Additive-free water-based room-temperature synthesis of Ce(IV)-MOFs using various aliphatic dicarboxylate ligands

Cerium-based metal-organic frameworks (Ce-MOFs), especially Ce(IV)-MOFs, have achieved significant attention in recent years due to their outstanding properties that make them good candidates for different applications. However, most Ce(IV)-MOFs are synthesized via conventional solvo/hydrothermal methods using aromatic compounds as organic ligands. Whereas, the synthesis of Ce(IV)-MOFs via water-based room-temperature (RT) methods using aliphatic organic compounds is still in its early stage and needs further efforts to accelerate. Hence, in the present work we report a green water-based RT synthesis strategy to synthesize a series of Ce(IV)-MOFs without using any toxic organic solvents. Therein, four aliphatic compounds with different lengths such as fumaric acid (Fum), succinic acid (Suc), glutaric acid (Glu), and adipic acid (Adi) were applied as organic ligands, different compounds such as sodium perchlorate monohydrate (NaClO4.H2O), sodium acetate, and formic acid were applied as additives, and water and ethanol were used for the washing of the resulting Ce(IV)-MOFs. It was found that not only the type of organic ligands but also the synthesis conditions and washing solvents could control the crystallinity, particle size, porosity, and adsorption performance of the resulting Ce(IV)-MOFs toward tetracycline (TC) antibiotics. Experimental results revealed that the additive-free water-washed sample (Ce-Fum-W-4) showed the optimized properties among all synthesized Ce(IV)-MOFs and can efficiently and rapidly remove TC from water, in which its maximum adsorption capacity reached 1296.52 mg/g only within a short period of time (≈16 min). In conclusion, this synthesis strategy has an acceptable yield and provides the possibility to control the crystallinity, particle size, and porosity of Ce(IV)-MOFs, without using any energy inputs, pretreatment steps, organic solvents, and additives, thereby paving the way for economical production and extending their applications.