Improving the ion sieving performance of MOF polycrystalline membranes based on interface modification

Metal-organic framework (MOF) membranes exhibit promising potential for high-precision molecule and ion sieving due to their uniform and tunable pore structures. Nevertheless, it remains a challenge to address interfacial compatibility to obtain a high-performance MOF membrane. This is because there is a weak interfacial interaction between the MOF and the substrate, which leads to non-selective areas. This work presents an interface-coating method to facilitate dense nucleation and rapid growth of MOF crystals on the substrate towards reinforcing interaction and eliminating defects. Polydopamine (PDA) and β-cyclodextrin (β-CD) were co-assembled on polyvinylidene fluoride (PVDF) substrates to modify the surface chemistry and enhance interfacial compatibility, thereby facilitating the dense growth of ZIF-8. The ZIF-8/PVDF membranes demonstrated an excellent K+ permeance of 0.33 mol m-2 h-1 and a K+/Mg2+ selectivity of 30.16. The simulation results indicate that the channel of Mg2+ through ZIF-8 must overcome a greater transport energy barrier than that of K+, resulting in a higher selectivity of K+/Mg2+.

Insights into the MOF-Based Classic Configuration for the Differences in Effective Dye Adsorption, Magnetic Properties, and Computational Analyses

Two 3D/2D anionic metal-organic frameworks (MOFs), [Cu(HL)]n (1) and [Mn3(L)2(DMF)4]n (2) (DMF = N,N-dimethylformamide), were synthesized by the solvothermal reaction of metal salts and 5'-(4-carboxyphenyl)-2',4',6'-triethyl-[1,1':3',1″-terphenyl]-4,4″-dicarboxylic acid (H3L). Single-crystal X-ray diffraction analyses revealed that complex 1 shows three-dimensional (3D) frameworks with a (3,6)-connected 3-fold interpenetrated topology with the Schläfli symbols of {4.62}2{42.610.83}, whereas the topology of the two-dimensional (2D) architecture can be defined as 2-fold stacked layers with the Schläfli symbols of {43}2{46.66.83} for complex 2. In addition, density functional theory calculations, together with UV-vis adsorption spectroscopy, zeta potential, effective aperture size analysis, TEM, and SEM, were also performed to determine the accurate adsorption sites and significant differences in dye adsorption for complexes 1 and 2. Interestingly, UV-vis studies confirm that Mn-MOF displays remarkable adsorption efficiency for cationic rhodamine B, methylene blue, malachite green, and methyl green, and the removal rate reached 95.2, 95.0, 87.0, and 78.0%, respectively, while almost no adsorption capacity was detected for anionic cresol red and methyl orange. However, Cu-MOF failed to efficiently adsorb any selected dyes. Moreover, the magnetic properties were also investigated through experimental and theoretical calculations in detail, which revealed the weak and stronger antiferromagnetic interactions that occurred between Cu(II) and Mn(II) centers, respectively. Finally, this work provides the profound mechanisms for magnetism and dye adsorption.

A series of novel Cu-based MOFs: syntheses, structural diversity, catalytic properties and mimic peroxidase activity for colorimetric detection of H2O2

Three MOFs with three different types of Cu clusters have been synthesized. MOFs 1–3 efficiently catalyze the oxidation of cycloalkanes under mild conditions. Besides, MOFs 1–3 exhibited high peroxidase-like activity and could be applied for colorimetric detection of H2O2.