Anionically engineered Ce-MOF for ultra-selective capture and separation of cationic dyes: Mechanistic insights and environmental remediation potential using methylene blue as a paradigm

A new anionic Ce-MOF ([CeL(CHOO - )]·(CH 3 ) 4 N + )) based on ligand H 3 L (2,4,6-tris(4-carboxyphenyl)-1,3,5-triazine) was successfully synthesised and its adsorption properties of organic dyes were deeply investigated. Due to its unique pore structure and anionic skeleton, Ce-MOF exhibits excellent adsorption capacity for cationic dyes such as methylene blue (MB), crystal violet (CV) and rhodamine B (RhB), while it has no adsorption effect on anionic dyes such as methyl orange (MO) and methyl red (MR). The adsorption kinetics and isothermal model of Ce-MOF were systematically investigated using methylene blue as a model, and it was found that the adsorption process conformed to the quasi-primary kinetic model and the Langmuir isothermal model, indicating monomolecular layer adsorption. After five cyclic adsorption experiments, Ce-MOF maintained efficient adsorption performance, showing excellent cyclic stability and structural integrity. In the selective adsorption experiment of mixed dyes, it was found that cationic dyes can be adsorbed by Ce-MOF, and small molecule cationic dyes have a faster adsorption rate than large molecules. In addition, through DFT theoretical calculations, we revealed the adsorption mechanism of Ce-MOF on cationic dyes, which provided a theoretical basis for the design of new and efficient adsorption materials. This study not only provides an effective strategy for the removal of organic dyes, but also opens up a new way for the application of MOF materials in environmental treatment.