•Interfacial modification was used to solve the compatibility issue in MMMs.•MOF fillers were coated by a thin and uniform PD layer to improve compatibility.•The record water flux and selectivity were obtained for dehydration of EG.In order to solve the issue of incompatibility between metal-organic frameworks (MOFs) and polymer matrix, mixed-matrix membranes (MMMs) on the basis of a hydrophilic polymer poly(vinyl alcohol) (PVA) and a MOF with hydrophilic sulfonic acid group (SO3H-MIL-101-Cr) coated by a thin and uniform polydopamine (PD) layer were prepared for separation of organic solvent from aqueous solutions by taking ethylene glycol (EG) as an example. The PD layer can control the thickness effectively on the surface of SO3H-MIL-101-Cr through a self-polymerization of dopamine and enhance the compatibility between MOF and PVA due to the formation of hydrogen bond between the abundant amine groups in PD and the hydroxyl in PVA matrix. As a result, the prepared SO3H-MIL-101-Cr@PD-PVA MMM exhibits a largely improved water permeability of 7.05×10−5 g m−1 h−1 kPa−1 (the water flux is 540 g m−2 h−1) and the selectivity is as high as 68.1 (the separation factor is 2864) for EG aqueous solution (water content: 10 wt%) separation at 343 K. Compared with those in pure PVA membrane, the water permeability and selectivity were increased by 483% and 567% respectively. To the best of our knowledge, this separation performance is superior to those in all of the reported membranes so far. Therefore, this interfacial modification of MOF fillers may be an effective way to enhance the PV separation performance of MMMs, which can be conveniently extended to prepare other kinds of membranes with advanced properties.Download high-res image (296KB)Download full-size image

•The anchored UiO-66 on GO layers can avoid the layer stacking of GO.•UiO-66@GO composite combined the unique properties of UiO-66 and GO.•UiO-66@GO/PES membranes show high water purification performance.•UiO-66@GO/PES membranes exhibit impressive antifouling performance.Developing advanced filtration membrane with high flux, good solute rejection and excellent antifouling performance is highly demanded. Hydrophilic graphene oxide (GO) nanosheets are attractive fillers for the preparation of composite membranes for water purification. However, strategies that can fully exploit the advantages and remedy the drawbacks of GO nanosheets are still needed. In this work, UiO-66 was specifically anchored to the GO layers as a porous modifier. The incorporated UiO-66 can effectively prevent the GO layers from stacking and introduce unique properties into the composite (UiO-66@GO). A series of novel composite membranes were prepared with the obtained UiO-66@GO composite and polyethersulfone (PES). As a result, the prepared composite membranes (UiO-66@GO/PES) exhibit high hydrophilicity and water purification performance. Especially, the water flux of composite membrane with 3.0 wt% UiO-66@GO loading shows an increase of 351% and 78% respectively in comparison with that of the PES and GO/PES membranes. Moreover, the UiO-66@GO/PES membranes exhibit good solute rejection and impressive antifouling performance, which is appealing for the application of industrial water purification.Download high-res image (228KB)Download full-size image

Graphene oxide (GO) membranes assembled by single-atom thick GO nanosheets have displayed huge potential application both in gas and liquid separation processes due to its facile and large-scale preparation resulting from various functional groups, such as hydroxyl, carboxyl, and epoxide groups. Taking advantage of these characters, GO membranes intercalated by superhydrophilic metal–organic frameworks (MOFs) as strengthening separation fillers were prepared on modified polyacrylonitrile (PAN) support by a novel pressure-assisted self-assembly (PASA) filtration technique instead of traditional vacuum filtration method for the first time. The synthesized MOF@GO membranes were characterized with several spectroscopic techniques including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS), as well as scanning electron microscopy (SEM). Compared with GO membrane, these MOF@GO membranes combine the unique properties of MOF and GO and thus have significant enhancements of pervaporation (PV) permeation flux and separation factor simultaneously for ethyl acetate/water mixtures (98/2, w/w) through the PV process, which are also superior to the reported other kinds of membranes. Especially, for MOF@GO-0.3 membrane (corresponding MOF loading: 23.08 wt %), the increments are 159% and 244%, respectively, at 303 K, and the permeate water content can reach as high as 99.5 wt % (corresponding separation factor, 9751) with a high permeation flux of 2423 g m–2 h–1. Moreover, the procedures of both the synthesis of MOF and membranes preparation are environmentally friendly that only water was used as solvent. Such a nanosized MOF-intercalating approach may be also extended to other laminated membranes, providing valuable insights in designing and developing of advanced membranes for effective separation of aqueous organic solution through nanostructure manipulation of the nanomaterials.Keywords: dehydration; graphene oxide; membrane separations; metal−organic frameworks; pervaporation;

Mixed-matrix membranes (MMMs) have exhibited advantages in membrane-based gas separation in recent years, however, there is still intensive demand for the development of a proper method to design effective fillers to further enhance the gas separation performance of MMMs. In this work, a nanoporous material to selectively facilitate CO2 transport was proposed through the loading of a task-specific ionic liquid (TSIL) into a metal–organic framework (MOF). [C3NH2bim][Tf2N] and NH2-MIL-101(Cr) were selected as a demonstrative TSIL and MOF, respectively. The amine-containing TSIL worked as a selective CO2 transport carrier, which can be beneficial for the improvement of CO2 permeability and CO2/N2 selectivity. Simultaneously, NH2-MIL-101(Cr) is an appropriate porous host material that can control the good dispersion of TSIL and can effectively expose more active adsorption sites of the TSIL. Meanwhile, the amine-containing porous MOF is helpful for rapid CO2 transport and further increases the CO2 permeability. We further incorporated the porous composite into PIM-1 to fabricate MMMs with different loadings. The prepared TSIL@NH2-MIL-101(Cr)/PIM-1 membrane exhibits largely improved gas permeability and selectivity for CO2/N2 separation, with CO2 permeation values of 2979 Barrer and a CO2/N2 separation selectivity of 37 at 5 wt% loading. Compared with NH2-MIL-101(Cr)/PIM-1 and PIM-1 membranes, the CO2/N2 separation selectivity was increased by 116% and 119%, respectively, at the same loading.

•Eu3+ was successfully incorporated into two water-stable UiO-MOFs.•The specific binding site between two free –COOH is the key of immobilization of Cu2+.•Eu3+@UiO-66-2COOH proves to be a highly selective and sensitive sensor for Cu2+.•Eu3+@UiO-66-2COOH is a fast-response fluorescence probe.Eu3+ was successfully incorporated into two isostructural MOFs with different distributions of carboxyl groups, UiO-66-COOH and UiO-66-2COOH. Utilizing the specific binding site between two free carboxyl groups for efficiently capturing Cu2+, Eu3+@UiO-66-2COOH shows highly selective and sensitive luminescence quenching effect for Cu2+ in aqueous solution, while Eu3+@UiO-66-COOH with single free carboxyl group on the ligand possesses relatively poor performance. Meanwhile, such immobilization behavior of Cu2+ makes Eu3+@UiO-66-2COOH remarkably sensitive for Cu2+ at nano-molar concentration, superior to the majority of reported MOF sensors.

In this work, ZIF-9 membranes were successfully synthesized using temperature-switching synthesis method. Compared with the conventional hydrothermal synthesis at a constant temperature, this method could promote the growth of crystals on the support. Scanning electron microscopy (SEM) demonstrated that the obtained membranes had continuous and well-intergrown layer with a denser surface and better crystal size uniformity. As a result, gas separation performance was enhanced. It is also found that the properties of membrane can remain almost stable at a relatively broad range of operating temperature and transmembrane pressure drop, which is beneficial for the practical operation of membrane in the separation process. More importantly, this synthesis strategy can be conveniently extended to the preparation of other MOF membranes with improved performance.

To enhance dispersion and adhesion, functionalized porous metal–organic polyhedrons were incorporated into polysulfone as a filler to obtain mixed-matrix membranes, which exhibit largely improved gas permeability and separation factor simultaneously for CO2–CH4 separation.

A ZIF-9 membrane covered by ionic liquid (ILs) functionalized carbon nanotubes (CNTs) was grown using heat treatment of the layer-by-layer deposition method. This hybrid membrane exhibits a high selectivity for H2/CO2 due to the cooperative effect of ZIFs, CNTs and ILs.

An ultrastable metal–organic framework can remain intact in pH = 0 to 12 solutions and boiling water, attributed to the steric hindrance and electronic effect of methyl groups as well as strong Zr–O bonds. This MOF exhibits good adsorption and sensing performance for Hg0 vapor because of the presence of thiophene.

Water stable Zr-based metal–organic frameworks (MOFs) with different functional groups were used for selective removal of Cu2+ over Ni2+ from aqueous solution. Due to the unique chelation effect of two carboxyl groups on the adjacent organic ligand as well as the Jahn–Teller effect, UiO-66(Zr)–2COOH exhibits the highest selectivity (up to about 27) for Cu2+/Ni2+ in aqueous solution among the reported adsorbents as far as we know. In addition, the removal process is fast with less than 60 min for equilibration, and the stability and regenerability are good. These results may be helpful not only for the efficient treatment of wastewater containing heavy transition metal ions, but also for metal enrichment and recycling.

Metal–organic frameworks (MOFs) have exhibited promising applications in gas and liquid separation. As a subclass of MOFs, zeolitic imidazolate frameworks (ZIFs) are attracting more and more interest because of their unique thermal and chemical stability. One of the representative ZIFs, ZIF-7, has super-hydrophobic pores, making it a perfect filler in polymer membranes for recovering acetone from fermentation broths. In this study, mixed matrix membranes (MMMs) based on ZIF-7 and polydimethylsiloxane (PDMS) were prepared, which display improved acetone–water total flux and separation factors simultaneously compared with a pure PDMS membrane. The separation factor can reach up to 39.1 with a high flux of 1236.8 g m−2 h−1 at 333 K, which is the highest value among those reported up to now to the best of our knowledge.

•Stability of MOFs in fluoride solution is controlled by the cooperative effects.•MOFs are promising adsorbents for defluoridation.•UiO-66(Zr) has a high adsorption capacity of 41.36 mg g−1.•Increasing the number of –OH group may improve the defluoridation performance..The stability of metal–organic frameworks (MOFs) in fluoride solutions was studied based on 11 water-stable MOFs (MIL-53(Fe, Cr, Al), MIL-68(Al), CAU-1, CAU-6, UiO-66(Zr, Hf) and ZIFs-7, -8, -9), and several factors were found to have large influence, such as the central metal activity, pore topology and coordination number. Furthermore, the defluoridation performance of UiO-66(Zr) was investigated comprehensively, which shows an adsorption capacity of 41.36 mg g−1 that is higher than most of the reported adsorbents. The initial pH of fluoride solution has little effect in neutral range, while shows a negative effect when pH >9.0; the adsorption data of UiO-66(Zr) fit well with the Langmuir model, and pseudo-second-order kinetic model was found to be suitable for depicting the F− adsorption process, and finally, it was observed that the extent of the effect of co-existing ions is largely ion-dependent. On the basis of the systemic study, this work suggests that increasing the number of –OH groups is an efficient strategy to improve the defluoridation performance of MOFs, and MOFs are promising adsorbents for defluoridation in waste water.

MIL-100(Fe) shows large adsorption uptakes for both MO and MB, while MIL-100(Cr) can selectively adsorb MB from a MO–MB mixture. This work demonstrates that MOFs are promising adsorbents for dye capture and highlights that framework metal ion replacement is an efficient way to tailor MOFs for different applications in liquid separation.

A ZIF-9-67 hybrid membrane on α-Al2O3 support was prepared using mixed-linker synthesis. The gas permeation and selectivity data demonstrate that this membrane may have potential applications for efficient CO2 capture from several industrial mixtures.

In this work, molecular simulations combined with experimental measurements were conducted to screen candidate metal–organic frameworks (MOFs) for aniline recovery from aqueous solution. The structure–property relationships that can correlate the recovery performance of the MOFs to their physicochemical features were analyzed. The results show that the interplay between the isosteric heat of adsorption of aniline and the free volume of the material is crucial to the aniline recovery capability of MOFs at low concentrations. In contrast, the aniline uptake at high concentrations is dominated by the material's free volume as usually expected. In addition, the requirements of the best MOF candidates for aniline recovery were suggested in this study. Based on the conclusions drawn from the screening route, several novel MOFs were further computationally designed, which possess high aniline uptake within the whole range of concentrations examined. The obtained information may be helpful for in-depth research to broaden the applications of MOFs in mixture separation under liquid phase conditions.

A new porous Zr-based MOF was synthesized by the solvothermal method using 2,6-naphthalenedicarboxylic acid (NDC) as the organic linker, and its luminescent performance and stability were investigated systematically. The material synthesized exhibits quite high chemical stability in addition to exceptional high thermal stability, better than the existing luminescent MOFs. The experiments combining with computations indicate that the electron transfer from inorganic moieties to organic moieties contributes to the luminescent behavior of the Zr-NDC MOF besides the NDC ligand. As far as we know, this is the first study of investigating the luminescent behaviors of such Zr-based MOFs. Moreover, the cycling measurements demonstrate an interesting prospect for the long-term reusability of this material. The results obtained in this work may provide useful information for the design of physicochemically stable MOFs with permanent porosity in sensing applications in the future.Graphical abstractHighlights► A new porous zirconium-based luminescent MOF with high physicochemical stability has been synthesized. ► The nitrogen adsorption data indicates that the specific pore volume is 0.67 cm3 g−1and the surface area is 1720 m2 g−1. ► The emission intensity is enhanced compared to that of the free ligand NDC. ► The luminescent behavior in different solvent solutions suggests the potential ability for sensing applications. ► The reusability is excellent.

In this work, the cooperative effect of temperature and linker functionality on CO2 capture in metal–organic frameworks (MOFs) was investigated using experimental measurements in combination with molecular simulations. To do this, four MOFs with identical topology but different functional groups on the linkers and three important CO2-containing industrial gas mixtures were adopted. The interplay between linker functionality and temperature was analyzed in terms of CO2 storage capacity, adsorption selectivity, working capacity of CO2 in temperature swing adsorption (TSA) processes, as well as sorbent selection parameter (Sssp). The results show that the effect of linker functionality on CO2 capture performance in the MOFs is strongly interconnected with temperature: up to moderate pressures, the lower the temperature, the larger the effect of the functional groups. Furthermore, the modification of a MOF by introducing more complex functional groups can not only improve the affinity of framework for CO2, but also reduce the free volume, and thus may contribute negatively to CO2 capture capability when the packing effect is obvious. Therefore, when we design a new MOF for a certain CO2 capture process operated at a certain temperature, the MOF should be designed to have maximized affinity for CO2 but with a negligible or small effect caused by the reduction of free volume at that temperature and the corresponding operating pressure.

In this work, a systematic computational study was performed to investigate the quantum sieving in nine typical metal–organic frameworks (MOFs) for the separation of hydrogen isotope mixtures. The results show that Cu(F-pymo)2 and CPL-1 exhibit exceptional selectivity that is higher than other MOFs as well as other nanoporous materials such as carbon nanotubes, slit-shaped graphites, and zeolites studied so far. A concept named “quantum effective pore size” (QEPS) was proposed in this work, which can incorporate the effects of quantum sieving, and thus is temperature-dependent. On the basis of the new pore size, good correlations between pore size and selectivity can be established for the MOFs considered; particularly, they can explain the different selectivity performance of the two MOFs with highest selectivity at 40 and 77 K. This work indicates that MOFs are suitable candidates for the separation of hydrogen isotopes through quantum sieving.

In this work, molecular simulations were performed to investigate the effect of trace amount of water on CO2 capture in natural gas upgrading process in a diverse collection of 25 metal–organic frameworks (MOFs). The results show that the interaction between water molecules and MOFs plays a crucial role: at the condition of weak interaction, water molecules move freely in the materials and show a negligible effect on the adsorption selectivity of CO2/CH4; while when the interaction is strong enough that water molecules are adsorbed to the preferential adsorption sites in MOFs, the effect can be significant, depending on the strength of water adsorption. In this case, the electrostatic interaction produced by the MOF framework is the dominant factor. This work provides a better understanding of the different behaviors of water effect on CO2 capture observed previously that may guide the future application of MOFs in industrial separations.

Highly diverse structures and pore sizes make metal–organic frameworks (MOFs) good candidates for the fabrication of gas separation membranes. The synthesis of continuous MOF membranes still remains a challenge. In this work, an integrated Cu-BTC membrane was successfully prepared on the novel potassium hexatitanate support for the first time by in situ solvothermal growth. This kind of support was found to be more suitable for the growth of Cu2+-containing MOF membranes than other traditional supports, such as a porous alumina support. The permeation results of Cu-BTC membranes obtained in this work show moderate separation selectivities of helium over other small gas molecules, including CO2, N2, and CH4. Compared to other MOF membranes, the Cu-BTC membrane exhibits higher ideal selectivity for helium under the condition of similar helium permeance, while it has higher helium permeance with similar ideal selectivity.

It is of great importance to establish a quantitative structure–property relationship model that can correlate the separation performance of MOFs to their physicochemical features. In complement to the existing studies that screened the separation performance of MOFs from the adsorption selectivity calculated at infinite dilution, this work aims to build a QSPR model that can account for the CO2/N2 mixture (15:85) selectivity of an extended series of MOFs with a very large chemical and topological diversity under industrial pressure condition. It was highlighted that the selectivity for this mixture under such conditions is dominated by the interplay of the difference of the isosteric heats of adsorption between the two gases and the porosity of the MOF adsorbents. On the basis of the interplay map of both factors that impact the adsorption selectivity, strategies were proposed to efficiently enhance the separation selectivity of MOFs for CO2 capture from flue gas. As a typical illustration, it thus leads us to tune a new MOF with outstanding separation performance that will orientate the synthesis effort to be deployed.

In this work, the effect of temperature on adsorption of CO2, CH4, CO, and N2 and separation of their binary mixtures in ZIF-8 were investigated using experimental measurements combining with molecular simulations. The results show that for pure gas adsorption, the effect of temperature is large when strong adsorption occurs, mainly due to the variation of the interaction energy between adsorbate molecules with temperature; while for gas mixtures, systems with large selectivity are more sensitive to temperature. In addition, this work shows that temperature influences the working capacity of CO2 in temperature swing adsorption (TSA) process with the interplay of pressure, which should be considered in the design of TSA process in practical applications.Highlights► A combined experimental and simulation study on effect of temperature on gas adsorption and separation in ZIF-8. ► For pure gases with large isosteric heat of adsorption, the effect of temperature is large. ► For gas mixtures, systems with large selectivity are more sensitive to temperature. ► Temperature influences the working capacity of CO2 with the interplay of pressure.

MIL-100(Fe) shows large adsorption uptakes for both MO and MB, while MIL-100(Cr) can selectively adsorb MB from a MO–MB mixture. This work demonstrates that MOFs are promising adsorbents for dye capture and highlights that framework metal ion replacement is an efficient way to tailor MOFs for different applications in liquid separation.

To enhance dispersion and adhesion, functionalized porous metal–organic polyhedrons were incorporated into polysulfone as a filler to obtain mixed-matrix membranes, which exhibit largely improved gas permeability and separation factor simultaneously for CO2–CH4 separation.

Mixed-matrix membranes (MMMs) have exhibited advantages in membrane-based gas separation in recent years, however, there is still intensive demand for the development of a proper method to design effective fillers to further enhance the gas separation performance of MMMs. In this work, a nanoporous material to selectively facilitate CO2 transport was proposed through the loading of a task-specific ionic liquid (TSIL) into a metal–organic framework (MOF). [C3NH2bim][Tf2N] and NH2-MIL-101(Cr) were selected as a demonstrative TSIL and MOF, respectively. The amine-containing TSIL worked as a selective CO2 transport carrier, which can be beneficial for the improvement of CO2 permeability and CO2/N2 selectivity. Simultaneously, NH2-MIL-101(Cr) is an appropriate porous host material that can control the good dispersion of TSIL and can effectively expose more active adsorption sites of the TSIL. Meanwhile, the amine-containing porous MOF is helpful for rapid CO2 transport and further increases the CO2 permeability. We further incorporated the porous composite into PIM-1 to fabricate MMMs with different loadings. The prepared TSIL@NH2-MIL-101(Cr)/PIM-1 membrane exhibits largely improved gas permeability and selectivity for CO2/N2 separation, with CO2 permeation values of 2979 Barrer and a CO2/N2 separation selectivity of 37 at 5 wt% loading. Compared with NH2-MIL-101(Cr)/PIM-1 and PIM-1 membranes, the CO2/N2 separation selectivity was increased by 116% and 119%, respectively, at the same loading.

In this work, the cooperative effect of temperature and linker functionality on CO2 capture in metal–organic frameworks (MOFs) was investigated using experimental measurements in combination with molecular simulations. To do this, four MOFs with identical topology but different functional groups on the linkers and three important CO2-containing industrial gas mixtures were adopted. The interplay between linker functionality and temperature was analyzed in terms of CO2 storage capacity, adsorption selectivity, working capacity of CO2 in temperature swing adsorption (TSA) processes, as well as sorbent selection parameter (Sssp). The results show that the effect of linker functionality on CO2 capture performance in the MOFs is strongly interconnected with temperature: up to moderate pressures, the lower the temperature, the larger the effect of the functional groups. Furthermore, the modification of a MOF by introducing more complex functional groups can not only improve the affinity of framework for CO2, but also reduce the free volume, and thus may contribute negatively to CO2 capture capability when the packing effect is obvious. Therefore, when we design a new MOF for a certain CO2 capture process operated at a certain temperature, the MOF should be designed to have maximized affinity for CO2 but with a negligible or small effect caused by the reduction of free volume at that temperature and the corresponding operating pressure.

A ZIF-9-67 hybrid membrane on α-Al2O3 support was prepared using mixed-linker synthesis. The gas permeation and selectivity data demonstrate that this membrane may have potential applications for efficient CO2 capture from several industrial mixtures.

A ZIF-9 membrane covered by ionic liquid (ILs) functionalized carbon nanotubes (CNTs) was grown using heat treatment of the layer-by-layer deposition method. This hybrid membrane exhibits a high selectivity for H2/CO2 due to the cooperative effect of ZIFs, CNTs and ILs.