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.