Water can easily be contaminated by many dye molecules because of its high solubility with dense color. Dye‐contaminated water requires purification via the adsorptive removal of dye molecules, employing various porous materials. To increase the removal efficiency and selectivity, demands for developing new metal–organic frameworks (MOFs) for dye removal continue to increase. Herein, we present a study on the dye‐adsorption properties of MOFs based on their structures and pore sizes. The effects of dye molecule charge and size were also investigated. Three different MOFs (Universitetet i Oslo; UiO‐66, UiO‐67, Materials of Institute Lavoisier; MIL‐100 [Fe]) and four dye molecules (Methylene Blue, Rhodamine B, Tropaeolin O, and Amaranth) were employed. The results suggest that the surface properties and framework structure of the MOFs affect dye adsorption capacity and kinetics, as characterized by UV–Vis spectroscopy and adsorption kinetics analysis. These results provide opportunities for the development of MOFs for dye removal from aqueous solution.
To date, numerous materials, including various quantum dots and dyes, have been widely used for the ultrasensitive detection of toxic metal ions and as security inks to hide information. Nevertheless, because of the poor dispersibility of solid-state materials, security inks based on such materials have been scarcely reported. Herein, a highly dispersible and water-stable metal−organic framework (MOF; NH 2 -MIL-125(Ti)) is used as an invisible security ink for data coding, encryption, and decryption via its "turn-on/off" switching by treatment with ethylenediaminetetraacetic acid and Pb 2+ . Notably, the concentration of the Pb 2+ solution used to turn off the fluorescence of the MOF was lower than the limit established by several regulatory agencies for drinking water. The MOF was also used as a sensitive probe for the rapid and ultrasensitive detection of Pb 2+ ions at a concentration of 7.7 pM which is one of the lowest detection limits reported for such a system. The MOF also shows high selectivity for various transition metal ions that can competitively bound on the ligand. Analyses using Fourier transform infrared spectroscopy,X-ray photoelectron, and UV photoemission spectroscopy clearly revealed the roles of the surface functional groups and the mechanism of the "on/off" switching behavior of the MOF.
Zr-based metal-organic frameworks (MOFs) were modified with pendant tetrazole ligands for proton conductivity studies. Although tetrazolate ligands coordinated to metal cations have been widely utilized to construct MOFs or porous coordination polymers, to date, the use of uncoordinated tetrazole groups in MOFs has been limited. In this study, a benzene-1,4-dicarboxylic acid with pendant tetrazole groups (BDC-N 4 ) was synthesized and used to prepare a Zr-based UiO-66 MOF using a mixed-ligand strategy. The tetrazolefunctionalized UiO-66-N 4 was compared to MOFs containing other acidic functional groups (hydroxyl, carboxylic acid, and sulfonic acid) with respect to their proton conductivities and acidities (calculated pK a ). Interestingly, UiO-66-N 4 showed a significant decrease in the activation energy with increase in the amount of added tetrazole groups, suggesting the Grotthuss proton conduction mechanism for uncoordinated tetrazole-containing MOFs.
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