Light-responsive and ultrapermeable two-dimensional metal-organic framework membrane for efficient ionic energy harvesting.

Nanofluidic membranes offer exceptional promise for osmotic energy conversion, but the challenge of balancing ionic selectivity and permeability persists. Here, we present a bionic nanofluidic system based on two-dimensional (2D) copper tetra-(4-carboxyphenyl) porphyrin framework (Cu-TCPP). The inherent nanoporous structure and horizontal interlayer channels endow the Cu-TCPP membrane with ultrahigh ion permeability and allow for a power density of 16.64 W m-2, surpassing state of-the-art nanochannel membranes. Moreover, leveraging the photo-thermal property of Cu-TCPP, light-controlled ion active transport is realized even under natural sunlight. By combining solar energy with salinity gradient, the driving force for ion transport is reinforced, leading to further improvements in energy conversion performance. Notably, light could even eliminate the need for salinity gradient, achieving a power density of 0.82 W m-2 in a symmetric solution system. Our work introduces a new perspective on developing advanced membranes for solar/ionic energy conversion and extends the concept of salinity energy to a notion of ionic energy.

A marine bacteria-inspired electrochemical regulation for continuous uranium extraction from seawater and salt lake brine.

Oceans and salt lakes contain vast amounts of uranium. Uranium recovery from natural water not only copes with radioactive pollution in water but also can sustain the fuel supply for nuclear power. The adsorption-assisted electrochemical processes offer a promising route for efficient uranium extraction. However, competitive hydrogen evolution greatly reduces the extraction capacity and the stability of electrode materials with electrocatalytic activity. In this study, we got inspiration from the biomineralisation of marine bacteria under high salinity and biomimetically regulated the electrochemical process to avoid the undesired deposition of metal hydroxides. The uranium uptake capacity can be increased by more than 20% without extra energy input. In natural seawater, the designed membrane electrode exhibits an impressive extraction capacity of 48.04 mg-U per g-COF within 21 days (2.29 mg-U per g-COF per day). Furthermore, in salt lake brine with much higher salinity, the membrane can extract as much uranium as 75.72 mg-U per g-COF after 32 days (2.37 mg-U per g-COF per day). This study provides a general basis for the performance optimisation of uranium capture electrodes, which is beneficial for sustainable access to nuclear energy sources from natural water systems.

Archaea-Inspired Switchable Nanochannels for On-Demand Lithium Detection by pH Activation.

With the rapid development of the lithium ion battery industry, emerging lithium (Li) enrichment in nature has attracted ever-growing attention due to the biotoxicity of high Li levels. To date, fast lithium ion (Li+) detection remains urgent but is limited by the selectivity, sensitivity, and stability of conventional technologies based on passive response processes. In nature, archaeal plasma membrane ion exchangers (NCLX_Mj) exhibit Li+-gated multi/monovalent ion transport behavior, activated by different stimuli. Inspired by NCLX_Mj, we design a pH-controlled biomimetic Li+-responsive solid-state nanochannel system for on-demand Li+ detection using 2-(2-hydroxyphenyl)benzoxazole (HPBO) units as Li+ recognition groups. Pristine HPBO is not reactive to Li+, whereas negatively charged HPBO enables specific Li+ coordination under alkaline conditions to decrease the ion exchange capacity of nanochannels. On-demand Li+ detection is achieved by monitoring the decline in currents, thereby ensuring precise and stable Li+ recognition (>0.1 mM) in the toxic range of Li+ concentration (>1.5 mM) for human beings. This work provides a new approach to constructing Li+ detection nanodevices and has potential for applications of Li-related industries and medical services.

Single Idiosyncratic Ionic Generator Working in Iso-Osmotic Solutions Via Ligand Confined Assembled in Gaps Between Nanosheets.

Numerous reported bioinspired osmotic energy conversion systems employing cation-/anion-selective membranes and solutions with different salinity are actually far from the biological counterpart. The iso-osmotic power generator with the specific ionic permselective channels (e.g., K+ or Na+ channels) which just allow specific ions to get across and iso-osmotic solutions still remain challenges. Inspired by nature, we report a bioinspired K+ -channel by employing a K+ selective ligand, 1,1,1-tris{[(2'-benzylaminoformyl)phenoxy]methyl}ethane (BMP) and graphene oxide membrane. Specifically, the K+ and Na+ selectivity of the prepared system could reach up to ≈17.8, and the molecular dynamics simulation revealed that the excellent permselectivity of K+ mainly stemmed from the formed suitable channel size. Thus, we assembled the K+ -selective iso-osmotic power generator (KSIPG) with the power density up to ≈15.1 mW/m2 between equal concentration solutions, which is higher than traditional charge-selective osmotic power generator (CSOPG). The proposed strategy has well shown the realizable approach to construct single-ion selective channels-based highly efficient iso-osmotic energy conversion systems and would surely inspire new applications in other fields, including self-powered systems and medical materials, etc.

Neuron-Inspired Nanofluidic Biosensors for Highly Sensitive and Selective Imidacloprid Detection.

Pesticides have caused concerns about food safety due to their residual effects in vegetables and fruits. Imidacloprid, as the frequently used neonicotinoid pesticide, could harm cardiovascular and respiratory function and cause reproductive toxicity in humans. Therefore, reliable methods for portable, selective, and rapid detection are desirable to develop. Herein, we report a neuron-inspired nanofluidic biosensor based on a tyrosine-modified artificial nanochannel for sensitively detecting imidacloprid. The functional tyrosine is modified on the outer surface of porous anodic aluminum oxide to rapidly capture imidacloprid through π-π interactions and hydrogen bonds. The integrated nanofluidic biosensor has a wide concentration range from 10-8 to 10-4 g/mL with an ultralow detection limit of 6.28 × 10-9 g/mL, which outperforms the state-of-the-art sensors. This work provides a new perspective on detecting imidacloprid residues as well as other hazardous pesticide residues in environmental and food samples.

Skeleton engineering of rigid covalent organic frameworks to alter the number of binding sites for improved radionuclide extraction.

Crystalline porous covalent frameworks (COFs) have been considered as a platform for uranium extraction from seawater and nuclear waste. However, the role of rigid skeleton and atomically precise structures of COFs is often ignored in the design of defined binding configuration. Here, a COF with an optimized relative position of two bidentate ligands realizes full potential in uranium extraction. Compared with the para-chelating groups, the optimized ortho-chelating groups with oriented adjacent phenolic hydroxyl groups on the rigid skeleton endow an additional uranyl binding site, thereby increasing the total number of binding sites up to 150%. Experimental and theoretical results indicate that the uranyl capture is greatly improved via the energetically favored multi-site configuration and the adsorption capacity reaches up to 640 mg g-1, which exceeds that of most reported COF-based adsorbents with chemical coordination mechanism in uranium aqueous solution. This ligand engineering strategy can efficiently advance the fundamental understanding of designing the sorbent systems for extraction and remediation technology.

Construction of a hierarchical membrane with angstrom-scale ion channels for enhanced Li+/Mg2+ separation.

A biomimetic hierarchical membrane consisting of ZIF-8 and MXene with controllable morphology could be fabricated by the facile electrochemical deposition method, well-realizing Li+/Mg2+ sieving. This membrane could work stably in real brine with perm-selectivity of Li+/Mg2+ up to 47.4.

Engineering Multi-field-coupled Synergistic Ion Transport System Based on the Heterogeneous Nanofluidic Membrane for High-Efficient Lithium Extraction.

The global carbon neutrality strategy brings a wave of rechargeable lithium-ion batteries technique development and induces an ever-growing consumption and demand for lithium (Li). Among all the Li exploitation, extracting Li from spent LIBs would be a strategic and perspective approach, especially with the low energy consumption and eco-friendly membrane separation method. However, current membrane separation systems mainly focus on monotonous membrane design and structure optimization, and rarely further consider the coordination of inherent structure and applied external field, resulting in limited ion transport. Here, we propose a heterogeneous nanofluidic membrane as a platform for coupling multi-external fields (i.e., light-induced heat, electrical, and concentration gradient fields) to construct the multi-field-coupled synergistic ion transport system (MSITS) for Li-ion extraction from spent LIBs. The Li flux of the MSITS reaches 367.4 mmol m-2 h-1, even higher than the sum flux of those applied individual fields, reflecting synergistic enhancement for ion transport of the multi-field-coupled effect. Benefiting from the adaptation of membrane structure and multi-external fields, the proposed system exhibits ultrahigh selectivity with a Li+/Co2+ factor of 216,412, outperforming previous reports. MSITS based on nanofluidic membrane proves to be a promising ion transport strategy, as it could accelerate ion transmembrane transport and alleviate the ion concentration polarization effect. This work demonstrated a collaborative system equipped with an optimized membrane for high-efficient Li extraction, providing an expanded strategy to investigate the other membrane-based applications of their common similarities in core concepts.

Efficient Solar-osmotic Power Generation from Bioinspired Anti-fouling 2D WS2 Composite Membranes.

Nanofluidic reverse electrodialysis provides an attractive way to harvest osmotic energy. However, most attention was paid to monotonous membrane structure optimization to promote selective ion transport, while the role of external fields and relevant mechanisms are rarely explored. Here, we demonstrate a Kevlar-toughened tungsten disulfide (WS2 ) composite membrane with bioinspired serosa-mimetic structures as an efficient osmotic energy generator coupling light. As a result, the output power could be up to 16.43 W m-2 under irradiation, outperforming traditional two-dimensional (2D) membranes. Both the experiment and simulation uncover that the generated photothermal and photoelectronic effects could synergistically promote the confined ion transport process. In addition, this membrane also possesses great anti-fouling properties, endowing its practical application. This work paves new avenues for sustainable power generation by coupling solar energy.

Confined Ionic-Liquid-Mediated Cation Diffusion through Layered Membranes for High-Performance Osmotic Energy Conversion.

Ion-selective membranes act as the core components in osmotic energy harvesting, but remain with deficiencies such as low ion selectivity and a tendency to swell. 2D nanofluidic membranes as competitive candidates are still subjected to limited mass transport brought by insufficient wetting and poor stability in water. Here, an ionic-liquid-infused graphene oxide (GO@IL) membrane with ultrafast ion transport ability is reported, and how the confined ionic liquid mediates selective cation diffusion is revealed. The infusion of ionic liquids endows the 2D membrane with excellent mechanical strength, anti-swelling properties, and good stability in aqueous electrolytes. Importantly, immiscible ionic liquids also provide a medium, allowing partial dehydration for ultrafast ion transport. Through molecular dynamics simulation and finite element modeling, that GO nanosheets induce ionic liquids to rearrange, bringing in additional space charges, which can be coupled with GO synergistically, is proved. By mixing 0.5/0.01 m NaCl solution, the power density can achieve a record value of ≈6.7 W m-2 , outperforming state-of-art GO-based membranes. This work opens up a new route for boosting nanofluidic energy conversion because of the diversity of the ILs and 2D materials.

A Bioinspired Free-Standing 2D Crown-Ether-Based Polyimine Membrane for Selective Proton Transport.

Biological proton channels play important roles in the delicate metabolism process, and have led to great interest in mimicking selective proton transport. Herein, we designed a bioinspired proton transport membrane by incorporating flexible 14-crown-4 (14C4) units into rigid frameworks of polyimine films by an interfacial Schiff base reaction. The Young's modulus of the membrane reaches about 8.2 GPa. The 14C4 units could grab water, thereby forming hydrogen bond-water networks and acting as jumping sites to lower the energy barrier of proton transport. The molecular chains present a vertical orientation to the membrane, and the ions travel between the quasi-planar molecular sheets. Furthermore, the 14C4 moieties could bond alkali ions through host-guest interactions. Thus, the ion conductance follows H+ ≫K+ >Na+ >Li+ , and an ultrahigh selectivity of H+ /Li+ (ca. 215) is obtained. This study provides an effective avenue for developing ion-selective membranes by embedding macrocycle motifs with inherent cavities.

Tunable Ion Transport in Two-Dimensional Nanofluidic Channels.

Layered two-dimensional (2D) materials with interlayer channels at the nanometer scale offer an ideal platform to control ion transport behaviors, including high-precision separation, ultrafast diffusion, and tunable permeation flux, which show great potential for energy conversion and storage, water treatment, catalysis, biosynthesis, and sensing. Recent advances in controlling the structure and functionality of 2D nanofluidic channels sustainably open doors for more revolutionary applications. In this Perspective, we first present a brief introduction to the fundamental mechanisms for ion transport in 2D nanofluidic channels and an overview of state-of-the-art assembly technologies of nanochannel membranes. We then point out new avenues for developing advanced nanofluidics, combining molecular-level cross-linking, and surface modification in nanoconfinement. Finally, we outline the potential applications of these 2D nanofluidic channel membranes and their technical challenges that need to be addressed to afford for practical applications.

Heterogeneous Electrospinning Nanofiber Membranes with pH-regulated Ion Gating for Tunable Osmotic Power Harvesting.

Biological ion channels existing in organisms are critical for many biological processes. Inspired by biological ion channels, the heterogeneous electrospinning nanofiber membranes (HENM) with functional ion channels are constructed by electrospinning technology. The HENM successfully realizes ion-gating effects, which can be used for tunable energy conversions. Introduction of pyridine and carboxylic acid groups into the HENM plays an important role in generating unique and stable ion transport behaviors, in which gates become alternative states of open and close, responding to symmetric/asymmetric pH stimulations. Then we used the HENM to convert osmotic energy into electric energy which reach a maximum value up to 12.34 W m-2 and the output power density of HENM-based system could be regulated by ion-gating effects. The properties of the HENM provide widespread potentials in application of smart nanofluidic devices, energy conversion, and water treatment.

Anion Concentration Gradient-Assisted Construction of a Solid-Electrolyte Interphase for a Stable Zinc Metal Anode at High Rates.

Coulombic efficiency (CE) and cycle life of metal anodes (lithium, sodium, zinc) are limited by dendritic growth and side reactions in rechargeable metal batteries. Here, we proposed a concept for constructing an anion concentration gradient (ACG)-assisted solid-electrolyte interphase (SEI) for ultrahigh ionic conductivity on metal anodes, in which the SEI layer is fabricated through an in situ chemical reaction of the sulfonic acid polymer and zinc (Zn) metal. Owing to the driving force of the sulfonate concentration gradient and high bulky sulfonate concentration, a promoted Zn2+ ionic conductivity and inhibited anion diffusion in the SEI layer are realized, resulting in a significant suppression of dendrite growth and side reaction. The presence of ACG-SEI on the Zn metal enables stable Zn plating/stripping over 2000 h at a high current density of 20 mA cm-2 and a capacity of 5 mAh cm-2 in Zn/Zn symmetric cells, and moreover an improved cycling stability is also observed in Zn/MnO2 full cells and Zn/AC supercapacitors. The SEI layer containing anion concentration gradients for stable cycling of a metal anode sheds a new light on the fundamental understanding of cation plating/stripping on metal electrodes and technical advances of rechargeable metal batteries with remarkable performance under practical conditions.

Wetting-Induced Water Promoted Flow on Tunable Liquid-Liquid Interface-Based Nanopore Membrane System.

Membrane separation provides effective methods for solving the global water crisis. Contemporary membrane systems depend on interfacial interactions between liquid and solid membrane matrixes. However, it may lead to a limiting permeate flux due to the large flow resistance at hydrophobic liquid-solid interfaces. Herein, the liquid-liquid interface with improved interface energy is reversibly introduced in membrane systems to boost wetting and reduce transport resistance. A series of interfaces were systematically explored to reveal mechanisms of wetting and boosted flow performances, which are further supported by simulations. Findings of this study highlight that interfacial liquids with lower surface energies, lower viscosities, and higher solubilities can effectively improve water flow without sacrificing rejection performance, achieving by transforming a solid-liquid interface into liquid-liquid interface interaction. It provides a concept to design advanced membrane systems for water purification (e.g., desalination and oil-water separation) and energy conversion processes.

Biomimetic KcsA channels with ultra-selective K+ transport for monovalent ion sieving.

Ultra-selective and fast transport of K+ are of significance for water desalination, energy conversion, and separation processes, but current bottleneck of achieving high-efficiency and exquisite transport is attributed to the competition from ions of similar dimensions and same valence through nanochannel communities. Here, inspired by biological KcsA channels, we report biomimetic charged porous subnanometer cages that enable ultra-selective K+ transport. For nanometer to subnanometer scales, conically structured double-helix columns exhibit typical asymmetric transport behaviors and conduct rapid K+ with a transport rate of 94.4 mmol m-2 h-1, resulting in the K+/Li+ and K+/Na+ selectivity ratios of 363 and 31, respectively. Experiments and simulations indicate that these results stem from the synergistic effects of cation-π and electrostatic interactions, which impose a higher energy barrier for Li+ and Na+ and lead to selective K+ transport. Our findings provide an effective methodology for creating in vitro biomimetic devices with high-performance K+ ion sieving.

Covalent organic frameworks embedded in polystyrene membranes for ion sieving.

A mixed matrix membrane composed of COF-300 and polystyrene (PS) with controllable thickness and porosity achieves ion sieving performance, which is dependent on the regular pore size and surface functional groups of COF-300. Hence, the selectivity of the COF-300/PS membrane for K+/Li+ and Mg2+/Li+ reached 31.5 and 14.7, respectively.

Crown Ether-Based Supramolecular Polymers: From Synthesis to Self-Assembly.

Supramolecular polymers not only possess many advantages of traditional polymers, but also have many unique characteristics. Supramolecular polymers can be constructed by self-assembly of various noncovalent interactions. Host-guest interaction, as one important type of noncovalent interactions, has been widely applied to construct supramolecular polymers. From the perspective of classification of the recognition system motifs, host-guest recognition motifs mainly include crown ether, cyclodextrin, calixarene, cucurbituril, and pillararene-based host-guest recognition pairs. Crown ethers, as the first-generation macrocyclic hosts, have played a very important part in the development of supramolecular chemistry. Due to the easy modification of crown ethers, various crown ether derivatives have been prepared by attaching some functional groups to the edges of crown ethers, which endowed them with some interesting properties and made them ideal candidates for the fabrication of supramolecular polymers. This review gives a review of the preparation of crown ether-based supramolecular polymers (CSPs) and summarizes crown ether-based recognition pairs, organization methods, topological structures, stimuli-responsiveness, and functional characteristics.

Ionic Crosslinking-Induced Nanochannels: Nanophase Separation for Ion Transport Promotion.

Charge-governed ion transport is crucial to numerous industries, and the advanced membrane is the essential component. In nature, the efficient and selective ion transport is mainly governed by the charged ion channels located in cell membrane, indicating the architecture with functional differentiation. Inspired by this architecture, a membrane by ionic crosslinking sulfonated poly(arylene ether ketone) and imidazolium-functionalized poly(arylene ether sulfone) is designed and fabricated to make full use of the charges. This ionic crosslinking is designed to realize nanophase separation to aggregate the ion pathways in the membrane, which results in excellent ion selectivity and high ion conductivity. With the excellent ion transport behavior, ionic crosslinking membrane shows great potential in osmotic energy conversion, which maximum power density can be up to 16.72 W m-2 . This design of ionic crosslinking-induced nanophase separation offers a roadmap for ion transport promotion.

Biomimetic Nanocomposite Membranes with Ultrahigh Ion Selectivity for Osmotic Power Conversion.

Ion transport in nanoconfinement exhibits significant features such as ionic rectification, ionic selectivity, and ionic gating properties, leading to the potential applications in desalination, water treatment, and energy conversion. Two-dimensional nanofluidics provide platforms to utilize this phenomenon for capturing osmotic energy. However, it is challenging to further improve the power output with inadequate charge density. Here we demonstrate a feasible strategy by employing Kevlar nanofiber as space charge donor and cross-linker to fabricate graphene oxide composite membranes. The coupling of space charge and surface charge, enabled by the stabilization of interlayer spacing, plays a key role in realizing high ion selectivity and the derived high-performance osmotic power conversion up to 5.06 W/m2. Furthermore, the output voltage of an ensemble of the membranes in series could reach 1.61 V, which can power electronic devices. The system contributes a further step toward the application of energy conversion.