Desirability of position 2, 2'-bipyridine group into COFs for the fluorescence sensing of Ni (II)

Covalent organic frameworks (COFs) with predesigned bipyridine recognition sites (donated as BPD-COFs) were prepared by using 2, 2'-bipyridine-5, 5'-diamine and benzene-1, 3, 5-tricarbaldehyde as monomers, and the corresponding small molecule model compound (2, 2'-bipyridine-5, 5'-diiminebenzene, donated as BPDB) was synthesized by using benzaldehyde and 2, 2'-bipyridine-5, 5'-diamine. The fluorescence sensing property between BPD-COFs and BPDB were compared as the fluorescence sensing platform for the sensitive, selective and rapid detection of Ni2+. The unique structure characteristics such as large conjugated structure, high surface area, regularity pore canals and predesigned bipyridine link endow BPD-COFs with prominent fluorescence emission, enough space and strong specificity for Ni2+. The fluorescence quenching degree of BPD-COFs is four times more than that of BPDB. Besides better selectivity, BPD-COFs also displays the prominent advantages, such as the wider concentration range (4.20 x 10-10-1.26 x 10-6 M) and lower limit of detection (6.80 x 10-11 M) compared to that of BPDB (1.00 x 10-7-5.00 x 10-7 M, 4.50 x 10-8 M). Good spiked recoveries (>92.0 %) in chocolate and tea support that BPD-COFs is competent to detect Ni2+ in real samples. All these results indicate that BPD-COFs is potential as a fast, sensitive, and accurate fluorescence sensing platform for the selective detection of Ni2+ in complex system.