Schiff base-stabilized electron-deficient copper species on MOFs as durable sensor of nitrate in water

Abstract

The electrochemical sensor has been considered an efficient and portable platform for the rapid quantification of nitrate ions in industrial wastewater and natural water bodies. Albeit of the high sensitivity to NO3−, the electron-deficient copper sites (Cuδ+) were unstable under the negative working potentials for detection (Cuδ+ was readily reduced to Cu0). Herein, the Schiff base was grafted on MIL-125 (Ti) via covalent binding to stabilize the Cuδ+, leading to a composite Cuδ+/Schiff base/MIL-125 (Ti) material (abbreviated as CuSM) for NO3− sensing. Moreover, the unique porous structure of CuSM can speed up the diffusion rate of NO3− from the bulk solution to the surface of the modified electrode, enhancing the sensitivity of NO3− assay. As a result, the CuSM-based sensor not only exhibited a wide linear range from 1.18 µM to 58.8 mM and a low detection limit (S/N = 3) of 0.253 µM but also possesses high specificity, excellent reproducibility (the RSD of the five inter-batch sensors was 1.138%) and the ability to detect real water samples.