Ion Sieve Research Articles

Selective Ion Transport in Two-Dimensional Ti3C2Tx Nanochannel Decorated by Crown Ether.

Ion sieving is a critical process employed in various applications, such as desalination and ion extraction. Nevertheless, achieving rapid and accurate ion sieving remains an exceptionally difficult task. Drawing inspiration from the effective ion sieving capabilities of biological ion channels, we present the development of two-dimensional Ti3C2Tx ion nanochannels incorporating 4-aminobenzo-15-crown-5-ether molecules as specific ion binding sites. These binding sites had a significant influence on the ion transport process and improved ion recognition. Permeation of both Na+ and K+ was facilitated because their ion diameters are compatible with the cavity in the ether ring. Moreover, owing to the strong electrostatic interactions, the permeation rate for Mg2+ increased by a factor of 55 compared to that for the pristine channels, which was higher than those of all monovalent cations. Furthermore, the transport rate for Li+ was relatively lower than those of Na+ and K+, which was attributed to difficult binding of the Li+ to the oxygens in the ether ring. Consequently, the ion selectivities of the composite nanochannel were up to 7.6 for Na+/Li+ and 9.2 for Mg2+/Li+. Our work presents a straightforward approach to creating nanochannels exhibiting precise ion discrimination.

Control over cathodic deposition of continuous UiO-66 films for ion-selective transport

Continuous UiO-66 films are promising for ion sieving because of their sub-nanometer-sized apertures and high chemical stability, but their preparation is challenging. Here, we report a direct cathodic deposition of UiO-66 films, which is fast, convenient, and controllable. Electrochemical measurements suggest that lithium nitrate accelerates deprotonation of carboxylic linkers and yields UiO-66 films within 1 h. Material characterizations reveal that the crystallinity of the deposited UiO-66 films improves with deposition temperature and that the morphology is controlled by the molar ratio of the ditopic linker to the monotopic modulator. Crystalline and continuous UiO-66 films are obtained with a linker-to-modulator ratio of 1:120 at 120°C. The anodic aluminum oxide membrane-supported continuous UiO-66 films display excellent selective ion transport performance with a lithium/magnesium selectivity of 286 and a lithium permeance of 11.2 mol m−2 h−1, placing them among the best metal-organic framework (MOF) membranes reported in literature.

The modification of MnO2·0.5H2O by Al/Mg doping to enhance lithium adsorption and reduce manganese dissolution with application to brines

Lithium extraction by ion sieve adsorption possesses the merits of a simple, low cost process of less pollution. In this article, lithium ion sieve MnO2·0.5H2O modified by doping with Al/Mg was obtained by hydrochloric acid pickling of precursor, which was formed by hydrothermal reaction of Mn2O3 with LiOH·H2O followed by a sintering process with Al2O3/MgO. The structure analysis indicated that the spinel structure of [MnO6] framework was observed in MnO2·0.5H2O. The lithium adsorption process reached equilibrium within 24 h and obeyed the pseudo second-order and Langmuir isotherm models. Attribute to the expanded surface area and increased Mn4+ proportion, the ion sieve doped with Al or Mg exhibited better performance in terms of lithium adsorption capacity and extent of manganese dissolution than undoped sample, and the best doping ratio were both 4%. Through doping 4% Al and 4% Mg, the adsorption capacity of doped samples in LiOH solution (CLi+ = 600 mg/L) was increased to 46.8 mg/g and 45.8 mg/g, respectively, from 40.1 mg/g, and the extent of manganese dissolution in the pickling dropped to 3.67% and 3.58% from 4.42%, respectively. Generally, adsorption capacity and selectivity of 4% Al-doped ion sieve is better than 4% Mg-doped ion sieve, therefore 4% Al-doped ion sieve is an ideal adsorbent. This study can provide a reference value to further research on efficient lithium adsorption.

3D-printed titanium-based ionic sieve monolithic adsorbent for selective lithium recovery from salt lakes

The recovery of lithium from salt lakes through the adsorption strategy has been receiving widespread attention, and titanium-based ion sieves stand out due to their high adsorption capacity and low dissolution loss. The forming of titanium-type lithium-ion sieves (Ti-LIS) is an important step in the application of Ti-LIS for the recovery of lithium from salt-lake brines. Here, the Ti-LIS monolithic adsorbent was developed by the 3D printing strategy for the recovery of lithium from brine. The adsorption properties, compressive strength and rheological properties of 3D printed Ti-LIS monolithic adsorbent were investigated. It was found that the content of Ti-LIS in the monolithic adsorbent prepared by the 3D printing strategy was up to 75 %, and the compressive strength can reach 51 MPa. The 3D-printed monolithic adsorbent has good adsorption performance, selectivity and mechanical properties, showing promising applications for lithium recovery from salt lakes.

H2Ti6O13 Nanosheet/ Polymethyl Methacrylate (PMMA) for the adsorption of cesium ions

Radioactive Cs+ is one of the most dangerous environmental pollutants. It is necessary for radioactive Cs+ management and removal. Titanium-type cesium ion sieve with a strong Ti–O bond has the advantages of structural stability, radiation resistance and no secondary contamination, which is a promising adsorbent material. In this paper, The CTO (Cs2Ti6O13) is prepared for the first time by sol-gel and de-templating methods, and cesium ion sieves (HTO/PMMA) are further obtained with diluted HCl elution. Compared with the ionic sieves (HTO) prepared by direct sol-gel method, the adsorption capacity is improved from 224.32 mg/g to 299.15 mg/g. The prepared HTO/PMMA has a larger specific surface area (67.282 m2/g). More exchange sites are provided for the adsorption of Cs ions. Moreover, Adsorption involves the cleavage of O–H bonds and the formation of O–Cs bonds, which is a typical ion exchange reaction. A series of batch experiments are carried out. The results showed that the equilibrium adsorption capacity of HTO/PMMA is 307.69 mg/g and remained high in the interfering ion solution as well (280.38 mg/g). The pseudo second order model and Freundlich model can well describe the ion exchange process. Thermodynamic study shows that adsorption is spontaneous and exothermic, and low temperature is conducive to adsorption in H+- Cs+ exchange system. Finally, the reusability of HTO/PMMA is evaluated. The adsorption capacity did not decrease significantly after 5 cycles of use. Therefore, HTO/PMMA is expected to be an excellent material for recovering radioactive Cs+.

Highly‐Efficient Ion Gating through Self‐Assembled Two‐Dimensional Photothermal Metal‐Organic Framework Membrane

AbstractBiological ion channels regulate the ion flow across cell membrane via opening or closing of the pores in response to various external stimuli. Replicating the function of high ion gating effects with artificial porous materials has been challenging. Herein, we report that the self‐assembled two‐dimensional metal‐organic framework (MOF) membrane can serve as an excellent nanofluidic platform for smart regulation of ion transport. The MOF membrane with good photothermal performance exhibits extremely high ion gating ratio (up to 104), which is among the highest values in MOF membrane nanochannels for light‐controlled ion gating reported so far. By repeatedly turning on and off the light, the nanofluidic device shows outstanding stability and reversibility that can be applied in the remote light‐switching system. This work may spark promising applications of MOF membrane with variety of stimuli responsive properties in ion sieving, biosensing, and energy conversion.

Highly-Efficient Ion Gating through Self-Assembled Two-Dimensional Photothermal Metal-Organic Framework Membrane.

Biological ion channels regulate the ion flow across cell membrane via opening or closing of the pores in response to various external stimuli. Replicating the function of high ion gating effects with artificial porous materials has been challenging. Herein, we report that the self-assembled two-dimensional metal-organic framework (MOF) membrane can serve as an excellent nanofluidic platform for smart regulation of ion transport. The MOF membrane with good photothermal performance exhibits extremely high ion gating ratio (up to 104 ), which is among the highest values in MOF membrane nanochannels for light-controlled ion gating reported so far. By repeatedly turning on and off the light, the nanofluidic device shows outstanding stability and reversibility that can be applied in the remote light-switching system. This work may spark promising applications of MOF membrane with variety of stimuli responsive properties in ion sieving, biosensing, and energy conversion.

Cellulose acetate network via ion pre-anchored strategy for simultaneous regulation of uniform Mg2+ flux and ion conductivity

Hybrid LiMg batteries stand out by combining the rapid lithium diffusion kinetics and the advantages of magnesium. However, the uneven Mg deposits may result in continuous parasitic reactions and penetrate the separator. Herein, cellulose acetate (CA), with functional groups, was applied to engineer coordination with MOFs and construct the evenly-distributed and ample nucleation sites. Moreover, the hierarchical MOFs@CA network was fabricated via the metal ion pre-anchored strategy to regulate the uniform Mg2+ flux and improve ion-conductivity simultaneously. Furthermore, the hierarchical CA networks with well-ordered MOFs provided efficient MOF-to-MOF ion-transportation channels and served as ion sieves to inhibit anion transportation, thereby mitigating polarization. The super dendrite-inhibition and interfacial compatibility was confirmed and the assembled Mo6S8//Mg batteries exhibited high capacity about 105 mAh g−1 and capacity decay of 4 % after 600 cycles at 30 C, which surpassed the state-of-the-art LMBs system employing Mo6S8 electrode. The fabricated GPE sheds fresh strategy for the design of CA-based GPEs and bright light on the promise of high-performance LMBs.

Large‐Scale and Controllable Syntheses of Covalently‐Crosslinked Poly(ionic liquid) Nanoporous Membranes

AbstractHerein, we report an exciting synthetic procedure for the scalable and controllable fabrication of covalently crosslinked poly(ionic liquid) (PIL) nanoporous membranes (CPILMs) in water solution under ambient conditions. We found that the pore sizes, flexibility and compositions of freestanding CPILMs can be finely tailored by a rational structural choice of PIL, diketone and aldehyde. Studies on the CPILM formation mechanism revealed that hydrogen bonding‐induced phase separation of amino‐functionalized homo‐PIL between its polar and apolar domains coupled with structural rearrangements due to the Debus Radsizewski reaction‐triggered ambient covalent crosslinking process created a stable three‐dimensionally interconnected pore system in water solution. Employing structurally stable CPILMs in ion sieving devices resulted in an excellent Li+/Mg2+ separation efficiency due to the positively charged nature and “Donann” effects. This green, facile yet versatile approach to the production of CPILMs is a conceptually distinct and commercially interesting strategy for making useful nanoporous functional polyelectrolyte membranes.

Large-Scale and Controllable Synthesis of Covalently-Crosslinked Poly(ionic liquid) Nanoporous Membranes.

Herein, we report an exciting synthetic procedure for the scalable and controllable fabrication of covalently crosslinked poly(ionic liquid) (PIL) nanoporous membranes (CPILMs) in water solution under ambient conditions. We found that the pore sizes, flexibility and compositions of freestanding CPILMs can be finely tailored by a rational structural choice of PIL, diketone and aldehyde. Studies on the CPILM formation mechanism revealed that hydrogen bonding-induced phase separation of amino-functionalized homo-PIL between its polar and apolar domains coupled with structural rearrangements due to the Debus Radsizewski reaction-triggered ambient covalent crosslinking process created a stable three-dimensionally interconnected pore system in water solution. Employing structurally stable CPILMs in ion sieving devices resulted in an excellent Li+/Mg2+ separation efficiency due to the positively charged nature and "Donann" effects. This green, facile yet versatile approach to the production of CPILMs is a conceptually distinct and commercially interesting strategy for making useful nanoporous functional polyelectrolyte membranes.

Metal Oxide Aerogels: A New Horizon for Stabilizing Anodes in Rechargeable Zinc Metal Batteries

AbstractDendritic deposition and side reactions have been long‐standing interfacial challenges of Zn anode, which have prevented the development of practical aqueous zinc‐based batteries. Herein, an oxygen vacancy‐rich CeO2 aerogel (VAG‐Ce) interface layer that simultaneously integrates Zn2+ selectivity, porosity, and is lightweight is reported as a new strategy to achieve dendrite‐free and corrosion‐free Zn anodes. The well‐defined and uniform nanochannels of VAG‐Ce can act as ion sieves that redistribute Zn2+ at the Zn anode surface by regulating Zn2+ flux, leading to uniform Zn deposition and significantly suppressing dendrite growth. Importantly, the abundant oxygen vacancies exposed on VAG‐Ce surface can strongly capture SO42−, forming a negatively charged layer that can attract Zn2+ and accelerate the Zn2+ migration kinetics, while the subsequent repulsion of additional anions can effectively suppress the generation of (Zn4SO4(OH)6·xH2O) byproducts, thereby realizing very stable Zn anodes. Consequently, VAG‐Ce modified Zn anode (VAG‐Ce@Zn) enables a long‐term lifespan over 4000 h at 4 mA cm−2 and a record‐high cycle life of 1200 h is achieved under an ultrahigh 85% Zn utilization at 8 mA cm−2, which enables excellent capacity retention and cycling performance of VAG@Zn/MnO2 cells. This work contributes an innovative design concept by introducing oxygen vacancy‐rich aerogels and provides a new horizon for stabilizing Zn anode for large‐scale energy storage.

Angstrom‐Level Ionic Sieve 2D‐MOF Membrane for High Power Aqueous Zinc Anode

AbstractAqueous Zn‐ion energy‐storage deviceswith metal Zn as anodes, including batteries and capacitors (ZIBs and ZICs), is largely hindered by dendritic growth and low coulombic efficiency since the side reactions between Zn anodes and electrolyte, originating fromthat targeted and efficient isolation of H2O and SO42− is extremely challenging. Herein, inspired by density functional theory (DFT) that the 2D angstrom level metal‐organic framework(2D‐MOF) is highly selective for the passage of ions, simultaneously excluding the SO42− and H2O but allowing Zn2+ selective conduction. Moreover, 2D‐MOF exhibits better mechanical strength compared with 3D‐MOF, which is more conducive to inhibit dendrite growth. Impressively, benefiting from the 2D‐MOFlayer, symmetric Zn cells survived up to 2000 h at 4 mA cm−2,near 20‐times that of bare Zn anodes. Coupling it with cathode for ZICs and ZIBs, excellent electrochemical performances are presented. Importantly, symmetric Na cells with 2D‐MOF as ionic sieve membrane also deliver small polarization and outstanding performance, indicating that this study provides an efficient strategy to develop long‐life metal anode.

Insights into High Li+/Mg2+ Separation Performance Using a PEI-Grafted Graphene Oxide Membrane

Lithium extraction from brine or seawater using membrane technology has attracted extensive attention in recent years. Graphene oxide (GO), as one of the two-dimensional materials, has been proven as a competitive candidate for membranes. However, the GO membranes still suffer challenges for ion sieving due to the swelling in the aqueous solution. In this work, a GO–PEI membrane with positively charged channels was constructed by polyelectrolyte polyethyleneimine (PEI) molecular chain-grafted GO nanosheets. The GO–PEI membrane showed a high selectivity of 22.2 for Li+/Mg2+, together with a competitive Li+ permeation rate of 0.09 mol m–2 h–1 in a binary permeation test. In addition, the membrane showed excellent stability during the separation process. The enhanced Li+/Mg2+ separation performance of the GO–PEI membrane could be mainly attributed to the synergistic effect of size sieving and electrostatic repulsion. We further systematically studied the influence of various variables, such as PEI molecular weight, PEI content, membrane thickness, and ion concentration, on separation performance. This work deepens the understanding of membrane ion selectivity from multiple perspectives and puts forward a strategy to design a two-dimensional membrane structure from microscopic materials.

Synthesis of Titanium Ion Sieves and Its Application for Lithium Recovery from Artificial Indonesian Geothermal Brine.

Synthesis of Titanium Ion Sieves and Its Application for Lithium Recovery from Artificial Indonesian Geothermal Brine.

Ion-sieving Janus separator modified by Ti3C2Tx toward dendrite-free zinc-ion battery

Aqueous zinc-ion batteries, as one of the promising substitutes for lithium-ion batteries, have received increasing attention due to their high safety, low cost, and non-toxicity. Nevertheless, the inevitable growth of zinc dendrites, hydrogen evolution, and side reactions on the Zn anode greatly hinder the further application of zinc-ion batteries. The current solutions mainly focused on electrolyte regulation, artificial interface layer introduction, and zinc alloy anode construction. MXene, as a novel generation of two-dimensional layered transition metals carbides/ nitrides, has been widely investigated in a variety of metal ion batteries in the last decade owing to excellent physical and chemical properties. Herein, we constructed an ion-sieving Janus separator for the aqueous zinc-ion battery by spraying Ti3C2Tx MXene ink on one side of the commercial glass fiber separator. Because of the advantages of MXene such as high conductivity, abundant surface functional groups, and highly matched lattice constants with the Zn anode, the composite separator can homogenize the surface electric field of the Zn anode, optimize the flux of Zn2+, and induce the uniform deposition of Zn2+. Most importantly, a unique ion sieving function was realized in the electrolyte because of the intrinsic electro-negativity of the MXene layer. The concentration of H+ and SO42- on the Zn anode side is largely reduced, and the hydrogen evolution and side reactions are greatly inhibited. Thus, for symmetrical cells, an ultralong cycling lifespan up to 2500 h and superior rate capability with dendrite-free deposition behavior were achieved. When further applying the Janus separator to aqueous zinc-ion batteries combined with the fabricated α-MnO2 cathode, Zn anode, and 2 M ZnSO4 + 0.2 M MnSO4 electrolyte, a superb capacity retention rate (85.7%) upon cycling for 500 cycles at 1.0 A g−1 was obtained. This ion-sieving separator possesses the giant potential for zinc-ion batteries.

Highly Conductive Proton Selectivity Membrane Enabled by Hollow Carbon Sieving Nanospheres for Energy Storage Devices

Ion conductive membranes (ICMs) with highly conductive proton selectivity are of significant importance and greatly desired for energy storage devices. However, it is extremely challenging to construct fast proton-selective transport channels in ICMs. Herein, a membrane with highly conductive proton selectivity was fabricated by incorporating porous carbon sieving nanospheres with a hollow structure (HCSNs) in a polymer matrix. Due to the precise ion sieving ability of the microporous carbon shells and the fast proton transport through their accessible internal cavities, this advanced membrane presented a proton conductivity (0.084 S·cm−1) superior to those of a commercial Nafion 212 (N212) membrane (0.033 S·cm−1) and a pure polymer membrane (0.049 S·cm−1). The corresponding proton selectivity of the membrane (6.68 × 105 S·min·cm−3) was found to be enhanced by about 5.9-fold and 4.3-fold, respectively, compared with those of the N212 membrane (1.13 × 105 S·min·cm−3) and the pure membrane (1.56 × 105 S·min·cm−3). Low-field nuclear magnetic resonance (LF-NMR) clearly revealed the fast proton-selective transport channels enabled by the HCSNs in the polymeric membrane. The proposed membrane exhibited an outstanding energy efficiency (EE) of 84% and long-term stability over 1400 cycles with a 0.065% capacity decay per cycle at 120 mA·cm−2 in a typical vanadium flow battery (VFB) system.

Dynamic Ion Sieve as the Buffer Layer for Regulating Li+ Flow in Lithium Metal Batteries

AbstractHow to realize uniform Li+ flow is the key to achieve even Li deposition for lithium metal batteries (LMBs). In this study, a concept of dynamic ion sieve is proposed to design the buffer layer nearby Li anode surface to regulate Li+ spatial arrangement by introducing tributylmethylphosphonium bis(trifluoromethanesulfonyl)imide (TMPB) into the carbonate electrolyte. The buffer layer induced by TMP+ can adjust the velocity of arriving solvated Li+ that gives solvated Li+ sufficient time to redistribute and accumulate on Li anode surface, resulting in a uniform and higher concentrated Li+ flow. Besides, TFSI− can participate in the generation of inorganic component‐rich solid electrolyte interphase (SEI) with Li3N, which can facilitate the Li+ conductivity of SEI. Consequently, the stable and uniform Li deposition can be obtained, achieving the excellent cycling performance up to 1000 h at 0.5 mA cm−2 in the Li||Li symmetric cell. Besides, the Li||NCM622 full cell also possesses excellent cycling stability with a high‐capacity retention rate of 66.7% after 300 cycles.

Highly selective lanthanide-doped ion sieves for lithium recovery from aqueous solutions

The increased global demand for lithium is rapidly depleting the lithium ore reserves. Therefore, attention has turned to the recovery of lithium from aqueous solutions, such as lithium-containing brine. Compared with other methods of lithium recovery, adsorption is energy efficient and simple to implement, increasing demand for selective lithium adsorbents. In this study, a selective lithium-ion adsorbent, H4Ti5– xLa xO12, was synthesized via the sol–gel method, followed by heat treatment and acid washing. The effects of the temperature and degree of lanthanum doping ( x) on the crystalline phase, morphology, lithium-ion adsorption capacity, and lithium-ion selectivity of the ion sieve were investigated, and the optimal synthetic conditions were determined. We found that doping with La3+ cations ( x = 0.01) increased the lithium-ion adsorption capacity (23.96 mg g−1 at 25 °C at pH = 12; 8.2% higher than before doping), rate, and selectivity. In addition, the ion sieve could be used over multiple adsorption–desorption cycles with only a minor reduction in the lithium-ion adsorption capacity (22.88 mg g−1). Overall, these results suggest that doping with La3+ cations stabilized the H4Ti5– xLa xO12 crystal structure, alleviated particle agglomeration, expanded the lithium-ion channels, and decreased the resistance to lithium-ion migration, thus improving adsorption performance. The findings suggest that the proposed ion sieve has practical applications in the selective recovery of lithium from aqueous solutions containing a mixture of metal ions.

Carboxymethylcellulose (CMC)/glutaraldehyde (GA)-modified Ti3C2Tx membrane and its efficient ion sieving performance

2D nanosheet membranes show promise for ion sieving. However, nanosheet swelling still adversely affects the ion sieving performance. In this study, Ti3C2Tx was mixed with carboxymethylcellulose sodium (CMC) and stirred in an ice bath; then, glutaraldehyde (GA) was added to cross-link the CMC distributed between Ti3C2Tx interlayers to obtain a CMC/GA-modified Ti3C2Tx membrane (C@TM). The strong chemical bonding between the Ti3C2Tx andd CMC prevented swelling of the Ti3C2Tx nanosheets in aqueous solutions. A stable effective interlayer spacing (4.8±0.1 Å) was obtained, and the mechanical strength of the membrane was improved. Due to size sieving and image force repulsions, C@TM exhibited efficient divalent ion retention performance. The C@TM selectivity for monovalent/divalent ions was approximately 30; this value was 14 times higher than that of the original Ti3C2Tx membrane (OTM). In addition, based on aldol condensation reaction, GA blocked the exposed oxygen-containing groups in the CMC to form a water-insoluble macromolecular network, which improved the water stability of the membrane. C@TM exhibited excellent membrane performance during long-term (72 h) operation. The effects of applied voltages on the separation performance were tested. The results showed that Mg2+ transport was significantly inhibited at -0.6 V, and the Li+/Mg2+ selectivity was increased.

Sub‐2‐nm Channels within Covalent Triazine Framework Enable Fast Proton‐Selective Transport in Flow Battery Membrane

AbstractIon conductive membranes (ICMs) with robust sub‐2‐nm channels show high proton transport rate in flow battery, but it remains a great challenge to precisely control the ion sieving of the membranes. Herein, as a promising proton‐selective carrier, sulfonated piperazine covalent triazine framework (s‐pCTF) with the channel size of ≈1.5 nm and abundant fast proton hopping sites is introduced into sulfonated poly(ether ether ketone) (SPEEK) to fabricate advanced ICM for vanadium flow battery (VFB) application. The interior protoplasmic channels of s‐pCTF demonstrate significant Donnan exclusion effect, resulting in a high proton/vanadium ion selectivity in theory (6.22 × 105). Meanwhile, the nitrogen‐rich sub‐2‐nm channels yield fast proton highway, and exterior‐grafted sulfonic acid groups further facilitate the proton transfer. By regulating the ion sieving and proton conductivity, the optimal hybrid membrane exhibits synchronously improved battery performance with an enhanced energy efficiency (92.41% to 78.53% at 40–200 mA cm−2) and long‐term stability for 900 cycles over 400 h (EE: 87.2–85% at 120 mA cm−2), outperforming pure SPEEK and Nafion212 membranes. This study validates the applicability of organic porous CTF with sub‐2‐nm channels and desired functionality in ICMs for high‐performance VFB application.