Site-selective synthesis of an amine-functionalized β-ketoenamine-linked covalent organic framework for improved detection and removal of Cu2+ ion from water

The development of new dual-functional materials for detection and removal of heavy metal ions is of great significance in environmental protection. Herein, a new amine-functionalized β-ketoenamine-linked covalent organic framework (termed as NH 2 –Th-Tfp COF) containing rich O , N , O ′-chelating sites and free amine groups has been synthesized through the site-selective synthesis strategy under solvothermal conditions. The as-synthesized NH 2 –Th-Tfp COF shows strong fluorescence in water dispersion and can be used as highly sensitive and selective fluorescent probe for Cu 2+ detection. As a sensing platform, the limit of detection for NH 2 –Th-Tfp COF toward Cu 2+ ion is estimated to be 0.19 μM. Besides, the NH 2 –Th-Tfp COF possesses high adsorption capacity of 153 mg/g toward Cu 2+ ion in aqueous solution. More importantly, this NH 2 –Th-Tfp COF exhibits higher sensitivity and larger adsorption capacity toward Cu 2+ ion in comparison with the non-amine functionalized Th-Tfp COF, which may be attributed to the large number of free amine groups in the pore walls of NH 2 –Th-Tfp COF. The coordination interactions between Cu 2+ ion with the O , N , O ′-chelating sites and free amine groups in the pore walls of NH 2 –Th-Tfp COF can greatly enhance its recognition and absorption performances toward Cu 2+ ion, as verified by X-ray photoelectron spectroscopy. This work may pave the way for designing new fluorescent COF materials with dual functions for simultaneous detection and removal of specific metal ions. A new amine-functionalized β-ketoenamine-linked NH 2 –Th-Tfp COF was prepared by the site-selective synthesis strategy, showing improved sensing ability and enhanced adsorption capacity towards Cu 2+ compared to the nonfunctionalized Th-Tfp COF. • A new amine-functionalized β-ketoenamine-linked NH 2 –Th-Tfp COF was prepared via the site-selective synthesis strategy. • The NH 2 –Th-Tfp COF showed dual function of simultaneous detection and removal of Cu 2+ from aqueous solution. • The amine-functionalized NH 2 –Th-Tfp COF exhibited superior sensitivity and adsorption capacity toward Cu 2+ compared to the nonfunctionalized Th-Tfp COF. • The introduction of free amino groups in the NH 2 –Th-Tfp COF plays a key role in improvement of sensitivity and adsorption ability to Cu 2+ ion.