Research progress of LMOFs containing aromatic carboxylic acid in anions recognition

At present, industrial wastewater and domestic sewage have caused serious water pollution, which not only affects the quality of human life, but also pollutes the ecological environment. Anions exist in water for a long time, causing serious water pollution, especially they are toxic. A new class of organic–inorganic hybrid material called metal–organic framework (MOF) has various benefits including a porous structure, adjustable pore size, and multi-metal sites. It is widely used in adsorption, storage, separation, catalyst and other fields. Aromatic carboxylic acids have many advantages over other N-containing ligand or S- or P- ligands or flexible carboxylic acid ligands. The aromatic ring structure of aromatic carboxylic acid molecules can accumulate π-π with other aromatic rings, which is conducive to enhancing the robustness of the coordination polymer. Aromatic carboxylic acid has a relatively rigid molecular structure, and has more degrees of freedom with other N-containing or S- or P- ligands or flexible carboxylic acid ligands, which is more conducive to the formation of specific spatial structures. Moreover, there are abundant π electrons in the aromatic ring, which provide abundant electrons in the coordination process. Most importantly, different substituents and functional groups can be introduced into the aromatic ring, and coordination polymers with specific properties can be designed and synthesized. By designing ligands and metal ions, MOFs can effectively regulate their luminescence properties, which has incomparable advantages over traditional luminescent materials. This review mainly introduces the detection of anions in water by using the unique fluorescence characteristics of MOFs. According to the changes of fluorescence sensing, detection and identification are divided into fluorescence enhancement "turn-on", fluorescence quenching "turn-off" and ratiometric fluorescence "ratiometric", and the detection mechanism of anions is briefly expounded.