A multi-dye containing MOF for the ratiometric detection and simultaneous removal of Cr2O72− in the presence of interfering ions

Among the heavy metals commonly found in wastewater, Cr2O72− is considered the most hazardous due to its high toxicity, carcinogenicity, and mutagenicity. Nevertheless, detection and removal of Cr2O72− remains a serious challenge as it competes with other metal cations and anions in wastewater. Herein, self-calibration of the emission intensities at two different wavelengths was introduced to microporous media to facilitate the ratiometric detection and simultaneous removal of Cr2O72− in the presence of excess interfering ions. Specifically, a multi-dye (7-amino-4-methylcoumarin and resorufin) containing metal-organic framework-801 (Dyes⊂MOF-801) was developed and tested for the detection and removal of Cr2O72− from wastewater. Dyes⊂MOF-801 exhibited accurate detection of Cr2O72− with high sensitivity in the presence of a 260-fold excess of potentially interfering ions. Its maximum removal capacity was 83 mg/g and was achieved within 3 min, even in the presence of excess metal ions and 10-fold excess concentrations of anions. In addition, the residual concentration of Cr2O72− was simultaneously checked using ratiometric detection of Dyes⊂MOF-801, so that the removal of Cr2O72− could be immediately confirmed.