Adsorbent-Assisted In Situ Electrocatalysis: Highly Sensitive and Stable Electrochemical Sensor Based on AuNF/COF-SH/CNT Nanocomposites for the Determination of Trace Cu(II)

The weak conductivity of covalent organic frameworks (COFs) limits their wide application in electrochemical sensors. Here, a novel electrochemical sensor (AuNFs/COF-SH/CNTs/GCE) was designed and constructed by a one-step electrochemical deposition of Au nanoflowers (AuNFs) on a hybrid nanocomposite of sulfhydryl-functional covalent organic framework/carbon nanotubes (COF-SH/CNTs) for the determination of Cu(II) in seawater. AuNFs/COF-SH/CNTs/GCE was prepared in a three-step method including in situ synthesis, post-synthesis, and one-step electrochemical deposition. The adsorption and catalytic performances of the modified electrode were improved based on the mechanism of "adsorption-catalysis stripping determination". By combining the excellent catalytic properties of the AuNFs with the good adsorption capacity of COF-SH toward Cu(II), as well as the good conductivity of CNTs, the AuNFs/COF-SH/CNTs/GCE exhibited excellent performance for the determination of Cu(II). Through optimization of the experimental conditions, a low detection limit of 0.47 nM and a wide linear range of 1.6 nM-4.7 μM were obtained. Moreover, the sensor possessed good stability with a relative standard deviation of less than 5% after 20 repeated measurements. The results are consistent with certified values when used for the determination of certified reference materials. In summary, the AuNFs/COF-SH/CNTs/GCE, with high stability and sensitivity, has been successfully applied for the determination of Cu(II) in seawater samples with satisfactory results.