Dual-emission of Eu based metal-organic frameworks hybrids with carbon dots for ratiometric fluorescent detection of Cr(VI)

A novel blue fluorescence nitrogen and cobalt(II) co-doped carbon dots (CDs) encapsulated in europium metal organic frameworks (CDs@Eu-MOFs) were synthesized to form a ratiometric fluorescent sensor for the detection of Cr(VI). The CDs@Eu-MOFs were characterized by transmission electron microscopic (TEM), scanning electron microscopic (SEM), Fourier transform infrared (FT-IR) and X-ray powder diffraction (XRD) techniques. The as prepared CDs@Eu-MOFs not only kept the fascinating optical properties of CDs and Eu3+ to give dual-emission but also had good stability in an aqueous solution. In the presence of Cr(VI), the fluorescence intensity of the CDs decreased and the intensity of the Eu-MOFs remained. Under optimized conditions, the synthesized CDs@EuMOFs showed high sensitivity and selectivity with a linear range from 2 to 100 mu M and a detection limit of 0.21 mu M for the detection of Cr(VI). The possible mechanism is discussed. Meanwhile, the fluorescence sensor was successfully utilized to detection of Cr(VI) in natural samples with good recoveries ranges.