A europium metal–organic framework for dual Fe³⁺ ion and pH sensing
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(Published version)
Date
2022
Authors
Rozenberga, L.
Skinner, W.
Lancaster, D.G.
Bloch, W.M.
Blencowe, A.
Krasowska, M.
Beattie, D.A.
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Scientific Reports, 2022; 12(1):11982-1-11982-12
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Linda Rozenberga, William Skinner, DavidG. Lancaster, Witold M. Bloch, Anton Blencowe, M. Krasowska, David A. Beattie
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Abstract
Metal-organic frameworks (MOFs) with ratiometric sensing properties are desirable for many applications due to their intrinsic self-calibration. We report the re-assessment of the sensing properties of a MOF, originally reported as containing europium(III) and 2-hydroxyterephtalic acid, and having fluorescent ratiometric iron(III) sensing properties. Synchrotron single-crystal X-ray diffraction and proton nuclear magnetic resonance (<sup>1</sup>H NMR) spectroscopy revealed that the MOF is composed of 2-methoxyterephthalate, not 2-hydroxyterephthalate as originally reported. We found that the MOF exhibits a sensor turn-off response towards Fe<sup>3+</sup> ion concentrations in the range 0.5-3.7 ppm (band 425 nm), and a turn-on response towards a decrease of pH from 5.4 to 3.0 (band 375 nm), both resulting from the addition of acidic Fe<sup>3+</sup> salt solution to a MOF suspension. Thus, the ratiometric sensing properties and the originally proposed mechanism no longer apply; our work reveals a dynamic quenching mechanism for the fluorescence turn-off response due to the presence of Fe<sup>3+</sup> ions, and a ligand protonation mechanism for the turn-on response to a decrease in pH. Our work highlights the importance of a thorough investigation of the structure of any newly synthesized MOF, and, in the case of potential sensors, their selectivity and any environmental effects on their sensing behavior.
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© The Author(s) 2022 Open Access Tis article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. Te images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.