Controllable Transformation of Aligned ZnO Nanorods to ZIF-8 as Solid-Phase Microextraction Coatings with Tunable Porosity, Polarity, and Conductivity

While a growing number of solid-phase microextraction (SPME) coatings have been developed, a generalized protocol is still needed to tailor-make SPME coatings with desirable properties for efficient extraction of diverse analytes from sample matrixes. In this work, we developed a versatile approach to prepare SPME coatings with tunable properties by controllable in situ transformation of well-aligned ZNRs into zeolitic imidazolate frameworks-8 (ZIF-8) via reaction with 2-methylimidazole (2-MI). During this process, ZNRs supplied Zn2+ and served as a hard template for the in situ growth of well-aligned ZIF-8 with enhanced surface area for adsorption. Because ZNRs and ZIF-8 exhibit markedly different properties, we obtained a series of ZNRs/ZIF-8 hybrid composites, whose morphology, porosity, polarity, and charge transfer resistance can be fine-tuned by simply controlling the concentration of 2-MI. Preparing ZNRs/ZIF-8 SPME coatings with desired properties enabled effective extraction of a wide range of polar and nonpolar compounds including aliphatic hydrocarbons, polycyclic aromatic hydrocarbons, alcohols, phenols, anilines, and ionic drugs.