Showing papers on "Membrane published in 2021"

Graphene oxide membranes with stable porous structure for ultrafast water transport.

Abstract: The robustness of carbon nanomaterials and their potential for ultrahigh permeability has drawn substantial interest for separation processes. However, graphene oxide membranes (GOms) have demonstrated limited viability due to instabilities in their microstructure that lead to failure under cross-flow conditions and applied hydraulic pressure. Here we present a highly stable and ultrapermeable zeolitic imidazolate framework-8 (ZIF-8)-nanocrystal-hybridized GOm that is prepared by ice templating and subsequent in situ crystallization of ZIF-8 at the nanosheet edges. The selective growth of ZIF-8 in the microporous defects enlarges the interlayer spacings while also imparting mechanical integrity to the laminate framework, thus producing a stable microstructure capable of maintaining a water permeability of 60 l m−2 h−1 bar−1 (30-fold higher than GOm) for 180 h. Furthermore, the mitigation of microporous defects via ZIF-8 growth increased the permselectivity of methyl blue molecules sixfold. Low-field nuclear magnetic resonance was employed to characterize the porous structure of our membranes and confirm the tailored growth of ZIF-8. Our technique for tuning the membrane microstructure opens opportunities for developing next-generation nanofiltration membranes. Highly stable and ultrapermeable membranes can be fabricated by the hybridization of zeolitic imidazolate framework-8 and graphene oxide.

Inverse desert beetle-like ZIF-8/PAN composite nanofibrous membrane for highly efficient separation of oil-in-water emulsions

Abstract: Purification of highly emulsified oily wastewater is of significance but challenging due to the critical limitations of low efficiency and serious membrane blocking. Herein, inspired by the desert beetle's capability of water-collection in air, we first constructed an inverse desert beetle-like membrane to achieve oil capture in water, thus improving the separation performances of the surfactant-stabilized oil-in-water emulsion. The as-prepared nanofibrous membrane consists of hydrophobic/oleophilic ZIF-8 bumps and underlying underwater superoleophobic polyacrylonitrile (PAN), and possesses a similar structure to desert beetles but with opposite wettability. In the process of emulsion demulsification, besides the sieving effect of the underlying traditional underwater superoleophobic PAN membrane, the bumpy oleophilic ZIF-8 particles of the composite membrane can capture oil, thus strengthening the demulsification ability of the membrane. Furthermore, the separation efficiency of the inverse desert beetle-like membrane is up to 99.92% for surfactant-stabilized oil-in-water emulsion, which is superior to that of traditional single underwater superoleophobic PAN membranes lacking the hydrophobic bump structure. Moreover, for light oil-in-water emulsion, the permeation flux also increases because the captured tiny oil droplets can aggregate subsequently and grow large enough to detach from the underlying surface which greatly reduces the incidence of filter cake formation and congestion. This inverse desert beetle-like membrane opens up new avenues for designing advanced membranes in the oil/water emulsion separation field.

Nanoscale control of internal inhomogeneity enhances water transport in desalination membranes

Abstract: Biological membranes can achieve remarkably high permeabilities, while maintaining ideal selectivities, by relying on well-defined internal nanoscale structures in the form of membrane proteins. Here, we apply such design strategies to desalination membranes. A series of polyamide desalination membranes—which were synthesized in an industrial-scale manufacturing line and varied in processing conditions but retained similar chemical compositions—show increasing water permeability and active layer thickness with constant sodium chloride selectivity. Transmission electron microscopy measurements enabled us to determine nanoscale three-dimensional polyamide density maps and predict water permeability with zero adjustable parameters. Density fluctuations are detrimental to water transport, which makes systematic control over nanoscale polyamide inhomogeneity a key route to maximizing water permeability without sacrificing salt selectivity in desalination membranes.

Molecularly soldered covalent organic frameworks for ultrafast precision sieving

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

MOF-in-COF molecular sieving membrane for selective hydrogen separation.

Abstract: Covalent organic frameworks (COFs) are promising materials for advanced molecular-separation membranes, but their wide nanometer-sized pores prevent selective gas separation through molecular sieving. Herein, we propose a MOF-in-COF concept for the confined growth of metal-organic framework (MOFs) inside a supported COF layer to prepare MOF-in-COF membranes. These membranes feature a unique MOF-in-COF micro/nanopore network, presumably due to the formation of MOFs as a pearl string-like chain of unit cells in the 1D channel of 2D COFs. The MOF-in-COF membranes exhibit an excellent hydrogen permeance (>3000 GPU) together with a significant enhancement of separation selectivity of hydrogen over other gases. The superior separation performance for H2/CO2 and H2/CH4 surpasses the Robeson upper bounds, benefiting from the synergy combining precise size sieving and fast molecular transport through the MOF-in-COF channels. The synthesis of different combinations of MOFs and COFs in robust MOF-in-COF membranes demonstrates the versatility of our design strategy.

Microporous framework membranes for precise molecule/ion separations.

Abstract: Microporous framework membranes such as metal-organic framework (MOF) membranes and covalent organic framework (COF) membranes are constructed by the controlled growth of small building blocks with large porosity and permanent well-defined micropore structures, which can overcome the ubiquitous tradeoff between membrane permeability and selectivity; they hold great promise for the enormous challenging separations in energy and environment fields. Therefore, microporous framework membranes are endowed with great expectations as next-generation membranes, and have evolved into a booming research field. Numerous novel membrane materials, versatile manipulation strategies of membrane structures, and fascinating applications have erupted in the last five years. First, this review summarizes and categorizes the microporous framework membranes with pore sizes lower than 2 nm based on their chemistry: inorganic microporous framework membranes, organic-inorganic microporous framework membranes, and organic microporous framework membranes, where the chemistry, fabrications, and differences among these membranes have been highlighted. Special attention is paid to the membrane structures and their corresponding modifications, including pore architecture, intercrystalline grain boundary, as well as their diverse control strategies. Then, the separation mechanisms of membranes are covered, such as diffusion-selectivity separation, adsorption-selectivity separation, and synergetic adsorption-diffusion-selectivity separation. Meanwhile, intricate membrane design to realize synergistic separation and some emerging mechanisms are highlighted. Finally, the applications of microporous framework membranes for precise gas separation, liquid molecule separation, and ion sieving are summarized. The remaining challenges and future perspectives in this field are discussed. This timely review may provide genuine guidance on the manipulation of membrane structures and inspire creative designs of novel membranes, promoting the sustainable development and steadily increasing prosperity of this field.

Organic molecular sieve membranes for chemical separations.

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

Gas diffusion electrodes and membranes for CO2 reduction electrolysers

Abstract: The CO2 reduction reaction (CO2RR) is a potential means of using renewable electricity to synthesize commodity chemicals and fuels. The CO2RR can be performed at industrially relevant product formation rates in an electrolyser, which must simultaneously manage the transport of electrons, water, CO2 and protons at a cathode. Gas diffusion electrodes (GDEs) and polymer electrolyte membranes are used to mediate these critical processes. Consequently, the design and development of GDEs and membranes tailored for the CO2RR is critical. In this Review, we discuss how the properties of GDEs and polymer electrolyte membranes affect CO2RR electrolysis. The CO2 reduction reaction can be used to produce carbon-neutral chemicals using renewable electricity. This Review presents material design strategies for controlling the transport of products and reactants in electrochemical reactors that convert CO2 emissions into chemicals and fuels.

Constructing Scalable Superhydrophobic Membranes for Ultrafast Water-Oil Separation.

Abstract: Superhydrophobic membranes are desirable for separation of water-in-oil emulsions, membrane distillation, and membrane condensation. However, the lack of large-scale manufacture methods of superhyd...

Hydrophilicity gradient in covalent organic frameworks for membrane distillation.

Abstract: Desalination can help to alleviate the fresh-water crisis facing the world. Thermally driven membrane distillation is a promising way to purify water from a variety of saline and polluted sources by utilizing low-grade heat. However, membrane distillation membranes suffer from limited permeance and wetting owing to the lack of precise structural control. Here, we report a strategy to fabricate membrane distillation membranes composed of vertically aligned channels with a hydrophilicity gradient by engineering defects in covalent organic framework films by the removal of imine bonds. Such functional variation in individual channels enables a selective water transport pathway and a precise liquid–vapour phase change interface. In addition to having anti-fouling and anti-wetting capability, the covalent organic framework membrane on a supporting layer shows a flux of 600 l m–2 h–1 with 85 °C feed at 16 kPa absolute pressure, which is nearly triple that of the state-of-the-art membrane distillation membrane for desalination. Our results may promote the development of gradient membranes for molecular sieving. Membrane distillation can use low-grade heat for salt water desalination, but the materials used can often suffer from limited permeance. Here, a strategy is proposed to construct a pore surface and size functionality gradient in a covalent organic framework, enabling a flux of 600 l m–2 h–1 with NaCl rejection of 99.99%.

Poly(fluorenyl aryl piperidinium) membranes and ionomers for anion exchange membrane fuel cells

Abstract: Low-cost anion exchange membrane fuel cells have been investigated as a promising alternative to proton exchange membrane fuel cells for the last decade. The major barriers to the viability of anion exchange membrane fuel cells are their unsatisfactory key components—anion exchange ionomers and membranes. Here, we present a series of durable poly(fluorenyl aryl piperidinium) ionomers and membranes where the membranes possess high OH− conductivity of 208 mS cm−1 at 80 °C, low H2 permeability, excellent mechanical properties (84.5 MPa TS), and 2000 h ex-situ durability in 1 M NaOH at 80 °C, while the ionomers have high water vapor permeability and low phenyl adsorption. Based on our rational design of poly(fluorenyl aryl piperidinium) membranes and ionomers, we demonstrate alkaline fuel cell performances of 2.34 W cm−2 in H2-O2 and 1.25 W cm−2 in H2-air (CO2-free) at 80 °C. The present cells can be operated stably under a 0.2 A cm−2 current density for ~200 h. Developing high-performance anion exchange membranes and ionomers is crucial for low-cost alkaline fuel cells. Here, the authors explore rigid and high ion conductive poly(fluorenyl aryl piperidinium) copolymers, extending their applications to anion exchange membrane fuel cells.

Alkaline membrane fuel cells: anion exchange membranes and fuels

Abstract: Alkaline anion exchange membrane fuel cells (AAEMFC) are attracting ever-increasing attention, as they are promising electrochemical devices for energy production, presenting a viable opponent to the more researched proton exchange membrane fuel cells (PEMFCs). Consequently, great progress has been made in the area of designing and developing synthetic or naturally-derived anion exchange membrane (AEM), the properties of which have been discussed in this review, i.e. ionic conductivity, ion exchange capacity, fuel crossover, durability, stability and cell performance. Major groups of natural polymers (e.g. chitosan (CS)) and nanocellulose, together with modification/crosslinking routes, have been mentioned as more ecologically and economically viable raw materials for AEM processing compared to synthetic ones. Performances of fuel cells are also discussed, with different fuels used as anode feeds. Although the AEMFC technology is promising, the longevity challenges remain, originating from the still-limited long-term stability of hydroxide-conducting ionomers, particularly when operating at higher cell temperatures.

Metal-Organic Framework Membranes Encapsulating Gold Nanoparticles for Direct Plasmonic Photocatalytic Nitrogen Fixation

Abstract: Photocatalytic nitrogen fixation reaction can harvest the solar energy to convert the abundant but inert N2 into NH3. Here, utilizing metal-organic framework (MOF) membranes as the ideal assembly of nanoreactors to disperse and confine gold nanoparticles (AuNPs), we realize the direct plasmonic photocatalytic nitrogen fixation under ambient conditions. Upon visible irradiation, the hot electrons generated on the AuNPs can be directly injected into the N2 molecules adsorbed on Au surfaces. Such N2 molecules can be additionally activated by the strong but evanescently localized surface plasmon resonance field, resulting in a supralinear intensity dependence of the ammonia evolution rate with much higher apparent quantum efficiency and lower apparent activation energy under stronger irradiation. Moreover, the gas-permeable Au@MOF membranes, consisting of numerous interconnected nanoreactors, can ensure the dispersity and stability of AuNPs, further facilitate the mass transfer of N2 molecules and (hydrated) protons, and boost the plasmonic photocatalytic reactions at the designed gas-membrane-solution interface. As a result, an ammonia evolution rate of 18.9 mmol gAu-1 h-1 was achieved under visible light (>400 nm, 100 mW cm-2) with an apparent quantum efficiency of 1.54% at 520 nm.

Highly selective and high-performance osmotic power generators in subnanochannel membranes enabled by metal-organic frameworks

Abstract: The electric organs of electric eels are able to convert ionic gradients into high-efficiency electricity because their electrocytes contain numerous “subnanoscale” protein ion channels that can achieve highly selective and ultrafast ion transport. Despite increasing awareness of blue energy production through nanochannel membranes, achieving high-performance energy output remains considerably unexplored. Here, we report on a heterogeneous subnanochannel membrane, consisting of a continuous UiO-66-NH2 metal-organic framework (MOF) and a highly ordered alumina nanochannel membrane. In the positively charged membrane, the angstrom-scale windows function as ionic filters for screening anions with different hydrated sizes. Driven by osmosis, the subnanochannel membrane can produce an exceptionally high Br−/NO3− selectivity of ~1240, hence yielding an unprecedented power of up to 26.8 W/m2 under a 100-fold KBr gradient. Achieving ultrahigh selective and ultrafast osmotic transport in ion channel–mimetic MOF-based membranes opens previously unexplored avenues toward advanced separation technologies and energy-harvesting devices.

Ion-capture electrodialysis using multifunctional adsorptive membranes.

Abstract: Technologies that can efficiently purify nontraditional water sources are needed to meet rising global demand for clean water. Water treatment plants typically require a series of costly separation units to achieve desalination and the removal of toxic trace contaminants such as heavy metals and boron. We report a series of robust, selective, and tunable adsorptive membranes that feature porous aromatic framework nanoparticles embedded within ion exchange polymers and demonstrate their use in an efficient, one-step separation strategy termed ion-capture electrodialysis. This process uses electrodialysis configurations with adsorptive membranes to simultaneously desalinate complex water sources and capture diverse target solutes with negligible capture of competing ions. Our methods are applicable to the development of efficient and selective multifunctional separations that use adsorptive membranes.