MOF-on-MOF derived nitrogen-doped carbon-graphitic carbon/carbon nanotubes as solid-phase microextraction coating for extraction of polychlorinated biphenyls

Advanced fiber coating materials are pivotal for achieving good performance in solid-phase microextraction (SPME). To enhance the adsorption capacity of metal-organic framework (MOF)-derived carbon materials, we developed a novel two-dimensional/three-dimensional (2D/3D) MOF co-growth strategy. This approach synthesizes a core-shell structured 2D ZIF-L@ZIF-67 hybrid framework through controlled crystallization of 3D ZIF-67 (Co) on 2D ZIF-L (Zn) substrates. Subsequent pyrolysis converts this material into nitrogen-doped carbon-graphite carbon/carbon nanotube heterostructures (NC@GC/CNTs) with hierarchical porosity. The NC@GC/CNTs were utilized as fiber coating material of SPME to enrich trace polychlorinated biphenyls (PCBs) in jasmine tea, barrel drinking water, and green tea beverages. The adsorption performance of the fiber toward PCBs were significantly improved, which can be attributed to cation-π interaction, π-π interaction, and strong hydrophobic effect between fiber coating and analytes. Using NC@GC/CNTs as fiber coating material, a headspace SPME (HS-SPME) coupling with gas chromatography-flame ionization detector (GC-FID) was developed to quantitative analysis of PCBs. Under the optimal conditions, the HS-SPME-GC-FID method exhibited a wide linear range (0.005–30 ng·mL −1 ) with a good linear correlation coefficient (R 2  ≥ 0.9947), low limits of detection (0.001–0.003 ng·mL −1 ), and high enrichment factors (11077–14,447). The recoveries of method to PCBs were obtained in the range of 83.2–119.6 % in real samples.