Efficient Sequestration and Sensitive Detection of Cd(II) in Food Using COF-LZU1: Performance, Modeling, and Mechanism

A two-dimensional imine-linked covalent organic framework, designated as COF-LZU1, was employed as a high-performance solid-phase extraction (SPE) adsorbent for the preconcentration of trace Cd(II) from complex food matrices. Systematic investigations of adsorption kinetics and isotherms revealed that Cd(II) uptake follows a pseudo-second-order model and aligns with the Langmuir isotherm, indicating a monolayer chemisorption process. The theoretical maximum adsorption capacity reached 114.94 mg g −1 , demonstrating highly competitive performance against traditional adsorbents. Structural and spectroscopic characterizations (SEM–EDS, BET, FT-IR, XPS, and XRD) before and after adsorption confirmed that the robust performance of COF-LZU1 originates from its high specific surface area and abundant nucleophilic imine linkages (-C = N-), which serve as primary coordination sites. Supported by the Hard and Soft Acids and Bases and density functional theory simulations, the adsorption mechanism involves a synergistic interplay of electrostatic attraction, chelation, and the channel effect. Under optimized conditions, the integrated SPE-GFAAS platform achieved a highly sensitive limit of detection (3.34 ng L −1 ) and excellent precision (RSD = 1.0%). The methodology was validated using certified reference materials and real food samples, yielding excellent recoveries (94.0–104.0%). These findings underscore the significant potential of COFs-LZU1 as specialized scaffolds for the robust enrichment and quantification of trace heavy metals in food safety applications. Graphical A novel two-dimensional imine-linked covalent organic framework, designated as COF-LZU1, was initially employed in a solid-phase extraction system to adsorb trace amounts of Cd(II) from food samples. The adsorption process is identified as a sophisticated multi-step mechanism: initially, Cd(II) ions are attracted to the vicinity of the nitrogen-rich binding sites via electrostatic forces; subsequently, they migrate into the interior pores through the channel effect and are ultimately anchored via strong coordination-chelation with the imine linkages. This study underscores the potential of COF-LZU1 as a high-performance and selective platform for the separation and detection of Cd(II) in complex food matrices.