Nanoporous Cerium-Doped MIL-53(Fe)-NH<sub>2</sub> for Effective and Selective Removal of Phosphate from Wastewater
Yuqian Zhu, Boxian Ren, Yewei Qiu, Qiaoshu Zhou, Jun Chang, Zhiguo Lin, Xiangjun Yang
Abstract
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)-NH 2 greatly improved its adsorption performance for phosphate. The maximum phosphate adsorption capacities of MIL-53(Fe)-NH 2, 0.5Ce-MIL-53(Fe)-NH 2, and Ce-BDC-NH 2 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)-NH 2, 0.5Ce-MIL-53(Fe)-NH 2, and Ce-BDC-NH 2 to reach equilibrium, respectively. Mechanism studies show that doping Ce with a larger ionic radius in MIL-53(Fe)-NH 2 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)-NH 2 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)-NH 2 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)-NH 2 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)-NH 2 is an outstanding phosphate adsorbent that could be potentially used to treat wastewater with significant application value in environmental remediation.