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Unraveling the origin of the “Turn-On” effect of Al-MIL-53-NO2 during H2S detection

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Abstract

Nitro-functionalized metal–organic frameworks (MOFs), such as Al-MIL-53-NO2, have been widely used in quantitative hydrogen sulfide (H2S) detection based on the “turn-on” effect, where fluorescence enhancements were observed upon contact with H2S. This was believed to be caused by the fact that the electron-withdrawing –NO2 groups in the initial non-luminescent MOFs were reduced to electron-donating –NH2 groups in the sensing process. However, since most H2S detection is conducted in a suspension system consisting of MOFs and solvents, it is still unclear whether these –NH2 groups are on MOFs or in the liquid. Using Al-MIL-53-NO2 as a model MOF, this work aims to answer this question. Specifically, the supernatant and undissolved particles separated from the Al-MIL-53-NO2 suspensions after being exposed to H2S were analyzed systematically. The results showed that it is the free BDC-NH2 (2-aminobenzene-1,4-dicarboxylic acid) in the solution rather than the formation of Al-MIL-53-NH2 that really caused the fluorescence enhancement. In particular, the formed BDC-NH2 was reduced from the shedded BDC-NO2 (2-nitrobenzene-1,4-dicarboxylic acid) during the decomposition of Al-MIL-53-NO2, which was attacked by OH in the NaHS solution. We anticipate that this work will offer new ways of tracing fluorophores for MOF-based sensing applications in aqueous systems.

Graphical abstract: Unraveling the origin of the “Turn-On” effect of Al-MIL-53-NO2 during H2S detection

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Publication details

The article was received on 09 Oct 2019, accepted on 19 Nov 2019 and first published on 20 Nov 2019


Article type: Paper
DOI: 10.1039/C9CE01595G
CrystEngComm, 2020, Advance Article
  • Open access: Creative Commons BY-NC license
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    Unraveling the origin of the “Turn-On” effect of Al-MIL-53-NO2 during H2S detection

    Z. Zhu, X. He and W. Wang, CrystEngComm, 2020, Advance Article , DOI: 10.1039/C9CE01595G

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