Carbon-coated Fe3O4 derived from metal-organic frameworks on reduced graphene as electrochemical sensor platform for Hg(II) determination

Mercury, a well-known neurotoxicant, mainly occurs as Hg0, Hg2+ or Hg (CH3)2 in the environment. Therefore, there is an urgent need to develop new analytical methods to rapidly screen for mercury in natural water. In this work, rGO-MIL-101(Fe) was fabricated using reduced graphene oxide (rGO) and MIL-101 by one spot solvothermal method, and then was pyrolyzed at 500 °C to yield carbon-coated Fe3O4 dispersed on rGO (hereafter rGO-Fe@C). The rGO-Fe@C was characterized by SEM, TEM, TGA, XRD, XPS and Raman spectroscopic methods for its morphological features, particulate size & gradations, element redox states. An electrochemical sensing interface was constructed for Hg2+ determination using rGO-Fe@C modified glassy carbon electrode(rGO-Fe@C/GCE) by square wave anode stripping voltammetry (SWASV). The rGO-Fe@C/GCE exhibits high sensitivity for Hg2+ determination with a sensitivity of 34.47 μA/μM and a limit detection of 4.5 nM. The sensitive mechanism of Hg2+ in the electrochemical interface was investigated by XPS and DFT calculations. The presence of common cations as Cd2+, Cu2+ and Pb2+ in comparable molarities does not interfere with Hg2+ detection. Moreover, the electrode sensor possesses good stability and reproducibility for repetitive analysis of samples. The rGO-Fe@C/GCE sensor can be used in Hg2+ detection with minimal matrix interference by ions ubiquitous in natural water.