Bimetallic metal-organic frameworks as electrode modifiers for enhanced electrochemical sensing of chloramphenicol

An electrochemical sensor is presented for the detection of the chloramphenicol (CAP) based on a bimetallic MIL-101(Fe/Co) MOF electrocatalyst. The MIL-101(Fe/Co) was prepared by utilizing mixed-valence Fe (III) and Co (II) as metal nodes and terephthalic acid as ligands with a simple hydrothermal method and characterized by SEM, TEM, XRD, FTIR, and XPS. Electrochemical measurements such as electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and differential pulse voltammetry (DPV) showed that bimetallic MIL-101(Fe/Co) had the faster electron transfer, larger electroactive area, and higher electrocatalytic activity compared with  their monometallic counterparts due to the strong synergistic effect between bimetals. Inspired by these results, the MIL-101(Fe/Co)-based sensor was used to detect CAP. Some experiment parameters of pH, Fe and Co molar ratio, MIL-101(Fe/Co) volume, and DPV quiet time were optimized. The direct reduction mechanism of CAP was verified to involve four electrons and four protons process. Finally, the sensitive and selective CAP detection in the concentration range 1 to 200 μM with a detection limit of 0.3 μM was realized by the proposed sensor. The satisfactory recoveries in tap water and lake water indicated the practicability of the proposed electrochemical sensor. It is expected that this work may open up a paradigm for the preparation of MOF-based electrode modifiers with desired electrocatalytic performance for environmental pollution monitoring.