Promising transport and high-selective separation of Li(I) from Na(I) and K(I) by a functional polymer inclusion membrane (PIM) system

Three-chamber electrochemical reactor for selective lithium extraction from brine

Efficient lithium recovery from geothermal brines is crucial for the battery industry. Current electrochemical separation methods struggle with the simultaneous presence of Na+, K+, Mg2+, and Ca2+ because these cations are similar to Li+, making it challenging to separate effectively. We address these challenges with a three-chamber reactor featuring a polymer porous solid electrolyte in the middle layer. This design improves the transference number of Li+ (tLi+) by 2.1 times compared to the two-chamber reactor and also reduces the chlorine evolution reaction, a common side reaction in electrochemical lithium extraction, to only 6.4% in Faradaic Efficiency. Employing a lithium-ion conductive glass ceramic (LICGC) membrane, the reactor achieved high tLi+ of 97.5% in LiOH production from simulated brine, while the concentrations of Na+ K+, Mg2+, and Ca2+ are below the detection limit. Electrochemical experiments and surface analysis elucidated the cation transport mechanism, highlighting the impact of Na+ on Li+ migration at the LICGC interface.

Lead Bromide Complex in Tri-n-Octylphosphine Oxide Matrix with Bright Photoluminance and Exceptional Thermoplasticity

Metal halide materials have recently drawn increasing research interest for their excellent opto-electronic properties and structural diversity, but their resulting rigid structures render them brittle and poor formability during manufacturing. Here we demonstrate a thermoplastic luminant hybrid lead halide solid by integrating lead bromide complex into tri-n-octylphosphine oxide (TOPO) matrix. The construction of the hybrid materials can be achieved by a simple dissolution process, in which TOPO molecules act as the solvents and ligands to yield the monodispersed clusters. The combination of these functional units enables the near-room-temperature melt-processing of the materials into targeted geometry by simple molding or printing techniques, which offer possibilities for fluorescent writing inks with outstanding self-healing capacity to physical damage. The intermarriage between metal halide clusters with functional molecules expands the range of practical applications for hybrid metal halide materials.

Dual-Channel-Ion Conductor Membrane for Low-Energy Lithium Extraction

The development of energy-efficient and environmentally friendly lithium extraction techniques is essential to meet the growing global demand for lithium-ion batteries. In this work, a dual-channel ion conductor membrane was designed for a concentration-driven lithium-selective ion diffusion process. The membrane was based on a porous lithium-ion conductor, and its pores were modified with an anion-exchange polymer. Thus, the sintered lithium-ion conductors provided highly selective cation transport channels, and the functionalized nanopores with positive charges enabled the complementary permeation of anions to balance the transmembrane charges. As a result, the dual-channel membrane realized an ultrahigh Li+/Na+ selectivity of ∼1389 with a competitive Li+ flux of 21.6 mmol·m-2·h-1 in a diffusion process of the LiCl/NaCl binary solution, which was capable of further maintaining the high selectivity over 7 days of testing. Therefore, this work demonstrates the great potential of the dual-channel membrane design for high-performing lithium extraction from aqueous resources with low energy consumption and minimal environmental impact.

High Proton Conductivity of the UiO-66-NH2-SPES Composite Membrane Prepared by Covalent Cross-Linking

A sulfonated poly(ethersulfone) (SPES)-metal-organic framework (MOF) film with excellent proton conductivity was synthesized by anchoring UiO-66-NH₂ to the main chain of the aromatic polymer through the Hinsberg reaction. The chemical bond was formed between the amino group in MOFs and the -SO₂Cl group in chlorosulfonated poly(ethersulfones) to conduct protons in the proton channel of the membrane, making the membrane have excellent proton conductivity. UiO-66-NH₂ is successfully prepared as a result of the consistency of the experimental and simulated powder X-ray diffraction (PXRD) patterns of MOFs. The existence of absorption peaks of characteristic functional groups in Fourier transform infrared (FTIR) spectra proved the successful preparation of SPES, PES-SO₂Cl, and a composite film. The results of the AC impedance test indicate that the composite film with a 3% mass fraction has the best proton conductivity of 0.215 S·cm^-1, which is 6.2 times higher than that of the blended film without a chemical bond at 98% RH and 353 K. To our knowledge, there are rarely any reports on the preparation of a composite membrane by directly linking MOFs and the membrane matrix with chemical bonds. This work provides a good way to synthesize the highly conductive proton exchange film.

Fabrication and characterisation of novel chitosan-based polymer inclusion membranes and their application in environmental remediation

Several water and wastewater technologies have been implored for the removal of dyes during wastewater treatments; however; different types have been reportedly found in surface and groundwater systems. Hence, there is a need to investigate other water treatment technologies for the complete remediation of dyes in aquatic environments. In this study, novel chitosan-based polymer inclusion membranes (PIMs) were synthesized for the removal of malachite green dye (MG) which is a recalcitrant of great concern in water. Two types of PIMs were synthesized in this study, the first PIM (PIMs-A) was composed of chitosan, bis-(2-ethylhexyl) phosphate (B2EHP), and dioctyl phthalate (DOP). While, the second PIMs (PIMs-B) were composed of chitosan, Aliquat 336, and DOP. The physico-thermal stability of the PIMs was investigated using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA), both PIMs demonstrated good stability with a weak intermolecular force of attraction amongst the various components of the membranes. The effects of the initial concentration of MG, pH of the MG solution, stripping solution, and time were investigated. At optimum conditions, both membranes (PIM-A and B) recorded the highest efficiencies of 96 % and 98 % at pH 4 and initial contaminants concentration of 50 mg/L, respectively. Finally, both PIMs were used for the removal of MG in different environmental samples (river water, seawater, and tap water) with an average removal efficiency of 90 %. Thus, the investigated PIMs can be considered a potential suitable technique for the removal of dyes and other contaminants from aquatic matrices.

The Use of Polymer Membranes for the Recovery of Copper, Zinc and Nickel from Model Solutions and Jewellery Waste

A polymeric inclusion membrane (PIM) consisting of matrix CTA (cellulose triacetate), ONPPE (o-nitrophenyl pentyl ether) and phosphonium salts (Cyphos 101, Cyphos 104) was used for separation of Cu(II), Zn(II) and Ni(II) ions. Optimum conditions for metal separation were determined, i.e., the optimal concentration of phosphonium salts in the membrane, as well as the optimal concentration of chloride ions in the feeding phase. On the basis of analytical determinations, the values of parameters characterizing transport were calculated. The tested membranes most effectively transported Cu(II) and Zn(II) ions. The highest recovery coefficients (RF) were found for PIMs with Cyphos IL 101. For Cu(II) and Zn(II), they are 92% and 51%, respectively. Ni(II) ions practically remain in the feed phase because they do not form anionic complexes with chloride ions. The obtained results suggest that there is a possibility of using these membranes for separation of Cu(II) over Zn(II) and Ni(II) from acidic chloride solutions. The PIM with Cyphos IL 101 can be used to recover copper and zinc from jewellery waste. The PIMs were characterized by AFM and SEM microscopy. The calculated values of the diffusion coefficient indicate that the boundary stage of the process is the diffusion of the complex salt of the metal ion with the carrier through the membrane.

β-Diketone-Driven Deep Eutectic Solvent for Ultra-Efficient Natural Stable Lithium-7 Isotope Separation

6Li and 7Li are strategic resources. Because Li+ ions have no outermost electrons and the radii of 6Li and 7Li differ by only one neutron, the separation of the naturally stable isotopes of Li, especially by solvent extraction, is recognized as a difficult problem worldwide. Therefore, in this paper, an advanced β-diketone-driven deep eutectic solvent (DES) extraction system containing 2-thenoyltrifluoroacetone (HTTA) and tri-n-octyl phosphine oxide (TOPO) is introduced to the extraction and separation of 6Li+ and 7Li+ ions. Compared with those of reported HTTA extraction systems and crown ether extraction systems, the separation coefficient (β7Li/6Li) of the β-diketone-driven DES extraction system can reach the best value of 1.068, which is now the highest known β-value reported in the extraction system. From the intramolecular hydrogen bond of HTTA to the intermolecular hydrogen bond of DES, the bond energy increases by 47.8%. Because the active site of the proton in DES provides a higher energy barrier for the separation of 7Li, the β7Li/6Li is significantly increased. The extractions were characterized by spectrum, using 1H nuclear magnetic resonance (NMR) spectroscopy, Fourier-transform infrared (FT-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The mechanism was determined on the basis of the reaction kinetics and density functional theory (DFT). The DES extractant shows excellent cycle performance with regard to stripping and reusability. In conclusion, the highly efficient, economical, and stable β-diketone-driven DES extraction system can be used for the separation of naturally stable Li isotopes, which provides good industrial application prospects.

Fabrication and Characterisation of MWCNT/Polyvinyl (PVC) Polymer Inclusion Membrane for Zinc (II) Ion Removal from Aqueous Solution

Heavy metal pollution has prompted researchers to establish the most effective method to tackle the impacts of heavy metals on living things and the environment, which include by applying nanoparticles. An example is the employment of multi-walled carbon nanotubes (MWCNTs) as an additive in an intermediate membrane or polymer inclusion membrane (PIM). The MWCNTs were added to enhance the properties and reinforce the transport performance of zinc (II) ion (Zn2+) removal from the source phase to the receiver phase by the PIMs. The present study constructed a membrane with a poly(vinyl chloride) (PVC)-based polymer, dioctyl phthalate (DOP) plasticiser, and bis-(2-ethylhexyl) phosphate (B2EHP) carrier incorporated with different concentrations of MWCNTs. The contact angle (CA), water uptake, ion exchange capacity (IEC), and porosity of the fabricated membranes were evaluated. The membrane was also characterised by employing scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and electrochemical impedance spectroscopy (EIS). Subsequently, the fabricated PIM (W1) and mixed matrix (MM)-PIM (W2−W5) samples were assessed under different parameters to acquire the ideal membrane composition and effectiveness. Kinetic modelling of Zn2+ removal by the fabricated PIMs under similar conditions was performed to reveal the mechanisms involved. The average removal efficiency of the membranes was >99% at different parameter conditions. Nevertheless, the W3 membrane with 1.0 wt% MWCNT immersed in a 5 mg/L initial Zn2+ concentration and 1.0 M receiver solution for seven hours at pH 2 demonstrated the highest percentage of Zn2+ removal. The experimental data were best fitted to the pseudo-first-order kinetic model (PFO) in kinetic modelling, and the permeability and flux of the W3 at optimum conditions were 0.053 m s−1 and 0.0532 mol m−2 s−1, respectively. In conclusion, the transport mechanism of Zn2+ was enhanced with the addition of the MWCNTs.

Polymer Inclusion Membranes with P507-TBP Carriers for Lithium Extraction from Brines

The separation of lithium and magnesium from salt-lake brines with high Mg2+/Li+ ratios is a main challenge for lithium extraction. In this work, novel polymer inclusion membranes (PIMs) were developed by incorporating 2-ethylhexyl phosphonic acid mono 2-ethylhexyl (P507) and tributyl phosphate (TBP) as the carriers into cellulose triacetate (CTA) polymers. The Li+ could be stripped from the P507-TBP extracting carriers using pure water eluents without adding concentrated hydrochloric acid, which can help decrease carriers’ leakage risk from membrane matrixes and keep the stability of PIMs. The morphology, composition, and wettability of P507-TBP-based PIMs were characterized systematically, and the carrier content in the PIM was also optimized. In the transport experiment with the feed of 0.1 mol/L LiCl and 4.0 mol/L MgCl2, the CTA/P507-TBP60% membrane exhibits a Li+ permeability of 4.76 × 10−3 mol·m−2·h−1 and a Li/Mg separation ratio of 10.2. After recycling seven times, the selectivity of the PIM is well-retained (>10), and the permeability of Li+ decreases slightly (less than 15%). With a decent selectivity and excellent stability, PIMs containing P507-TBP carriers show great potential for sustainable and efficient lithium recovery from brines with high Mg/Li ratios.

PVC/EVA-based polymer inclusion membranes with improved stability and Cr(VI) extraction capacity: Water plasticization effect

Polymer inclusion membranes (PIMs) are far investigated for their ability to extract heavy metals and small organic compounds from aqueous media. Polyvinyl chloride (PVC) is one of the most widely used base polymers for the PIM elaboration. However, its use requires the incorporation of a relatively expensive liquid plasticizer. In the present work, poly(ethylene-co-vinyl acetate) (EVA) serves as a polymer plasticizer for the elaboration of PIMs based on PVC as a base polymer and Aliquat 336 as a carrier. The composition of PIMs was optimized in terms of the PVC/EVA ratio and the vinyl acetate (VA) groups content (x) of EVA (i.e. EVA_x). Physical-chemical properties of the resulting membranes are analyzed and correlated with their structure. The results of SEM analysis revealed miscible PVC/EVA₇₀ blends (i.e. with 70 wt% of VA groups) and partially miscible PVC/EVA₄₀ blends. The plasticizing effect of the EVA copolymer was confirmed by the tensile test results. The results of transport measurements showed that PIMs containing EVA₄₀ and PVC are more efficient for the Cr(VI) extraction than those with only PVC. Thus, EVA₄₀ can effectively replace the conventional liquid plasticizers while improving the Cr(VI) permeability. Besides, it is stated that EVA₄₀-based PIMs are more stable as compared with conventional PIMs due to the water plasticizing effect. After the membrane optimization, the highest Cr(VI) transport flux (54.7 µmol·m^-2·s^-1) was measured. Moreover, the addition of 10 wt% of tetradecanol causes the increase of the water plasticizing effect and allows obtaining a PIM with high stability (up to 24 cycles) required for the membrane long-term operation.

Lithium Harvesting from the Most Abundant Primary and Secondary Sources: A Comparative Study on Conventional and Membrane Technologies

The exponential rise in lithium demand over the last decade, as one of the largest sources for energy storage in terms of lithium-ion batteries (LIBs), has posed a great threat to the existing lithium supply and demand balance. The current methodologies available for lithium extraction, separation and recovery, both from primary (brines/seawater) and secondary (LIBs) sources, suffer not only at the hands of excessive use of chemicals but complicated, time-consuming and environmentally detrimental design procedures. Researchers across the world are working to review and update the available technologies for lithium harvesting in terms of their economic and feasibility analysis. Following its excessive consumption of sustainable energy resources, its demand has risen sharply and therefore requires urgent attention. In this paper, different available methodologies for lithium extraction and recycling from the most abundant primary and secondary lithium resources have been reviewed and compared. This review also includes the prospects of using membrane technology as a promising replacement for conventional methods.

Role of Counterions in the Adsorption and Micellization Behavior of 1:1 Ionic Surfactants at Fluid Interfaces─Demonstrated by the Standard Amphiphile System of Alkali Perfluoro-n-octanoates

In our latest communication, we proved experimentally that the ionic surfactant's surface excess is exclusively determined by the size of the hydrated counterion.[Lunkenheimer , Langmuir, 2017, 33, 10216-1022410.1021/acs.langmuir.7b00786]. However, at this stage of research, we were unable to decide whether this does only hold for the two or three lightest ions of lithium, sodium, and potassium, respectively. Alternatively, we could also consider the surface excess of the heavier hydrated alkali ions of potassium, rubidium, and cesium, having practically identical ion size, as being determined by the cross-sectional area of the related anionic extended chain residue. The latter assumption has represented state of art. Searching for reliable experimental results on the effect of the heavier counterions on the boundary layer, we have extended investigations to the amphiphiles' solutions of concentrations above the critical concentration of micelle formation (cmc).We provided evidence that the super-micellar solutions' equilibrium surface tension will remain constant provided the required conditions are followed. The related σ_cmc-value represents a parameter characteristic of the ionic surfactant's adsorption and micellization behavior. Evaluating the amphiphile's surface excess obtained from adsorption as a function of the related amphiphile's σ_cmc-value enables you to calculate the radius of the hydrated counterion valid in sub- and super-micellar solution likewise. The σ_cmc-value is directly proportional to the counterion's diameter concerned. Taking additionally into account the radii of naked ions known from crystal research, we succeeded in exactly discriminating the hydrated alkali ions' size from each other. There is a distinct sequence of hydration radii in absolute scale following the inequality, Li⁺ > Na⁺ > K⁺ > (NH₄)⁺ > Rb⁺ > Cs⁺. Therefore, we have to extend our model of counterion effectiveness put forward in our previous communication. It represents a general principle of the counterion effect.

Characterization and Kinetic Studies of Poly(vinylidene fluoride-co-hexafluoropropylene) Polymer Inclusion Membrane for the Malachite Green Extraction

Textile industry effluent contains a high amount of toxic colorants. These dyes are carcinogenic and threats to the environment and living beings. In this study, poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) was used as the based polymer for PIMs with bis-(2-ethylhexyl) phosphate (B2EHP) and dioctyl phthalate (DOP) as the carrier and plasticizer. The fabricated PIMs were employed to extract the cation dye (Malachite Green; MG) from the feeding phase. PIMs were also characterized by scanning electron microscopy (SEM), atomic force microscope (AFM), contact angle, water uptake, Fourier-transform infrared spectroscopy (FTIR) and ions exchange capacity. The performance of the PIMs was investigated under various conditions such as percentage of carrier and initial dye concentration. With permeability and flux values of 0.1188 cm/min and 1.1913 mg cm/min, PIM produced with 18% w/w PVDF-co-HFP, 21% w/w B2EHP, 1% w/w DOP and 40% w/w THF and was able to achieve more than 97% of MG extraction. The experimental data were then fitted with a pseudo-second-order (PSO) model, and the calculated R2 value was ~0.99. This shows that the data has a good fit with the PSO model. PIM is a potential alternative technology in textile industry effluent treatment; however, the right formulation is crucial for developing a highly efficient membrane.

Electro-membrane extraction of cadmium(II) by bis(2-ethylhexyl) phosphate/kerosene/polyvinyl chloride polymer inclusion membrane

The development of the electroplating and battery industries has increased the environmental problems and the needs for resource recovery of Cd(II). In this study, the Electro-membrane extraction (EME) behaviour of Cd(II) was investigated by using polymer inclusion membrane with bis(2-ethylhexyl) phosphate as carrier and polyvinyl chloride as base polymer(PD-PIM) at 0-80 V. Results showed that the EME of Cd(II) by PD-PIM can be obtained in the feed phase with pH 3-8 and stripping phase of dilute acid. Voltage is the main factor to increase the mass transfer rate of Cd(II). The applied electric field reduced the mass transfer activation energy of Cd(II) by PD-PIM and weakened the mass transfer interference of Cd(II) on the background material of the feed phase. After using kerosene-stabilised PD-PIM for operation at pH5, 60 V for 120 h, Cd(II) in the 1 L solution reduced from 15 mg/L to 0.08 mg/L, and the enrichment factor was 9.79.

Selective Separation of Acetic and Hexanoic Acids across Polymer Inclusion Membrane with Ionic Liquids as Carrier

This paper first reports on the selective separation of volatile fatty acids (VFAs) (acetic and hexanoic acids) using polymer inclusion membranes (PIMs) containing quaternary ammonium and phosphonium ionic liquids (ILs) as the carrier. The affecting parameters such as IL content, VFA concentration, and the initial pH of the feed solution as well as the type and concentration of the stripping solution were investigated. PIMs performed a much higher selective separation performance toward hexanoic acid. The optimal PIM composed of 60 wt% quaternary ammonium IL with the permeability coefficients for acetic and hexanoic acid of 0.72 and 4.38 µm s⁻¹, respectively, was determined. The purity of hexanoic acid obtained in the stripping solution increased with an increase in the VFA concentration of the feed solution and decreasing HCl concentration of the stripping solution. The use of Na₂CO₃ as the stripping solution and the involvement of the electrodialysis process could dramatically enhance the transport efficiency of both VFAs, but the separation efficiency decreased sharply. Furthermore, a coordinating mechanism containing hydrogen bonding and ion exchange for VFA transport was demonstrated. The highest purity of hexanoic acid (89.3%) in the stripping solution demonstrated that this PIM technology has good prospects for the separation and recovery of VFAs from aqueous solutions.

Chromium(VI) Removal by Polyvinyl Chloride (PVC)/Aliquat-336 Polymeric Inclusion Membranes in a Multiframe Flat Sheet Membrane Module

A new multiframe flat sheet membrane contactor module containing several flat membranes was designed and implemented. Each frame contains a chamber (central hole) in which the feed and the receiving phases are put in contact with polyvinyl chloride (PVC)/Aliquat-336 polymeric flat sheet membranes for Cr(VI) removal from aqueous solutions (feed phase). To evaluate the efficiency of the system, the experimental design methodology was used to analyze the effect of temperature (T, °C), PVC/Aliquat-336 ratio, and Cr (VI) concentration in the feed phase and the concentration of sodium chloride (NaOH-NaCl) in the receiving phase. Two representative mathematical models of the two responses (extraction and back-extraction) were respectively obtained. A good correlation between the experimental results and those predicted (RS2 = 97.77 and RR2 = 97.87) was achieved, allowing the optimization of the different factors selected for each response, separately. The proposed system showed a good separation performance, leading to Cr(VI) extractions up to 93% when working at the optimized operating conditions.