AUTHOR=Xu Ming , Wang Li-Le , Chen Gang , Chen Yin-Yun , Liu Dan , Liao Jiang-Tao 

TITLE=A Red-Emitting COF Ionic Exchanged With Green-Emitting Tb(III) Complex Anion: Synthesis, Characterization, Ratiometric Emission Sensing, and Removal of Picric Acid

JOURNAL=Frontiers in Chemistry

VOLUME=Volume 10 - 2022

YEAR=2022

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2022.865304

DOI=10.3389/fchem.2022.865304

ISSN=2296-2646

ABSTRACT=Picric acid (PA) is an important chemical product which has been widely used for dye manufacturing, antiseptics and pharmaceuticals. Owing to its extreme electron-deficient structure, PA natural degradation is hard, leading to accumulation in environment and finally threatening ecosystem and human health. In this case, PA detection and removal becomes more and more important, concerning environmental protection and human health. In this paper, an ionic covalent organic framework (I-COF) was synthesized and modified with luminescent Tb(III) emitter (Tb(DPA)33-, DPA= pyridine-2,6-dicarboxylic acid) via ionic exchange. The resulting composite material (Tb-COF) was fully characterized by geometric analysis, IR, XRD, porosity analysis, SEM/TEM and elemental analysis. It was found that Tb(DPA)33- was loaded into the hexagonal cage in I-COF host with ionic exchange ratio of 41%. The as-synthesized Tb-COF showed weak Tb(III) emission and strong red COF emission, after adding PA, Tb(III) emission was increased with COF emission weakened greatly, showing sensing behavior. Linear working curves were observed with good selectivity. The sensing mechanism was revealed as follows. PA molecules replaced the [Tb(PDA)3]3- component trapped in Tb-COF, releasing free luminescent [Tb(PDA)3]3-. After incorporating PA in the hexagonal cage, the COF emission was quenched. This sensing mechanism ensured a good selectivity over competing species, including cations, anions and nitrocompounds. The adsorption and removal performance of I-COF for PA was investigated as well.