Double -shelled hollow ZnO/carbon nanocubes as an efficient solid-phase microextraction coating for the extraction of broad-spectrum pollutants

Efficient extraction of pollutants with different chemical properties from environmental samples has attracted great attention in the development of analytical chemistry. However, it is still a challenge to develop an appropriate and sensitive adsorbent for determining broad-spectrum analytes. Herein, zeolitic imidazole framework-8 (ZIF-8)-derived double-shelled hollow zinc oxide/carbon (ZnO/C) nanocubes were reported as a novel coating for solid-phase microextraction (SPME). The nanocubes with a unique structure and composition were obtained by controlled etching of ZIF-8 with tannic acid (TA) followed by pyrolysis. When a ZnO/C nanocube-coated fiber (ZnO/C-F) was used to extract the complex environmental samples containing both nonpolar (benzene compounds (BTEX)) and polar (chlorophenols (CPs)) pollutants, excellent extraction performance was achieved; we obtained low detection limits (0.14-0.56 ng L-1 for BTEX and 1.10-2.84 ng L-1 for CPs), good repeatability (2.2-5.9% for six replicated extractions) and excellent reproducibility (0.61-7.8%, fiber to fiber). The broad-spectrum SPME performance was ascribed to the synergistic effect between the composition and structure of ZnO/C nanocubes. Compositionally, the uniform dispersion of ZnO and carbon framework could provide abundant adsorption active sites, where Zn-OHs bound CPs by hydrogen bonding and carbon absorbed BTEX through π-π stacking interaction and hydrophobic interaction. Structurally, the double-shelled hollow morphology of the nanocubes was favorable for the sensitive extraction. Finally, the established ZnO/C-F-based headspace-SPME method was used for the preconcentration and determination of abundant analytes from real water samples. These findings open the door for the practical use of double-shelled hollow multicompositional inorganic materials.