Selective Molecular Separation Research Articles

Hyperbranched aromatic poly(amidoamine) mediated interfacial polymerization for high-performance thin film composite membranes

The escalating global demand for clean water has driven a growing interest in developing thin-film composite (TFC) membranes with high permeability and selectivity for wastewater treatment and desalination processes. Engineering polymer materials with precisely tunable properties for selective molecular separation remains a challenging step toward achieving this goal. Herein, we have fabricated a highly permselective asymmetric polyamide nanofilm with a dual-layer structure in which the bottom layer is a porous hyperbranched aromatic polyamide (HBPA) interlayer, and the top layer is a dense polyamide layer with a nanostrip structure. The HBPA porous layer was covalently assembled in situ via oxidative coupling reaction with ammonium persulfate on a polysulfone (PSF) substrate. The hydrophilic porous HBPA interlayer forms nanosized cavities that may enhance the storage and confine amine monomer diffusion, leading to the construction of a striped pattern PA nanofilm. The resulting asymmetric PA membrane exhibits excellent water permeability of 18.39 ± 1 L m−2 h−1 bar−1 (3.98 times that of control membranes) and improved divalent salt (Na2SO4) rejection (≥98 %), surpassing most of the commercial and reported nanofiltration membranes. The HBPA-regulated interfacial polymerization provides a groundbreaking framework for developing high-performance membranes for precisely controlled nanofiltration.

Enhanced reactivity and selective adsorption: Unveiling the potential of metal-decorated graphene membranes for biosensing

This study investigates the structural, stability, electronic, and optical properties of finite graphene membranes through a comprehensive computational analysis. The 2D membranes are constructed from hexagonal graphene quantum dots and are decorated with Co, Mn, and Ni. Stability assessments, based on binding energies, affirm the stable formation of the 2D membrane and its derivatives. Electronic investigations reveal a reduction in the energy gap upon metal decoration, indicating enhanced reactivity. Membrane studies demonstrate effective adsorption of creatinine and uric acid on both edge and surface sites, supported by negative adsorption energies. Electronic transitions and absorption spectra shifts indicate dynamic interactions, emphasizing the materials' potential for selective molecular separation. Non-covalent interaction analysis confirmed the role of van der Waals interactions in creatinine and uric acid adsorption. Overall, the findings suggest that the graphene membrane and its decorated derivatives hold promise for selective adsorption applications, especially in the context of biosensing.

A pH‐ and Light‐Responsive Nanoporous Lyotropic Gyroid Polymer Network

AbstractBicontinuous cubic (Q) lyotropic liquid crystal (LLC)‐derived polymer networks possess periodic, uniform‐size, 3D‐interconnected nanopores that make them highly desirable organic materials for selective molecular separation and uptake applications. To date, there are no reported examples of a Q‐phase network with additional functional properties, such as catalytic reactivity, response to external stimuli, or gated transport, that would expand the usefulness of this class of porous materials. Here, a functionalized gyroid‐type Q polymer network material that can be used for potential gated transport or adaptive uptake applications is presented. This material contains a novel spiropyran‐containing dopant monomer that upon blending and cross‐linking with a gyroid‐forming LLC monomer, yields a gyroid polymer material that retains its phase architecture while reversibly responding to changes in external solution and vapor pH. Studies also demonstrate that this system is capable of strongly binding to aq. Pb2+ ions when activated by UV light, allowing it to function as a potential colorimetric sorbent or gated‐response material.

High-Purity, High-Yield Synthesis of Covalent Organic Framework Nanosheets for Fast and Selective Molecular Separation

High-Purity, High-Yield Synthesis of Covalent Organic Framework Nanosheets for Fast and Selective Molecular Separation

Selective molecular separation with conductive MXene/CNT nanofiltration membranes under electrochemical assistance

MXene-based membranes have drawn tremendous attention due to their high permeability and selectivity. To prevent MXene from restacking and enrich nanochannels for water transport, carbon nanotubes (CNT) are intercalated between MXene nanosheets to fabricate MXene/CNT nanofiltration membranes in the present study. The membrane shows a high permeance of 30.4 L m−2 h−1 bar−1 and a high rejection ratio (>90%) toward organic molecules with the size larger than 2 nm. More importantly, the rejection ability for the negatively charged chemicals can be further improved by a voltage applied during filtration process. The rejections of orange G and methyl orange increase from 64.8 ± 1.9% and 27.2 ± 3.8% to 96.3 ± 3.2% and 87.8 ± 3.1%, respectively when a voltage of 3.0 V is applied with the membranes as the cathode. The improvement is ascribed to the enhanced electrostatic repulsion between the negatively charged dyes and the membrane cathode. With the benefit of the mechanism, binary and ternary dye mixtures with different charges can be selectively separated by the MXene/CNT membrane for wastewater treatment and selective recycling of reusable resources from wastewater.

Detachable all-carbon-linked 3D covalent organic framework films for semiconductor/COF heterojunctions by continuous flow synthesis

Detachable all-carbon-linked 3D covalent organic framework films for semiconductor/COF heterojunctions by continuous flow synthesis

Polycarbene-bearing membrane surface containing silver species for size and charge selective molecular separation

A very simple yet powerful strategy is developed for surface modification of poly(ionic liquid)-based membranes under natural sunlight, resulting in improved molecular separation efficiency.

Nitrogen-doped nanoporous graphene induced by a multiple confinement strategy for membrane separation of rare earth.

SummaryRare earth separation is still a major challenge in membrane science. Nitrogen-doped nanoporous graphene (NDNG) is a promising material for membrane separation, but it has not yet been tested for rare earth separation, and it is limited by multi-complex synthesis. Herein, we developed a one-step, facile, and scalable approach to synthesize NDNG with tunable pore size and controlled nitrogen content using confinement combustion. Nanoporous hydrotalcite from Zn(NO3)2 is formed between layers of graphene oxide (GO) absorbed with phenylalanine via confinement growth, thus preparing the sandwich hydrotalcite/phenylalanine/GO composites. Subsequently, area-confinement combustion of hydrotalcite nanopores is used to etch graphene nanopores, and the hydrotalcite interlayer as a closed flat nanoreactor induces two-dimensional space confinement doping of planar nitrogen into graphene. The membrane prepared by NDNG achieves separation of Sc3+ from the other rare earth ions with excellent selectivity (∼3.7) through selective electrostatic interactions of pyrrolic-N, and separation selectivity of ∼1.7 for Tm3+/Sm3+.

Azobenzene-assisted exfoliation of 2D covalent organic frameworks into large-area, few-layer nanosheets for high flux and selective molecular separation membrane

The porous 2D covalent organic nanosheets (CONs) membrane has become a new generation of membrane material due to its ultrahigh permeation flux. The main challenge in fabricating CONs membrane is how to exfoliate covalent organic frameworks (COFs) into large-scale, few-layer nanosheets. Herein, we presented a simple and economical azobenzene template approach for exfoliating 2D COFs into large nanosheets and achieved fabrication of ultrathin CONs membrane successfully. Three COFs with different skeleton structures were chosen to explore the influencing factors for effective exfoliating. We found that the compatibility between azobenzene molecules and COFs skeleton structure was the key point for exfoliation. When the COF skeleton matching with the azobenzene molecular structure, COFs can be easily exfoliated into larger-scale CONs than nanosheets prepared by conventional exfoliation methods. The as-exfoliated nanosheets membrane showed a higher water flux (596 L m2 h-1 bar-1) than a graphene oxide (GO) membrane (4.3 L m2 h-1 bar-1) and high rejection of dye molecules, due to the nano-channels perpendicular to the surface of the membrane.

Self-assembly of robust graphene oxide membranes with chirality for highly stable and selective molecular separation

Self-assembly of robust cooperative nanostructured graphene oxide nanofiltration membranes with chirality was realized for highly stable and selective molecular separation.

Covalent Self-Assembly in Two Dimensions: Connecting Covalent Organic Framework Nanospheres into Crystalline and Porous Thin Films.

Insolubility of covalent organic frameworks (COFs) in organic solvents is one of the major obstacles for the potential application of these extended networks such as drug delivery, sensing, optoelectronics, and semiconductor device fabrication. The present work proposes a unique way to make uniform, solution-processable, crystalline, and porous COF nanospheres directly from the homogeneous solution of amine and aldehyde via spatial and temporal control of the nucleation and growth. This strategy of direct nucleation simultaneously showcases the caliber to tune the size of the COF nanospheres from 25 to 570 nm. We have also demonstrated the concept of mesoscale covalent self-assembly of those solution-processable COF nanospheres in the liquid-liquid interface (DCM-water bilayer) for the very first time, transmuting them into self-standing COF thin films with long-range ordered arrangements in two dimensions. The crystalline and porous (with TpAzo showing highest SBET of 1932 m2 g-1) free-standing COF thin films could be fabricated in a wide range of thicknesses from as low as 21 nm to as high as 630 nm. Both β-ketoenamine (TpAzo, TpDPP) and imine (TpOMeAzo, TpOMeDPP) linked COF thin films have been synthesized via mesoscale covalent self-assembly of the solution-processable COF nanospheres illustrating the generality of this eloquent methodology. Further, the solution processability has been tested and utilized to cast COF thin films uniformly in the inner and outer surface of an alumina hollow fiber membrane. The COF thin film-alumina hollow fiber membrane composites have showcased promising selective molecular separation of He and O2, He and CO2, and He and N2.

Filamentous virus-based membrane prepared by chemical cross-linking at liquid/liquid interface for a tailored molecular separation system

Membranes with selective separation capability are desirable for use in energy-efficient processes. However, precise control of target selectivity for separation is still challenging due to difficulty in controlling porous membrane structures and interactions between membrane components and target molecules. In this study, we report a filamentous virus (M13 phage)-based membrane prepared by chemical cross-linking at liquid/liquid interfaces for selective molecular separation. The M13 phage membrane composed of oriented M13 phage assemblies showed a molecularly porous structure, enabling the size-selective separation of small organic compounds. Furthermore, the pore structure was controlled by the initial concentration of M13 phage solution, enabling broad size selectivity. The rejection rates of positively charged molecules tend to be greater than those of negatively charged molecules with similar molecular weights, possibly due to the negatively charged M13 phage membrane, indicating certain electrostatic interactions. Membrane preparation using M13 phage modified by peptides with a specific affinity for neodymium ions (Nd3+) was performed to realize the selective separation of small Nd3+. The membrane preferentially adsorbed Nd3+ over iron ions, demonstrating that the molecular recognition capability of the peptide clearly remained even after the chemical cross-linking reaction. This broad-spectrum separation membrane has potential applicability in various fields, such as wastewater treatment, the food industry, and the life sciences.

Selective molecular separation of lignin model compounds by reduced graphene oxide membranes from solvent-water mixture

Selective separation of lignin depolymerization products is key to fractionating and isolating high-value aromatic compounds from the depolymerization process. The primary aim of this study was to synthesis graphene oxide (GO) membranes for selective separations of lignin oligomeric units from polar organic solvent-water media. GO membranes were synthesized on a polymeric substrate by a shear assisted casting of aqueous GO dispersion using a wire-wound rod. Deposited GO was then reduced to different extents by controlled thermal incubation, and the impact on membrane performance was investigated. The extent of reduction of GO was established by extensive characterization with FTIR, XPS, Raman Spectroscopy, XRD, and contact angle measurements. Impressive performance with the rejection of over 70% for the model compound trimer BMP (2,6-bis[(2-hydroxy-5-methyl phenyl) methyl]-4-methylphenol) was achieved compared to only 20% rejection for the dimer GGE (guaiacylglycerol-β-guaiacylether) with isopropanol-water (90–10% by volume) as a solvent. This corresponds to an encouraging selective separation with selective permeation of dimer (GGE) 3.5 times higher compared to trimer (BMP). rGO membranes exhibited a stable performance over 84 h of operation at a shear rate of 1.1 Pa in a cross-flow mode of operation. Selective separation of GO can be effectively modulated by controlling the O/C ratio by the extent of reduction of GO; indeed, the retention of trimeric compounds increased with increasing GO reduction. The remarkable performance of GO membranes could enable energy-efficient fractionation of lignin oligomeric compounds from polar organic solvents.

Ultrafast molecular sieving through functionalized graphene membranes

Graphene shows great promise for advanced filtration membranes with high permeance and enhanced rejection. Here we demonstrate filtration membranes with a nanochannel network for superior separation performance using 100-500 nm-wide graphene nanoplatelets (GnPs) that are efficiently prepared via a green method. The resulting membranes exhibit a well packed layer structure formed by GnPs and are highly stable in water and organic solvents and even in strongly acidic and alkaline media. Moreover, the GnP membranes possess high fluxes and good selectivity in both water and organic solvents based on the small size nanoplatelets and the stable nanochannels between the GnPs. The exfoliated GnPs and the subsequent membranes show great potential for practical applications in water purification and organic solvent filtration.

Selective Molecular Separation on Ti3C2Tx-Graphene Oxide Membranes during Pressure-Driven Filtration: Comparison with Graphene Oxide and MXenes.

In this work, we prepared 90 nm thick Ti3C2Tx-graphene oxide (GO) membranes laminated on a porous support by mixing GO with Ti3C2Tx. This process was chosen to prevent the penetration of target molecules through inter-edge defects or voids with poor packing. The lattice period of the prepared membrane was 14.28 Å, as being swelled with water, resulting in an effective interlayer spacing of around 5 Å, which corresponds to two layers of water molecules. The composite membranes effectively rejected dye molecules with hydrated radii above 5 Å, as well as positively charged dye molecules, during pressure-driven filtration at 5 bar. Rejection rates were 68% for methyl red, 99.5% for methylene blue, 93.5% for rose Bengal, and 100% for brilliant blue (hydrated radii of 4.87, 5.04, 5.88, and 7.98 Å, respectively). Additionally, the rejections of composite membrane were compared with GO membrane and Ti3C2Tx membrane.

Selective Molecular Separation by Interfacially Crystallized Covalent Organic Framework Thin Films.

Exponential interest in the field of covalent organic frameworks (COFs) stems from the direct correlation between their modular design principle and various interesting properties. However, existing synthetic approaches to realize this goal mainly result in insoluble and unprocessable powders, which severely restrict their widespread applicability. Therefore, developing a methodology for easy fabrication of these materials remains an alluring goal and a much desired objective. Herein, we have demonstrated a bottom-up interfacial crystallization strategy to fabricate these microcrystalline powders as large-scale thin films under ambient conditions. This unique design principle exploits liquid-liquid interface as a platform, allowing simultaneous control over crystallization and morphology of the framework structure. The thin films are grown without any support in free-standing form and can be transferred onto any desirable substrate. The porous (with Tp-Bpy showing highest SBET of 1 151 m2 g-1) and crystalline thin films, having high chemical as well as thermal stability, also hold the merit to tune the thickness as low as sub-100 nm. These nanostructured thin COF films demonstrate remarkable solvent-permeance and solute-rejection performance. A prominent instance is the Tp-Bpy thin film, which displays an unprecedented acetonitrile permeance of 339 L m-2 h-1 bar-1.

Preparation of diclofenac-imprinted polymer beads for selective molecular separation in water.

Molecular imprinting technique is an attractive strategy to prepare materials for target recognition and rapid separation. In this work, a new type of diclofenac (DFC)-imprinted polymer beads was synthesized by Pickering emulsion polymerization using 2-(dimethylamino)ethyl methacrylate as the functional monomer. The selectivity and capacity of the molecularly imprinted polymers (MIPs) were investigated in aqueous solution. Equilibrium binding results show that the MIPs have a high selectivity to bind DFC in a wide range of pH values. Moreover, in liquid chromatography experiment, the imprinted polymer beads were packed into column to investigate the binding selectivity under nonequilibrium conditions. The retention time of DFC on the MIP column is significantly longer than its structural analogues. Also, retention of DFC on the MIP column was significantly longer than on the nonimprinted polymer column under aqueous condition. As the new MIP beads can be used to achieve direct separation of DFC from water, the synthetic method and the affinity beads developed in this work opened new possibilities for removing toxic chemicals from environmental and drinking water.

A graphene oxide membrane with highly selective molecular separation of aqueous organic solution.

A graphene oxide (GO) membrane is supported on a ceramic hollow fiber prepared by a vacuum suction method. This GO membrane exhibited excellent water permeation for dimethyl carbonate/water mixtures through a pervaporation process. At 25 °C and 2.6 wt % feed water content, the permeate water content reached 95.2 wt% with a high permeation flux (1702 g m(-2) h(-1)).

A Graphene Oxide Membrane with Highly Selective Molecular Separation of Aqueous Organic Solution

AbstractA graphene oxide (GO) membrane is supported on a ceramic hollow fiber prepared by a vacuum suction method. This GO membrane exhibited excellent water permeation for dimethyl carbonate/water mixtures through a pervaporation process. At 25 °C and 2.6 wt % feed water content, the permeate water content reached 95.2 wt % with a high permeation flux (1702 g m−2 h−1).

Imprinted polymer beads enabling direct and selective molecular separation in water

In this paper, we describe the synthesis of water-compatible Molecularly Imprinted Polymer (MIP) microspheres by nanoparticle-stabilized emulsion (Pickering emulsion) polymerization. During the polymerization, the amount of the porogen used not only affected the stability of the Pickering emulsion but also the specific molecular recognition of the obtained MIP microspheres. Under optimized conditions, the MIP microspheres synthesized had a porous and hydrophilic surface. Scanning electron microscopy and fluorescent labeling experiments indicated that the MIP microspheres had particle sizes of 165 ± 38 μm. Selective molecular recognition with the MIP microspheres was studied through equilibrium binding analysis and liquid chromatography experiments under pure aqueous conditions. Using the new MIP microspheres as solid phase extraction (SPE) absorbents, low concentration organic pollutants (β-blockers) were effectively enriched from tap water and easily detected using HPLC-MS analysis.