Highly Discriminative Detection of Nitrophenol Isomers by Covalent Organic Framework Membrane-Modified Electrochemical Sensors

Nitrophenol isomers (NPs), namely, <i>ortho</i>-, <i>meta</i>-, and <i>para</i>-nitrophenol (<i>o</i>-NP, <i>m</i>-NP, and <i>p</i>-NP) are an important class of organic compounds widely employed in industrial fields. Due to their high chemical stability, resistance to natural degradation, and toxicity, NPs pose significant risks to both the environment and human health. Their discriminative detection is of paramount significance; however, it is highly challenging because of the structural and physicochemical similarities of NPs. Herein, we present a fluorine-doped tin oxide (FTO) electrode comodified with a covalent organic framework (COF) membrane and gold nanoparticles (designated as gcFTO) as a powerful sensing platform for the selective detection of NPs. The unique structural characteristics and physicochemical properties of the COF, together with the catalytic activity of comodified gold nanoparticles, precisely modulate the electrochemical redox behaviors of NPs. In particular, the electrochemically reduced intermediates of NPs can be stabilized and accumulated by the COF, thus allowing their detection via anodic stripping analysis of the reduced intermediates. Furthermore, the COF can also modulate the oxidation behaviors of these intermediates, leading to well-separated oxidation peak potentials that enable accurate identification and quantification of each NP. It is also demonstrated that gcFTO exhibits excellent performance in the analysis of NPs in real environmental conditions, including river water and soil. This work highlights the potential of COF-based electrochemical sensors for the selective detection of structurally similar pollutants, providing an efficient and accurate tool for environmental monitoring and industrial quality control.