A Highly Stable Eu-MOF as an Excellent Fluorescent Probe for Efficient Detection of Trace CrO42− in Water Solutions

It is of urgent significance to develop highly stable and efficient CrO 4 2− detection technology in the fields of drinking water distribution and sewage treatment. A highly stable europium metal-organic framework (Eu-MOF) was designed as fluorescent probe for the efficient detection of trace CrO 4 2− in water solutions. This was achieved through the self-assembly of the lanthanide Eu 3+ and a rigid conjugated organic ligand [2,2’- biquinoline]-4,4’-dicarboxylic acid (H 2 L) under hydrothermal conditions. The obtained Eu-MOF exhibits excellent water stability, thermal stability and photostability. The Eu-MOF can quantitatively detect trace amounts of CrO 4 2− through fluorescence quenching effect. Its detection sensitivity is 4.48 × 10 4 M − 1 , with a detection limit as low as 0.06 µM (9.7 µg/L). This is one of the lowest values for the detection limit of CrO 4 2− in aqueous solution and is far below the allowable level for drinking water specified by World Health Organization. The Eu-MOF sensor also demonstrates excellent selectivity, anti-interference ability, repeatability (after 4 cycles), reproducibility and practical feasibility. Furthermore, the fluorescent luminescence and senseing mechanism were studied in detail. The fluorescence senseing mechanism of the Eu-MOF for CrO 4 2− detection involves the competitive absorption of excitation energy. The fluorescence-based sensing technology using the Eu-MOF provides a reference for environmental pollution detection and holds potential practical value.