs) as heavy metal extracting agents by contrasting extraction capabilities with algal toxicity. The compounds tested were trihexyltetradecylphosphonium-, methyltrioctylphosphonium- and methyltrioctylammonium 3-hydroxy-2-naphthoates. Experiments were performed to assess if these ILs can provide environmentally safe residual concentrations of the target metals after extraction. Both pure water and natural mineral water samples were spiked with 20 mu g L-1 of Cu, Ag, Cd, Hg and Pb, respectively. Quantitative extraction (> 99%) of Hg and Ag was achieved. Cu and Hg were below the respective no-observed-effect-concentrations (NOECs) after extraction and Ag below 0.03 mu g L-1. Acute toxicity assays were conducted using two freshwater green algae Raphidocelis subcapitata and Tetradesmus obliquus. Growth inhibition and maximum photochemical quantum yield of photosystem II after 72 h were assessed. ILs were less toxic than similar compounds, but still must be classified as acute toxicants for algae. An inhibiting effect on both growth and chlorophyll fluorescence was observed. The leaching of the ILs into the samples remains a limitation regarding their environmental-friendly applicability. Nonetheless, the extremely efficient removal of Cu, Ag and Hg under environmentally relevant conditions calls for further research, which should focus on the immobilization of the ILs

Schwermetallextraktion mithilfe von in Hohlfasern immobilisierten auf Aliquat® 336 und Cyphos® IL 101 basierenden ionischen Flüssigkeiten

Die Schwermetallbelastung von Gewässern aufgrund des Eintrags aus anthropogenen Quellen stellt weltweit ein großes Umweltproblem dar. Folglich werden neue, erfolgreiche Methoden zur besseren Analyse und Entfernung ebendieser benötigt. Die nur aus Ionen bestehenden, unter 100°C, jedoch meist bereits bei Raumtemperatur flüssigen Salze, welche als ionische Flüssigkeiten (IL) bezeichnet werden, konnten bereits erfolgreich als Alternative zu traditionellen Extraktionsmitteln eingesetzt werden.Ein großes Problem vieler IL, welches ihren Einsatz stark beeinträchtigt, ist jedoch ihr teilweise starkes Leaching in die wässrige Phase. Die Immobilisierung von ILs ist eine mögliche Umgehung dieser Problematik. Die hier vorgestellte Methode der Immobilisierung besteht aus dem Einschluss der IL in Hohlfasern aus Polypropylen, deren Poren es erlauben, Metallionen aus wässrigen Lösungen in die IL diffundieren zu lassen, ohne ein starkes Leaching der IL in die wässrige Phase zu ermöglichen. Ziel der vorliegenden Arbeit war es, Hohlfasern mit ausgewählten ILs zu füllen und ihre Extraktionseffizienz von umwelttoxisch relevanten Metallen und das Leaching der ionischen Flüssigkeiten in die wässrige Phase zu untersuchen. Die quantitative Analyse der Metalle erfolgte dabei durch Flammen- sowie Graphitofen-Atomabsorptionsspektrometrie. Das Leaching der Flüssigkeiten in die wässrige Phase während der Extraktion wurde durch die Bestimmung des organischen Kohlenstoffes (TOC/DOC) mittels eines TOC-Analyzers ermittelt. Es konnte gezeigt werden, dass der Einschluss der ILs in Hohlfasern im Vergleich zu flüssig-flüssig Extraktionen zur gewünschten Verringerung des Leachings führt und gleichzeitig ebenfalls eine erfolgreiche Extraktion gewährleistet wird. Für jedes Metall konnte mindestens eine IL gefunden werden, welche sich durch eine sehr gute Extraktionseffizienz auch bei Anwesenheit störender Ionen in künstlichen Trinkwasserproben auszeichnet.The pollution of waterbodies with heavy metals from anthropogenic sources is a large environmental problem worldwide. Therefore, new and effective methods for a better analysis and removal of these pollutants are required. As shown in various publications, ionic liquids (IL), which are salts solely consisting of ions that are liquid under 100°C, could be used as a working alternative to traditional extracting agents. A huge drawback of many ILs, lowering their usability, however is the leaching into the aqueous phase. Immobilizing ILs is one way of eliminating this problem. The used method of immobilization may consist of the inclusion of IL inside polypropylene hollow fibers, whose pores are able to let metal ions diffuse from the aqueous solution into the IL while reducing the leaching of the IL back into the solution. The aim of this master thesis was to fill hollow fibers with selected ILs and analyse the ability of extracting environmentally toxic heavy metals while keeping the leaching to a minimum. Quantitative analysis was carried out by flame and graphite furnace atomic absorption spectroscopy. Leaching was measured as the content of organic carbon in solution after the extraction by means of a TOC-analyzer. The obtained results show that the inclusion of IL inside the fibers could reduce the leaching compared to liquid-liquid extractions while additionally guaranteeing a successful extraction of metals. Furthermore, for each metal at least one ionic liquid with good extraction efficiency - even in presence of competitive ions in artificial drinking water – could be found

Novel 3-Hydroxy-2-Naphthoate-Based Task-Specific Ionic Liquids for an Efficient Extraction of Heavy Metals

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

Solvent Bar Micro-Extraction of Heavy Metals from Natural Water Samples Using 3-Hydroxy-2-Naphthoate-Based Ionic Liquids

Developments in the liquid micro-extraction of trace metals from aqueous phases have proven to be limited when extended from pure water to more complex and demanding matrices such as sea water or wastewater treatment effluents. To establish a system that works under such matrices, we successfully tested three task-specific ionic liquids, namely trihexyltetradecyl- phosphonium-, methyltrioctylphosphonium- and methyltrioctylammonium 3-hydroxy-2-naphthoate in two-phase solvent bar micro-extraction (SBME) experiments. We describe the influence of pH, organic additives, time, stirring rate and volume of ionic liquid for multi-elemental micro-extraction of Cu, Ag, Cd and Pb from various synthetic and natural aqueous feed solutions. Highest extraction for all metals was achieved at pH 8.0. Minimal leaching of the ionic liquids into the aqueous phase was demonstrated, with values < 30 mg L−1 DOC in all cases. Sample salinities of up to 60 g L−1 NaCl had a positive effect on the extraction of Cd, possibly due to an efficient extraction mechanism of the present chlorido complexes. In metal-spiked natural feed solutions, the selected SBME setups showed unchanged stability under all conditions tested. We could efficiently (≥85%) extract Cu and Ag from drinking water and achieved high efficacies for Ag and Cd from natural sea water and hypersaline water, respectively. The method presented here proves to be a useful tool for an efficient SBME of heavy metals from natural waters without the need to pretreat or modify the sample

Data_Sheet_1_Novel 3-Hydroxy-2-Naphthoate-Based Task-Specific Ionic Liquids for an Efficient Extraction of Heavy Metals.DOCX

<p>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.</p

Novel 3-Hydroxy-2-Naphthoate-Based Task-Specific Ionic Liquids for an Efficient Extraction of Heavy Metals

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.© 2018 Pirkwieser, López-López, Kandioller, Keppler, Moreno and Jirs

Solvent Bar Micro-Extraction of Heavy Metals from Natural Water Samples Using 3-Hydroxy-2-Naphthoate-Based Ionic Liquids

Developments in the liquid micro-extraction of trace metals from aqueous phases have proven to be limited when extended from pure water to more complex and demanding matrices such as sea water or wastewater treatment effluents. To establish a system that works under such matrices, we successfully tested three task-specific ionic liquids, namely trihexyltetradecyl- phosphonium-, methyltrioctylphosphonium- and methyltrioctylammonium 3-hydroxy-2-naphthoate in two-phase solvent bar micro-extraction (SBME) experiments. We describe the influence of pH, organic additives, time, stirring rate and volume of ionic liquid for multi-elemental micro-extraction of Cu, Ag, Cd and Pb from various synthetic and natural aqueous feed solutions. Highest extraction for all metals was achieved at pH 8.0. Minimal leaching of the ionic liquids into the aqueous phase was demonstrated, with values < 30 mg L−1 DOC in all cases. Sample salinities of up to 60 g L−1 NaCl had a positive effect on the extraction of Cd, possibly due to an efficient extraction mechanism of the present chlorido complexes. In metal-spiked natural feed solutions, the selected SBME setups showed unchanged stability under all conditions tested. We could efficiently (≥85%) extract Cu and Ag from drinking water and achieved high efficacies for Ag and Cd from natural sea water and hypersaline water, respectively. The method presented here proves to be a useful tool for an efficient SBME of heavy metals from natural waters without the need to pretreat or modify the sample.© 2018 by the author