An ionic covalent organic framework loaded with terbium-based probe for the sensing and removal of chrysolepic acid: Characterization and ratiometric behavior

Abstract

Chrysolepic acid (CA) is a widely-used chemical product and considered hazardous for ecosystem and human health, which makes its removal as important as its sensing. In this work, a composite structure (denoted as Tb–COF, with a structural composition of C 162 H 120 N 18 O 12 Br 3 ·C 21 H 9 N 3 O 12 Tb 1 ) was synthesized, consisting of an ionic covalent organic framework (denoted as I–COF, with a structural composition of C 162 H 120 N 18 O 12 Br 6 ) and a terbium-based dopant/emitter (denoted as Tb(DPA) 3 3− , DPA = pyridine-2,6-dicarboxylic acid). Tb–COF was identified by means of single crystal analysis, infrared (IR) spectra, X-ray diffraction (XRD), porosity analysis, SEM (scanning electron microscope)/TEM (transmission electron microscope) and elemental composition analysis. The dopant loading level in Tb–COF was determined as 41%. Both green emission from Tb-based dopant and red emission from I–COF host were observed. The presence of CA quenched I–COF emission but enhanced dopant emission, resulting in ratiometric sensing signal. A linear calibration curve was demonstrated, with fitting equation of I/I 0 = 1.223 + 6.709 × 10 5 M −1 [CA], R 2 = 0.996, within [CA] region of 0–9 μM. The key sensing/adsorption process was revealed as the adsorption of I–COF micropores for CA molecules, which endowed Tb–COF with a good selectivity over competing species. I–COF adsorption/removal feature for CA was tentatively evaluated. • An ionic covalent organic framework was synthesized and modified with luminescent ionic Tb(III) emitter. • The as-synthesized Tb–COF showed weak Tb(III) emission and strong red COF emission. • After adding CA, Tb(III) emission was increased with COF emission weakened greatly, showing sensing behavior. • The adsorption and removal performance of Tb–COF was investigated as well.