Molecular Sieving Effect Research Articles

MOF-based membranes for pervaporation

Pervaporation competes with conventional separation techniques, such as distillation and adsorption in organic liquid dehydration, removal or recovery of organic compounds from aqueous solutions, and separation of organic-organic mixtures. Pervaporation is a separation technique relying on the concentration gradient, often expressed as partial vapor pressures, across polymeric or polymer-composite membranes. Those membranes often exhibit a strong trade-off between permeability and selectivity of target compounds, making the search for alternative materials with advanced performance characteristics highly desirable. Metal–organic frameworks (MOFs), a sub-group of porous functionalised materials, have recently demonstrated potential to become a valuable building block in the fabrication of future high-performance pervaporation membranes. MOFs feature unique properties, such as molecular sieve effects, preferential adsorption to the target molecular compounds, and thermal and chemical stability, being suitable for direct applications in pervaporation separation of liquid mixtures. This paper comprehensively examines the current design strategies of MOF-based membranes in pervaporation. The main developments of MOF-based membranes in pervaporation are discussed and the performance of pervaporation processes using MOF-based membranes is also analysed. Furthermore, some perspectives for future development of MOF-based membranes in pervaporation are given.

Microporous carbon with highly dispersed nano-lanthanum oxide (La2O3) for enhanced adsorption of methylene blue

• Nano La 2 O 3 is ideal to induce extra microporosity on carbon granules by heat treatment at 873 K. • Resulted carbon retained their inherent honey comb structures where nucleated metal oxide are occupied on the edges. • Material is ideal to scavenge cationic dyes by electrostatic activation because of O 2− ions of these occupied nano La 2 O 3 with organics. • John-Sivanandan Achari isotherms of GACLaO873 has three phases identified as due to molecular sieve effects, donor–acceptor and electrostatic attraction type adsorptions in the liquid phase. Activated carbon doped with Lanthanum compounds are prepared and used as a preferred material for adsorption treatment systems. In this study, use of nano La 2 O 3 and La 3+ is attempted as tuning agents for granular activated carbons (GAC) and products are marked as GACLaX and GACLaOX series, produced under controlled activation (473–1273 K) for a Lanthanum/carbon ratio 0.04. They were tested for their physico-chemical features, textural superiority, and efficiency determined by XRD, FTIR, SEM, XPS, Raman, and N 2 /BET and t-plots. It is found that carbon GACLaO873 (GAC activated with nano lanthanum oxide at 873 K) has good microporosity and adsorption efficiency. Nano La 2 O 3 and La 3+ incorporated extra microporosity ( SA micro ) measured as 707 m 2 /g for GACLaO873 compared to native carbon GAC (589 m 2 /g). The respective surface area ( SA BET ) of these new carbons are determined as 946 m 2 /g (GACLaO873), 953 m 2 /g (GACLa1073), and 997 m 2 /g (GAC383). Suitability of the new carbon materials in solid–liquid batch reactor systems is studied for methylene blue (MB) in concentration ranges 25–1500 mg/L. Analysis of equilibrium isotherm uptake data by John-Sivanandan Achari isotherm model found distinct features of different adsorption phases (kinks) in their plots. For GACLaO873, monolayer coverage q m (J-SA) has been 256 mg/g against the basic carbon GAC383 (190 mg/g). Lanthanum activated carbon GACLa1073 has been noted with adsorption efficiency for metal ions, Mn (99.3%), Fe (99.1%), Co (96.6%), As (76.3%), Ba (63.0%), Li (50.4%), Al (71.3%), Cr (47.7%), Ni (99.2%), Cu (7.11%), Zn (24.3%), Cd (55.1%), Tl (32.6%) and Pd (94.9%) tested for a contaminated groundwater sample as a field trial. Lanthanum, La 3+ , and nano La 2 O 3 doped activated carbon series (GACLaX and GACLaOX) prepared under a controlled condition and activation temperature X, bears good microporosity and adsorption efficiency for organic and metal ion contaminants.

Water adsorption and hydrothermal stability of CHA zeolites with different Si/Al ratios and compensating cations

Zeolites are well known crystalline aluminosilicates, which may be used in processes that take advantage of their molecular sieving effect, such as natural gas drying. They are often used in cyclic processes that swing pressure and/or temperature to perform adsorption and desorption steps. It is recognized that thermal stress may decrease process performance upon prolonged use. In this work, chabazite (CHA) zeolite with two different Si/Al ratios and compensating cations was investigated by thermally aging the samples using a laboratory-scale protocol. A Premature Aging Protocol – PAP was proposed that took into account the conditions which the adsorbent is exposed to in Temperature Swing Adsorption (TSA) process for natural gas drying. The sample was previously saturated with water and n-heptane vapors (as a reference hydrocarbon) followed by pressurization (30 bar) and heating (573 K) with a mixture of CO2 and CH4 (1:4, v/v). The Si/Al ratios of the CHA samples under study were 2 and 5 and the compensating cations were Na and K. Aged materials presented a lower CO2 and water vapor adsorption capacity with an increasing content of carbon in the bulk composition. The sample with higher Si/Al ratio (≈5) had a larger pore volume but adsorbed less water. Despite having the highest carbon content after aging and modest acidity, it was the most thermally stable sample, together with the sample containing potassium. Even with a lower Si/Al ratio (≈2), the presence of potassium provided the sample a protective effect against aging.

Efficient Separation of Acetylene-Containing Mixtures Using ZIF-8 Membranes.

Metal–organic framework (MOF) membranes show great potential in the separation of acetylene mixtures. In this work, we have prepared ZIF-8 membranes on polyamide (PA) substrates for the highly selective separation of acetylene/methane and acetylene/carbon dioxide mixtures. The C2H2/CH4 and C2H2/CO2 mixtures can be successfully separated using the ZIF-8 membranes, with separation factors of 12.1 and 1.8, respectively. Based on the results of the cross-permeation tests of C2H2/CH4, CO2/CH4, and C2H2/CO2, the separation mechanism of C2H2/CH4 in our ZIF-8 membrane can be attributed to a higher affinity for acetylene and molecular sieving effect, while C2H2/CO2 separation is related to thermodynamic factors. It is worth noting that this is the first example of MOF membranes to successfully separate C2H2 from CH4 and CO2.

Mono- and di-valent ion exchange of mordenite membranes for dehydration of acetic acid by pervaporation

The conventional Na-mordenite (Na-MOR) zeolite membranes prepared on α-Al2O3 tubes by secondary hydrothermal growth method. To improve membrane performances in dehydration of acetic acid by pervaporation, the Na+ as counter ions in MOR membranes were exchanged by a series of mono- and di-valent cations to adjusted the channel structure and water affinity. Langmuir surface areas for monovalent ion-exchanged MOR zeolites were consistent with the reverse order of ion radii as H+>Li+>Na+>K+>Cs+, while for those exchanged by divalent ions the zeolites surface areas followed the reverse order of hydrated ion radii instead of natural radii as Ba2+>Ca2+>Mg2+. The water adsorption of MOR by mono- and di-valent cations exchange were all disordered, and H+, K+ and Ca2+ exchanged MOR showed higher water capacity than that of Na-MOR. In pervaporation, monovalent ion-exchanged membranes with molecular sieving effect showed higher performances than those of divalent ion-exchanged membranes with augmented steric effect and weakened molecular sieving. Among these membranes, H-MOR showed the largest flux of 3.68 kg m−2 h−1 with a normal separation factor of 472 in pervaporation of 90 wt% acetic acid/water under 348 K due to a larger pore size and higher water adsorption, which were supplemented for acid-treated membranes. To get better separation ability, H+ exchange conditions on MOR membranes were investigated in detail. The optimized H-MOR membrane showed a flux of 1.52 kg m−2·h−1and separation factor of 1443 with good stability for 100 h. A simple water wash with a recovered performance proved a previously reported phenomenon that reduced flux with time was affected by acetic acid blockage.

Multivariate Polycrystalline Metal-Organic Framework Membranes for CO2/CH4 Separation.

Membrane technology is attractive for natural gas separation (removing CO2, H2O, and hydrocarbons from CH4) because of membranes' low energy consumption and small environmental footprint. Compared to polymeric membranes, microporous inorganic membranes such as silicoaluminophosphate-34 (SAPO-34) membrane can retain their separation performance under conditions close to industrial requirements. However, moisture and hydrocarbons in natural gas can be strongly adsorbed in the pores of those membranes, thereby reducing the membrane separation performance. Herein, we report the fabrication of a polycrystalline MIL-160 membrane on an Al2O3 substrate by in situ hydrothermal synthesis. The MIL-160 membrane with a thickness of ca. 3 μm shows a remarkable molecular sieving effect in gas separation. Besides, the pore size and environment of the MIL-160 membrane can be precisely controlled using reticular chemistry by regulating the size and functionality of the ligand. Interestingly, the more polar fluorine-functionalized multivariate MIL-160/CAU-10-F membrane exhibits a 10.7% increase in selectivity for CO2/CH4 separation and a 31.2% increase in CO2 permeance compared to those of the MIL-160 membrane. In addition, hydrophobic MIL-160 membranes and MIL-160/CAU-10-F membranes are more resistant to water vapor and hydrocarbons than the hydrophilic SAPO-34 membranes.

Porosity of Rigid Dendrimers in Bulk: Interdendrimer Interactions and Functionality as Key Factors.

The porous structure of second- and third-generation polyphenylene-type dendrimers was investigated by adsorption of N2, Ar, and CO2 gases, scanning electron microscopy and small-angle X-ray spectroscopy. Rigid dendrimers in bulk are microporous and demonstrate a molecular sieve effect. When using CO2 as an adsorbate gas, the pore size varies from 0.6 to 0.9 nm. This is most likely due to the distances between dendrimer macromolecules or branches of neighboring dendrimers, whose packing is mostly realized due to intermolecular interactions, in particular, π–π interactions of aromatic fragments. Intermolecular interactions prevent the manifestation of the porosity potential inherent to the molecular 3D structure of third-generation dendrimers, while for the second generation, much higher porosity is observed. The maximum specific surface area for the second-generation dendrimers was 467 m2/g when measured by CO2 adsorption, indicating that shorter branches of these dendrimers do not provide dense packing. This implies that the possible universal method to create porous materials for all kinds of rigid dendrimers is by a placement of bulky substituents in their outer layer.

Highly Selective Adsorption of Carbon Dioxide over Acetylene in an Ultramicroporous Metal-Organic Framework.

Separating carbon dioxide from fuel gases like hydrocarbons by physical adsorbents is industrially important and more energy-efficient than traditional liquid extraction or cryogenic distillation methods. It is very important while very challenging to develop CO2 -selective adsorbents, considering CO2 is less polarizable than light hydrocarbon molecules, particularly those simultaneously with almost identical molecular dimensions and physical properties, such as acetylene. Herein, an ultramicroporous metal-organic framework constructed from copper(II) and 5-fluoropyrimidin-2-olate, termed Cu-F-pymo, is carefully studied under different activations for inverse separation of CO2 from C2 H2 . The partially desolvated Cu-F-pymo can exclusively capture CO2 over C2 H2 with very high selectivity exceeding 105 under ambient conditions, the highest ever reported. Sorption experiments and modeling studies reveal that such molecular sieving effect is attributed to the suppression of C2 H2 adsorption from the blockage of the preferential sites for C2 H2 by residual water molecules. The inverse separation is further confirmed by column breakthrough studies given that highly pure acetylene (>99.9%) can be directly harvested from the gas mixture. Cu-F-pymo also shows remarkable stability under harsh conditions.

Site-Selective Deposition of Metal–Organic Frameworks on Gold Nanobipyramids for Surface-Enhanced Raman Scattering

Site-selective deposition of metal-organic frameworks (MOFs) on metal nanocrystals has remained challenging because of the difficult control of the nucleation and growth of MOFs. Herein we report on a facile wet-chemistry approach for the selective deposition of zeolitic imidazolate framework-8 (ZIF-8) on anisotropic Au nanobipyramids (NBPs) and nanorods. ZIF-8 is selectively deposited at the ends and waist and around the entire surface of the elongated Au nanocrystals. The NBP-based nanostructures with end-deposited ZIF-8 exhibit the best surface-enhanced Raman scattering (SERS) performance, implying that molecules can be concentrated by ZIF-8 at the hot spots. In addition, the SERS signal exhibits good selectivity for small molecules because of the molecular sieving effect of ZIF-8. This study opens up a promising route for constructing plasmonic nanostructures with site selectively deposited ZIF-8, which hold enormous potential for molecular sensing, optical switching, and plasmonic catalysis.

Development of Methanol Permselective FAU-Type Zeolite Membranes and Their Permeation and Separation Performances.

The separation of non-aqueous mixtures is important for chemical production, and zeolite membranes have great potential for energy-efficient separation. In this study, the influence of the framework structure and composition of zeolites on the permeation and separation performance of methanol through zeolite membranes were investigated to develop a methanol permselective zeolite membrane. As a result, the FAU-type zeolite membrane prepared using a solution with a composition of 10 SiO2:1 Al2O3:17 Na2O:1000 H2O showed the highest permeation flux of 86,600 μmol m−2 s−1 and a separation factor of 6020 for a 10 wt% methanol/methyl hexanoate mixture at 353 K. The membrane showed a molecular sieving effect, reducing the single permeation flux of alcohol with molecular size for single-component alcohols. Moreover, the permeation flux of methanol and the separation factor increased with an increase in the carbon number of the alcohols and methyl esters containing 10 wt% methanol. In this study, the permeation behavior of FAU-type zeolite membranes was also discussed based on permeation data. These results suggest that the FAU-type zeolite membrane has the potential to separate organic solvent mixtures, such as solvent recycling and membrane reactors.

Comparison of Physicochemical Properties of Fly Ash Precursor, Na-P1(C) Zeolite-Carbon Composite and Na-P1 Zeolite-Adsorption Affinity to Divalent Pb and Zn Cations.

Considering the growing needs of environmental remediation, new effective solutions should be sought. Therefore, the adsorbed amounts of heavy metal ions, such as lead(II) and zinc(II), on the surface of high-carbon fly ash (HiC FA), zeolite-–carbon composite (Na-P1(C)) and pure zeolite (Na-P1), were investigated. The applied solids were characterized using the following techniques: XRD, SEM-EDS, TEM, porosimetry, SLS, electrophoresis and potentiometric titration. The heavy metal concentration in the probes was determined by applying ICP-OES spectroscopy. Adsorption/desorption and electrokinetic measurements were performed in the systems containing one or two adsorbates. The obtained results indicated that Pb(II) ions are adsorbed in larger amounts on the investigated solid surface due to the molecular sieving effect. The largest adsorption capacity relative to lead(II) ions was observed for pure Na-P1 zeolite (407 mg/g). The simultaneous presence of Pb(II) + Zn(II) mixed adsorbates minimally affects the amount of adsorbed Pb(II) ions and causes a significant decrease of Zn(II) ion adsorption (in comparison with analogous systems containing single adsorbates). It was also shown that all solids can be efficiently regenerated using hydrochloric acid. Thus, the selected pure zeolite can be successfully applied in soil remediation or other purifying technologies as an effective Pb(II) adsorbent.

Molecular Sieving of Acetylene from Ethylene in a Rigid Ultra-microporous Metal Organic Framework.

Rigid molecular sieving materials are the ideal candidates for gas separation (e. g., C2 H2 /C2 H4 ) due to their ultrahigh adsorption selectivity and the absence of gas co-adsorption. However, the absolute molecular sieving effect for C2 H2 /C2 H4 separation has rarely been realized because of their similar physicochemical properties. Herein, we demonstrate the absolute molecular sieving of C2 H2 from C2 H4 by a rigid ultra-microporous metal-organic framework (F-PYMO-Cu) with 1D regular channels (pore size of ca. 3.4 Å). F-PYMO-Cu exhibited moderate acetylene uptake (35.5 cm3 /cm3 ), but very low ethylene uptake (0.55 cm3 /cm3 ) at 298 K and 1 bar, yielding the second highest C2 H2 /C2 H4 uptake ratio of 63.6 up to now. One-step C2 H4 production from a binary mixture of C2 H2 /C2 H4 and a ternary mixture of C2 H2 /CO2 /C2 H4 at 298 K was achieved and verified by dynamic breakthrough experiments. Coupled with excellent thermal and water stability, F-PYMO-Cu could be a promising candidate for industrial C2 separation tasks.

Solubility selectivity-enhanced SIFSIX-3-Ni-containing mixed matrix membranes for improved CO2/CH4 separation efficiency

The unstable nature of SIFSIX-3-Zn to most organic solvents hinders its application for gas separation albeit its excellent molecular sieving effect and a high affinity towards CO2. Here, we report the enhanced organic solvent resistance of SIFSIX-3-Ni by characterizing their crystallinity and gas adsorption properties after exposure to organic solvents including tetrahydrofuran and N, N-dimethylformaide. SIFSIX-3-Ni microparticles were incorporated into a 6FDA-DAM:DABA (3:2) polyimide (PI) and polysulfone (PSF) matrix to prepare mixed matrix membranes (MMMs) for CO2/CH4 separation. While PI was an unsuitable matrix for high loading MMMs due to the strong hydrogen bonding between the carboxylic groups of PI and the SiF62− anions of SIFSIX-3-Ni, PSF/SIFSIX-3-Ni MMMs with loading up to 30% were successfully prepared with the aid of the weak interaction between sulfonate groups in PSF and the fluorine atoms of SIFSIX-3-Ni. Interestingly, the CO2 permeability of PSF/SIFSIX-3-Ni MMMs monotonically decreased with increasing CO2/CH4 selectivity as the SIFSIX-3-Ni concentration increased. Also, the PSF/SIFSIX-3-Ni (70/30) MMM showed lower CO2 permeability with higher CO2/CH4 selectivity compared to PSF under an equimolar CO2/CH4 mixed gas condition. Monte Carlo simulations suggest that the strong Coulombic interactions between SIFSIX-3-Ni and CO2 significantly increased the free energy barrier of transport for CO2 over CH4, leading to a reduction in the CO2/CH4 diffusive selectivity of the MMMs. In contrast, the CO2 solubility of PSF/SIFSIX-3-Ni MMMs increased with increasing SIFSIX-3-Ni contents due to the strong interaction between SiF62− of SIFSIX-3-Ni and CO2, significantly enhancing the CO2/CH4 adsorptive selectivity.

A [Th 8 Co 8 ] Nanocage-Based Metal–Organic Framework with Extremely Narrow Window but Flexible Nature Enabling Dual-Sieving Effect for Both Isotope and Isomer Separation

The synthesis of nanoporous materials that display a combination of molecular sieving (MS) and quantum sieving (QS) effects is still a challenging task. In this work, we have demonstrated the synth...

Polyvinylamine/ZIF-8-decorated metakaolin composite membranes for CO2/N2 separation

• ZIF-8-d-MK hybrid with the interlayer spaces was developed by coordinating ZIF-8 particles to amorphous MK sheets. • PVAm/ZIF-8-d-MK MMCMs for CO 2 /N 2 separation were successfully fabricated. • The interlayer spaces of ZIF-8-d-MK in the MMCMs function as CO 2 transport pathways. • The ZIF-8-d-MK hybrid was homogenously dispersed in PVAm matrix due to amorphous structure of MK sheets. Mixed-matrix composite membranes (MMCMs) have great potential in chemical separation process due to high performance, but the dispersibility of the filler is an enormous challenge we face. In this study, a ZIF-8-decorated metakaolin (ZIF-8-d-MK) hybrid was prepared by the AlO 4 tetrahedron oxygens in amorphous MK coordinating with the zinc ions of ZIF-8. MMCMs by coating polysulfone (PSf) ultrafiltration membranes with a mixture of hybrid and polyvinylamine (PVAm) were obtained, which can efficiently separate CO 2 from N 2 . SEM and TEM results indicated that ZIF-8 particles were present between the amorphous MK sheets, and the coordination between the two phases was validated by FTIR. ZIF-8-d-MK, with a partially amorphous structure, exhibited homogeneous distribution in the PVAm matrix, as verified by SEM and XRD, and ZIF-8-d-MK had a strong interaction with the polymer matrix as certified by attenuated total reflectance-FTIR. A highest CO 2 permeance of 169 GPU with CO 2 /N 2 selectivity of 86.7 were acquired for MMCMs, loaded with 3 wt% ZIF-8-d-MK under pure gas conditions, which were much higher than those of MMCMs loaded with MK, ZIF-8, or a mixture of MK and ZIF-8. The improved values were primarily ascribed to the well-dispersed ZIF-8-d-MK serving as CO 2 transport pathways because of its molecular sieving effect for CO 2 /N 2 . Importantly, under mixed gas feed conditions, the stability measurement demonstrated that the MMCMs adding 3 wt% ZIF-8-d-MK did long-term operation for over 360 h, and maintained great CO 2 separation performance.

Direct Measurement of Initial Rate of Enzyme Reaction by Electrokinetic Filtration Using a Hydrogel-plugged Capillary Device.

A novel electrokinetic filtration device using a plugged hydrogel was developed to directly measure the initial rate of enzyme reactions. In the proposed method, the enzyme reaction proceeded only for a short time when the substrate was passed through a thin layer of enzyme trapped by the hydrogel without any lag times for mixing and detection. In experimental conditions, alkaline phosphatase (enzyme) was filtrated at a cathodic-side interface of the plugged hydrogel by molecular sieving effect, providing the thin enzyme zone whose thickness was approximately 100 μm. When 4-methylumberiferyl phosphate (substrate) was electrokinetically introduced into the device after trapping the enzyme, 4-methylumberiferone (product) was generated by the enzyme reaction for only 1.26 s as the substrate passed through the trapped enzyme zone. As a result, the initial rate of the enzyme reaction could be directly calculated to 31.0 μM/s by simply dividing the concentration of the product by the tunable reaction time. Compared to the initial rate obtained by mixing the enzyme and substrate solutions, the value of the maximum velocity of the enzyme reaction was 30-fold larger than that in the mixing method due to the preconcentration of the enzyme by trapping. The Michaelis-Menten constant in the proposed method was 2.7-fold larger than that in the mixing method, suggesting the variation of changes in the equilibrium of complex formation under the experimental conditions.

Use of carbonized corn cob biomass to reduce acidity of residual frying oil

The objective of this work was to evaluate the ability of CCC as an adsorbent material for the acidity removal of RFO, aiming at the application of the oil in biodiesel production. For that, a RCCD was used for FFA removal by applying the CCC and CAC for comparative purposes. In the RCCD removal assays the effect of the Temperature, Agitation and Mass factors were assessed over acidity removal of the oil. Under the best conditions from RCCD, an evaluation of adsorption kinetics was performed, wherein it was observed the equilibrium was reached within 4 h, for the CCC. Also, the influence of the adsorbent dosage was performed. It was verified that 4 g was sufficient to allow the system to reach the maximum FFA removal. Overall, the CCC presented results approximately twice as high than those obtained by the CAC, mainly due to the pore size distribution which led to a “molecular sieving effect” for the CCC adsorbent. It allowed the major diffusion of the FFA molecules inside its narrow-distributed pores, whereas the CAC with a wider pore distribution (up to 260 Å) resulted in the larger molecules competition for the active sites inside the porous structure. The adsorbents’ characterization also evidenced that CCC adsorbent presented a higher content of oxygenated groups in its surface which acted as potential active sites for the FFA molecules resulting in an enhanced adsorbent-adsorbate affinity. Lastly, the wastes generated in the adsorption experiments, were evaluated as to their calorific power resulting in a value of 31,933 J g-1, suggesting that it could be further used for energetic purposes, such as a solid fuel for boilers and furnaces to generate thermal energy. Based on these results, the CCC stands out as a promising material for RFO acidity removal.

Metal-Loaded Hollow Carbon Nanostructures as Nanoreactors: Microenvironment Effects and Prospects for Biomass Hydrogenation Applications

Over the past decade, metal-loaded hollow carbon nanostructures have been hailed as man-made nanoreactors (MHC nanoreactors) for extensive applications in dealing with energy and environmental issues due to their tailorable structure and electronic properties. Unlike conventional reports of hollow nanostructures with regard to synthetic methodologies or structural properties, a distinctive viewpoint on the microenvironment effects of MHC nanoreactors, i.e., metal–support interaction effect, reactant enrichment effect, molecular sieving effect, spatial compartmentation effect, and metal stabilization effect, is highlighted herein from this perspective. Furthermore, to emphasize the great potential of MHC nanoreactors in constructing a sustainable energy system to achieve a greener modern lifestyle, a review of the applications of MHC nanoreactors in the hydrogenation of typical biomass-derived molecules is presented. Additionally, prospects for broader biomass valorization applications of MHC nanoreactors, i.e., in situ hydrogen source-assisted hydrogenation, hydrogenation-involved cascade-type reactions, hydrogenation product distribution modulation, stability prolongation and recyclability enhancement, are forecasted. Toward the end of this paper, some feasible suggestions are further proposed for the enhancement of the catalytic reactivity, selectivity, stability, and sustainability of MHC nanoreactors in biomass hydrogenation, with a sincere expectation to contribute to the development of a highly efficient biomass refining system.

Integrated High Water Affinity and Size Exclusion Effect on Robust Cu-Based Metal–Organic Framework for Efficient Ethanol–Water Separation

Purification of ethanol from ethanol/water mixtures is important in industrial separation processes, especially for bioethanol fuel purification. In this work, a robust Cu-triazole metal–organic framework (Cu-Tria) with interconnected 3D supermicroporous channels containing tridentate bridging triazole ligands and rich open Cu2+ sites was identified to separate ethanol/water mixtures. By virtue of the size exclusion effect for ethanol and excellent water affinity, this MOF exhibits an ideal molecular sieving effect for ethanol/water separation. The DFT calculation results reveal that a water molecule can form coordination bonds with Cu2+ open metal sites, and the subsequent water molecules can form multiple hydrogen bonds with the coordinated water. Breakthrough experiments of water/ethanol mixtures (v/v = 5/95) show that complete water/ethanol separation can be achieved, and online mass spectrometry results reveal that the purity of the collected ethanol from the outlet is up to 99.99%. More importantly, this MOF displays excellent water, alkali, and acid stability, as well as outstanding recyclability for water/ethanol separation. Consequently, the Cu-Tria can be deemed as a potential porous adsorbent for the purification of bioethanol fuel.

ZIF-301 MOF/6FDA-DAM polyimide mixed-matrix membranes for CO2/CH4 separation

Compared with traditional separation methods, membrane-based technology shows advantages in energy efficiency for natural gas purification. To overcome the performance trade-off of conventional polymeric membranes, in this study, ZIF-301 MOF was employed as novel filler to fabricate 6FDA-DAM polyimide mixed-matrix membranes (MMMs) for CO2/CH4 separation. A solvent exchange approach was proposed to remove the high-boiling-point solvent used for fabricating the MMMs. The microstructures and physico-chemical properties of the ZIF-301 fillers and ZIF-301/6FDA-DAM MMMs were characterized by SEM, EDX, XRD, IR, TGA, DSC and high-pressure sorption isotherms. The CO2/CH4 transport properties through the MMMs were evaluated by permeation measurement at various feed pressures and analyzed by solution-diffusion model. The results showed that the incorporation of ZIF-301 into 6FDA-DAM enhanced both the CO2 permeability and CO2/CH4 selectivity, attributing to the preferential CO2 sorption and aperture molecular sieving effect of the ZIF-301 filler. The MMM with optimal ZIF-301 loading of 20 wt% exhibited CO2 permeability of 891 barrer and CO2/CH4 of 29.3 that surpassed the 2008 Robeson upper-bound, suggesting that ZIF-301 based membrane could be a potential candidate for natural gas purification.