Ultraefficient Phosphate Adsorption via Monocarboxylic Acid-Regulated Defective Ce-MOFs: Pore Size Regulation, Valence State Modulation, and Unsaturated Center Design

Introducing defects into Metal-organic frameworks (MOFs) is an effective measure to increase adsorption sites, which is of great significance for improving phosphorus (P) adsorption performance. In this study, various defect-containing cerium (Ce)-based MOFs (Ce-MOFs) were prepared by introducing different types and equivalents of monocarboxylates. Among them, butyric acid (BA)-regulated Ce-MOF (Ce-MOF(40BA)) exhibited excellent adsorption performance with a maximum phosphate adsorption capacity of 117.28 mg P/g. When the initial phosphate concentration was 3 mg P/L, the adsorption equilibrium could be reached within 10 min with a phosphate removal rate of 96.6%. Thermogravimetry analysis (TGA) showed that the average coordination number of Ce-MOF (40BA) was only 4.33 compared to six of the pristine Ce-MOF, indicating an abundant defect content. By increasing defects, mesopores were introduced, enriching the material's pore structure and achieving a mesopore proportion up to 58.81%. X-ray photoelectron spectroscopy (XPS) analysis revealed that the introduction of defects created numerous unsaturated metal centers, leading to a significant increase in Ce(III) contents. Further density functional theory (DFT) calculations indicated that the defective Ce-MOF had a lower binding energy compared to the pristine Ce-MOF, making it more favorable for phosphate adsorption. This study provides a strategy for preparing efficient defect-containing MOF adsorbents. The excellent adsorption performance of Ce-MOF(40BA) in practical wastewater bodies makes it a promising material for solving water eutrophication.