An Eu(III)-functionalized Sr-based metal-organic framework for fluorometric determination of Cr(III) and Cr(VI) ions

An Eu(III)-functionalized strontium-organic framework (Eu3+@Sr-MOF) was synthesized by encapsulating Eu3+ ions into the pores of Sr-MOF via postsynthetic modification (PSM) and fully characterized by XRD, SEM, EDS, FTIR, and TGA. The luminescent properties of Eu3+@Sr-MOF were measured and investigated in detail, which demonstrated that Eu3+@Sr-MOF not only possessed excellent water and chemical stabilities in a wide pH range (5-10) but also displayed red luminescence with excitation/emission maxima at 332/617 nm. The Eu3+@Sr-MOF can be considered as a highly selective and sensitive recyclable luminescence probe for sensing Cr(III) and Cr(VI) based on strong luminescence quenching effects; it can be recycled at least five times. The luminescence probe for Cr3+, CrO42-, and Cr2O72- shows low detection limits (0.15 mu M, 0.17 mu M, and 0.13 mu M, respectively), relatively broad linear ranges (0.6-150 mu M, 0.1-200 mu M and 0.4-180 mu M, respectively), and high quenching constants K-SV. The signals can be observed by the naked eye under UV light of 365 nm. The method was applied to the determination of total Cr in environmental water samples.