The Effects of Functional Groups and Missing Linkers on the Adsorption Capacity of Aromatic Hydrocarbons in UiO-66 Thin Films

Abstract

The adsorption of benzene, toluene, ethylbenzene, and xylene isomers, also known as BTEX, from the gas phase into porous thin films of the metal–organic framework UiO-66-X, where X = H, NH2, and NO2, was measured to quantify adsorption capacity. The thin films were grown by a vapor-conversion method onto Au-coated quartz microbalance crystals. The MOF thin films were characterized by IR and Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy. The thin films were activated by heating under high vacuum and exposed to each gas to calculate the Henry’s constant. The results demonstrate that the functional groups in the organic linker and missing-linkers both play important roles in the adsorption capacity. Several trends can be observed in the data. First, all the compounds in the BTEX family have lower Henry’s constants in the UiO-66-H films compared to the UiO-66-NH2 and UiO-66-NO2 films, which can largely be attributed to the absence of a functional group on the linker. Second, at 25 °C, the Henry’s constants for all the BTEX compounds in UiO-66-NO2 films are larger than UiO-66-NH2 films. Third, the role of missing linkers is addressed by comparing the measured adsorption capacity to ideal pore filling. The results show that the UiO-66-H films are the most defect-free and the UiO-66-NO2 films have the most missing linker defects.

Controlling the Adsorption and Release of Ocular Drugs in Metal–Organic Frameworks: Effect of Polar Functional Groups

“…At this point, it is interested to highlight that, in spite of the proper crystallinity, functionalization gives rise to significant changes in the I (111) / I (002) ratio. Previous results described in the literature have shown that these variations are a clear indication of the presence of structural defects in UiO-66 samples. , More specifically, these changes are consistent with the presence of missing linker defects (the 002 reflection is systematically more intense when linkers are missing). The I (111) / I (002) ratio changes from 2.8 in the nonfunctionalized UiO-66 down to 1.4 for UiO-66-NH 2 and 1.2 for UiO-66-NO 2 (see the inset in Figure ).…”

“…At this point, it is interesting to highlight that whereas the nonfunctionalized UiO-66 loses more than 60% of its weight at 800 °C, functionalized derivatives lose less than 55% of the original weight. The higher residual weight at 800 °C in the functionalized MOFs could be another indication of the structural defects (missing linkers) anticipated by the XRD measurements. ,, From the TG analysis, a higher number of defects can be inferred for samples UiO-66-NH 2 (after removing humidity), although UiO-66-NO 2 has a larger structural instability.…”

“…Previous results described in the literature have shown that these variations are a clear indication of the presence of structural defects in UiO-66 samples. 32,35 2.8 in the nonfunctionalized UiO-66 down to 1.4 for UiO-66-NH 2 and 1.2 for UiO-66-NO 2 (see the inset in Figure 1). The morphology and particle size of synthesized nanomaterials are essential parameters to take into consideration for their use in biomedical applications.…”

Vapor-Phase Adsorption of Xylene Isomers and Ethylbenzene in MOF-74 Thin Films

“…The adsorption capacities is larger for the C 8 isomers within Ni-MOF-74 and Co-MOF-74 thin films than for UiO-66 thin films. 64 Presumably, this is due to the larger pores and presence of channels lined by open metal coordination sites in the MOF-74 framework that promotes Lewis acid−base πcomplexation.…”

Performance enhancement strategies for surface plasmon resonance sensors in direct glucose detection using pristine and modified UiO-66: effects of morphology, immobilization technique, and signal amplification

“…Furthermore, the peak increase at 1613 cm À1 can be indexed to the C-C bond stretching mode of the linker aromatic ring. 80 Several other peaks also experience slight enhancements, indicating the appearance of functional groups belonging to glucose. The peaks at 200-500 cm À1 represent the main skeletal vibrational motions of glucose, which correspond to d (C-C-C), d (C-C-O), and s (C-C).…”