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

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 C162H120N18O12Br3.C21H9N3O12Tb1) was synthesized, consisting of an ionic covalent organic framework (denoted as I-COF, with a structural composition of C(16)2H(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 x 10(5 )M(-1)[CA], R-2 = 0.996, within [CA] region of 0-9 mu M. 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.