Multifunctional MOF-based probes for efficient detection and discrimination of Pb2+, Fe3+ and Cr2O72-/CrO42-

Developing metal-organic framework (MOF)-based fluorescent probes for efficient detection and discrimination of polluting ions in groundwater is vital for environmental protection and human health. In this paper, we prepared two luminescence-active transition MOFs, namely, Zn-MOF and Cd-MOF, and conducted sensing experiments. The results show that they both exhibit multiple-target detection for Fe3+, Pb2+ and Cr(vi) with high sensitivity, good anti-interference ability and good recyclability even with different frameworks. In addition, Eu3+-incorporated samples, Eu3+@MOFs, with dual-emission have been fabricated via efficient encapsulation of Eu3+ ions into the MOF host. As expected, Eu3+@MOF hybrids also act as multi-target and self-calibrated probes to selectively detect Fe3+ and Cr(vi) ions. However, the quenching efficiencies of the original MOFs towards Fe3+ are higher than those of Eu3+@MOFs. Thus, we could differentiate Fe3+, Pb2+ and Cr(vi) ions by comparing the changes of fluorescence emission between Eu3+@MOFs and the original MOFs. The recognition mechanism may be attributed to the competitive energy absorption between MOFs or Eu3+@MOFs and the analytes.