Fluorescence of A100 MOF and Adsorption of Water, Indole, and Naphthalene on A100 by the Spectroscopic, Kinetic, and DFT Studies

Abstract

Metal−organic frameworks (MOFs) are promising materials for adsorption and separations. It is important to understand the details of chemical bonding between the adsorbate and structural units in the MOFs. In A100 MOF, the near-UV− visible fluorescence is found to be the intralinker fluorescence. Naphthalene and indole form the stoichiometric "host-guest" π−π adsorption complexes with A100 that contain one adsorbate molecule per two BDC linkers, and adsorption of indole causes a strong quenching of the intralinker fluorescence. The excitation wavelength dependent steadystate fluorescence spectra, the nanosecond time-resolved fluorescence spectra, and DFT calculations indicate the strong π−π interactions between adsorbed indole and naphthalene and aromatic ring of the BDC linker, as well as hydrogen bonding between adsorbed indole and COO group of the linker. Activated A100 adsorbs up to four water molecules per BDC linker. Kinetic study of adsorption of naphthalene and indole from n-alkane on hydrated A100 yields the preferential adsorption of indole as determined by the in-situ time-dependent fluorescence spectroscopy and complementary ex-situ UV−vis absorption spectroscopy.

Insights into the water adsorption mechanism in the chemically stable zirconium-based MOF DUT-67 – a prospective material for adsorption-driven heat transformations

“…In addition, analysis of the temperature prole allowed us to estimate the kinetics of water adsorption, which is rarely explored. 55 Analysis of adsorption peaks shows that under the current experimental conditions, the temperature curve reaches a base temperature aer 1400 s, while complete desorption of water from the pores occurs aer 2100 s of purging with dry nitrogen gas (Fig. 6a).…”

“…6a). 55 Multiple exposure of the adsorbent to a working uid during the lifetime of the device requires an enhanced chemical stability of the material. In previous studies, DUT-67(Zr), synthesized in DMF, was claimed as a MOF with reduced chemical stability against water and acids, 24 and therefore, we performed a comprehensive stability study on the MOF, synthesized using a "green" synthesis procedure, under normal working conditions, but also under harsh conditions, which are rather not typical for adsorption heat pumps.…”

Interactions of Multiple Water Molecules with MIL-53(Al) and Understanding the Mechanism of Breathing: The DFT Study

“…Modeling MIL-53(Al) Clusters with Three Water Molecules. In the recent experimental study, 16 we showed that Basolite A100 with framework of MIL-53(Al) adsorbs water…”

“…Recently, we successfully used the DFT with the M06-2X functional to calculate the energies and geometry of binding sites of naphthalene and indole to the MIL-53(Al) cluster. 16 In this study, we build a discrete model of the MIL-53(Al) cavity, where the large-pore and narrow-pore forms and the transition between the two can be modeled as a function of temperature. We describe the systematic DFT computations with the M06-2X functional and 6-31G(d) and LANL2DZ basis sets, as well as computations at the B3LYP-D3BJ/6-31G(d,p)//M06-2X/6-31G(d) level to investigate the MIL-53(Al) cluster with three water molecules.…”

“…Recently, we successfully used the DFT with the M06-2X functional to calculate the energies and geometry of binding sites of naphthalene and indole to the MIL-53­(Al) cluster . In this study, we build a discrete model of the MIL-53­(Al) cavity, where the large-pore and narrow-pore forms and the transition between the two can be modeled as a function of temperature.…”