Carbon dots-magnetic nanocomposites for the detection and removal of Hg2

•The Fe3O4/CDs exhibited excellent performance on detection and removal of Hg2+.•Reach a LOD of 0.3 nM for Hg2+detection.•The detection and removal can be fulfilled within 2 min.•The Fe3O4/CDs can recover the Hg2+ from real water samples. The dual functional detection and removal of heavy ion metals by carbon dots has become an urgent matter of concern. Here, a unique fluorescent carbon dot-magnetic nanocomposite (Fe3O4/CDs) was prepared by hydrothermal methods for sensitive detection of Hg2+. The Fe3O4/CDs serve as fluorescent probes with higher selectivity and sensitivity for Hg2+, with the lowest detectable limit of 0.3 nM. Hg2+ statically quenched the blue emission of Fe3O4/CDs, which can be restored in the presence of saturated EDTA solution. The utilization of Fe3O4/CDs was fulfilled by recovering their emission conveniently. The recovery of Hg2+ in Chagan Lake water, tap water and drinks was calculated at 96.5 ~ 108.8%, which demonstrates the feasibility of the Fe3O4/CDs sensing system in natural samples. Notably, the Fe3O4/CDs can drive the effective removal of Hg2+ from samples, which is of outstanding significance as a promising probe in environmental monitoring.