Ion Sieve Research Articles

Substrate-Tight Graphene Transmembrane-nanofluidic Devices.

Nanopores in 2D membranes like graphene have great potential for applications such as single-molecule sensing, ion sieving, and harvesting osmotic power. A critical challenge, however, has been to ensure the stability of these nanofluidic transmembrane devices, as the ultrathin graphene membranes tend to delaminate and peel away from their substrates when exposed to aqueous solutions. In this study, it is shown that using a pyrene-based coating prevents delamination and allows graphene to remain freestanding over a SiN aperture for several days in an electrolyte. The pyrene molecules interact strongly with the graphene through π-π bonding, adhering the graphene to the substrate. Additionally, the pyrene-based adhesion layer remarkably increases the success rates of the graphene transmembrane devices from 4% to 76.2%. The results underscore the importance of using adhesion layers to enhance the stability of graphene in nanofluidic devices and prolong their operational lifespan. It enables the development of more robust graphene-based nanofluidic devices for a wide range of applications necessitating free-standing graphene.

Quasi-vertically asymmetric channels of graphene oxide membrane for ultrafast ion sieving

The high performance of two-dimensional (2D) channel membranes is generally achieved by preparing ultrathin or forming short channels with less tortuous transport through self-assembly of small flakes, demonstrating potential for highly efficient water desalination and purification, gas and ion separation, and organic solvent waste treatment. Here, we report the construction of vertical channels in graphene oxide (GO) membrane based on a substrate template with asymmetric pores. The membranes achieved water permeance of 2647 L m−2 h−1 bar−1 while still maintaining an ultrahigh rejection rate of 99.9% for heavy metal ions, which is superior to the state-of-the-art 2D membranes reported. Furthermore, the membranes exhibited excellent stability during long-term filtration experiments for at least 48 h, as well as resistance to ultrasonic treatment for over 100 minutes. The vertical channels possess very short pathway for almost direct water transport and a highly effective channel area, meanwhile the asymmetric porous template enhances the packing of the inserted GO nanosheets to avoid the swelling effect of membrane. Our work provides a simple way to fabricate vertical channels of 2D nanofiltration membranes with high water purification performance.

Asymmetric ion transport through heterogeneous bilayers of covalent organic frameworks

In recent years, with the development of interfacial polymerization methodologies, the successful preparation of covalent organic framework (COF) monolayers featuring ultrahigh pore density and molecule-scale thickness has become a reality. This advancement has enabled ion transport with ultrahigh flux across extremely short paths. Owing to these processes, the COF monolayers have shown wide potential applications ranging from energy conversion and artificial mechanosensing to ion sieving. To date, nanofluidic systems based on COF monolayers are homogeneous, leading to nearly symmetric ion transport properties. Studies on the ionic transport behavior within ultrathin COF heterojunctions are limited and remain challenging. Herein, using a two-step sequential self-assembly and subsequent interfacial polymerization strategy, bi-layered heterogeneous tetraphenylporphyrin-based COF membranes composed of negatively charged and positively charged monolayers were prepared. Using an electric field as a driving force, rectified ion transport was observed for the first time. Notably, this ionic current rectification property could be modulated by the salt concentration and the structural composition of the membrane, and it was universal for various COF heterojunctions with different chemical ingredients. These findings are beneficial for promoting the development of innovative nanofluidic materials and devices.

Imine-Linked 3D Covalent Organic Framework Membrane Featuring Highly Charged Sub-1nm Channels for Exceptional Lithium-Ion Sieving.

Coupling ion exclusion and interaction screening within sub-nanoconfinement channels in novel porous material membranes hold great potential to realize highly efficient ion sieving, particularly for high-performance lithium-ion extraction. Diverse kinds of advanced membranes have been previously reported to realize this goal but with moderate performance and complex operations gained. Herein, these issues are circumvented by preparing the consecutive and intact imine-linked three-dimensional covalent organic framework(i.e., COF-300) membranes via a simple solvothermal approach and employing the intrinsically interconnected sub-1nm one-dimensional channels for exceptional lithium-ion sieving. The synthesized membranes with highly charged angstrom scale channels of ≈0.78nm achieve an excellent Li+ permeance (0.123mol m-2 h-1) with an ultrahigh Li+/Mg2+ of 36 in the binary system. The experimental measurement and theoretical calculation reveal that a channel size right exactly between Li+ and Mg2+ enables restricted Mg2+ penetration. Meanwhile, the ion affinity interaction screening with imine groups further strengthens the fast Li+ permeability but severely suppresses the Mg2+ passage. In particular, the synthesized three-dimensional covalent organic framwork membranes also have a remarkable separation performance during a long-term operation test without sacrificing trade-off, demonstrating chemistry stability and mechanical integrity under the high-salinity aqueous environment.

Unraveling the Atomistic Mechanisms Underlying Effective Reverse Osmosis Filtration by Graphene Oxide Membranes.

The graphene oxide (GO) membrane displays promising potential in efficiently filtering ions from water. However, the precise mechanism behind its effectiveness remains elusive, particularly due to the lack of direct experimental evidence at the atomic scale. To shed light on this matter, state-of-the-art techniques are employed such as integrated differential phase contrast-scanning transmission electron microscopy and electron energy loss spectroscopy, combined with reverse osmosis (RO) filtration experiments using GO membranes. The atomic-scale observations after the RO experiments directly reveal the binding of various ions including Na+, K+, Ca2+, and Fe3+ to the defects, edges, and functional groups of GO. The remarkable ion-sieving capabilities of GO membranes are confirmed, which can be attributed to a synergistic interplay of size exclusion, electrostatic interactions, cation-π, and other non-covalent interactions. Moreover, GO membranes modified by external pressure and cation also demonstrated further enhanced filtration performance for filtration. This study significantly contributes by uncovering the atomic-scale mechanism responsible for ion sieving in GO membranes. These findings not only enhance the fundamental understanding but also hold substantial potential for the advancement of GO membranes in reverse osmosis (RO) filtration.

Preparation of zirconium-doped titanium ion sieve composites and lithium adsorption from salt-lake brine

Preparation of zirconium-doped titanium ion sieve composites and lithium adsorption from salt-lake brine

Novel and Sustainable Materials for the Separation of Lithium, Rubidium, and Cesium Ions from Aqueous Solutions in Adsorption Processes-A Review.

The growing demand for alkali metals (AMs), such as lithium, cesium, and rubidium, related to their wide application across various industries (e.g., electronics, medicine, aerospace, etc.) and the limited resources of their naturally occurring ores, has led to an increased interest in methods of their recovery from secondary sources (e.g., brines, wastewater, waste leachates). One of the dynamically developing research directions in the field of separation of AMs ions from various aqueous solutions is the search for novel, efficient, and "green" materials that could be used in adsorption processes, also on a larger industrial scale. This review concerns the latest achievements (mainly from 2023 to 2024) in the development of innovative adsorption materials (e.g., ion sieves, aluminum-based adsorbents, mineral adsorbents, composites, resins) for the separation of Li+, Cs+, and Rb+ ions from solutions, with particular emphasis on their most important advantages and limitations, as well as their potential impact on the environment.

Interface Engineering of MOF Nanosheets for Accelerated Redox Kinetics in Lithium-Sulfur Batteries.

Modifying the separator is considered as an effective strategy for achieving high performance lithium-sulfur (Li-S) batteries. However, most modification layers are excessively thick, with catalytic active sites primarily located within the material's interior. This configuration severely impacts Li+ transport and the efficient catalytic conversion of polysulfides. Therefore, there is an urgent need to develop a multifunctional separator that integrates ultrathin design, catalytic activity, and ion sieving capabilities. Herein, we successfully linked TCPP(Ni) as a secondary ligand with Zr-BTB nanosheets to create an ultra-thin separator modification layer (Zr-TCPP(Ni)) with efficient ion sieving and catalytic properties. The resultant multifunctional separators provide robust ion sieving capabilities that promote rapid Li+ transport and intercept polysulfides shuttling. Therefore, The Zr-TCPP(Ni)@PP cell maintains 70.0 % of its initial capacity after 600 cycles at a high rate of 3 C, while achieving an impressive areal capacity of 4.55 mA h cm-2 even with high sulfur content of 80 wt% at 0.5 C. This work provides valuable insights for rational design of MOF interface engineering in high energy density Li-S batteries.

Staggered-Stacking Two-Dimensional Covalent Organic Framework Membranes for Molecular and Ionic Sieving.

Two-dimensional covalent organic frameworks (2D COFs), a family of crystalline materials with abundant porous structures offering nanochannels for molecular transport, have enormous potential in the applications of separation, energy storage, and catalysis. However, 2D COFs remain limited by relatively large pore sizes (>1 nm) and weak interlayer interactions between 2D nanosheets, making it difficult to achieve efficient membranes to meet the selective sieving requirements for water molecules (0.3 nm) and hydrated salt ions (>0.7 nm). Here, we report a high-performance 2D COF membrane with narrowed channels (0.7 × 0.4 nm2) and excellent mechanical performance constructed by the staggered stacking of cationic and anionic 2D COF nanosheets for selectively sieving of water molecules and hydrated salt ions. The mechanical performance has been improved by two times than that of single-phase 2D COF membranes due to the enhanced interlayer interactions between nanosheets. The stacked 2D COF membranes exhibit significantly improved monovalent salt ions rejection ratio (up to 77.9%) compared with single-phase COF membranes (∼49.2%), while maintaining comparable water permeability. The design of stacked 2D COF membranes provides a potential strategy for constructing high-performance nanoporous membranes to achieve precise molecular and ionic sieving.

Reviving Zn Dendrites to Electroactive Zn2+ by Ion Sieve Interface.

Zn0 dendrite formation during repeated plating/stripping processes limits the practical use of Zn-metal anodes in reliable and affordable energy storage. Traditional methods, including dendrite suppression and dendrite regulation, fail under demanding performance conditions due to Zn2+ diffusion limitations and concentration gradients. Here, using an in situ pre-zincation approach, a Li2ZnxTi3-xO8 (LZTO, 0<x<3) layer with uniform ion channels is introduced. This layer acts as an ionic sieve, reviving Zn0 dendrite into Zn2+ through redox reactions and enhancing Zn2+ diffusion kinetics. Experiment and simulation results reveal that Zn2+ migrates along the (111) crystal plane of LZTO through the successive replacement of Zn atoms in tetrahedral positions, with a high transference number of 0.796. LZTO@Zn performs better in coin cells at high currents (e.g., 50mA cm-2) and operates at higher Zn utilization (300h at 56.98%Zn utilization), with four times the lifespan at -40°C and six times longer in alkaline electrolytes compared to bare Zn. Pouch cells with LZTO@Zn anodes operate in a low N/P ratio (6.9) and lean electrolyte (E/C is 20µL mA h-1), achieving enhanced cycling stability. The findings indicate the significance of ion sieves with ordered ion channels in mitigating Zn0 dendrites and promoting rapid Zn2+ transport.

Fabrication of N,C-H2TiO3 Ion Sieves for Rapid Adsorption of Lithium Using Rheological Phase Methods

Modifying β-H2TiO3 by elemental doping improves its adsorption capacity and shortens the equilibrium adsorption time, which is of positive significance for its industrial application.Herein, a novel N, C co-doped Li2TiO3 lithium ion sieve precursor N,C-Li2TiO3-3 (noted as N,C-LTO-3) was successfully prepared via the rheological phase method using urea as a vital raw material. Crystal structure of N,C-LTO-3 was characterized via XRD, XPS, FT-IR, and Raman. The morphology of N,C-LTO-3 was analysed by SEM and HR-TEM. The N,C-LTO-3 was pickled and obtained to N,C-H2TiO3-3, namely N,C-HTO-3. The equilibrium adsorption capacity (Qe) of N,C-HTO-3 was as high as 40.6mg⋅g-1 in LiOH solution of 100mg·L-1 at 293K. Ti4+ dissolution loss rate is below 0.5% in the fifth cycle. Adsorption isothermal curve, kinetics, and thermodynamic behaviour were fitted with the according equations. The exchange energy of N,C-HTO-3 for Li+ was calculated by density functional theory (DFT) to assess the feasibility of lithium absorption. Furthermore, N,C-HTO-3 exhibited high regeneration and selectivity for Li+ in lithium-containing brine, making N,C-HTO-3 an ideal candidate for Li+ extraction.

Preparation of hydrophilic Cr-doped LiTi2(PO4)3 ion sieves with expanded cell structure for enhanced lithium extraction

Phosphate-based HTi2(PO4)3 was a novel lithium ion with a NASICON network structure. In this work, Cr doped was used to improve the adsorption performance by expanding the Li+ transport channel and increasing the hydrophilicity of the adsorbent. The crystal structure of Cr-LTPO-0.5 was characterized by XRD, XPS, Contact angle and FT-IR analysis, and the morphology of Cr-LTPO-0.5 was analyzed by SEM and HR-TEM. Cr-HTPO-0.5 was obtained after acid washing of Cr-LTPO-0.5. The adsorption of Li+ on Cr-HTPO-0.5 was consistent with the Langmuir isothermal model and pseudo-2nd-order kinetic model, in which the adsorption was endothermic and spontaneous process. The structure and adsorption energy of Li+ on Cr-HTPO-0.5 were calculated by the density function theory (DFT) to assess the feasibility of lithium uptake. Cr-HTPO-0.5 showed remarkable selectivity for Li+ on heteroatoms in artificial brines. These results made Cr-HTPO-0.5 as a highly promising candidate for applications in Li+ recovery.

Performance study of lithium ion sieve composite in high gravity for Li+ adsorption

The demand for lithium-ion batteries in new energy vehicles and energy storage technologies is rapidly increasing, making the efficient extraction of lithium resources from salt lakes, which are rich in lithium reserves, crucial. To address the issues of slow adsorption rate and low adsorption capacity of lithium ion sieves in the adsorption column, In this paper, the high-gravity rotating packed bed (RPB) is utilized for the first time to enhance the adsorption process of Li+ on lithium ion sieve composite material(CTS/L-HMO), thereby investigating its adsorption mechanism. Specifically, CTS/L-HMO was prepared by combining manganese-based lithium ion sieves with chitosan, and used as the filler for the RPB to adsorb lithium containing solution. The research showed that chitosan successfully coated the manganese-based lithium ion sieves and the distribution of various elements was uniform. In the RPB, the adsorption capacity of CTS/L-HMO increased first and then decreased with the increase of liquid flow rate and high gravity factor. Compared to a fixed bed, the adsorption capacity and adsorption rate in the RPB increased by 43.30 % and 33.33 %, respectively. After 10 cycles of regeneration experiments, the adsorption capacity of CTS/L-HMO remained as high as 30.19 mg/g, and it exhibited high selective adsorption for Li+.

Lattice-defective metal-organic framework membranes from filling mesoporous colloidal networks for monovalent ion separation

Ionic separations are critical to various chemical, environmental, and energy-related industries, but precise discrimination of monovalent ions with similar properties is extremely difficult. Nanoporous metal-organic framework (MOF) membranes attract intensive attention for ionic separations. However, precise adjusting transport nanochannels of frameworks and simplifying formation mechanisms of membranes remain extremely challenging. In this study, we report controllable construction of lattice-defective MOF membranes for sharp ion sieving, through filling mesoporous MOF colloidal layers by confined interior growth. By utilizing highly processable mesoporous colloidal networks to provide abundant nucleation sites, decelerate precursor diffusions, and serve as membrane-forming hosts, interior MOF growth can be confined in the mesopores of hosts, thereby eliminating any avoid spaces and constructing pinhole-free membranes in a scalable route. Moreover, through creating linker-missing lattice defects in frameworks, the microporous pathways can be accurately expanded at angstrom level, consequently, selectively improving the accessibilities for specific monovalent cations but maintaining the large resistances for others. Importantly, the prepared 150-nm MOF membranes exhibit good long-term stability and superb ion-sieving performance, especially for monovalent cations, with mixture selectivities as high as 7.5 for K+/Li+ and 51 for K+/Mg2+ during concentration-driven separations, which outperform most membranes. This study provides an alternative methodology to construct high-performance ion-sieving polycrystalline membranes.

PVA-enhanced green synthesis of CMC-based lithium adsorption films

The titanium-based lithium ion sieve (HTO), renowned for its exceptional adsorption performance and cyclic stability, was utilized in addressing the global shortage of lithium resources. However, the recovery and reuse efficiency of HTO in powder form is relatively low, which limits its application in industrial fields. To address this issue, this study utilized carboxymethyl cellulose (CMC) as the principal matrix material, while polyvinyl alcohol (PVA) played a dual function as both matrix and crosslinker, negating the necessity for supplementary crosslinking materials. Employing water as the only solvent, HTO was embedded into the CMC-PVA blended film matrix. It was observed that augmenting the CMC content substantially elevates the adsorptive capability of the film. However, this enhancement comes at the cost of reduced mechanical robustness and diminished stability in solution. Consequently, by balancing the influence of adsorptive capacity and stability through fine-tuning the CMC-to-PVA ratio. Even when HTO powder is encapsulated within the film, the adsorption film retains the excellent adsorption properties of HTO, achieving an adsorption capacity for lithium of 29.21 mg g−1 within 12 h. This study provides an innovative pathway and ideas for the large-scale, low-cost production of sustainable lithium-ion adsorption materials.

Lysine-regulated turing structure membrane via interfacial polymerization for enhanced Li+/Mg2+ separation

The development of advanced membranes with precise ion selectivity is essential for efficient Li+/Mg2+ separation. In this study, we synthesized a novel Lys-TMC membrane via a nucleophilic addition reaction between Lysine and trimesoyl chloride (TMC), yielding in a negatively charged surface interconnected by amide bonds. We systematically investigated the effects of varying Lys:TMC ratios on the membrane’s chemical structure, surface morphology, and ion separation performance. Our results revealed that the degree of cross-linking increases initially with the Lysine content, reaching an optimum at a Lys:TMC ratio of 10:1, where the membrane exhibited prominent Turing patterns on its surface. These patterns were critical for achieving effective ion separation. In contrast, excessive Lysine led to spontaneous polymerization, resulting in irregular ‘stone-like’ structures and the loss of Turing patterns. The optimally cross-linked Lys-TMC membrane displayed superior Li+/Mg2+ separation performance, highlighting the crucial role of controlled cross-linking and Turing structure formation in enhancing ion selectivity. This work provides a mechanistic understanding of the relationship between Turing structure formation and ion sieving performance, offering a promising strategy for designing advanced separation membranes.

Nanoconfined electrostatic interaction for efficient anion sieving in graphene oxide membranes

Controllable ion transport and precise ion sieving are crucial for sustainable water treatment and resource recovery. 2D materials, including graphene oxide (GO) with tunable nanochannels, are emerging as ideal material platforms to develop ion sieving membranes. However, accurate ion sieving remains challenging due to the swollen and enlarged interlayer spacing of GO membranes in aqueous solution, resulting in the non-selective of small ions. Here, we reformed the GO nanosheets by physical reduction method and modified them with negatively charged molecule chains. The nanochannel sizes and electronegativity of the stacked 2D membranes were precisely controlled simultaneously. As a result, 2D nanochannel membrane with fast permeability, high efficiency and accurate Cl−/SO42− separation was constructed. The characterization and performance analysis further proved that the interlayer spacing and electrification of 2D nanochannels are strongly related to ion sieving. By precisely adjusting the synergy between the two, Cl−/SO42− selectivity up to 91.83 with Cl− permeation rate of 1.03 mol m−2 h−1 was achieved, which is superior to state-of-the-art ion sieving membranes. Our study provides new insights into understanding ion separation mechanisms within nanochannels and enables the development for the precise construction of nanochannels to manipulate the selective transport of ions.

Lithium in drinking water: Review of chemistry, analytical methods, and treatment technologies

AbstractLithium was included in the fifth Unregulated Contaminants Monitoring Rule, signaling the Environmental Protection Agency's interest in regulating lithium. Many questions regarding occurrence, health effects, and treatability of lithium exist. This review primarily focuses on the relationship between lithium chemistry and treatability. Sampling indicates nationwide lithium occurrence in drinking water. Yet, lithium is not included in the Integrated Risk Information System, reflecting a lack of censuses regarding its health effects. Aqueous lithium is a monovalent cation with size, charge density, and solubility properties that present treatment challenges. Lithium's growing economic value is stimulating new extraction and isolation technologies, but these may not be transferable to drinking water treatment. Currently, reverse osmosis is the only full‐scale drinking water treatment technology that can reliably remove significant levels (&gt;50%) of lithium. Focusing future research efforts on electrodialysis and inorganic ion sieves may yield significant gains in effectiveness and readiness for the drinking water industry.

Synergistic effect of Fe/Zr dual doping endows hydrophilic spinel-structured H4Ti5O12 ion sieves for efficient lithium extraction from liquid resources

The practical application of spinel-structured H4Ti5O12(HTO) lithium-ion sieves (LISs) is hampered by their poor adsorption properties and recyclability. Within this research, the surface properties and internal structure of lithium-ion sieve (LIS) materials were modulated by co-doping Fe and Zr metal ions to enhance their adsorption properties. The results show that Fe and Zr have been successfully introduced to the LIS lattice, increasing Li-O bond length of position 8a and O2− content. The synthesized H4Ti4.77Fe0.2Zr0.03O12 (HTFZO-II) LIS was made up of evenly distributed nanosheets layered on top of one another to create an open laminar structure, which possesses a hydrophilic surface (contact angle: 17.8°), a high surface area (95.89 m2/g), and hierarchical porous structure. Compared with the undoped HTO, the HTFZO-II LISs enjoy a high capacity for Li+ adsorption (28.72 mg/g), a strong cycling stability (Ti4+ dissolving loss: 0.12 %), and a fast reaching of the equilibrium in adsorption (adsorption equilibrium: 4 h). Theoretical calculation of DFT shows that Li(H2O)4+ on HTFZO-II and HTO dehydration were partially dehydrated into Li(H2O)+. The energy required for the dehydration of Li(H2O)4+ on HTFZO-II is lower than that on undoped HTO, indicating that metal ion doping modification was beneficial for the dehydration of hydrated lithium ions on the adsorbent surface, thereby accelerating the exchange reaction between H+ and dehydrated Li+ ions. This study reveals the key role of the synergistic effect of multi-element co-doping in enhancing the adsorption performance and structural stability of LISs.

Heterogeneous Covalent Organic Framework Membranes Mediated by Polycations for Efficient Ions Separation.

Precise ions sieving at angstrom-scale is gaining tremendous attention thanks to its significant impact at the water-energy nexus. Herein, a novel polycation-modulated interfacial polymerization (IP) strategy is developed to prepare a heterogeneously charged covalent organic frameworks (COFs) membrane. Cationic poly(diallyldimethylammonium chloride) (PDDA) regulates the growth and assembly of anionic COFs nanosheets, which thus provides a negative, smooth top surface and positive, rough bottom surface, indicating the presence of heterogeneously charged angstrom-scale channels through the membrane. Experiments and simulations are conducted to understand the facilitated ions transport behavior relative to specific interactions raised by heterogeneously charged channels and angstrom-scale steric hinderance as well, rendering the membrane with robust mono-/divalent cations sieving capabilities. The selectivity (61.6) of Li+ to Mg2+ in mixed saline under the continuous cross-flow filtration mode is superior to most of the reported nanofiltration membranes. This polycation-mediated interfacial polymerization strategy offers a compelling opportunity to develop versatile heterogeneously charged COF membranes for exquisite ion sieving.