Efficient Sequestration and Sensitive Detection of Cd(II) in Food Using a Two-dimensional Imine-linked Covalent Organic Framework: Performance, Modeling, and Mechanism

A two-dimensional imine-linked covalent organic framework, named COF-LZU1, was strategically utilized as a high-performance solid-phase extraction (SPE) adsorbent for the ultratrace sequestration of Cd(II) from complex food matrices. Systematic investigations into adsorption kinetics and isotherms revealed that the uptake of Cd(II) follows a pseudo-second-order model and aligns with the Langmuir isotherm, suggesting a monolayer chemisorption process. The maximum theoretical adsorption capacity reached 114.94 mg g ^− 1 , significantly outperforming many traditional adsorbents. Structural and spectroscopic characterizations (SEM-EDS, BET, FT-IR, and XPS) confirmed that the robust performance of COF-LZU1 originates from its high specific surface area and the abundance of nucleophilic imine linkages (-C = N-) which serve as primary coordination sites. According to the Hard and Soft Acids and Bases principle and DFT simulations, the adsorption mechanism involves a synergistic interplay of electrostatic attraction, chelation, and pore-channel effects. Under optimized conditions, the integrated SPE-GFAAS platform achieved a remarkable limit of detection (3.34 ng L ^− 1 ) and excellent precision (RSD = 1.0%). The methodology was rigorously validated using various Standard Reference Materials and real food samples, yielding satisfactory recoveries (94.0-104.0%). These findings underscore the immense potential of COFs as specialized scaffolds for the sensitive enrichment and quantification of heavy metals in food safety and environmental monitoring.