Tuning microscopic structure of Al-based metal-organic frameworks by changing organic linkers for efficient phosphorus removal

Abstract

In this study, five aluminum-based metal-organic frameworks ( i.e. Al-BDC, Al-BDC-NH 2 , Al-BHTA, Al-PMA and Al-BPDC) were synthesized by changing the organic linker. Among the five Al-MOFs, Al-BDC, which used 1,4-benzenedicarboxylate as a linker, showed the highest phosphorus adsorption capacity (97.50 mg P/g), while Al-PMA, which used 1,2,4,5-benzenetetracarboxylic acid as a linker, exhibited the lowest phosphorous adsorption capacity (42.25 mg P/g). The adsorption capacity was higher than most adsorbents reported in the literature. In addition, Al-PMA and Al-BPDC are more cost-effective for removing low concentrations of phosphorous from water. When the aqueous phosphorus concentration was less than 1.0 mg P/L, and the dosage of the five Al-MOFs was only 0.10 g/L, more than 90% of phosphorus was removed. The Al-MOFs are suitable for phosphorus removal from water over a wide pH range (5.0–9.0). In this pH range, almost no Al was detected in water after phosphorus removal, indicating that the Al-MOFs can remove phosphorus from water without causing secondary pollution. Moreover, in a NaCl (0.01 mol/L) background electrolyte solution, the Al-MOFs showed high phosphorus removal stability. The Al-MOFs have the potential to remove phosphorus from natural water. Furthermore, the mechanism study shows that electrostatic interaction and ligand exchange were defined as the main phosphorus removal pathways using the prepared Al-MOFs. These findings demonstrate that the synthesized Al-MOFs are promising candidates for removal of phosphorus from eutrophic water. • The microscopic structures of Al-MOFs were tuned with different organic linkers. • Surface area and pore structure of MOFs significantly affect the phosphorus adsorption performance. • Al-BDC shows high adsorption capacity of 97.50 mg P/g for phosphorus. • Excellent phosphorus removal efficiency was obtained in real water. • Electrostatic interaction and ligand exchange are responsible for the adsorption mechanism.