Carbon dots-based hydrogel fluorescent composites for Fe(II) detection and separation

Fluorescent hydrogel were developed for Fe(II) detection to overcome the shortcomings of simple carbon dots solutions (CDs), which are difficult to store and use. CDs were prepared using the hydrothermal synthesis with o -phenylenediamine and dopamine as the carbon sources. Fluorescent hydrogel (CACDs) were obtained by doping CDs in and impregnating them with carboxymethyl cellulose hydrogel (CA) prepared using crosslinked carboxymethyl cellulose (CMC), which was grafted using acrylamide as the substrate. Using CDs and CA as a fluorescent group and a backbone, respectively, enhanced the fluorescence performance and facilitated Fe(II) detection. The surface groups, elemental composition and optical properties of the prepared CDs and CACDs were systematically studied using FTIR, XRD, UV–Vis and fluorescence spectrometer. The effects of pH, temperature, NaCl salt solution and UV irradiation on the stability of CDs in the hydrogel were discussed. CACDs exhibited strong, bright yellow fluorescence with a fluorescence intensity 4.35 times higher than that of CDs. CACDs can be used as fluorescent probes to realise real-time detection of Fe(II) at a low detection limit (0.22 μM), allowing them to be employed for Fe(II) detection in real water samples. CACDs had stable adsorption properties for Fe(II). The adsorption process of metal ions conformed to pseudo-second order kinetics and Langmuir model, respectively. Therefore, CACDs are expected to be bifunctional materials for effective detection and removal of Fe(II).