Crystalline Membranes Research Articles

Piezocatalytic property of PVDF/Graphene self-assembling piezoelectric membrane for environmental remediation

In recent years, industrial pollution has become an inescapable global issue. The catalytic degradation processes driven by environmental sources, such as photocatalysis and piezocatalysis, are among the effective solutions. However, the difficulty in recycling catalysts leads to secondary pollution, limiting their practical application. This study develops a graphene-based self-assembled piezocatalytic membrane. Through Non-solvent Induced Phase Separation (NIPS), polyvinylidene fluoride (PVDF)/graphene asymmetrical membrane was prepared. The addition of graphene induced the self-assembly of PVDF crystalline phases into piezoelectric β phase. The membrane generates the ROS species to degrade the pollutant by the screen charge from material surface under a piezoelectric field. The optimal membrane exhibits the highest Vpp value of 4.26 V, and significant degradation efficiency of 80.2 % and 85.6 % for methylene blue (MnB) and crystal violet (CV), respectively, which are positively charged dyes. Meanwhile, the degradation efficiency within 2 h reached 73.8 % for negatively charged methyl orange (MO) and 96.1 % for toxic rhodamine B (RhB). This study successfully developed a crystalline self-assembled piezocatalytic membrane, providing fundamental insights into its piezoelectric response and various pollutant degradation. It introduces new directions and possibilities for the future development of membrane-based piezocatalysis.

Spectral Multiplexing of Rare‐Earth Emitters in a Co‐Doped Crystalline Membrane

AbstractThe spectral addressing of many individual rare‐earth dopants in optical resonators offers great potential for realizing distributed quantum information processors. To this end, it is required to understand and control the spectral properties of the emitters in micron‐scale devices. Here, erbium emitters are investigated in a Fabry–Perot resonator that contains a 10 µm thin membrane of crystalline yttrium orthosilicate that is co‐doped with europium. The co‐doping allows for tailoring the inhomogeneous distribution of the emitter frequency. With this approach, more than 360 spectrally resolved emitters are observed with Purcell factors exceeding 35, each of which constitutes an individually addressable qubit within the micron‐scale resonator. In addition to this spectral multiplexing, the optical coherence is preserved up to 0.62(3) ms under dynamical decoupling. Without decoupling, the coherence still reaches the lifetime limit for the emitters with the strongest Purcell enhancement that leads up to a 110‐fold lifetime reduction, down to 0.104(9) ms. Future work may combine this with long‐lived nuclear spin memories, which makes the investigated co‐doped membranes a promising platform for quantum repeaters and distributed quantum computers.

Ultra-thin size-sieving gas separation membrane by precisely contra-diffusion-match growth of ZIF-67 among GO laminates

Ultrathin and defect-free MOF membranes are actively pursued to realize high-performance hydrogen purification and carbon capture, which are of great significance for energy conservation and environmental sustainability. Zeolitic imidazolate framework-67 (ZIF-67) possesses exceptional pore apertures for sieving hydrogen from other larger gases. However, the preferential heterogeneous nucleation and growth of ZIF-67 crystals greatly challenge the synthesis of ZIF-67 membranes. In this work, a tunable-reaction-zone contra-diffusion synthesis is proposed to effectively assemble ZIF-67 nanocrystals into ultrathin GO laminates. The contra-diffusion-match growth of ZIF-67 constructs a compact ZIF-67@GO hybrid structure with superior H2/CO2 separation factor of 140.8 and H2 permeance of 1.7 × 10−7 mol m−2 s−1 Pa−1, transcending the state-of-art upper bounds. The excellent separation performance is attributed to the collaborative effect of the size-sieving and the selective attraction of the ZIF-67@GO hybrid structure. Long-term operation also reveals the superior stability of the ZIF-67@GO hybrid membrane for H2/CO2 separation. The rational-design approach grants a novel way to fabricate ultrathin and defect-free ZIF-67 crystalline membranes for high-performance gas separation.

Hydrogen-Bonded Structures of Water Molecules in Hydroxy-Functionalized Nanochannels of Columnar Liquid Crystalline Nanostructured Membranes Studied by Soft X-ray Emission Spectroscopy.

Here, we report a synchrotron-based high-resolution soft X-ray emission spectroscopy study on hydrogen-bonded structures of water molecules in the self-organized, hydroxy-group-functionalized one-dimensional nanochannels of liquid crystalline nanostructured membranes. The water molecules confined in the uncharged hydroxy-functionalized nanochannels (which have a diameter of about 1.5 nm) exhibit hydrogen-bonded structures close to those of bulk liquid water, even directly interacting with diol groups. These hydrogen-bonded structures contrast with the more distorted hydrogen bonding of water molecules confined in self-organized channels with a diameter of 0.6 nm formed by an analogous nanostructured membrane with a cationic moiety, which was explained by the ability of the channel functional groups to donate and accept hydrogen bonds in a confined space and the nanochannel diameter.

Entropic pressure on fluctuating solid membranes

Biological and crystalline membranes exhibit noticeable fluctuations at room temperature due to their low bending stiffness. These fluctuations have a significant impact on their overall mechanical behavior and interactions with external objects. When two membranes come into proximity, they mutually suppress each other’s fluctuations, leading to a repulsive force that plays a pivotal role in the mechanical behavior of these membranes. From the mechanics point of view, crystalline membranes are modeled as solid membranes with inherent shear resistance, whereas biological membranes are commonly described as fluidic entities without shear resistance. Under this premise, the entropic force between two fluctuating biological membranes is proposed to scale as p∝1/d3, where d is the intermembrane distance. Yet, there are numerous instances where these membranes display shear resistance and behave akin to solid membranes. In this paper, we develop a statistical mechanics model within nonlinear elasticity to study the entropic force acting on a confined, fluctuating solid membrane. We demonstrate that, due to the nonlinear elasticity of solid membranes, the entropic force scales differently compared to that of fluid membranes. Our predictions align well with the results obtained from molecular dynamics simulations involving graphene, a representative of a solid membrane, confined between two rigid walls.

Nano‐confined Supramolecular Assembly of Ultrathin Crystalline Polymer Membranes for High‐Performance Nanofiltration

AbstractPolymer membranes with high permeability, high salt rejection, and mechanical integrity are desirable in water treatment and purification. However, it remains a daunting challenge to achieve ultrathin yet robust polymer membranes harvesting all the above features for nanofiltration. Here, a new approach of nano‐confined supramolecular assembly to fabricate ultrathin crystalline polymer membranes with a modulus of 1 GPa and a thickness of 6.5 nm is reported. The microdroplet carrying amphiphilic tetra‐oligomers can quickly spread at the air–‐water interface, where the hydrophilic motifs such as carbonyl and hydroxyl groups can reconfigurably anchor down to water molecules via abundant hydrogen bonding interactions, significantly promoting the alignment and orientation of hydrophobic alkyl chains within the nano‐confined space. The resultant nano‐films exhibit mechanical robustness as well as excellent ion sieving with improved NaCl rejection of 81.3% and unprecedented Na2SO4 rejection of 99.9% without compromising water permeation, outperforming the reported and commercial state‐of‐the‐art polymer membranes. This work enables the rapid production of over 100 cm2 ultrathin crystalline polymer membranes with great nanofiltration potential and highlights the critical role of supramolecular assembly in the chemical and structural configurations in a nano‐confined space.

Designed Metal-Containing Peptoid Membranes as Enzyme Mimetics for Catalytic Organophosphate Degradation.

The detoxification of lethal organophosphate (OP) residues in the environment is crucial to prevent human exposure and protect modern society. Despite serving as excellent catalysts for OP degradation, natural enzymes require costly preparation and readily deactivate upon exposure to environmental conditions. Herein, we designed and prepared a series of phosphotriesterase mimics based on stable, self-assembled peptoid membranes to overcome these limitations of the enzymes and effectively catalyze the hydrolysis of dimethyl p-nitrophenyl phosphate (DMNP)─a nerve agent simulant. By covalently attaching metal-binding ligands to peptoid N-termini, we attained enzyme mimetics in the form of surface-functionalized crystalline nanomembranes. These nanomembranes display a precisely controlled arrangement of coordinated metal ions, which resemble the active sites found in phosphotriesterases to promote DMNP hydrolysis. Moreover, using these highly programmable peptoid nanomembranes allows for tuning the local chemical environment of the coordinated metal ion to achieve enhanced hydrolysis activity. Among the crystalline membranes that are active for DMNP degradation, those assembled from peptoids containing bis-quinoline ligands with an adjacent phenyl side chain showed the highest hydrolytic activity with a 219-fold rate acceleration over the background, demonstrating the important role of the hydrophobic environment in proximity to the active sites. Furthermore, these membranes exhibited remarkable stability and were able to retain their catalytic activity after heating to 60 °C and after multiple uses. This work provides insights into the principal features to construct a new class of biomimetic materials with high catalytic efficiency, cost-effectiveness, and reusability applied in nerve agent detoxification.

Crystalline membranes under stress: A Monte Carlo study based on the Nelson-Peliti Hamiltonian

Crystalline membranes under stress: A Monte Carlo study based on the Nelson-Peliti Hamiltonian

Cryo-EM elucidates the uroplakin complex structure within liquid-crystalline lipids in the porcine urothelial membrane

The urothelium, a distinct epithelial tissue lining the urinary tract, serves as an essential component in preserving urinary tract integrity and thwarting infections. The asymmetric unit membrane (AUM), primarily composed of the uroplakin complex, constitutes a critical permeability barrier in fulfilling this role. However, the molecular architectures of both the AUM and the uroplakin complex have remained enigmatic due to the paucity of high-resolution structural data. In this study, we utilized cryo-electron microscopy to elucidate the three-dimensional structure of the uroplakin complex within the porcine AUM. While the global resolution achieved was 3.5 Å, we acknowledge that due to orientation bias, the resolution in the vertical direction was determined to be 6.3 Å. Our findings unveiled that the uroplakin complexes are situated within hexagonally arranged crystalline lipid membrane domains, rich in hexosylceramides. Moreover, our research rectifies a misconception in a previous model by confirming the existence of a domain initially believed to be absent, and pinpointing the accurate location of a crucial Escherichia coli binding site implicated in urinary tract infections. These discoveries offer valuable insights into the molecular underpinnings governing the permeability barrier function of the urothelium and the orchestrated lipid phase formation within the plasma membrane.

Novel translucent hollow fiber polyvinylidene fluoride photocatalytic membrane for highly efficient oil-produced wastewater treatment: The role of translucency on degradation efficiency

A novel method, Thermally Modified Non-Solvent Induced Phase Separation (T-NIPS) has been developed to fabricate translucent hollow fiber (THF) photocatalytic membrane for membrane’s photodegradation efficiency enhancement. The process involves two-step temperature treatment that attacks crystalline property of polyvinylidene fluoride (PVDF). Graphitic carbon nitride in a modified morphological structure (hollow nanofiber) was used as photocatalyst to investigate the effect of translucency on membrane’s photodegradation efficiency. UV-Vis analysis coupled with FTIR highlighted different crystalline phase appearance and membrane’s translucency. The membranes showed high translucency, ranging from 60.0% to 93.9%, with THF-PVDF/PVP-GCN (2.0) exhibiting the highest. The filtration experiment showed that membrane with GCN photocatalyst had high PWF (1200 L/m2h) and rejection (90%) OPW compared to neat THF-PVDFs. In suspended mode, GCN demonstrated an impressive photodegradation efficiency of 99.98%. When immobilized in opaque PVDF membrane, the photodegradation has decreased substantially to 49.40%. However, when immobilized in a translucent PVDF membrane, the photodegradation efficiency of HN-GCN significantly improved compared to the opaque PVDF membrane, reaching 95%. Translucent membrane was subjected to five cycle regeneration test and showed 90% recovery even after the fifth cycle. The 10% reduction in the recovery was investigated using FESEM analysis revealed that there is a cake layer formation on the membrane surface. Therefore, this study proved that translucency of membrane has significant effect on immobilized photocatalyst’s photocatalytic efficiency.

PTSA-mediated interfacial catalytic polymerization of crystalline dense covalent organic framework membranes for enhanced desalination

Construction of covalent organic frameworks (COF) membranes for desalination applications was challenging, mainly due to the poor crystallinity and large intrinsic pore size of COFs. Herein, the p-toluenesulfonic acid (PTSA)-mediated interfacial catalytic polymerization (ICP) strategy was proposed to fabricate COF membranes with high crystallinity and sub-nano pores on the polysulfone substrate to enhance desalination and selectivity performance. The proposed PTSA-mediated ICP strategy facilitated the amorphous-to-crystalline transformation and regulated the stacking behavior of COF crystals. Via PTSA meditated ICP process, a ribbon-like crystal structure was observed on the membrane surface. The amorphous COF layers with a thickness of 122–412 nm transformed into crystalline COF layers with a thickness of approximately 245–390 nm, while the pore radius of the COF membranes decreased from 0.65-1.25 nm to 0.17–0.25 nm due to the multilayer stacking of COF crystals on the membrane surface. Meanwhile, the crystalline degree of these COF membranes increased from 21.45% to 73.95% with increasing PTSA concentration and ICP time. The optimal TpPa3%-15 membrane had a water permeability of approximately 3.74 L−1 m−2 h−1 bar−1 and substantial enhancement of Na2SO4 rejection from 19.7% to 90.4%. The 30-day duration of the cross-flow operation measurement demonstrated excellent stability and robust selectivity of SO42− and Cl− for the optimal TpPa3%-15 membrane. In addition, the optimal membrane exhibited excellent desalination performance for divalent ions in petrochemical wastewater and shale gas produced water than that of pristine membrane, rendering their applicability for industrial wastewater desalination. The mechanisms analysis verified that PTSA induced disorder multilayer stacking of crystalline COF crystals on the substrate surface, resulting in reduced pore sizes and increased desalination of the COF membranes. As the traditional IP process, this work proposed that PTSA mediated ICP process was a facile, scalable and time-saving approach for the construction of highly crystalline COF membranes with sub-nanometer pores to achieve enhanced desalination performance.

On the Role of the Sr3−xCaxAl2O6 Sacrificial Layer Composition in Epitaxial La0.7Sr0.3MnO3 Membranes

AbstractThe possibility to fabricate freestanding single crystal complex oxide films has raised enormous interest to be integrated in next‐generation electronic devices envisaging distinct and novel properties that can deliver unprecedented performance improvement compared to traditional semiconductors. The use of the water‐soluble Sr3Al2O6 (SAO) sacrificial layer to detach the complex oxide film from the growth substrate has significantly expanded the complex oxide perovskite membranes library. Nonetheless, the extreme water sensitivity of SAO hinders its manipulation in ambient conditions and restricts the deposition approaches to those using high vacuum. This study presents a pioneering study on the role of Ca‐substitution in solution processed SAO (Sr3−xCaxAl2O6 with x ⩽ 3) identifying a noticeable improvement on surface film crystallinity preserving a smooth surface morphology while favoring the manipulation in a less‐restricted ambient conditions. Then, the study focuses on the effect of the sacrificial composition on the subsequent ex situ deposition of La0.7Sr0.3MnO3 (LSMO) by pulsed laser deposition, to obtain epitaxial films with a variable degree of strain. Finally, epitaxial and strain‐free LSMO membranes with metal‐insulator transition at 290 K are delivered. This study offers a hybrid and versatile approach to prepare and easily manipulate crystalline perovskite oxide membranes by facilitating ex situ growth on SAO‐based sacrificial layer.

Fluctuating Flexoelectric Membranes in Asymmetric Viscoelastic Media: Power Spectrum through Mechanical Network and Transfer Function Models

Flexoelectric liquid crystalline membranes immersed in asymmetric viscoelastic media is a material system model with physiological applications such as outer hair cells (OHCs), where membrane oscillations generate bulk flow. Motivated by this physiological process, here we extend our previous work by characterizing the force transmission output of our model in addition to viscoelastic fluid flow, since solid–fluid interactions are an essential feature of confined physiological flow and flow in immersed elastic structures. In this work, the rigidity of the confinement results in a passive force reception, while more complete solid–fluid interactions will be considered in the future. A significant contribution of this work is a new asymmetry linear viscoelastic electro-rheological model and the obtained implicit relation between force transmission and flow generation and how this relation is modulated by electric field frequency and the material properties of the device. Maximal force and flow are found at resonant frequencies of asymmetry viscoelastic bulk phases, flexoelectric and dispersion mechanisms through the elastic and Womersley numbers.

Stepwise Monomicelle Assembly for Highly Ordered Mesoporous TiO2 Membranes with Precisely Tailored Mesophase and Porosity.

Mesoporous materials with crystalline frameworks have been acknowledged as very attractive materials in various applications. Nevertheless, due to the cracking issue during crystallization and incompatible hydrolysis and assembly, the precise control for crystalline mesoscale membranes is quite infertile. Herein, we presented an ingenious stepwise monomicelle assembly route for the syntheses of highly ordered mesoporous crystalline TiO2 membranes with delicately controlled mesophase, mesoporosity, and thickness. Such a process involves the preparation of monomicelle hydrogels and follows self-assembly by stepwise solvent evaporation, which enables the sensitive hydrolysis of TiO2 oligomers and dilatory micelle assembly to be united. In consequence, the fabricated mesoporous TiO2 membranes exhibit a broad flexibility, including tunable ordered mesophases (worm-like, hexagonal p6mm to body-centered cubic Im3̅m), controlled mesopore sizes (3.0-8.0 nm), and anatase grain sizes (2.3-8.4 nm). Besides, such mesostructured crystalline TiO2 membranes can be extended to diverse substrates (Ti, Ag, Si, FTO) with tailored thickness. The great mesoporosity of the in situ fabricated mesoscopic membranes also affords excellent pseudocapacitive behavior for sodium ion storage. This study underscores a novel pathway for balancing the interaction of precursors and micelles, which could have implications for synthesizing crystalline mesostructures in higher controllability.

High Efficient CO2 Separation at High Pressure by Grain-Boundary-Controlled CHA Zeolite Membrane Investigated by Non-Equilibrium Molecular Dynamics

The CO2 permeability and selectivity of CHA-type zeolite membranes in the separation of a CO2/CH4 mixture gas at high pressure were evaluated using non-equilibrium molecular dynamics (NEMD). It was found that in a perfectly crystalline, defect-free CHA membrane, the adsorption of CH4, which diffuses slowly in the pores, hinders CO2 permeation. Therefore, an increase in the amount of CH4 adsorbed at high pressure decreases the CO2 permeability and significantly reduces the CO2 selectivity of the CHA membrane. CHA membranes with grain boundaries parallel to the permeation direction were found to show higher CO2 selectivity than perfectly crystalline CHA membranes at high pressure, as the blocking effect of CH4 on CO2 permeation occurring within the grain boundary is not significant. This paper is the first to show that the CO2 permeability of CHA membranes with controlled grain boundaries can exceed the intrinsic performance of fully crystalline zeolite membranes at high pressure.

Direct observation of large-area strain propagation on free-standing nanomembranes

Investigations on epitaxial nanostructures with size of tens of nanometers have been a challenging issue for techniques that present high strain sensitivity but restricted spatial resolution. This is the case of recently developed x-ray nanoprobe techniques. Despite its inherent nondestructive character, submicron x-ray spots have only been successfully applied to the study of individual nanostructures which are either strain free or present extremely mild spatial lattice parameter gradients. Such limitation, with an uttermost barrier given by the diffraction limit, leads to voxel or pixel sizes between 5 and 10 nm obtained in coherent diffraction imaging or ptychographic reconstructions of real-space objects. Whenever the strain field of a nanostructure is successfully reconstructed from reciprocal space measurements, it cannot vary considerably in short distances since this would induce diffraction peak broadening and cause abrupt phase variations, leading to convergence issues on reconstruction algorithms. Here we show how epitaxial systems with large lattice mismatch and appreciable interfacial strain can be identified and directly analyzed throughout their strain field propagation in nanometer-thin crystalline membrane platforms, using the InGaAs/GaAs Stranski-Krastanov system as a model. The strain-induced footprint becomes observable along a few microns if the membrane thickness is comparable to the nanostructure size. It is possible to retrieve both interfacial strain and nanostructure size by probing individual objects.

In Situ Fabrication of Metal–Organic Framework Thin Films with Enhanced Pervaporation Performance

AbstractThe intrinsic porosity in the periodic structures of metal–organic frameworks (MOFs) endows them with a great potential for membrane separation. However, facile fabrication of crystalline MOF membranes has been challenging and limited to few materials for economic and environmental considerations. Herein, a continuous Zr‐MOF thin film with a thickness of ≈180 nm has been fabricated via in situ recrystallization of MOF nanoparticles on the porous support under formic acid vapor. Owing to the inherent microporosity and the well‐established hydrophilicity during membrane fabrication, the MOF thin films exhibit excellent pervaporation performance with separation factors of 2630, 501 and fluxes of 1.45, 1.41 kg m−2 h−1) for n‐butanol dehydration and methanol/methyl tert‐butyl ether (MeOH/MTBE) separation, respectively. The structural stability of the film has been further confirmed by its steady performance in the 10‐day pervaporation test. This in situ recrystallization method induced by a trace amount of acid vapor with no extra ingredients opens a new avenue for the facile membrane fabrication of various MOF materials to feasibly realize their versatile potential as membrane materials.

Annexin proteins involved in plasma membrane repair reshape a membrane edge: Direct evidence from molecular simulations.

The Annexin (ANX) family of Ca+2-dependent membrane-binding proteins are implicated in plasma membrane repair in animal cells. The inward flux of Ca+2 upon formation of a plasma membrane lesion/pore drives the binding of cytoplasmic ANX proteins to the membrane, close to the pore. Annexins are deemed responsible for plasma membrane repair and are overexpressed in cancer cells where the plasma membrane is in the need for frequent repair. Annexin A5 (ANXA5) trimers form crystalline arrays solid-supported membranes (1), and owing to their concave disc-like shape, induce negative curvature on a flat plasma membrane (2), and are therefore likely to reshape the membrane in the vicinity of the membrane pore to support membrane repair (3). However, no direct evidence of membrane shaping has yet emerged. Here, we simulate ANXA5 binding on a bicelle, which models a membrane pore under periodic boundary conditions, and demonstrate that increasing concentration of ANXA5 trimers induces a monotonically increasing out-of-plane upward curvature in the bicelle. Interestingly, this overall curvature amounts to half the curvature induced by a single ANXA5 trimer on a flat lipid bilayer. The out of plane curvature induced by ANXA5 trimers near a membrane pore is demonstrated for the first time. Our results have important implications in the membrane-reshaping properties of Annexins and their ability to repair membranes.

A Straightforward Method to Prepare MOF-Based Membranes via Direct Seeding of MOF-Polymer Hybrid Nanoparticles.

Metal Organic Frameworks (MOFs) present high surface areas, various pore topology as well as good stabilities. The functionalities and porosity can be tuned by using different linkers with various functional groups and a wide range of linker lengths. These properties make them good candidates in membrane separation applications. In this work, we propose a simple UiO-66 MOF-based membrane fabrication method following two steps. First, the α-alumina tubular membrane support was dip-coated with MOF-polymer hybrid nanoparticles (NPs). These NPs were prepared via one-pot synthesis by adding poly (methacrylic acid)-b-poly (methyl methacrylate) (PMAA-b-PMMA) NPs to the classical acetic acid-modulated UiO-66 or UiO-66-NH2 synthesis formulation. Second, secondary membrane growth was applied to give rise to a continuous and homogeneous crystalline MOF membrane layer. The gas permeances (He, N2, CO2 and SF6) tests confirmed high membrane permeability with no macro-defects. The as-prepared membranes that were used for dye separation (Rhodamine B) showed relatively good separation capacity.

Highly crystalline and robust covalent organic framework membranes for predictable solvent transport and molecular separation

Covalent organic frameworks (COFs) with well-ordered nanopores and stable structures have excited exponential interest as potent membrane platforms for molecular separation in organic solvent systems.