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Highly Efficient Luminescent Metal-Organic Framework for the Simultaneous Detection and Removal of Heavy Metals from Water

  • Author(s): Rudd, ND
  • Wang, H
  • Fuentes-Fernandez, EMA
  • Teat, SJ
  • Chen, F
  • Hall, G
  • Chabal, YJ
  • Li, J
  • et al.
Abstract

© 2016 American Chemical Society. We have designed and synthesized an isoreticular series of luminescent metal-organic frameworks (LMOFs) by incorporating a strongly emissive molecular fluorophore and functionally diverse colinkers into Zn-based structures. The three-dimensional porous networks of LMOF-261, -262, and -263 represent a unique/new type of nets, classified as a 2-nodal, (4,4)-c net (mot-e type) with 4-fold, class IIIa interpenetration. All compounds crystallize in a body-centered tetragonal crystal system (space group I41/a). A systematic study has been implemented to analyze their interactions with heavy metals. LMOF-263 exhibits impressive water stability, high porosity, and strong luminescence, making it an excellent candidate as a fluorescent chemical sensor and adsorbent for aqueous contaminants. It is extremely responsive to toxic heavy metals at a parts per billion level (3.3 ppb Hg2+, 19.7 ppb Pb2+) and demonstrates high selectivity for heavy metals over light metals, with detection ratios of 167.4 and 209.5 for Hg2+/Ca2+and Hg2+/Mg2+, respectively. Mixed-metal adsorption experiments also show that LMOF-263 selectively adsorbs Hg2+over other heavy metal ions in addition to light metals. The Pb2+KSVvalue for LMOF-263 (55,017 M-1) is the highest among LMOFs reported to date, and the Hg2+KSVvalue is the second highest (459,446 M-1). LMOF-263 exhibits a maximum adsorption capacity of 380 mg Hg2+/g. The Hg2+adsorption process follows pseudo-second-order kinetics, removing 99.1% of the metal within 30 min. An in situ XPS study provides insight to help understand the interaction mechanism between Hg2+and LMOF-263. No other MOFs have demonstrated such a high performance in both the detection and the capture of Hg2+from aqueous solution.

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