Metal-coordinated sub-10 nm membranes for water purification

GO-based antibacterial composites: Application and design strategies

Graphene oxide (GO), for its unique structure with high biocompatibility and designability, is widely used in the antibacterial field. Various strategies have been designed to fabricate GO-based composites with antibacterial properties. This review summarized these strategies, divided them into three types and interpreted their antibacterial mechanisms: (i) "GO*/non-GO" type in which GO acts as the single antibacterial core, (ii) "GO*/non-GO*" type in which GO and non-GO components function synergistically as dual antibacterial cores, (iii) "GO/non-GO*" type in which non-GO acts as the single antibacterial core, while GO component plays a supportive, not a dominant role in antibiosis. Besides, the fields suiting their applications and factors influencing their antibacterial properties were analyzed. Finally, the limitations and prospects in the current researches were discussed. In summary, GO-based composites have revolutionized antibacterial strategies. This review may serve as a reference to inspire further research on GO-based antibacterial composites.

Rational ion transport management mediated through membrane structures

Unique membrane structures endow membranes with controlled ion transport properties in both biological and artificial systems, and they have shown broad application prospects from industrial production to biological interfaces. Herein, current advances in nanochannel-structured membranes for manipulating ion transport are reviewed from the perspective of membrane structures. First, the controllability of ion transport through ion selectivity, ion gating, ion rectification, and ion storage is introduced. Second, nanochannel-structured membranes are highlighted according to the nanochannel dimensions, including single-dimensional nanochannels (i.e., 1D, 2D, and 3D) functioning by the controllable geometrical parameters of 1D nanochannels, the adjustable interlayer spacing of 2D nanochannels, and the interconnected ion diffusion pathways of 3D nanochannels, and mixed-dimensional nanochannels (i.e., 1D/1D, 1D/2D, 1D/3D, 2D/2D, 2D/3D, and 3D/3D) tuned through asymmetric factors (e.g., components, geometric parameters, and interface properties). Then, ultrathin membranes with short ion transport distances and sandwich-like membranes with more delicate nanochannels and combination structures are reviewed, and stimulus-responsive nanochannels are discussed. Construction methods for nanochannel-structured membranes are briefly introduced, and a variety of applications of these membranes are summarized. Finally, future perspectives to developing nanochannel-structured membranes with unique structures (e.g., combinations of external macro/micro/nanostructures and the internal nanochannel arrangement) for mediating ion transport are presented.

Confined assembly of ultrathin nanoporous nitrogen-doped graphene nanofilms with dual metal coordination chemistry

Graphene oxide (GO) nanosheets with unique structure have received much attention in providing opportunity for high-performance membranes in separation. However, the rational design of ultrathin graphene membranes with controlled structures remains a big challenge. Here, we report a methodology to synthesize dual metal-coordinated ultrathin nanoporous graphene nanofilms by tailoring well-aligned nanocrystals as building blocks on heteroatom-doped GO nanosheets with tunable architectures. Manipulation of metal nitrate as bifunctional dopants realizes N-doping of graphene oxide and preferential growth of α-Mn₂O₃ nanocrystals. Generation of Mn-O-C bond during cross-linking greatly strengthens the stability of membranes for long-term steady operation. Meanwhile, because of spatial confinement effects and high binding energy, N-doped reduced GO nanosheets are desirable supports to construct numerous Mn-N-C bonds, thus generating artificial nanopores to significantly increase nanochannels for ultrafast mass transport. Moreover, the size-selective permeability of ultrathin nanoporous GO-based nanofilms can be optimized by managing the types of metal source for target coordination.

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Dual metal-coordinated GO-based nanofilms are achieved by a general and facile method

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Mn-N-C bonds are constructed in rGO nanosheets with N-containing coordinated links

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Artificial nanopores are used to increase nanochannels for ultrafast mass transport

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Generation of Mn-O-C bond greatly strengthens the stability of nanofilms in separation

Organic molecular sieve membranes for chemical separations

Molecular separations that enable selective transport of target molecules from gas and liquid molecular mixtures, such as CO2 capture, olefin/paraffin separations, and organic solvent nanofiltration, represent the most energy sensitive and significant demands. Membranes are favored for molecular separations owing to the advantages of energy efficiency, simplicity, scalability, and small environmental footprint. A number of emerging microporous organic materials have displayed great potential as building blocks of molecular separation membranes, which not only integrate the rigid, engineered pore structures and desirable stability of inorganic molecular sieve membranes, but also exhibit a high degree of freedom to create chemically rich combinations/sequences. To gain a deep insight into the intrinsic connections and characteristics of these microporous organic material-based membranes, in this review, for the first time, we propose the concept of organic molecular sieve membranes (OMSMs) with a focus on the precise construction of membrane structures and efficient intensification of membrane processes. The platform chemistries, designing principles, and assembly methods for the precise construction of OMSMs are elaborated. Conventional mass transport mechanisms are analyzed based on the interactions between OMSMs and penetrate(s). Particularly, the 'STEM' guidelines of OMSMs are highlighted to guide the precise construction of OMSM structures and efficient intensification of OMSM processes. Emerging mass transport mechanisms are elucidated inspired by the phenomena and principles of the mass transport processes in the biological realm. The representative applications of OMSMs in gas and liquid molecular mixture separations are highlighted. The major challenges and brief perspectives for the fundamental science and practical applications of OMSMs are tentatively identified.

Electrostatic-modulated interfacial polymerization toward ultra-permselective nanofiltration membranes

Interfacial polymerization (IP) is a platform technology for ultrathin membranes. However, most efforts in regulating the IP process have been focused on short-range H-bond interaction, often leading to low-permselective membranes. Herein, we report an electrostatic-modulated interfacial polymerization (eIP) via supercharged phosphate-rich substrates toward ultra-permselective polyamide membranes. Phytate, a natural strongly charged organophosphate, confers high-density long-range electrostatic attraction to aqueous monomers and affords tunable charge density by flexible metal-organophosphate coordination. The electrostatic attraction spatially enriches amine monomers and temporally decelerates their diffusion into organic phase to be polymerized with acyl chloride monomers, triggering membrane sealing and inhibiting membrane growth, thus generating polyamide membranes with reduced thickness and enhanced cross-linking. The optimized nearly 10-nm-thick and highly cross-linked polyamide membrane displays superior water permeance and ionic selectivity. This eIP approach is applicable to the majority of conventional IP processes and can be extended to fabricate a variety of advanced membranes from polymers, supermolecules, and organic framework materials.

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Electrostatic-modulated interfacial polymerization is proposed for the first time

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Electrostatic attraction regulates the spatial-temporal distribution of amine monomers

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Monomer regulation leads to reduced thickness and enhanced cross-linking of membrane

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Ultrathin and highly cross-linked polyamide membrane displays superior permselectivity

Molecularly soldered covalent organic frameworks for ultrafast precision sieving

The weak interlamellar interaction of covalent organic framework (COF) nanocrystals inhibit the construction of highly efficient ion/molecular sieving membranes owing to the inferior contaminant selectivity induced by defects in stacked COF membranes and stability issues. Here, a facile in situ molecularly soldered strategy was developed to fabricate defect-free ultrathin COF membranes with precise sieving abilities using the typical chemical environment for COF condensation polymerization and dopamine self-polymerization. The experimental data and density functional theory simulations proved that the reactive oxygen species generated during dopamine polymerization catalyze the nucleophilic reactions of the COF, thus facilitating the counter-diffusion growth of thin COF layers. Notably, dopamine can eliminate the defects in the stacked COF by soldering the COF crystals, fortifying the mechanical properties of the ultrathin COF membranes. The COF membranes exhibited ultrafast precision sieving for molecular separation and ion removal in both aqueous and organic solvents, which surpasses that of state-of-the-art membranes.

A Gold Nanocluster Constructed Mixed-Metal Metal-Organic Network Film for Combating Implant-Associated Infections

The development of modular strategies for programming self-assembled supramolecular architectures with distinct structural and functional features is of immense scientific interest. We reported on the intrinsic antibacterial capability of anionic amphiphilic gold nanoclusters (GNCs) capped by para-mercaptobenzoic acid, which was closely related to the protonation level of terminal carboxylate groups. By using of the metal-ligand coordination-driven and solvent evaporation-induced self-assembly, we constructed GNCs-based mixed-metal metal-organic network (MM-MON) films on titanium disks as antibacterial nanocoatings. Taking the reasonable utilization of tetravalent metal ions M⁴⁺ (Ti, Zr, Hf; hard Lewis acid) and bactericidal divalent metal ions M²⁺ (Cu, Zn; borderline acid) co-incorporated metal-carboxylate coordination bonds, the MM-MON films exhibited superior stability due to the robust M⁴⁺-O bonds and M²⁺ releasing behavior resulting from the labile M²⁺-O coordinating. Together, the MM-MON films integrated the bacteria-responsive character of GNCs, exceptional chemical stability, and greatly enhanced antibacterial activity, ultimately killing adherent bacteria and initiating a self-defensive function. In a rat model for subcutaneous implant-associated infection, the MM-MON nanocoating showed an approximately 2 and 1 log lower multidrug-resistant Staphylococcus aureus implant and tissue colonization, respectively. The generalizable modular strategy of the GNC-metal networks is amenable to facilitate the functionalization of metal surfaces for combating implant-associated infections.