Non-ionic deep eutectic solvents for membrane formation

Effect of Choline Chloride-Based DES on the Pore-Forming Ability and Properties of PVDF Membranes Prepared with Triethyl Phosphate as Green Solvent

This study explores the influence of various additives on the morphological, chemical, and thermal properties of poly(vinylidene fluoride) (PVDF) membranes prepared via the non-solvent induced phase separation (NIPS) technique. The use of a green solvent such as triethyl phosphate (TEP) was shown to be successful. A particular focus was dedicated to pore formers based on choline chloride-based deep eutectic solvents (DES) in combination with ethylene glycol and glycerol, i.e., ChCl/EG and ChCl/GLY, and its benchmark with traditional counterparts such as poly(ethylene glycol) (PEG) and glycerol (GLY). Comprehensive characterization was conducted using FESEM, FTIR, XRD, and DSC techniques to evaluate changes in membrane morphology, porosity, and crystallinity. PEG acted as a pore-forming agent, transitioning the internal structure from spherulitic to sponge-like with consistent pore sizes, while GLY produced a nodular morphology at higher concentrations due to increased dope solution viscosity. DES induced significant shifts in crystalline phase composition, decreasing α-phase fractions and promoting β-phase formation at higher concentrations. While the overall porosity remained unaffected by the addition of GLY or PEG, it was dependent on the DES concentration in the dope at lower values than those obtained by GLY and PEG. Membrane pore size with ChCl/GLY was lower than with ChCl/EG and GLY. All membranes showed performance at the hydrophobic regime. The findings demonstrate that ChCl/EG and ChCl/GLY can tailor the structural and thermal properties of TEP-driven PVDF membranes, providing a green and versatile approach to customize the membrane properties for specific applications.

Filling the gaps: Introducing plasticizers into π-conjugated OPE-NH2 Langmuir layers for defect-free anisotropic interfaces and membranes towards unidirectional mass, charge, or energy transfer

The construction of ultrathin membranes from linearly aligned π-electron systems is advantageous for targeted energy, charge, or mass transfer. The Langmuir-Blodgett (LB) technique enables the creation of such membranes, especially with amphiphilic π-electron systems. However, these systems often aggregate, forming rigid Langmuir monolayers with defects or holes. In this study we introduce plasticizers to effectively address this issue. To create anisotropic membranes, we used an oligo(phenylene ethynylene) derivative (OPE-NH2) as an linear amphiphile and bisphenol A di-tert-butyl ester (BPAE) as a plasticizer. We analyzed surface pressure (mean molecular area) (Π(mma)) isotherms and characterized Langmuir monolayers with Brewster Angle Microscopy (BAM), to determine the optimal miscibility of OPE-NH2 with BPAE. Detailed analysis of hole areas filled was performed through image binarization. We identified an optimal BPAE concentration of 4 mol-% in the OPE-NH2 Langmuir monolayer. Our BAM image evaluation via binarization determined the difference between the mean molecular areas of close-packed Langmuir domains and those quantified via the Π(mma) isotherm. This study presents an automated method for BAM image analysis and a new approach for fabricating defect-free anisotropic molecular monolayers of π-conjugated amphiphiles.

Synergistic effects of deep eutectic solvents on the morphology and performance of polysulfone ultrafiltration membranes

This study investigates the synthesis of flat sheet asymmetric Polysulfone (PSF) membranes using the Non-Solvent Induced Phase Separation (NIPS) method, enhanced by incorporating Deep Eutectic Solvents (DES) composed of Choline Chloride (ChCl) and DL-Malic Acid (MA). The research explores the individual and combined effects of ChCl and MA on membrane morphology and performance. Comprehensive characterization techniques, including Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy-Universal Attenuated Total Reflectance (FTIR-UATR), and Atomic Force Microscopy (AFM), were employed to analyze the structural and surface properties of the membranes. Key performance metrics such as Pure Water Permeability (PWP), protein and dye rejection, fouling behavior, porosity, surface hydrophilicity, and mechanical strength were evaluated. Results demonstrated that integrating DES into the PSF matrix significantly improved membrane properties. The 3% DES membrane exhibited the highest Pure Water Permeability (PWP) of 186.82 L/m2h/bar, the lowest water contact angle of 68.8°, and optimal balance in surface roughness parameters, leading to superior antifouling properties with high flux recovery ratio (FRR) and balanced reversible (Rr) and irreversible fouling (Rir) components. The ChCl (HBA) membrane displayed a notable PWP of 121.62 L/m2h/bar, large pore sizes (42.72 nm), and moderate surface roughness (Ra of 3.32 nm). In contrast, the MA (HBD) membrane demonstrated the highest hydrophilicity with the lowest contact angle (70.7°) and a compact, robust structure, despite its smallest pore sizes and lack of permeability. The findings underscore the synergistic effect of DES formation in the membrane, improving overall performance for ultrafiltration applications. This study provides valuable insights into the distinct roles of ChCl as an HBA and MA as an HBD in DES-modified PSF membranes, revealing their individual contributions and the importance of optimizing DES components and concentrations for specific filtration applications.

A Review on the Application of Deep Eutectic Solvents in Polymer-Based Membrane Preparation for Environmental Separation Technologies

The use of deep eutectic solvents (DESs) for the preparation of polymer membranes for environmental separation technologies is comprehensively reviewed. DESs have been divided into five categories based on the hydrogen bond donor (HBD) and acceptor (HBA) that are involved in the production of the DESs, and a wide range of DESs' physicochemical characteristics, such as density, surface tension, viscosity, and melting temperature, are initially gathered. Furthermore, the most popular techniques for creating membranes have been demonstrated and discussed, with a focus on the non-solvent induced phase separation (NIPS) method. Additionally, a number of studies have been reported in which DESs were employed as pore formers, solvents, additives, or co-solvents, among other applications. The addition of DESs to the manufacturing process increased the presence of finger-like structures and macrovoids in the cross-section and, on numerous occasions, had a substantial impact on the overall porosity and pore size. Performance data were also gathered for membranes made for various separation technologies, such as ultrafiltration (UF) and nanofiltration (NF). Lastly, DESs provide various options for the functionalization of membranes, such as the creation of various liquid membrane types, with special focus on supported liquid membranes (SLMs) for decarbonization technologies, discussed in terms of permeability and selectivity of several gases, including CO2, N2, and CH4.

Adsorptive Membranes Incorporating Ionic Liquids (ILs), Deep Eutectic Solvents (DESs) or Graphene Oxide (GO) for Metal Salts Extraction from Aqueous Feed

Water scarcity is a significant concern, particularly in arid regions, due to the rapid growth in population, industrialization, and climate change. Seawater desalination has emerged as a conventional and reliable solution for obtaining potable water. However, conventional membrane-based seawater desalination has drawbacks, such as high energy consumption resulting from a high-pressure requirement, as well as operational challenges like membrane fouling and high costs. To overcome these limitations, it is crucial to enhance the performance of membranes by increasing their efficiency, selectivity, and reducing energy consumption and footprint. Adsorptive membranes, which integrate adsorption and membrane technologies, offer a promising approach to address the drawbacks of standalone membranes. By incorporating specific materials into the membrane matrix, composite membranes have demonstrated improved permeability, selectivity, and reduced pressure requirements, all while maintaining effective pollutant rejection. Researchers have explored different adsorbents, including emerging materials such as ionic liquids (ILs), deep eutectic solvents (DESs), and graphene oxide (GO), for embedding into membranes and utilizing them in various applications. This paper aims to discuss the existing challenges in the desalination process and focus on how these materials can help overcome these challenges. It will also provide a comprehensive review of studies that have reported the successful incorporation of ILs, DESs, and GO into membranes to fabricate adsorptive membranes for desalination. Additionally, the paper will highlight both the current and anticipated challenges in this field, as well as present prospects, and provide recommendations for further advancements.

Total biflavonoids extraction from Selaginella chaetoloma utilizing ultrasound-assisted deep eutectic solvent: Optimization of conditions, extraction mechanism, and biological activity in vitro

In this study, the deep eutectic solvent based ultrasound-assisted extraction (DES-UAE) was investigated for the efficient and environmentally friendly extraction of Selaginella chaetoloma total biflavonoids (SCTB). As an extractant for optimization, tetrapropylaminium bromide-1,4-butanediol (Tpr-But) was employed for the first time. 36 DESs were created, with Tpr-But producing the most effective results. Based on response surface methodology (RSM), the greatest extraction rate of SCTB was determined to be 21.68 ± 0.78 mg/g, the molar ratio of HBD to HBA was 3.70:1, the extraction temperature was 57 °C, and the water content of DES was 22 %. In accordance with Fick's second rule, a kinetic model for the extraction of SCTB by DES-UAE has been derived. With correlation coefficients 0.91, the kinetic model of the extraction process was significantly correlated with the general and exponential equations of kinetics, and some important kinetic parameters such as rate constants, energy of activation and raffinate rate were determined. In addition, molecular dynamics simulations were used to study the extraction mechanisms generated by different solvents. Comparing the effect of several extraction methods on S.chaetoloma using ultrasound-assisted extraction and conventional methods, together with SEM examination, revealed that DES-UAE not only saved time but also enhanced SCTB extraction rate by 1.5-3 folds. SCTB demonstrated superior antioxidant activity in three studies in vitro. Furthermore, the extract could suppress the growth of A549, HCT-116, HepG2, and HT-29 cancer cells. Alpha-Glucosidase (AG) inhibition experiment and molecular docking studies suggested that SCTB exhibited strong inhibitory activity against AG and potential hypoglycemic effects. The results of this study indicated that a Tpr-But-based UAE method was suitable for the efficient and environmentally friendly extraction of SCTB, and also shed light on the mechanisms responsible for the increased extraction efficiency, which could aid in the application of S.chaetoloma and provide insight into the extraction mechanism of DES.

Low-condensed lignin and high-purity cellulose production from poplar by synergistic deep eutectic solvent-hydrogenolysis pretreatment

This paper presented a green and environmentally friendly method to obtain lignin with a structure similar to milled wood lignin (MWL) and high-purity cellulose from biomass in a two-step process. The first step, maleic acid (MA), choline chloride (ChCl), and ethylene glycol (EG) ternary deep eutectic solvent (DES) pretreatment was performed to obtain lignin with less-condensed structure. The results showed that the obtained lignin had similar properties to MWL under the condition (MA/ChCl/EG = 1:5:15, 80°C, 10 h). The DES recovered still had good cycle performance. The second step, the cellulose-rich residue was hydrogenated with isopropanol-water solvent and Raney nickel to obtain high-purity cellulose. The results showed that the purity of cellulose obtained by catalytic hydrogenolysis was > 94%. The glucose yield after enzymatic hydrolysis was 243.72 mg/g, which was 14.7 times higher than the untreated poplar. Overall, this work was of great significance for the effective separation of biomass.