Facile synthesis of porous covalent organic frameworks for the effective extraction of nitroaromatic compounds from water samples.

Novel porous covalent organic frameworks (COFs) were synthesized via a facile approach at room temperature by using 1,3,5-tris(4-aminophenyl)benzene and 2,3,5,6-tetrafluoroterephthalaldehyde as two building blocks for the first time. And the COFs were applied as dispersive solid phase extraction (dSPE) adsorbents for the extraction of six nitroaromatic compounds (NACs) from diverse water samples. The COFs were characterized by scanning electron microscopy (SEM), energy dispersive spectrum (EDS), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), the nitrogen adsorption-desorption isotherms and Zeta potentiometric analysis. The results indicated that the COFs possessed high specific surface area, good thermal and chemical stability. Moreover, some parameters (including adsorbent dosage, extraction time, pH, ion strength, desorption solvent, desorption time and desorption frequency) which influenced the extraction efficiencies of NACs were investigated in details. By combining COFs-based dSPE with HPLC-DAD analysis, a simple, fast and effective method was developed for the extraction and determination of six NACs. The method demonstrated good linearity in the range of 0.01-50 μg mL (R > 0.9973) with low limits of quantification (0.1-0.25 μg mL, S/N = 10) and low limits of detection (0.03-0.09 μg mL, S/N = 3). Good precision with relative standard deviations (RSD) lower than 3.56% for intra-day and 4.78% for inter-day were also obtained. Finally, COFs-based dSPE was applied to the effective extraction of six NACs from three kinds of actual water samples, and good recoveries (ranged from 84.00 to 112.29%) were observed. These results demonstrated that the COFs had promising potential to be adsorbents for dSPE of NACs in complex samples.