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High desalination efficiency in principle could be achieved by layer-by-layer graphene oxide (GO) membranes, which benefits from their entrance-functionalized channels assembled by edge-functionalized GO nanosheets. The effects of these edge functional groups on desalination, however, are not fully understood yet. To study the isolated influence of three typical edge functional groups, namely, carboxyl (-COOH), hydroxyl (-OH), and hydrogen (-H), molecular dynamics simulation was used in this work. The results revealed that the edge volumetric blockage effect, resulting in ion permeability at G-H > G-OH > G-COOH membranes, was the dominant mechanistic effect inside the GO membranes with 7 A interlayer channels. The OH edge has the same effect as the H edge in NaCl/water selectivity because of a unique "ion pulling" effect. Moreover, the OH and H edge-functionalized membranes with 7 A interlayer channels showed preferential Na+ and Cl- rejections, respectively. This kind of preference leads to a cycle of charging and neutralization in the penetrant reservoir throughout the filtration process. The results from this work suggested that it would be strategic to keep the COOH and H edge functional groups, to maintain the size of interlayer channels in order to stimulate the effects of edge functional groups, and to increase the membrane porosity for designing higher desalination efficiency GO membranes.

Graphene oxide (GO) membranes assembled by GO nanosheets exhibit high water flux because of the unique water channels formed by their functionalized layer-by-layer structure. Although water transport in the GO membrane is in principle influenced by the functional groups at the edges of GO nanosheets, this is yet to be fully understood. To fill this knowledge gap, molecular dynamics simulation was employed in this work to gain insights into the influences of three typical edge functional groups of GO nanosheets: carboxyl (COOH), hydroxyl (OH), and hydrogen (H). A well-controlled numerical analysis with complete isolation of the functional groups at the edges was undertaken. The results reveal that the COOH group has a negative impact on water transport because of its relatively large steric geometric structure, which resists water flow. By contrast, the OH group promotes water transport by uniquely "pulling" water molecules across the nanosheet layer because of its relatively stronger interaction with water. The H atom promotes water transport as well, mainly because of its low-resistance steric structure. Moreover, the size of the inter-edge hub has an apparent impact on the influence of these functional groups on water transport. The results suggest that in the design of high water flux GO membranes, it would be strategic to remove COOH edge functional groups while maintaining a mixture of OH and H edge functional groups.

Summary Effective design of bifunctional catalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is important but remains challenging. Herein, we report a three-dimensional (3D) hierarchical structure composed of homogeneously distributed Ni-Fe-P nanoparticles embedded in N-doped carbons on nickel foams (denoted as Ni-Fe-P@NC/NF) as an excellent bifunctional catalyst. This catalyst was fabricated by an anion exchange method and a low-temperature phosphidation of nanotubular Prussian blue analogue (PBA). The Ni-Fe-P@NC/NF displayed exceptional catalytic activity toward both HER and OER and delivered an ultralow cell voltage of 1.47 V to obtain 10 mA cm−2 with extremely excellent durability for 100 h when assembled as a practical electrolyser. The extraordinary performance of Ni-Fe-P@NC/NF is attributed to the abundance of unsaturated active sites, the well-defined hierarchical porous structure, and the synergistic effect between multiple components. Our work will inspire more rational designs of highly active non-noble electrocatalysts for industrial energy applications., Graphical Abstract, Highlights • Nanotubular Prussian blue analogue as a precursor is synthesized by anion exchange • The catalyst exhibits excellent catalytic activity for hydrogen and oxygen production • The catalyst-based electrolyser has a low cell voltage of 1.47 V to obtain 10 mA cm−2 • The electrolyser shows an extremely excellent durability for 100 h at 50 mA cm−2, Catalysis; Materials Chemistry; Nanomaterials; Energy Materials

Molecular-level understanding of protein adsorption on uncharged solid surfaces has been a challenge due to experimental limitations. Recent computational efforts have demonstrated that the adsorption process starts from a biased diffusion phase, where the peptide or protein tends to move towards the solid surface from a position beyond the interaction range that the surface can reach. The strong interactions between the solid surface and the water molecules adjacent or near it would establish well-oriented water molecular ‘layers’, which are said to bring the ‘net’ electrostatic interactions hence exhibiting longer distance attractions. In this work, the peptide adsorption process has been investigated by resorting to a unique mesoscale modeling approach. Here, quantitative analyses on the adsorption of an A3 peptide on uncharged solid surfaces that strongly interact with water have revealed that, different from previous reports, the biased diffusion could be mainly attributed to the Lennard-Jones (LJ) forces, whose ‘net’ value could reach one order of magnitude bigger than the ‘net’ electrostatic force originated from the aggregated water ‘layers’ close to the surface. In addition to offering the new understanding of the adsorption mechanisms, promising applications of the current method for large systems beyond a single peptide are also discussed.

An ultrathin porous membrane can completely separate ions from water., Owing to the rich porosity and uniform pore size, metal-organic frameworks (MOFs) offer substantial advantages over other materials for the precise and fast membrane separation. However, achieving ultrathin water-stable MOF membranes remains a great challenge. Here, we first report the successful exfoliation of two-dimensional (2D) monolayer aluminum tetra-(4-carboxyphenyl) porphyrin framework (termed Al-MOF) nanosheets. Ultrathin water-stable Al-MOF membranes are assembled by using the exfoliated nanosheets as building blocks. While achieving a water flux of up to 2.2 mol m−2 hour−1 bar−1, the obtained 2D Al-MOF laminar membranes exhibit rejection rates of nearly 100% on investigated inorganic ions. The simulation results confirm that intrinsic nanopores of the Al-MOF nanosheets domain the ion/water separation, and the vertically aligned aperture channels are the main transport pathways for water molecules.

Layer-by-layer graphene oxide (GO) membrane in principle has great potential in separating Li+ from monovalent cations, which is achieved by their functionalized interlayer entrance. The edge effects on different monovalent ions, however, are not fully understood. Therefore, molecular dynamics simulations were utilized in this study to separately elucidate the filtration effects of three typical edge functional groups, which were carboxyl (COOH), hydroxyl (OH), and hydrogen (H), on the LiCl, NaCl, and KCl solutions. The results revealed that the water permeance was dominantly influenced by the steric size of edge functional groups. It could also be affected by the ions blocked at the entrance. The drastic dehydration of the hydrated Na+ and K+ caused by the OH edge required more energy that led to higher ion rejection. The compressed-dehydrated hydration shell, which was tuned by the edge functional groups, introduced repulsion from Na+ and attraction from Li+ on Cl− when they were 3–5 A away from each other. It would be strategic to use all three edge functional groups to retain NaCl in the retentate stream while allowing selective permeance of LiCl and the OH edge could additionally retain KCl.

Laminar membranes stacked by 2D materials are an emerging selective unit in separating processes across disciplines for their controllable mass transport properties. In general, parallel nanochannels formed between neighboring layers, owing to their adjustable size and surface chemistry, are considered the dominant transport regulator. Besides these flat interlayer channels, wrinkled morphology has also existed in 2D membranes, but the structure and potential transporting role of such curved channel remain largely unexplored. This study demonstrates that nanowrinkles are intrinsically formed in graphene‐based membranes, featuring an arc‐like shape with around 2.5 nm high center and two narrow wedge corners. By a facile “solvent‐treatment” during assembly, the membranes are tuned to possess different wrinkle density. In transport tests involving water and ions, the appearance of more wrinkles yields higher water permeation yet has limited effect on ion passage. These findings suggest that nanowrinkles by themselves serve as fast transporting ways while their connection with narrow interlayer channels can form a selective network. Results here are expected to deepen the understanding of mass transport mechanisms in current laminar membranes (e.g., graphene‐based) and provide strategies for designing future 2D membranes via wrinkle engineering.