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Improving the Cd2+ detection capability of a new anionic rare earth metal–organic framework based on a [RE63-OH)8]10+ secondary building unit: an ion-exchange approach towards more efficient sensors

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Abstract

The synthesis and characterization of a new family of rare earth (RE) MOFs based on a hexanuclear (RE3+)6 secondary building unit (SBU) and the angular dicarboxylic ligand 4,4′-oxybisbenzoic acid (H2OBA) with the formula {((CH3)2NH2)2[RE63-OH)8(OBA)6]} (((CH3)2NH2)2(1)(RE); RE: Y, Tb, Dy, Ho) is reported. Gas sorption studies indicated a moderate Langmuir area of 377 m2 g−1. Photoluminescence studies in the visible region of the ((CH3)2NH2)2(1)(Y) doped with 5% Eu3+ or 5% Tb3+ revealed the presence of the characteristic emission bands for these RE3+ ions. Cd2+ sensing studies of ((CH3)2NH2)2(1)(Y) doped with Eu3+ however, indicated slow exchange kinetics prohibiting the use of this material for sensing applications. Successful counter ion exchange of the as synthesized compound with Na+ and Mg2+ led to the isolation of Na2(1)(Y) and Mg(1)(Y). Interestingly, the exchanged analogue Na2(1)(Y) doped with 5% Eu3+ exhibited fast Cd2+ sorption kinetics and was proven to be a greatly improved sensor for this metal ion both in terms of kinetics and sensitivity. Batch Cd2+ sorption experiments at room temperature of Na2(1)(Y) revealed a maximum sorption capacity of 63 ± 2 mg g−1 corresponding to the insertion of ∼1.25 equivalents Cd2+ per (Y3+)6 SBU. Overall this work demonstrates the post-synthetic ion exchange of the bulky ((CH3)2NH2)+ counter-ions by inorganic cations as an excellent method for the improvement of the sensing capability of RE-based anionic MOFs.

Graphical abstract: Improving the Cd2+ detection capability of a new anionic rare earth metal–organic framework based on a [RE6(μ3-OH)8]10+ secondary building unit: an ion-exchange approach towards more efficient sensors

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Article information


Submitted
16 Dec 2019
Accepted
23 Apr 2020
First published
23 Apr 2020

Mol. Syst. Des. Eng., 2020, Advance Article
Article type
Paper

Improving the Cd2+ detection capability of a new anionic rare earth metal–organic framework based on a [RE63-OH)8]10+ secondary building unit: an ion-exchange approach towards more efficient sensors

N. Panagiotou, K. Evangelou, A. Psalti, N. Varnava, G. K. Angeli, P. N. Trikalitis, J. C. Plakatouras, T. Lazarides and A. J. Tasiopoulos, Mol. Syst. Des. Eng., 2020, Advance Article , DOI: 10.1039/C9ME00176J

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