Tailoring pore surface properties of covalent organic framework via side-chain thiol engineering: Toward a hydrogen bonding mediated adsorbent for dispersive solid-phase microextraction

In this work, a facile side-chain thiol engineering strategy was presented to tailor the COF pore surface properties and to construct a hydrogen bonding mediated covalent organic framework (COF) adsorbent. A special thiol-functionalized COF (COF-V-SH) was fabricated with a high thiol grafting ratio of 60.84%. The successful synthesis of COF-V-SH microspheres was confirmed by the diverse characterization of SEM, EDS, FT-IR, XRD and XPS. The resultant COF-V-SH microspheres were then utilized as a dispersive solid-phase microextraction (dSPME) adsorbent for effective melamine extraction via the hydrogen bonding interaction. Several dSPME factors, including the percentage of formic acid and ACN in the extraction solution, the adsorbent dosage, the extraction and desorption time, and the desorption solution, were optimized to achieve the satisfactory extraction performance. The extraction mechanism and the adsorption properties of COF-V-SH were further investigated. By combining this COF-based dSPME with HPLC, a simple and effective method was proposed for the extraction and detection of melamine in real samples, which demonstrated good linearity in the range of 0.005–10 μg/mL (R² ≥ 0.9906) with low limit of detection (0.7 ng/mL). This work breaks the conventional nonpolar adsorption profile of COF adsorbents, endowing them with the dominant polar adsorption through facile side-chain thiol engineering, expanding the action modes of COF adsorbents.