Metal–Organic Framework-Derived Nanozyme with Enhanced Laccase-like Activity for Capturing and Detection of Lead Ions

Metal–organic frameworks (MOFs) have garnered significant interest in environmental monitoring and remediation due to their tailorable porosity and tunable functional properties. In this work, a dual-functional nanozyme, denoted as PCN-224@Co3O4, was synthesized through combined hydrothermal and coprecipitation methods. The immobilization of Co3O4 nanoparticles within the PCN-224 framework not only enhances its laccase-like catalytic activity but also preserves the intrinsic fluorescence of the MOF. The innovation of this nanomaterial lies in the strategic synergy between the confinement effect of the MOFs and the catalytic properties of Co3O4, leading to the construction of an integrated colorimetric and fluorescence dual-mode sensing nanoplatform for Pb2+. Specifically, Pb2+ ions selectively coordinate with the TCPP ligands within the MOF pores, thereby simultaneously modulating both the catalytic activity and the fluorescence emission, which underpins a highly reliable dual-mode sensing mechanism. Experimental results confirm that the PCN-224@Co3O4 nanozyme efficiently catalyzes the oxidation of 2,4-dichlorophenol (2,4-DCP) in the presence of 4-aminoantipyrine (4-AAP), producing a colored quinoneimine dye with a characteristic absorption peak at 510 nm. Upon introduction of Pb2+, the ions diffuse into the MOF channels and coordinate with nitrogen atoms on the TCPP ligands, which not only suppresses the catalytic activity of Co3O4 but also quenches the fluorescence of PCN-224. Based on this dual-response mechanism, a highly sensitive detection platform for Pb2+ was established, achieving a detection limit as low as 0.1 nM. Moreover, the nanocomposite demonstrates excellent performance in capturing and immobilizing Pb2+ from aqueous media, underscoring its potential for the development of integrated “detection–remediation” technologies that align with the principles of green chemistry.