Enhanced Electrochemical Detection of Heavy Metal Ions via Post-synthetic Schiff Base Modification of MWCNT-MOF Composites

Abstract

In this study, we present a novel approach to improve electrochemical heavy metal ion (HMI) sensing responses via post-synthetic modification of carbon nanotube-based metal-organic framework (MOF) nanocomposites with a Schiff base. UiO66-NH2 was employed as the MOF and incorporated with multi-walled carbon nanotubes (MWCNT) through in-situ growth, enhancing the electrical conductivity of the MWCNT-UiO66-NH2 composite. Subsequently, the Schiff base, which has been proven to be an excellent ligand for metal ion detection, was functionalized onto MWCNT-UiO66-NH2 via post-synthetic modification to improve its HMI absorption capacity. To evaluate the effect of the Schiff base on HMI detection capacity, electrochemical sensing of Cd2+, Pb2+, Cu2+, and Hg2+ was performed in an aqueous solution utilizing the MWCNT-UiO66-Schiff modified electrode as well as the bare electrode. Individual differential pulse anodic stripping voltammetry results revealed that the modified electrode with MWCNT-UiO66-Schiff exhibited increased HMI sensing properties, especially with 1.82-fold improvement in average oxidation currents toward 10 µM of Cu2+ compared to that for a bare glassy carbon electrode. The selective Cu2+-sensing properties of MWCNT-UiO66-Schiff were reflected in the highly selective Cu2-binding affinity of the Schiff base-containing model molecules compared to those of Cd2+, Hg2+, and Pb2+. Our work provides a new strategy for improving the sensing properties of electrochemical HMI sensors by the post-synthetic modification of MWCNT-UiO66 with a Schiff base.