In situ secondary growth of Eu(III)-organic framework film for fluorescence sensing of sulfur dioxide

Sulfur dioxide (SO2) is a common air pollutant; however, the fluorescence sensing of gaseous SO2 has never been reported yet. In this work, we developed a new strategy, named “in situ secondary growth”, to fabricate an Eu(III)-organic framework film on common glass for fluorescence sensing of gaseous SO2 for the first time. The UiO-66-NH2 film was firstly synthesized on common glass as a seed layer. Because of their matched components and structures, the Eu-BDC-NH2 (H2BDC-NH2, 2-aminoterephthalic acid) film can be successfully fabricated on the UiO-66-NH2 layer through in situ secondary growth. The Eu-BDC-NH2 film exhibits strong characteristic Eu3+ emissions, which can be fast and remarkably quenched by SO2 gas. The limit of detection (LOD) to SO2 gas is calculated to be 0.65 ppm and the response time is as short as 6 s. Further, we reveal that the quenching effect is caused by the intermolecular charge transfer between the ligand and SO2 molecules, as supported by the luminescence spectra and simulated calculation results.