Laminar Membranes Research Articles

MXene-based composite forward osmosis (FO) membrane intercalated by halloysite nanotubes with superior water permeance and dye desalination performance

MXene two-dimensional (2D) laminate membranes have attracted many researchers in the field of membrane separation due to its adjustable interlayer spacing. However, MXene 2D laminate membranes has been inability to achieve dye desalination due to simultaneous rejection of both dyes and salts in salt-containing dye.The looser MXene/C-HNTs composite forward osmosis (FO) membrane was successfully prepared via vacuum filtering, in which halloysite nanotubes modified with cetyltrimethylammonium bromide (C-HNTs) and MXene (Ti3C2Tx) nanosheets were self-assembled by electrostatic interactions. The insertion of C-HNTs effectively increased the interlayer spacing and enhanced the compression resistance of the composite membranes. With a mass ratio of 1:3 between Ti3C2Tx nanosheets and C-HNTs, the composite membrane's pure water flux was raised to 191.4 L/(m2·h). The insertion of C-HNTs not only enabled the composite membrane to keep a superior dye rejection rate (CR rejection rate >99%), but also effectively reduced the rejection rate of monovalent salt (NaCl <5%) and divalent salt (<13% and <10% for Na2SO4 and MgSO4, respectively).

Ultrafast and selective gas transport through highly ordered black phosphorene nanochannels

Two-dimensional (2D) materials bring a great opportunity to fabricate molecular sieving membranes that can potentially break the permeability-selectivity trade-off. Although 2D laminar membranes with interlayer nanochannels as molecular sieving channel were widely studied, for most of reported 2D laminar membranes, it is of a great challenge to fabricate highly ordered interlayer nanochannels for mass transport. Herein, we report a novel kind of black phosphorene membrane which is made from the stacking of highly ordered 2D black phosphorene nanoflakes. The as prepared black phosphorene membrane shows H2 permeance > 1000 GPU and H2/CO2 selectivity > 100 for H2/CO2 mixed gas, demonstrating an extremely high gas separation performance. The DFT calculation results demonstrate that the interlayer galleries in the black phosphorene membrane allow the H2 passing through easily while block the other gases with bigger kinetic diameters, matching well with the experimental findings. The present results indicate that the interlayer galleries in the black phosphorene membrane can be applied as molecular sieving channels for gas separation.

A promising scalable route to construct GO-based laminate membranes for antifouling ultrafiltration

Graphene oxide (GO) laminate membranes have been deemed as promising membrane materials for a variety of applications, but they suffer from poor stability in solvents and difficulty in large-scale preparation.

Minimising non-selective defects in ultrathin reduced graphene oxide membranes with graphene quantum dots for enhanced water and NaCl separation

• Ultrathin GQDs/rGO membranes are prepared through a two-step assembly method. • The strong π–π interaction between GQDs and rGO enables the coverage of defects. • GQDs/rGO membranes achieve both high water permeance and high NaCl rejection. Reduced graphene oxide (rGO) membranes have been intensively evaluated for desalination and ionic sieving applications, benefiting from their stable and well-confined interlayer channels. However, rGO membranes generally suffer from low permeability due to the high transport resistance resulting from the narrowed two-dimensional (2D) channels. Although high permeability can be realized by reducing membrane thickness, membrane selectivity normally declines because of the formation of non-selective defects, in particular pinholes. In this study, we demonstrate that the non-selective defects in ultrathin rGO membranes can be effectively minimised by a facile posttreatment via surface-deposition of graphene quantum dots (GQDs). The resultant GQDs/rGO membranes obtained a good trade-off between water permeance (14 L⋅m −2 ⋅h −1 ⋅MPa −1 ) and NaCl rejection (91%). This work provides new insights into the design of high quality ultrathin 2D laminar membranes for desalination, molecular/ionic sieving and other separation applications.

Laminar HNb3O8-based membranes supported on anodic aluminum oxide with enhanced anti-swelling property for organic solvent nanofiltration

Organic solvent nanofiltration (OSN) is an energy-efficient alternative to distillation and evaporation for the separation of mixtures containing organic liquids. Laminar membranes using nanosheets as building blocks have great potential for OSN; however, a swelling of the interlayer spacing causes a severe decrease in the separation performance. Here, we present laminar HNb3O8-based composite membranes fabricated by vacuum filtration on an anodic aluminum oxide support for OSN applications. The laminar HNb3O8 membranes and composite (graphene oxide (GO) and HNb3O8) membranes were found to possess stable structures in various alcohols without severe swelling. As a result, the HNb3O8-based membranes showed higher dye rejections than the GO membrane. Among the HNb3O8-based membranes, the layered GO/HNb3O8 membrane had superior dye rejections in methanol (89.6% for Evans blue, 73.4% for acid red 265, and 43.4% for methyl orange) compared with the GO membranes. Alcohol permeation tests implied that the molecular diameter, rather than the solvent viscosity, was the dominant factor in the superior performance of the layered GO/HNb3O8 membrane. Molecular dynamics simulations suggest a stable GO/HNb3O8 interlayer ranging from around 1.165 to 1.333 nm, and a dense heterolayer formation at the interface between the HNb3O8 and GO layers. This heterolayer formation performs important roles in alcohol permeation and separation of organic dyes. Furthermore, the layered GO/HNb3O8 membrane showed stable permeation of a model photoresist waste liquid for 6 weeks and an excellent rejection of the photoresist waste, over 91%. We propose that laminar HNb3O8-based membranes have great potential for OSN applications.

Controlling interlayer spacing and organic solvent permeation in laminar graphene oxide membranes modified with crosslinker

Two-dimensional (2D) laminar membranes are attracting much attention in organic solvent nanofiltration owing to the promising permeation and selective performance derived from their 2D ultrathin separation layer. However, owing to easy swelling (enlargement of interlayer spacing), controlling the interlayer spacing in organic solvents and stable solvent permeation are major issues for their application to organic solvent systems. In this study, laminar GO membranes were fabricated on a porous polyketone (PK) support membrane using triethanolamine (TEOA) as crosslinker (GO-TEOA/PK). The interlayer spacing (d) between GO sheets was characterized by X-ray diffraction. The TEOA crosslinker effectively suppressed swelling of the GO laminar structure. For GO-TEOA/PK, the variation in d corresponded well with the affinity between TEOA and each solvent, Ra(TEOA–solvent), as estimated using the Hansen solubility parameters. Furthermore, common linear correlation between the permeance of alcohols and the parameter combining affinity, viscosity, and equivalent molar diameter was clearly observed. Therefore, the affinity between crosslinker and solvent was an important factor in controlling interlayer spacing and solvent permeation in the laminar GO membranes containing crosslinker.

Selective Ion Permeation through Stabilized Metal–Phenolic Grafted Graphene Oxide Membranes

AbstractThe structural stability and high permeability of 2D materials‐based membranes are key research interests for separation membranes. However, the instability of their microstructures due to the aqueous‐induced swelling phenomenon affects their performance. It is highly desirable to explore anti‐swelling approaches able to mitigate this challenge as well as develop 2D lamellar membranes with ion selective capabilities beyond the limits based on size exclusion mechanism. Herein, graphene oxide (GO) laminate membranes covalently anchored and intercalated with metal‐phenolic networks display suppressed swelling durability and resist delamination in aqueous media. The resultant Fe@TA‐GO membrane with confined d‐spacing boasts high water fluxes of up to 15.0 L m−2 h−1 under osmotic pressure (2 m sucrose). Furthermore, the permeation tests reveal that the interaction between the metal ions and the immobilized cation–ligand molecules influences the ion permeances through the functionalized GO membranes conducing to fast ion permeation rates with ion diffusion permselectivity as well as effective selective separation of organic contaminants. These results will help advance the applications of GO membranes for challenging ion separations related to sustainable resource recovery and environmental remediation of organic dye and metal ion contaminated wastewaters.

Graphene-like MOF nanosheets stabilize graphene oxide membranes enabling selective molecular sieving

Thin laminar membranes assembled by 2D nanomaterials evince the potential to achieve rapid and efficient molecular transport due to precisely amendable in-plane pores and interlayer distances. Despite the extensive use of graphene oxide (GO) membranes for water treatment, water-induced instability and the barrier effect remain challenging issues to be addressed. Here, a water-stable, graphene-like MOF nanosheet (Cu-TCPP) was implemented as a framework bridge to stabilize the GO laminates against swelling and redispersion into water. A stable heterostructure was established by the electrostatic interaction between porphyrin and oxygen-containing groups, and metal coordination of the carboxyl groups of GO nanosheets. The presence of ultrathin Cu-TCPP nanosheets promotes the formation of a nano-wrinkled surface with vertical-slit and in-plane pores that dominate the significantly improved water transport. The resultant composite membranes evince a 7-fold-higher water permeance (165.2 L m−2 h−1 bar−1) than that of GO membranes with remarkable solute retention (Congo red: 99.1%). Furthermore, this membrane shows an excellent sieving ability either for RB5/MO solutions or for CR/salt mixtures, while achieving a remarkable antibacterial activity against E. coli. The combination of rigid and flexible nanosheets opens an avenue to construct a water-stable multi-channel frame for the next generation of porous 2D materials for water purification.

Electric field modulated ion-sieving effects of graphene oxide membranes

Precise and selective separation of ions using two-dimensional (2D) laminar membranes is a budding research field with potential applications in water treatment, desalination, sensing, biomimicry and energy storage.

Transition Metal Dichalcogenide (TMD) Membranes with Ultrasmall Nanosheets for Ultrafast Molecule Separation.

Two-dimensional (2D) transition metal dichalcogenide membranes have entered the spotlight for nanofiltration application owing to the novel mass transport properties in nanochannels. However, further improving the water permeability with high molecular separation rate simultaneously is challenging. In this work, to achieve ultrafast molecule separation, MoS2 and WS2 nanosheets with ultrasmall lateral size (<100 nm) are fabricated by sucrose-assisted mechanochemical exfoliation. Ultrasmall nanosheets in the membranes cut down average length of water-transporting paths and create more nanochannels and nanocapillaries for water molecules to pass through membranes. The water flux of these kinds of MoS2 and WS2 membranes are significantly enhanced to 918 and 828 L/m2 h bar, respectively, which is four and two times higher than those of previously reported MoS2 and WS2 membranes with larger lateral size nanosheets. In addition, MoS2 and WS2 membranes display excellent rejection performance for rhodamine B and Evans blue with a high rejection rate (∼99%). This study provides a promising method to improve the performance of 2D laminar membranes for nanofiltration application by using ultrasmall 2D nanosheets.

Toward the Highly Ordered Lamellar Hybrid Membrane for Molecular Sieving by One-Pot Self-Assembly of Hybrid Hyperbranched Polymer

Ordered lamellar hybrid membranes are of great interest, due to their application as functional materials, including molecular sieving, biosensors, optical devices, and drug, as well as gene delive...

Controlled reduction and fabrication of graphene oxide membrane for improved permeance and water purification performance

It has been found that moderately reduced graphene oxide (RGO) membrane which was applicable to the field of nanofiltration had both good hydrophilicity and appropriate layer spacing. However, existing GO reduction technologies are usually toxic, complex and uncontrollable. Therefore, it is necessary to seek a green and controllable method to develop the partially RGO membrane (RGOM) which has outstanding water purification ability. In this work, GO laminar membranes (GOM) were prepared via vacuum filter, and L ( +)-ascorbic acid (LAA) was employed as a reduction agent to prepare the RGOM. Subsequently, SEM, XPS, Raman and XRD tests were conducted to characterize the physical and chemical properties of RGOM. Furthermore, the effect of reduction degree on water purification performance was determined. Owing to the combined effect of D-spacing and sp2 domains with ultralow friction, GOM treated in LAA for 10 min (10-RGOM) exhibited a great water flux of 27.62 L m−2 h−1 bar−1 which was 238% higher than that of GOM and also showed excellent dye rejection. Furthermore, compared with GO, 10-RGOM exhibited better structural stability and superior separation performance in different pH environments.

Layer-by-layer assembled GO-based membranes with high long-standing stability and chemical resistance applied in dye separation and desalination

The Graphene oxide (GO) membranes, as the most studied and accessible two-dimensional (2D) membranes, have performed their expected separation performance, but instability of these delicate membranes still hinders their development. Layer-by-layer (LBL) self-assembly is one smart method for preparing versatile 2D membranes with stable structure by chemical bonds or other forces. Herein, the 2D GO laminar membranes were prepared on the modified Nylon-6 substrates via LBL method by employing positively charged P–GO (guanidine modified GO nanosheets) and negatively charged S–GO (sulfonated GO nanosheets) as assembly flakes. This smart strategy was established on the superiority of LBL method by adjusting the assembly layer number and outermost charge when faced up with the different targeted contaminants. Benefited from the compact structures and intense charge, the LBL membranes can almost remove all the employed dyes (above 98% rejection for ML11 membrane). Furthermore, these membranes also show the high selectivity to water molecular in desalination (93.4% rejection to Na2SO4 and 72.7% rejection to NaCl for ML11 membrane). The membranes can endure the filtration of dye wasterwater and salt solution for above 168 h under cross-flow mode without rejection decline. Also, these versatile LBL membranes reveal high resistance to both chemical corrosion and bacterial attack, which is suitable for the continuous separation even under hostile external environment.

Selective Permeation of Water through Angstrom-Channel Graphene Membranes for Bioethanol Concentration.

Graphene-based laminate membranes have been theoretically predicted to selectively transport ethanol from ethanol-water solution while blocking water. Here, robust angstrom-channel graphene membranes (ACGMs) fabricated by intercalating carbon sheets derived from chitosan into thermally reduced graphene oxide (GO) sheets are reported. ACGMs with robust and continuous slit-shaped pores (an average pore size of 3.9 Å) are investigated for the dehydration of ethanol. Surprisingly, only water permeates through ACGMs in the presence of aqueous ethanol solution. For the water-ethanol mixture containing 90wt% ethanol, water can selectively permeate through ACGMs with a water flux of 63.8±3.2kg m-2 h-1 at 20°C and 389.1±19.4kg m-2 h-1 at 60°C, which are over two orders of magnitude higher than those of conventional pervaporation membranes. This means that ACGMs can effectively operate at room temperature. Moreover, the ethanol can be fast concentrated to high purity (up to 99.9wt%). Therefore, ACGMs are very promising for production of bioethanol with high efficiency, thus improving its process sustainability.

The Role of Nanowrinkles in Mass Transport across Graphene‐Based Membranes

AbstractLaminar 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.

High permeability sub-nanometre sieve composite MoS2 membranes

Two-dimensional membranes have gained enormous interest due to their potential to deliver precision filtration of species with performance that can challenge current desalination membrane platforms. Molybdenum disulfide (MoS2) laminar membranes have recently demonstrated superior stability in aqueous environment to their extensively-studied analogs graphene-based membranes; however, challenges such as low ion rejection for high salinity water, low water flux, and low stability over time delay their potential adoption as a viable technology. Here, we report composite laminate multilayer MoS2 membranes with stacked heterodimensional one- to two-layer-thick porous nanosheets and nanodisks. These membranes have a multimodal porous network structure with tunable surface charge, pore size, and interlayer spacing. In forward osmosis, our membranes reject more than 99% of salts at high salinities and, in reverse osmosis, small-molecule organic dyes and salts are efficiently filtered. Finally, our membranes stably operate for over a month, implying their potential for use in commercial water purification applications.

The influence of cations intercalated in graphene oxide membranes in tuning H2/CO2 separation performance

Graphene oxide (GO) laminate membranes of controlled interlayer spacing were synthesized for the investigation in H2/CO2 separation. The interlayer distance of GO flakes was tuned by crosslinking and intercalation of La3+ or Co2+ cations between GO layers. Investigation via field-emission scanning electron microscope showed that a continuous selective layer was present in the GO-La3+, GO-Co2+ and GO membranes. Gas permeation results revealed that the GO-La3+ membrane had better H2 permeability and H2/CO2 selectivity than the other membranes, due to an increase in d-spacing between the GO layers and restricted defect formation in the GO laminate membranes. In addition, the H2/CO2 separation performance of GO-La3+ membrane was found to be close to the upper bound limit of conventional polymer membranes established in 2008.

Minimizing Non-selective Nanowrinkles of Reduced Graphene Oxide Laminar Membranes for Enhanced NaCl Rejection

Reduced graphene oxide membranes (rGOMs) have been intensively studied for desalination and molecular sieving applications, benefiting from their selective and stable two-dimensional (2D) nanochann...

Two-Dimensional Membranes: New Paradigms for High-Performance Separation Membranes.

Two-dimensional (2D) materials with atomic thicknesses have aroused great interest as promising building blocks for the preparation of ultrathin 2D membranes. These 2D membranes can exhibit unprecedentedly high separation permeance owing to their ultrasmall membrane thicknesses and superior selectivity because of their size-selective nanopores and/or nanochannels. Until now, a large number of 2D membranes with good performance have been reported, highlighting the potential of these novel membranes for efficient liquid and gas separations. Summarized in this review are the latest advances in 2D membranes, with a special focus on industrially attractive separation processes, fabrication methods of laminar membranes, choices of membrane materials, designs of membrane structures, and unique membrane transport properties. Opportunities and challenges of 2D membranes for commercial applications are also briefly discussed.

Ultrathin Membranes: A New Opportunity for Ultrafast and Efficient Separation

AbstractDeveloping advanced membranes with both high permeance and selectivity to enable ultrafast and efficient separation is a persistent pursuit by materials scientists. In recent years, diverse ultrathin membranes with nanometer‐scale thickness and unique membrane structures have been developed. These materials show ultrahigh permeance and excellent selectivity in water desalination, dye rejection, oil–water purification, and gas separation applications. Herein, current state‐of‐the‐art ultrathin membranes are introduced, including polyamide membranes, diamond‐like carbon membranes, single‐walled carbon nanotube network membranes, metal hydroxide nanostrand network membranes, protein membranes, and graphene laminar membranes and their derivatives. The designs, fabrication techniques, and performance advantages of these ultrathin membranes are discussed. A summary of the remaining challenges and potential future directions are also presented.