Zhong Liu

Precise regulation of the transport properties of monovalent and divalent cations is essential for applications in biosensors, membrane separation, nanofluidic devices, and energy conversion systems. For artificial ion channels, the cooperative interaction and release of target ions with affinity sites are significant for enhancing ion recognition and selectivity. Here, we constructed a series of ion channels by embedding crown ether molecules (12C4, 15C5, 18C6) into a covalent organic framework (COF) membrane via in situ assembly. Experiments have demonstrated that the presence of crown ethers results in reduced water permeability and induces forced dehydration of ions, with their interaction depending on the hydration state of ions. Molecular simulations further reveal that monovalent cations experience moderate binding and lower dehydration barriers within the 12C4-confined nanochannels, enabling rapid ion release, whereas divalent cations are kinetically trapped by excessively strong coordination. The interaction between 12C4 molecules and monovalent cations is optimal, facilitating dehydration within the membrane and expediting their rapid release, achieving an ideal equilibrium between thermodynamic adsorption and kinetic transmission of monovalent ions and enhancing their efficient transport while obstructing the passage of divalent ions. The 12C4@COF membrane showed the highest K⁺/Mg²⁺ selectivity (232) under concentration dialysis and retained strong performance (K⁺/Mg²⁺~100, K⁺ permeance ~612 mmol·m^-2·h^-1) under electrodialysis. This work demonstrates a generalizable strategy for tuning ion transport via molecular-level binding affinity modulation, providing a robust and generalizable strategy for high-performance mono/divalent cation separation.

Direct lithium extraction using LiMn ₂ O ₄ spinel suffers from structural instability and capacity fading due to Mn dissolution and Jahn–Teller distortion. Inspired by redox shuttle chemistry, this work presents a dynamic valence‐state engineering strategy utilizing redox‐active Cr ³⁺ /Cr ⁴⁺ , Ni ²⁺ /Ni ³⁺ , and Co ²⁺ /Co ³⁺ pairs to stabilize the spinel framework. Among these, the Co ²⁺ /Co ³⁺ pair functions as an active “electronic buffer pool,” enabling redox‐mediated stabilization that mitigates lattice instabilities during operation. In situ Raman spectroscopy provides spectroscopic evidence of the reversible Co‐O redox dynamics, suggesting possible redox interactions between Co and Mn species (Co ³⁺ + Mn ²⁺ → Co ²⁺ + Mn ³⁺ ) that help regulate the local electronic environment prior to structural degradation. The optimized LiCo _1.0 Mn _1.0 O ₄ electrode achieves a remarkable 75.52% capacity retention over 500 cycles (vs. 14.26% for pristine LiMn ₂ O ₄ ) in authentic salt lake brine, while suppressing Mn dissolution by 92.3%. Beyond electrochemical superiority, techno‐economic analysis and life‐cycle assessment (TEA/LCA) suggest that this “self‐healing” architecture reduces chemical remediation costs and environmental footprints, aligning with Green Chemistry principles. This redox‐mediated stabilization offers a promising strategy for engineering durable spinel electrodes for sustainable lithium recovery from brines, paving the way for next‐generation selective extraction systems.

The rapidly growing demand for lithium in energy storage technologies necessitates more efficient lithium extraction methods from salt lakes. Direct lithium extraction (DLE) has gained attention, as it addresses more than 50% lithium losses in traditional salt-pond–based processes. However, separating lithium ion from sodium ion or potassium ion remains challenging due to their similar charge and hydration radii. To overcome this, we developed a covalent organic framework–based ion trap membrane by embedding lithiophilic diketone molecules [2-thenoyltrifluoroacetone (HTTA)] into subnanometer channels, enabling a “bind-jump” transport mechanism. HTTA sites selectively bind lithium ion, assist its partial dehydration (bind step), and promote hopping to adjacent HTTA sites (jump step). The optimized HTTA ₁ –1,3,5-triformylphloroglucinol–tris(4-aminophenyl)amine/polyacrylonitrile membrane exhibited high lithium ion/sodium ion selectivity (>320) and lithium ion permeance (~143 millimoles per square meter per hour) under electrodialysis, outperforming leading membranes. The membrane also showed stable performance over 10 cycles. This work demonstrates a scalable strategy combining thermodynamic and kinetic modulation for efficient lithium ion extraction from complex brines.

The development of multifunctional materials capable of simultaneously capturing and immobilizing uranium(VI) [U(VI)] in complex saline environments remains a significant challenge for sustainable uranium recovery. In this study, a novel phosphate covalent organic framework (TFPD-COF-HP) that integrates both adsorption and photocatalytic functions was successfully constructed. The introduced phosphate groups function as a "dual-engine," orchestrating both thermodynamic coordination stability and kinetic excited-state dynamics to increase U(VI) adsorption capacity. The U(VI) adsorption capacity of TFPD-COF-HP increased by 28% compared to that of unmodified COF (TFPD-COF) with 389.7 mg g-1 under light irradiation at pH 5. Importantly, in the untreated Mahai saltlake (Qinghai), TFPD-COF-HP reached adsorption equilibrium after 20 days, with an adsorption capacity of was 2.59 mg g-1 and an adsorption rate of 0.129 mg g-1 day-1. Combined experimental characterizations and theoretical calculations were employed to elucidate the coordination behavior and orbital interactions between the adsorbent and uranyl ions. ETS-NOCV analysis uncovers a unique push–pull electron adsorption mechanism, where U to O σ polarization and O to U π back-donation synergistically stabilize the uranium complexes. Excited-state charge transfer studies confirm that phosphorylation extends hole–electron separation, suppresses radiative recombination, and promotes interfacial charge transfer. Based on the above analysis, the robust adsorption performance of TFPD-COF-HP stems from the synergy between its high-affinity uranium binding capability and efficient photocatalytic induced uranium precipitation, highlighting its potential for sustainable uranium recovery.

Membranes offering high ion permeability with exceptional selectivity are crucial for applications ranging from sustainable water treatment to resource extraction. Inspired by "artificially constructed molecular locks" (ion imprinting) and the voltage-gated behavior of biological ion channels, we combine a carbon nanotube (CNT) conductive network with a Prussian blue (PB) ion-imprinted lattice to fabricate an electrochemically gated ion-selective membrane. Meanwhile, the anchoring of specific cations in the crystal lattice allowed for the precise tuning of subnanometer transport channel sizes. The combined action of ion-imprinted channels and redox gating enables the PB membrane to achieve an ultrahigh K⁺/Li⁺ selectivity of 481.2, far exceeding the performance (1.5-40) of previously reported electro-responsive membranes. Electrochemical characterization and DFT simulations show that applying a redox potential accelerates diffusion, improves lattice conductivity, and weakens the ion-imprinting bias. Under voltage control, the membrane preferentially transports K⁺, significantly increasing K⁺/Li⁺ selectivity. This work provides fundamental insights into redox-regulated transport in crystalline lattices and proposes an approach for designing next-generation ion-imprinted separation membranes with voltage-sensitive ultrahigh selectivity.

The development of multifunctional materials capable of simultaneously capturing and reducing uranium(VI) [U(VI)] in complex saline environments remains a significant challenge for sustainable uranium recovery. In this study, a novel phosphate covalent organic framework (TFPD-COF-HP) that integrates both adsorption and photocatalytic functions was successfully constructed. The introduced phosphate groups function as a "dual-engine," orchestrating both thermodynamic coordination stability and kinetic excited-state dynamics to increase U(VI) adsorption capacity. The U(VI) adsorption capacity of TFPD-COF-HP increased by 28% compared to that of unmodified COF (TFPD-COF) with 390.7 mg g-1 under light irradiation at pH 5. Importantly, in the untreated Mahai saltlake (Qinghai), the adsorption capacity of TFPD-COF-HP was 2.64 mg g-1 after 30 days, with an adsorption rate of 0.13 mg g-1 day-1. Moreover, the experimental characterization with theoretical calculations are integrated to elucidate the coordination mechanisms and orbital interactions between the adsorbent and uranyl ions, thereby revealing the adsorption mechanism of TFPD-COF-HP. ETS-NOCV analysis uncovers a unique push–pull electron adsorption mechanism, where U to O σ polarization and O to U π back-donation synergistically stabilize the uranium complexes. Excited-state charge transfer studies confirm that phosphorylation extends hole–electron separation, suppresses radiative recombination, and enhances the availability of reductive electrons. Based on the above analysis, the robust adsorption performance of TFPD-COF-HP stems from the synergy between its high-affinity uranium binding capability and efficient photocatalytic reduction, highlighting its potential for sustainable uranium recovery.

LiMn2O4, owing to its unique lattice sieving properties, has become a key material for electrochemical lithium extraction from high-magnesium-to-lithium-ratio brines. However, its commercialisation remains challenging due to Mn dissolution issues during cycling. In this study, an interfacial synergistic strategy is proposed with the aim of mitigating Mn leaching from LiMn2O4. By carbon-coating LiMn2O4 crystals, and incorporating sulfonated ionic polymers (Nafion) during film electrode assembly, the curved carbon pore pathways and the trapping effect of Nafion increase the resistance to Mn2+ dissolution at the carbon layer interface, leading to higher Mn2+ concentrations within the carbon layer, thereby inhibiting the dissolution of Mn3+ disproportionation reaction in LiMn2O4 crystals. Experimental results demonstrate that the modified carbon-coated LiMn2O4 electrode exhibits a Mn dissolution rate of merely 0.336% after 20 adsorption-desorption cycles in simulated brine. Both the separation factor and adsorption capacity show significant enhancement. Concurrently, XPS and EPR analyses confirmed the effective immobilisation of Mn2+ within the film electrode assembly. This study demonstrates that rational design and optimisation of the electrode's critical interface layer substantially prolongs the cycling life of LiMn2O4 electrodes, providing a robust material foundation for practical applications.

LiMn2O4, owing to its unique lattice sieving properties, has become a key material for electrochemical lithium extraction from high-magnesium-to-lithium-ratio brines. However, its commercialisation remains challenging due to Mn dissolution issues during cycling. In this study, an interfacial synergistic strategy is proposed with the aim of mitigating Mn leaching from LiMn2O4. By carbon-coating LiMn2O4 crystals, and incorporating sulfonated ionic polymers (Nafion) during film electrode assembly, the curved carbon pore pathways and the trapping effect of Nafion increase the resistance to Mn2+ dissolution at the carbon layer interface, leading to higher Mn2+ concentrations within the carbon layer, thereby inhibiting the dissolution of Mn3+ disproportionation reaction in LiMn2O4 crystals. Experimental results demonstrate that the modified carbon-coated LiMn2O4 electrode exhibits a Mn dissolution rate of merely 0.336% after 20 adsorption-desorption cycles in simulated brine. Both the separation factor and adsorption capacity show significant enhancement. Concurrently, XPS and EPR analyses confirmed the effective immobilisation of Mn2+ within the film electrode assembly. This study demonstrates that rational design and optimisation of the electrode's critical interface layer substantially prolongs the cycling life of LiMn2O4 electrodes, providing a robust material foundation for practical applications.

Direct lithium extraction (DLE) from brine using electrosorption processes offers an environmentally sustainable alternative to evaporation-based mining, but its advancement has been hindered by the lack of electrode materials that combine high selectivity, fast kinetics, and long-term stability. Lithium titanate (LTO) is structurally robust and chemically selective yet remains electrochemically inactive under aqueous conditions. In contrast, manganese-based spinels exhibit strong redox activity but suffer from structural degradation. Here, we report a site-selective doping strategy that integrates the strengths of both material classes by incorporating Mn into the spinel framework of LTO. Crystallographic, spectroscopic, and electrochemical analyses reveal that Mn substitution of specific lattice sites modulates both Li⁺ transport pathways and redox-active centers, enabling enhanced intercalation kinetics and electronic conductivity without compromising the structural integrity of the crystal lattice. The optimized electrode material (H₁.₃₃Ti₁.₁₇Mn₀.₅O₄) achieves a record Li⁺ adsorption capacity of 43.58 mg/g at 350 ppm of Li⁺ with high selectivity and minimal capacity loss after repeated cycling with real salt lake brine. This approach transforms an electrochemically inert but stable spinel into a redox-active host, providing a generalizable pathway for designing acid-free and energy-efficient electrodes for sustainable lithium recovery from complex saline resources.