Tailor-Made Heterocharged Covalent Organic Framework Membrane for Efficient Ion Separation.

Pore size sieving, Donnan exclusion, and their combined effects seriously affect ion separation of membrane processes. However, traditional polymer-based membranes face some challenges in precisely controlling both charge distribution and pore size on the membrane surface, which hinders the ion separation performance, such as heavy metal ion removal. Herein, the heterocharged covalent organic framework (COF) membrane is reported by assembling two kinds of ionic COF nanosheets with opposite charges and different pore sizes. By manipulating the stacking quantity and sequence of two kinds of nanosheets, the impact of membrane surface charge and pore size on the separation performance of monovalent and multivalent ions is investigated. For the separation of anions, the effect of pore size sieving is dominant, while for the separation of cations, the effect of Donnan exclusion is dominant. The heterocharged TpEBr/TpPa-SO3H membrane with a positively charged upper layer and a negatively charged bottom layer exhibits excellent rejection of multivalent anions and cations (Ni2+, Cd2+, Cr2+, CrO4 2-, SeO3 2-, etc). The strategy provides not only high-performance COF membranes for ion separation but also an inspiration for the engineering of heterocharged membranes.

Crystalline Porous Organic Cage Membranes Constructed Using Fortified Intermolecular Interactions for Molecular Sieving.

Among the various types of materials with intrinsic porosity, porous organic cages (POCs) are distinctive as discrete molecules that possess intrinsic cavities and extrinsic channels capable of facilitating molecular sieving. However, the fabrication of POC membranes remains highly challenging due to the weak noncovalent intermolecular interactions and most reported POCs are powders. In this study, we constructed crystalline free-standing porous organic cage membranes by fortifying intermolecular interactions through the induction of intramolecular hydrogen bonds, which was confirmed by single-crystal X-ray analysis. To elucidate the driving forces behind, a series of terephthaldehyde building blocks containing different substitutions were reacted with flexible triamine under different conditions via interfacial polymerization (IP). Furthermore, density functional theory (DFT) calculations suggest that intramolecular hydrogen bonding can significantly boost the intermolecular interactions. The resulting membranes exhibited fast solvent permeance and high rejection of dyes not only in water, but also in organic solvents. In addition, the membrane demonstrated excellent performance in precise molecular sieving in organic solvents. This work opens an avenue to designing and fabricating free-standing membranes composed of porous organic materials for efficient molecular sieving.

Single-exposure 3D label-free microscopy based on color-multiplexed intensity diffraction tomography.

We present a 3D label-free refractive index (RI) imaging technique based on single-exposure intensity diffraction tomography (sIDT) using a color-multiplexed illumination scheme. In our method, the chromatic light-emitting diodes (LEDs) corresponding R/G/B channels in an annular programmable ring provide oblique illumination geometry that precisely matches the objective's numerical aperture. A color intensity image encoding the scattering field of the specimen from different directions is captured, and monochromatic intensity images concerning three color channels are separated and then used to recover the 3D RI distribution of the object following the process of IDT. In addition, the axial chromatic dispersion of focal lengths at different wavelengths introduced by the chromatic aberration of the objective lens and the spatial position misalignment of the ring LED source in the imaging system's transfer functions modeling are both corrected to significantly reduce the artifacts in the slice-based deconvolution procedure for the reconstruction of 3D RI distribution. Experimental results on MCF-7, Spirulina algae, and living Caenorhabditis elegans samples demonstrate the reliable performance of the sIDT method in label-free, high-throughput, and real-time (∼24 fps) 3D volumetric biological imaging applications.

Two-dimensional nanochannel membranes for molecular and ionic separations.

Two-dimensional (2D) nanosheets have emerged as promising functional materials owing to their atomic thickness and unique physical/chemical properties. By using 2D nanosheets as building blocks, diverse kinds of two-dimensional nanochannel membranes (2DNCMs) are being actively explored, in which mass transport occurs in the through-plane and interlayer channels of 2D nanosheets. The rational construction and physical/chemical microenvironment regulation of nanochannels are of vital significance for translating these 2D nanosheets into molecular separation membranes and ionic separation membranes. Focusing on the recent advances of 2DNCMs, in this review, various porous/nonporous 2D nanosheets and their derived nanochannels are first briefly introduced. Then we discuss the emerging top-down and bottom-up methods to synthesize high-quality 2D nanosheets and to prepare high-performance 2DNCMs. As the major part of this review, we focus on three types of nanochannels, which are based on nonporous nanosheets, intrinsically porous nanosheets and perforated nanosheets. The strategies for regulating the physical and chemical microenvironments in the nanochannels are emphasized. The representative applications of 2DNCMs in molecular separations (gas separation, liquid separation) and ionic separations are presented. Finally, the current challenges and future perspectives are highlighted.

Solid-Vapor Interface Engineered Covalent Organic Framework Membranes for Molecular Separation.

Covalent organic frameworks (COFs) with intrinsic, tunable, and uniform pores are potent building blocks for separation membranes, yet poor processing ability and long processing time remain grand challenges. Herein, we report an engineered solid-vapor interface to fabricate a highly crystalline two-dimensional COF membrane with a thickness of 120 nm in 9 h, which is 8 times faster than that in the reported literature. Due to the ultrathin nature and ordered pores, the membrane exhibited an ultrahigh permeance (water, ∼411 L m-2 h-1 bar-1 and acetonitrile, ∼583 L m-2 h-1 bar-1) and excellent rejection of dye molecules larger than 1.4 nm (>98%). The membrane exhibited long-term operation which confirmed its outstanding stability. Our solid-vapor interfacial polymerization method may evolve into a generic platform to fabricate COFs and other organic framework membranes.

Evidence for Magnetic Skyrmions at the Interface of Ferromagnet/Topological-Insulator Heterostructures.

The heterostructures of the ferromagnet (Cr2Te3) and topological insulator (Bi2Te3) have been grown by molecular beam epitaxy. The topological Hall effect as evidence of the existence of magnetic skyrmions has been observed in the samples in which Cr2Te3 was grown on top of Bi2Te3. Detailed structural characterizations have unambiguously revealed the presence of intercalated Bi bilayer nanosheets right at the interface of those samples. The atomistic spin-dynamics simulations have further confirmed the existence of magnetic skyrmions in such systems. The heterostructures of ferromagnet and topological insulator that host magnetic skyrmions may provide an important building block for next generation of spintronics devices.

Antifouling membranes for sustainable water purification: strategies and mechanisms.

One of the greatest challenges to the sustainability of modern society is an inadequate supply of clean water. Due to its energy-saving and cost-effective features, membrane technology has become an indispensable platform technology for water purification, including seawater and brackish water desalination as well as municipal or industrial wastewater treatment. However, membrane fouling, which arises from the nonspecific interaction between membrane surface and foulants, significantly impedes the efficient application of membrane technology. Preparing antifouling membranes is a fundamental strategy to deal with pervasive fouling problems from a variety of foulants. In recent years, major advancements have been made in membrane preparation techniques and in elucidating the antifouling mechanisms of membrane processes, including ultrafiltration, nanofiltration, reverse osmosis and forward osmosis. This review will first introduce the major foulants and the principal mechanisms of membrane fouling, and then highlight the development, current status and future prospects of antifouling membranes, including antifouling strategies, preparation techniques and practical applications. In particular, the strategies and mechanisms for antifouling membranes, including passive fouling resistance and fouling release, active off-surface and on-surface strategies, will be proposed and discussed extensively.

In situ reaction enabled surface segregation toward dual-heterogeneous antifouling membranes for oil-water separation.

Fabricating membranes with superior antifouling property and long-term high performance is in great demand for efficient oil-water separation. Herein, we reported a reaction enabled surface segregation method for antifouling membrane fabrication, in which the pre-synthesized fluorinated ternary copolymer Pluronic F127 was coordinated with Ti4+ as segregation additive in the membrane casting bath. Additionally, tannic acid was utilized to enhance the self-assembly of the copolymer in the coagulation bath, and freshly-biomineralized TiO2 was anchored into the membrane surface through hydrogen bond. A hydrogel layer was constructed onto the membrane surface with synergistically tailored heterogeneous chemical composition and heterogeneous geometrical roughness. The dual-heterogeneous membrane exhibited hydrophilic and underwater superoleophobic features, resulting in high water flux (621.7 L m-2 h-1) at low operation pressure of 0.05 MPa and an excellent antifouling property (only 4.8% flux decline during 24-hour filtration). In situ reaction enabled surface segregation method will accelerate the development of antifouling membranes for oil-in-water emulsion separation.

Esterase-Labile Quaternium Lipidoid Enabling Improved mRNA-LNP Stability and Spleen-Selective mRNA Transfection.

Ionizable cationic lipids are recognized as an essential component of lipid nanoparticles (LNPs) for messenger RNA (mRNA) delivery but can be confounded by low lipoplex stability with mRNA during storage and in vivo delivery. Herein, the rational design and combinatorial synthesis of esterase-triggered decationizable quaternium lipid-like molecules (lipidoids) are reported to develop new LNPs with high delivery efficiency and improved storage stability. This top lipidoid carries positive charges at the physiological condition but promptly acquires negative charges in the presence of esterase, thus permitting stable mRNA encapsulation during storage and in vivo delivery while balancing efficient mRNA release in the cytosol. An optimal LNP formulation is then identified through orthogonal optimization, which enables efficacious mRNA transfection selectively in the spleen following intravenous administration. LNP-mediated delivery of ovalbumin (OVA)-encoding mRNA induces efficient antigen expression in antigen-presenting cells and elicits robust antigen-specific immune responses against OVA-transduced tumors. The work demonstrates the potential of decationizable quaternium lipidoids for spleen-selective RNA transfection and cancer immunotherapy.

Aqueous Two-Phase Interfacial Assembly of COF Membranes for Water Desalination.

Aqueous two-phase system features with ultralow interfacial tension and thick interfacial region, affording unique confined space for membrane assembly. Here, for the first time, an aqueous two-phase interfacial assembly method is proposed to fabricate covalent organic framework (COF) membranes. The aqueous solution containing polyethylene glycol and dextran undergoes segregated phase separation into two water-rich phases. By respectively distributing aldehyde and amine monomers into two aqueous phases, a series of COF membranes are fabricated at water-water interface. The resultant membranes exhibit high NaCl rejection of 93.0-93.6% and water permeance reaching 1.7-3.7 L m-2 h-1 bar-1, superior to most water desalination membranes. Interestingly, the interfacial tension is found to have pronounced effect on membrane structures. The appropriate interfacial tension range (0.1-1.0 mN m-1) leads to the tight and intact COF membranes. Furthermore, the method is extended to the fabrication of other COF and metal-organic polymer membranes. This work is the first exploitation of fabricating membranes in all-aqueous system, confering a green and generic method for advanced membrane manufacturing.

Assembling covalent organic framework membranes via phase switching for ultrafast molecular transport.

Fabrication of covalent organic framework (COF) membranes for molecular transport has excited highly pragmatic interest as a low energy and cost-effective route for molecular separations. However, currently, most COF membranes are assembled via a one-step procedure in liquid phase(s) by concurrent polymerization and crystallization, which are often accompanied by a loosely packed and less ordered structure. Herein, we propose a two-step procedure via a phase switching strategy, which decouples the polymerization process and the crystallization process to assemble compact and highly crystalline COF membranes. In the pre-assembly step, the mixed monomer solution is casted into a pristine membrane in the liquid phase, along with the completion of polymerization process. In the assembly step, the pristine membrane is transformed into a COF membrane in the vapour phase of solvent and catalyst, along with the completion of crystallization process. Owing to the compact and highly crystalline structure, the resultant COF membranes exhibit an unprecedented permeance (water ≈ 403 L m-2 bar-1 h-1 and acetonitrile ≈ 519 L m-2 bar-1 h-1). Our two-step procedure via phase switching strategy can open up a new avenue to the fabrication of advanced organic crystalline microporous membranes.

Photo-tailored heterocrystalline covalent organic framework membranes for organics separation.

Organics separation for purifying and recycling environment-detrimental solvents is essential to sustainable chemical industries. Covalent organic framework (COF) membranes hold great promise in affording precise and fast organics separation. Nonetheless, how to well coordinate facile processing-high crystalline structure-high separation performance remains a critical issue and a grand challenge. Herein, we propose a concept of heterocrystalline membrane which comprises high-crystalline regions and low-crystalline regions. The heterocrystalline COF membranes are fabricated by a two-step procedure, i.e., dark reaction for the construction of high-crystalline regions followed by photo reaction for the construction of low-crystalline regions, thus linking the high-crystalline regions tightly and flexibly, blocking the defect in high-crystalline regions. Accordingly, the COF membrane exhibits sharp molecular sieving properties with high organic solvent permeance up to 44-times higher than the state-of-the-art membranes.

Charged Nanochannels in Covalent Organic Framework Membranes Enabling Efficient Ion Exclusion.

Controllable ion transport through nanochannels is crucial for biological and artificial membrane systems. Covalent organic frameworks (COFs) with regular and tunable nanochannels are emerging as an ideal material platform to develop synthetic membranes for ion transport. However, ion exclusion by COF membranes remains challenging because most COF materials have large-sized nanochannels leading to nonselective transport of small ions. Here we develop ionic COF membranes (iCOFMs) to control ion transport through charged framework nanochannels, the interior surfaces of which are covered with arrayed sulfonate groups to render superior charge density. The overlap of an electrical double layer in charged nanochannels blocks the entry of co-ions, narrows their passageways, and concomitantly restrains the permeation of counterions via the charge balance. These highly charged large-sized nanochannels within the iCOFM enable ion exclusion while maintaining intrinsically high water permeability. Our results reveal possibilities for controllable ion transport based on COF membranes for water purification, ionic separation, sensing, and energy conversion.

Assembling covalent organic framework membranes with superior ion exchange capacity.

Ionic covalent organic framework membranes (iCOFMs) hold great promise in ion conduction-relevant applications because the high content and monodispersed ionic groups could afford superior ion conduction. The key to push the upper limit of ion conductivity is to maximize the ion exchange capacity (IEC). Here, we explore iCOFMs with a superhigh ion exchange capacity of 4.6 mmol g-1, using a dual-activation interfacial polymerization strategy. Fukui function is employed as a descriptor of monomer reactivity. We use Brønsted acid to activate aldehyde monomers in organic phase and Brønsted base to activate ionic amine monomers in water phase. After the dual-activation, the reaction between aldehyde monomer and amine monomer at the water-organic interface is significantly accelerated, leading to iCOFMs with high crystallinity. The resultant iCOFMs display a prominent proton conductivity up to 0.66 S cm-1, holding great promise in ion transport and ionic separation applications.

Antifouling graphene oxide membranes for oil-water separation via hydrophobic chain engineering.

Engineering surface chemistry to precisely control interfacial interactions is crucial for fabricating superior antifouling coatings and separation membranes. Here, we present a hydrophobic chain engineering strategy to regulate membrane surface at a molecular scale. Hydrophilic phytic acid and hydrophobic perfluorocarboxylic acids are sequentially assembled on a graphene oxide membrane to form an amphiphilic surface. The surface energy is reduced by the introduction of the perfluoroalkyl chains while the surface hydration can be tuned by changing the hydrophobic chain length, thus synergistically optimizing both fouling-resistance and fouling-release properties. It is found that the surface hydration capacity changes nonlinearly as the perfluoroalkyl chain length increases from C4 to C10, reaching the highest at C6 as a result of the more uniform water orientation as demonstrated by molecular dynamics simulations. The as-prepared membrane exhibits superior antifouling efficacy (flux decline ratio <10%, flux recovery ratio ~100%) even at high permeance (~620 L m-2 h-1 bar-1) for oil-water separation.

Nanomedicine from amphiphilizedprodrugs: Concept and clinical translation.

Nanomedicines generally consisting of carrier materials with small fractions of active pharmaceutical ingredients (API) have long been used to improve the pharmacokinetics and biodistributions, augment the therapeutic efficacies and mitigate the side effects. Amphiphilizing hydrophobic/hydrophilic drugs to prodrugs capable of self-assembly into well-defined nanostructures has emerged as a facile approach to fabricating nanomedicines because this amphiphilized prodrug (APD) strategy presents many advantages, including minimized use of inert carrier materials, well-characterized prodrug structures, fixed and high drug loading contents, 100% loading efficiency, and burst-free but controlled drug release. This review comprehensively summarizes recent advances in APDs and their nanomedicines, from the rationale and the stimuli-responsive linker chemistry for on-demand drug release to their progress to the clinics, clinical performance of APDs, as well as the challenges and perspective on future development.

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.

Author Correction: Metal-coordinated sub-10 nm membranes for water purification.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Topological Hall Effect in Traditional Ferromagnet Embedded with Black-Phosphorus-Like Bismuth Nanosheets.

Topological Hall effect is an abnormal Hall response arising from the scalar spin chirality of chiral magnetic textures. Up to now, such an effect is only observed in certain special materials, but rarely in traditional ferromagnets. In this work, we have implemented the molecular beam epitaxy technique to successfully embed black-phosphorus-like bismuth nanosheets with strong spin-orbit coupling into the bulk of chromium telluride Cr2Te3, as evidenced by atomically resolved energy dispersive X-ray spectroscopy mapping. Distinctive from pristine Cr2Te3, these Bi-embedded Cr2Te3 epitaxial films exhibit not only pronounced topological Hall effects, but also magnetoresistivity anomalies and differential magnetic susceptibility plateaus. All these experimental features point to the possible emergence of magnetic skyrmions in Bi-embedded Cr2Te3, which is further supported by our numerical simulations with all input parameters obtained from the first-principle calculations. Therefore, our work demonstrates a new efficient way to induce skyrmions in ferromagnets, as well as the topological Hall effect by embedding nanosheets with strong spin-orbit couplings.

Metal-coordinated sub-10 nm membranes for water purification.

Ultrathin membranes with potentially high permeability are urgently demanded in water purification. However, their facile, controllable fabrication remains a grand challenge. Herein, we demonstrate a metal-coordinated approach towards defect-free and robust membranes with sub-10 nm thickness. Phytic acid, a natural strong electron donor, is assembled with metal ion-based electron acceptors to fabricate metal-organophosphate membranes (MOPMs) in aqueous solution. Metal ions with higher binding energy or ionization potential such as Fe3+ and Zr4+ can generate defect-free structure while MOPM-Fe3+ with superhydrophilicity is preferred. The membrane thickness is minimized to 8 nm by varying the ligand concentration and the pore structure of MOPM-Fe3+ is regulated by varying the Fe3+ content. The membrane with optimized MOPM-Fe3+ composition exhibits prominent water permeance (109.8 L m-2 h-1 bar-1) with dye rejections above 95% and superior stability. This strong-coordination assembly may enlighten the development of ultrathin high-performance membranes.