Attracted by the exceptional structural rigidity and inherent porous structures of the Hf-based metal–organic frameworks (MOFs), we adopted a rapid synthesis approach to preparing three nanoscale MOFs, Hf-UiO-66 (1), Hf-UiO-66-(OH)2 (2), and Hf-UiO-66-NH2 (3), and systematically explored the water-assisted proton conductivities of the original ones and the post-modified products. Interestingly, the proton conductivities (σ) of all three MOFs exhibit significant temperature and humidity dependence. At 98% RH and 100 °C, their optimal σ values can reach up to 10–3 S·cm–1. Consequently, imidazole units are loaded into 1–3 to obtain related MOFs, Im@1, Im@2, and Im@3, and the σ values of the imidazole-loaded products are boosted to 10–2 S·cm–1. Note that these modifications not only do not change the frameworks of the pristine MOFs but also do not affect their high chemical and water stability. The proton-conductive mechanisms of these MOFs before and after modification have been thoroughly discussed based on structural analyses, N2 and H2O vapor adsorptions, and activation energy values. The excellent structural stability as well as the durability and stability of their proton conduction ability indicate that these MOFs can be used in the field of fuel cells and so on.

Recently, researchers have focused on preparing and studying proton exchange membranes. Metal−organic frameworks (MOFs) are candidates for composite membrane fillers due to their high crystallinity and structural characteristics, and Hf-based MOFs have attracted our attention with their high porosity and high stability. Therefore, in this study, Hf-based MOFs were doped into a costeffective chitosan matrix as fillers to fabricate composite films having excellent proton conductivity (σ). First, the nanoscale MOFs Hf-UiO-66-(OH) 2 (1) and Hf-UiO-66-NH 2 (2) were chemically modified by a ligand design strategy to obtain SA-1 and CBD-2 bearing free −COOH units. The proton conductivities of SA-1 and CBD-2 under optimal test conditions reached 1.23 × 10 −2 and 0.71 × 10 −2 S cm −1 . After that, we prepared composite membranes CS/SA-1 and CS/ CBD-2 by the casting method; tests revealed that the introduction of MOFs improved the stabilities and σ values of the membranes, and their best σ could reach above 10 −2 S cm −1 under 100 °C/98% RH. Further structural characterization and activation energy calculation revealed the conductive mechanism of the composite films. This investigation not only proposes a novel chemical modification method for optimizing the σ of MOFs but also promotes the development of MOF-doped composite membranes and provides a basis for future applications of MOFs in fuel cells.

Two new supramolecular polyoxmetalates were synthesized from 1, 4-bis[4-nitrile-pyridine)-N-methylene]phenyldibromide (L1) and 1, 2-bis[4-nitrile-pyridine)-N-methylene]phenyldibromide (L2) and (NH4)6Mo7–O24·4H2O under hydrothermal conditions. They are named p-[C20H18N2O4][Mo8O26] 0.5·H2O (1) and o-[C20H18N2O4][Mo8O26] ċ 0.5·H2O (2) respectively. The structures have been confirmed through single-crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectra. The adsorption test of compound 1 and compound 2 in organic dyes were carried out. It was found that compound 1 had a good adsorption effect on methylene blue (MB) and rhodamine B (RhB). The adsorption effect of compound 2 on MB is stronger than that of compound 1.