Polymer inclusion membranes for the separation, speciation and monitoring of inorganic pollutants in natural waters

ENG- Polymer inclusion membranes (PIMs) are a type of functionalized membrane mainly composed of an extractant embedded in a polymeric matrix. These membranes are easy to prepare and are highly versatile, enabling the separation of a wide range of analytes. This thesis has focused on the development of PIMs for both environmental and analytical purposes. On the one hand, the membrane composition has been optimized to enable the removal of inorganic pollutants from natural waters or industrial effluents. On the other hand, the thesis has investigated the use of PIMs as sensors to both assess metal complexation in natural waters, and to be used as passive samplers for the evaluation of metal pollution in rivers. Moreover, in light of current global challenges, particular emphasis has been placed on integrating sustainability principles into the design of PIM-based systems. This includes exploring the use of cost-effective and non-toxic alternatives for PIMs manufacturing, as well as developing novel functionalized membranes with better stability to reduce the environmental impact. In a first stage, PIMs were prepared using commercial reagents, such as the extracting agent Aliquat 336, the plasticizer tributyl phosphate (TBP), and cellulose triacetate (CTA) as the base polymer. These PIMs were investigated for the removal of fluoride from natural waters. It was demonstrated that the addition of TBP enhanced the performance of the PIMs compared to other plasticizers. Furthermore, the developed PIMs proved effective in removing fluoride from natural water samples, reducing its concentration to levels that comply with World Health Organization standards. Moreover, the preparation of functionalized membranes with enhanced sustainability has been investigated. In one approach, the plasticizer butyl stearate (BTS) was explored, for the first time, as a component for PIMs, offering a more environmentally friendly and cost-effective alternative to common reagents. In this case, PIMs were prepared using the polymers CTA and polyvinyl chloride (PVC), incorporating a task-specific ionic liquid as an extractant specifically designed to extract Hg, and different plasticizers. The measured properties of the PIMs containing BTS, such as hydrophilicity and mechanical properties, and the transport efficiencies of CTA-based PIMs, were within the range of those of PIMs with the other plasticizers tested. Thus, given the low cost and minimal environmental impact of BTS, it is an attractive alternative to consider for manufacturing PIMs. Additionally, the possibility of using polymerizable ionic liquids (PILs) based on the imidazolium cation to produce stable membranes has been explored for the first time. The membrane containing the PIL 1-hexyl-3-(4-vinylbenzyl)-1H-imidazol-3-ium bis((trifluoromethyl)sulfonyl)amide was shown to effectively remove Cr(VI). The remarkable stability of the PIL-based membrane was demonstrated by its high reusability, with only a 15% decrease in the recovery efficiency after 18 cycles. Finally, this novel membrane was successfully employed for the recovery of Cr(VI) from industrial effluent waters, highlighting its potential to contribute to the development of a sustainable system for the removal and recovery of hexavalent chromium. To advance the analytical applications of PIMs, a membrane incorporating the extractant di(2-ethylhexyl)phosphoric acid has been proposed as both a tool for speciation studies of metal complexation and a passive sampler for metal monitoring. First, laboratory experiments demonstrated that the accumulation of Zn and Cu in the receiving phase of the PIM sensor depended on the concentration of free metal ions in the donor phase. Finally, the aforementioned PIM was investigated as a passive sampler for determining the time-weighted average (TWA) concentrations of free Zn in Catalan rivers. To achieve this, a novel calibration approach was described, based on kinetic studies conducted at the specific sampling point under investigation. The resulting calibration enabled the determination of TWA-free Zn concentrations in the Osor River. Furthermore, PIM-passive samplers were employed as a screening tool to detect Zn contamination in the waters of other Catalan rivers, revealing no evidence of pollution by this metal