Metal-organic framework-derived nitrogen-doped carbon nanotube cages as efficient adsorbents for solid-phase microextraction of polychlorinated biphenyls

An efficient and stable adsorbent is of critical importance for solid-phase microextraction (SPME). In this study, we prepared metal-organic framework-derived nitrogen (N)-doped carbon (C) nanotube cages (N-CNTCs) with unique N-doped active sites and C-rich nanotubes to coat SPME adsorbents. This new material was obtained via a simple thermal treatment with ZIF-67, and exhibited high porosity and excellent chemical and thermal stability. Compared with commercial fibers and traditional C nanotubes-coated fiber (15 nm), N-CNTC-coated fiber exhibited better extraction properties, mainly due to its π-π interactions, abundant active sites, and hollow cage structure, which is composed of interconnected crystalline N-doped C nanotubes. N-CNTC-coated fiber exhibited better extraction performance and shorter extraction equilibrium time than the solid N-doped C-coated fiber due to its hollow cage structure. The N-CNTC-coated fiber was then used to identify polychlorinated biphenyls (PCBs) with wide linear range (0.3-1000.0 ng L^-1), low limits of detection (0.10-0.22 ng L^-1), good repeatability (intra-day, 2.6-3.8%; inter-day, 3.3-4.8%), and good reproducibility (<8.6%). We then successfully applied the N-CNTC-coated fiber to detect PCBs in river water samples from six cities in Fujian Province and obtained satisfactory recovery levels. Thus, the novel N-CNTCs coating proposed in this study is a promising candidate for SPME coating.