Nanoporous Cerium-Doped MIL-53(Fe)-NH2 for Effective and Selective Removal of Phosphate from Wastewater

In this work, nanoporous cerium (Ce)-doped Fe-based MOFs were successfully synthesized by a convenient solvent-thermal method, which was designed to efficiently remove phosphate. Adsorption experiments showed that doping Ce into MIL-53(Fe)-NH2 greatly improved its adsorption performance for phosphate. The maximum phosphate adsorption capacities of MIL-53(Fe)-NH2, 0.5Ce-MIL-53(Fe)-NH2, and Ce-BDC-NH2 were 213.0 mg g–1, 301.5 mg g–1, and 246.0 mg g–1, respectively. Moreover, they all had fast kinetics, and it took 80, 80, and 30 min for MIL-53(Fe)-NH2, 0.5Ce-MIL-53(Fe)-NH2, and Ce-BDC-NH2 to reach equilibrium, respectively. Mechanism studies show that doping Ce with a larger ionic radius in MIL-53(Fe)-NH2 increases the number of unsaturated coordination centers and defects in MOF crystals, resulting in more active sites for phosphate adsorption. Phosphate adsorption by 0.5Ce-MIL-53(Fe)-NH2 includes ligand exchange and electrostatic attraction. In this process, Ce–O–P and Fe–O–P complexes are formed between phosphate and metal central ions, and surface hydroxyl groups play an important role. In addition, nanoporous bimetallic 0.5Ce-MIL-53(Fe)-NH2 proved to be stable over a wide pH range and could be recycled at least 4 times. A low solid-to-liquid ratio of 0.5Ce-MIL-53(Fe)-NH2 could remove phosphate from real wastewater, which exhibited excellent removal performance, excellent environmental adaptability, and high selectivity. All of the results indicate that bimetallic nanoporous 0.5Ce-MIL-53(Fe)-NH2 is an outstanding phosphate adsorbent that could be potentially used to treat wastewater with significant application value in environmental remediation.