Metal-organic frameworks (MOFs) are being intensively explored as filler materials for polymeric proton exchange membranes (PEMs) due to their potentials for the systematic design and modification of proton-conducting properties. S-UiO-66, a stable MOF with functional groups of -SOH in its ligands, was selected here to prepare S-UiO-66@graphene oxide (GO) hybrid nanosheets via a facile in situ growth procedure, and then a series of composite PEMs were prepared by hybridizing S-UiO-66@GO and sulfonated poly(ether ether ketone) (SPEEK). The resultant hybrid nanosheets not only possessed abundant -SOH groups derived from the ligands of S-UiO-66 but also yielded a uniform dispersion of S-UiO-66 onto GO nanosheets, thus effectively eliminating the agglomeration of S-UiO-66 in the membrane matrix. Thanks to the well-tailored chemical composition and nanostructure of S-UiO-66@GO, the as-prepared SPEEK/S-UiO-66@GO composite PEMs present a significant increase in their proton conductivity under various conditions. In particular, the proton conductivity of the SPEEK/S-UiO-66@GO-10 membrane was up to 0.268 S·cm and 16.57 mS·cm at 70 °C-95% RH and 100 °C-40% RH (2.6 and 6.0 times that of recast SPEEK under the same condition), respectively. Moreover, the mechanical property of composite membranes was substantially strengthened and the methanol penetration was well-suppressed. Our investigation indicates the great potential of S-UiO-66@GO in fabricating composite PEMs and also reveals that the high proton conductivity of MOFs can be fully utilized by means of MOF/polymer composite membranes.

Metal-organic framework (MOF)/polymer composite proton exchange membranes (PEMs) are being intensively investigated due to their potentials for the systematic design of proton-conducting properties. However, the development of MOF/polymer composite PEMs possessing high selectivity remains exceedingly desirable and challenging for practical application. Herein, two-dimensional (2D) zeolitic imidazolate framework (ZIF-8)/carbon nanotube (CNT) hybrid cross-linked networks (ZCN) were synthesized via the rational design of the physical form of ZIF-8, and then a series of composite PEMs were prepared by hybridizing ZCN with sulfonated poly(ether ether ketone) (SPEEK) matrix. The effect of the incorporation of zero-dimensional (0D) raw ZIF-8 nanoparticles and 2D ZCN on the proton conduction and methanol permeability of the composite membranes was systemically studied. Benefiting from the morphological and compositional advantages of ZCN, the SPEEK/ZCN composite membranes displayed a significant enhancement in proton conductivity under various conditions. In particular, the proton conductivity of SPEEK/ZCN-2.5 membrane was up to 50.24 mS cm at 120 °C-30% RH, which was 11.2 times that of the recast SPEEK membrane (4.50 mS cm) and 2.1 times that of SPEEK/ZIF membrane (24.1 mS cm) under the same condition. Meanwhile, the methanol permeability of the SPEEK/ZCN composite membranes was greatly reduced. Therefore, novel MOF/polymer composite PEMs with high selectivity were obtained. Our investigation results reveal that the proton conductivity and methanol permeability of the MOF/polymer composite membranes can be effectively tailored via creating more elaborate superstructures of MOFs rather than altering the chemical component. This effective strategy may provide a useful guideline to integrate with other interesting MOFs to design MOF/polymer composite membranes.

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Metal-organic frameworks (MOFs) are being intensively explored as filler materials for polymeric membranes primarily due to their high polymer affinity, large pore volumes, and alterable pore functionalities, but the development of MOF-based ultrafiltration (UF) membranes for water treatment lags behind. Herein, poly(sulfobetaine methacrylate) (PSBMA)-functionalized MOF UiO-66-PSBMA was developed, and incorporated into polysulfone (PSf) casting solution to fabricate novel hybrid UF membranes via phase-inversion method. The resultant UiO-66-PSBMA/PSf membrane exhibited significantly improved water flux (up to 602 L m h), which was 2.5 times that of the pristine PSf membrane (240 L m h) and 2 times that of UiO-66-NH/PSf membrane (294 L m h), whereas the rejection of UiO-66-PSBMA/PSf membrane was still maintained at a high level. Moreover, UiO-66-PSBMA/PSf membrane exhibited improved antifouling performance. The improvement of membrane performances could be attributed to the well-tailored properties of UiO-66-PSBMA. On one hand, the excellent dispersion and compatibility of UiO-66-PSBMA ensured the formation of a uniform structure with few defects. On the other hand, the superhydrophilicity of UiO-66-PSBMA could accelerate the exchange rate between solvent and nonsolvent, resulting in a more hydrophilic surface and a more porous structure. Besides, UiO-66-PSBMA nanoparticles in the thin layer provided additional flow paths for water permeation through their hydrophilic porous structure as well as the tiny interspace between PSf matrix. This study indicates the great application potential of UiO-66-PSBMA in fabricating hybrid UF membranes and provides a useful guideline to integrate other modified hydrophilic MOFs to design UF membranes for water treatment.

Tannic acid-Fe functionalized multiwall carbon nanotubes (TA-MWNTs) were successfully obtained through a simple and rapid procedure by forming a stable TA-Fe complex coating on the MWNT surface. Hydrophilic TA-MWNTs can disperse well in the aqueous phase and help the formation of a polyamide (PA) thin film nanocomposite (TFN) membrane through interfacial polymerization. TA-MWNT concentration in the aqueous phase was adjusted to achieve the optimal water flux and salt rejection of the TFN membrane. The results reveal that, when 0.03% of TA-MWNTs are added, the optimized water flux of the TFN membrane reaches up to 31.4 L/mh, 2.36 times of that of the neat PA membrane, along with a well-maintained NaSO rejection. Furthermore, the as-prepared TFN membrane shows improved antifouling ability and good long-term stability. A significantly enhanced chlorine resistant capability of the TFN membrane is also presented, which can be ascribed to the radical capturing capability of phenol groups of TA as well as more oxidation-stable polyester bonds produced by the interaction between the phenol groups of TA and the acyl chloride groups of TMC. Assisted by TA-MWNTs, the TFN membrane is found to have prominent advantages over PA and MWNTs/PA TFN membranes.