Magnetic solid-phase extraction of organophosphate esters from water sample based on MOF-derived hollow cactus-like...

Hollow cactus-shaped carbon sheets/carbon nanotubes (HCS/CNTs) were prepared by domain-limited pyrolysis of polydopamine coated Zn, Co-ZIF. This composite was employed as a magnetic solid-phase extraction (MSPE) adsorbent for the rapid and sensitive enrichment of organophosphate esters (OPEs) from water samples. Various parameters, including the amount of adsorbent, type of elution solvent, extraction time, and pH were systematically optimized. Furthermore, the possible extraction mechanisms involved were discussed. The hollow two-dimensional layered structure of HCS/CNTs provided a shortened diffusion pathway, while the carbon nanotubes on their surface offered an increased number of adsorption sites for OPEs. Consequently, HCS/CNTs exhibited shorter equilibrium time and superior extraction performance compared to carbon nanosheets derived from Zn, Co-ZIF without polydopamine. Moreover, the synthesized HCS/CNTs possessed a large specific surface area and abundant functional groups capable of forming hydrogen bonds, π-π stacking interactions and hydrophobic interactions with OPEs. When coupled with high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS), the MSPE method based on HCS/CNTs demonstrated a broad linear range of 5-2000 ng L^-1 and low limits of detection ranging from 1.4 to 6.1 ng L^-1. Finally, the developed method achieved reliable quantification and high recoveries (90.15%-114.61%) for OPEs in actual environmental water samples, thereby demonstrating its applicability for the determination of  trace environmental pollutants.