Unlocking Direct Lithium Extraction in Harsh Conditions through Thiol-Functionalized Metal-Organic Framework Subnanofluidic Membranes.

Metal-organic framework (MOF) membranes with high ion selectivity are highly desirable for direct lithium-ion (Li+) separation from industrial brines. However, very few MOF membranes can efficiently separate Li+ from brines of high Mg2+/Li+ concentration ratios and keep stable in ultrahigh Mg2+-concentrated brines. This work reports a type of MOF-channel membranes (MOFCMs) by growing UiO-66-(SH)2 into the nanochannels of polymer substrates to improve the efficiency of MOF membranes for challenging Li+ extraction. The resulting membranes demonstrate excellent monovalent metal ion selectivity over divalent metal ions, with Li+/Mg2+ selectivity up to 103 since Mg2+ should overcome a higher energy barrier than Li+ when transported through the MOF pores, as confirmed by molecular dynamics simulations. Under dual-ion diffusion, as the Mg2+/Li+ mole ratio of the feed solution increases from 0.2 to 30, the membrane Li+/Mg2+ selectivity decreases from 1516 to 19, corresponding to the purity of lithium products between 99.9 and 95.0%. Further research on multi-ion diffusion that involves Mg2+ and three monovalent metal ions (K+, Na+, and Li+, referred to as M+) in the feed solutions shows a significant improvement in Li+/Mg2+ separation efficiency. The Li+/Mg2+ selectivity can go up to 1114 when the Mg2+/M+ molar concentration ratio is 1:1, and it remains at 19 when the ratio is 30:1. The membrane selectivity is also stable for 30 days in a highly concentrated solution with a high Mg2+/Li+ concentration ratio. These results indicate the feasibility of the MOFCMs for direct lithium extraction from brines with Mg2+ concentrations up to 3.5 M. This study provides an alternative strategy for designing efficient MOF membranes in extracting valuable minerals in the future.

Surface-Enriched Room-Temperature Liquid Bismuth for Catalytic CO2 Reduction.

Bismuth-based electrocatalysts are effective for carbon dioxide (CO2) reduction to formate. However, at room temperature, these materials are only available in solid state, which inevitably suffers from surface deactivation, declining current densities, and Faradaic efficiencies. Here, the formation of a liquid bismuth catalyst on the liquid gallium surface at ambient conditions is shown as its exceptional performance in the electrochemical reduction of CO2 (i.e., CO2RR). By doping a trace amount of bismuth (740 ppm atomic) in gallium liquid metal, a surface enrichment of bismuth by over 400 times (30 at%) in liquid state is obtained without atomic aggregation, achieving 98% Faradic efficiency for CO2 conversion to formate over 80 h. Ab initio molecular simulations and density functional theory calculations reveal that bismuth atoms in the liquid state are the most energetically favorable sites for the CO2RR intermediates, superior to solid Bi-sites, as well as joint GaBi-sites. This study opens an avenue for fabricating high-performing liquid-state metallic catalysts that cannot be reached by elementary metals under electrocatalytic conditions.

Ion-Specific Nanoconfinement Effect in Multilayered Graphene Membranes: A Combined Nuclear Magnetic Resonance and Computational Study.

Ion adsorption within nanopores is involved in numerous applications. However, a comprehensive understanding of the fundamental relationship between in-pore ion concentration and pore size, particularly in the sub-2 nm range, is scarce. This study investigates the ion-species-dependent concentration in multilayered graphene membranes (MGMs) with tunable nanoslit sizes (0.5-1.6 nm) using nuclear magnetic resonance and computational simulations. For Na+-based electrolytes in MGMs, the concentration of anions in graphene nanoslits increases in correlation with their chaotropic properties. As the nanoslit size decreases, the concentration of chaotropic ion (BF4-) increases, whereas the concentration of kosmotropic ions (Cit3-, PO43-) and other ions (Ac-, F-) decreases or changes slightly. Notably, anions remain more concentrated than counter Na+ ions, leading to electroneutrality breakdown and unipolar anion packing in MGMs. A continuum modeling approach, integrating molecular dynamic simulation with the Poisson-Boltzmann model, elucidates these observations by considering water-mediated ion-graphene non-electrostatic interactions and charge screening from graphene walls.

Screening of Alkali Metal-Exchanged Zeolites for Nitrogen/Methane Separation.

Methane (CH4) is the primary component of natural gas and must be purified to a certain level before it can be used as pipeline gas or liquified natural gas (LNG). In particular, nitrogen (N2), a common contaminant in natural gas needs to be rejected to increase the heating value of the gas and meet the LNG product specifications. The development of energy-efficient N2 removal technologies is hampered by N2's inertness and its resemblance to CH4 in terms of kinetic size and polarizability. N2-selective materials are so rare. Here, for the first time, we screened 1425 alkali metal cation exchange zeolites to identify the candidates with the best potential for the separation of N2 from CH4. We discovered a few extraordinary zeolite frameworks capable of achieving equilibrium selectivity toward N2. Particularly, Li+-RRO-3 zeolite with a specific two-dimensional structure demonstrated a selective N2 adsorption capacity of 2.94 mmol/g at 283 K and 1 bar, outperforming the capacity of all known zeolites. Through an ab initio density functional theory study, we found that the five-membered ring of the RRO framework is the most stable cationic site for Li+, and this Li+ can interact with multiple N2 molecules but only one CH4, revealing the mechanism for the high capacity and selectivity of N2. This work suggests promising adsorbents to enable N2 rejection from CH4 in the gas industry without going for energy-intensive cryogenic distillations.

Nitrogen rejection in natural gas using NaZSM-25 zeolite.

Natural gas reservoirs usually contain considerable amounts of nitrogen (N2). Methane (CH4) as the main component in natural gas must be purified before transferring to the pipeline or storing as liquified natural gas (LNG). Currently, energy-intensive cryogenic distillation is the only industrial approach for N2 rejection in natural gas. The adsorption process based on a N2-selective adsorbent can minimize the separation cost. However, the search for an adsorbent that can selectively reject N2 in natural gas has lasted for decades. Here, we report a microporous zeolite called NaZSM-25 capable of adsorbing N2 over CH4 with an exceptional selectivity of 47 at room temperature that outperforms all previously known N2-selective adsorbents. At 295 K and 100 kPa, the N2 and CH4 uptakes on NaZSM-25 were 0.25 and 0.005 mmol g-1, respectively. CH4 showed negligible external surface adsorption in the whole temperature range of 273-323 K. Theoretical studies through replica exchanged Monte Carlo, molecular dynamics, and ab initio density functional theory (DFT) proved the diffusion limitation of CH4 as a result of 8-membered ring (8MR) pore opening deformation by Na+ cation. The DFT results showed the diffusion energy barriers of 63 and 96 kJ mol-1 for N2 and CH4, respectively, when passing an 8MR occupied with a Na+. NaZSM-25 is a promising adsorbent to be utilized in a pressure swing adsorption process at room temperature to minimize the energy consumption in N2 rejection units.

Nitrogen Rejection from Methane via a "Trapdoor" K-ZSM-25 Zeolite.

Nitrogen (N2) rejection from methane (CH4) is the most challenging step in natural gas processing because of the close similarity of their physical-chemical properties. For decades, efforts to find a functioning material that can selectively discriminate N2 had little outcome. Here, we report a molecular trapdoor zeolite K-ZSM-25 that has the largest unit cell among all zeolites, with the ability to capture N2 in favor of CH4 with a selectivity as high as 34. This zeolite was found to show a temperature-regulated gas adsorption wherein gas molecules' accessibility to the internal pores of the crystal is determined by the effect of the gas-cation interaction on the thermal oscillation of the "door-keeping" cation. N2 and CH4 molecules were differentiated by different admission-trigger temperatures. A mild working temperature range of 240-300 K was determined wherein N2 gas molecules were able to access the internal pores of K-ZSM-25 while CH4 was rejected. As confirmed by experimental, molecular dynamic, and ab initio density functional theory studies, the outstanding N2/CH4 selectivity is achieved within a specific temperature range where the thermal oscillation of door-blocking K+ provides enough space only for the relatively smaller molecule (N2) to diffuse into and through the zeolite supercages. Such temperature-regulated adsorption of the K-ZSM-25 trapdoor zeolite opens up a new approach for rejecting N2 from CH4 in the gas industry without deploying energy-intensive cryogenic distillation around 100 K.

Efficient metal ion sieving in rectifying subnanochannels enabled by metal-organic frameworks.

Biological ion channels have remarkable ion selectivity, permeability and rectification properties, but it is challenging to develop artificial analogues. Here, we report a metal-organic framework-based subnanochannel (MOFSNC) with heterogeneous structure and surface chemistry to achieve these properties. The asymmetrically structured MOFSNC can rapidly conduct K+, Na+ and Li+ in the subnanometre-to-nanometre channel direction, with conductivities up to three orders of magnitude higher than those of Ca2+ and Mg2+, equivalent to a mono/divalent ion selectivity of 103. Moreover, by varying the pH from 3 to 8 the ion selectivity can be tuned further by a factor of 102 to 104. Theoretical simulations indicate that ion-carboxyl interactions substantially reduce the energy barrier for monovalent cations to pass through the MOFSNC, and thus lead to ultrahigh ion selectivity. These findings suggest ways to develop ion selective devices for efficient ion separation, energy reservation and power generation.

Ferromagnetism of 1T'-MoS2 Nanoribbons Stabilized by Edge Reconstruction and Its Periodic Variation on Nanoribbons Width.

Nanoribbons (NRs) of two-dimensional (2D) materials have attracted intensive research interests because of exotic physical properties at edges as well as tunable properties via width control. In this paper, using density functional theory (DFT) calculations, we discover sensitive dependence of magnetic properties of 1T'-MoS2 NRs, that is, periodic variation of magnetic moments between 0.1 and 1.2 µ B, on NR width (even or odd number of MoS2 units). Our results reveal that a special edge reconstruction, which is not recognized before, stabilizes the ferromagnetic (FM) ground state. Our results also suggest that the FM state could be stable under ambient condition. This study indicates a promising means to integrate multiple magnetic units for small-scale functional devices, such as information storage and spintronics, on a single piece of MoS2 NR by designing segments with different width.

Electric Field Induced Reversible Phase Transition in Li Doped Phosphorene: Shape Memory Effect and Superelasticity.

Phosphorene, the single-layer form of black phosphorus, as a new member of atomically thin material family, has unique puckered atomistic structure and remarkable physical and chemical properties. In this paper, we report a discovery of an unexpected electromechanical energy conversion phenomenon-shape memory effect-in Li doped phosphorene P4Li2, using ab initio density functional theory simulations. Two stable phases are found for the two-dimensional (2D) P4Li2 crystal. Applying an external electric field can turn on or off the unique adatom switches in P4Li2 crystals, leading to a reversible structural phase transition and thereby the shape memory effect with an tunable strain output as high as 2.06%. Our results demonstrate that multiple temporary shapes are attainable in one piece of P4Li2 material, offering programmability that is particularly useful for device designs. Additionally, the P4Li2 displays superelasticity that can generate a pseudoelastic tensile strain up to 6.2%. The atomic thickness, superior flexibility, excellent electromechanical strain output, the special shape memory phenomenon, and the programmability feature endow P4Li2 with great application potential in high-efficient energy conversion at nanoscale and flexible nanoelectromechanical systems.

Sustaining GHz oscillation of carbon nanotube based oscillators via a MHz frequency excitation.

There have been intensive studies to investigate the properties of gigahertz nano-oscillators based on multi-walled carbon nanotubes (MWCNTs). Many of these studies, however, revealed that the unique telescopic translational oscillations in such devices would damp quickly due to various energy dissipation mechanisms. This challenge remains the primary obstacle against its practical applications. Herein, we propose a design concept in which a GHz oscillation could be re-excited by a MHz mechanical motion. This design involves a triple-walled CNT, in which sliding of the longer inner tube at a MHz frequency can re-excite and sustain a GHz oscillation of the shorter middle tube. Our molecular dynamics (MD) simulations prove this design concept at ∼10 nm scale. A mathematical model is developed to explore the feasibility at a larger size scale. As an example, in an oscillatory system with the CNT's length above 100 nm, the high oscillatory frequency range of 1.8-3.3 GHz could be excited by moving the inner tube at a much lower frequency of 53.4 MHz. This design concept together with the mechanical model could energize the development of GHz nano-oscillators in miniaturized electro-mechanical devices.

Unravelling the atomistic mechanisms underpinning the morphological evolution of Al-alloyed hematite.

Hydrothermal synthesis based upon the use of Al3+ as the dopant and/or ethanol as the solvent is effective in promoting the growth of hematite into nanoplates rich in the (001) surface, which is highly active for a broad range of catalytic applications. However, the underpinning mechanism for the flattening of hematite crystals is still poorly comprehended. To close this knowledge gap, in this work, we have attempted intensive computational modelling to construct a binary phase diagram for Fe2O3-Al2O3 under typical hydrothermal conditions, as well as to quantify the surface energy of hematite crystal upon coverage with Al3+ and ethanol molecules. An innovative coupling of density functional theory calculation, cluster expansion and Monte Carlo simulations in analogy to machine learning and prediction was attempted. Upon successful validation by experimental observation, our simulation results suggest an optimum atomic dispersion of Al3+ within hematite in cases when its concentration is below 4 at% otherwise phase separation occurs, and discrete Al2O3 nano-clusters can be preferentially formed. Computations also revealed that the adsorption of ethanol molecules alone can reduce the specific surface energy of the hematite (001) surface from 1.33 to 0.31 J m-2. The segregation of Al3+ on the (001) surface can further reduce the specific surface energy to 0.18 J m-2. Consequently, the (001) surface growth is inhibited, and it becomes dominant after the disappearance of other surfaces upon their continual growth. This work provides atomistic insights into the synergistic effect between the aluminium textural promoter and the ethanol capping agent in determining the morphology of hematite nanoparticles. The established computation approach also applies to other oxide-based catalysts in controlling their surface growth and morphology, which are critical for their catalytic applications.

Assessment of Self-report, Palpation, and Surface Electromyography Dataset During Isometric Muscle Contraction.

Measuring muscle fatigue involves assessing various components within the motor system. While subjective and sensor-based measures have been proposed, a comprehensive comparison of these assessment measures is currently lacking. This study aims to bridge this gap by utilizing three commonly used measures: participant self-reported perceived muscle fatigue scores, a sports physiotherapist's manual palpation-based muscle tightness scores, and surface electromyography sensors. Compensatory muscle fatigue occurs when one muscle group becomes fatigued, leading to the involvement and subsequent fatigue of other muscles as they compensate for the workload. The evaluation of compensatory muscle fatigue focuses on nine different upper body muscles selected by the sports physiotherapist. With a cohort of 30 male subjects, this study provides a valuable dataset for researchers and healthcare practitioners in sports science, rehabilitation, and human performance. It enables the exploration and comparison of diverse methods for evaluating different muscles in isometric contraction.

New Engineering Science Insights into the Electrode Materials Pairing of Electrochemical Energy Storage Devices.

Pairing the positive and negative electrodes with their individual dynamic characteristics at a realistic cell level is essential to the practical optimal design of electrochemical energy storage devices. However, the complex relationship between the performance data measured for individual electrodes and the two-electrode cells used in practice often makes an optimal pairing experimentally challenging. Taking advantage of the developed tunable graphene-based electrodes with controllable structure, experiments with machine learning are successfully united to generate a large pool of capacitance data for graphene-based electrode materials with varied slit pore sizes, thicknesses, and charging rates and numerically pair them into different combinations for two-electrode cells. The results show that the optimal pairing parameters of positive and negative electrodes vary considerably with the operation rate of the cells and are even influenced by the thickness of inactive components. The best-performing individual electrode does not necessarily result in optimal cell-level performance. The machine learning-assisted pairing approach presents much higher efficiency compared with the traditional trial-and-error approach for the optimal design of supercapacitors. The new engineering science insights observed in this work enable the adoption of artificial intelligence techniques to efficiently translate well-developed high-performance individual electrode materials into real energy storage devices.

Out-of-plane pressure and electron doping inducing phase and magnetic transitions in GeC/CrS2/GeC van der Waals heterostructure.

Out-of-plane pressure and electron doping can affect interlayer interactions in van der Waals materials, modifying their crystal structure and physical and chemical properties. In this study, we used magnetic monolayer 1T/1T'-CrS2 and high symmetry 2D-honeycomb material GeC to construct a GeC/CrS2/GeC triple layered van der Waals heterostructure (vdWH). Based on density functional theory calculations, we found that applying out-of-plane strain and doping with electrons could induce a 1T'-to-1T phase transition and consequently the ferromagnetic (FM)-to-antiferromagnetic (AFM) transition in the CrS2 layer. Such a phase and magnetic transition arises from the pressure and electron-induced interlayer interaction enhancement. The electron doping can effectively decrease the critical compressive stress from ∼4.3 GPa (charge neutrality) to ∼664 MPa (Q = 9 × 10-3 e- per atom) for the FM-to-AFM transition. These properties could be used to fabricate and program the 2D lateral FM/AFM heterostructures for artificial controlled spin texture and miniaturized spintronic devices.

Binding and interlayer force in the near-contact region of two graphite slabs: experiment and theory.

Via a novel experiment, Liu et al. [Phys. Rev. B 85, 205418 (2012)] estimated the graphite binding energy, specifically the cleavage energy, an important physical property of bulk graphite. We re-examine the data analysis and note that within the standard Lennard-Jones model employed, there are difficulties in achieving internal consistency in the reproduction of the graphite elastic properties. By employing similar models which guarantee consistency with the elastic constant, we find a wide range of model dependent binding energy values from the same experimental data. We attribute some of the difficulties in the determination of the binding energy to: (i) limited theoretical understanding of the van der Waals dispersion of graphite cleavage, (ii) the mis-match between the strong bending stiffness of the graphite-SiO2 cantilever and the weak asymptotic inter-layer forces that are integrated over to produce the binding energy. We find, however, that the data do support determination of a maximum inter-layer force that is relatively model independent. We conclude that the peak force per unit area is 1.1 ± 0.15 GPa for cleavage, and occurs at an inter-layer spacing of 0.377 ± 0.013 nm.

A Preliminary Usability Study of Integrated Electronic Tattoo Surface Electromyography (sEMG) Sensors.

Surface electromyography (sEMG) sensor measures the user's muscle activities by noninvasively placing electrodes on the surface of the user's skin. It has been widely used in monitoring various human movements. Recently a wearable and flexible epidermal sensor system called Electronic Tattoo (E-Tattoo) has been developed to enable intimate attachment of electrodes on the skin, improving long-term comfort. In order to make the E-Tattoo usable in monitoring muscle activities, it is always connected with a connector and signal processing blocks to collect and process the measured sEMG signals. We call it an integrated system. This paper investigates the usability of a prototype of the integrated system developed in the laboratory for monitoring muscle activities by testing its comfort with user experience surveys and comparing the quality of the sEMG signals by widely used performance metrics. Two typical movements, maximum voluntary isometric and non-isometric contractions, are considered for the experiments. Our preliminary results on five subjects demonstrate the effectiveness of the proposed integrated system. This system showed a comparable signal quality for these two movements as the commercial product with a much better comfort feeling from the user. It is also interesting to note that this prototype shows a much better signal-to-motion artifact ratio (SMR), which reflects the ability to measure muscle activities during active movements, compared with the commercial product, showing the potential of using this integrated system in monitoring sEMGs during active and dynamic movements.

Size Limiting Elemental Ferroelectricity in Bi Nanoribbons: Observation, Mechanism, and Opportunity.

Combined with the inherent spin-orbital coupling effect, the elemental ferroelectricity of monolayer Bi (bismuthene) is the critical property that renders this system a 2D ferroelectric topological insulator. Here, using first-principles calculations, we systematically investigate the ferroelectric polarization in bismuthene nanoribbons and discover the width size limiting effect arising from the edge effects. The decreasing width led to the spontaneous transformation of the zigzag (ZZ) and armchair (AC) paired Bi nanoribbons into newly discovered high-symmetric nonpolarized nanoribbons. For ZZ-paired nanoribbons, the driving force of the phase transition is attributed to the depolarization field, similar to the conventional perovskite ferroelectric thin films. Instead, edge stress as a novel mechanism played a major role in the phase transition of AC-paired nanoribbons. Inspired by such a revealed mechanism, the phase transition and related ultrahigh piezoelectricity can be achieved by strain engineering in Bi nanoribbons, which could enable new applications for 2D ferroelectric devices.

Writing-Speed Dependent Thresholds of Ferroelectric Domain Switching in Monolayer α-In2 Se3.

An electrical-biased or mechanical-loaded scanning probe written on the ferroelectric surface can generate programmable domain nanopatterns for ultra-scaled and reconfigurable nanoscale electronics. Fabricating ferroelectric domain patterns by direct-writing as quickly as possible is highly desirable for high response rate devices. Using monolayer α-In2 Se3 ferroelectric with ≈1.2 nm thickness and intrinsic out-of-plane polarization as an example, a writing-speed dependent effect on ferroelectric domain switching is discovered. The results indicate that the threshold voltages and threshold forces for domain switching can be increased from -4.2 to -5 V and from 365 to 1216 nN, respectively, as the writing-speed increases from 2.2 to 10.6 µm s-1 . The writing-speed dependent threshold voltages can be attributed to the nucleations of reoriented ferroelectric domains, in which sufficient time is needed for subsequent domain growth. The writing-speed dependent threshold forces can be attributed to the flexoelectric effect. Furthermore, the electrical-mechanical coupling can be employed to decrease the threshold force, achieving as low as ≈189±41 nN, a value smaller than those of perovskite ferroelectric films. Such findings reveal a critical issue of ferroelectric domain pattern engineering that should be carefully addressed for programmable direct-writing electronics applications.

Dehydration-enhanced ion-pore interactions dominate anion transport and selectivity in nanochannels.

State-of-the-art ion-selective membranes with ultrahigh precision are of significance for water desalination and energy conservation, but their development is limited by the lack of understanding of the mechanisms of ion transport at the subnanometer scale. Herein, we investigate transport of three typical anions (F-, Cl-, and Br-) under confinement using in situ liquid time-of-flight secondary ion mass spectrometry in combination with transition-state theory. The operando analysis reveals that dehydration and related ion-pore interactions govern anion-selective transport. For strongly hydrated ions [(H2O)nF- and (H2O)nCl-], dehydration enhances ion effective charge and thus the electrostatic interactions with membrane, observed as an increase in decomposed energy from electrostatics, leading to more hindered transport. Contrarily, weakly hydrated ions [(H2O)nBr-] have greater permeability as they allow an intact hydration structure during transport due to their smaller size and the most right-skewed hydration distribution. Our work demonstrates that precisely regulating ion dehydration to maximize the difference in ion-pore interactions could enable the development of ideal ion-selective membranes.

An artificial sodium-selective subnanochannel.

Single-ion selectivity with high precision has long been pursued for fundamental bioinspired engineering and applications such as in ion separation and energy conversion. However, it remains a challenge to develop artificial ion channels to achieve single-ion selectivity comparable to their biological analogs, especially for high Na+/K+ selectivity. Here, we report an artificial sodium channel by subnanoconfinement of 4'-aminobenzo-15-crown-5 ethers (15C5s) into ~6-Å-sized metal-organic framework subnanochannel (MOFSNC). The resulting 15C5-MOFSNC shows an unprecedented Na+/K+ selectivity of tens to 102 and Na+/Li+ selectivity of 103 under multicomponent permeation conditions, comparable to biological sodium channels. A co-ion-responsive single-file transport mechanism in 15C-MOFSNC is proposed for the preferential transport of Na+ over K+ due to the synergetic effects of size exclusion, charge selectivity, local hydrophobicity, and preferential binding with functional groups. This study provides an alternative strategy for developing potential single-ion selective channels and membranes for many applications.