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 Eu 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@Eu-MOFs showed high sensitivity and selectivity with a linear range from 2 to 100 μM and a detection limit of 0.21 μM 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.