Multifunctional vesicular coacervates as engineered supramolecular solvents for wastewater treatment

Ribbon-shaped supramolecular solvents: Synthesis, characterization and potential for making greener the microextraction of water organic pollutants

Liquid-liquid microextraction (LLME) techniques have experienced a tremendous growth over the last years but still face major challenges related to the use of more efficient and environmentally friendly solvents. Supramolecular solvents (SUPRASs) have proved outstanding efficiency in LLME, but many of the experimental conditions required for SUPRAS formation and/or application cannot be considered green or experimentally convenient. This paper was intended to make greener both SUPRAS formation and their application to the LLME of low-concentration organic pollutants in environmental waters. For this purpose, a variety of SUPRASs were produced at room temperature by simply mixing alkyl phosphonates (A_6-12PO₃H^- and A_6-12PO₃^-2) and tetrahexylammonium (He₄N⁺) ions in aqueous media. Among them, the SUPRASs produced from decyl hydrogen phosphonate (DePO₃H^-) and He₄N⁺ allowed, for the first time, the development of SUPRAS-based LLMEs where the SUPRAS previously synthesized was added to the liquid sample, instead of being formed in situ as usual, which was proved particularly advantageous for analyses involving large sample/SUPRAS volume ratios. At near equimolar amounts of DePO₃H^- and He₄N⁺, the amphiphile arranged in the SUPRAS as planar ribbons consisting of water (21 ± 3%, w/v) and DePO₃H^- and He₄N⁺ in the concentration range 1.0-1.4 M. The application of these SUPRASs to LLMEs was proved by extracting carcinogenic polycyclic aromatic hydrocarbons (CPAHs) from drinking (tap and bottled) and natural (river, reservoir and underground) water (recoveries between 84 and 117% with standard deviations varying between 1 and 14%). The developed method was simple (it only required the addition of 500 μL of SUPRAS to 75 mL of sample, stirring and centrifugation), sensitive (method quantitation limits were below the maximum allowed limits set by the EU; were 0.6-7.1 ng L^-1) and selective (SUPRAS extracts were directly analyzed by liquid chromatography-fluorimetry). This research proves that SUPRASs can be operationally used in LLMEs similarly to conventional solvents, which should favor their routine application in high-sample throughput laboratories.

An Overview of Coacervates: The Special Disperse State of Amphiphilic and Polymeric Materials in Solution

Individual amphiphiles, polymers, and colloidal dispersions influenced by temperature, pH, and environmental conditions or interactions between their oppositely charged pairs in solvent medium often produce solvent-rich and solvent-poor phases in the system. The solvent-poor denser phase found either on the top or the bottom of the system is called coacervate. Coacervates have immense applications in various technological fields. This review comprises a concise introduction, focusing on the types of coacervates, and the influence of different factors in their formation, structures, and stability. In addition, their physicochemical properties, thermodynamics of formation, and uses and multifarious applications are also concisely presented and discussed.

Double-headed amphiphile-based sponge droplets: synthesis, characterization and potential for the extraction of compounds over a wide polarity range

Supramolecular solvents (SUPRASs) are gaining momentum in the multi-residue analysis of liquid samples thanks to the delimited hydrophilic and hydrophobic microenvironments in their nanostructures. In this work, SUPRASs with increased hydrophilicity were synthesized with the aim of enhancing the extractability of polar compounds. For this purpose, a double-headed amphiphile, 1,2-decanediol, was self-assembled in hydro-organic media in the presence and absence of sodium chloride. The SUPRASs formed, characterized by scanning electron microscopy, consisted of sponge droplets made up of a highly convoluted three-dimensional (3D) network of amphiphile. The network contained interconnected bilayers that were intersected by similarly interconnected aqueous channels with high and nearly constant water content (∼30%, w/w). Both the inherently open structure of the sponge morphology and the increased hydrophilic-hydrophobic balance of the amphiphile, provided highly hydrophilic microenvironments into the aggregates that rendered in increased recovery factors for 15 perfluorinated compounds (PFCs, C₄-C₁₈, log P_ow values from 0.4 to 11.6) in natural waters. Extraction took 15 min without further clean-up or evaporation of extracts which were readily compatible with LC-MS/MS quantitation. Absolute recoveries for PFCs, at the level of a few ng L^-1, were in the range 70-120%, except for perfluoropentanoic acid (40%) and perfluorobutane sulfonic acid (51%). Detection limits for PFCs in water were in the range 0.01-0.02 ng L^-1, which allowed their determination in slightly polluted waters (0.07-2.33 ng L^-1). This work proves that hydrophilicity in SUPRASs can be tailored through the amphiphile and the morphology of their aggregates, and that this characteristic improves compound extractability in multi-residue analysis.

Trimeric Cationic Surfactant Coacervation as a Versatile Approach for Removing Organic Pollutants

A versatile method to remove a broad spectrum of dye pollutants from wastewater rapidly and efficiently is highly desirable. Here, we report that the complex coacervation of cationic trimeric imine-based surfactants (TISn) with negatively charged hydrolyzed polyacrylamide (HPAM) can be used for this purpose. The coacervation occurs in a wide concentration and composition range and requires the HPAM and TISn concentrations as low as 0.1 g/L and 0.1 mM, respectively. Dye effluents treated by trimeric surfactants and HPAM complete phase separation within 30 s under turbulent conditions, which generates an exceedingly small volume fraction (0.4%) of viscoelastic coacervate and a clear supernatant with a dye removal efficiency of up to 99.9% for anionic and neutral dyes in dosages of up to 120 mg/L. Crowded molecular arrangement and thick framework in coacervate are responsible for the rapid phase separation rate and low volume fraction. The trimeric imine surfactant/polymer coacervation provides a simple, effective, and sustainable approach for the rapid removal of dyes and other organic pollutants.

A rapid and simple method for the removal of dyes and organophosphorus pesticides from water and soil samples using deep eutectic solvent embedded sponge

A new treatment method using a deep eutectic solvent embedded melamine sponge (DES-MS) was studied for the removal of organic pollutants from water and soil samples. Five organophosphorus pesticides (OPPs) consisting of azinphos-methyl (AZP), parathion-methyl (PRT), fenitrothion (FNT), diazinon (DIZ) and chlorpyrifos (CPF), and two dyes including acid blue 29 (AB29) and malachite green (MG) were used as the model pollutants. DESs were easily prepared from tetrabutylammonium bromide (TBABr) and various fatty acids. The synthesised DESs were loaded into the sponge before being utilized for the removal of the studied pollutants. After the removal, the residual OPPs or dyes in the supernatant was quantified by high performance liquid chromatography or derivative spectrophotometry, respectively. The proposed method was simple, rapid, environmentally friendly and effective with the removal efficiency higher than 70% for various samples. Moreover, the removal of various dyes was successfully achieved with the efficiency greater than 65% under the optimum condition.

Twenty years of supramolecular solvents in sample preparation for chromatography: achievements and challenges ahead

Supramolecular solvents (SUPRAS) have progressively become a suitable alternative to organic solvents for sample preparation in chromatographic analysis. The inherent properties of these nanostructured solvents (e.g. different polarity microenvironments, multiple binding sites, possibility of tailoring their properties, etc.) offer multiple opportunities for the development of innovative sample treatment platforms not approachable by conventional solvents. In this review, major achievements attained in the combination SUPRAS-chromatography in the last 20 years as well as the challenges that should be addressed in the near future are critically discussed. Among achievements, particular attention is paid to the theoretical and practical knowledge gained that has helped make substantial progress in the area. In this respect, advances in the understanding of the mechanisms involved in SUPRAS formation and SUPRAS-solute interactions driving extractions are discussed, with a view to the setting up of knowledge-based extraction procedures. Likewise, the strategies followed to improve the compatibility of SUPRAS extracts with liquid and gas chromatography and adapt SUPRAS-based extractions to different formats are presented. Ongoing efforts to apply SUPRAS in multicomponent extractions and synthesize tailored SUPRAS for the development of innovative sample treatments are highlighted. Among challenges identified, discussion is focused on the automation of SUPRAS-based sample treatment and the elucidation of SUPRAS nanostructures, which are considered essential for their acceptance in routine labs and the design of tailored SUPRAS with programmed functions. Graphical abstract.

Vesicle based ultrasonic-assisted extraction of saponins in Panax notoginseng

A simple and effective vesicle based ultrasonic-assisted extraction (UAE) method was developed for extraction of active compounds in functional food. The target analytes were determined by ultra-high performance liquid chromatography with ultraviolet detector. Surfactant vesicle was adopted as extraction solvent. Different operating conditions including the type and concentration of vesicle, extraction time and solid to liquid ratio were investigated by single-factor experiments and response surface methodology. Optimized experimental conditions were 1% (w/v) of DTAB/SDS vesicle, 20 min of extraction time and 160 mg/mL of solid to liquid ratio. The proposed method provided good linearity in the linear range of 10-1000 μg/mL with regression coefficients larger than 0.999, low limits of detection of 27.64-55.67 ng/mL, good precision with relative standard deviations below 0.35%, and satisfactory recoveries of 83.84-90.92% for tested saponins. Consequently, the proposed vesicle based UAE method was well suited for the extraction of saponins in Panax notoginseng.