One-Step Construction of the Positively/Negatively Charged Ultrathin Janus Nanofiltration Membrane for the Separation of Li+ and Mg2

Nanofiltration Membranes for Efficient Lithium Extraction from Salt-Lake Brine: A Critical Review

The global transition to clean energy technologies has escalated the demand for lithium (Li), a critical component in rechargeable Li-ion batteries, highlighting the urgent need for efficient and sustainable Li+ extraction methods. Nanofiltration (NF)-based separations have emerged as a promising solution, offering selective separation capabilities that could advance resource extraction and recovery. However, an NF-based lithium extraction process differs significantly from conventional water treatment, necessitating a paradigm shift in membrane materials design, performance evaluation metrics, and process optimization. In this review, we first explore the state-of-the-art strategies for NF membrane modifications. Machine learning was employed to identify key parameters influencing Li+ extraction efficiency, enabling the rational design of high-performance membranes. We then delve into the evolution of performance evaluation metrics, transitioning from the traditional permeance-selectivity trade-off to a more relevant focus on Li+ purity and recovery balance. A system-scale analysis considering specific energy consumption, flux distribution uniformity, and system-scale Li+ recovery and purity is presented. The review also examines process integration and synergistic combinations of NF with emerging technologies, such as capacitive deionization. Techno-economic and lifecycle assessments are also discussed to provide insights into the economic viability and environmental sustainability of NF-based Li+ extraction. Finally, we highlight future research directions to bridge the gap between fundamental research and practical applications, aiming to accelerate the development of sustainable and cost-effective Li+ extraction methods.

Enhancing Ion Selectivity of Nanofiltration Membranes via Heterogeneous Charge Distribution

Nanofiltration technology holds significant potential for precisely separating monovalent and multivalent ions, such as lithium (Li) and magnesium (Mg) ions, during lithium extraction from salt lakes. This study bridges a crucial gap in understanding the impact of the membrane spatial charge distribution on ion-selective separation. We developed two types of mixed-charge membranes with similar pore sizes but distinct longitudinal and horizontal distributions of oppositely charged domains. The charge-mosaic membrane, synthesized and utilized for ion fractionation for the first time, achieved an exceptional water permeance of 15.4 LMH/bar and a Li/Mg selectivity of 108, outperforming the majority of published reports. Through comprehensive characterization, mathematical modeling, and machine learning methods, we provide evidence that the spatial charge distribution dominantly determines ion selectivity. The charge-mosaic structure excels by substantially promoting ion selectivity through locally enhanced Donnan effects while remaining unaffected by variations in feedwater concentration. Our findings not only demonstrate the applicability of charge-mosaic membranes to precise nanofiltration but also have profound implications for technologies demanding advanced ion selectivity, including those in the sustainable water treatment and energy storage industries.

Space-Confined Synthesis of Thinner Ether-Functionalized Nanofiltration Membranes with Coffee Ring Structure for Li+/Mg2+ Separation

Positively charged nanofiltration membranes have attracted much attention in the field of lithium extraction from salt lakes due to their excellent ability to separate mono- and multi-valent cations. However, the thicker selective layer and the lower affinity for Li+ result in lower separation efficiency of the membranes. Here, PEI-P membranes with highly efficient Li+/Mg2+ separation performance are prepared by introducing highly lithophilic 4,7,10-Trioxygen-1,13-tridecanediamine (DCA) on the surface of PEI-TMC membranes using a post-modification method. Characterization and experimental results show that the utilization of the DCA-TMC crosslinked structure as a space-confined layer to inhibit the diffusion of the monomer not only increases the positive charge density of the membrane but also reduces its thickness by ≈35% and presents a unique coffee-ring structure, which ensures excellent water permeability and rejection of Mg2+. The ion-dipole interaction of the ether chains with Li+ facilitates Li+ transport and improves the Li+/Mg2+ selectivity (SLi,Mg = 23.3). In a three-stage nanofiltration process for treating simulated salt lake water, the PEI-P membrane can reduce the Mg2+/Li+ ratio of the salt lake by 400-fold and produce Li2CO3 with a purity of more than 99.5%, demonstrating its potential application in lithium extraction from salt lakes.

Supramolecular-coordinated nanofiltration membranes with quaternary-ammonium Cyclen for efficient lithium extraction from high magnesium/lithium ratio brine

Ion-selective membranes (ISM) with sub-nanosized pore channels hold significant potential for applications in saline wastewater treatment and resource recovery. Herein, novel synergistic ion channels featuring bi-periodic structures were constructed through the coordination of functional Cyclen (quaternary_1,4,7,10-tetraazacyclododecane, Q_Cyclen) and Cu2+-m-Phenylenediamine (Cu2+-MPD) to develop supramolecular membranes for lithium extraction. The exterior quaternary ammonium-rich sites exhibit a significant Donnan exclusion effect, resulting in tremendous mono/divalent (Li+/Mg2+) ion selectivity; while the interior regular-confined channels of Cyclen yield a fast vehicular pathway, facilitating water molecules and Li+ ion-selective transport. The optimized membrane exhibited an increased water permeance of 19.2 L·m-2·h-1·bar-1 and simultaneously promoted Li+/Mg2+ selectivity (achieving a selectivity of 18.5 under a Mg2+/Li+ mass ratio of 30), surpassing the trade-off limit of conventional nanofiltration membranes. Due to the acquired excellent Li+/Mg2+ selectivity, lithium extraction from simulated salt-lake brines was successfully achieved through a two-stage nanofiltration process, reducing the Mg2+/Li+ mass ratio from 40 to 1.1. This work validates the applicability of macrocyclic with intrinsic sub-nanosized channels and desired multifunctionality for developing high-performance ISM for efficient lithium separation and beyond.

Controllable Design of Polyamide Composite Membrane Separation Layer Structures via Metal-Organic Frameworks: A Review

Optimizing the structure of the polyamide (PA) layer to improve the separation performance of PA thin-film composite (TFC) membranes has always been a hot topic in the field of membrane preparation. As novel crystalline materials with high porosity, multi-functional groups, and good compatibility with membrane substrate, metal-organic frameworks (MOFs) have been introduced in the past decade for the modification of the PA structure in order to break through the separation trade-off between permeability and selectivity. This review begins by summarizing the recent progress in the control of MOF-based thin-film nanocomposite (TFN) membrane structures. The review also covers different strategies used for preparing TFN membranes. Additionally, it discusses the mechanisms behind how these strategies regulate the structure and properties of PA. Finally, the design of a competent MOF material that is suitable to reach the requirements for the fabrication of TFN membranes is also discussed. The aim of this paper is to provide key insights into the precise control of TFN-PA structures based on MOFs.

Optimizing Epoxy Interfacial Bonding Properties and Failure Mechanism between Carbon Textile-Reinforced Mortar Composites and Concrete Substrates

Textile-reinforced mortar (TRM) composites have been extensively utilized in building reinforcement due to their exceptional mechanical properties. The weakest link in the entire structure is the interface between the TRM composites and the concrete; however, it plays a crucial role in effectively transferring stress. Researchers have taken measures to improve the strength of the interface, but the results are relatively scattered. In this paper, the surface treatment of the substrate, the thickness of the surfactant, and the physical doping of the surfactant on the interfacial bonding strength of the concrete were comparatively studied. The results demonstrate that the sandblasting treatment on the surface of the concrete enhances the bonding area between the mortar and the concrete of the reinforcement layer, leading to a 50% increase in the bending resistance of the structure. When the surfactant thickness increases to 0.5 kg/m2, more surfactants penetrate the mortar and concrete. This significantly inhibits the occurrence of cracks in the structure. The addition of 2.5% Al2O3 nanomaterials to the surfactant diminishes the shrinkage rate of the curing process, enhances the impact toughness, and improves the flexural and compressive properties of the bonding layer. The ultimate load of the structure increases by 65%. Physical doping of the surfactant is the most effective measure with the most apparent improvement result. It significantly enhances the bonding strength of the interface and can be widely used in construction.

Interface Bonding Properties and Mechanism of Steel Fiber and Hot Melt Adhesive via Interface Design Engineering

Steel fiber textile, which is composed of steel fibers and glass fibers, has a support layer impregnated with hot melt adhesive (HMA). During long-term service, the bonding force between the steel fiber/HMA system interfaces is poor. In order to improve the bond strength and durability of the interface, this paper introduced sandblasting, acid-etching, and phosphating treatments on the surface of the steel fibers. Also, the effects of these three pretreatment methods on the bond strength of the steel fiber/HMA interface were investigated. The results indicate that the interfacial bond strength of composites made from steel fibers is improved via surface treatment. Under a hydrothermal and simulated concrete pore solution environment, the durability of the steel fiber/HMA interface after sandblasting and acid-etching pretreatment is not as good as that after phosphating pretreatment. The mechanical properties of the phosphating/HMA composite were maintained at 4.56 and 2.24 times compared to those of the untreated/HMA composite, respectively. This is because the pinning effect formed by the phosphating film on the surface of steel fibers at the interface of steel fiber/HMA can serve as a physical barrier against corrosion, preventing the invasion of chloride ions and water vapor and improving the durability of the interface.

A humidity/thermal dual response 3D-fabric with porous poly(N-isopropyl acrylamide) hydrogel towards efficient atmospheric water harvesting

Atmospheric water harvesting is a promising approach for obtaining freshwater resources, but achieving high levels of light absorption, hygroscopic capacity, and desorption efficiency simultaneously remains a challenge. In this study, we developed an innovative atmospheric water harvester that incorporates a poly(N-isopropylacrylamide) hydrogel and a polydopamine/polypyrrole-modified 3D raised-fabric. The interlacing structure and polydopamine/polypyrrole synergistically enhance the harvester's photothermal conversion capability, while the hydrogel-modified raised-fabric with its increased pore structure and high specific surface area ensures effective contact between the internal adsorbent and external moisture, thereby improving moisture capture and storage capacity. Our results indicate that the hydrogel-modified 3D raised-fabric has excellent photothermal conversion performance, as evidenced by its rapid temperature rise to 75.9 °C under 1 sun light intensity, which effectively promotes water evaporation and harvesting. Furthermore, the 3D raised-fabric exhibits exceptional water absorption (3.1 g g-1, RH 90%) and water desorption (1.75 kg m-2h-1, 1 sun) properties. Overall, the 3D raised-fabric with its integrated photothermal, hygroscopic, and hydrophobic properties can effectively collect water under low humidity conditions, making it a promising solution for water scarcity issues.

Advanced Lithium Extraction Membranes Derived from Tagged-Modification of Polyamide Networks

Efficient Mg2+ /Li+ separation is crucial to combating the lithium shortage worldwide, yet current nanofiltration membranes suffer from low efficacy and/or poor scalability, because desirable properties of membranes are entangled and there is a trade-off. This work reports a "tagged-modification" approach to tackle the challenge. A mixture of 3-bromo-trimethylpropan-1-aminium bromide (E1 ) and 3-aminopropyltrimethylazanium (E2 ) was designed to modify polyethylenimine - trimesoyl chloride (PEI-TMC) membranes. E1 and E2 reacted with the PEI and TMC, respectively, and thus, the membrane properties (hydrophilicity, pore sizes, charge) were untangled and intensified simultaneously. The permeance (34.3 L m-2  h-1  bar-1 ) and Mg2+ /Li+ selectivity (23.2) of the modified membranes are about 4 times and 2 times higher than the pristine membrane, and they remain stable in a 30-days test. The permeance is the highest among all analogous nanofiltration membranes. The tagged-modification method enables the preparation of large-area membranes and modules that produce high-purity lithium carbonate (Li2 CO3 ) from simulated brine.

Sustainable Lithium Recovery from Hypersaline Salt-Lakes by Selective Electrodialysis: Transport and Thermodynamics

Evaporative technology for lithium mining from salt-lakes exacerbates freshwater scarcity and wetland destruction, and suffers from protracted production cycles. Electrodialysis (ED) offers an environmentally benign alternative for continuous lithium extraction and is amenable to renewable energy usage. Salt-lake brines, however, are hypersaline multicomponent mixtures, and the impact of the complex brine-membrane interactions remains poorly understood. Here, we quantify the influence of the solution composition, salinity, and acidity on the counterion selectivity and thermodynamic efficiency of electrodialysis, leveraging 1250 original measurements with salt-lake brines that span four feed salinities, three pH levels, and five current densities. Our experiments reveal that commonly used binary cation solutions, which neglect Na+ and K+ transport, may overestimate the Li+/Mg2+ selectivity by 250% and underpredict the specific energy consumption (SEC) by a factor of 54.8. As a result of the hypersaline conditions, exposure to salt-lake brine weakens the efficacy of Donnan exclusion, amplifying Mg2+ leakage. Higher current densities enhance the Donnan potential across the solution-membrane interface and ameliorate the selectivity degradation with hypersaline brines. However, a steep trade-off between counterion selectivity and thermodynamic efficiency governs ED's performance: a 6.25 times enhancement in Li+/Mg2+ selectivity is accompanied by a 71.6% increase in the SEC. Lastly, our analysis suggests that an industrial-scale ED module can meet existing salt-lake production capacities, while being powered by a photovoltaic farm that utilizes <1% of the salt-flat area.