Recent progress in ternary mixed matrix membranes for CO_(2) separation

Mixed matrix membranes(MMMs)could combine the advantages of both polymeric membranes and porousfillers,making them an effective alternative to conventional polymer membranes.However,interfacial incompatibility issues,such as the presence of interfacial voids,hardening of polymer chains,and blockage of micropores by polymers between common MMMsfillers and the polymer matrix,currently limit the gas sep-aration performance of MMMs.Ternary phase MMMs(consisting of afiller,an additive,and a matrix)made by adding a third compound,usually functionalized additives,can overcome the structural problems of binary phase MMMs and positively impact membrane separation performance.This review introduces the structure and fabrication processes for ternary MMMs,categorizes various nanofillers and the third component,and summarizes and analyzes in detail the CO_(2) separation performance of newly developed ternary MMMs based on both rubbery and glassy polymers.Based on this separation data,the challenges of ternary MMMs are also discussed.Finally,future directions for ternary MMMs are proposed.

Design and synthesis of Al-MOF/PPSU mixed matrix membrane with pollution resistance

To enhance the performance of the polyphenylene sulfone(PPSU) membrane,a novel mixed matrix membrane with hydrophilicity and antifouling properties was prepared.Using PPSU as the ba sic membrane material,polyvinyl pyrrolidone(PVP) as the porogen,N-Methyl pyrrolidone(NMP) as the solvent,and MOF-CAU-1(Al_(4)(OH)_(2)(OCH_(3))_4(H_2 N-BDC)_(3)·xH_(2) O) as the filler,PPSU/CAU-1 mixed matrix membrane(MMM) was prepared by an immersion precipitation and phase transformation technique.By changing the amount of MOF-CAU-1,the properties and performance of the MMM membrane were investigated in terms of hydrophilicity,pore morphology,surface roughness,and dye removal.The results show that the highest pure water flux of the mixed reached 47.9 L·m^(-2)·h^(-1), when the CAU-1 addition amount was 1.0 wt%, which was 23% higher than that of the pure PPSU membrane.Both the rejection rate and the antifouling performance of the MMM membrane also noticeably improved.

Preparation and properties of PPSU/GO mixed matrix membrane

Polyphenylene sulfone/graphene oxide(PPSU/GO) mixed matrix membranes with different GO contents are prepared by phase inversion technique using, PEG-1000 as porogen, and N,N-dimethylacetamide(DMAC) as solvent.The hydrophilicity and pure water flux of the membrane are investigated. The morphology, hydrophilicity, thermodynamic stability and compatibility of the membranes are characterized by various techniques such as SEM,TGA, FTIR and so on. The permeation properties of the membrane are measured in terms of pure water flux and bovine serum albumin(BSA) retention. The results indicate that when the GO content is 1.5 wt%, an evenly distributed finger structure has been formed in the mixed matrix membranes. Owing to the presence of GO,the hydrophilicity and the thermal stability of the membranes are improved, and the fouling resistance is also enhanced.

Amino-functionalized UiO-66-doped mixed matrix membranes with high permeation performance and fouling resistance

For the reduction of bovine serum proteins from wastewater,a novel mixed matrix membrane was prepared by functionalizing the substrate material polyaryletherketone(PAEK),followed by carboxyl groups(C-SPAEKS),and then adding amino-functionalized UiO-66-NH_(2)(Am-UiO-66-NH_(2)).Aminofunctionalization of UiO-66 was accomplished by melamine,followed by an amidation reaction to immobilize Am-UiO-66-NH_(2),which was immobilized on the surface of the membrane as well as in the pore channels,which enhanced the hydrophilicity of the membrane surface while increasing the negative potential of the membrane surface.This nanoparticle-loaded ultrafiltration membrane has good permeation performance,with a pure water flux of up to 482.3 L·m^(-2)·h^(-1) for C-SPAEKS/AmUiO-66-NH_(2) and a retention rate of up to 98.7%for bovine serum albumin(BSA)-contaminated solutions.Meanwhile,after several hydrophilic modifications,the flux recovery of BSA contaminants by this series of membranes increased from 56.2%to 80.55%of pure membranes.The results of ultra-filtration flux time tests performed at room temperature showed that the series of ultrafiltration membranes remained relatively stable over a test time of 300 min.Thus,the newly developed mixed matrix membrane showed potential for high efficiency and stability in wastewater treatment containing bovine serum proteins.

Metal confined in metal-organic framework-based mixed matrix membranes for efficient butadiene recognition separation

The efficient separation of butadiene(1,3-C_(4)H_(6))from C_(4)hydrocarbons is a critical step in petrochemical processes.However,the traditional cryogenic distillation suffers from energy-intensity and serious environmental stress,necessitating the development of alternative technologies for efficient 1,3-C_(4)H_(6)separation.Herein,a 1,3-C_(4)H_(6)recognition mixed matrix membrane is reported via incorporating metal copper encapsulated a metal-organic framework(CuBTC@Cu)into elastic poly(dimethylsiloxane)(PDMS).The resulting CuBTC@Cu/PDMS membrane can efficient separate 1,3-C_(4)H_(6)from various C_(4)hydrocarbons including 1,3-C_(4)H_(6)/n-C_(4)H_(8),1,3-C_(4)H_(6)/iso-C_(4)H_(8),1,3-C_(4)H_(6)/n-C_(4)H_(10)and 1,3-C_(4)H_(6)/iso-C_(4)H_(10),yielding superior selectivity of 5.11,6.35,4.78,and 10.30,respectively,with 1,3-C_(4)H_(6)permeability of 53240 Barrer.Notably,the appropriateπ-complexation interaction between butadiene molecules and CuBTC@Cu as well as suitable transmission channel size enable the membrane only permeable to 1,3-C_(4)H_(6)and block the permeation of other C_(4)hydrocarbons,showing a unique 1,3-C_(4)H_(6)recognition behavior in membrane separation.The concept of affinity-relying separation combining molecular sieving would open a new direction for designing gas membranes for efficient light hydrocarbon separations.

G-CNTs/PVDF mixed matrix membranes with improved antifouling properties and filtration performance

Although carbon nanomaterials have been widely used as effective nanofillers for fabrication of mixed matrix membranes(MMMs)with outstanding performances,the reproducibility of the fabricated MMMs is still hindered by the non-homogenous dispersion of these carbon nanofillers in membrane substrate.Herein,we report an effective way to improve the compatibility of carbon-based nanomaterials with membrane matrixes.By chemically conjugating the oxidized CNTs(o-CNTs)and GO using hexanediamine as cross-linker,a novel carbon nanohybrid material(G-CNTs)was synthesized,which inherited both the advanced properties of multi-walled carbon nanotubes(CNTs)and graphene oxide(G0).The G-CNTs incorporated polyvinylidene fluoride(PVDF)MMMs(GCNTs/PVDF)were fabricated via a non-solvent induced phase separation(NIPS)method.The filtration and antifouling performances of G-CNTs/PVDF were evaluated using distillate water and a1g/L bovine serum albumin(BSA)aqueous solution under 0.10 MPa.Compared to the MMMs prepared with o-CNTs,GO,the physical mixture of o-CNTs and GO and pure PVDF membrane,the G-CNTs/PVDF membrane exhibited the highest water flux up to 220 L/m%and a flux recovery ratio as high as 90%,as well as the best BSA rejection rate.The excellent performances should be attributed to the increased membrane pore size,porosity and hydrophilicity of the resulted membrane.The successful synthesis of the novel nanohybrid G-CNTs provides a new type of nanofillers for MMMs fabrication.

Mixed matrix membrane containing metal oxide nanosheets for efficient CO_(2)separation

The two-dimensional(2D)nanosheet zinc cobaltate(ZnCo_(2)O_(4))was added into polyether block amide(Pebax)matrix to prepare mixing matrix membrane(MMM)for separating carbon dioxide(CO_(2))/methane(CH4)gas mixture.The 2D porous ZnCo_(2)O_(4)nanosheets were composed of chemically interconnected metal oxide nanoparticles.The ZnCo_(2)O_(4)nanoparticles in the nanosheets constructed large-quantity pores of 11.78 nm and provided abundant transfer channels for gas molecule.Moreover,the synergistic effect of bimetallic Zn^(2+)and Co^(2+)would promote the generation of oxygen vacancies(Oδ-),which could provide more CO_(2)(Cδ+)adsorption sites,thereby increased the selectivity of the membrane.The large aspect ratio of the ultra-thin ZnCo_(2)O_(4)nanosheets showed better dispersion in the membrane.The pure gas separation performance data showed the CO_(2)permeability and CO_(2)/CH4 selectivity of Pebax/ZnCo_(2)O_(4)membrane were 139.10 Barrer and 15.38,respectively,when the filling amount was 0.5 wt%.Compared with pure Pebax membrane,the separation performance(permeability and selectivity)were increased with 165.67%and 75.57%,respectively.

Smart light-responsive hierarchical metal organic frameworks constructed mixed matrix membranes for efficient gas separation

One type of new light-responsive hierarchical metal organic framework(MOF) has been successfully prepared using Co(NO_(3))_(3)·6H_(2)O as the metal salt and 4,4’-azobenzenedicarboxylic acid as the ligand by microwave method for the first time. It is found that MOF [Co(Az DC)] exhibits a light-responsive characteristic to SO_(2)adsorption due to the presence of azo group from the ligand. The light-responsive hierarchical MOFs are incorporated into Matrimid■ 5218(PI) matrix to prepare mixed matrix membranes(MMMs) for gas separation application. The morphology, crystallinity, chain mobility and thermal stability of MMMs are explored. Results show that Co(Az DC) may elevate both the CO_(2)(SO_(2)) permeability and CO_(2)(SO_(2))/N_(2)selectivity of the MMMs. In particular,the Co(Az DC) doped MMMs exhibit the significantly improved CO_(2)(SO_(2))/N_(2)selectivity from 33(123) for PI control membrane to 78(420) for MMMs, overcoming the 2008 Robeson upper bound for CO_(2)/N_(2)system. Sizesieving effect of Co(Az DC) with pore size 0.35 nm enhances the selectivity, while the –N=N– group from Co(Az DC) shows affinity to CO_(2)molecular rather than N_(2), also elevating selectivity of MMMs. In brief, enhanced selectivity of high-performance membrane is attributed to incorporation of Co(Az DC) particles, which displays synergistic effects both in size-sieving and CO_(2)-philic interaction for CO_(2)/N_(2)separation. Smart highly selective interface is constructed in MMMs by switching the configuration of MOFs from cis to trans. The SO_(2)permeability and SO_(2)/N_(2)selectivity of MMMs are investigated under both visible light and ultraviolet light states, and the SO_(2)/N_(2)separation performance under visible light is notably improved in comparison with that under ultraviolet light state.

Assembling ionic liquid into porous molecular filler of mixed matrix membrane to trigger high gas permeability,selectivity,and stability for CO_(2)/CH_(4) separation

As an emerging zero-dimensional nano crystalline porous material,porous organic cages(POCs)with soluble properties in organic solvents,are promising candidates as molecular fillers in mixed matrix membranes(MMMs).The pore structure of POCs should be adjusted to trigger efficient gas separation performance,and the interaction between filler and matrix should be optimized.In this work,ionic liquid(IL)was introduced into the molecular fillers of CC3,to construct the IL@CC3/PIM-1 membrane to effectively separate CO_(2) from CH_(4).The advantages of doping IL include:(1)narrowing the cavity size of POCs from 4.4 to 3.9Åto enhance the diffusion selectivity,(2)strengthening the CO_(2) solubility to heighten the gas permeability,and(3)improving the compatibility between filler and matrix to upgrade membrane stability.After the optimization of the membrane composite,the IL@CC3/PIM-1-10%membrane possesses the CO_(2) permeability of 7868 Barrer and the CO_(2)/CH_(4) selectivity of 73.4,which compared to the CC3/PIM-1-10%membrane,improved by 15.9%and 106.2%,respectively.Furthermore,the membrane has maintained a stable separation performance at varied temperatures and pressures during the long-term test.The proposed method offers an efficient way to improve the performance of POCs-based MMMs in gas separation.

Breakthroughs on tailoring membrane materials for ethanol recovery by pervaporation

Bioethanol, as a clean and renewable fuel, has gained increasing attention due to its major environmental benefits. Pervaporation(PV) is a promising and competitive technique for the recovery of ethanol from bioethanol fermentation systems due to the advantages of environmental friendliness, low energy consumption and easy coupling with fermentation process. The main challenge for the industrial application of ethanol perm-selective membranes is to break the trade-off effect between permeability and selectivity. As membrane is the heart of the pervaporation separation process, this article attempts to provide a comprehensive survey on the breakthroughs of ethanol perm-selective PV membranes from the perspectives of tailoring membrane materials to enhance PV separation performance. The research and development of polymeric and organic/inorganic hybrid membranes are reviewed to explore the fundamental structure-property-performance relationships. It is found that mixed matrix membranes with welldesigned membrane structures offer the hope of better control overphysi-/chemical microenvironment and cavity/pore size as well as size distribution, which may provide both high permeability and membrane selectivity to break the trade-off effect. The tentative perspective on the possible future directions of ethanol perm-selective membranes is also briefly discussed, which may provide some insights in developing a new generation of high-performance PV membranes for ethanol recovery.

The effect of ZIF-90 particle in Pebax/Psf composite membrane on the transport properties of CO2,CH4 and N2 gases by Molecular Dynamics Simulation method

Nowadays,mixed matrix membranes(MMMs)have considered by many researchers to overcome the problems of polymeric membranes.In addition,molecular dynamics(MD)and Monte Carlo(MC)simulation Methods are suitable tools for studying transport properties and morphology in MMMs.For this purpose,in this study using material studio 2017(MS)software,the transport properties of CO2,CH4 and N2 in Pebax,Psf neat Pebax/Psf composite and Pebax/Psf composite filled with ZIF-90 particles have been investigated.By adding Psf to Pebax matrix,the selectivity of CO2/CH4 and CO2/N2 gases has significantly increased.In addition,adding ZIF-90 particles to the Pebax/Psf composite increased the permeability of CO2,CH4 and N2 compared to neat and composite membranes.The morphological properties of the membranes,such as the fractional free volume(FFV),radial distribution function(RDF),glass transition temperature(TG),X-ray diffraction(XRD)and equilibrium density have calculated and acceptable results have obtained.

Ultrapermeable membranes based on connected cluster of hollow polydimethylsiloxane nanoparticles for gas separation

Mixed matrix membranes(MMMs)with the performance between the matrix and the filler is a promising strategy for membranes with excellent gas permeability-selectivity.In this study,the hollow polydimethylsiloxane nanoparticles were synthesized and then incorporated with the poly(oxide ethylene)monomer and tri-functional cross-linker to form mixed matrix membranes by in situ poly-merization.The hollow nanoparticles formed the independent closed nanocavities in membranes,which enhanced the gas permeability contributed by both the improved diffusivity and solubility.At high loading,the hollow polydimethylsiloxane nanoparticle was converted into the continuous phase with the cross-linked poly(oxide ethylene)as the dispersed phase.Gases preferred to permeate through the connected cluster of hollow polydimethylsiloxane nanoparticles,finally leading to ultrahigh gas per-meabilities far going beyond the instinct values of polydimethylsiloxane and the cross-linked poly(oxide ethylene).The optimized membrane with 34 wt%hollow nanoparticles loadings exhibited ultrahigh permeabilities with the values of 44186 Barrer for CO_(2) and 11506 Barrer for O_(2),accompanied with a CO_(2)/N_(2) selectivity of 9.9 and an O_(2)/N_(2) selectivity of 2.6,which exceeded the 2008 Robeson upper bound for O_(2)/N_(2) and located at the 2008 Robeson upper bound for CO_(2)/N_(2).

Recent developments of anti-plasticized membranes for aggressive CO_(2)separation

Membrane separation technology provides an effective alternative to mitigate the massive carbon emission with high carbon capture productivity and efficiency.In the context of operating membranes under high CO_(2)pressures allows increased separation productivity and reduced gas compression cost,which,however,often leads to CO_(2)induced plasticization,a key hurdle for current gas separation membranes.In this review,we reviewed the latest development of membranes with anti-plasticization resistance,potentially suited for operation under high CO_(2)feed streams.Specifically,the separation performance of polymeric membranes,inorganic membranes,and mixed matrix membranes under high CO_(2)feed pressures are discussed.Approaches to enhance CO_(2)induced plasticization of those membranes are also summarized.We conclude the recent progress of membranes for high CO_(2)pressures with perspectives and an outlook for future development.

Recent developments in polymeric nano-based separation membranes

Polymeric nanomaterials,which have tuneable chemical structures,versatile functionalities,and good compatibility with polymeric matrices,have attracted increasing interest from researchers for the construction of polymeric nano-based separation membranes.With their distinctive nanofeatures,polymeric nano-based membranes show great promise in overcoming bottlenecks in polymer membranes,namely,the trade-off between permeability and selectivity,low stability,and fouling issues.Accordingly,recent studies have focused on tuning the structures and tailoring the surface properties of polymeric nano-based membranes via exploitation of membrane fabrication techniques and surface modification strategies,with the objective of pushing the performance of polymeric nano-based membranes to a new level.In this review,first,the approaches for fabricating polymeric nano-based mixed matrix membranes and homogeneous membranes are summarized,such as surface coating,phase inversion,interfacial polymerization,and self-assembly methods.Next,the manipulation strategies of membrane surface properties,namely,the hydrophilicity/hydrophobicity,charge characteristics,and surface roughness,and interior microstructural properties,namely,the pore size and content,channel construction and regulation,are comprehensively discussed.Subsequently,the separation performances of liquid ions/molecules and gas molecules through polymeric nano-based membranes are systematically reported.Finally,we conclude this review with an overview of various unsolved scientific and technical challenges that are associated with new opportunities in the development of advanced polymeric nano-based membranes.

Enhanced Gas Separation Performance by Embedding Submicron Poly(ethylene glycol) Capsules into Polyetherimide Membrane

Recently, hollow filler as an emerging concept is attracting more attention in preparation of mixed matrix membranes(MMMs). Herein,poly(ethylene glycol) microcapsules(PMC) are synthesized via distillation precipitation polymerization and embedded into the polyetherimide(Ultem■1000) matrix to fabricate MMMs for CO_(2) capture. The PMC exhibits a preferential hollow structure within the Ultem matrix to furnish highways within membrane, and thus achieve high gas permeability. Meanwhile, the favorable affinity of poly(ethylene glycol)(PEG)microcapsule with ether oxygen group(EO) towards CO_(2) enhances the CO_(2) solubility selectivity. Such integration of physical and chemical microenvironments in the as-designed PEG microcapsule affords highly enhanced CO_(2) separation performance. Compared to pristine Ultem■1000, the membrane with 2.5 wt% PMC loading exhibits 310% increment in CO_(2) permeability and 22% increment in CO_(2)/N_(2) selectivity,which shows the promising prospects of designing PEG-containing microcapsules as the filler of MMMs for CO_(2) capture.

Recent Advances in Metal-Organic Cages-Based Composite Membranes

Conventional polymeric membranes face several limitations,such as the trade-off between permeability and selectivity,and physical aging or membrane fouling.In this case,fabrication of composite membranes,usually including mixed matrix membranes(MMMs)or thin film nanocomposite(TFN)membranes by introduction of porous materials as fillers has gained much attention.To achieve excellent membrane performance,it is of great importance to select proper porous materials to avoid agglomeration or precipitation during the composite membrane fabrication processes.Metal-organic cages(MOCs)have been explored as additives for the fabrication of defectfree composite membranes owing to their diversified topologies,well-defined pore structures,nanoscale size,and excellent solubility.This review mainly focuses on the recent advances in applications of MOCs for membrane separation,including synthetic artificial channels,reverse osmosis,nanofiltration,pervaporation and gas separation.Besides,two types of MOCs that have been extensively investigated for composite membrane fabrication are also highlighted.Furthermore,challenges and possible directions are also discussed in details,hoping to provide insightful guidance on the development of more MOC-based membranes with impressive separation performance.