Robust ultrathin nanoporous MOF membrane with intra-crystalline defects for fast water transport

Rational design of high-performance stable metal–organic framework (MOF) membranes is challenging, especially for the sustainable treatment of hypersaline waters to address critical global environmental issues. Herein, a molecular-level intra-crystalline defect strategy combined with a selective layer thinning protocol is proposed to fabricate robust ultrathin missing-linker UiO-66 (ML-UiO-66) membrane to enable fast water permeation. Besides almost complete salt rejection, high and stable water flux is achieved even under long-term pervaporation operation in hash environments, which effectively addresses challenging stability issues. Then, detailed structural characterizations are employed to identify the type, chemical functionality, and density of intra-crystalline missing-linker defects. Moreover, molecular dynamics simulations shed light on the positive atomistic role of these defects, which are responsible for substantially enhancing structural hydrophilicity and enlarging pore window, consequently allowing ultra-fast water transport via a lower-energy-barrier pathway across three-dimensional sub-nanochannels during pervaporation. Unlike common unfavorable defect effects, the present positive intra-crystalline defect engineering concept at the molecular level is expected to pave a promising way toward not only rational design of next-generation MOF membranes with enhanced permeation performance, but additional water treatment applications.

The development of highly water-permeable membranes is key for the treatment of high salinity waters. Here the authors enhance the water permeability of a metal-organic framework nanoporous membrane via an intra-crystalline defect engineering strategy.

Hetero-lattice intergrown and robust MOF membranes for polyol upgrading

Metal-organic framework membranes are frequently used in gas separations, but rare in pervaporation for liquid chemical upgrading, especially for separating water from polyols, due to lack of highly compact and robust micro-architecture. Here, we report hetero-lattice intergrown membranes in which amino-MIL-101 (Cr) particles embedded into the micro-gaps of MIL-53 (Al) rod arrays after secondary growth. By means of high-resolution TEM and two-dimensional topologic simulation, the connection between these two distinct MOF lattices at molecular-level and their crystallographic geometry harmony is identified, which leads to a close-knit structure at crystal boundaries of membranes. Typically, the membrane shows a separation factor as high as 13,000 for 90/10 ethanediol/water solution in pervaporation, yields polymer-grade ethanediol, and saves ca. 32% of energy consumption vs. vacuum distillation. It has a highly robust micro-architecture, with great tolerance to high pressure, durability against ultrasonic therapy and long-term separation stability over 600 h.

Construction of Stable Metal-Organic Framework Platforms Embedding N-Heterocyclic Carbene Metal Complexes for Selective Catalysis

We report a bottom-up approach to immobilize catalysts into MOFs, including copper halides and gold chloride in a predictable manner. Interestingly, the structures of MOFs bearing NHC metal complexes maintained a similar 4-fold interpenetrated cube. They exhibited exceptionally high porosity despite the interpenetrated structure and showed good stability in various solvents. Moreover, these MOFs possess high size activity depending on the size of the substrates in various reactions, compared to homogeneous catalysis. Also, the high catalytic activity of MOFs can be preserved 4 times without significant loss of crystallinity. Incorporation of the various metal complexes into MOFs allows for the preparation of functional MOFs for practical applications.

Recent advances in metal-organic framework membranes for water treatment: A review

Among many separation membranes reported to date, the favorable polymer affinity and unique physio-chemical performances of metal-organic frameworks (MOFs) including ultra-high surface area, regular and highly controlled porosity have drawn widespread attention in industrial and academic communities. In this comprehensive review, the developmental timeline of MOF containing membranes for water treatment were clarified. The removal efficiencies, elimination mechanisms, as well as possible influencing factors of various MOF containing membranes that applied to water treatment were systematically summarized. The excellent removal performances of MOF containing membranes for various pollutants were determined by the size-exclusion, π-π stacking interaction, electrostatic interaction, hydrogen bonding and so on. Since the progress of engineered MOF containing membranes for practical wastewater treatment applications lags, we further analyzed the potential environmental application of MOF containing membranes from four aspects (stability of MOFs, antifouling performance of membranes, compatibility between MOF fillers and polymer matrix, dispersity of MOF nanoparticles in matrix), hoping to provide some meaningful insights.

A Zn(II)-Based Sql Type 2D Coordination Polymer as a Highly Sensitive and Selective Turn-On Fluorescent Probe for Al3

A luminescent coordination polymer with the overall formula {[Zn(tr2btd)(bpdc)]∙DMF}n (where tr2btd = 4,7-di(1H-1,2,4-triazol-1-yl)-2,1,3-benzothiadiazole; bpdc = 4,4'-biphenyldicarboxylate) was synthesized and characterized by single-crystal and powder X-ray diffraction, thermogravimetric, infrared spectroscopy, and elemental analyses. Luminescent properties of the obtained compound were studied in detail both in the solid state and as a suspension in N,N-dimethylacetamide (DMA). It was found that {[Zn(tr2btd)(bpdc)]∙DMF}n exhibits bright turquoise luminescence with excellent quantum efficiency and demonstrates turn-on fluorescence enhancement effect upon soaking in DMA Al3+ solution. Fluorescence titration experiments were carried out and the detection limit for Al3+ ions was calculated to be 120 nM, which is among the lowest reported values for similar materials. Moreover, compound demonstrated excellent selectivity and reusability, and the mechanism of the response is discussed. These results indicate that {[Zn(tr2btd)(bpdc)]∙DMF}n is a promising probe for sensitive fluorescent Al3+ detection.

Membrane bioreactors for hospital wastewater treatment: recent advancements in membranes and processes

Discharged hospital wastewater contains various pathogenic microorganisms, antibiotic groups, toxic organic compounds, radioactive elements, and ionic pollutants. These contaminants harm the environment and human health causing the spread of disease. Thus, effective treatment of hospital wastewater is an urgent task for sustainable development. Membranes, with controllable porous and nonporous structures, have been rapidly developed for molecular separations. In particular, membrane bioreactor (MBR) technology demonstrated high removal efficiency toward organic compounds and low waste sludge production. To further enhance the separation efficiency and achieve material recovery from hospital waste streams, novel concepts of MBRs and their applications are rapidly evolved through hybridizing novel membranes (non hydrophilic ultrafiltration/microfiltration) into the MBR units (hybrid MBRs) or the MBR as a pretreatment step and integrating other membrane processes as subsequent secondary purification step (integrated MBR-membrane systems). However, there is a lack of reviews on the latest advancement in MBR technologies for hospital wastewater treatment, and analysis on its major challenges and future trends. This review started with an overview of main pollutants in common hospital waste-water, followed by an understanding on the key performance indicators/criteria in MBR membranes (i.e., solute selectivity) and processes (e.g., fouling). Then, an in-depth analysis was provided into the recent development of hybrid MBR and integrated MBR-membrane system concepts, and applications correlated with wastewater sources, with a particular focus on hospital wastewaters. It is anticipated that this review will shed light on the knowledge gaps in the field, highlighting the potential contribution of hybrid MBRs and integrated MBR-membrane systems toward global epidemic prevention.

Nanofiltration for drinking water treatment: a review

In recent decades, nanofiltration (NF) is considered as a promising separation technique to produce drinking water from different types of water source. In this paper, we comprehensively reviewed the progress of NF-based drinking water treatment, through summarizing the development of materials/fabrication and applications of NF membranes in various scenarios including surface water treatment, groundwater treatment, water reuse, brackish water treatment, and point of use applications. We not only summarized the removal of target major pollutants (e.g., hardness, pathogen, and natural organic matter), but also paid attention to the removal of micropollutants of major concern (e.g., disinfection byproducts, per- and polyfluoroalkyl substances, and arsenic). We highlighted that, for different applications, fit-for-purpose design is needed to improve the separation capability for target compounds of NF membranes in addition to their removal of salts. Outlook and perspectives on membrane fouling control, chlorine resistance, integrity, and selectivity are also discussed to provide potential insights for future development of high-efficiency NF membranes for stable and reliable drinking water treatment.

2D MOFs-based Materials for the Application of Water Pollutants Removing: Fundamentals and Prospects

Water quality can have serious impacts on human health. One crucial issue of water pollution seriously affects our safety due to the continually emerging of discovered anthropogenic pollutants. The water treatment technologies are persistent improvement to adapt such new contaminants, which accelerates the evolution of materials science to explore solving the problems. Metal-organic Frameworks (MOFs) as the significant porous and multi-dimensional networks has been concerned for toxic pollutant elimination, especially probed the applications of outstanding layered 2D skeletons MOFs-based materials. The emphases of this review highlight the 2D MOFs-based materials used in water remediation and treatment strategies including adsorption and catalysis methods. Further, the prospects and challenges of 2D MOFs-based materials for water treatments applications would be surveyed meticulously for the future research and development.

New Ln-MOFs based on mixed organic ligands: synthesis, structure and efficient luminescence sensing of the Hg2+ ions in aqueous solutions

In view of Hg²⁺ ion sensing by luminescence, a series of new, phenanthroline-decorated 3D lanthanide metal organic frameworks (Ln-MOFs) valorising an original combination of four different lanthanides and two organic ligands, i.e. thiobis(4-methylene-benzoic acid) (H₂tmba) and 1,10-phenanthroline (phen), have been successfully synthesized, namely {[Ln₄(tmba)₆(phen)₄]·m(H₂O)(phen)}_n [Ln = Ce, m = 3 (1); Pr, m = 1 (2); Eu, m = 3 (3); and Tb, m = 3 (4)]. Compounds 1-4 were characterised by single-crystal X-ray diffraction, elemental and thermogravimetric analyses, and powder X-ray diffraction. The luminescence properties of complexes 3 and 4 were thoroughly investigated. It is herein proved that compound 3 sensitively and selectively acts as an excellent luminescent probe for the detection of Hg²⁺ ions in waters, with a detection limit of 1.00 μM. As additional assets, 3 displays superb stability over a wide pH range (3-12) of the aqueous media, as well as convenient recycling after completion of the detection experiments. The rationale for the observed luminescence quenching effect of mercury might be a strong interaction arising between Hg²⁺ ions and the carboxylate oxygen atoms of the tmba^2- ligand. The results open new perspectives for applications in environmental remediation.

Eliminating the Detrimental Effect of Secondary Doping on PEDOT : PSS Hole Transporting Material Performance

Secondary doping has a long history of use in conductivity enhancement in poly(3,4-ethylenedioxythiophene) : poly(styrene sulfonate) (PEDOT : PSS). However, very little research has addressed its detrimental effect on application performance of PEDOT : PSS in organic solar cells. Herein, it was shown that the uneven drying of secondary dopant-water mixture results in a nonuniform/continuous film structure, causing severe damage to the device efficiencies (dropping about 8 and 23 % for poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b']dithiophene))-alt-(5,5-(1',3'-di-2-thienyl-5',7'-bis(2-ethylhexyl)benzo[1',2'-c:4',5'-c']dithiophene-4,8-dione))] (PBDB-T) : 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2',3'-d']-s-indaceno[1,2-b:5,6-b']dithiophene (ITIC) and poly[(2,6-(4,8-bis(5-(2-ethylhexyl)-4-fluorothiophen-2-yl)benzo[1,2-b:4,5-b']dithio-phene))-co-(1,3-di(5-thiophene-2-yl)-5,7-bis(2-ethylhexyl)-benzo[1,2-c:4,5-c']dithiophene-4,8-dione))](PM6) : (3,9-bis(1-oxo-2-methylene-3-(1,1-dicyanomethylene)-5,6-difluoroindanone)-5,5,11,11-tetrakis(4-n-hexylphenyl)-dithieno[2,3d:2',3'd']-s-indaceno[1,2b:5,6b']dithiophene (IT-4F) cells, respectively) and thermal stabilities. Moreover, a simple yet robust dialysis treatment was proposed to solve the issue of noncontinuity and retain the secondary doping's advantages of quinoid structure simultaneously, thus demonstrating a significant enhancement in device performance. This study will be of great importance to the future exploration of the next generation of post-treatment strategy.

Fabrication of Ultrathin Membranes Using 2D-MOF Nanosheets for Tunable Gas Separation

Two-dimensional (2D) metal-organic frameworks (MOF) nanosheets have emerged as novel membrane materials for gas separation. However, the development of ultrathin MOF membranes with tunable separation performances is still a challenge. Herein, we developed a facile GO-assisted restacking method to fabricate defect-free membranes with monolayer Zr-BTB nanosheets. Obtained ultrathin membranes ranging from 130 nm to 320 nm show tunable separation performances and exceed the 2008 Robeson upper bound by changing the amount of nanolayers in vertical stacking direction. Furthermore, a heating filtration method was used to change the restacking process of nanosheets in the horizontal direction. As a result, H₂ /CO₂ selectivity can be enhanced by two times with the same membrane thickness (130 nm) and H₂ permeance is almost maintained to be 7.0×10^-7  mol m^-2  s^-1  pa^-1 . This method may provide a possible way to efficiently tune the gas separation performances of MOF membranes.

In Situ Assembly of Polyamide/Fe(BTC) Nanocomposite Reverse Osmosis Membrane Assisted by Fe3+-Polyphenolic Complex for Desalination

The metal-organic framework (MOF)-based polyamide (PA) membranes applied for desalination with high permeability and selectivity are attracting more and more attention. However, the design and fabrication of high-quality and stable MOF-based PA nanocomposite reverse osmosis (RO) membrane still remain a big challenge. Herein, Fe³⁺-polyphenolic complex coating via interfacial coordination was first explored as an interlayer of an in situ assembled stable and high-quality Fe(BTC)-based PA nanocomposite RO membranes for desalination. Although depositing the Fe³⁺-polyphenolic complex on the polymer support, sufficient heterogeneous nucleation sites for the in situ synthesizing Fe(BTC) are provided. Using this strategy, we can not only facilely prepare continuous MOF-based PA nanocomposite RO membranes, ignoring the complicated and time-consuming co-blending process and the MOF-particle aggregation, but also restrict the formation of PA matrix inside the pores of the support membrane and increase the rigidity of the polyamide chain. The method also gives a proper level of generality for the fabrication of versatile stable MOF-based PA RO membranes on various supports. The prepared PA/Fe(BTC) composite membrane exhibited excellent separation performance with a large permeate flux of 2.93 L m^-2 h^-1 bar^-1 and a high NaCl rejection of 96.8%.

Facile fabrication of zeolitic imidazolate framework hollow fibre membranes via a novel scalable continuous fluid circulation process

A novel continuous fluid circulation system was designed and employed for the impregnation seeding and fabrication of zeolitic imidazolate framework (ZIF) crystals on the internal surface of polymeric hollow fibre membranes. Application of impregnation seeding has been proven effective to decrease crystal size, consequently increasing surface roughness and wettability of the membrane. Evaluation of the as-synthesised membrane demonstrated excellent separation efficiencies (>99%) of surfactant stabilised oil-in-water emulsions. Owing to the simple impregnation strategy assisted by the continuous fluid circulation, the active ZIF layer formed was visibly thinner and denser than typical seeding techniques, hence a high pure water flux of >1150 L m^-2 h^-1 bar^-1 was achieved. The membranes were highly selective and ultra-permeable to water, however, almost impermeable to oils in a water environment, e.g., n-hexane, n-heptane, chloroform and dichloromethane, as well as their emulsion mixtures, with a separation efficiency higher than 99%. Besides, this new continuous fluid circulation method was also found promising for the synthesis of other types of ZIF on hollow fibre membranes.

Suppressing Defect Formation in Metal-Organic Framework Membranes via Plasma-Assisted Synthesis for Gas Separations

Metal-organic frameworks (MOFs) are considered as promising materials for membrane gas separations. Structural defects within a pure MOF membrane can considerably reduce its selectivity and possibly result in a nonselective separation. This work proposes a solution-phase synthesis with dielectric barrier discharge (DBD) plasma to suppress the formation of defects in the pure MOF membrane of CPO-8-BPY. Through comprehensive solid-state characterization with XRD, SEM, XPS, solid-state NMR, and XAFS, DBD plasma is demonstrated to facilitate deprotonation in the H₂aip linker, which leads to a smaller and more uniform particle size of CPO-8-BPY. The narrow grain size distribution effectively reduces the pinhole-type defects in the pure CPO-8-BPY membrane and endows it with good ideal selectivity for H₂/CH₄ (α_H2/CH4 = 28.2) and N₂/CH₄ (α_N2/CH4 = 5.4). The selectivity for H₂/CH₄ of this membrane from a mixed-gas permeation test is found to be 15.4. Molecular simulations are also performed to gain insights into the gas transport properties of this MOF. The results suggest that ligand rotation plays an important role in CPO-8-BPY when being applied to the membrane separation of N₂/CH₄.

Superfast Water Transport Zwitterionic Polymeric Nanofluidic Membrane Reinforced by Metal-Organic Frameworks

Nanofluidics derived from low-dimensional nanosheets and protein nanochannels are crucial for advanced catalysis, sensing, and separation. However, polymer nanofluidics is halted by complicated preparation and miniaturized sizes. This work reports the bottom-up synthesis of modular nanofluidics by confined growth of ultrathin metal-organic frameworks (MOFs) in a polymer membrane consisting of zwitterionic dopamine nanoparticles (ZNPs). The confined growth of the MOFs on the ZNPs reduces the chain entanglement between the ZNPs, leading to stiff interfacial channels enhancing the nanofluidic transport of water molecules through the membrane. As such, the water permeability and solute selectivity of MOF@ZNPM are one magnitude improved, leading to a record-high performance among all polymer nanofiltration membranes. Both the experimental work and the molecular dynamics simulations confirm that the water transport is shifted from high-friction-resistance conventional viscous flow to ultrafast nanofluidic flow as a result of rigid and continuous nanochannels in MOF@ZNPM.

Thin-Film Composite Membrane Prepared by Interfacial Polymerization on the Integrated ZIF-L Nanosheets Interface for Pervaporation Dehydration

Thin-film composite (TFC) membranes are attracting wide attention because their ultrathin selective layer usually corresponds to the higher membrane flux for pervaporation. However, the direct preparation of the TFC membranes on ceramic substrates confronted with the great difficulties because the larger pores on ceramic substrate surfaces are detrimental to the formation of an intact polyamide (PA) selective layer produced by interfacial polymerization (IP) reaction. Here, the integrated ZIF-L nanosheets were proposed to be used as an assistance interlayer for the first time to eliminate the existence of the pores of the ceramic support, and provides a better basis for the formation of an intact PA selective layer by IP reaction between TMC and ethylenediamine (EDA). The experimental data obtained in pervaporation (PV) show that the increased flux from 1.1 to 2.9 kg/m²h corresponds to the decreased separation factor from 396 to 110 when the feed concentration of ethanol decreases from 95 wt % to 80 wt % at 50 °C. In addition, the membrane flux increases from 0.8 to 2.5 kg/m²h with a change of the separation factor from 683 to 111 when the operational temperature varies from 30 to 60 °C. These results demonstrate the great potential of the fabricated TFC membranes in practical application for PV dehydration of organic solutions.

Recent advances in simulating gas permeation through MOF membranes

In the last two decades, metal organic frameworks (MOFs) have gained increasing attention in membrane-based gas separations due to their tunable structural properties. Computational methods play a critical role in providing molecular-level information about the membrane properties and identifying the most promising MOF membranes for various gas separations. In this review, we discuss the current state-of-the-art in molecular modeling methods to simulate gas permeation through MOF membranes and review the recent advancements. We finally address current opportunities and challenges of simulating gas permeation through MOF membranes to guide the development of high-performance MOF membranes in the future.

Preparation and Desalination Performance of PA/UiO-66/PES Composite Membranes

UiO-66 nanoparticles are considered highly potential fillers for the application in desalination membranes. In this study, UiO-66 nanoparticles were anchored to PES membrane substrates, which were subsequently subjected to the interfacial polymerization reaction to coat a layer of polyamide (PA) on their surface. For comparison, a blank membrane incorporating no UiO-66 and a reference membrane incorporating ZrO2 (instead of UiO-66) were prepared. All prepared membranes were tested for their desalination performance. The membranes containing UiO-66 were found to outperform the blank and the reference counterparts. The reason for this outperformance is possibly attributed to the hydrophilicity of UiO-66 nanoparticles and the presence of nanochannels in their structure.

Emerging graphitic carbon nitride-based membranes for water purification

Membrane separation is a promising technology that can effectively remove various existing contaminants from water with low energy consumption and small carbon footprint. The critical issue of membrane technology development is to obtain a low-cost, stable, tunable and multifunctional material for membrane fabrication. Graphitic carbon nitride (g-C₃N₄) has emerged as a promising membrane material, owing to the unique structure characteristics and outstanding catalytic activity. This review paper outlined the advanced material strategies used to regulate the molecule structure of g-C₃N₄ for membrane separation. The presentative progresses on the applications of g-C₃N₄-based membranes for water purification have been elaborated. Essentially, we highlighted the innovation integration of physical separation, catalysis and energy conversion during water purification, which was of great importance for the sustainability of water treatment techniques. Finally, the continuing challenges of g-C₃N₄-based membranes and the possible breakthrough directions in the future research was prospected.

Millimeter-Scale Zn(3-ptz)2 Metal-Organic Framework Single Crystals: Self-Assembly Mechanism and Growth Kinetics

The solvothermal synthesis of metal-organic frameworks (MOFs) often proceeds through competing crystallization pathways, and only partial control over the crystal nucleation and growth rates is possible. It challenges the use of MOFs as functional devices in free-space optics, where bulk single crystals of millimeter dimensions and high optical quality are needed. We develop a synthetic protocol to control the solvothermal growth of the MOF [Zn(3-ptz)2] n (MIRO-101), to obtain large single crystals with projected surface areas of up to 25 mm2 in 24 h, in a single reaction with in situ ligand formation. No additional cooling and growth steps are necessary. We propose a viable reaction mechanism for the formation of MIRO-101 crystals under acidic conditions, by isolating intermediate crystal structures that directly connect with the target MOF and reversibly interconverting between them. We also study the nucleation and growth kinetics of MIRO-101 using ex situ crystal image analysis. The synthesis parameters that control the size and morphology of our target MOF crystal are discussed. Our work deepens our understanding of MOF growth processes in solution and demonstrates the possibility of building MOF-based devices for future applications in optics.

Electrospun pullulan/PVA nanofibers integrated with thymol-loaded porphyrin metal-organic framework for antibacterial food packaging

Pathogenic microorganisms posed perniciousness for postharvest fruits and vegetables, as well as brought potential risks for human health. In this work, pullulan/polyvinyl alcohol (PUL/PVA) nanofibers incorporated with thymol-loaded porphyrin metal-organic framework nanoparticles (THY@PCN-224 NPs) were developed for antibacterial food packaging. PCN-224 MOFs not only act as thymol loading carriers but also highly produce singlet oxygen (¹O₂) with bactericidal activity. PUL/PVA nanofiber was a promising sustainable substrate because of its good flexibility, biocompatibility and biodegradability. The loading capacity of PCN-224 for thymol was about 20%. The THY@PCN/PUL/PVA nanofibers exhibited synergistic antibacterial activities against E. coli (~99%) and S. aureus (~98%) under light irradiation. The cell viability assays and fruit preservation study demonstrated good biosafety of the polymeric film. The results suggested that this novel nanofiber has potential application prospects for food packaging.

Thin-Film Nanocomposite Membrane Incorporated with Porous Zn-Based Metal-Organic Frameworks: Toward Enhancement of Desalination Performance and Chlorine Resistance

Metal-organic framework (MOF) materials have received extensive attention for the design of advanced thin-film nanocomposite (TFN) membranes with excellent permselectivity. However, the relationship between the unique physicochemical properties and performance of engineered MOF-based membranes has yet to be extensively investigated. In this work, we investigate the incorporation of porous zinc-based MOFs (Zn-MOFs) into a polyamide active layer for the fabrication of TFN membranes on porous poly(phenylsulfone) (PPSU) support layers through an interfacial polymerization approach. The actual effects of varying the amount of Zn-MOF added as a nanofiller on the physicochemical properties and desalination performance of TFN membranes are studied. The presence and layout of Zn-MOFs on the top layer of the membranes were confirmed by X-ray photoelectron spectroscopy, scanning electron microscopy, and ζ potential analysis. The characterization results revealed that Zn-MOFs strongly bind with polyamide and significantly change the membrane chemistry and morphology. The results indicate that all four studied TFN membranes with incorporated Zn-MOFs enhanced the water permeability while retaining high salt rejection compared to a thin-film composite membrane. Moreover, the highest-performing membrane (50 mg/L Zn-MOF added nanofiller) not only exhibited a water permeability of 2.46 ± 0.12 LMH/bar but also maintained selectivity to reject NaCl (>90%) and Na₂SO₄ (>95%), similar to benchmark values. Furthermore, the membranes showed outstanding water stability throughout 72 h filtration and chlorine resistance after a 264 h chlorine-soaking test because of the better compatibility between the polyamide and Zn-MOF nanofiller. Therefore, the developed TFN membrane has potential to solve trade-off difficulties between permeability and selectivity. Our findings indicate that porous Zn-MOFs play a significant role in the development of a TFN membrane with high desalination performance and chlorine resistance.

2D Metal-Organic Framework-Based Thin-Film Nanocomposite Membranes for Reverse Osmosis and Organic Solvent Nanofiltration

Metal-organic frameworks (MOFs) are promising candidates for membrane-based liquid separations due to their intrinsic microporosity, but many are limited by their insufficient stability. In this work, a copper-benzoquinoid (Cu-THQ) MOF was synthesized and demonstrated structural stability in water and organic solvents. After incorporation into the polyamide layer, the hydrophilicity of the membranes was enhanced. The resultant thin-film nanocomposite (TFN) membranes broke the permeability-selectivity tradeoff by showing 242 % increase in water permeance and slightly enhanced salt rejection at MOF loading of 0.0192 mg cm^-2 . The underlying mechanism was probed by different chemical and morphological characterizations. The membranes also showed improved tolerance to chlorine oxidation. With their excellent stability, the Cu-THQ MOF-based membranes further demonstrated impressive performance in organic solvent nanofiltration involving dimethylformamide.

Templated interfacial synthesis of metal-organic framework (MOF) nano- and micro-structures with precisely controlled shapes and sizes

Metal-organic frameworks (MOF) are an emerging class of microporous materials with promising applications. MOF nanocrystals, and their assembled super-structures, can display unique properties and reactivities when compared with their bulk analogues. MOF nanostructures of 0-D, 2-D, and 3-D dimensions can be routinely obtained by controlling reaction conditions and ligand additives, while formation of 1-D MOF nanocrystals (nanowires and nanorods) and super-structures has been relatively rare. We report here a facile templated interfacial synthesis methodology for the preparation of a series of 1-D MOF nano- and micro-structures with precisely controlled shapes and sizes. Specifically, by applying track-etched polycarbonate (PCTE) membranes as the templates and at the oil/water interface, we rapidly and reproducibly synthesize zeolitic imidazolate framework-8 (ZIF-8) and ZIF-67 nano- and micro structures of sizes ranging from 10 nm to 20 μm. We also identify a size confinement effect on MOF crystal growth, which leads to single crystals under the most restricted conditions and inter-grown polycrystals at larger template pore sizes, as well as surface directing effects that influence the crystallographic preferred orientation. Our findings provide a potentially generalizable method for controlling the size, morphology, and crystal orientations of MOF nanomaterials, as well as offering fundamental understanding into MOF crystal growth mechanisms.

Organic molecular sieve membranes for chemical separations

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.