Preparation of Carboxy-Functionalized Covalent Organic Framework for Efficient Removal of Hg2+ and Pb2+ from Water

A carboxy-functionalized covalent organic framework COOH@COF for efficient removal of Pb2+ and Hg2+ ions from water has been prepared. Fourier transform infrared spectroscopy, solid-state C-13 NMR spectra, and elemental analysis indicate that the carboxy function has been grafted to COF materials via the click reaction. Its crystallinity remains unchanged after post-synthetic modification, as confirmed by the powder X-ray diffraction. Scanning electron microscopy images reveal that the COOH@COF possesses the thorn ball structure assembled by numerous nanowires with a diameter of 90 nm. This COOH@COF features excellent adsorption capacities for Pb2+ (123.8) and Hg2+ (99.1 mg/g) in water. The adsorption isotherms follow the Langmuir model, and their kinetics adsorption fits the pseudo-second-order model. Particularly, the COOH@COF can be recycled 20 times without loss of the adsorption capacity in water, showing its latent potential for practical application in the future.