Fabrication of a MOF-on-MOF composite for efficient enrichment of trace bisphenols in food and environmental samples

A core-shell UiO-66-NH₂@PCN-222 heterostructure was fabricated via a two-step solvothermal epitaxial growth method for extraction and determination of bisphenols in food and environmental samples. UiO-66-NH₂ was selected as the core by virtue of its high stability, large specific surface area, and abundant amino sites for post-synthetic modification. However, its intrinsic microporosity hinders the mass transfer of large molecules. PCN-222 possesses mesoporous channels (∼3.7 nm) to accelerate analyte diffusion, offsetting the structural drawback of UiO-66-NH₂. The porphyrin ligands of PCN-222 also create an extended π-conjugated system, allowing efficient capture of bisphenols via π-π interactions. Therefore, benefiting from the complementary pore architecture and functional properties, the core-shell UiO-66-NH₂@PCN-222 composite was rationally constructed for dispersive solid-phase extraction (DSPE) of bisphenols. Its morphology and structure were systematically characterized. The multiple synergistic mechanisms were involved in adsorption which significantly boost performance of UiO-66-NH₂@PCN-222 composite. Impressively, the composite could extract over 90% of bisphenol within 5 min, which evidenced its rapid mass transfer behavior due to its hierarchical porous structure. It also exhibited excellent reusability and strong anti-interference ability. The established DSPE-HPLC method delivered outstanding analytical performance with detection limits as low as 0.05-0.19 ng mL^-1, enrichment factors up to 294, and recoveries of 89.63%-109.41%. When applied to six real matrices (milk, honey, tea, thermal paper, wastewater, and lake water), bisphenol A was detected in both wastewater (0.84 ng mL^-1) and thermal paper (15.2 ng g^-1), highlighting a potential exposure risk from thermal paper that deserves public attention.